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Earthquake Environmental Effects (EEEs) such as surface faulting, landslides, liquefaction and tsunamis are widely distributed following strong seismic events and may account for a significant part of the overall damage. Here, we investigate EEEs generated by two earthquakes with different source parameters, both occurring along the Mexican subduction zone: the Sept. 8, 2017, Mw 8.2, moderate depth, normal fault, intraslab event; and the June 23, 2020, Mw 7.0, shallow depth, thrust fault, interface event. We document all the EEEs for each event, assign an intensity value using the Environmental Seismic Intensity (ESI-2007) scale, and derive the macroseismic fields. Finally, we compute the attenuation of intensity with distance and we compare it with other subduction zone earthquakes worldwide, demonstrating the repeatability of EEEs. This work represents the first application of the ESI-2007 scale to an intraslab earthquake and documents its wide applicability in different seismotectonic settings. We argue that EEEs provide useful information that should not be neglected in seismic hazard assessment procedures.

On May 29, 2017, the MW6.6 Poso earthquake occurred in Central Sulawesi, Indonesia, causing moderate damages. The mainshock rupture and primary aftershock cluster occurred in the active Palolo-Sausu tectonic zone, and some aftershocks also took place around the Tokararu fault. However, the rupture mechanism of this earthquake and its relation to regional tectonics are not clear. In this study, the rupture process of the Poso mainshock is estimated by finite-fault waveform inversion, which is constrained by teleseismic bodies and surface waves. The rupture propagates upward unilaterally in a southwest-dipping moderate-angle (∼34°) normal fault beneath Tokorondo Mountains, with a notable ∼15% initial moment release at the first 4s of the ∼12s rupture duration. The average and peak slip are 0.5 m and 1.5 m, respectively. The rupture velocity is relatively slow (less than 2.5 km/s), and the Coulomb stress changes due to the mainshock are obtained using the inverted coseismic slip.

Dinar Fault is an active breakaway fault that plays an essential role in the southwestern Anatolia extensional tectonic regime's neotectonic development. The Dinar Fault's seismicity was proven by October 1, 1995, Dinar Earthquake (Mw 6.2). It consists of three geometric segments called Gumussu, Kizilli and Dikici, respectively, from northwest to southeast. The October 1, 1995 Dinar Earthquake occurred on the Kizilli Segment, approximately 10 km long, located in the middle of the Dinar Fault. In this study, active tectonic and kinematic characteristics and paleoseismic history of the Dinar Fault were investigated. Based on the fault plane slip data obtained from the Dinar Fault, it is a normal fault with a minor right-lateral strike-slip component. A total of four trenches were excavated across the 1995 surface rupture. According to paleoseismological trench studies, the Dinar Fault's slip rate was estimated as 0.37–0.56 mm/year and the average earthquake recurrence interval was 523 years in the last 3660 years. A number of these earthquakes destroyed the ancient city of Apameia Kibotos (ancient Dinar). The last earthquake that occurred on the Dinar Fault is the October 1, 1995 Dinar Earthquake. The date of the penultimate event occurring on the Dinar Fault was determined as AD 1318–1486, while the antepenultimate event was determined as AD 916–1155. The oldest event occurring on the Dinar Fault was determined as AD 916–111 BC. Structural and paleoseismological data indicate that the other sub-segments of the Dinar Fault, which did not rupture in the 1995 earthquake, have the potential to produce earthquakes with magnitudes varying between Mw: 6.2 to Mw: 6.6.

[Abstract Normal faults grow either by radial propagation and segment linkage or by accruing displacement without a proportional increase in fault length. To test these competing models of fault growth, a novel 2D seismic stratigraphic interpretation of the recent Fucino Basin of the central Apennines (Italy) has been performed. The Fucino is a major Pliocene‐Quaternary non‐marine ‘extensional collapse basins’, developed immediately after the Apenninic compressional strain had locally abated, and bounded by seismogenic faults that generate strong (Mw = 6–7) and destructive earthquakes. The Fucino is an overall dual polarity half‐graben, built around two border fault systems: the northern one lies along the east‐northeast striking Avezzano‐Bussi regional fault‐zone; the other, south‐eastern trending, bounds the basin to the east. Two separate fault‐driven depocentres of fluvio‐lacustrine sequences (maximum thicknesses of ~1,750 m) are present. One is associated to the northern border faults, with mainly Late Pliocene activity; the second is to the hanging‐wall of the eastern border‐faults and reveals a stepwise Pleistocene‐Recent activity. Tectonic depocentres have migrated clockwise through time, and new‐born fault systems have developed at the south‐eastern basin periphery (Gioia dei Marsi area). This, together with the progressive accumulation of throw in time without significant fault lengthening, suggests that the model of fault growth by segment linkage is not the best explanation for this basin. Instead, the stepwise onset and growth of the Fucino extensional collapse faulting, and its ongoing earthquake hazard, may have been promoted by polyphase inversion tectonics of inherited deep‐seated zones of weaknesses (e.g. Avezzano‐Bussi Line)., The Fucino is an overall dual polarity half‐graben, built around two border fault systems: the northern one lies along the east‐northeast striking Avezzano‐Bussi regional fault‐zone; the other, south‐eastern trending, bounds the basin to the east. Two separate fault‐driven depocentres of fluvio‐lacustrine sequences (maximum thicknesses of ~1,750 m) are present. The northern border fault showed mainly a Late Pliocene activity; the eastern border‐faults reveal a stepwise Pleistocene‐Recent activity. Tectonic depocentres have migrated clockwise through time, and new‐born fault systems have developed at the south‐eastern basin periphery (Gioia dei Marsi area). This, together with the progressive accumulation of throw in time without significant fault lengthening, suggests that the model of fault growth by segment linkage is not the best explanation for this basin. ]

Normal faults are commonly segmented along strike, with segments that localize strain and influence propagation of slip during earthquakes. Although the geometry of segments can be constrained by fault mapping, it is challenging to determine seismically relevant segments along a fault zone. Because slip histories, geometries, and strengths of linkages between normal fault segments fundamentally control the propagation of rupture during earthquakes, and differences in segment slip rates result in differential uplift of adjacent footwalls, we used along-strike changes in footwall morphology to detect fault segments and the relative strength of the mechanical links between them.We applied a new geomorphic analysis protocol to the Wassuk Range fault, Nevada, within the actively deforming Walker Lane. The protocol examines characteristics of footwall morphology, including range-crest continuity, bedrock-channel long profiles, catchment area variability, and footwall relief, to detect changes in strike-parallel footwall characteristics. Results revealed six domains with significant differences in morphology that we used to identify seismically relevant fault segments and segment boundaries. We integrated our results with previous studies to determine relative strength of links between the six segments, informing seismic hazard assessment. When combined with recent geodetic studies, our results have implications for the future evolution of the Walker Lane, suggesting changes in the accommodation of strain across the region. Our analysis demonstrates the power of this method to efficiently detect along-strike changes in footwall morphology related to fault behavior, permitting future researchers to perform reconnaissance assessment of normal fault segmentation worldwide.

Rupture source directivity and its potential frequency dependence remains an open question in seismology, especially for small-to-moderate earthquakes. In this research, we first calibrate a non-ergodic empirical model of the acceleration Fourier Amplitude Spectra (FAS), and then we adapt our tool in Spectral Amplitude (SA). Thanks to the large amount of high-quality seismic recordings (consisting of more than 400 earthquakes from magnitude 3.4 to 6.5, 460 stations, thus involving more than 30’000 waveforms in the time frame 2008-2018), we provide a statistical overview based on empirical evidence of seismological observations in the Central Italy area, which represents a unique natural laboratory for earthquakes occurring on normal faults. The non-ergodicity enables to remove all the other components of variability (i.e. the event-, site- and path-related) in the ground motion model (GMM) and hence allowing to better isolate the effects connected to source-directivity, that are not unaccounted in the epistemic variability of the ground motion. According to our criteria, about 36% of the analyzed events (162 out of 456) exhibits directivity. The distribution of the rupture directions is aligned, as expected, with the strikes of the major faults of the Central Apennines. We find that the directivity is a band-limited phenomenon, which spans from corner frequency (fc) up to approximately 5 times the event’s fc; in case of not very pronounced directivity, this band tends to be narrow, suggesting that the complex rupture processes at high-frequency are mainly stochastic. Moreover, we observe directivity not only during seismic sequences, but also in background seismicity. Preliminary results provide a useful hint regarding directivity’s parameterization as a frequency-dependent band-limited phenomenon, to be implemented in future ground motion modeling and scenario’s predictions.

We present high-resolution mapping and surface faulting measurements along the Lost River fault (Idaho-USA), a normal fault activated in the 1983 (Mw 6.9) earthquake. The earthquake ruptured ~35 km of the fault with a maximum throw of ~3 m. From new 5 to 30 cm-pixel resolution topography collected by an Unmanned Aerial Vehicle, we produce the most comprehensive dataset of systematically measured vertical separations from ~37 km of fault length activated by the 1983 and prehistoric earthquakes. We provide Digital Elevation Models, orthophotographs, and three tables of: (i) 757 surface rupture traces, (ii) 1295 serial topographic profiles spaced 25 m apart that indicate rupture zone width and (iii) 2053 vertical separation measurements, each with additional textual and numerical fields. Our novel dataset supports advancing scientific knowledge about this fault system, refining scaling laws of intra-continental faults, comparing to other earthquakes to better understand faulting processes, and contributing to global probabilistic hazard approaches. Our methodology can be applied to other fault zones with high-resolution topographic data. Machine-accessible metadata file describing the reported data: https://doi.org/10.6084/m9.figshare.13198259

We used the audio magnetotelluric (AMT) method to delineate subsurface resistivity structures associated with the western Ilan Plain, which is emerged from the orogenic belt in northeastern Taiwan and is thought to be influenced by the opening Okinawa Trough. The most recent extension phase of the Okinawa Trough starting from approximately 0.1 Ma involved ENE- and WSW-trending normal faults off the Ilan Plain. Nevertheless, the region was originally a thrust-and-fold belt related to the subduction of the Philippine Sea Plate under the Eurasia Plate. Our study focuses on how the later opening of the Okinawa Trough has affected this previously compressional region. From the results of the AMT surveys, we found that the area features a series of N-S trending fracture zones in addition to the E-W normal fault systems. Comparing the AMT data with the data from seismic reflection profiles, we found that the normal fault systems are truncated by young strike-slip faults and modified the relief of the rock basement in a recent stage of formation. The western part of the study area is dominated by left-lateral strike-slip faults while the eastern part is dominated by right-lateral strike-slip faults. The findings drawn from our AMT resistivity images as well as from the reinterpreted seismic profiles constitute new evidence that the extrusion regime may have gradually taken over the regional stress state and reset the regional stress-strain conditions that was one dominated by the Okinawa extension in the western and southern part of the Ilan plain.

K-Ar dating of fault gouge from the intersection of the WNW-striking Ohika Detachment of the Paparoa Metamorphic Core Complex and a NNE-striking high-angle normal fault (Ohikaiti Fault) yielded an ...

In the northwest of the Himalayan-Tibetan Orogen, the ∼250 km-long Kongur Shan extensional system in the eastern Pamir was formed during the convergence between the Indian and Asian plates. Tectonic activity of the Kongur Shan normal fault and the Tashkurgan normal fault can help to reveal the origin of east-west extension along the Kongur Shan extensional system. The Kongur Shan fault has been extensively studied, while the Tashkurgan fault calls for systemic research. In this study, low-temperature thermochronology including apatite fission track analysis and apatite and zircon (U-Th)/He analyses is applied to constrain the timing of activity of the Tashkurgan fault. Results indicate that the Tashkurgan fault initiated at 10−5 Ma, and most likely at 6−5 Ma. The footwall of the Tashkurgan fault has been exhumed at an average exhumation rate of 0.6−0.9 mm/a since the initiation of the Tashkurgan fault. Combined with previous research on the Kongur Shan fault, we believe that the origin of east-west extension along the Kongur Shan extensional system was driven by gravitational collapse of over-thickened Pamir crust.

Mountain tunnel crossing a normal fault in seismically active zone is easily affected by normal fault slip and earthquake. It is necessary to study tunnel dynamic response under action of normal fault slip and earthquake. In this paper, a three-dimensional normal fault sliding device was designed, and a shaking table test was carried out to study tunnel seismic performance under normal fault slip. The results show that peak acceleration of lining is dominated by an existence of fault and direction of seismic excitation, not normal fault slip. And the incremental strains of lining in critical zone with 1.7 times fault thickness and centered in faults induced by normal fault slip and seismic excitation are larger than ones only by seismic excitation. And the incremental strains in critical zone increase with the increase of normal fault slip magnitude ranging from 0 to 2 mm. And normal fault slip results in a significant reduction of overall tunnel stiffness subjected to an earthquake. These experimental results provide a scientific reference for prevention and control measurement of tunnel damage under earthquake and normal fault slip.

The identification and characterisation of faults in urban environments is important to inform seismic and landslide hazard, yet urban development often obscures geological and geomorphological evi...

The quantitative morphology of bedrock fault surfaces combined with aerial surveys and field identification is a useful approach to identify paleoearthquakes, obtain coseismic slips, and evaluate the seismogenic capacity of active faults in bedrock areas where traditional trenching methods are not applicable. Here, we report a case study of the Jiaocheng Fault (JCF) in the Shanxi Rift, China. Although several studies have been conducted on the JCF, its coseismic slip history and seismogenic capacity are still unclear. To address these problems, we investigated two bedrock fault surfaces, Sixicun (SXC) and Shanglanzhen (SLZ), on the JCF’s northern segment using quantitative morphological analysis together with aerial and field surveys. Quantitative fractal analysis based on the isotropic empirical variogram and moving window shows that both bedrock fault surfaces have the characteristics of vertical segmentation, which is likely due to periodic earthquakes, the coseismic slip of which can be determined by the height of the segments. Three seismic events at SXC, with a coseismic vertical slip of 1.74, 1.65, and 1.99 m, and three seismic events at SLZ, with a coseismic vertical slip of 1.32, 2.35, and 1.88 m, are identified. Compared with the previous studies, these three seismic events may occur in the Holocene, but it requires absolute dating ages to support, which is also the focus of our future work. Considering the seismologic capability (M>7.5) and the relationship between the recurrence interval of ~2.6 kyr and elapsed time of more than 3 kyr, the seismic hazard of the northern and middle segments of the JCF requires immediate attention.

Based on the interpretation of 2D seismic profiles integrated with surface geological investigations, a mechanism responsible for the formation of a large scale normal fault zone has been proposed. The fault, here referred to as the Rycerka Fault, has a predominantly normal dip-slip component with the detachment surface located at the base of Carpathian units. The fault developed due to the formation of an anticlinal stack within the Dukla Unit overlain by the Magura Units. Stacking of a relatively narrow duplex led to the growth of a dome-like culmination in the lower unit, i.e., the Dukla Unit, and, as a consequence of differential uplift of the unit above and outside the duplex, the upper unit (the Magura Unit) was subjected to stretching. This process invoked normal faulting along the lateral culmination wall and was facilitated by the regional, syn-thrusting arc–parallel extension. Horizontal movement along the fault plane is a result of tear faulting accommodating a varied rate of advancement of Carpathian units. The time of the fault formation is not well constrained, however, based on superposition criterion, the syn -thrusting origin is anticipated.

This study reports on the cosmogenic 36Cl dating of two normal fault scarps in western Turkey, that of the Manastır and Mugırtepe faults, beyond existing historical records. These faults are elements of the western Manisa Fault Zone (MFZ) in the seismically active Gediz Graben. Our modeling revealed that the Manastır fault underwent at least two surface ruptures at 3.5 ± 0.9 ka and 2.0 ± 0.5 ka, with vertical displacements of 3.3 ± 0.5 m and 3.6 ± 0.5 m, respectively. An event at 6.5 ± 1.6 ka with a vertical displacement of 2.7 ± 0.4 m was reconstructed on the Mugırtepe fault. We attribute these earthquakes to the recurring MFZ ruptures, when also the investigated faults slipped. We calculated average slip rates of 1.9 and 0.3 mm yr−1 for the Manastır and Mugırtepe faults, respectively., Geosciences, 11 (11), ISSN:2076-3263

Normal fault linkage has significant impacts on uplift patterns and erosional processes in extensional regions. However, geomorphic process-based constraints on landscape response to normal fault linkage are still scarce. Here, we use landscape evolution models to examine how a landscape responds to the linkage of two normal faults. The results demonstrate that topography dynamically responds to the changes in uplift patterns that accompany fault linkage. Specifically, our results indicate that after fault linkage, (1) the steepest topography and the highest erosion rate shift from the center of each fault segment to the linkage zone; and (2) the main drainage divide evolves from an M-shape to a bow-shape. We apply these findings to the Langshan Mountains in northern China, and suggest that the two piedmont fault segments have linked and that a high geohazard risk exists near the linkage zone, where the steep, transient topography is experiencing intense erosion.

Many low-angle normal faults (dip ≤30°) accommodate tens of kilometers of crustal extension, but their mechanics remain contentious. Most models for low-angle normal fault slip assume vertical maximum principal stress σ1, leading many authors to conclude that low-angle normal faults are poorly oriented in the stress field (≥60° from σ1) and weak (low friction). In contrast, models for low-angle normal fault formation in isotropic rocks typically assume Coulomb failure and require inclined σ1 (no misorientation). Here, a data-based, mechanical-tectonic model is presented for formation of the Whipple detachment fault, southeastern California. The model honors local and regional geologic and tectonic history and laboratory friction measurements. The Whipple detachment fault formed progressively in the brittle-plastic transition by linking of “minidetachments,” which are small-scale analogs (meters to kilometers in length) in the upper footwall.Minidetachments followed mylonitic anisotropy along planes of maximum shear stress (45° from the maximum principal stress), not Coulomb fractures. They evolved from mylonitic flow to cataclasis and frictional slip at 300–400 °C and ∼9.5 km depth, while fluid pressure fell from lithostatic to hydrostatic levels. Minidetachment friction was presumably high (0.6–0.85), based upon formation of quartzofeldspathic cataclasite and pseudotachylyte. Similar mechanics are inferred for both the minidetachments and the Whipple detachment fault, driven by high differential stress (∼150–160 MPa). A Mohr construction is presented with the fault dip as the main free parameter. Using “Byerlee friction” (0.6–0.85) on the minidetachments and the Whipple detachment fault, and internal friction (1.0–1.7) on newly formed Reidel shears, the initial fault dips are calculated at 16°–26°, with σ1 plunging ∼61°–71° northeast. Linked minidetachments probably were not well aligned, and slip on the evolving Whipple detachment fault probably contributed to fault smoothing, by off-fault fracturing and cataclasis, and to formation of the fault core and fractured damage zone.Stress rotation may have occurred only within the mylonitic shear zone, but asymmetric tectonic forces applied to the brittle crust probably caused gradual rotation of σ1 above it as a result of: (1) the upward force applied to the base of marginal North America by buoyant asthenosphere upwelling into an opening slab-free window and/or (2) basal, top-to-the-NE shear traction due to midcrustal mylonitic flow during tectonic exhumation of the Orocopia Schist. The mechanical-tectonic model probably applies directly to low-angle normal faults of the lower Colorado River extensional corridor, and aspects of the model (e.g., significance of anisotropy, stress rotation) likely apply to formation of other strong low-angle normal faults.

The 1983 Mw 6.9 Borah Peak earthquake generated ∼36 km of surface rupture along the Thousand Springs and Warm Springs sections of the Lost River fault zone (LRFZ, Idaho, USA). Although the rupture is a well-studied example of multisegment surface faulting, ambiguity remains regarding the degree to which a bedrock ridge and branch fault at the Willow Creek Hills influenced rupture progress. To explore the 1983 rupture in the context of the structural complexity, we reconstruct the spatial distribution of surface displacements for the northern 16 km of the 1983 rupture and prehistoric ruptures in the same reach of the LRFZ using 252 vertical-separation measurements made from high-resolution (5–10-cm-pixel) digital surface models. Our results suggest the 1983 Warm Springs rupture had an average vertical displacement of ∼0.3–0.4 m and released ∼6% of the seismic moment estimated for the Borah Peak earthquake and

The mobile south flank of Kīlauea Volcano hosts two normal fault systems, the Koa'e fault system (KFS) and the Hilina fault system (HFS). In historical time, at least three M>6.5 earthquakes have occurred on the basal detachment of the Kīlauea Volcano's south flank, with the most recent being the 4 May 2018 M6.9 earthquake. Here we analyze kinematic Global Positioning System data collected from 2001 to 2017 and interferometric synthetic aperture radar data before, during, and after the 2018 M6.9 earthquake to determine the crustal motion across the HFS and KFS faults. Our results indicate that the HFS faults did not significantly slip during the interseismic period from 2007 to 2011. Despite its substantial magnitude, interferometric synthetic aperture radar (InSAR) data show that the 2018 M6.9 earthquake triggered subcentimeter level slip along sections of the previously mapped HFS branches. Up to 20 cm of offset occurred on what appears to be a newly formed (or previously unknown) fault near the eastern end of the HFS. During the 3 months following the M6.9 earthquake, up to ~30 cm of slip occurred along the KFS, which helps accommodate rapid large‐scale subsidence of Kīlauea's summit region as large volumes of summit reservoir magma fed the lower East Rift Zone eruption. The HFS appears to activate only in concert with large earthquakes on the basal detachment. The KFS, on the other hand, moves both seismically during small local earthquakes and aseismically in response to nearby earthquakes and caldera subsidence.

Normal faulting earthquakes rarely rupture the entire extent of active normal faults, and can also jump between neighbouring faults. This confounds attempts to use segmentation models to define the likelihood of future rupture scenarios. We attempt to study this problem comparing the offsets produced in single earthquakes with those produced by multiple earthquakes over longer timescales, together with detailed studies of the structural geology. We study the active normal fault system that caused the Mw 6.3 2009 L'Aquila earthquake in central Italy, comparing the spatial distribution of coseismic offsets, cumulative offsets that have developed since 15 ± 3 ka, and the total offsets that have accumulated since the faults initiated at 2–3 Ma. Our findings suggest that: 1) faults within a segmented fault system behave as a single interacting fault segment over time periods including multiple earthquake cycles (e.g. 2–3 Ma or 15±3ka), with single earthquakes causing either partial or total ruptures of the entire system; 2) an along-strike bend causes throw and throw-rates enhancements within the bend throughout the seismic history of the fault system. We discuss the synchronised and geometrically controlled activity rates on these faults in terms of the propensity for floating earthquakes, multi-fault earthquakes, and seismic hazard.

We adopted a multidisciplinary approach to investigate the seismotectonic scenario of the 30 October 2016, Mw 6.5, Norcia earthquake, the largest shock of the 2016–2017 central Italy earthquake sequence. First, we used seismological and geodetic data to infer the dip of the main slip patch of the seismogenic fault that turned out to be rather low‐angle (~37°). To evaluate whether this is an acceptable dip for the main seismogenic source, we modeled earthquake deformation using single‐ and multiple‐fault models deduced from aftershock pattern analyses. These models show that the coseismic deformation generated by the Norcia earthquake is coherent with slip along a rather shallow‐dipping plane. To understand the geological significance of this solution, we reconstructed the subsurface architecture of the epicentral area. As the available data are not robust enough to converge on a single fault model, we built three different models encompassing all major geological evidence and the associated uncertainties, including the tectonic style and the location of major décollement levels. In all models the structures derived from the contractional phase play a significant role: from controlling segmentation to partially reusing inherited faults, to fully reactivating in extension a regional thrust, geometrically compatible with the source of the Norcia earthquake. Based on our conclusions, some additional seismogenic sources falling in the eastern, external portions of the Apennines may coincide with inherited structures. This may be a common occurrence in this region of the chain, where the inception of extension is as recent as Middle‐Upper Pleistocene.

Multi-channel seismic reflection and sub-bottom profiling data reveal landward-dipping normal faults as potential conduits for mantle-derived fluids in the coseismic slip area of the 2011 Tohoku earthquake (Mw9.0). Normal faults below the helium isotope anomaly sites appear to develop through the forearc crust (i.e., the seafloor sedimentary section and Cretaceous basement) and to evolve to lower dip angles as extension progresses deeper, potentially extending down to the mantle wedge, despite their intermittently continuous reflections. The faults are characterized by high-amplitude, reverse-polarity reflections within the Cretaceous basement. Moreover, deep extension of the faults connecting to a low-velocity region spreading from the Cretaceous basement into the mantle wedge across the forearc Moho suggests that the faults are overpressured by local filling with mantle-derived fluids. The locations of the normal faults are roughly consistent with aftershocks of the 2011 Tohoku earthquake, which show normal-faulting focal mechanisms. The 2011 Tohoku mainshock and subsequent aftershocks can lead the pre-existing normal faults to be reactive and more permeable so that locally trapped mantle fluids can migrate up to the seafloor through fault fracture zones. The reactivated normal faults may be an indicator of shallow coseismic slip to the trench. Locally elevated fluid pressures can decrease the effective normal stress for the fault plane, facilitating easier slip along the fault and local tsunami. The landward-dipping normal faults developing from the seafloor down into the Cretaceous basement are predominant in the middle slope region of the forearc. A possible shear zone with high-amplitude, reverse-polarity reflections above the plate interface, which is almost localized to the middle slope region, suggests more intense basal erosion of the overlying plate in that region.

Understanding active tectonics and seismicity in extensional settings requires the analysis of high-angle normal faults (HANFs) and the transfer of deformation at depth. The debate surrounds the role of low-angle normal faults (LANFs) in triggering high magnitude earthquakes. The central Betic Cordillera is an active seismic zone affected by the NNW-SSE Eurasia-Nubia convergence and orthogonal extension. The seismicity and present-day stress determined by earthquake focal mechanisms reveals the activity of a NE-SW extensional system in the shallowest 12 km of the Granada Basin. The structure of the sedimentary infill, as derived by geological field and gravimetric techniques, suggests the formation of a half-graben tilted to the N-NE. Seismologic data suggest the activity of HANFs above 6–7 km depth and a LANF zone around 6–12 km depth, with related earthquakes of up to Mw 4.0 and 20° to 30° fault dips. High-precision leveling lines highlight the importance of the Granada Fault in the system, with average vertical displacement rates of 0.35–1.1 mm/yr. These data suggest creep fault behavior at the surface and increased seismicity at depth. The upper crustal extension in the collisional Betic Cordillera is accommodated by a top-to-the-WSW extensional detachment related to westward motion and rollback in the Gibraltar Arc and the gravitational collapse of the cordillera, in a framework of NNW-SSE shortening. This comprehensive study draws a new scenario that advances understanding of relationships between HANFs and LANFs., Spanish projects DAMAGE. Grant Number: CGL2016-80687-R AEI/FEDER, Evaluación de la Peligrosidad de Inestabilidades de Laderas Asociadas a Terremotos. Grant Number: CGL2015-65602-R AEI-FEDER, Junta de Andalucia; European Regional Development Fund. Grant Numbers: AGORA P18-RT-3275, PAPEL B-RNM-301-UGR18, Programa Operativo FEDER-Andalucia 2014–2020, University of Jaén. Grant Number: POAIUJA 21/22, Junta de Andalucía (Andalusian Board). Grant Numbers: RNM-148, RNM-282, RNM-370

The 30 October 2020 M7 Samos earthquake occurred offshore the Greece-Turkey cross border region, and will be recalled as among the deadliest (118 fatalities) that affected both countries. It genera...

SUMMARYThe 2016–2017 central Italy earthquake sequence began with the first main shock near the town of Amatrice on August 24 (Mw 6.0), and was followed by two subsequent large events near Visso on October 26 (Mw 5.9) and Norcia on October 30 (Mw 6.5), plus a cluster of four events with Mw > 5.0 within few hours on 18 January 2017. The affected area had been monitored before the sequence started by the permanent Italian National Seismic Network (RSNC), and was enhanced during the sequence by temporary stations deployed by the National Institute of Geophysics and Volcanology and the British Geological Survey. By the middle of September, there was a dense network of 155 stations, with a mean separation in the epicentral area of 6–10 km, comparable to the most likely earthquake depth range in the region. This network configuration was kept stable for an entire year, producing 2.5 TB of continuous waveform recordings.Here we describe how this data was used to develop a large and comprehensive earthquake catalogue using the Complete Automatic Seismic Processor (CASP) procedure. This procedure detected more than 450 000 events in the year following the first main shock, and determined their phase arrival times through an advanced picker engine (RSNI-Picker2), producing a set of about 7 million P- and 10 million S-wave arrival times. These were then used to locate the events using a non-linear location (NLL) algorithm, a 1-D velocity model calibrated for the area, and station corrections and then to compute their local magnitudes (ML). The procedure was validated by comparison of the derived data for phase picks and earthquake parameters with a handpicked reference catalogue (hereinafter referred to as ‘RefCat’). The automated procedure takes less than 12 hr on an Intel Core-i7 workstation to analyse the primary waveform data and to detect and locate 3000 events on the most seismically active day of the sequence. This proves the concept that the CASP algorithm can provide effectively real-time data for input into daily operational earthquake forecasts,The results show that there have been significant improvements compared to RefCat obtained in the same period using manual phase picks. The number of detected and located events is higher (from 84 401 to 450 000), the magnitude of completeness is lower (from ML 1.4 to 0.6), and also the number of phase picks is greater with an average number of 72 picked arrival for a ML = 1.4 compared with 30 phases for RefCat using manual phase picking. These propagate into formal uncertainties of ±0.9 km in epicentral location and ±1.5 km in depth for the enhanced catalogue for the vast majority of the events. Together, these provide a significant improvement in the resolution of fine structures such as local planar structures and clusters, in particular the identification of shallow events occurring in parts of the crust previously thought to be inactive. The lower completeness magnitude provides a rich data set for development and testing of analysis techniques of seismic sequences evolution, including real-time, operational monitoring of b-value, time-dependent hazard evaluation and aftershock forecasting.

The legacy of Tohoku-oki Ten years ago, the magnitude 9 Tohoku-oki earthquake rocked Japan and caused massive damage. The earthquake also generated a destructive tsunami, the impacts of which are still being managed today. Kodaira et al. review what was learned from the tremendous number of observations from the great earthquake that unexpectedly ruptured into a shallow part of the megathrust fault. Postseismic deformation is ongoing, as is the risk of another very large normal fault earthquake seaward of the Japan Trench. Science , this issue p. eabe1169

We present the results of a detailed geological mapping project performed in the southernmost part of the Sibillini Mts., where the Sibillini Thrust (ST), one of the longest compressional structures of the Central Apennines, crops out. In the studied area the Meso-Cenozoic Umbria-Marche carbonate succession overthrusts the Messinian siliciclastic deposits of the adjacent Laga foredeep Basin. After the Messinian/Pliocene compressional tectonic phase, linked with the development of essentially W-dipping thrust systems, the E-verging Apennines accretionary wedge was affected by a Quaternary extensional tectonic phase during which SW-dipping normal fault systems developed. Among these normal faults, the Mt. Vettore extensional system (which includes the Castelluccio Plain fault (CPF) and the Mt. Vettoretto fault (MVF)) is one of the most important, being capable to produce destructive earthquakes (Mw 6.5 October 20, 2016). A long-lasting debate exists in literature concerning the cross-cutting relationships between the ST and the Mt. Vettore normal fault system: i.e., the thrust was alternatively considered as being nondisplaced by the normal faults or variously displaced with throws ranging between ~200 m and >2 km. Unfortunately, where normal faults should cut the thrust, a thick debris cover hides the tectonic structures and only speculative hypotheses can, thus, be done about this issue. In addition, important evidence of pre-thrusting extension is known in the area, that make difficult to discriminate the effective Quaternary activity of faults if the intersection with the compressional structures is not exposed. The aim of this study is to constrain the position of the ST under the debris cover and its relationship with the CPF and MVF, based on the following field data: i) thrust plane attitude; ii) position of the Laga Fm. outcrops, representing the footwall of the ST; iii) hanging wall anticline geometry; iv) geometry of normal faults and their recent activity; v) thickness of the Castelluccio Plain Quaternary infill at the hanging wall of the ST. The thrust position under the debris cover has been determined considering the variation of the hanging wall anticline geometry. In fact, where the Jurassic-Paleogene basinal formations crop out, the hanging wall anticline is well developed with vertical to overturned forelimb and fold axis essentially parallel to the thrust trend. This is crucial, because the occurrence in the field of an incomplete anticline (i.e., lacking the vertical to overturned forelimb) juxtaposed to the Laga Fm. (originally the footwall of the thrust) suggests the displacement of the anticline by a normal fault, allows us to infer the cross-cutting relationship between the tectonic lineaments and to estimate Quaternary normal fault throws. We conclude that the ST was displaced by the CPF with max throw ~250 m, which is consistent with the thickness of the Quaternary infill of the Castelluccio Plain. Both the CPF and the ST are in turn cut by the MVF (the youngest fault of the area, active in the 2016 earthquake) with a ~50 m throw, and is also inferred to partly reuse with negative inversion the ST plane where the plane geometry was favorable to extension.

Quantifying lithospheric strength is essential to better understand seismicity in continental regions. We estimate differential stresses and principal stress orientations driving rapid slip (~10 mm...

We use shear wave splitting (SWS) analysis and double-difference relocation to examine temporal variations in seismic properties prior to and accompanying magmatic activity associated with the 2008 eruption of Okmok volcano, Alaska. Using bispectrum cross-correlation, a multiplet of 25 earthquakes is identified spanning five years leading up to the eruption, each event having first motions compatible with a normal fault striking NE-SW. Cross-correlation differential times are used to relocate earthquakes occurring between January 2003 and February 2009. The bulk of the seismicity prior to the onset of the eruption on 12 July 2008 occurred southwest of the caldera beneath a geothermal field. Earthquakes associated with the onset of the eruption occurred beneath the northern portion of the caldera and started as deep as 13 km. Subsequent earthquakes occurred predominantly at 3 km depth, coinciding with the depth at which the magma body has been modeled using geodetic data. Automated SWS analysis of the Okmok catalog reveals radial polarization outside the caldera and a northwest-southeast polarization within. We interpret these polarizations in terms of a magma reservoir near the center of the caldera, which we model with a Mogi point source. SWS analysis using the same input processing parameters for each event in the multiplet reveals no temporal changes in anisotropy over the duration of the multiplet, suggesting either a short-term or small increase in stress just before the eruption that was not detected by GPS, or eruption triggering by a mechanism other than a change of stress in the system. © 2010 by the American Geophysical Union.

On October 30, 2020, an earthquake with a magnitude of 6.8 (Mw) struck the northern coast of Samos Island in the Kusadast Gulf. The solution to the focal mechanism indicates that the earthquake of 30 October 2020 occurred on a normal fault with nodal planes of E-W strike; thus, indicating extension in N-S direction. The fault plane solutions show a N-S trending extension for normal faults, which are obtained by inverting the moment tensor waveforms of 23 earthquakes and the P-wave first motion polarities of 11 aftershocks. A normal fault stress regime of approximately N-S (N6 degrees E) sigma 3 axis is given by the inversion of slip vectors measured at sites located on land in Kuxadast. The mean R value is 0.84, suggesting that the stress regime is triaxial extensional stress state. The inversion of the focal mechanism of earthquakes occurring on land and in the Gulf of Kusadast describes an extensional stress regime active today, characterized by an approximately N-S (N9 degrees E) sigma 3 axis. The calculated R value of 0.31 indicates a triaxial stress state. For the 30 October 2020 earthquake (Mw:6.8), the Coulomb failure stress change analysis shows a substantial reduction in stress in the N-S direction supporting the kinematic results. The N-S extension in Western Anatolia-Aegean is largely influenced by the relatively fast movement of the Hellenic trench southwards, related to the sinking of the African plate beneath Aegean.

We study the surface deformation following a moderate size M5+ earthquake sequence that occurred close to Tyrnavos village (Thessaly, Greece) in March 2021. We adopt the interferometric synthetic aperture radar (InSAR) technique to exploit several pairs of Sentinel-1 acquisitions and successfully retrieve the ground movement caused by the three major events (M5+) of the sequence. The mainshocks occurred at depths varying from ~7 to ~10 km, and are related to the activation of at least three normal faults characterizing the area previously unknown. Thanks to the 6-day repeat time of the Sentinel-1 mission, InSAR analysis allowed us to detect both the surface displacement due to the individual analyzed earthquakes and the cumulative displacement caused by the entire seismic sequence. Especially in the case of a seismic sequence that occurs over a very short time span, it is quite uncommon to be able to separate the surface effects ascribable to the mainshock and the major aftershocks because the time frequency of radar satellite acquisitions often hamper the temporal separation of such events. In this work, we present the results obtained through the InSAR data analysis, and are able to isolate single seismic events that were part of the sequence.

Foreshocks in the form of microseismicity are among the most powerful tools to study the physical processes that occur before main earthquakes. However, their detection and precise characterization is still sparse, especially for small-to-moderate-size earthquakes (Mw

© 2021 Elsevier LtdOn October 30th of 2020, 14:51 (GMT+3:00), Izmir city was hit by an earthquake of Mw = 7.0 magnitude (according to USGS). A rupture of 30–40 km of a west-east normal fault, which is roughly 12 km north to Samos Island caused significant damage, particularly in Izmir (Bornova plain). This study aims to present the preliminary field investigations, evaluation of structural damage as well as the possible geotechnical phenomenon affecting the damage that occurred. In this context, an extensive analysis of spectral characteristics of the earthquake and local site effects is presented. Field investigations reveal that there is a significant amplification of the rock acceleration along with a basin effect in the region, which results in a wider constant acceleration region. In addition, analysis of earthquake records shows a remarkable level of soil nonlinearity. Considering all these aspects, a detailed assessment of structural damage observed in Izmir Bayrakli District is presented. It is evident that, structures of poor construction details behaved as if they were affected by a near field earthquake. The structures to be constructed in alluvial zones such as Manavkuyu neighborhood should be designed considering the effects of soil amplification including basin effects and soil nonlinearity. To fulfill this aim, comparative results of 1D/2D/3D ground response analyses should be performed, for revising current earthquake codes.

Fluids play an important role in seismic faulting both at hypocentral depths during earthquake nucleation and at shallower crustal levels during rupture propagation. Pre- to co-seismic anomalies of crustal fluid circulation have been identified by hydrogeochemical and seismological monitoring and interpreted as potential precursors of strong earthquakes. To shed light on the role of fluids in seismic and precursory mechanisms, the active carbonate-hosted principal slip zone (7-8 cm thick) of the exhumed (exhumation < 3 km) normal Mt. Morrone Fault (central Apennines) has been investigated with a multi-disciplinary approach from the macro- to the nano-scale. The distal slip zone consists of white cementitious calcite-rich bands and red cataclastic bands composed of dolomite and calcite clasts embedded in a clay-rich matrix. The proximal slip zone consists of subparallel ultracataclastic layers separated by sharp slip surfaces. The ultracataclastic layers mutually inject/overprint, bearing evidence of granular fluidization, dolomite thermal decomposition, and clay amorphization. Fluid inclusions and the distribution of both trace and major elements reveal the inflow of both shallow and deep external fluids into the slip zone. Presumably, the deep fluids originated from a magmatic-like source and ascended along the fault during pre-seismic dilation and seismic ruptures, interacting with shallow phyllosilicate-rich flysch deposits and the fluids hosted within them. In this context, vanadium-rich fluidized microlayers along the exhumed Mt. Morrone Fault are reminiscent of vanadium-rich potential hydrogeochemical precursors arose in the shallow aquifers of the study area since a few months before the 2016 Mw 6.0 Amatrice earthquake.

Hydrogeochemical changes before Mw ≥ ∼5.0 earthquakes are hoped to be applicable as seismic precursors. It is now necessary to pass from single experiences to structured networks, systematically monitoring large seismic areas for long periods. Our aim is to provide a pilot methodological experience for how such networks could be realized and the types of results they could deliver. We present the method and some initial results to document the method’s applicability. In 2017, we started the HydroQuakes project in seismically active central Italy, with the Sulmona and Matese areas selected as the two monitoring nodes. Each node includes 5–6 monitored springs, and for each spring, we performed laboratory analyses of major and trace elements and some isotopes. We installed in situ probes for continuous monitoring. Between December 2017 and January 2020, the most energetic earthquakes were three events with Mw of 3.9, 4.1, and 4.4. They were not preceded by significant hydrogeochemical anomalies, except for the Mw 4.1 event. Despite its low Mw, this earthquake occurred over a large normal fault at a great depth in the crust (∼17 km) and was preceded by weak but detectable hydrogeochemical anomalies of boron and δ11B that were similar but milder than the hydrogeochemical anomalies before the 2016 Mw 6.0 earthquake in the central Apennines. This and previous evidence show the B and δ11B hydro-seismo-sensitivity and indicates that pre-seismic hydrogeochemical anomalies could arise mostly before Mw ≥ ∼5.0 earthquakes, with weak exceptions occurring in specific conditions such as long and deep faults.

Active normal faults on the Mediterranean island of Crete form prominent limestone scarps together with basin and range topography. These faults mainly strike E‐ESE and N‐NNE in southern and northern Crete, respectively, with fault sets commonly intersecting and northerly trending faults being a factor of 3 more abundant. Lengths, displacements, and displacement rates have been analyzed for 84 active faults sampled over 2 ± 0.5 Ma (long‐term) and 16.5 ± 2 ka (short‐term) time‐intervals, with half showing no resolvable short‐term activity. Active faults record earthquake processes on timescales of thousands to million years and constrain sampling biases, which can lead to under and over estimates of fault parameters. The available data provide no evidence for fault propagation and support a model in which fault lengths were established early in the development of the fault system. Short‐term displacement rates (0.09–1.2 mm/year) are generally higher than long‐term rates (0.002–0.7 mm/year), with a factor of 4 disparity in the average recurrence intervals for the two time periods (∼2.5 Kyr vs. ∼11 Kyr). We attribute these differences to “clustering” of surface‐rupturing (e.g., >Mw6) earthquakes on individual faults over millennial timescales, and to preferential sampling of the most seismically active faults during the short‐term. Displacement rates are comparable when averaged for each time interval on the longest faults (>10 km), indicating that for these faults earthquake “clustering” spans time‐intervals of Mw6 on Crete are at least three times more frequent than historical earthquakes since ∼1920, possibly because multi‐fault surface‐rupturing earthquakes are double counted in the paleo‐record.

We monitored electric and magnetic fields synchronously and continuously in an Italian area prone to moderate-to-high magnitude seismic activity. Identifying and monitoring of potential precursors may contribute to risk mitigation. A decade after the Central Italy Electromagnetic Network started, nine strong shakes with magnitudes between 5.0 and 6.6 occurred in Central Italy between August 2016 and January 2017. The events produced a fault offset of up to 2.8 m along a NNW–SSE normal fault system, 75 km long and located NW of the fault system, which generated the destructive L’Aquila 2009 earthquake sequence. This paper describes the electric and magnetic variations in the extremely low frequency band recorded at the Chieti Station of the network. Meteorological and geomagnetic data were compared to the recordings of these electric and magnetic activities by statistical correlations. Werecorded several abrupt increases in electric and magnetic activities not simultaneous to the main seismic events and presumptively related to them. Electrical signals consist in discrete electric field oscillations between 50 and 200 Hz, with time lapses lasting between 3 and 45 minutes. In addition, magnetic signals consisting of magnetic field pulses with time lapses greater than 10 ms were recorded in the same time interval. Similar signals occurred during the 2009 L'Aquila, Central Italy, sequence. Days before each strong earthquake, both electric and magnetic phenomena increased in intensity and number. Two physical models are proposed to describe and interpret electric and magnetic signal events. A number of hypotheses about the origin of recorded electric and magnetic signals may fit coherently with electromagnetic theory and are discussed in the light of a consistent dataset.

We use densely spaced campaign GPS observations and laboratory friction experiments on fault rocks from one of the world's most rapidly slipping low-angle normal faults, the Mai'iu fault in Papua New Guinea, to investigate the nature of interseismic deformation on active low-angle normal faults. GPS velocities reveal 8.3 ± 1.2 mm/year of horizontal extension across the Mai'iu fault, and are fit well by dislocation models with shallow fault locking (above 2 km depth), or by deeper locking (from ~5–16 km depth) together with shallower creep. Laboratory friction experiments show that gouges from the shallowest portion of the fault zone are predominantly weak and velocity-strengthening, while fault rocks deformed at greater depths are stronger and velocity-weakening. Evaluating the geodetic and friction results together with geophysical and microstructural evidence for mixed-mode seismic and aseismic slip at depth, we find that the Mai'iu fault is most likely strongly locked at depths of ~5–16 km and creeping updip and downdip of this region. Our results suggest that the Mai'iu fault and other active low-angle normal faults can slip in large (Mw > 7) earthquakes despite near-surface interseismic creep on frictionally stable clay-rich gouges.

This chapter presents the typical structural patterns and seismic profile characteristics of major petroliferous basins in China, including typical extensional structural patterns such as listric, rotary normal fault, flower structure, as well as large slip compression structures such as fault-propagation fold deformation and thrust.

The Alto Tiberina normal fault (ATF) in Central Italy is a 50 km long crustal structure that deepens at a low angle (15-20◦). Events on the fault plane are about ten times less than those located i...

International audience; In 2016, the Mt. Vettore-Mt. Bove normal fault system (VBFS) broke during three earthquakes (Mw 6.0, Mw 5.9, and Mw 6.5), associated with clear coseismic ruptures. Based on high-resolution topography and geological field data, we determined the displacements of the VBFS. The distributions of the coseismic and postglacial displacements exhibit similar asymmetric shapes, suggesting self-similar slip profiles over the last 18 kyr. The highest displacement during the 2016 events is localized on the southern Mt. Vettore segments, the southern tip of the VBFS, which also showed the maximum throw of 32 m over the last 18 kyr yielding to a very fast throw rate of 1.6 ± 0.5 mm/yr. Assuming a constant throw rate, the geological displacement we determined suggests an inception age of 200–250 kyr for the surface rupturing faults that ruptured in 2016 on the Mt. Vettore sector. This value can be interpreted as the minimum age for the onset of those faults in the Mt. Vettore and might result from a southward shift of VBFS activity with a change of the fault system pattern. We infer that the observed slip distribution, maximum at Mt. Vettore and tapering-off southward, might be due to the VBFS lengthening processes towards the Laga Fault and its interaction with pre-existing structure such as Olevano-Antrodoco-Sibillini thrust that might play a key role in controlling the VBFS's evolution.