Potential Earthquake Research Articles

Along-Strike Variation in the Shallow Velocity Structure beneath the Chenghai Fault Zone, Yunnan, China, Constrained from Methane Sources and Dense Arrays

Abstract The fine structure of the fault zone and the surrounding area is the basis for understanding the process of earthquake nucleation and rupture propagation. To obtain the high-resolution structure of the Chenghai fault (CHF) and the nearby basins, we deployed two dense arrays and excited eight methane sources across the fault from October to November 2020. Based on the 611 P-wave travel times, we obtained the shallow velocity structure beneath the arrays using the simul2000 travel-time inversion program, and the results are as follows: (1) the shallow velocity structure beneath the CHF is very complex, with obvious velocity contrasts on both the sides of the regional fault; (2) low-velocity zones (LVZs) beneath the CHF show clear along-strike variations. The LVZs extend to ∼500 m in depth with widths of ∼2 km and ∼5 km beneath the Qina and Pianjiao arrays, respectively, which are consistent with the Quaternary sediments, and the velocity contrasts along the interface of the LVZ can reach 20%–50%; and (3) the distribution of shallow surface tectonic geomorphology is mainly controlled by regional fault activities that are formed under the combined action of regional near-east–west stretching and clockwise rotation of microblocks. Our results can help improve cognition and seismic hazard assessment for potential earthquakes on the CHF, as well as lay the foundation for understanding the seismic wave velocity variation mechanism in the fault zone.

Local Moho distribution in the eastern Mediterranean region from gravity inversion: eastern Mediterranean Sea

This study investigates the variations of surface Moho inverted from Bouguer gravity data beneath the northwestern Arabian plate. The results were obtained by applying the 3DINVER program developed in a MATLAB environment using the Parker–Oldenburg method. The calculation results show that the maximum Moho depth observed in the western Arabian shield approaches more than 40 km, while the minimum values of 16–20 km are mainly concentrated beneath the Mediterranean Sea. A key innovation of this study is its implementation of exponential density contrast decrease in the sediment–basement interface in the Syrian part of the Arabian plate. The gravity anomaly of the sediment is computed using a density contrast which varies exponentially with depth, leading to a more accurate representation of the subsurface structure and offering valuable insights into the geodynamic processes and seismogenic potential of the area. To validate the inverted results from the 3DINVER program, the study compares these findings with seismic results that show good agreement with our results from the same region. This leads to a better understanding of the crustal structure and provides insights into its implications for the geodynamic and seismogenic nature of the northwestern Arabian plate—critical for assessing the potential for earthquakes and other geological hazards. The density contrast between the Earth’s crust and mantle can be related to variations in the composition, temperature, and pressure of the rocks. These factors influence the mechanical properties of the crust, ultimately affecting the tectonic processes and seismic activity in the region.

Dynamic Rupture Models, Fault Interaction and Ground Motion Simulations for the Segmented Húsavík‐Flatey Fault Zone, Northern Iceland

AbstractThe Húsavík‐Flatey Fault Zone (HFFZ) is the largest strike‐slip fault in Iceland and poses a high seismic risk to coastal communities. To investigate physics‐based constraints on earthquake hazards, we construct three fault system models of varying geometric complexity and model 79 3‐D multi‐fault dynamic rupture scenarios in the HFFZ. By assuming a simple regional prestress and varying hypocenter locations, we analyze the rupture dynamics, fault interactions, and the associated ground motions up to 2.5 Hz. All models account for regional seismotectonics, topo‐bathymetry, 3‐D subsurface velocity, viscoelastic attenuation, and off‐fault plasticity, and we explore the effect of fault roughness. The rupture scenarios obey earthquake scaling relations and predict magnitudes comparable to those of historical events. We show how fault system geometry and segmentation, hypocenter location, and prestress can affect the potential for rupture cascading, leading to varying slip distributions across different portions of the fault system. Our earthquake scenarios yield spatially heterogeneous near‐field ground motions modulated by geometric complexities, topography, and rupture directivity, particularly in the near‐field. The average ground motion attenuation characteristics of dynamic rupture scenarios of comparable magnitudes and mean stress drop are independent of variations in source complexity, magnitude‐consistent and in good agreement with the latest regional empirical ground motion models. However, physics‐based ground motion variability changes considerably with fault‐distance and increases for unilateral compared to bilateral ruptures. Systematic variations in physics‐based near‐fault ground motions provide important insights into the mechanics and potential earthquake hazard of large strike‐slip fault systems, such as the HFFZ.

Buried Alive: Imaging the 9 November 2022, Mw 5.5 Earthquake Source on the Offshore Adriatic Blind Thrust Front of the Northern Apennines (Italy)

AbstractThe prompt identification of faults responsible for moderate‐to‐large earthquakes is fundamental for understanding the likelihood of further, potentially damaging events. This is increasingly challenging when the activated fault is an offshore buried thrust, where neither coseismic surface ruptures nor GPS/InSAR deformation data are available after an earthquake. We show that on 9 November 2022, an Mw 5.5 earthquake offshore Pesaro ruptured a portion of the buried Northern Apennines thrust front (the Cornelia thrust system [CTS]). By post‐processing and interpreting the seismic reflection profiles crossing this thrust system, we determined that the activated fault (CTS) is an arcuate 30‐km‐long, NW‐SE striking, SW dipping thrust and that older structures at its footwall possibly influenced its position and geometry. The activation of adjacent segments of the thrust system is a plausible scenario that deserves to be further investigated to understand the full earthquake potential of this offshore seismogenic source.

Present-day Crustal Deformation in West Sumatra After Series of Sumatran Great Earthquake from 2004-2010

Present-day crustal deformation was an attempt to estimate earthquake potential, yet the presence of postseismic deformation should be carefully identified. Studying crustal deformation in West Sumatra has been important for this purpose since the series of Sumatran Great Earthquake from 2004-2010. This study utilized present-day GNSS data (2017-2021) and pre-2004 GNSS velocities to understand the present-day crustal deformation. Bernese 5.2 was used to process the GNSS data and linear regression was used to calculate present-day velocities. These velocities were transformed into an ITRF2000-based Sundaland plate reference frame and then the velocities were compared to pre-2004 velocities in the same reference frame. The present-day velocities were ranging from 28.4 mm/yr to 58.3 mm/yr in ITRF2014 and from 8.8 to 44.8 mm/yr in the Sundaland plate reference frame. This suggests West Sumatra was located on the Sumatra block of the Sundaland plate. The low velocity difference ( 11.7 mm/yr) with the random vector direction between present-day velocities and pre-2004 velocities shows that there is no postseismic deformation affecting West Sumatra. This proposes the utilization of present-day velocities for earthquake potential estimation in West Sumatra.

Incremental Dynamic Analysis and Seismic Fragility Analysis of Reinforced Concrete Frame

Abstract Due to technological developments in last decade, new methods of seismic evaluation are in use like simulation based, algorithm based, probabilistic, software based etc. These developments have enabled researchers to move from linear to non-linear methods of analysis. Incremental dynamic analysis (IDA) is performance evaluation method where a suite of ground motions applied to structure are further scaled to particular levels of seismic intensity. Seismic fragility curves become significant in estimation of structures risk possibility from the point of view of potential earthquakes and helps in predicting the economic consequences for forthcoming earthquakes. The paper reflects IDA and seismic fragility analysis of ground storey + 7 floor (G + 7) reinforced concrete frame subjected to suite of eleven ground motions. Primary objective was to perform equivalent static and linear-dynamic analysis to meet the National and International codal requirements. Then, pushover analysis is carried out by introducing parametric auto hinges as per ASCE 41-13 tables. To carry out pushover analysis, both geometric and material non-linearity was introduced. Strong ground motions were selected as per suitable criteria of seismic intensity. IDA is then carried out as per SeismoStruct 2022 software and using IDA curves, the fragility analysis was carried out. The results of study found useful for researchers to predict the probability of damage of the structure under earthquakes.

Long silence on the East Anatolian Fault Zone (Southern Turkey) ends with devastating double earthquakes (6 February 2023) over a seismic gap: implications for the seismic potential in the Eastern Mediterranean region

On 6 February 2023, an earthquake with magnitude M w c . 7.0 on the Narlı Fault, a fault sub-parallel to the East Anatolian Fault Zone (EAFZ), initiated a chain of large earthquakes on the EAFZ. The earthquakes occurred in a seismic gap with low geodetic strain rates and low background seismicity, where deformation is distributed across a wide fault zone and a long recurrence time of historical earthquakes. The c. 50 km long rupture of the Narlı Fault towards Pazarcık led to an M w 7.8 left-lateral strike-slip earthquake breaking a c. 300 km section of the c. 600 km long EAFZ bilaterally with a total duration of more than 80 s. Toward the SW, the rupture propagated on the c. 100 km long Amanos segment with a peak surface offset of 5 m, before diminishing toward the Hatay graben. In the NE direction, the rupture reached a peak surface offset of 7 m before sharply declining at the termination of the 2020 M w 6.8 Sivrice earthquake rupture. A second large earthquake with M w 7.6 occurred 9 h later on the Çardak Fault, located at the western margin of (and sub-parallel to) the EAFZ and breaking the surface with almost 9 m of left-lateral slip (average of c. 4 m). Following these large earthquakes, the increase in the regional stress led to a rapid seismic activation in a broad region from central to eastern Anatolia, loading the faults at various scales and increasing seismic hazard. Two weeks after the initiation of the seismic crisis, a third earthquake with M w 6.4 occurred at the southern boundary of the Hatay graben, near the southwestern termination of the Amanos rupture. The earthquakes caused significant loss of human life, devastating 12 cities. We evaluate the observations prior to the ruptures, and present preliminary seismological results with surface displacements from sub-pixel correlation of optical satellite images and the stress perturbations computed on the nearby faults based on preliminary slip models. The re-evaluation of the seismic potential in light of the recent and historical earthquakes provides some new insight on seismic hazard assessment. The recent series of events on the EAFZ is an important reminder that large faults can generate very large earthquakes on multiple segments. The seismic potential of large earthquakes on these fault zones can be estimated only by considering multiple seismic cycles and moment deficits from very large earthquakes. Supplementary material : Supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.6567094

The largest induced earthquakes during the GEOVEN deep geothermal project, Strasbourg, 2018–2022: from source parameters to intensity maps

SUMMARYBetween 2019 November and 2021 July, four induced earthquakes of local magnitude equal to or greater than than three were felt by the population of Strasbourg, France. These events were related to activity at the deep geothermal site GEOVEN located in Vendenheim in the northern suburb area of the city of Strasbourg. The first earthquake, with a local magnitude (Mlv) of 3.0, occurred on 2019 November 12, at the same depth as the bottom of the wells (approximately 4 km) but 5 km to the south. The second (Mlv 3.6) occurred a year later, on 2020 December 4, below the wells, and led to the termination of the project by the authorities. The third (Mlv 3.3) was initiated three weeks after shut-in on 2021 January 22, while the largest earthquake to date (Mlv 3.9) occurred on 2021 June 26, more than 6 months after shut-in. We constrained these four events’ absolute locations using a 3-D velocity model of the area and here present regional intensity maps. We estimated moment magnitude and focal mechanism trough waveform inversion and inferred the fault plane activated during the largest event from an analysis of rupture directivity effects in the recorded waveforms. Our analysis highlights the existence of a critically stressed fault that hosted three of these widely felt events. We show how the derived source properties of these four earthquakes are directly linked to ground shaking observations at the surface. Notably, we demonstrate how earthquake moment, location, direction of rupture and stress drop impact the regional intensity distribution. Our results suggest that the traffic light system could benefit from including ground shaking scenarios based on realistic subsurface properties and potential earthquake source models.

Detailed sedimentary structure of the Mianning segment of the Anninghe fault zone revealed by H/V spectral ratio

The Anninghe fault is a major left-lateral strike-slip fault in southwest China and a seismic gap with a potential earthquake larger than MW 7.0 lies in the Mianning-Xichang segment according to recent observations. The shallow structure of this region can offer a glimpse into the geometry of the fault, which plays an important role in earthquake hazard mitigation. To further investigate the sedimentary structure of the Anninghe fault zone, two dense linear arrays with a station spacing of around 80 ​m were deployed across the fault. In this study, the H/V spectral ratio (HVSR), together with its peak frequency at each station site, was obtained by applying the Nakamura method. Our findings demonstrate that the peak frequency behaves in high correlation with lithology and is controlled by topography. HVSR in foothills or regions with magmatic intrusion shows a single peak at about 2–3 ​Hz. In locations with abundant Quaternary sedimentation, such as Anninghe valleys and fracture zones, another low-frequency peak around 0.4 ​Hz can be noticed in HVSR. By using the empirical relationship, the thickness of the sedimentary layer around the fault fracture zone is estimated to be 300–600 ​m. Furthermore, the sedimentary interface shows a downward dip to the east, possibly influenced by the east-west extrusion stress. Considering the resonance effect, buildings with 6–9 stories in the valley area of the Anninghe require additional attention in earthquake hazard prevention.

Interseismic Coupling, Asperity Distribution, and Earthquake Potential on Major Faults in Southeastern Tibet

AbstractSoutheastern (SE) Tibet is one of the most seismically active regions in mainland China, but the spatial distribution of interseismic coupling that quantifies seismic hazard is unknown along most major faults. In this study, we constructed an elastic block model to invert Global Positioning System data for slip rates and locking coefficients along 20 major faults in SE Tibet. Our results identify 27 strongly coupled fault segments with locking coefficients >0.5, defined as potential seismogenic asperities, extending laterally for 36–330 km. Quantitative calculations of seismic moment budgets on these seismogenic asperities indicate that they are capable of generating Mw 6.4–7.7 earthquakes in the next few decades, of which the Anninghe, Daliangshan and Red River faults have the potential for Mw ≥ 7.5 earthquakes. The interseismic coupling model provides a component for probabilistic analysis of future seismic hazards in densely populated Southwest China.

The Northern Chile forearc constrained by 15 years of permanent seismic monitoring

In this review article, we compile seismological observations from the different constituent parts of the Northern Chile forearc: the downgoing Nazca Plate, the plate interface, the upper South American Plate as well as the mantle wedge beneath it. As Northern Chile has been monitored by a network of permanent seismic stations since late 2006, there is a wealth of observations that enables us to characterize the structure as well as ongoing processes in the forearc throughout the last 15 years. We put an emphasis on the analysis of seismicity, for which we have extended a massive earthquake catalog that now contains >180,000 events for the years 2007–2021. Moreover, we draw on published results for earthquake mechanisms, source properties, seismic velocity structure, statistical seismology and others, and discuss them in context of results from neighboring disciplines. We thus attempt to provide a comprehensive overview on the seismological knowledge about the structure and ongoing processes in the Northern Chile forearc, a breviary of which is found in the following: The Northern Chile megathrust hosted two major earthquake sequences during the analyzed time period. The 2007 Mw 7.8 Tocopilla earthquake broke the deep part of the megathrust just north of Mejillones Peninsula, whereas the 2014 Mw 8.1 Iquique earthquake ruptured the central segment in the north of the study region. The latter event has a highly interesting preparatory phase, including a significant foreshock sequence as well as aseismic slip transients. Besides these large events, background seismicity elsewhere on the megathrust may be helpful for characterizing the earthquake potential and locking state in the remaining seismic gap. The downgoing Nazca Plate in Northern Chile exhibits very high seismicity rates, with the vast majority of earthquakes occurring at depths of ∼80-140 km with downdip extensive mechanisms. While seismic tomography shows no sudden changes in slab geometry along strike, seismicity describes peculiar offsets that may be linked to subducted features on the oceanic plate. Upper plate seismicity likewise shows strong variations along strike, with the north and south of the study area showing only weak activity, whereas the central segment shows pervasive microseismicity throughout the upper plate, all the way to the plate interface. These earthquakes have thrust and strike-slip mechanisms with P-axes striking roughly N-S, indicating margin-parallel compression that may be connected to the concavity of the margin.

A High‐Order Accurate Summation‐By‐Parts Finite Difference Method for Fully‐Dynamic Earthquake Sequence Simulations Within Sedimentary Basins

AbstractWe present an efficient numerical method for earthquake sequences in 2D antiplane shear that incorporates wave propagation. A vertical strike‐slip fault governed by rate‐and‐state friction is embedded in a heterogeneous elastic half‐space discretized using a high‐order accurate Summation‐by‐Parts finite difference method. Adaptive time‐stepping is applied during the interseismic periods; during coseismic rupture we apply a non‐stiff method, enabling a variety of explicit time stepping methods. We consider a shallow sedimentary basin and explore sensitivity to spatial resolution and the switching criteria used to transition between solvers. For sufficient grid resolution and switching thresholds, simulations results remain robust over long time scales. We explore the effects of full dynamics and basin depth and stiffness, making comparisons with quasi‐dynamic counterparts. Fully‐dynamic ruptures generate higher stresses, faster slip rates and rupture speeds, producing seismic scattering in the bulk. Because single‐event dynamic simulations penetrate further into sediments compared to the quasi‐dynamic simulations, we hypothesize that the incorporation of inertial effects would produce sequences of only surface‐rupturing events. However, we find that subbasin ruptures can still emerge with elastodynamics, for sufficiently compliant basins. We also find that full dynamics can increase the frequency of surface‐rupturing events, depending on basin depth and stiffness. These results suggest that an earthquake's potential to penetrate into shallow sediments should be viewed through the lens of the earthquake sequence, as it depends on basin properties and wave‐mediated effects, but also on self‐consistent initial conditions obtained from seismogenic cycling.

The risk of fluid-injection-induced fault reactivation in carbonate reservoirs: an investigation of a geothermal system in the Ruhr region (Germany)

In this study, we investigate the potential for fluid-injection-induced fault reactivation and induced seismicity risk during simultaneous injection-extraction operation in a theoretical geothermal doublet system in a carbonate reservoir in the Ruhr region. Using a coupled three-dimensional thermo-hydro-mechanical approach, we investigate the probability of injection-induced fault rupture. We perform a sensitivity study assuming variability of the fault and matrix permeability, injection/production flow rates, well placement options, rock thermal properties, and evaluate the influence of thermally induced stresses. The ruptured fault areas were calculated based on a Coulomb friction law and a notion that the shear slip is controlled by the ratio of shear to effective normal stresses acting on a pre-existing plane of weakness in the in situ stress field configuration. Ruptured fault areas in the intrinsically not critically-stressed environment, using location-specific empirical correlations, were used to compute local moment magnitudes of potential earthquakes. Based on this study, we conclude that, in the long-term, thermally-induced stresses play a dominant role during fault reactivation and greatly increase the likelihood for induced seismicity. We, therefore, propose that a minimum safe distance between an injection well and a fault should be based primarily on the radius of a thermal plume generated during the expected lifetime of a geothermal system. Results from this study provide valuable insights for the development of future deep geothermal systems in the Ruhr region and other geothermal reservoirs worldwide.

Influences of across-strike heterogeneous viscosity on the earthquake cycle in a three-dimensional strike-slip fault model

Geodetic observations have shown that there exist large differences in the viscosity of the deep lithosphere across many large strike-slip faults. Heterogeneity in lithospheric viscosity structure can influence the efficiency of stress transfer and thus may have a significant effect on the earthquake cycle. Until now, how the lateral viscosity variation across strike-slip faults affects the earthquake cycles is still not well understood. Here, we investigate the effects of across-strike viscosity variation on long-term earthquake behaviors with a three-dimensional strike-slip fault model. Our model is a quasi-static model which is controlled by the slip-weakening friction law and power-law rheology. By comparing with the reference case, we find that low viscosity on one side of the fault results in a smaller rupture area but with a higher Coulomb stress drop on the ruptured fault region. In addition, low viscosity also leads to a small Coulomb stress accumulation rate. These combined effects increase the earthquake recurrence interval by approximately 10% and the earthquake moments by about 30% when the low viscosity is related to a geothermal gradient of 30 ​K/km. In addition, across-strike viscosity variation causes asymmetric interseismic ground surface deformation rate. As the viscosity contrast increases, the difference in the interseismic ground surface deformation rate between the two sides of the fault gradually increases, although the asymmetric feature is not pronounced. This asymmetry of interseismic ground deformation rate across a strike-slip fault is supposed to result in asymmetric coseismic deformation if the long-term plate motion velocity is invariant. As a result, this kind of asymmetry of interseismic deformation may influence the evaluation of potential earthquake hazards along large strike-slip faults with lateral viscosity contrast.

Megathrust complexity and the up-dip extent of slip during the 2021 Chignik, Alaska Peninsula earthquake

The up-dip extent of slip during large megathrust earthquakes is important for both tsunami excitation and subsequent tsunami earthquake potential, but it is unclear whether frictional properties and/or fault structure determine the up-dip limit. A finite-fault slip model for the 2021 MW 8.2 Chignik, Alaska Peninsula earthquake obtained by joint inversion of seismic-geodetic data with model spatial extent constraints from the tsunami waves provides unusually good constraints on the up-dip edge of coseismic slip. Rupture initiated ∼35 km deep and propagated unilaterally northeastward with large-slip (up to 8.4 m) distributed over a depth range of 26 to 42 km beneath the continental shelf. Aftershocks concentrate up-dip of the coseismic slip around a strong megathrust reflector with high Coulomb stress change. The ∼25 km deep up-dip edge of slip strongly correlates with a change in plate interface reflectivity apparent in reflection profiles, indicating that a structural and frictional transition provided a barrier to shallower rupture.

Determination of buried active faults and earthquake potential for Izmir and its surroundings (western Turkey) using aeromagnetic anomalies and seismological data

The paper aims to delineate buried faults in Izmir city and its surroundings, western Turkey using aeromagnetic and seismological data. In this context, the geophysical data processing techniques including reduced‑to‑pole transform (RTP), power spectrum analysis, high-pass filter and second vertical derivative method (SVD) have been applied to the total field aeromagnetic data of the study area. First, to remove the undesirable effects caused by the dipolar nature of the Earth field, RTP transform has been applied to those data. Second, the average depths of the regional and residual sources in the region have been calculated as 16.84 km and 3.75 km, respectively using power spectrum analysis. After, to emphasize the effects of the residual anomalies, the high-pass filter has been applied to the RTP data. Finally, the second vertical derivative method (SVD) has applied to the filtered data for delineating the uncovering buried faults and their lineaments in the eastern part of the Aegean extension. The results from those methods show five major fault zones that could cause devastating earthquakes in the area. Especially, the study reveals for the first time that one of these faults which lies from Doganbey to the city center of Izmir in the literature actually reaches out to Manisa city in the NE direction. As a result, these lineaments can be evaluated as traces of buried faults could be an important clue in predicting earthquake potential. A comparison of seismicity map and the heat flow map shows that the region (between Cesme and Seferihisar) represented with a low b‑value has a high potential earthquake. The spatial distribution of the earthquakes, b‑values and heat flow values in the depths may be related to the existence thin lithospheric mantle. Furthermore, the region represented by strong aeromagnetic anomalies may be considered to be magmatic material arising from the magma filling inside the strike-slip faults. The fault structure observed on the SVD map are also important for the geothermal energy potential of the region as well.

Arrest of the Mw 6.8 January 24, 2020 Elaziğ (Turkey) earthquake by shallow fault creep

It has long been conjectured that creeping sections of strike slip faults arrest or subdue earthquake rupture, partly because of their reduced slip potential and partly because of their velocity-strengthening frictional properties. However, no instrumentally recorded large earthquake (Mw ≥ 6.8) on any well instrumented continental strike-slip fault has thus far occurred that has clearly been arrested at a region of fault creep, rendering it difficult to identify experimentally the parameters that control rupture arrest. Nearfield GPS, InSAR and creepmeter data from the 2020 Elazığ (Turkey) earthquake reveal not only how rupture propagation of a large earthquake is hindered by shallow creep reducing the earthquake size, but also provide important quantitative insights into the late interseismic, coseismic and post seismic behavior of a creeping fault, which has important implications for evaluating hazard potential of a major earthquake on a creeping fault, such as has been forecast for the Hayward fault in California.

Tectonic geomorphology of Bozdoğan and Karacasu grabens, western Anatolia

Western Anatolia is one of the most rapidly extending and seismically active regions in the world. The circa N-S extension since the Early Miocene caused the formation of E-W trending major grabens and intervening horsts, having earthquake potentials with magnitude ≥5. The E-W oriented Büyük Menderes graben cross-cuts the broadly N-S oriented Bozdoğan and Karacasu grabens, of which the boundary faults of the latter are the source of seismic activity. Geomorphic indices, including drainage basin asymmetry, mountain front sinuosity, valley-floor width to valley height ratio, stream length-gradient index and normalized channel steepness index, were used to evaluate the boundary fault segments of the Bozdoğan and Karacasu grabens. The results indicate that both grabens are tectonically active and therefore regions of earthquake potential, consistent with the epicenters of earthquakes. Thus, it can be inferred that fault segments of second-order grabens, which are crosscut by the boundary faults of seismically active main depressions, are apparently reactivated by ongoing tectonism and may represent seismic activity. This suggestion applies also for similar basins located in the western Anatolia.

First Results on the Systematic Search of Land Surface Temperature Anomalies as Earthquakes Precursors

Every year, earthquakes cause thousands of casualties and high economic losses. For example, in the time frame from 1998 to 2018, the total number of casualties due to earthquakes was larger than 846 thousand people, and the recorded economic losses were about USD 661 billion. At present, there are no earthquake precursors that can be used to trigger a warning. However, some studies have analyzed land surface temperature (LST) anomalies as a potential earthquake precursor. In this study, a large database of global LST data from the Geostationary Operational Environmental Satellite (GOES) and AQUA satellites during the whole year 2020 has been used to study the LST anomalies in the areas affected by earthquakes. A total of 1350 earthquakes with a magnitude larger than M4 were analyzed. Two methods widely used in the literature have been used to detect LST anomalies in the detrended LST time series: the interquartile (IQT) method and the standard deviation (STD). To the authors’ knowledge, it is the first time that the confusion matrix (CM), the receiver operating characteristic curve (ROC), and some other figures of merit (FoM) are used to assess and optimize the performance of the methods, and to select the optimum combination that could be used as a proxy for their occurrence. A positive anomaly was found a few days before the studied earthquakes, followed by the LST decrease after the event. Further studies over larger regions and more extended periods will be needed to consolidate these encouraging results.

A Potential Earthquake with Magnitude Mw 7.2 on the Northern Xiaojiang Fault Revealed by GNSS Measurement

We used near-field and regional GNSS (Global Navigation Satellite System) data to quantify the deformation and locking ratio of the Xiaojiang fault (XJF) in southeastern Tibet. The inversion based on the dislocation model shows that the slip rate of the XJF is 9–11 mm/a; the locking depths of the northern, central, and southern segments are 25.5 km, 12 km, and 22.5 km, respectively. The inversion with DEFNODE program shows that the locking of the northern segment is the strongest above a depth of 20 km, while the locking between 20 km and 26 km is intermediate, and the weakest locking is found below 26 km. In the central segment, the depths of the interface are 6 km and 12 km. Additionally, a locked asperity that has the potential of generating an Mw 7.2 earthquake along the northern segment is delineated. The asperity and the shallow locking zone are basically consistent with the rupture area of the 1733 M 7.8 Dongchuan earthquake and the 1833 M 8 Songming earthquake, respectively. Both the activity of the historical strong earthquakes and the seismicity of the microearthquakes recorded over recent years seem to suggest that a potential earthquake is imminent.