Mainshock Research Articles

An analysis of the spatial distribution of geophysical filds in the source region of the 2013 Ilin-Tas (Aby) earthquake

This article analyzes the powerful Ilin-Tas earthquake that occurred in the Chersky Range system in the territory of the Republic of Sakha (Yakutia) in 2013. The mountain system of the Chersky Range system is confied to the Chersky seismotectonic zone, which is part of the Arctic-Asian seismic belt separating the Eurasian and North American lithospheric plates in Northeast Asia. The earthquake magnitude at the epicenter was 9.0. Geophysical filds were used as a material to clarify the structural-tectonic features of the study area and their relationship with seismicity. Involving the data on spatial distribution of anomalies of magnetic and gravity filds made it possible to detail the parameters of the position of the Ilin-Tas fault, where the epicentre of the Ilin-Tas earthquake originated. This fault traces between the Indigirka and Kolyma rivers along the border of the junction of the Moma Range with the Indigiro-Zyryansk depression, and is traced by gradient transition zones from negative to positive values of ΔTa and Δg. The main seismic shock is confied to thickening of Δg isoanomalies, forming a gravitational step, within which gravity values decrease from south to north. The epicentral fild of this earthquake with aftershocks captures the western slope of the Andrey-Tas Range (northwestern flnk of the Moma Range). A qualitative analysis of the geophysical filds in the epicentral region of the earthquake is carried out. Materials of instrumental and macroseismic data, focal mechanism and seismotectonic setting of the focal zone are given in the article. The data obtained as a result of studying the Ilin-Tas earthquake consequences allows to reveal local seismic activity in details and specify seismodanger degree of north-east Yakutia.

Clustering features and seismogenesis of the 2014 M6.6 Jinggu earthquake in Yunnan Province, China

Seismic activities can be seen as the composition of background and clustering earthquakes. It is important to identify seismicity clusters from background events. Based on the Nearest Neighbour Distance algorithm proposed by Zaliapin, we use the Gaussian mixture model (GMM) to fit its spatiotemporal distribution and use the probability corresponding to clustering seismicity in the GMM model as the clustering ratio. After testing with synthetic catalogues under the ETAS (epidemic-type aftershock sequence) model, We believe the method can discriminate cluster events from randomly occurring background seismicity in a more physical background. We investigate the seismicity and its clustering features before the M6.6 Jinggu earthquake in Yunnan Province, China on 7 October 2014. Our results show the following: 1) The seismogenic process of this strong earthquake has three stages, which are already described by the IPE model (the model is similiar to dilatancy diffusion model, growth of cracks is also involved but diffusion of water in and out of the focal region is not required); 2) The main shock might have been caused by the breaking of a local locked barrier in the hypocentre, and the meta-instability stage was sustained for about 1 year on the fault. From this study, we conclude that the evolution of seismicity clustering features can reflect changes in stress in the crust, and it is closely connected to the seismogenic process of a strong earthquake.

Kalman Filter, ANN-MLP, LSTM and ACO Methods Showing Anomalous GPS-TEC Variations Concerning Turkey’s Powerful Earthquake (6 February 2023)

On 6 February 2023, at 1:17:34 UTC, a powerful Mw = 7.8 earthquake shook parts of Turkey and Syria. Investigating the behavior of different earthquake precursors around the time and location of this earthquake can facilitate the creation of an earthquake early warning system in the future. Total electron content (TEC) obtained from the measurements of GPS satellites is one of the ionospheric precursors, which in many cases has shown prominent anomalies before the occurrence of strong earthquakes. In this study, five classical and intelligent anomaly detection algorithms, including median, Kalman filter, artificial neural network (ANN)-multilayer perceptron (MLP), long short-term memory (LSTM), and ant colony optimization (ACO), have been used to detect seismo-anomalies in the time series of TEC changes in a period of about 4 months, from 1 November 2022 to 17 February 2023. All these algorithms show outstanding anomalies in the period of 10 days before the earthquake. The median method shows clear TEC anomalies in 1, 2 and, 3 days before the event. Since the behavior of the time series of a TEC parameter is complex and nonlinear, by implementing the Kalman filter method, pre-seismic anomalies were observed in 1, 2, 3, 5, and 10 days prior to the main shock. ANN as an intelligent-method-based machine learning also emphasizes the abnormal behavior of the TEC parameter in 1, 2, 3, 6, and 10 days before the earthquake. As a deep-learning-based predictor, LSTM indicates that the TEC value in the 10 days prior to the event has crossed the defined permissible limits. As an optimization algorithm, the ACO method shows behavior similar to Kalman filter and MLP algorithms by detecting anomalies 3, 7, and 10 days before the earthquake. In a previous paper, the author showed the findings of implementing a fuzzy inference system (FIS), indicating that the magnitude of the mentioned powerful earthquake could be predicted during about 9 to 1 day prior to the event. The results of this study also confirm the findings of another study. Therefore, considering that different lithosphere–atmosphere–ionosphere (LAI) precursors and different predictors show abnormal behavior in the time period before the occurrence of large earthquakes, the necessity of creating an earthquake early warning system based on intelligent monitoring of different precursors in earthquake-prone areas is emphasized.

A new seismic damage assessment method for single-layer spherical reticulated shells based on structural residual displacement under sequential earthquakes

Single-layer Spherical Reticulated Shell (SSRS) is usually utilized as an emergency shelter or a command post for disaster relief. However, the structural damage indicators in current studies are difficult to observe or record so as to hardly assess the damage state after the main shock. In order to explore the damage state assessment timely and accurately for SSRS, a new seismic damage assessment method based on structural residual displacement under main shock-aftershock ground motions is proposed in this paper. The finite element model of Kiewit 8-SSRS (K8-SSRS) is established in the ANSYS with 40 groups of actual sequential earthquake from the Pacific Earthquake Engineering Research Center (PEER) seismic database. Then, the dynamic responses of the model are analyzed to calculate the damage index and eight structural dynamic response indicators. Moreover, the correlation study between the damage index and eight indicators is carried out to make the comparison analyses. Finally, it is verified that the structural plasticity appeared under main shock can develop further under strong aftershock to cause greatly additional damage or even result in structural strength failure. It is concluded that the maximum residual displacement has the strongest correlation with the damage index of the structure under sequential earthquake, which means the most feasible indicator to characterize the structural damage under sequential earthquake.

Did U.S. and Chinese investors respond differently to the exogenous shocks from COVID-19 and the war in Ukraine?

This paper investigates the U.S. and Chinese stock markets' long-run responses to COVID-19 and the Russia–Ukraine war, the main shocks that have recently battered the globalized economy. The investigation uses both static data analysis and ARMA-GARCH and DCC-GARCH dynamic risk models incorporating both events' impacts. Model fitting reveals opposite reactions of the two stock markets' long-run volatilities to the pandemic, but both volatilities have been enhanced by the war, with a much stronger reaction from the U.S. than from the Chinese market. Furthermore, the war has reduced the linkage between the two markets, while the pandemic has had no significant effect. The different responses of U.S. and Chinese investors may be attributed to the two countries' very different virus containment strategies, pandemic severities, and policy approaches to the geopolitical conflict. Our results have important practical implications for regulators' risk mitigation policy design and investors' cross-market hedging strategy development.

Effect of seismic sequences on behavior of mid-rise steel moment-resisting frames equipped with fluid viscous dampers

This study aims to investigate the seismic response of mid-rise steel frames equipped with fluid viscous dampers under seismic sequences. For this purpose, 4-, 6-, and 8-story steel frames with and without fluid viscous dampers are analyzed under sequences of main shock and after shock, both with near and far field acceleration records. Thus, sets of 20 near-field and 20 far-field time histories are selected, each containing the main-shock and an after-shock. Using nonlinear dynamic analysis, the responses of the frames are calculated and plotted in various diagrams. Output parameters of displacement, interstory drifts, base shear, absolute acceleration and velocity are extracted and compared. Results show that viscous dampers significantly decrease structural responses comparing to the frames without damper. Also, structural responses have increased under combination of main-shock and after-shock which shows the important role of after-shocks in structural damages. Responses to near field record are also generally greater than far field ones.

The seismogenic structure of March 2021 Tyrnavos (central Greece) doublet (Mw 6.3 andMw 6.0), constrained by aftershock locations and geodetic data

SUMMARYThe Northern Thessaly Basin in central Greece ranks amongst the most well pronounced extensional (graben) basins in the backarc Aegean Sea region, with well-mapped faults having an ∼E–W orientation, compatible with the ongoing predominant ∼N–S extension. The southern margin of the basin is bounded by major faults associated with strong (M6 to M7) earthquakes, whereas along its northern margin, strong events are more scarce, in the documented catalogues. Along this northern margin, a weak, albeit persisting foreshock activity, culminated within 3 d, to an Mw 6.3 earthquake on 3 March 2021 associated with a 15-km-long NE dipping fault segment. It was followed the next day, by the second Mw 6.0 main shock associated with a 13-km-long NE dipping fault segment and 9 d later by an Mw 5.5 earthquake associated with an 8-km-long SW dipping fault segment, with its aligned epicentres, showcasing the cascade type activation of adjacent fault segments. The sequence, evolved to be very productive, with aftershocks extending ∼50 km along a ∼NW–SE trending narrow seismic zone. All events indicate pure normal faulting, with an NNE–SSW oriented extensional axis, oblique to our previous consensus of the prevalence of ∼N–S extension. This observation documents that inherited fault fabric can be reactivated within the modern tectonic stress field. We use high-quality seismological data, alongside Interferometric Synthetic Aperture Radar (InSAR) methodology and Global Navigation Satellite System (GNSS) data, to study the temporal and spatial evolution of the sequence, and to provide inferred kinematic models that describe the complexity of the seismic process, in terms of heterogeneous slip distribution, activated fault planes, fault geometry and displacement field. Cross-sections show that the activity defines the crustal seismogenic layer at depths between 5 and 10 km, associated with low-angle fault segments dipping to the NE. Other faults, both antithetic and secondary ones, appear active and accommodated aftershocks clusters. Using our preferred finite fault source model, we calculated the changes of Coulomb failure stress on the neighbouring faults.

Nonlinear time-domain soil-structure interaction analysis of a mid-rise building benchmarked against earthquake recordings: A case study of the BRI's annex building

Performing soil-structure interaction (SSI) analysis under strong shaking scenarios using the direct method is becoming more prevalent in engineering practice. However, given the pronounced nonlinearity in soil, structure, and foundation response, the robustness of current methodologies is open to question, and benchmarking these methodologies against instrumented case histories is needed to identify the strengths and weaknesses in the approach. In this study, a three-dimensional (3D) Nonlinear (NL) Soil-Structure Interaction (SSI) analysis methodology in the time-domain code LS-DYNA is benchmarked against the actual recordings for a mid-rise building. The well-instrumented Building Research Institute (BRI) Annex Building (ANX) in Tsukuba City northeast of Tokyo, Japan, which features an adjacent free-field geotechnical downhole array, is used for this case study. A Finite Element (FE) three-dimensional 3D SSI model of the site, including the BRI ANX building, that considers both material and geometric nonlinearities is first developed. Two events are applied to the model: the 2011 Tohoku-Oki earthquake main shock (Mw9.1), referred to as the Great East Japan Earthquake (GEJE), and the 2002 Southern Ibaraki Prefecture earthquake (Mw4.9), selected from the BRI strong motion network due to the relatively wide amplitudes recorded at the site. The former event induced maximum shear strains in the soil of 1.6%, while the latter event induced maximum shear strains of 0.08%. For both horizontal and vertical components of shakings, the predicted response of the structure and adjacent free-field downhole array are compared with the corresponding recordings. The results show that the structural response is significantly affected by the accuracy of the predicted free-field ground surface response, especially at the structural fundamental period as opposed to the site period. In addition, results indicate that the fixed-base and flexible-base structural models’ responses are substantially different, mainly attributed to the SSI effects that cannot be captured in the fixed-base model. Finally, a comprehensive discussion on the minimum amount of data required to adequately capture nonlinear structural response using the proposed SSI methodology is provided in this case study.

The upward propagating ionospheric hiss waves during the seismic time observed by the China seismo-electromagnetic satellite

The ionospheric hiss wave is a broadband incoherent and structureless electromagnetic emission. They appear in a relatively narrower frequency range between −0.1 and 1.5 kHz. However, according to previous observations, abnormal electromagnetic emissions during seismic activities also preferentially appear in the same frequency range of ionospheric hiss. This work studies the propagation features of the ionospheric hiss during seismic time based on the observations from the CSES (China Seismo-Electromagnetic Satellite). The wave vector analysis shows that during seismic activities, except for the downward propagating ionospheric hiss which is a common phenomenon in the ionosphere, there are upward propagating emissions mixed with the downward propagating ionospheric hiss. We made a statistical analysis of the shallow strong earthquakes (M ≥ 6.0, depth below 30 km) that occurred in mainland China from 2019 to 2022. We selected the ionospheric hiss events recorded by orbits passing over the epicenters within a time window (the 1-month prior to and 1-week after the main shock). We found that although most of the events are the typical downward propagating ionospheric hiss waves, however, there are certain events mixed with the upward propagating emissions. The statistical distribution analysis of wave propagation parameters shows that the major part of wave normal angles vary from 40 to 60, the azimuthal angles predominately attain below 40, and the ellipticity shows a more complicated feature varying around ± 0.5, and the planarity values predominate at values between 0.6 and 1. The frequency band of the upward propagating ionospheric hiss mostly varies between 300 Hz and 800 Hz. To further study the behavior of such upward propagating ionospheric hiss wave during the seismic time, we compared the wave activities under non-seismic activity and quiet space weather conditions, and the results confirm that the occurrence rate of the upward propagating emissions under quiet conditions is far less than that in the seismic time. We suggest that there is a link between the upward propagating ionospheric hiss and the seismic activity, but the physical reason behind it still remains a puzzle to us.

Seismicity parameters dependence on main shock-induced co-seismic stress

SUMMARY The Gutenberg–Richter (GR) and the Omori–Utsu (OU) law describe the earthquakes’ energy release and temporal clustering and are thus of great importance for seismic hazard assessment. Motivated by experimental results, which indicate stress-dependent parameters, we consider a combined global data set of 127 main shock–aftershock sequences and perform a systematic study of the relationship between main shock-induced stress changes and associated seismicity patterns. For this purpose, we calculate space-dependent Coulomb Stress (ΔCFS) and alternative receiver-independent stress metrics in the surrounding of the main shocks. Our results indicate a clear positive correlation between the GR b-value and the induced stress, contrasting expectations from laboratory experiments and suggesting a crucial role of structural heterogeneity and strength variations. Furthermore, we demonstrate that the aftershock productivity increases nonlinearly with stress, while the OU parameters c and p systematically decrease for increasing stress changes. Our partly unexpected findings can have an important impact on future estimations of the aftershock hazard.

Anomalous Seismic Noises from the December 9, 2020 MW = 5.6 KUDARA Earthquake in the Baikal Basin

Studies have been conducted on the variations of microseismic noise recorded by broadband and short-period seismic stations in the area of South Baikal before and after the large December 9, 2020 Kudara earthquake with Mw = 5.6. Ten days before the earthquake, there was a gradual increase of oscillation amplitudes in the frequency range from 0.01 to 0.1 Hz, with an increasing background observed also during 4 days after the main shock (period from December 1, 2020 to January 12, 2021). The maximum amplitude increase is 19.5 against the background. During this time, there were recorded 48 aftershocks. The analysis of direction of particle motion in seismic waves over the reporting period showed an abrupt change in the orientation of oscillations, which is fully consistent with the azimuth for the main shock epicenter. The analysis of seismograms over the next period (from December 13) did not show similar effects in the microseismic noise field. Apparently, the microseismic noise field reflected the process of slow faulting before the earthquake and after the main shock with subsequent attenuation.

Van Gölü Havzası ve Civarının Depremselliğine Genel Bir Bakış

Bu çalışma kapsamında, Van Gölü Havzası ve civarı için özellikle aletsel dönemde meydana gelmiş depremler ve bunların artçı şok verileri kullanılarak yapılan çalışmalardan elde edilen sonuçlar değerlendirilmiştir. Farklı sismolojik parametrelerin kullanıldığı bu çalışmaların bulguları derlenerek, bölgenin gelecekteki deprem riski/tehlikesi karşısındaki durumu ortaya koyulmaya çalışılmıştır. Aletsel ve tarihsel dönemde büyüklüğü 5.0 ve üzerinde olan birçok depremin meydana geldiği bölgede, son olarak 23 Ekim 2011 (Mw=7.1) ve 09 Kasım 2011 (Mw=5.8) tarihlerinde Van şehir merkezi civarında meydana gelen yıkıcı/hasar verici iki deprem bölgenin farklı özelliklerdeki aktif fay mekanizmalarına sahip olduğunu göstermiştir. Sonuç olarak, özellikle Van Gölü’nün hemen doğusu ile Çaldıran, Muradiye, Özalp, Saray ve Erciş civarında yakın gelecekte deprem tehlikesi diğer bölgelere göre büyük olarak ifade edilebilir. Ayrıca, Van Gölü Havzası ve civarının gerek jeofizik yöntemlere gerekse yapısal incelemelere dayalı farklı parametreler (zemin büyütmesi ve sismik hasar indisi gibi) kullanılarak zemin mühendislik özellikleri ve yapı-zemin etkileşimi açısından değerlendirmesi de bu çalışmada incelenmiştir.

Resilience in the shadow of systemic risks

Systemic risks possess a high level of complexity and uncertainty that can be latent behind the veil of initial stress of possible disasters. They refer to, on the one hand, the functionality of interconnected systems and, on the other hand, the probability of indirect losses which can propagate through larger territories. Once considering the solid definition of resilience by the United Nations, the emphasis tends on systems’ ability to different facets of disturbance rather than the performance of the sum of each singular entity confronting the main shock. This paper aims to provide a broader perspective and a systematic review focusing on the commons of resilience and systemic risks in the frame of risk mitigation. The outcomes highlight the urgency of multidisciplinary actions, which have not been achieved yet since the 1999s earthquakes.

An Approximate Analytical Model of a Jet Flow with Mach Reflection and Pulsed Energy Supply at the Main Shock

The supersonic flow of a reactive gas mixture with Mach reflection of oblique shocks and pulsed energy supply at the Mach stem is considered within the framework of the Chapman–Jouguet theory. An approximate analytical model is proposed that quickly determines the shape and size of the shock-wave structure as well as the flow parameters in various flow regions. As an example of the application of the proposed analytical model, the “first barrel” of a highly overexpanded jet flow of an air-methane mixture with a high supersonic velocity, is studied. Flows of hydrogen–air and hydrogen–oxygen mixtures were also considered for comparison with preceding numerical results. The height of the triple point of the Mach reflection is determined in the presence of a change in the chemical composition of the mixture and an isobaric pulsed energy supply at the main shock.

PERL: a dataset of geotechnical, geophysical, and hydrogeological parameters for earthquake-induced hazards assessment in Terre del Reno (Emilia-Romagna, Italy)

Abstract. In 2012, the Emilia-Romagna region (Italy) was struck by a seismic crisis characterized by two main shocks (ML 5.9 and 5.8) which triggered relevant liquefaction events. Terre del Reno is one of the municipalities that experienced the most extensive liquefaction effects due to its complex geostratigraphic and geomorphological setting. This area is indeed located in a floodplain characterized by lenticular fluvial channel bodies associated with crevasse and levee clay–sand alternations, related to the paleo-Reno River. Therefore, it was chosen as a case study for the PERL project, which aims to define a new integrated methodology to assess the liquefaction susceptibility in complex stratigraphic conditions through a multi-level approach. To this aim, about 1800 geotechnical, geophysical, and hydrogeological investigations from previous studies and new realization surveys were collected and stored in the PERL dataset. This dataset is here publicly disclosed, and some possible applications are reported to highlight its potential.

Slip model with supershear rupture velocity and stress drop for an M4.5 aftershock of the 2019 Ridgecrest, California, earthquake sequence

SUMMARY We use records from 24 stations with epicentral distances under 50 km to invert for slip and rupture time of an M4.5 aftershock of the 2019 Ridgecrest, California, earthquake sequence. Slip was determined by inverting source time functions (STFs), which were obtained at each station by decomposing a main shock, in this case an M4.5 aftershock, into a series of subevents using an empirical Green's function (eGf) as a template. The technique is iterative in the time domain with a positivity constraint. The STFs are characterized by a single pulse with durations that were longer in the southeast direction (about 1.0 s) and shorter in the northwest direction (about 0.6 s) suggesting rupture directivity to the northwest. We inverted the STFs for slip using a tomographic algorithm from that uses a high-frequency approximation to ray theory for the forward problem. The tomographic algorithm solves for slip and rupture time on a grid of points, which provides a better strategy for elucidating directivity than a model that uses subfaults. We solve for the strike-slip intensity on a near-vertical plane striking northwest, similar to the M7.1. After nine iterations, the slip model reduces the chi-squared estimate of fit by 68 per cent. Most of the slip is to the northwest, with a narrow well-defined peak in slip about 0.3 km NW of the origin. The peak is fairly symmetrical and about 1.5 km across its base. The model shows significant directivity to the northwest as suggested by the azimuthal variation of the STF pulse widths. Rupture velocity increases from nucleation to the peak in slip, becomes supershear, and then slows to about 3.2 km s−1, but there is little slip beyond 0.8 s contour in the forward direction. It appears that the peak in slip contributed stress to accelerate the rupture to the northwest. Low-level, parabolic-shaped slip patterns are seen to the northwest, which could be where the rupture front is dying out. Similar, but fainter curves facing the southeast suggests some bilateral rupture but the rupture to the northwest was stronger. Static stress drop was calculated using a formula for an elastic half-space giving a maximum of 35 bars at the peak in slip, but smoothing controls the absolute value. The average over a presumed fault plane is about 1.4 bars, much less than the peak. Slip and stress drop are highly heterogeneous.

Deep Machine Learning Based Possible Atmospheric and Ionospheric Precursors of the 2021 Mw 7.1 Japan Earthquake

Global Navigation Satellite System (GNSS)- and Remote Sensing (RS)-based Earth observations have a significant approach on the monitoring of natural disasters. Since the evolution and appearance of earthquake precursors exhibit complex behavior, the need for different methods on multiple satellite data for earthquake precursors is vital for prior and after the impending main shock. This study provided a new approach of deep machine learning (ML)-based detection of ionosphere and atmosphere precursors. In this study, we investigate multi-parameter precursors of different physical nature defining the states of ionosphere and atmosphere associated with the event in Japan on 13 February 2021 (Mw 7.1). We analyzed possible precursors from surface to ionosphere, including Sea Surface Temperature (SST), Air Temperature (AT), Relative Humidity (RH), Outgoing Longwave Radiation (OLR), and Total Electron Content (TEC). Furthermore, the aim is to find a possible pre-and post-seismic anomaly by implementing standard deviation (STDEV), wavelet transformation, the Nonlinear Autoregressive Network with Exogenous Inputs (NARX) model, and the Long Short-Term Memory Inputs (LSTM) network. Interestingly, every method shows anomalous variations in both atmospheric and ionospheric precursors before and after the earthquake. Moreover, the geomagnetic irregularities are also observed seven days after the main shock during active storm days (Kp > 3.7; Dst < −30 nT). This study demonstrates the significance of ML techniques for detecting earthquake anomalies to support the Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) mechanism for future studies.

Amplification of turbulent kinetic energy and temperature fluctuation in a hypersonic turbulent boundary layer over a compression ramp

In this paper, direct numerical simulations in a Mach 6.0 hypersonic turbulent boundary layer over a 30 ° compression ramp are performed. The influence of shock wave/boundary layer interactions on the amplification of turbulent kinetic energy (TKE) and temperature fluctuation (TF) is explored, to provide an insight into the physical mechanism. In the initial part of the interaction region before the detachment of the shear layer, the amplification of the TKE and TF is found, via a frequency spectrum analysis, to be closely related to the low-frequency unsteadiness of the shock wave. Once the free shear layer is established, the shear component of the TKE production defined in the shear layer coordinate appears to act as the main contributor for the TKE amplification, owing to the mixing layer turbulence and the resultant Kelvin–Helmholtz instability. This is consistent with the result from the spectrum analysis that the TKE and TF amplification and their streamwise evolution are dominated by the spectral energy in the median-frequency range, arising from the mixing layer turbulence. As the flow moves downstream along the shock wave, the high-frequency spectral energy content of TF shows a decreasing trend, while the low-frequency spectral energy tends to increase gradually, implying that the shock wave low-frequency unsteadiness exists not only in the initial stage of the interaction region but also around the main shock wave. Under the combined influence of the shock wave intensity and interaction intensity, the median-frequency content appears to weaken first and then tends to increase before decreasing again. The variation amplitude appears to be small and generally dominates the distribution of the TF intensity.

Coseismic and post-seismic characteristics of the 2021 Ganaveh earthquake along the Zagros foredeep fault based on InSAR data

SUMMARY The Ganaveh earthquake on 2021 April 18 (Mw 5.8) occurred in the southwest of the Dezful embayment of the Zagros Mountain belt, Iran, as a mainly compressive event. The InSAR coseismic displacement maps reveal a maximum of 17 cm of surface displacement in the satellite line of sight direction. InSAR inversion indicates a low-angle NE-dipping causative fault plane with a maximum slip of 95 cm at ∼6 km depth. It highlights the occurrence of the Ganaveh earthquake within the competent layers of the Zagros sedimentary cover, beneath the Gachsaran formation. A slight sinistral slip component (2.9 cm) is retrieved which is compatible with the USGS focal mechanism. Time-series analysis of SAR images after the main shock until the end of 2021 indicates a maximum of 7 cm of post-seismic surface displacement with a similar strike and pattern as the coseismic phase. This similarity and the distribution of aftershocks suggest an afterslip mechanism for the post-seismic phase. The inversion of post-seismic cumulative displacement evaluates a maximum of 30 cm slip at a depth of ∼5 km along the coseismic causative fault. A regional compressional stress regime (N041°E for the direction of the σ1 stress axis) is constrained by using the focal mechanisms of 39 earthquakes occurring between 1968 and 2021, including the Ganaveh main shock and its five larger aftershocks. Applying this direction of compression on the Ganaveh fault plane also results in a minor sinistral movement, consistent with the geodetic results. The relocated main shock and aftershocks as well as our InSAR coseismic displacement situations on the hanging wall of the Zagros Foredeep fault highlight it as the causative fault of the Ganaveh earthquake. To fit the geometry of the Ganaveh rupture plane with the Zagros Foredeep fault, we modelled a listric fault plane and its slip distribution using the available geological data. The retrieved slip variation on the listric plane is in close agreement with the slip pattern on the modelled planar geometry. The low dip angle of the rupture plane combined with a listric geometry highlights the thin-skin characteristics of the Zagros Foredeep fault as the causative fault of the Ganaveh earthquake. The occurrence of this moderate magnitude earthquake on the Zagros Foredeep fault underlines its role as the western structural boundary for the recurrence of Mb > 5 events in the Dezful embayment.

Kinematic Rupture Process and Its Implication of a Thrust and Strike-Slip Multi-Fault during the 2021 Haiti Earthquake

A devasting Mw7.2 earthquake struck southern Haiti on 14 August 2021, leading to over 2000 casualties and severe structural failures. This earthquake, which ruptured ~70 km west of the 2010 Mw7.0 event, offers a rare opportunity to probe the mechanical properties of southern Haiti. This study investigates the kinematic multi-fault coseismic rupture process by jointly analyzing teleseismic and interferometric synthetic aperture radar (InSAR) datasets. We determined the optimal dip of different segment faults through finite-fault inversion, and the results show that the dips of the first, second and third faults are 62°, 76° and 76°, respectively, coinciding with the relocated aftershock distribution. The results estimated from our joint inversion revealed that the slip was dominated by reverse motion in the first segment and strike-slip motion in the second and third segments. Three slip patches were detected along the strike, with a peak slip of 3.0 m, and the rupture reached the surface at the second segment. The kinematic rupture process shows a unilateral rupture with a high centroid rupture velocity (5.5 km/s), and the rupture broke through the stepover and caused a cascade rupture. The rupture front experiences a directivity pulse of high ground motions with high amplitude and short duration, which may be an additional factor explaining the many landslides concentrated on the western end of the fault. The Coulomb failure stress change result indicates the increases in the probability of future events to the east and west of the 2021 main shock.