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During the last decade, in several localities of the Cuban provinces of Matanzas, Villa Clara, Cienfuegos and Sancti Spíritus, seismic movements have been perceived, causing great concern on their population and institutional managers. The purpose of this research was to evaluate the possible causes of the seismicity originating in the aforementioned provinces based on the analysis of the Cuban seismic catalogues and the available geological and geophysical articles and reports. It was possible to reveal that release of seismic energy accumulated in the rocks is the cause of reactivating regional and minor order faults, what justifies the seismicity in this zone. The different performance of seismic activity recorded in these territories is due to the unequal response to tensions accumulated mainly by the geologicaltectonic complexity and its relationship or not with gravitational and isostatic blocks. [ABSTRACT FROM AUTHOR]

An alternative methodology is presented to generate elastic design spectra by levels of selected confidence, using the lognormal distribution, based on the seismic zoning maps that exist in the standard codes or seismic tectonics on place, using base seismological data, supplemented with studies of wave propagation and the type of soil profile. [ABSTRACT FROM AUTHOR]

The Isla del Coco (also known as Cocos Island), in the Eastern Pacific Ocean, has a rough topography, an area of 24km², and is the only sub-aerial topographic height of the summit of a volcano located in the margin of the Cordillera Volcánica del Coco (also known as Cocos Ridge). The Cocos Ridge is a well defined linear bathymetric height, issued from the active volcanism of the Galápagos hotspot during the last 15 million years (Ma); it is the largest geographic feature of Costa Rica, as a volcanic range of 780km long in its territorial seawaters. Isla del Coco is part of a submarine shield volcano of complex evolution, which erupted several times above sea level during the Lower Pleistocene (2.2-1.5Ma). The island and other seamounts are the result from a mantle thermal anomaly that erupted through volcano-tectonic fissures in the oceanic crust. The rocks consist mainly of alkali basaltic lava flows (aa, pahoehoe, blocky lavas) and dikes, minor trachyte lava flows, volcanic domes and dikes, with subordinate pyroclastic and epivolcanic rocks. Colluvial, soils and local littoral deposits such as sand and gravel beaches are also present. The island has a juvenile erosive stadium, but their submarine erosive arcs and platforms (90-110m and 183m depth) are probably the result of the erosion occurred during last two glacial maxima, besides slow subsidence events of the island due the thermal cooling of the volcanic shield and its oceanic crust. The most important current external geodynamic hazards are landslides, tsunamis and rare seismic events, Mw ≤ 5.8 in a 300km radio associated to N-S right lateral strike slip faults. However, the limited seismic data available, and geomorphological alignments, indicates that there is some seismic activity related to local faults oriented N-S, ENE and in a lesser extend NW trend. Seismicity and rainfall have triggered landslides; liquefaction is restricted to Chatham and Wafer bays' beaches. Moderate historical and prehistorical tsunamis were related to regional seismic events. The relative young age of Isla del Coco makes it an interesting place to study the evolution and migration of species, and their genetic features. More detailed studies related to tephrostratigraphy, neotectonics, marine geomorphology, evolution of seamounts, lava flow morphology, and submarine hydrothermal activity, are still necessary to understand the expression of internal geodynamic processes in this region. [ABSTRACT FROM AUTHOR]

A geometric model for the subduction of the Nazca plate beneath the South American plate in southwestern of Colombia is proposed based on the relocation of hypocenters of local and distant earthquakes. By means of the simultaneous inversion of teleseismic P and SH body waves, the depths of the 15 events with Mw = 5.8 were constrained, and the hypocenters of the 250 earthquakes recorded between 1990 and 2005 by the International Seismological Centre (ISC) and U.S. Geological Survey, National Earthquake Information Center (NEIC) were constrained and relocated. A model is proposed for the hypocentral sections taking into account the trench along of the Earth and Colombia-Ecuador. Three different possible shapes of subduction of the Nazca plate in the Colombia-Ecuador trench were obtained: The first configuration, in the Cali A segment, the dip angle changes from17° to 45° down to a maximum depth of 100km; the second configuration, in the Popayán B and Nariño C segments, the dip angle holds approximately constant at 30° down to a maximum depth of 200 km; and the third configuration, in the Quito D segment, the dip angle changes of 9° to 50° to a maximum depth 220 km. The maximum depth of seismicity along the Colombia-Ecuador trench shows two increases, the first between latitudes 4.5°N-5°N and the second between the latitudes 1°S-2°S, which suggest that the presence of the Malpelo and Carnegie Ridges may generate a differential blockage at the Pacific Colombia-Ecuador basin. [ABSTRACT FROM AUTHOR]

The Romeral Fault System (RFS) extends 1600 km from Barranquilla-Colombia to Talara city-Peru and before the Pliocene. In the Middle Eocene RFS defined the northwestern border of the South America plate, being originated by a triple junction rift — rift — rift occurred from lower to middle Jurassic, when the South American sector separated from Chortis, Oaxaca and Yucatan blocks. From Late Mesozoic until Early Paleocene, the Paleo Pacific plate converged on NW South America corner being subducted when an anomalous thick oceanic crust, represented by the Caribbean plate, was accreted extinguishing gradually from the North of Peru to the North of Colombia. The collision generated a transtensive field stress in back arc region, due to the ancestral Central Cordillera rising in continental border. The RFS rocks suffered low grade metamorphism and some rocks of extinct subduction zone suffered metamorphic inversion. During Late Paleogene until Early Miocene, the convergence South America, Farallon and North America plates produced clockwise rotation in Caribbean Plate, which moved to NE producing a dextral displacement in the suture, generating big milonyte belts in the RFS rocks. With the Farallon Plate break, in the Middle Miocene, due to Galapagos triple junction activation, the Caribbean plate moved to the NNE colliding with the south of the North American plate, being trapped between South and North American plates. This caused the Costa Rica-Panama-Choco block (CRCB) collision with the NW of South America plate, deforming the north of the Northern Andes generating a change in the convergence of Nazca plate in this sector. From Late Pliocene, when convergence change finish, Carnegie Ridge collision in the south of NW South America configuring the actual lithosphere geometry and the orogenic styles of the Northern Andes. Based on Petrogenetic correlations supported by interpretation of secondary sources in geology, tectonic, petrogenesis and geophysics, a model for a regional seismotectonic characterization of this zone was done. The deformed zone represents an extinct subduction zone including fore arc basin rocks with fragments of a Lower — Late Cretaceous volcanic arc and some continental fragments of South America plate. I conclude that RFS is a weak rheologic area and a lithosphere contrast between a thick oceanic and the continental crust, presenting a high seismological activity with historically great earthquakes in Colombia and Ecuador. [ABSTRACT FROM AUTHOR]

Global Positioning System (GPS) data from southern Central America and northwestern South America collected between 1991 and 1998 reveal wide plate margin deformation along a 1400 km length of the North Andes. Also associated with the oblique subduction of the Nazca plate at the Colombia-Ecuador trench is the 'escape' of the North Andes block (NAB). The NAB is delineated by the Bocono-East Andean fault systems and the Dolores Guayaquil Megasheare to the east, the South Caribbean deformed belt on the north and the Colombia-Ecuador trench and Panama on the west. Within the NAB many damaging crustal earthquakes have occurred which is most recently exemplified on January 25, 1999 (Mw = 6.1) Armenia earthquake. Preliminary analysis of recent occupations (2003 GEORED GPS) of several previously observed (1996-2001) GPS sites suggest shear strain accumulation rates in the Cauca valley near Cali of approximately 2.1 × 10-7 yr-1 and 1.6 × 10-7 yr-1. These strain rates are measured within 2 Delaunay triangles with common vertices at Cali and Restrepo, which encompass areas, located north and west of Cali. Seismicity has been monitored in the Cauca Valley for the last 17 years by the "Observatorio Sismolégico del Suroccidente" (OSSO) since 1987 and by the Red Sismolégica Nacional del INGEOMINAS since 1993. Their catalogs list numerous shallow earthquakes near Cali but nothing larger than magnitude 5. Historically, however, several large earthquakes are associated with the "Falla Cauca Almaguer" in locations both to the south and north of Cali in the Cauca valley. Preliminary calculations using the strain rates determined for these Delaunay triangles and a simplified Kostrov formula suggest possible decadal (30 . 90 years) recurrence intervals for Mw = 6.0 . 6.3 earthquakes, centenary (90 . 900 years) recurrence intervals for Mw = 6.4 . 6.9 earthquakes and millennial (900+ years) recurrence intervals for Mw ≥ 7 earthquakes. [ABSTRACT FROM AUTHOR]

Several methods for seismic risk calculation were analyzed in order to obtain the more adequate one in relation with real data and conditions, available for seismic risk determination in Bayamo city. The seismotectonic risk, which expresses the periodicity of occurrence in determined zone, is analyzed using the computer techniques and systems. [ABSTRACT FROM AUTHOR]

The "La Salina" Fault, located in a region of high seismicity was studied in an area of 294 km² in the Santander Department, it's defined as an inverse fault. In general it doesn't present clear morphological or actual activity evidences. In the area of the Hydroelectrical Project of the Sogamoso River by ISAGEN S.A., a six stations seismic network was installed in an area near to the fault. During 124 days, 2.367 seismic events were evaluated; from these, 339 acceptable quality events were chosen for doing maps and profiles. Most of the seismicity is related to the "Bucaramanga Nest", other 131 seismic events ware related to the mapped faults. Only two events were related to the "La Salina" Fault, defining a indicating low activity. [ABSTRACT FROM AUTHOR]

Focal mechanism solutions of twenty recent earthquakes occurred at different depthes and tectonics environment have been analysed to establish the seismotectonic framework of the central region of Colombian territory. The intermediate earthquakes in the western part of the region, in the majority respond to traction force and correspond to the subduction phenomenon of the oceanic lithospheric material beneath continental plate. While the superficial events occurred at the continent crustal in the majority being of compressional type are related with the activity of different faults that cross the region. This activity is derived from the collision of the Nazca plate with the Andean Block. On the East Andean frontal fault system is noted a continuation of the tectonic stresses at the interior of the crustal to the earth's surface. In general, the geodymanic regimen of the nothwestern corner of the South American continent is governed by the collision of three major tectonic plates, that cause the deformation and displacement of the Andean Block in NNE direction. [ABSTRACT FROM AUTHOR]