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El sistema de fallas Morelia-Acambay (SFMA), situado en la región centro-occidental de la Faja Volcánica Transmexicana (FVTM), se desarrolla como una franja transtensiva de ~30 km de ancho, constituido por fallas E-O y ENE-OSO. La sismotectónica del SFMA controla desde el Mioceno medio (7–9 Ma) la evolución de las cuencas lacustres y depresiones alargadas E-O (Zacapu, Cuitzeo, Morelia y Acambay). Este trabajo estudia el SFMA en su sector centro-occidental enfocándose en la variación espacial del estado de deformación reciente a través del análisis estructural de poblaciones de fallas medidas en el campo y la definición del régimen de esfuerzos regional a partir del análisis de los mecanismos focales de sismos intraplaca someros. Los datos cinemáticos indican que el SFMA se formó a partir de un régimen de deformación con una dirección NE-SO de máxima compresión horizontal (Ey). Hoy en día las fallas NE-SO están asociadas al sistema transtensivo lateral izquierdo, donde las principales morfoestructuras de fallas E-O son paralelas y tienen movimiento normal-direccional izquierdo, mientras que las fallas normales NE-SO responden a la cinemática con una geometría en échelon. La dirección de máxima compresión horizontal (Ey) del SFMA resulta variable pero constantemente en el cuadrante NE-SO, evidenciando una rotación en el sentido horario del campo de esfuerzos que hace que Ey pase de direcciones NNE-SSO en el sector occidental (Pázcuaro-Zacapu-Morelia-Cuitzeo-Acámbaro) hasta direcciones E-O en su sector oriental (Maravatio-Acambay). La integración de los resultados muestra que las trayectorias del campo de deformación reciente y las trayectorias del campo de esfuerzos actual son claramente paralelas, indicando que el régimen neotectónico del Plioceno se ha mantenido constante durante el Cuaternario hasta el presente. Algunas fallas del SFMA son actualmente activas y han sido epicentro de sismos históricos (1858, 1912, 1979 y 2007). Esta definición del campo de deformación y esfuerzos se convierte en una información de primer orden para estudios futuros de paleosismología y el análisis del peligro sísmico. Esta visión espacial permite considerar la orientación de las fallas con respecto a las trayectorias del campo de esfuerzos como uno de los criterios para que dichas fallas se deban considerar o no potencialmente activas. La propuesta más pausible para explicar la deformación transtensiva en el sector central de la FVTM es el modelo de la convergencia oblicua de las placas y la partición del ángulo de subducción de la parte norte de la Trinchera Mesoamericana.

Se presenta la estratigrafía volcánica de la porción suroeste del Lago de Cuitzeo, Michoacán dentro del sector central de la provincia de la Faja Volcánica Transmexicana, donde se registró una estructura caldérica tipo graben. Se identificaron seis secuencias volcánicas con edades que van del Mioceno temprano al Pleistoceno tardío que incluyen: 1) Secuencia Copándaro-Tarímbaro (SCoT): originada durante el Mioceno temprano, contiene intercalaciones de flujos de lavas de andesita basáltica e ignimbritas con alto grado de alteración hidrotermal, 2) Secuencia Tarímbaro (ST): fechada en 18.7 Ma, consiste de lavas andesítico basálticas acompañadas de traquiandesitas, 3) Secuencia de Ignimbritas Chucándiro (SICh): con edades de 16.88 ± 0.34, 16.72 ± 0.24 y 16.88 ± 0.22, que contiene tres litofacies de ignimbritas que consisten en mesas con notorio basculamiento ortogonal a las fallas NE-SO. En la base de las ignimbritas se observaron depósitos brechoides cuyos rasgos se interpretan como brechas de rezago, que siguen la traza del sistema de fallas Morelia-Acambay (SFMA). Estas cubren a la 4) Secuencia El Caracol (SEC): con edades de 13.73 ± 0.24 Ma a 3.02± 0.03 Ma; constituidas por cuatro unidades volcánicas de basaltos, andesitas y andesitas basálticas. Estos productos están intercalados con una unidad lacustres, donde se encontró un fósil índice del Mioceno tardío. Los depósitos lacustres sobreyacen a la 5) Secuencia Quinceo-Tetillas (SQT) fechada en 1.48 ± 0.016 Ma, conformada por depósitos de caída con intercalaciones de lahares (flujos hiperconcentrados); sobreyacidos por los productos de los volcanes Quinceo (1.5 ± 0.14 Ma) y Tetillas (0.4 ± 0.08 Ma). Finalmente, la secuencia 6) está representada por el cono cinerítico Chucándiro (CCh): con una edad de 0.161 ± 0.014 Ma, de composición andesítica, correspondiente al Campo Volcánico Michoacán Guanajuato (CVMG). Los análisis de geología estructural y geoquímica muestran que las secuencias Copándaro-Tarímbaro (SCoT), Tarímbaro (ST) e ignimbrita de Chucándiro (SICh) están estrechamente asociadas a eventos de transición entre el vulcanismo de la SMO y la FVTM. Con base en la geometría del Graben Chucándiro, la ubicación de los depósitos de brechas de rezago, las fallas secundarias de dirección NE-SO y la distribución de las Ignimbritas Chucándiro, se propone que estas ignimbritas se originaron en el Mioceno temprano a partir de una caldera tipo graben del mismo nombre y producto del régimen extensivo del SFMA, cuya edad inicial de la transtensión en esta porción central de la FVTM se asigna al Mioceno temprano, con edades mayores a 17.1 Ma. Nuestros resultados indican que el inicio de la FVTM dentro del área inició durante el Mioceno temprano con la conformación de un graben en donde se emplazaron volcanes monogenético seguido del relleno con sedimentación lacustre que continua en la actualidad.

La falla Cerritos pertenece a la porción oeste del Sistema de Fallas Morelia-Acambay, ubicada al suroeste de la ciudad de Morelia, en el estado de Michoacán, México; es una zona con alta densidad de fallas activas con geometrías segmentadas y arreglos en échelon, donde se han desarrollado semi-grabens y grabens de dimensiones variables que inclusive influyen en el alineamiento y distribución del vulcanismo monogenético holocénico. En la superficie, estas fallas afectan unidades litológicas de edades miocénicas hasta suelos modernos. Debido a la peligrosidad sísmica que se ha reportado para algunas de las fallas de Morelia, se realizó un análisis interdisciplinario de la falla Cerritos, que había permanecido poco estudiada hasta la fecha. La falla Cerritos es una falla normal con una ligera componente lateral izquierda, una longitud de 12 km y un relieve topográfico bien definido de 130±5 m (100 m de desplazamiento visible + 30 m de desplazamiento subsuperficial obtenido por el estudio de resistividad invertida). Esta falla muestra un rumbo ENE-OSO (255°) y un echado de 76° hacia el NNO. En un afloramiento de la falla Cerritos, a unos cuantos metros del trazo de falla principal, se identificó una cuña coluvial con abundante materia orgánica, fechada con el método de radiocarbono en 3.37–3.21 cal ka AP. El análisis geológico y geomorfológico de la falla reveló que es una estructura tectónicamente activa, relativamente joven y con índices geomórficos que indican mayor actividad en su sector oriental. El escarpe y la acumulación de sedimentos lacustres en el bloque caído sugieren movimiento activo vertical (levantamiento y subsidencia, respectivamente) a lo largo de esta falla. Los resultados obtenidos mediante los análisis de sísmica de refracción, tomografía de resistividad eléctrica y magnetometría terrestre revelaron la geometría de la falla en profundidad, en donde sobresale la presencia de un plano principal lístrico y una zona de deformación en el bloque caído que se extiende en superficie hasta 75 m desde el pie del escarpe principal. Esta zona de deformación se caracteriza por la formación de anticlinales tipo roll-over y dos grabens de colapso crestal delimitados por estructuras secundarias, los cuales funcionan como depocentros de materiales clásticos y bloques caídos. Finalmente, el análisis de actividad y potencialidad indicó que esta estructura tiene tasas de desplazamiento de 0.03±0.01 mm/año, con desplazamientos verticales promedio de 0.5 m por evento, y un tiempo de recurrencia promedio de 16700 años. La Falla Cerritos tiene la capacidad de producir eventos de ruptura con magnitudes de Mw 6.2 a 6.6 por sí sola, o bien, puede interaccionar en un evento extremo con las fallas adyacentes Morelia y Cointzio, produciendo eventos de ruptura multi-falla con magnitudes de hasta Mw 6.9.

La deformación frágil se relaciona con la presencia de fallas y fracturas que afectan a la corteza superior de la Tierra. La distribución que tiene la deformación frágil y el arreglo que presentan las fallas y fracturas son variables poco conocidas, a pesar de que tienen una gran influencia en la generación de permeabilidad y son importantes para entender fenómenos como la deformación localizada. En este trabajo se explora la distribución de la deformación frágil y el arreglo de las fracturas que afectan a rocas andesíticas del Mioceno en el área de Morelia-Cuitzeo mediante un análisis cuantitativo de la deformación a escala mesoscópica. Las rocas miocénicas del área de estudio están afectadas por dos familias de fracturas (F1 y F2) relacionadas con dos eventos de deformación frágil (D1 y D2) ocurridos entre el Mioceno y el Holoceno. Las fracturas F1 tienen un rumbo preferencial NNW-SSE y acomodan una extensión ENE-WSW de ~2.5 %. Por otro lado, las fracturas F2 cortan a las fracturas F1, tienen un rumbo ENE-WSW y se relacionan con una extensión ~N-S de 6.8 %. Ambas familias de fracturas tienen un arreglo de fracturas agrupadas y una intensidad de fracturas promedio similar de aproximadamente 17 fracturas/metro. Este comportamiento en la intensidad de fracturas, ante una cantidad de deformación por extensión distinta, se atribuye al tipo de roca. La cantidad de extensión asociada a las dos familias de fracturas se distribuye de manera heterogénea en las rocas, lo que contribuye de manera significativa con la porosidad secundaria (porosidad de fracturas). Adicionalmente, la cantidad y el arreglo de las fracturas sugieren que las rocas miocénicas pueden ser la capa permeable del sistema geotérmico de la zona del lago de Cuitzeo.

En la zona geotérmica de San Agustín del Maíz (Michoacán) se han identificado depósitos de sínter de sílice coexistiendo con manifestaciones hidrotermales activas. Estos depósitos, considerando el modo de deposición, se separan en bandeados de fractura y estratificados. Los primeros están asociados a los conductos a través de los cuales los fluidos ascienden a la superficie, mientras que los segundos se forman a partir de los fluidos que logran llegar a la superficie. Los depósitos estratificados presentan diferentes litofacies que se pueden agrupar en un rango con dos miembros finales: por un lado, un depósito hidrotermal puro, denso, de aspecto vítreo y compacto. Por el otro lado, un depósito hidrotermal limo-arenoso, deleznable, con impresiones de plantas y algunos líticos. El depósito vítreo se considera geiserita, formado por salmueras con temperaturas superiores a los 70 °C, mientras que el depósito limo-arenoso se considera que se ha formado por salmueras con temperaturas inferiores a los 70 °C y en algunos casos, distantes de la surgente termal. Los depósitos vítreos están constituidos mineralógicamente solo por ópalo (C y CT), mientras que los depósitos limo-arenosos están formados por ópalo en conjunto con otras fases mineralógicas asociadas a sedimentos. Se ha establecido que las litofacies y la mineralogía de los depósitos de sínter de sílice pueden dar información de las temperaturas y las tasas de deposición de las surgentes hidrotermales que les dieron origen. Esta información es de utilidad para la identificación de áreas donde existió mayor emergencia de fluidos hidrotermales a la superficie y con mayor temperatura (e.g. facies de geiserita), especialmente en zonas geotérmicas con un contexto geológico similar al de San Agustín del Maíz (e.g. sector central del Cinturón Volcánico Trans-Mexicano). Dichas áreas con importante circulación de fluidos pueden coincidir localmente con intersección de fallas, terminación de fallas y rampas de relevo.

Este trabajo da a conocer los niveles de concentración de gas radón (222Rn) en suelos de la zona urbana en la ciudad de Morelia, Michoacán y su relación con fallas geológicas potencialmente sísmicas y las asociadas con el proceso de subsidencia-fluencia-falla. La medición promedio de la concentración de gas radón de 86 estaciones distribuidas en la ciudad de Morelia es de 4028.56 Bq/m3. Además, se realizó un análisis variográfico de los datos de concentraciones de gas 222Rn para determinar la posible existencia de anisotropía. De este análisis se infiere que el gas radón en la ciudad de Morelia presenta una anisotropía híbrida, con dirección preferencial N50°E, lo que sugiere que su distribución espacial obedece al campo de esfuerzos extensional del sistema de fallas Morelia-Acambay (σ2=NE-SW y σ3=NW-SE). Utilizando la técnica de vecinos naturales se construyó un mapa interpolado de las concentraciones de gas radón de la zona urbana, para visualizar su distribución y además, mediante el cálculo del umbral línea base – anomalía, poder identificar las zonas con concentraciones anómalas. Los resultados de esta investigación permiten relacionar las zonas de alto riesgo por radón con fallas activas. Un ejemplo claro es la falla La Paloma, donde 4 de las 7 estaciones de medición ubicadas cerca de esta falla resultaron con valores de concentración de gas 222Rn por encima del umbral. Los resultados obtenidos en esta investigación pueden servir de base para hacer mediciones a mayor detalle en la zona urbana de la ciudad de Morelia y para monitorear las fallas activas. También, pueden utilizarse como guía para planear el crecimiento y desarrollo de la ciudad, permitiendo una ubicación segura de futuras escuelas, centros de salud y fábricas, sin dejar a un lado el aspecto normativo que pudiera derivarse de los resultados de esta investigación. Al final, utilizando la técnica de vecinos naturales se construyó el mapa interpolado de las concentraciones de gas Radón de la zona urbana, para visualizar su distribución y además, mediante el cálculo del umbral línea base–anomalía poder identificar las zonas con concentraciones anómalas. Los resultados de esta investigación permiten relacionar las zonas de alto riesgo por radón con fallas activas. Un ejemplo claro es la falla La Paloma, donde 4 de las 7 estaciones de medición ubicadas cerca de esta falla resultaron con valores de concentración de gas 222Rn por encima del umbral. Además los resultados obtenidos en esta investigación pueden servir de base para hacer mediciones a mayor detalle en la zona urbana de la ciudad de Morelia y para monitorear las fallas activas. También, pueden utilizarse como guía para planear el crecimiento y desarrollo de la ciudad, permitiendo una ubicación segura de futuras escuelas, centros de salud y fábricas, sin dejar a un lado el aspecto normativo que pudiera derivarse de los resultados de esta investigación.

Interactions between volcanic and tectonic processes affect the distribution, morphology, and volume of eruptive products in space and time. The Queréndaro area in the eastern Michoacán-Guanajuato Volcanic Field affords an exceptional opportunity to understand these relationships. Here, a Pleistocene lava plateau and 20 monogenetic volcanoes are vented from an active ENE-striking segment of the Morelia-Acambay fault system. Thirteen scoria cones are aligned along this structure, vented from an extensional gap in between two rotated hanging wall blocks of a listric fault. A new geological map, volcanic stratigraphy, and 40Ar/39Ar dating indicate that this lava plateau and volcanic cluster were emplaced from 0.81 to 0.25 Ma by 11 intermittent eruptive epochs separated by ca. 0.05 Ma, emplacing a total magma volume of 5 km3. Petrography and chemistry of rocks suggest that all volcanic structures were fed by three different magma batches but vented from independent feeder dikes. Our results indicate that preexisting faults exert a strong influence on volcanic spatial and temporal distribution, volcanic morphology, magma volume, and eruptive dynamics in this area. ENE-breached and ENE-elongated scoria cones indicate parallel subsurface fissure and feeder dikes. Additionally, points of maximum fault dilation at depth related to a transtensive state of stress coincide with less fragmented deposits and larger magma volumes. Furthermore, this study raises important questions on the geodynamics of volcano-tectonic interactions possible in similar monogenetic volcanic alignments worldwide.

espanolPara el desarrollo de un campo geotermico, el conocimiento de la distribucion de fracturas, la hidrologia y la evolucion tectonica del sitio a traves de la caracterizacion estructural del sistema natural es un requisito previo a la perforacion de pozos exploratorios. Fallas y fracturas representan vias preferenciales por el flujo de fluidos en el subsuelo y pueden ser detectadas mediante investigaciones geologicas en la superficie y geofisicas en el subsuelo. Una anomalia magnetica positiva y de forma sub-circular en planta se encuentra en el medio del lago Cuitzeo, Mexico. A traves de un levantamiento geomagnetico dentro y alrededor del area que comprende la anomalia tratamos caracterizar el reservorio geotermico que, al sur del lago, esta notificado por manifestaciones hidrotermales. Utilizando filtros computacionales basados sobre el uso de operaciones con las derivadas de valores de campo a los datos magneticos grabados, hemos puesto en luz algunas de las estructuras que influencian la circulacion de los fluidos en el sistema geotermal. Nuestra atencion se focalizo sobre fallas ~N-S and E-W, pertenecientes respectivamente a la tectonica Basin & Range (B&R) y a la del Cinturon Volcanico Mexicano (CVM). Segun nuestra interpretacion, la interaccion de dos o mas estructuras de diferentes origenes (B&R y CVM), ademas del entorno geodinamico especifico (subduccion de zona de fracturas), facilito el surgimiento de cuerpos magmaticos basicos del profundo que, bloqueados por la capa argilosa de sedimentacion lacustre del Cuitzeo, dieron lugar, enfriandose lentamente, al sistema geotermal y contribuyeron a la formacion de la anomalia magnetica. EnglishFor the development of a geothermal field, the understanding of fracture distribution, hydrology and tectonic evolution of the site through structural characterization of the natural system is a prerequisite to the drilling of exploratory wells. In order to image the underground shape of approximately planar, relatively permeable, geologic features (fractured rock-volumes around fault planes) and to detect hot rock volumes, geologic and geophysical surveying is carried out. A strong positive magnetic anomaly, nearly circular in 2D, characterizes the middle of Cuitzeo lake, Michoacan, Mexico, apparently not related with a volcanic structure on the surface. It may instead be associated to the geothermal system in the area which yields at present hot springs at the southern shore of the lake, at boiling temperatures. In this study, we conducted a ground magnetic survey within and around Lake Cuitzeo with the aim of characterizing this anomaly, following one-kilometer-spaced survey-lines and covering an area of approximately 100 km2. To enhance interpretability, we applied computational filters based on directional derivatives (vertical and horizontal) to our reduced-to-pole magnetic-field raw data – illuminating underground faults and other permeable pathways for fluids and delineating contacts between differently magnetized rocks, through maxima and minima on maps. While most filters used were able to define the basic configuration of the system, we found that computational filters working with ratios of derivatives (vertical and horizontal) were able to better account for the depth of a magnetic source. Also, faults were more clearly imaged on maps. We could mainly highlight ~E-W and ~N-S striking fault-systems, respectively belonging to the ~N-S TransMexican Volcanic Belt extensional tectonics and to the ~E-W Basin & Range, both with lateral movements and still active today. We interpret the magnetic source as a magma body (related to the volcanism of Michoacan-Guanajuato Volcanic Field) that remained trapped during its ascent under Cuitzeo lacustrine sedimentation, during the last 500 ka, forming the once stronger geothermal system.

The Patzcuaro–Acambay fault system (PAFS), located in the central part of the Trans-Mexican Volcanic Belt (TMVB), is delimited by an active transtensive deformation area associated with the oblique subduction zone between the Cocos and North American plates, with a convergence speed of 55 mm yr−1 at the latitude of the state of Michoacan, Mexico. Part of the oblique convergence is transferred to this fault system, where the slip rates range from 0.009 to 2.78 mm yr−1 . This has caused historic earthquakes in Central Mexico, such as the Acambay quake ( Ms=6.9 ) on 19 November 1912 with surface rupture, and another in Maravatio in 1979 with Ms=5.6 . Also, paleoseismic analyses are showing Quaternary movements in some faults, with moderate to large magnitudes. Notably, this zone is seismically active, but lacks a dense local seismic network, and more importantly, its neotectonic movements have received very little attention. The present research encompasses three investigations carried out in the PAFS. First, the estimation of the maximum possible earthquake magnitudes, based on 316 fault lengths mapped on a 15 m digital elevation model, by means of three empirical relationships. In addition, the Hurst exponent Hw and its persistence, estimated for magnitudes Mw (spatial domain) and for 32 slip-rate data (time domain) by the wavelet variance analysis. Finally, the validity of the intrinsic definition of active fault proposed here. The average results for the estimation of the maximum and minimum magnitudes expected for this fault population are 5.5 ≤ M w ≤ 7 . Also, supported by the results of H at the spatial domain, this paper strongly suggests that the PAFS is classified in three different zones (western PAFS, central PAFS, and eastern PAFS) in terms of their roughness ( H w = 0.7 , H w = 0.5 , H w = 0.8 respectively), showing different dynamics in seismotectonic activity and; the time domain, with a strong persistence Hw=0.949 , suggests that the periodicities of slip rates are close in time (process with memory). The fractal capacity dimension ( Db ) is also estimated for the slip-rate series using the box-counting method. Inverse correlation between Db and low slip-rate concentration was observed. The resulting Db=1.86 is related to a lesser concentration of low slip-rates in the PAFS, suggesting that larger faults accommodate the strain more efficiently (length ≥3 km ). Thus, in terms of fractal analysis, we can conclude that these 316 faults are seismically active, because they fulfill the intrinsic definition of active faults for the PAFS.

Aligned volcanism is very common in many monogenetic volcanic fields around the world, which can reveal volcano-tectonic interactions at different scales. For instance, volcanic distribution discloses the tectonic stress orientation on regional scales. On more local scales, preexisting faults or fractures may control magma intrusions and their propagation through the upper crust, as faults are zones of crustal weakness that magma intrusions can intercept during its ascent, partly controlling the volcanic vent spatial distribution. But it is not quite understood how do these alignments occur; if they erupted at the same time (within a few dozens of years), if they erupted during a short time interval (hundreds of years) or during a long time interval (thousands of years); if the eruptive style and magma volumes are controlled by these faults and the regional tectonic stress regime, etc.This study aims to understand the magmatic and structural conditions that favored the emission of a lava plateau followed by Strombolian explosions that built 13 aligned and six dispersed scoria cones through preexisting E-W– to ENE-striking faults in the Queréndaro area. Our results indicate that volcanism in the Michoacán-Guanajuato Volcanic Field occurs as intermittent magma fluxes, sometimes represented by independent volcanic vents and sometimes by clustered or aligned volcanoes. Moreover, preexisting faults exert a strong influence on volcanic spatial and temporal distribution, volcanic morphology, magma volume, and eruptive dynamics in this area.

The analysis of syn-sedimentary deformations is a helpful tool for paleoenvironmental reconstructions; these structures are better preserved in fluvio-lacustrine sequences. In the Zacapu basin, lacustrine sedimentation has been active since late Pliocene until modern times. During the Holocene, the lake evolved into a wetland that was the home of the first P’urhepecha settlements in Michoacan, Mexico. Since the beginning, the Zacapu basin was affected by volcanic activity from the Michoacan-Guanajuato Volcanic Field and seismicity from the Morelia-Acambay Fault System. The effects of these geologic events were recorded in the basin sediments and in the pictorial records of the P’urhepecha people. According to archeological studies, P’urhepechas settled in the Zacapu basin around 150 BC (2100 y BP) (Loma Alta phase) occupying the site for at least 1700 years until the Milpillas phase (also known as Late Uricho phase). In this time span, the population may have witnessed the volcanic activity of the Capaxtiro volcano (between 193 BC (2143 y BP) and 84 BC (2034 y BP) and the Malpais Prieto volcano (AD 826 - 962 or 1124 - 988 y BP), but also the tectonic activity of nearby faults (i.e., Villa Jimenez fault). In this work, we analyze the syn-sedimentary deformations exposed in the sedimentary record of trenches at the uplifted area of Las Lomas, and identify the presence of liquefaction structures, folding, microfaulting, and slumps, which have characteristics that suggest that they are related to seismic activity. We propose the occurrence of at least four earthquakes with moderate to high magnitude (MI ≥ 5) in the basin based in the deformations. The oldest syn-sedimentary deformations recorded in the lacustrine sequence are liquefied dikes and flames dated around 40 ka. Meanwhile, the youngest syn-sedimentary deformation are microfaulted layers which contain fragments of P’urhepecha pottery dated in the Milpillas/Late Uricho phase (1350 AD). Because of the time span when the volcanic and seismic events occurred, we discuss their relation with the human activities of the early settlements in the Zacapu basin.

In this study, three geophysical techniques were used to identify, localize, and characterize a partly blind fault in the Llano Grande basin within the Agua Fría Graben. This tectonic basin is located in the Los Azufres Volcanic Complex, one of the major silicic volcanic centers in the Trans-Mexican Volcanic Belt. The 1 km wide Agua Fría graben could be considered as an analogous of the larger graben structures bounded by the Morelia-Acambay Fault System. Since it is filled by recent sediments, it represents a challenge for the recognition and characterization of active faults that lack clear surface expression. Newly collected magnetic data led to the identification of lineaments interpreted as structural discontinuities. Ground penetrating radar and seismic refraction surveys were carried out across one of these magnetic lineaments crossing the basin to characterize the nature and geometry of the inferred discontinuity. The ground penetrating radar profiles allowed the identification of buried deformational structures interpreted as the northern segment of the Agua Fría fault. The subsurface reflectors displaced 1 to 1.5 m by the fault indicate that this structure is potentially active. The opening of trenches based on these results makes it possible to confirm the interpretation of the geophysical profiles, to discuss the precision of the data and to validate their use for such studies. On seismic refraction profiles, the deformation zones are related to low P-wave velocity zones. These geophysical studies demonstrate the potential of such techniques to locate faults in the subsurface, partially characterize the width of the fault zone and the associated displacement within the uppermost of the subsurface. Our results may be applied to define ideal sites for paleoseismic excavations which are essential for the identification and description of historical and prehistoric earthquakes, and thus, for the characterization of the local seismic hazard.

Some large landslide deposits are recognized within and around the Mitla archaeological site, which is located in a very seismically active region cut by the Tehuacan‐Oaxaca fault system. Previous studies have shown that this fault system has produced coseismic ruptures and associated earthquakes in the past. Our work on the Mitla landslide deposits clearly demonstrates that their morphology and nature are typical of dry‐rock avalanches. Thus, collapses of rock already weakened by alteration and/or weathering, and unstably mobilized by intense rainfall, are discarded as possible triggers of the avalanche events. We instead propose that the landslides were triggered by earthquake activity. Moreover, our data indicate that part of the original Mitla settlement lies buried under a large rock‐avalanche deposit produced sometime during the post‐Classic period (900–1520 AD). At that time, the city of Mitla was inhabited by over 10,000 people as estimated from archaeological reconstructions. This devastating landslide almost entirely obliterated Mitla, which at the time of the Spanish arrival still existed as a city, but much reduced in area and populations.

Earthquakes-related soft-sediment deformations (seismites) are relevant structures to help reconstructing the palaeoseismicity in a region. Nevertheless, although seismites have been described for a large variety of palaeo-environments and stratigraphic settings, they are rare and, in some cases, ambiguous structures. In this paper, we document, for the first time, impressive seismites affecting a latest Quaternary travertine deposit located in southern Tuscany (Serre di Rapolano, Italy). These structures are extremely relevant, as seismites have been never described for this kind of terrestrial deposits. The seismites developed within a 2.5 m thick stratigraphic succession made of alternating terrigenous and carbonate sediments, embedded within the travertine deposits. Earthquake produced liquefaction and fluidization of some terrigenous levels and the injection of fluidized silty sediments (dykes and sills) into carbonate and terrigenous levels; slumped levels and associated decollement surfaces produced highly non-cylindrical folds, overall induced by the loss of brittle shear strength along the basin slopes. The occurrence of these soft-sediment deformations implies an important seismic event that took place in a time spam encompassed between 84 ± 8 and 48.92 ± 5.08 ka, in an area characterized by low seismicity and scarce knowledge of its seismotectonic setting. Their spectacular exposition and preservation in saw-cuts of an abandoned quarry (Cava Oliviera quarry) highlights their relevance and importance.

The Tzirate volcanic complex (TVC) is located in the central part of the Michoacan-Guanajuato volcanic field (MGVF), central Mexico. It is characterized by a series of andesitic-dacitic domes and by active faulting of the Morelia-Acambay fault system. Its age and the relationship between the magmatic processes that generated the TVC rocks and the evolution of the local stress field were determined with field work, structural analysis, 40Ar-39Ar dating, geochemistry and petrography of the lavas. The dacitic volcanism of the TVC occurred during the Pleistocene (1 Ma) with the eruption of lavas that formed a series of domes (SiO2 = 63–69 wt.%) aligned in NNE-SSW and NW-SE directions. The area is covered by andesitic-basaltic cinder-lava cones and andesitic lava cones of Pleistocene-Holocene age (2.5 Ma – 0.011 Ma) produced by monogenetic volcanism of the MGVF that surrounds the TVC. The TVC magmas produced rocks that can be classified in four mineral groups. One group contains olivine and pyroxene phenocrysts. The second biotite and amphibole euhedral phenocryst, and the other two contain biotite euhedral phenocryst, amphibole microphenocrysts and biotite subhedral crystals surrounded by a rim of plagioclase microcrysts. The diversity of textures in biotite crystals and the linear trends of major and trace elements between La Huacana granite and the less evolved lavas of the TVC suggest that assimilation of a granitic body in the crust might have influenced the evolution of the TVC rocks. The results of the structural analysis show that when the minimum principal stress was vertically oriented the rise of magma to the surface is hindered, favoring the entrapment of magma in shallow magma chambers. The magmatic assimilation process possibly occurred during the same phase, forming the felsic magmas. Subsequently, the local stress field became extensional, and the vertical principal maximum stress developed normal or extensional faults that affected the magma chamber and served as plumbing system for the rise of felsic lava.

Based on a detailed geological map and stratigraphy aided by new 230Th/238U and 206P/238U age determinations we established the eruptive chronology of the Tres Virgenes Volcanic Complex (TVVC). The complex consists of three northeast-southwest aligned stratovolcanoes, which from older to younger are El Viejo, El Azufre, and La Virgen and associated cinder cones and domes. The alignment was fed from fissures that mark the southern trace of the left-lateral Cimarron Fault. The TVVC was built upon the basement rocks of the Peninsular Ranges Batholith (~99 Ma), the Santa Lucia Formation (21.6 Ma), the Esperanza basalt (7.6 Ma), and the 1.1 Ma ignimbrite of El Aguajito caldera. The TVVC began its formation at ca. 300 ka mainly with dacitic lava flows and domes that formed El Viejo volcano (4.2 km3). At around 173 ka, activity migrated to the southwest to build El Azufre volcano (3.8 km3) with the emission of dacitic lavas and several phases of dome construction and destruction with the generation of pyroclastic density currents. El Azufre's activity ended ~128 ka with the extrusion of the summit dome. At about 112 ka, volcanism migrated 4.2 km to the southwest to begin the construction of La Virgen Volcano through the emission of andesitic and dacitic lavas that built the largest cone of the complex until ~22 ka (31.2 km3). This volcano was built upon several stages of cone construction with the emission of lava flows and peripheral dacitic domes and cinder cones. Between 128 and 112 ka six cinder cones vented along the Cimarron Fault between the La Virgen and El Azufre volcanoes. By assuming a constant emission of magma the total volume of the TVVC (39 km3) was erupted at an average rate of 0.13 km3/kyr. Of this volume, effusive eruptions dominated the evolution of the complex (89%) of which 62% are dacites and 38% andesites. The TVVC rocks have compositions of 50–67 wt% in silica, and low-medium K (0.5–2.5 wt% K2O). Trace element signatures of the TVVC rocks (Sr/Y 2 km within the Peninsular Ranges Batholith as confirmed by geobarometry, aeromagnetic data, and the drill-holes of the geothermal field. Today, the Tres Virgenes geothermal field generates 10 MW of electricity although future exploration of several nearby areas may increase such capacity.

Monogenetic volcanic fields occur in many tectonic settings representing an unpredictable and uncertain volcanic hazard. The Patzcuaro Lake is located in the central part of the Michoacan-Guanajuato Volcanic Field (MGVF). Field mapping of an area of 560 km2, stratigraphy and new radiometric ages (40Ar/39Ar and 14C) aided in the identification of 45 individual volcanic landforms formed during the past 3.9 Ma. These landforms comprise five medium-size shield volcanoes, 25 scoria cones, 10 lava domes, two lavas associated to scoria cones, one fissural lava flow, and two volcanic complexes. These volcanic edifices erupted a minimum volume of 20 km3 since Pliocene with an output rate of 0.02 km3/ka. Chemical composition of magmas ranges from 47.6 to 65.3 wt% silica, being dominantly andesites (~76 vol%), followed by basaltic-andesites (~12 vol%), dacites (~9 vol%) and basalts (~3 vol%). Volcanic products vary from mainly andesitic during the Pliocene, basaltic to dacitic during the Pleistocene and basaltic-andesitic to andesitic during the Holocene. All these rocks are the result of low-dipping slab subduction-related magmatism. Alignment of cones and structures follow NE-SW, N-S and E-W directions. The youngest faults are associated with the E-W Morelia-Acambay Fault System, with historic earthquake activity. The volcanic complexes, El Estribo and La Muela, have cone collapses to the north that correspond with the direction of maximum regional extension associated with the E-W fault system. The 3.9 Ma history of monogenetic volcanism around the Patzcuaro Lake demonstrates that monogenic fields can be long-lived volcanic features.

The Quaternary Acoculco ( Coevally to the Miocene NE-SW and Pliocene-Quaternary NW-SE tectonic extensional phases, NE-SW and NW-SE transfer faults were developed. NE-SW normal faults and NW-SE strike-slip faults correspond to fault systems optimally oriented with the current stress field, thus, these faults can be considered as potentially active structures controlling magma emplacement and the distribution of volcanic structures at the surface.

A reasonable estimation of the geothermal potential of any geothermal system depends on the reliable knowledge of its geological, geophysical and geochemical parameters. The heat flow is an important geophysical criterion used to describe the subsurface temperature profiles in prospecting areas. These profiles are helpful tools to locate high temperatures and thermal disturbances (heating or cooling) that could indicate permeable or fractured zones in the subsurface. A good area to apply this approach is the La Primavera caldera (LP), Mexico, with an estimated geothermal potential high enough to install a 75 MW power plant. A conductive model of La Primavera would provide vital information to understand the heat flow during future work on and eventual exploitation of the geothermal field. We developed a 2D conceptualized numerical model of La Primavera based on the heat transfer equations. Then, we applied the Tri-Diagonal Matrix Algorithm (TDMA) method to discretize the equations. The resulting model described the temperature distribution as a function of depth in 10 geothermal wellbores drilled within an area of 4 km2 inside the caldera. The lithology of these exploration wellbores (subsurface stratigraphy) was used to correlate the proposed 2D geological profiles and to construct the model geometry and thermal conductivity at depth. The temperature profiles were used as boundary conditions to calibrate and validate the numerical model. The results indicate that estimated temperatures (450-500 °C) occur at depths of 3 km hosted within the granitic basement beneath La Primavera. These high temperatures may be linked to remnant intrusive bodies located in depth. These results suggest that La Primavera is a promising target for future geothermal exploitation.

Las culturas mesoamericanas prehispánicas del altiplano mexicano, y en concreto los imperios P’urhepecha y Azteca (Periodo Posclásico tardío, 1300 – 1500 AD), experimentaron grandes terremotos destructivos que dejaron una impronta en su sociedad y determinó tanto sus ritos espirituales como su urbanismo. Este trabajo describe varios paleoterremotos que los P’urhepechas experimentaron en la ribera del Lago de Pátzcuaro a partir de técnicas de paleosismología. Se constata que grandes bloques basálticos asociados a los ritos religiosos P’urhepechas fueron colocados en el bloque hundido de dos grandes rupturas superficiales de origen sismogénico que afectaron a la geografía del propio lago. Los P’urhepechas colocaron dos grandes bloques de roca basáltica de más de 1 m3 de volumen y con su superficie tallada para utilizarlos en sus ritos espirituales. Los estudios paleosísmicos sugieren que ocurrieron varios terremotos de magnitud entre M 6,5 y M 7 con ruptura superficial y probablemente con una migración de la orilla del lago (Garduño-Monroy et al., 2009 y 2011a). Además, este trabajo demuestra que dichos terremotos se suceden desde el periodo Preclásico (3000 BP). En tiempos posteriores, durante la conquista española, se esculpió en el bloque basáltico una gran cruz cristiana de tipo maltesa que correspondería con el proceso de evangelización cristiana a lo largo del siglo XVI en la zona de Michoacán, lo que afianza el significado espiritual de dichos bloques. En cualquier caso, estamos ante una de las manifestaciones humanas más antiguas de los efectos de los sismos sobre culturas ancestrales.

The Trans-Mexican Volcanic Belt is an active continental volcanic arc characterized by several arc-parallel Miocene-Holocene tectonic lake basins, such as the Cuitzeo, Zacapu, Chapala, and Zacoalco. Normal faults and related continental seismicity shape these basins. In the central part of this volcanic arc, the Cuitzeo Lake basin presents neotectonic fault activity, accommodating oblique extension through ENE-striking normal fault zones of the Morelia-Acambay Fault System and transfer faulting. Specific faults have been described in the basin, and various geological and structural studies have outlined its kinematics and structural geometry. However, these fault zones have not been fully characterized. Characterizing earthquake sources in the Cuitzeo Lake basin is essential to constrain the regional potential seismic hazard, aiming toward better territory planning. This study presents the first regional fault compilation in the Cuitzeo Lake basin that characterizes 21 fault zones from geomorphic data. We integrated previous volcanic and tectonic studies with new geomorphic and paleoseismic evaluations to assess potential seismic sources in the Cuitzeo Lake basin. Furthermore, we evaluate fault zone segmentation, fault slip distribution, transtensional partitioning, seismic hazard implications, and basin development. We improved the current understanding of the basin's transformation, subsidence, and sedimentation with all this information. Here, fault zones present a mean vertical slip-rate of 0.17 ± 0.27 mm/yr for 1 Ma, capable of generating Mw 6.2 to 7.0 earthquakes and average single-event displacements from 0.2 to 1.2 m. Multi-fault ruptures could be up to 63 km-long, capable of generating Mw 7.0 to 7.2 earthquakes, representing an important regional seismic hazard.

This paper provides the first wide-area Interferometric Synthetic Aperture Radar (InSAR) survey of the whole eastern Trans-Mexican Volcanic Belt (42,200 km2). The aims are to identify ground deformation hotspots within major urbanized areas and rural valleys, establish baselines in geothermal exploration sites, and analyze deformation at geothermal exploitation sites and its relationship with energy production. The whole 2003−2010 ENVISAT C-band SAR archive available over the region was processed with the Small BAseline Subset (SBAS) InSAR method to retrieve over 840,000 coherent targets and estimate their ground displacement rates and time series. Land subsidence hotspots due to aquifer drawdown are found within the city of Puebla (up to −53 mm/year vertical rates, groundwater pumping for industrial use), Tlaxcala and Apizaco (−17 mm/year, industrial and public), the valley of Tecamachalco (−22 mm/year, agricultural), Tulancingo (−55 mm/year, public, industrial and agricultural), and in the eastern Mexico City metropolitan area (−44 mm/year, agricultural). The baseline for the Acoculco caldera complex shows widespread ground stability. Conversely, localized subsidence patterns of −5 to −10 mm/year exist around Las Derrumbadas and Cerro Pinto in the Serdán-Oriental basin, due to intense groundwater pumping for agriculture. A well-defined land subsidence area with −11 mm/year maximum rates is found at Los Humeros volcanic complex within Los Potreros collapse, correlating well with energy production infrastructure location and historical steam production rates. Field surveys carried out in Acoculco and Los Humeros in 2018 provide supporting evidence for the identification of hydrothermal manifestations, and understanding of the landscape and surface deformation patterns within the geothermal fields.

The geological map of the Tres Vírgenes Volcanic Complex (TVVC) Baja California Sur, México consists of three northeast-southwest aligned stratovolcanoes named from older to younger, El Viejo, El Azufre, and La Virgen. The map (scale 1:20,000) comprises an area of 856 km2 edited on an ArcMap data set. The map compiles previous studies combined with new mapping and stratigraphy supported by 5 new 230Th/U geochronology in zircons. The TVVC sits on top of Cretaceous granite, Cenozoic volcaniclastics, the Esperanza basalt (7.64 Ma), and the Aguajito ignimbrite (1.17 Ma). The TVVC commenced its activity around 300 ka by constructing El Viejo volcano, followed by El Azufre volcano (∼173–128 ka), la Virgen scoria cones (∼128–112 ka), and La Virgen stratovolcano (∼112–22 ka). The La Virgen volcano emplaced the La Virgen rhyolitic tephra (∼31 ka), and the Upper Andesite lavas (∼22 ka).

The La Alberca-Teremendo fault is a 26 km-long, complex fault composed of an en échelon array of short crustal fault segments, belonging to the Morelia-Acambay fault system. This fault system shows parallel scarps with morphological evidence of recent activity such as drainage alteration, maximum throws of 50 m and minimum throws of 1.4 m that displace the recent soils. The fault acted as a conduit for the formation of the La Alberca de Guadalupe maar (23000 to 21000 years ago) and displaced afterwards its phreatomagmatic sequences. The paleoseismic analysis indicates that the La Alberca-Teremendo fault moved three times in the past 23000 years (age of the maar); this activity caused an average vertical displacement of 87 cm, and might have generated earthquakes with magnitudes Mw between 6.6 and 7, as well as volcano-tectonic earthquakes with magnitudes Mw between 4 and 5.5. The displacements were identified on the fault through the superposition of soils differentiated by a disconformity and an anomalous increase in the percentage of clay and organic matter. The La Alberca-Teremendo fault has dominant dip slip with a minor left-lateral component, a slip rate of 0.114 mm/year, and an average recurrence interval of 7726 ± 68 years. According to scaling relations that use the surface rupture length, if we assume that the La Alberca-Teremendo fault moves tectonically, it could generate earthquakes with maximum magnitudes of Mw between 6.7 and 7.3, however because of the active volcanic processes in the area, we could expect moderate volcano-tectonic earthquakes (Mw 4–5.5) rather than catastrophic ones.

Before the arrival of the Spanish conquerors, Mitla was the second most important city in the valleys of Oaxaca, México. However, the ruins that are visible today do not seem to match the size of a city of more than 10,000 inhabitants. Geological and geophysical studies suggest that part of the city was covered by the deposits of a dry landslide likely to have been caused by an earthquake with a magnitude that could vary between 6 and 7. This landslide is monolithological, which is why two geophysical methods were used in order to evaluate its geometrical characteristics and to suggest the possible existence of archeological remains under the landslide.

Antes de la llegada de los españoles a América, entre los siglos XIV y XVI, los hechos y acontecimientos de la vida diaria fueron registrados por los pueblos nativos con símbolos en los códices. Muchos de esos códices fueron destruidos por los españoles al ser considerados una forma de idolatría. Sin embargo, en México y en el extranjero existen aún varios códices que fueron dibujados por los tlacuilos, personas con conocimientos en diferentes disciplinas como los procesos naturales, la biodiversidad, las guerras y los problemas sociales y religiosos. Uno de ellos, con una gran cantidad de información, es el códice conocido como Telleriano Remensis. Este contiene representaciones de diversos procesos naturales como el clima, las erupciones volcánicas y los sismos, así como de procesos de tipo social, político y religioso, entre otros. Un análisis geocientífico cuidadoso de este códice, consultando la literatura relacionada, ha permitido encontrar evidencias de doce eventos sísmicos que quedaron registrados en el espacio y en el tiempo. Los sismos se representaron con dos símbolos combinados correspondientes a la tierra y al movimiento. Por separado, ninguno de estos dos símbolos está relacionado con los sismos, si bien juntos sí representan un evento sísmico cuyos efectos podrían reflejar una intensidad o grado V en la escala de intensidad sísmica ambiental conocida como ESI (Environmental Seismic Intensity) 2007. Pero también se plantea la posibilidad de que el pueblo náhuatl hubiera conseguido una escala de intensidades de sismos antes de las escalas modernas. ENGLISH: Before the arrival of the Spaniards in America, between the fourteenth and sixteenth centuries A.D., events and daily life were described through symbols in documents called codices. During the conquest, the Spaniards destroyed many of the codices because they were viewed as idolatrous. In Mexico and overseas there exist a number of codex that were artistically and consistently drawn by the Tlacuilo people who had strong knowledge in different disciplines, including natural processes, biodiversity, war, and social and religious problems. These codices contain five kinds of glyphs: numerals, calendrical, pictographic, ideographic and phonetic. One codex that contains an especially large amount of information about natural processes such as climate, volcanic eruptions, and major earthquakes, is the Telleriano Remensis. A careful analysis of this codex and related documents provides evidence for 12 earthquakes defined in space and time. Earthquakes were represented by two combined symbols: motion and earth. These symbols are not related to earthquakes themselves, but together, represent a seismic event, whose effects could be related to intensities of V in the ESI 2007 scale. The effects interpreted in the codex (tilted buildings, rolling stones, landslides, and human migration) suggest that earthquake strengths are very similar to those described in the 2007 ESI scale. The Mexicas, influenced by the Mayan culture, assigned a determined number of bars (tlalli) to each earthquake giving them a numerical representation and scale. This indicates that prehispanic cultures, such as the Aztec (Mexicas), Mixtec and Zapotec, already had some assessment criteria to scale earthquakes and their effects.

Hot springs and related deposits are common features in active geothermal areas around the world. In this study, centered on the Ixtlan de los Hervores geothermal zone (Michoacan, Mexico), we analyzed the distribution of active hydrothermal manifestations and hot-spring deposits as well as the local stratigraphy to determine the influence of the faults in the hydrothermal fluid circulation. The hydrothermal manifestations are mainly represented by hot springs with water temperatures up to 92 °C (depositing silica sinter at the surface). All the hydrothermal features are located within a tectonic depression controlled by the potentially active Ixtlan-Encinal fault. Inside this depression, lacustrine sediments were deposited from Pliocene up to the Hispanic colony period (~XVI–XIX centuries). A pre-Hispanic silica-sinter layer was identified beneath the lacustrine sediments, as well as a debris flow deposit, rich in pottery, suggesting that the debris flow may have affected local inhabitants during pre-Hispanic times.

There is an increasingly growing literature on the use of advanced multi-temporal Interferometric Synthetic Aperture Radar (InSAR) to monitor surface deformation with millimeter precision in urban and rural environments, including applications over wide areas spanning hundreds to thousands of square kilometers. In this work, we survey the eastern sector of the Trans-Mexican Volcanic Belt, extending from the state of Hidalgo, through Tlaxcala, Puebla and up to Veracruz, for a total of 19,000 km2. The surveyed area includes both the geothermal exploration site of the Acoculco caldera complex, and Los Humeros geothermal field, one of the largest geothermal exploitation sites of Mexico. Using the multi-temporal Small BAseline Subset (SBAS) InSAR method, we process the whole ENVISAT Advanced SAR (ASAR) IS2 image archive acquired in 2003-2010. Estimated subsidence rates are as high as 3.1 cm/year within the region, and a number of land deformation hotspots are identified within the urban areas of Tulancingo, Tlaxcala and Apizaco, the Tecamachalco valley, as well as within Los Humeros caldera. The surveying of such a scientifically interesting test region provides a proof of concept on how to investigate natural and anthropogenic processes in urban and rural areas using big SAR datasets and InSAR methods.

The Morelia-Acambay fault System (MAFS), located in the central part of the Trans-Mexican Volcanic Belt (TMVB) is delimited by an active transtensive deformation zone associated with the oblique subduction zone between the Cocos and North American plates, with a convergence velocity of 55 mm/yr at the latitude of the state of Michoacan, Mexico. Part of the oblique convergence is transferred to the central TMVB, just in the MAFS zone, where the slip rates range from 0.009 to 2.78 mm/year. The occurrence of great earthquakes like the Acambay earthquake ( M s = 6.7) on November 19, 1912 with a surface rupture, and in Maravatio, 1979 with M b = 5.3 are located into the MAFS. The zone is seismically active but with large periods of recurrence, as revealed by the seismic sequence (2.5 M w 3.0) occurred near the city of Morelia in October 2007, with focal mechanisms corresponding to normal faulting with left-lateral components. Moreover, there are some paleoseismic analyses showing quaternary movements of some faults with magnitudes between 6.0–7.1 M w . The purpose of this work is to probe an intrinsic definition of Active Faults for the MAFS as well as the estimation of possible maximum earthquake magnitudes, in order to understand the dynamic of seismic activity along the MAFS. For the new fault dimensions and using three empirical relationships, we found a maximum magnitude of M w = 7. Additionally, a slip-rates series were compiled and analyzed, the results show a temporal strong persistence behavior and a high value of fractal dimension ( D b = 1.86) related with a less concentration of small slip-rates. In other words, there is not an excess of the deformation in the MAFS in a single or restricted range of scales, and furthermore, this represents a migration of the ruptures to larger scales (3 ≤ length ≤ 38 km).

Soft-sediment deformation structures identified in lacustrine sediments of the San Pedro el Alto area, within the Acambay graben, Mexico, can be attributed to Pleistocene-Holocene seismic events. The analysis of these deformation structures, seismites, is a key tool for the characterization of parameters such as the intensity and magnitude of the events, and the measurement of the affected area. Analysis of the shape, distribution, abundance and genesis of these secondary structures in lacustrine basins, also provide guidelines for assessing seismic hazard. The analysis of seismites enabled the identification of three M ≥ 5 earthquakes, minimum magnitude required for the formation of such structures, these on ESI 2007 scale (Environmental Seismic Intensity Scale) correspond to VII-X intensities. The structures were identified with coseismic stratigraphy analysis in three trenches and three sediment cores from the dam within the locality. The basin infill consists of lacustrine sediments with intercalation of volcanic material. The soft-sediment deformation structures appear in different sectors of the study area and consist of surficial ruptures, vertical displacements, slumps, pseudonodules, clastic dikes, cracks filled with recent material, and diapir-like and load-flame structures.

El Estribo Volcanic Complex (EVC) is located in the northern part of the Michoacán–Guanajuato Volcanic Field within the Trans-Mexican Volcanic Belt (TMVB). El Estribo is located at the southern edge of the E-W Pátzcuaro fault that belongs to the Pátzcuaro-Jarácuaro graben, a western extension of the E-W Morelia–Acambay fault system. Stratigraphy, geochronology, chemistry, and mineral assemblages suggest that the volcanic complex was constructed in two periods separated by a ~ 100 ka volcanic hiatus: a) emission of lava flows that constructed a shield volcano between 126 ka, and b) mixed phreatomagmatic to Strombolian activity that formed a cinder cone ~ 28 ka. The magmas that fed these monogenetic volcanoes were able to use the same feeding system. The cinder cone itself was constructed by Strombolian fallouts and remobilized scoria beds, followed by an erosion period, and by a mixed phreatomagmatic to magmatic phase (Strombolian fallouts ending with lava flows). Soft-sedimentary deformation of beds and impact sags, cross-bedding, as well as pitting and hydrothermal cracks found in particles support the phreatomagmatic phase. The erupted magmas through time ejected basaltic andesitic lava flows (56.21–58.88% SiO2) that built the shield volcano and then basaltic andesitic scoria (57.65–59.05% SiO2) that constructed the cinder cone. Although they used the same feeding system, the geochemical data and the mineral chemistry of the magmas indicate that the shield volcano and the cinder cone were fed by different magma batches erupted thousands of years apart. Therefore, the location of El Estribo Volcanic Complex along an E-W fault that has generated two sector collapses of the shield volcano to the north may be directly linked to this complex redistribution of the magmatic paths to the surface. Our findings show that magmatic feeding systems within monogenetic volcanic fields could be long lived, questioning the classic view of the monogenetic nature of their volcanoes and yielding information about the potential volcanic risk of these settings, usually considered risk-free. We gratefully acknowledge UNAM and CONACYT for the postdoctoral financial support.

The Sierra de Mil Cumbres is a Miocene volcanic range located in central Mexico, in the north-eastern part of the State of Michoacan, near the city of Morelia. Structurally it is a ENE-trending horst that covers an area of 1022 km2 (approximately 20 km wide × 60 km long) and contains exposures of chemically-bimodal volcanism in the form of ignimbrites, lava domes, lava flows, cinder cones, and related deposits. The main volcanic manifestations of this range are the La Escalera Caldera (16.3–23 Ma), the Garnica Volcanic Complex (18.3–17.9 Ma), the Atecuaro Caldera (16.3–19.4 Ma), and the Indaparapeo Volcanic Complex (14.1–17.5 Ma). The Sierra de Mil Cumbres stands in space and time at the intersection between the Miocene–Recent Trans-Mexican Volcanic Belt and the Late Cretaceous–Early Miocene Sierra Madre Occidental, and so provides new insights into the geological evolution of central Mexico. Arc volcanism in the Sierra de Mil Cumbres was initiated by a massive NNW–SSE extension, probably during the counterclockwise rotation of the Sierra Madre Occidental. New geological mapping, stratigraphic analysis, detailed geochemistry and 40Ar/39Ar geochronology demonstrates that this intra-plate volcanism was emplaced between 14 and 23 Ma.

On 27 May 1937, after one week of sustained heavy rainfall, a voluminous flood caused the death of at least 300 people and the destruction of the historic El Carmen church and several neighborhoods in the mining region of Tlalpujahua, Michoacán, central Mexico. This destructive flood was triggered by the breaching of the impoundment of the Los Cedros tailings and the sudden release of circa 16 Mt of water-saturated waste materials. The muddy silty flood, moving at estimated speeds of 20–25 m s−1, was channelized along the Dos Estrellas and Tlalpujahua drainages and devastated everything along its flow path. After advancing 2.5 km downstream, the flood slammed into El Carmen church and surrounding houses at estimated speeds of ~ 7 m s−1, destroying many construction walls and covering the church floor with ~ 2 m of mud and debris. Revision of eyewitness accounts and newspaper articles, together with analysis of archived photographic materials, indicated that the flood consisted of three muddy pulses. Stratigraphic relations and granulometric data for selected proximal and distal samples show that the flood behaved as a hyperconcentrated flow along most of its trajectory. A total volume of the Lamas flood deposit was estimated as 1.5 × 106 m3. The physically based bidimensional (2-D) hydraulic model FLO-2D was implemented to reproduce the breached flow (0.5 sediment concentration) with a maximum flow discharge of 8000 m3 s−1 for a total outflow volume (sediment + water) of 2.5 × 106 m3, similar to the calculations obtained using field measurements. Even though premonitory signs of possible impoundment failure were reported days before the flood, and people living downstream were alerted, authorities ordered no evacuations or other mitigative actions. The catastrophic flood at Tlalpujahua provides a well-documented, though tragic, example of impoundment breaching of a tailings dam caused by the combined effects of intense rainfall, dam weakness, and inadequate emergency-management protocols – unfortunately an all-too-common case scenario for most of the world's mining regions.

Cacahuamilpa cave is one of the largest karst systems in Central Mexico. The cave contains numerous massive speleothems broken and fallen following oriented directions, damaged during cataclysmic geological events. One fallen and two broken speleothems were sampled in the Cacahuamilpa cave for dating the rupture event using measured U–Th disequilibrium ages. A total of eight small carbonate cores were drilled perpendicular and longitudinal to the rupture surface. Results showed three groups of ages (weighted average): 0.95 ± 0.02 ka, 28.8 ± 0.2 ka and 88.0 ± 0.7 ka. This indicates that the construction of the Cacahuamilpa karst system, for which no absolute ages existed before this study, initiated at least since Late Pleistocene. The first two groups of ages might be related to two distinct episodes of intense seismic activity. Calculated minimum horizontal ground acceleration and frequency values of the seismic events needed to create the rupture of the stalagmites dated at 0.95 ± 0.02 ka and 28.8 ± 0.2 ka range between 1.3 and 2.0 m s −2 and between 13.4 and 20.8 Hz, respectively. These parameters are compatible with earthquakes of magnitude equal or higher than 7 M, with an epicentral distance between 50 and 100 km from the Cacahuamilpa cave. The stalagmite rupture dated at 88.0 ± 0.7 ka might result from the invasion of the cave by one of the older lahars deposits of the nearby volcano Nevado del Toluca, and successively fell by gravity instability.

The El Estribo volcanic complex is located in the north-central part of Michoacan State (Mexico) within the Michoacan–Guanajuato Volcanic Field. It consists of a ~ 126 kr shield volcano crowned by a cinder cone, separated by a paleosol dated at 28,360 ± 170 BP. The shield volcano has been cut by the E–W normal Patzcuaro fault that exposes 200-m of piled up lavas flows. Our field reconstruction suggests that two collapses have been originated from this fault. Two debris avalanche deposits with hummocky topography are exposed between this fault and the southern shore of the Patzcuaro Lake. The basal debris avalanche deposit (BDAD) covers lacustrine sediments and is covered by a paleosol that at 28,110 ± 720 yr BP yielding a minimum age for the event. It had a maximum run out of 3.2 km with a H/L of 0.0062. The upper debris avalanche deposit (UDAD) is overlain by a paleosol dated at 14,110 ± 60 yr BP that yields a minimum age of the event. It had a maximum run out of 2.3 km with a H/L of 0.0086. No pyroclastic deposits have been found in association with these debris avalanches and the shield volcano rocks show signs of intense hydrothermal alteration or abundant clay minerals for which we assume that failure was triggered by seismic–tectonic activity. The older debris avalanche was more mobile because it moved on water and on top of water-saturated sediments deforming them and likely originating a tsunami across the lake. Instead, the younger debris avalanche moved across the previous rugged hummocky topography of the basal avalanche resulting in a more restricted dispersion. These collapse events of El Estribo, the morphology of the scarp and historic and modern seismicity indicate that a future failure represents a serious threat to the surrounding communities of the Patzcuaro Lake. Consequently, some preventive measurements as seismic and deformation rate monitoring are necessary. Today five villages with circa 1500 inhabitants live upon the mass waste deposits.

The Cerro Prieto Volcanic Complex (CPVC), located in northwestern Mexico, is the only surface manifestation of the Cerro Prieto Geothermal Field, the third largest producer of geothermal energy in the world. This geothermal field and the Salton Sea in the USA sit in a pull-apart basin that belongs to the trans-tensional tectonic zone that includes the San Andreas Fault system and the Salton Trough basin to the NW and the East Pacific Rise to the SE. In spite of its strategic importance in the generation of geothermal energy, the origin of Cerro Prieto and its relationship with the geothermal reservoir were unknown. In this contribution, we discuss the origin, evolution, and mechanisms of formation of this small monogenetic volcano and the magmas that fed the system. The volcanic complex is located on top of the Cerro Prieto left lateral fault to the northwest of the Cerro Prieto Geothermal Field. The complex consists of a lava cone and a series of domes (∼0.15 km3) protruding from Tertiary sandstones and recent unconsolidated sediments of the alluvial plain of the Colorado River. The Cerro Prieto Volcanic Complex consists of seven stratigraphic units emplaced in a brief time span around 78–81 ka. Its activity began with the extrusion of a dacitic lava that came into contact with water-saturated sediments, causing brecciation of the lava. The activity continued with the emplacement of dacitic domes and a dyke that were destroyed by a phreatic explosion emplacing a lithic-rich breccia. This phreatic explosion formed a 300-m-wide and 40-m-deep circular crater. The activity then migrated ∼650 m to the SW where three dacitic lava domes were extruded and ended with the emplacement of a fissure-fed lava flow. Subsequent remobilization of the rocks in the complex has generated debris and hyperconcentrated flow deposits interbedded with fluviatile sediments in the surrounding terrain. All rocks of the CPVC are dacites with phenocrysts of plagioclase, orthopyroxene, and Fe-Ti oxides and minor quartz. Gabbro-dioritic dykes intruded in Tertiary sandstones and siltstones of the local basement contain phenocrysts of plagioclase, clinopyroxene, Fe-Ti oxides, and olivine. All CPVC rocks are chemically homogeneous suggesting discrete modifications by crustal assimilation, fractional crystallization, or magma mixing processes during upper crustal residence. Aeromagnetic results suggest that the depth of the magmatic source in the area is located below 3.5 km. CPVC rocks contain chemical anomalies typical of subduction zones, which suggests that all CPVC magmas could have been generated by partial melting of the remains of the subducted Farallon plate.

Mexico, largely a tropical mountainous region, is continually subjected to natural hazards like landslides induced by heavy rainfalls. At the end of January 2010, two cold fronts and low-pressure storms moved over the State of Michoacan (central Mexico) and in February the town of Angangueo, in the eastern sector of the Monarch Butterfly Biosphere Reserve, was devastated by a huge muddy debris flow. The in situ observations after the event showed that considerable material was removed from the countryside surrounding the urban area. In this framework two low order streams were indicated as the main suppliers of granular material to the Angangueo River: Melon and Catingon creeks. To evaluate the residual risk and slope stability along these two torrential watercourses, specific investigations were carried out. A GIS-based map of the most relevant hazardous features was performed at high level of detail by means of targeted field surveys that distinguished natural and anthropogenic elements like: (i) riverbanks and slopes with new signs of instability and already collapsed areas; (ii) large accumulations of debris and plant remains in channels and slopes; (iii) deposits of mining waste and abandoned mining areas; (iv) hydraulic works along the riverbeds and (v) cultural elements potentially at risk. In both circumstances, a generalized criticality emerged; moreover, all the riverbanks along the Catingon creek are almost still under unstable conditions, whereas Melon creek has precarious riverbanks only for about 1/3 of the considered slopes. In both cases, the depth of their rupture surfaces seems directly related to the different geotechnical properties of existing materials with some influence from gradients.

Earthquake Environmental Effects describe the geological features of an earthquake, including the surface faulting, ground cracks, soil liquefaction and landslides, among others. Historical large earthquakes could be classified according to the EEE macroseismic geological scale (ESI07), with the advantage that it is possible to compare different earthquakes which have occurred in different places and estimate the parameterization of their seismogenic sources. Hence, we have determined the ESI07 scale by the EEE description of the geological effects observed during the 1912 Acambay earthquake, which took place in the central basin of Mexico. Additionally, we have estimated the epicentral area of this earthquake, the total rupture length and the potential seismicity of the Acambay-Tixmadejé fault zone. Furthermore, we have estimated the earthquake archaeological effects (EAEs) of the oriented damage. To do this, we have modelled the S-wave travelling by assuming different epicentre locations at several active fault segments and thus, we have compared with the oriented damage mapped by Urbina and Camacho (1913) at different villages. Therefore, we propose a model of rupture of 1912 Acambay earthquake, releasing a M ≥ 7 earthquake and with the epicentre located at Tixmadejé. This rupture model implies earthquake directivity towards East and the S-wave travelling towards South. The total rupture length was estimated 33 km and the maximum coseismic offset 52 cm., Instituto Geológico y Minero de España, España, Instituto de Investigaciones Metalúrgicas, Universidad Michoacana de San Nicolás de Hidalgo, México

Volcanic rocks, especially ignimbrites, exhibit complex mechanical behaviours due to their large variation in welding, porosity, textural and granulometrical characteristics. Moreover, there is a lack of knowledge of how alteration processes affect their intrinsic properties. Main objective of this research is to characterize the physical, mechanical, and hydraulic behaviour of different lithofacies of the Cuitzeo ignimbrites (Mexico). These volcaniclastic mixtures of lithics and pumice supported by a fine-rich matrix are characterized by different textural and granulometric features. A general lithostratigraphic section and geological mapping of the study area were accomplished to attain the temporal and spatial distribution of the ignimbrites. Strength, deformation and the failure mode of selected lithofacies were directly related to micro-textural and granulometric characteristics by a series of uniaxial and pre- and post-failure non-destructive analyses (e.g. ultrasonic pulse velocity and X-ray image tomographies). Results for four different lithofacies were compared, allowing us to explore the variation in the mechanical properties associated with characteristics derived from diagenesis. Petrophysical properties show that there is a large dependence on the textural characteristics and particularly on the pumice fragments content. Results derived from laboratory observations and X-ray image reconstruction analysis, show that the main differences in the average values of porosity are associated to the geometry and morphology of the grains and pore network. These are closely related to the stress – strength relationship and the mode of failure of each specimen. In general, the strength for all lithofacies tends to increase linearly with several of the physical properties (e.g. ultrasonic pulse velocity, bulk density). Slake durability tests demonstrate that a large part of the mechanical degradation could be attributed to swelling during wetting-drying cycles. This decay is significant in lithofacies with groundmass rich in expansible clays.

Twenty three ENVISAT Synthetic Aperture Radar (SAR) images acquired in 2003–2010 were processed with conventional SAR Interferometry (InSAR) and Persistent Scatterer Interferometry techniques, to investigate spatial and temporal patterns of land subsidence in Morelia, Mexico. Subsiding areas are distributed as either concentrated circular patterns corresponding to intense groundwater extraction (e.g., Rio Grande meander area; maximum deformation of 7–8 cm/yr) or as elongate patterns oriented along NE–SW or E–W directions and parallel to major faults (i.e. La Colina, La Paloma and Central Camionera; maximum deformation of 4–5 cm/yr). High subsidence rates are also measured on the hanging wall of major normal faults, where the thickest sequences of compressible Quaternary sediments crop out. Strong contrasts in subsidence rates are identified across major faults, suggesting that these faults act as barriers to horizontal movement of groundwater. Subsidence rates show a weak positive correlation with the total thickness of compressible deposits, while there is no correlation with either water extraction rates or changes in static water level. Time-lapse analysis of ground deformation with conventional InSAR reveals temporal variations of subsidence north of the La Colina fault and the Rio Grande meander area. For this latter area, cross sections and 3D perspectives of InSAR measures, and analysis of subsidence rates through time, show an acceleration of subsidence velocities since 2005, corresponding to recasing of the Prados Verdes II well, whose location is centered in the area of highest subsidence.

The Michoacan-Guanajuato Volcanic Field displays about 1040 monogenetic volcanoes mainly composed of basaltic cinder cones. This monogenetic volcanic field is the consequence of a dextral transtensive tectonic regime within the Transmexican Volcanic Belt (TMVB), the largest intra continental volcanic arc around the world, related to the subduction of the Rivera and Cocos plates underneath the North American Plate. We performed a statistical analysis for the size-distribution of the basal diameter (Wco) for cinder cones. Dataset used here was compiled by Hasenaka and Carmichael (1985). Monogenetic volcanoes obey a power-law very similar to the Gutenberg–Richter law for earthquakes, with respect to their size-distribution: log 10 ( N >= Wco ) = α − β log 10 ( Wco ), with β = 5.01 and α = 2.98. Therefore, the monogenetic volcanoes exhibit a (Wco) size-distribution empirical power-law, suggesting a self-organized criticality phenomenon.

Some 3600 years ago the SW flank of Volcan de Colima collapsed, generating a debris avalanche that travelled 25 km to the Armeria River and stopped against the Cerro Grande limestone escarpment. The debris avalanche deposit covers an area of 48 km2, has an average thickness of 35 m, and a volume of 1.7 km3, with an H/L ratio of 0.13. Along the La Lumbre ravine, the deposit forms a series of flat terraces up to 65 m thick. A pyroclastic flow deposit overlies the debris avalanche deposit, suggesting that the Colima collapse was accompanied by a magmatic component. The debris avalanche deposit dammed the Armeria River, forming a temporary lake that accumulated a water volume of ∼ 0.19 km3. The subsequent breaking of the dam formed a debris flow that travelled at least 20 km along the Armeria River, emplacing 15–70 m thick deposits. The debris flow deposits cover a surface of 6.4 km2 and have a volume of ∼ 0.2 km3. The avalanche deposit contains fragments of carbonized wood that where dated at 3600 ± 120 yr. BP by Komorowski et al. (1997). This deposit underlies a younger debris avalanche (2505 ± 45 yr BP), and a debris flow deposit with pottery shards and charcoal dated at 1940 ± 90 yr BP. These pottery shards likely related to the Capacha people (820–300 yr BC) indicating that the region has been inhabited during the last 3000 years. A future collapse of Volcan de Colima in the same direction may affect several towns for a total population of circa 40,000.

Pronounced lacustrine sedimentation developed in west-central Mexico during the late Miocene, between approximately 11 and 7 Ma. This was in response to tectonic extension associated with the initial emplacement of the late Miocene substrata of the Trans-Mexican Volcanic Belt. Climatic conditions in west-central Mexico during this interval were relatively warm and humid based on the widespread distribution of interpreted lacustrine beds. Following a latest Miocene (8.0–5.4 Ma) stage of arid conditions and greatly reduced deposition of fine-grained lacustrine sediments, extensive, east–west oriented, relatively deep, perennial lakes ensued. They mark the early Pliocene (5.3–4.0 Ma). Lower Pliocene diatomites contain the same diatom species (e.g., Stephanodiscus carconensis and Tertiarius aff. baikalensis) found in rocks of this age in the western United States. The relatively warm and humid conditions that characterized this interval in central Mexico coincide with a period of high-latitude warming, higher global sea level, and a reduction in size of the Antarctic Ice sheets. Because the Central American Seaway persisted until at least the latest Miocene, it might have acted to increase precipitation in central Mexico. This could have continued into the earliest Pliocene. Mexican Pliocene mammalian faunas also support a savanna setting with moist and warm conditions prevailing at the time. Shallow lakes and fluvial conditions dominate after 4.0 Ma, until the end of Pleistocene. A combination of reduced precipitation, due to general global cooling and drying, as well as volcanic and tectonic processes, are presumed to have been the cause for this mid-Pliocene reduction in lake size and extent in central Mexico.

A new methodology is introduced to estimate the most probable epicentral area for a paleoearthquake interpreted from seismites within a Quaternary basin. Seismites were described from various detailed stratigraphic logs within the Tierras Blancas Basin (TBB), a Pleistocene lacustrine area located in the central part of the Trans-Mexican Volcanic Belt (TMVB). The lacustrine landscape evolution of TBB has been determined by the recent fault activity of the Morelia-Acambay Fault System (MAFS). The TBB is bounded by active normal faults striking E-W. This fault activity has generated soft-sediment deformation structures, sand, silt and gravel dikes, pillows, diapirs, and decametric slumps, disturbing the sedimentary infilling. From these seismites and their stratigraphic spatial correlation, five strong-moderate paleoearthquakes (E1–E5) have been established in the basin. The spatial distribution of these seismites exhibits a gradient of perturbation defined by the intensity of deformation. Three different degrees of intensity deformation (DDI) are associated with the liquefacted grain size sediments: I (silt liquefaction), II (silt and sand liquefaction), and III (silt, sand and gravel liquefaction). This spatial gradient indicates an increase of the energy involved from the seismic activity, related with the proximity of the source. Mapping the boundaries among these zones of deformation and interpolation of each DDI limit for paleoearthquake E4 was used to construct paleoseismic isolines of deformation as a potential indicator of the most probable paleoepicentral zone. A 1.5 km 2 elongate zone oriented NNW-SSE is the potential paleoepicentral area associated with paleoearthquake E4 within the TBB.

Most of the urban areas located in the Central and Northern sectors of the Mexican Volcanic Belt (MVB) during the last two decades registered differential ground subsidence along preferential directions parallel to the regional fault system. The combination of the consolidation of soft terrains due to groundwater withdrawal with the presence of regional and local systems of normal faults has been addressed as the controlling factors of the spatial distribution of the ground movements. In this paper we present the preliminary results of a DInSAR analysis carried out over the main cities of the MVB using ENVISAT data spanning the period 2003-2006. The analysis revealed the presence of ground displacements along the same linear structures as identified in the field, reaching at some locations velocities up to 6-7 cm/year.