Fault Rupture Research Articles

Rapid damage assessment effectiveness for the 2023 Kahramanmaraş Türkiye earthquake sequence

The recent devastating 2023 Türkiye earthquakes underscored the urgent need for an early estimate of quantitative losses following destructive seismic events. This study aims to propose and validate a Rapid Damage Assessment (RDA) methodology based solely on open data and tools, easily and readily available globally immediately after a seismic event. In this context, the 2023 Türkiye earthquakes are used as a case study. For the application of the proposed methodology there are two prerequisites: (1) ground shaking data, herein obtained from the US Geological Survey (USGS) ShakeMap system, and (2) a predictive seismic risk model appropriate for the area of interest, consisting of an exposure and a vulnerability model, derived from the 2020 European Seismic Risk Model (ESRM20). Scenario-type analyses for the two major events, the M7.8 - Pazarcik and the M7.5 – Elbistan earthquake, are performed, and the results are compared with the officially reported damages. The main goal is to assess the accuracy of RDA immediately after an earthquake, and whether and to what extent the RDA results can be improved as the USGS ShakeMaps are updated with the incorporation of additional data, and with disaggregation of the exposure model at a finer resolution. The results indicate that the exposure model's disaggregation reduces the damage estimates' standard deviation. At the same time, the effect of the ShakeMap version is minimized when the complete fault rupture is incorporated into the model. The estimated damages are in good agreement with the officially announced data at large scale, which corroborates the proposed methodology, as well as the adopted components of ESRM20.

Cascading rupture of large strike-slip fault bends: Evidence from paleoearthquakes in the Xianshuihe fault zone, Eastern Tibetan Plateau

The restraining and releasing bend region, encompassing the South Qianning, Kangding, and North Moxi segments, occupies a distinctive position within the Xianshuihe fault zone and plays a pivotal role in the analysis of seismic hazards. Our study focused on paleoearthquake research on the Qianning segment of the Xianshuihe fault zone through the integration of tectonic geomorphology, trench excavations, and radiocarbon dating methodologies. Three events, designated as ET1-ET3, have been found, occurring at 635–519, 823–672, and 3515–1482 yr B.P., respectively. A chronological framework for earthquake events has been established since the Holocene. The coefficient of variation (CoV) (0.75 reveals a weakly periodic recurrence model governing the activity of the Qianning segment. Moreover, both the Qianning and Kangding segments exhibit heightened susceptibility to cascading ruptures within the context of a single earthquake. The integration of shallow and deep data reveals a noteworthy transformation in the fault structure, transitioning from a solitary deep structure within the Qianning segment to a flower structure in the Kangding segment. This structural evolution is attributed to the migration of activity from the Yalahe Fault to the Selaha Fault and Zheduotang Fault, resulting in the short-cutting process within the Xianshuihe Fault Zone.

Multi-layer non-hydrostatic free-surface flow model with kinematic seafloor for seismic tsunami generation

Earthquake induced tsunamis pose devastating threat to coastal communities worldwide. Accurate description of tsunami generation by kinematic fault rupture is of importance to investigate earthquake events and evaluate tsunami impacts. The paper develops a multi-layer non-hydrostatic model with a kinematic bottom boundary condition and conducts comprehensive validation to examine the model’s capability in resolving seismic tsunami generation. The two-dimensional governing equations of the multi-layer non-hydrostatic free-surface flow system equipped with kinematic seafloor displacement is first introduced in Cartesian coordinates. A combined finite difference and finite volume scheme is utilized to discretize the governing equations with flow variables arranged on a staggered Arakawa C-grid. Application of pressure correction technique to the discretized formulations yields Poisson-type equations from which the non-hydrostatic pressure is solved for the next time step to complete the temporal integration. Based on existing analytical solutions, four groups of tsunami generation cases considering broad ranges of source parameters, including horizontal scale, rise time, and rupture velocity, are designed to demonstrate performance of the proposed non-hydrostatic model with one-, two-, and three-layers as well as the hydrostatic one. Comparison of 59 generation cases including extreme scenarios indicates the non-hydrostatic model performs better than the hydrostatic model in reproducing the entire waveform and predicting the maximum wave amplitude. High modeling accuracy can be achieved through incorporation of more layers. The proposed multi-layer non-hydrostatic model is a powerful tool for investigating earthquake source mechanisms and evaluating coastal tsunami hazards.

Numerical investigation on the deformation of railway embankment under normal faulting

Active faults in the earthquake region are consistently regarded as a potential geological hazard to the construction and operation of railway engineering. However, the effects of normal faulting on railway embankments have not been investigated thoroughly. For bridging this knowledge gap, three-dimensional finite element analysis considering the influence of faulting offset, the soil layer’s thickness, the fault dip angle and the embankment cross-fault angle are conducted to clarify the normal faulting effects on the railway embankment. Emphasis is given to the stress and strain characteristic in the fault rupture outcropping regions on the embankment, the deformation of the embankment centerline for design purposes, and the determination of the affected zones for railway embankment preservation. The analysis shows that the normal fault rupture outcropping regions on railway embankment are tensile yield in most cases. The existence of the soil layer and its thickening would widen the affected zones and the regions where the fault ruptures outcrops. The fault dip angle and the cross-fault angle of the embankment have a complex effect on the behaviors of the crossing embankment. The depth of the subsidence zone of the embankment would increase with the decrease of the fault dip angle and the large fault dip angle would change the primary fault rupture to be a compressive one directly above the fault line. If the embankment crosses the fault line obliquely, the curvature radius of the centerline would hardly meet the design code.

Effects of fault roughness on estimating critical slip-weakening distance from fault slip history: A laboratory study

Earthquakes are the dynamic rupture of faults governed by fault weakening processes. Critical slip-weakening distance (Dc) is a crucial source parameter of earthquakes, and the determination of Dc is of great concern to semiologists. However, determining Dc for natural earthquakes is challenging due to the trade-off in inversed source models. To solve this problem, Fukuyama and his coworkers proposed a simple method (denoted as the F&M method) to estimate Dc directly from slip-velocity functions. According to the F&M method, the fault slip at the peak slip velocity (Dc') can be used as an approximation of Dc. However, the feasibility of this method has not been completely resolved. Here, we performed laboratory earthquake rupture experiments to examine the validity of the F&M method. Experiments were conducted on faults with different roughness and stress level. We studied the effect of fault roughness on the validity of the F&M method. Our results show that the increase in fault roughness could complicate the fault weakening process, producing repeated weakening and strengthening phase, which leads to a prominent deviation between Dc' and Dc. Furthermore, we also observed a correlation between the critical slip-weakening distance Dc and the final fault slip D. Such correlation implies the scale-dependent nature of Dc, which is consistent with seismic observations in the field.

Fault system dynamics of the Kashmir, NW Himalaya, India using continuous GPS observations and geomorphic evidences

We collected data from the continuous Global Positioning System (cGPS) sites across the Kashmir Valley, situated at latitude 34◦N, spanning from 2008 to 2021. Inter-site velocities define a region of approximately 15,000 km2 with broadly distributed strain accumulation at −7.22×10−8 nano strain/year (compression component) and the maximum shear strain γmax of 1.9051×10−7 nano strain/year. The estimated site velocity in the ITRF14 ranges between 30.5±1–42.85±3 mm/yr. It was observed that the average deformation rate of the GPS sites in the Kashmir region ranges between 2.86±1–15.47±3 mm/yr relative to the India fixed reference frame, suggesting a predominant N-S directed compressional tectonic regime. The focal mechanism solutions of the earthquakes in and around the Kashmir Valley suggest dominant thrust faulting followed by normal faulting. Analysis of the vertical component of the GPS time series shows that the northwest segment of the valley subsides at the rate of −1.71± 0.70 mm/yr, while the southeast segment uplifts at the rate of 5.4 ± 0.5 mm/yr. In addition to vertical component, we observed differential movement of the sites relative to IISC site on the northwest and southeast segments. The rate of baseline change of the GPS sites indicates 7.30 ± 0.75 mm/yr extension in SE-NW direction and −5.32 ± 0.75 mm/yr NE-SW compression across and along the Kashmir Valley. Geodetic observations reveal a transition that aligns with the Magam lineament/fault previously identified by Ganju and Khar (1984) using gravity and magnetic data. The observation was supported by the field investigations and remote sensing techniques, confirming the existence of Magam Fault. During the field investigations, various geomorphic expressions of fault were observed, including fault ruptures, fault scarps, offset ridges, deflected drainages/rivers, linear alignment of springs, linear drainage lines, triangular facets and offset Recent sedimentary deposits (Karewas) were observed. The field evidence suggests exposure of normal faults at Kondabal, Nasrullapora, Biru and Radbugh. These exposed extensional structures, trends in NE-SW direction and dip in NW direction with varying offset and dip amount. GPS observations supplemented by geomorphic evidences infer the presence of normal fault ̴ 80 Km extending from northeast to southwest.

Sealing faults and fluid-induced seismicity.

Sealing faults are nearly impermeable barriers that can form boundaries between subsurface pore-pressure domains. In hydrocarbon systems, sealing faults commonly form part of a structural trap; they are thus important elements for future storage of CO2 and other gases in depleted reservoirs. The Triassic Montney Formation in western Canada hosts low-permeability gas reservoirs containing sealing faults that have previously been assumed to compartmentalize pressure domains. In this study, we show that the distribution of induced seismicity associated with hydraulic fracturing (HF) exhibits a statistically significant spatial correlation with zones of high lateral gradient in pore pressure. These high-gradient zones are interpreted as sealing fault systems. The largest induced seismicity sequence, including a 4.5 ML mainshock on 30 November 2018, occurred during HF treatments in two horizontal wells, between which there is an exceptionally large contrast (~10 MPa) in measured pore pressure. Numerical simulation of a simplified model of a hydraulic fracture intersecting a nearby vertical fault, followed by fault rupture using rate-and-state friction rheology, generates results that are in good agreement with observed strike-slip faulting near one of the HF wells. Our study demonstrates that sealing faults exhibit previously unrecognized behaviour that may be important for understanding induced seismicity risk. This article is part of the theme issue 'Induced seismicity in coupled subsurface systems'.

“Earthquake Response of the Transportation Infrastructure in the Region Affected by the February 6 Türkiye Earthquakes’’ Part I-Roads, Railroads and Ports

ABSTRACT On February 6, 2023, two devastating earthquakes with magnitudes larger than 7,5 occurred in Türkiye, within the nine hours of each other. Damage was observed on inter-provincial roads, railroads as well as some air and seaports. Passenger and freight transportation was interrupted for a few days. The fault rupture was close to or crossing many roads and railroads, causing displacements. The secondary effects of the earthquakes such as liquefaction and landslides also caused damage. This paper presents the earthquake response of the transportation infrastructures affected by the Kahramanmaras earthquake sequence based on findings from field investigations conducted after the earthquakes.

Late Quaternary right-lateral slip rate along the Tangyuan segment of the Yilan–Yitong Fault Zone on the NE China Plain

The slip rate of strike-slip active faults is crucial for fault rupture behavior analysis and seismic hazard assessment. Although many segments of the Yilan–Yitong Fault Zone (YYFZ) in NE China have been strongly deformed since the late Quaternary, little progress has been made on its slip rate. With the help of high-resolution satellite images, detailed field investigations, seismic reflections, and Quaternary chronological dating, we mainly studied the late Quaternary right-slip rate of the YYFZ. Field investigations revealed an ∼15 km long by ∼1–2 m high-surface scarp belt extending along the Tangyuan graben interior, with a series of sag ponds and small parallel bulges. Research has revealed that the most recent paleoearthquake (∼M 7.0) occurred between 2,800± 600 a BP and 1,700 ± 200 a BP, with evidence of coseismic surface rupture. The T2 terrace abandonment age of the Heijin River is approximately 55.13 ± 1.78 ka (OSL), and the maximum cumulative right-lateral offset may reach 110 ± 5 m. Thus, the maximum right-slip rate of the Tangyuan segment of the YYFZ since the late Quaternary is constrained to 1–2 mm/a according to the upper terrace model. This study suggests that the presence of a new fault in the basin interior merits more attention when assessing the influential surface range and earthquake potential along the YYFZ, and the features of “low tectonic loading rate, activity migration in space, and clustering in time separated by ten thousand years of seismic quiescence” observed along the YYFZ are highly important for earthquake model construction and tectonic deformation studies in stable continental regions (SCRs).

Изучение дизъюнктивной сети о. Кунашир (Курильские острова) с целью реконструкции особенностей его тектонического развития

The paper is devoted to the study of the faults on Kunashir Island, focusing on their classification, morphology, kinematics, timing, and causes of formation, which are key to understanding the tectonic evolution of the area. The magma-supporting role of these faults is noted, contributing to the understanding of the distribution of volcanic and plutonic formations in the Great Kuril Ridge. The ore-controlling role of the faults was evaluated, which may contribute to the discovery of new mineral deposits. Additionally, studying these faults is important for improving the prediction of earthquakes and tsunamis. The research methodology includes an integrated approach that combines traditional geological observations with modern remote sensing methods, allowing us to detail the map of the Kunashir Island rupture faults. The results of the work confirm the presence of three systems of tectonic structures that differ in depth of emplacement, length, timing, kinematics, and causes of formation. The study contributes to our understanding of the complex geological structure of Kunashir Island and the entire island arc and provides a basis for further research in this area."

An SPH framework for drained and undrained loading over large deformations

AbstractWe propose a new approach for performing drained and undrained loading of elastoplastic geomaterials over large deformations using smoothed particle hydrodynamics (SPH), a meshfree continuum particle method, combined with the modified Cam Clay (MCC) model of critical state soil mechanics. The numerical approach draws upon a novel one‐particle two‐phase penalty‐method based formulation for handling undrained loading in saturated soils, which allows tracking of the buildup of pore‐water pressures under combined shearing and compression. Large‐scale parallelized simulations are employed to accommodate a significant number of degrees of freedom in a three‐dimensional setting. After verification and benchmark testing, the SPH based formulation is used to analyze the propagation of reverse faults through fluid‐saturated clay deposits and the rupture of strike‐slip faults across earthen embankments. The computational methodology tests the robustness of the meshfree approach in situations where the soil tends to dilate on the ‘dry’ side of the critical state line and to compact on the ‘wet’ side, but cannot, because of the incompressibility constraint imposed by undrained loading. Our results extend the current understanding of fault rupture modeling and further demonstrate the potential of our framework together with the SPH method for large deformation analyses of complex problems in geotechnics.

A Multiplex Rupture Sequence Under Complex Fault Network Due To Preceding Earthquake Swarms During the 2024 Mw 7.5 Noto Peninsula, Japan, Earthquake

AbstractA devastating earthquake with moment magnitude 7.5 occurred in the Noto Peninsula in central Japan on 1 January 2024. We estimate the rupture evolution of this earthquake from teleseismic P‐wave data using the potency‐density tensor inversion method, which provides information on the spatiotemporal slip distribution including fault orientations. The results show a long and quiet initial rupture phase that overlaps with regions of preceding earthquake swarms and associated aseismic deformation. The following three major rupture episodes evolve on segmented, differently oriented faults bounded by the initial rupture region. The irregular initial rupture process followed by the multi‐scale rupture growth is considered to be controlled by the preceding seismic and aseismic processes and the geometric complexity of the fault system. Such a discrete rupture scenario, including the triggering of an isolated fault rupture, adds critical inputs on the assessment of strong ground motion and associated damages for future earthquakes.

Structural features and Holocene activity of the Motuo fault zone, eastern Himalaya syntaxis

The Motuo Fault zone (MTF), the southeast boundary of the eastern Himalaya syntaxis, is an important information carrier to understand the present-day kinematics and geodynamics of the Tibetan Plateau. However, little knowledge has been obtained about its Holocene activity and structural features of the MTF due to the ubiquitous vegetation covering. Interpretations of satellite imageries, outcrop and trench observations, together with the radiocarbon and Optically Stimulated Luminescence (OSL) dating results reveal that (1) the MTF consists of multiple NE–SW-trending branch faults, forming a wide fault system that could be generally divided into the western segment, central segment and eastern segment; (2) the drainage systems, mountain ridges and alluvial fans have been systematically left-laterally deflected or offset along the MTF; (3) two surface-rupturing earthquakes occurred close to or slightly earlier than 9.41 ± 0.94 ky BP and after ∼1540 yr BP, respectively, indicating that the MTF is an Holocene active fault. Due to the very limited exposure, it is quite possible that many paleoseismic events have not been revealed by this study and previous publications. For a better understanding and assessment of the seismogenic behavior of the MTF, a complete paleoseismic sequence and reasonable earthquake recurrence model need to be set up, especially considering the complex geometry of the fault system that probably suggests intricate fault rupturing.

Paleoseismic Investigation of the Thousand Springs Fault, Northwestern Basin and Range, Oregon

ABSTRACT Earthquake recurrence intervals, surface-rupture extents, and interactions between faults provide insight into how faults behave and are critical for seismic hazard mitigation and earthquake forecasting. Investigating the paleoseismology of spatially related faults can reveal strain distribution and whether faults rupture as a system or independently. Summer Lake basin, a graben in the northwestern Basin and Range with four active faults (three of which have prior paleoseismic investigations), provides an opportunity to investigate fault interactions. To expand the paleoseismic record, two trenches were excavated across the previously undocumented Thousand Springs fault, exposing a normal fault zone that offsets a sequence of deep- to shallow-water lake sediments, sand dunes containing reworked Mazama ash, and other Cascades-sourced tephra. Tephra units were correlated to known units by their physical characteristics, stratigraphic sequence, glass chemistry, and two new radiocarbon dates from the uppermost lake sediments. Using trench exposures, measured vertical separations through auguring, colluvial wedges, and extrapolated offsets based on a constant sedimentation rate, we identified at least five surface-rupturing earthquakes with a total offset of 3.4 + 2/−1 m in the past ∼65 ka. The oldest event (EH5) occurred at 63.8 ± 1.5 ka, event horizon 4 at 36.2 ± 12.7 ka (which could be more than one event), and event horizon 3 at 24.6 ± 0.3 ka. Event horizon 2, a warping event at our site, is likely more than one event and occurred between 7.5 and 10 ka; and the most recent event (EH1+), most likely more than one event, occurred between 3.3 and 7.7 ka. Several events correlate, within error, with events on other faults in the Summer Lake basin, suggesting that (1) the faults generally rupture together as a system, (2) the most recent earthquake may have ruptured all faults in the region, and (3) fault rupture is influenced by the rapid regression of Lake Chewaucan (∼13 ka).

Coseismic deformation and fault slip distribution of the 2023 MW7.8 and MW7.6 earthquakes in Türkiye

On February 6, 2023, a devastating earthquake with a moment magnitude of MW7.8 struck the town of Pazarcik in south-central Türkiye, followed by another powerful earthquake with a moment magnitude of MW7.6 that struck the nearby city of Elbistan 9 h later. To study the characteristics of surface deformation caused by this event and the influence of fault rupture, this study calculated the static coseismic deformation of 56 stations and dynamic displacement waveforms of 15 stations using data from the Turkish national fixed global navigation satellite system (GNSS) network. A maximum static coseismic displacement of 0.38 m for the MW7.8 Kahramanmaras earthquake was observed at station ANTE, 36 km from the epicenter, and a maximum dynamic coseismic displacement of 4.4 m for the MW7.6 Elbistan earthquake was observed at station EKZ1, 5 km from the epicenter. The rupture-slip distributions of the two earthquakes were inverted using GNSS coseismic deformation as a constraint. The results showed that the Kahramanmaras earthquake rupture segment was distinct and exposed on the ground, resulting in significant rupture slip along the Amanos and Pazarcik fault segments of the East Anatolian Fault. The maximum slip in the Pazarcik fault segment was 10.7 m, and rupture occurred at depths of 0–15 km. In the Cardak fault region, the Elbistan earthquake caused significant ruptures at depths of 0–12 km, with the largest amount of slip reaching 11.6 m. The Coulomb stress change caused by the Kahramanmaras earthquake rupture along the Cardak fault segment was approximately 2 bars, and the area of increased Coulomb stress corresponded to the subsequent rupture region of the MW7.6 earthquake. Thus, it is likely that the MW7.8 earthquake triggered or promoted the MW7.6 earthquake. Based on the cumulative stress impact of the MW7.8 and MW7.6 events, the southwestern segment of the East Anatolian Fault, specifically the Amanos fault segment, experienced a Coulomb rupture stress change exceeding 2 bars, warranting further attention to assess its future seismic hazard risk.

Quake-DFN: A Software for Simulating Sequences of Induced Earthquakes in a Discrete Fault Network

ABSTRACT We present an earthquake simulator, Quake-DFN, which allows simulating sequences of earthquakes in a 3D discrete fault network governed by rate and state friction. The simulator is quasi-dynamic, with inertial effects being approximated by radiation damping and a lumped mass. The lumped mass term allows for accounting for inertial overshoot and, in addition, makes the computation more effective. Quake-DFN is compared against three publicly available simulation results: (1) the rupture of a planar fault with uniform prestress (SEAS BP5-QD), (2) the propagation of a rupture across a stepover separating two parallel planar faults (RSQSim and FaultMod), and (3) a branch fault system with a secondary fault splaying from a main fault (FaultMod). Examples of injection-induced earthquake simulations are shown for three different fault geometries: (1) a planar fault with a wide range of initial stresses, (2) a branching fault system with varying fault angles and principal stress orientations, and (3) a fault network similar to the one that was activated during the 2011 Prague, Oklahoma, earthquake sequence. The simulations produce realistic earthquake sequences. The time and magnitude of the induced earthquakes observed in these simulations depend on the difference between the initial friction and the residual friction μi−μf, the value of which quantifies the potential for runaway ruptures (ruptures that can extend beyond the zone of stress perturbation due to the injection). The discrete fault simulations show that our simulator correctly accounts for the effect of fault geometry and regional stress tensor orientation and shape. These examples show that Quake-DFN can be used to simulate earthquake sequences and, most importantly, magnitudes, possibly induced or triggered by a fluid injection near a known fault system.

Seismic Resistance and Performance Evaluation of Masonry Dwellings After the February 6, 2023, Kahramanmaraş Earthquake Sequence in Türkiye

On February 6, 2023, two catastrophic earthquakes occurred on the East Anatolian Fault. The earthquakes had magnitudes of Mw = 7.7 and 7.6 and struck Kahramanmaraş-Pazarcık and Kahramanmaraş-Elbistan, respectively. The Kahramanmaraş-Pazarcık earthquake was triggered at 04:17 local time on the Dead Sea Fault (a branch of the East Anatolian Fault). The last earthquake on the addressed fault occurred about 500 years ago. The recorded peak ground acceleration (PGA) at the Pazarcık station reached 2.05g. In addition, the Pazarcık earthquake triggered two independent earthquakes, the Nurdağı and Islahiye earthquakes, which occurred 10 min later than the Pazarcık earthquake. However, the last earthquake, with its epicenter in Kahramanmaraş-Elbistan, struck at 13:24 local time. The recorded PGA for the Elbistan earthquake is 0.68g. This study aims to present the fault rupture mechanism of the February 6, 2023, Kahramanmaraş earthquakes, earthquake characteristics, and to evaluate the performance of masonry dwellings during the Kahramanmaraş earthquake doublet, which affected 10 provinces and numerous towns and villages. This paper also aims to illustrate the damage and failure mechanisms of the masonry dwellings, despite unexpectedly high accelerations that exceeded the design spectrum in the field, specifically in Kahramanmaraş, Gaziantep, Hatay, and Malatya, according to the current earthquake code in use.

Multiple Fold Earthquakes Recorded by the Paleoseismic Surface Ruptures of Bending-Moment Faults in the Qiulitage Anticline, South Tianshan, China

Abstract Bending-moment faults (BMFs), as a fundamental type of secondary faulting, are intrinsically linked to the primary causative faults within active thrust-fold belts. When these faults thrust through the ground surface, the resulting geomorphic scarps offer the characteristics of local earthquake recurrence. This information helps to fill a gap left by main faults, which often lack coseismic surface ruptures. The Qiulitage anticline where the 1949 M 7¼ Kuqa earthquake occurred is an active thrust-and-fold belt predominantly governed by blind faults. In addition, several typical BMFs extensively crop out as surface scarps in the front of the mountain. Our research concentrates on the well-developed BMF scarps in this region and seeks to explore the recurrence characteristics of paleoearthquakes, which remain inadequately comprehended. Our study reveals that (1) secondary BMF with high enough magnitude can directly generate coseismic ground ruptures, and (2) the seismic behavior of BMFs exhibits a degree of repeatability, potentially linked to the concurrent movement of various BMFs or the solitary action of a single fault. However, the case study presented in this article also highlights the limitation of fold earthquake research because of the swift attenuation of coseismic fault slip as it approaches the ground surface.

Rapid Finite-Fault Models for the 2023 Mw 7.8 Kahramanmaraş, Türkiye, Earthquake Sequence

Abstract In the immediate aftermath of devastating earthquakes such as in the 6 February 2023 Kahramanmaraş sequence in southcentral Türkiye, key stakeholders and the public demand timely and accurate earthquake information. Especially for large events, finite-fault models provide important insights into the rupture process and enable interpretation of the observed ground shaking, which can improve situational awareness and facilitate rapid assessment of future hazards. Using strong-motion waveforms recorded during the Kahramanmaraş sequence, we simulate a real-time playback and calculate how a finite-source model computed with the Finite-fault rupture Detector (FinDer) algorithm would evolve for the Mw 7.8 Pazarcık, Mw 7.6 Elbistan, and Mw 6.4 Yayladağı earthquakes. Using template matching FinDer compares observed and predicted ground-motion acceleration amplitudes to determine the orientation and spatial extent of fault rupture. We test both generic crustal and fault-specific templates from ground-motion models and rupture geometries of the east Anatolian and Çardak–Sürgü faults. In the second step, we estimate the seismic slip along the source models from the backprojection of the seismic displacement amplitudes. The algorithms achieve excellent performance for all three earthquakes, and the final source models and slip profiles available within tens of seconds of the rupture nucleation match well with models computed days to weeks after the events occurred. The temporal evolution of the source models for the Pazarcık and Elbistan earthquakes suggests that FinDer can provide insight into the rupture kinematics of large earthquakes. Cascading instrument failures as well as power and data telemetry interruptions during the Pazarcık earthquake led to an early termination of signals at a significant number of near-source stations. We show that FinDer is robust enough to cope with this type of degradation in network performance that can occur in large earthquakes, in general.

Effects of Dilatant Hardening on Fault Stabilization and Structural Development

AbstractDilatant hardening is one proposed mechanism that causes slow earthquakes along faults. Previous experiments and models show that dilatant hardening can stabilize fault rupture and slip in several lithologies. However, few studies have systematically measured the mechanical behavior across the transition from dynamic to slow rupture or considered how the associated damage varies. To constrain the processes and scales of dilatant hardening, we conducted triaxial compression experiments on cores of Crab Orchard sandstone and structural analyses using micro‐computed tomography imaging and petrographic analysis. Experiments were conducted at an effective confining pressure of ∼10 MPa, while varying confining pressure (10–130 MPa) and pore fluid pressure (1–120 MPa). Above 15 MPa pore fluid pressure, dilatant hardening slows the rate of fault rupture and slip and deformation becomes more distributed amongst multiple faults as microfracturing increases. The resulting increase in fracture energy has the potential to control fault slip behavior.