Kinematic Rupture Research Articles

Coseismic Deformation and Kinematic Rupture Process of the 2023 Türkiye MW7.8-7.5 Earthquake Doublet Deduced from High-rate GNSS Observations

Summary On February 6, 2023, a devastating earthquake doublet struck in Türkiye, which caused tremendous damage including about 54000 fatalities. We use high-rate GNSS data to study the coseismic static and kinematic displacement, and invert for fault slip distribution of the earthquake doublet. The maximum static coseismic displacements for the Mw7.8 (EQ1) and Mw7.5 earthquake (EQ2) are 0.38 m and 4.4 m respectively. The kinematic displacement recorded by GNSS stations reflect clearly the earthquake rupture process in more detail. We utilize 1-Hz GNSS waveforms, GNSS static displacements and surface rupture measurements to invert for the kinematic rupture model of the earthquake doublet. Our results show a rupture duration of ∼80 s, faulting length ∼350 km, and maximum slip ∼7.4 m for EQ1, and a rupture duration of ∼35 s, rupture length ∼190 km, and maximum slip ∼9.2 m for EQ2. The slip distributions inverted solely from GNSS coseismic deformation are basically consistent with the results from multi-source data. The rupture velocity of EQ1 towards east is about 4.5 km/s towards the east and 3.2 km/s towards the west. EQ2 nucleates on Çardak fault with bilateral supershear rupture velocity of 5.0∼5.5 km/s within the first 0-12 s, subsequently transitioning to subshear rupture at a speed of 1.2 km/s towards the east and 3.0 km/s towards the west. Our finding of the bilateral supershear ruptures of EQ2 contrasts with the results of unilateral westward supershear rupture of previous studies. We think that this discrepancy could be attributed to the utilization of more geodetic data of the relatively denser GNSS stations in the east flank of EQ2’s epicenter and calculating the mean velocities for individual rupture intervals in this study.

Kinematic rupture modeling of broadband ground motion from the 2022 MS6.9 Menyuan earthquake

AbstractWe propose a novel kinematic rupture modeling procedure for synthesizing broadband ground motions derived from the frequency-wavenumber integration algorithm. This procedure addresses two key issues in characterizing the rupture processes relevant to broadband seismic radiation: an accurate Green's function and a well-constrained kinematic source model. For the first issue, we derive the theoretical Green's function based on an improved dynamic stiffness matrix approach that effectively handles wave propagation in a 1D crustal velocity structure across a broad frequency band. For the second issue, we generate the hybrid source model that combines asperity slip and random slip over the fault plane to effectively implement constraints on the radiated energy during the whole rupture process. The accuracy and effectiveness of the proposed methodology are verified by comparing with the surface acceleration traces and Fourier spectra calculated by spectral element method. With the hybrid source model and crustal velocity structure applicable to the target area, the broadband (0–10 Hz) ground motion of the 2022 MS6.9 Menyuan earthquake is synthesized. The amplitude, duration, and frequency content of the synthetic motions are systematically compared with those of the available observed records and ground motion attenuation relationships, as well as the spatial distribution characteristics of the near-field ground motions from the earthquake scenarios are presented. In conclusion, the case study of the Menyuan MS6.9 earthquake demonstrates that the presented modeling procedure can estimate broadband ground motions rapidly and reliably from a physics-based kinematic rupture perspective.

Ground-Motion Modeling of the 2016 Mw 6.2 Amatrice, Italy, Earthquake, by a Broadband Hybrid Kinematic Approach, Including Empirical Site Effects

Abstract The region of Central Italy is well known for its moderate to large earthquakes. Events such as the 2016 Mw 6.2 Amatrice earthquake generated in the shallow extensional tectonic regime motivate numerical simulations to gain insights into source-related ground-motion complexities in the near-source region. We utilize a hybrid integral-composite kinematic rupture model by Gallovič and Brokešová (2007) to simulate the Amatrice earthquake in a broadband frequency range (up to 10 Hz). In the first step, we optimize the input source parameters using a grid-search method by minimizing the spectral acceleration bias between synthetic and recorded strong-motion data at reference rock stations within 50 km of the source. To verify the robustness of the optimal model, we simulate the ground motions at 400 virtual stations and compare their spectral accelerations with the predictions of an empirical nonergodic ground-motion model (GMM) for rock sites in Central Italy (Sgobba et al., 2021). The synthetics show a good agreement with the empirical model regarding both median and variability. Finally, we account for local site effects at nonreference stations by combining the simulations on rock with empirical site terms derived by the nonergodic GMM. The site-corrected spectral responses generally improve the match with the observations, demonstrating a successful fusion of numerical simulations with empirical estimates toward reproducing near-source ground motions.

Constraining Between-Event Variability of Kinematic Rupture Scenarios by Empirical Ground-Motion Model: A Case Study in Central Italy

ABSTRACT The region of central Italy is well known for its moderate-to-large earthquakes. Events such as 2016 Mw 6.2 Amatrice, generated in the shallow extensional tectonic regime, motivate numerical simulations to gain insights into source-related ground-motion complexities. We utilize a hybrid integral–composite kinematic rupture model by Gallovič and Brokešová (2007) to predict ground motions for other hypothetical Amatrice fault rupture scenarios (scenario events). The synthetic seismograms are computed in 1D crustal velocity models, including region-specific 1D profiles for selected stations up to 10 Hz. We create more than ten thousand rupture scenarios by varying source parameters. The resulting distributions of synthetic spectral accelerations at periods 0.2–2 s agree with the empirical nonergodic ground-motion model of Sgobba et al. (2021) for central Italy in terms of the mean and total variability. However, statistical mixed-effect analysis of the residuals indicates that the between-event variability of the scenarios exceeds the empirical one significantly. We quantify the role of source model parameters in the modeling and demonstrate the pivotal role of the so-called stress parameter that controls high-frequency radiation. We propose restricting the scenario variability to keep the between-event variability within the empirical value. The presented validation of the scenario variability can be generally utilized in scenario modeling for more realistic physics-based seismic hazard assessment.

Discontinuous transtensional rupture during the Mw 7.2 1995 Gulf of Aqaba earthquake

The Gulf of Aqaba earthquake occurred on 22 November 1995 in the Northern Red Sea and is the largest instrumentally recorded earthquake in the region to date. The event was extensively studied during the initial years following its occurrence. However, it remained unclear which of the many faults in the gulf were activated during the earthquake. We present results from multi-array back projection that we use to inform Bayesian kinematic rupture models constrained by geodetic and teleseismic data. Our results indicate that most of the moment release was on the Aragonese fault via left-lateral strike slip and shallow normal faulting that may have been dynamically triggered by an early rupture phase on the Arnona fault. We also identified a predominantly normal fault-segment on the eastern shore of the gulf that was activated in the event. We dismiss the previously proposed hypothesis of a co-seismic sub-event on the western shore of the gulf and confirm that observed deformation can be rather attributed to post-seismic activity. In conclusion, the gulf shows many signs of active tectonic extension. Therefore, more events close to the shorelines are to be expected in the future and should be considered conducting infrastructure projects in the region.

Rapid rupture characterization for the 2023 MS 6.2 Jishishan earthquake

On December 18, 2023, the MS 6.2 Jishishan earthquake occurred in the northeastern region of the Qinghai-Xizang Plateau, causing heavy casualties and property damage in Gansu and Qinghai Provinces. In this study, we integrate space imaging geodesy, finite fault inversion, and back-projection methods to decipher its rupture property, including fault geometry, coseismic slip distribution, rupture direction, and propagation speed. The results reveal that the seismogenic fault dips to the southwest at an angle of 29°. The major slip asperity is dominated by reverse slip and is concentrated within a depth range of 7–16 ​km, which explains the significant uplift near the epicenter observed by both the Sentinel-1 ascending and descending InSAR data. Moreover, the teleseismic array waveforms indicate a northwest propagating rupture with an overall slow rupture velocity of ∼1.91 ​km/s (AK array) or 1.01 ​km/s (AU array).

Multi-scale free oscillations and resonances over the continental shelf of the East China Sea from the 2011 Tohoku-Oki tsunami

A number of coastal tide gauges and offshore Deep-ocean Assessment and Reporting of Tsunamis (DART) buoys across the Pacific Basin recorded persistent oscillations excited by the 2011 Tohoku-Oki tsunami. The hazardous persistent oscillations prompted authorities to maintain a tsunami warning for dozens of hours. Tsunami waves reached the eastern China coast about five hours after the earthquake. The duration of detected prolonged oscillations was more than 80 h. In this study, we accurately reproduced tsunami generation and its evolution over the shallow and wide continental shelf of the East China Sea (ECS). For resonance analysis, we used an advanced numerical model that can consider simultaneously the effects of kinematic rupture process, horizontal displacement on tsunami generation, and Earth elasticity, seawater compressibility, and wave dispersion on tsunami propagation. The consistency of the simulated results was validated with both coastal and offshore tsunami records. In addition, we performed a combined spectral analysis of the observed tsunami records, background noise, and synthetic tsunami wave fields to identify tsunami oscillation modes and estimate their spatial distribution, including the spectral amplitude and phase angles. Eight main oscillation modes of the 2011 Tohoku tsunami were determined with periods of 24, 28, 37, 47, 57, 93, 136, and 157 min. They were all constrained within the 200-m isobaths for dozens of hours. The 57 min oscillations mode had the highest energy amplification across most of eastern China's coast. The spatial patterns of the resonance oscillations were used to propose hazard-prone areas. Based on the comprehensive spectral analysis results, the local and shelf topography properties played a key role in the dominant resonance modes of 136, 57, and 37 min. Identification of the shelf resonance oscillations coupled with the nearshore basin oscillations can provide valuable information for coastal tsunami hazard mitigation.

Evaluation of the Inter-frequency Correlation of New Zealand CyberShake Crustal Earthquake Simulations

The inter-frequency correlation of ground-motion residuals is related to the width of peaks and troughs in the ground-motion spectra (either response spectra or Fourier amplitude spectra; FAS) and is therefore an essential component of ground-motion simulations for representing the variability of structural response. As such, this component of the simulations requires evaluation and validation when the intended application is seismic fragility and seismic risk. This article evaluates the CyberShake NZ [1] crustal earthquake ground-motion simulations for their inter-frequency correlation, including comparisons with an empirical model developed from a global catalogue of shallow crustal earthquakes in active tectonic regions, and with results from similar simulations (SCEC CyberShake; [2]). Compared with the empirical model, the CyberShake NZ simulations have a satisfactory level of total inter-frequency correlation between the frequencies 0.1 – 0.25 Hz. At frequencies above 0.25 Hz, the simulations have lower (statistically significant at 95% confidence level) total inter-frequency correlation than the empirical model and therefore require calibration. To calibrate the total correlation, it is useful to focus on the correlation of the residual components. The between-event residual correlations, physically related to source effects (e.g., stress drop) which drive ground motions over a broad frequency range, are low at frequencies greater than about 0.25 Hz. Modifications to the cross-correlation between source parameters in the kinematic rupture generator can improve the inter-frequency correlations in this range [3]. The between-site residual correlations, which represents the correlation between frequencies of the systematic site amplification deviations, are larger (statistically significant at 95% confidence level) than the empirical model for frequencies less than about 0.5 Hz. We postulate that this relates to the relative simplicity of site amplification methods in the simulations, which feature less variability than the amplification observed in the data. Additional insight would be gained from future evaluations accounting for repeatable path and basin effects, using simulations with refined or alternative seismic velocity models, and using simulations with a higher crossover frequency to deterministic methods (e.g., 1 Hz or higher).

Kinematic Rupture Model of the 6 February 2023 Mw 7.8 Türkiye Earthquake from a Large Set of Near-Source Strong-Motion Records Combined with GNSS Offsets Reveals Intermittent Supershear Rupture

ABSTRACT The 2023 Mw 7.8 southeast Türkiye earthquake was recorded by an unprecedentedly large set of strong-motion stations very close to its rupture, opening the opportunity to observe the rupture process of a large earthquake with fine resolution. Here, the kinematics of the earthquake source are inferred by finite-source inversion based on strong-motion records and coseismic offsets from permanent Global Navigation Satellite Systems stations. The strong-motion records at stations NAR and 4615, which are the closest to the splay fault (SPF) where the rupture initiated and which were previously interpreted to contain the signature of supershear rupture speeds, are successfully modeled here by a subshear rupture propagating unilaterally to the northeast. Once the rupture on the SPF reaches the east Anatolian fault (EAF), it propagates on the EAF bilaterally, extending about 120 km northeast and 180 km southwest. To the south, the depth extent of the rupture decreases, as it passes a bend of the EAF. Although the rupture velocity remains globally subshear along the EAF, we identify three portions of the fault where the rupture is transiently supershear. The transitions to supershear speed coincide with regions of reduced fault slip, which suggests supershear bursts generated by the failure of local rupture barriers. Toward the southwest termination, the rupture encircles an asperity before its failure, which is a feature that has been observed only on rare occasions. This unprecedented detail of the inversion was facilitated by the proximity to the fault and the exceptional density of the accelerometric network in the area.

Dynamic Rupture Models of the 2016 ML 5.8 Gyeongju, South Korea, Earthquake, Constrained by a Kinematic Rupture Model and Seismic Waveform Data

ABSTRACT The ML 5.8 earthquake that jolted Gyeongju in southeastern Korea in 2016 was the country’s largest inland event since instrumental seismic monitoring began in 1978. We developed dynamic rupture models of the Gyeongju event constrained by near-source ground-motion data using full 3D spontaneous dynamic rupture modeling with the slip-weakening friction law. Based on our results, we propose two simple dynamic rupture models with constant strength excess (SE) and slip-weakening distance (Dc) that produce near-source ground-motion waveforms compatible with recorded ones in the low-frequency band. Both dynamic models exhibit relatively large stress-drop values, consistent with previous estimates constrained by source spectrum analyses. The fracture energy estimates were also larger than those predicted by a scaling relationship with the seismic moment. The dynamic features constrained in this study by spontaneous rupture modeling and waveform comparison may help understand the source and ground-motion characteristics of future large events in southeastern Korea and thus the seismic hazard of the region.

Simulation‐based characterization of the variability of earthquake risk to buildings in the near‐field

AbstractRecent advancements in high performance computing platforms and computational workflow for regional‐scale simulations are enabling unprecedented modeling of fault‐to‐structure earthquake processes. Regional simulations resolving ground motions at frequencies relevant to engineered systems are becoming computationally viable and provide a new capability to improve understanding of the geographical distribution and intensity of risk to buildings and critical infrastructure. As computational capabilities advance, it is essential to move beyond illustrative single rupture realizations for scenario earthquake events towards the development of a full suite of rupture realizations that appropriately characterize the range of risk to building systems. The work described in this article investigates the application of a suite of fault rupture realizations with the objective of assessing near‐fault, site‐specific seismic demand variability for building structures. A representative high‐performance regional‐scale computational model is utilized to execute ground motion and building response simulations based on 18 kinematic rupture realizations of an M7 strike‐slip scenario earthquake. The fault rupture models for the scenario earthquake are created by systematically perturbing the hypocenter location and stochastically generating rupture parameters (slip, rise time, rake angle) to represent a breadth of ground motion intensities resulting from the spatial and temporal variabilities of an earthquake rupture process. The resulting seismic demand variability for three‐story (short period) and forty‐story (long period) steel moment‐resisting frame buildings is characterized in terms of the median and distribution of peak inter‐story drift ratio for a range of near‐fault sites. The full suite of 18 fault rupture realizations and approximately 280,000 nonlinear dynamic building simulations indicate that the three‐story building undergoes higher median seismic demand and significantly greater variability of demand at a given site than the forty‐story building, which has important implications for the level of certainty in predicting building performance during an earthquake. The simulations performed provide deeper insight into the relationship between fault rupture parameterization and building response, which is essential information for developing a representative suite of rupture realizations for specific earthquake scenarios.

Shallow Fault Slip of the 2020 M 5.1 Sparta, North Carolina, Earthquake

Abstract The 2020 M 5.1 Sparta, North Carolina, earthquake is the largest in the eastern United States since the 2011 M 5.8 Mineral, Virginia, earthquake and produced a ∼2.5-km-long surface rupture, unusual for an event of this magnitude. A geological field study conducted soon after the event indicates oblique slip along a east-southeast-trending fault with a consistently observed thrust component. My analysis of regional seismic waveforms, Interferometric Synthetic Aperture Radar, and Global Positioning System survey data yields a compact shallow rupture extending from Earth’s surface down-dip to the southwest over a ∼3 km fault length. The inferred kinematic rupture is primarily toward the up-dip and eastward along-strike directions and has predominantly thrust motion in the west, transitioning to roughly equal thrust and left-lateral strike-slip motion in the east. No normal faulting component, as proposed in an earlier geophysical study, is necessary to explain the data. The prevalence of only dip-slip motions observed at Earth’s surface may demand slip partitioning between dip slip and lateral motions at depth.

Complex multi-fault rupture and triggering during the 2023 earthquake doublet in southeastern Türkiye

Two major earthquakes (MW 7.8 and MW 7.7) ruptured left-lateral strike-slip faults of the East Anatolian Fault Zone (EAFZ) on February 6, 2023, causing >59,000 fatalities and ~$119B in damage in southeastern Türkiye and northwestern Syria. Here we derived kinematic rupture models for the two events by inverting extensive seismic and geodetic observations using complex 5-6 segment fault models constrained by satellite observations and relocated aftershocks. The larger event nucleated on a splay fault, and then propagated bilaterally ~350 km along the main EAFZ strand. The rupture speed varied from 2.5-4.5 km/s, and peak slip was ~8.1 m. 9-h later, the second event ruptured ~160 km along the curved northern EAFZ strand, with early bilateral supershear rupture velocity (>4 km/s) followed by a slower rupture speed (~3 km/s). Coulomb Failure stress increase imparted by the first event indicates plausible triggering of the doublet aftershock, along with loading of neighboring faults.

Geological earthquake simulations generated by kinematic heterogeneous energy-based method: Self-arrested ruptures and asperity criterion

Abstract The lack of clarity regarding slip distribution within heterogeneous rupture areas has a significant impact on characterizing the seismic source and the role of heterogeneities in determining ground motion. One approach to understand the rupture process is through dynamic simulations, which require substantial computational resources, thereby limiting our comprehension of seismic rupture processes. Consequently, there is a need for methods that efficiently describe the spatial complexities of seismic rupture in a realistic manner. To address this, the statistics of real self-arrested ruptures that conform to the asperity criterion are investigated. This research demonstrates that power law distributions can describe the final slip statistics. Regarding the computational efficiency, a simple heterogeneous energy-based (HE-B) method is proposed. The HE-B method is characterized by the spatial correlation between the rupture parameters, such as the final slip or the rupture velocity, and the distribution of residual energy which determines the zones where the rupture could occur. In addition, the HE-B method defines the rupture area in those zones of the fault where the coupling function exceeds the energy required for rupture initiation. Therefore, the size of the earthquake is directly influenced by the distribution of coupling within faults. This method also leads to the successful reproduction of the statistical characteristics of final slip and generates slip rates that match the kinematic behavior of seismic sources. Notably, this kinematic rupture simulation produces seismic moment rates characterized by f − 1 {f}^{-1} and f − 2 {f}^{-2} spectra with a double corner frequency. Finally, it is observed that the maximum fracture energy value within the ruptured area is strongly correlated with both the magnitude and peak seismic moment rate. Thus, by employing this method, realistic rupture scenarios can be generated efficiently, enabling the study of spatial correlations among rupture parameters, ground motion simulations, and quantification of seismic hazard.

Ground-Motion Variability from Kinematic Rupture Models and the Implications for Nonergodic Probabilistic Seismic Hazard Analysis

Abstract The variability of earthquake ground motions has a strong control on probabilistic seismic hazard analysis (PSHA), particularly for the low frequencies of exceedance used for critical facilities. We use a crossed mixed-effects model to partition the variance components from simulated ground motions of Mw 7 earthquakes on the Salt Lake City segment of the Wasatch fault zone. Total variability of simulated ground motions is approximately equivalent to empirical models. The high contribution from rupture speed suggests an avenue to reducing variability through research on the causes and predictions of rupture speed on specific faults. Simulations show a strong spatial heterogeneity in the variability that manifests from directivity effects. We illustrate the impact of this spatial heterogeneity on hazard using a partially nonergodic PSHA framework. The results highlight the benefit of accounting for directivity effects in nonergodic PSHA, in which models that account for additional processes controlling ground motions are paired with reductions in the modeled ground-motion variability.

Rupture imaging of the 2021 Ms 6.4 Yangbi, China, earthquake: Implications for the diffuse deformation in the northern region of the Red River fault

In May 2021, a Ms 6.4 earthquake occurred in the Yangbi Country, Yunnan, China, located in the northern region of the Red River fault, resulting in three deaths. It is a typical foreshock-mainshock-aftershock sequence. However, the kinematic rupture process and the interplay between foreshocks, the mainshock, and aftershocks associated with the Yangbi event remain controversial. Here, we decipher the detailed rupture process associated with this moderate event by jointly inverting the teleseismic body waves, three-component regional waveform, near-field Global Positioning System offsets, and Interferometric Synthetic Aperture Radar data. Results show that the rupture expands as a narrow slip-pulse that propagates southeastward. This event is dominated by the dextral movements with minor normal components, cohere with the tectonic shear and dilation strain partitioning. The high slip is concentrated within the depth range of 5–13 km, spanning ∼12 km along strike. A significant shallow slip deficit is identified, perhaps related to the fault being immature. The foreshocks, coseismic slips, and aftershocks reveal a complementary pattern, together releasing the accumulated stresses on the fault. Their distribution areas and Coulomb stress changes suggest that the Yangbi seismic sequence follows the rupture cascade. The absence of large earthquakes, dispersed seismicity, and diffuse strain rate patterns indicate that strain accumulates over a wide area around the northern region of the Red River fault, leading to small-scale ruptures distributed over the area and a low possibility of M ≥ 6.5 events in the near future.

How Does Thermal Pressurization of Pore Fluids Affect 3D Strike-Slip Earthquake Dynamics and Ground Motions?

ABSTRACT Frictional heating during earthquake rupture raises the fault-zone fluid pressure, which affects dynamic rupture and seismic radiation. Here, we investigate two key parameters governing thermal pressurization of pore fluids – hydraulic diffusivity and shear-zone half-width – and their effects on earthquake rupture dynamics, kinematic source properties, and ground motions. We conduct 3D strike-slip dynamic rupture simulations assuming a rate-and-state dependent friction law with strong velocity weakening coupled to thermal-pressurization of pore fluids. Dynamic rupture evolution and ground shaking are densely evaluated across the fault and Earth’s surface to analyze the variations of rupture parameters (slip, peak slip rate, rupture speed, and rise time), correlations among rupture parameters, and variability of peak ground velocity. Our simulations reveal how variations in thermal-pressurization affect earthquake rupture properties. We find that the mean slip and rise time decrease with increasing hydraulic diffusivity, whereas mean rupture speed and peak slip-rate remain almost constant. Mean slip, peak slip-rate, and rupture speed decrease with increasing shear-zone half-width, whereas mean rise time increases. Shear-zone half-width distinctly affects the correlation between rupture parameters, especially for parameter pairs (slip, rupture speed), (peak slip-rate, rupture speed), and (rupture speed, rise time). Hydraulic diffusivity has negligible effects on these correlations. Variations in shear-zone half-width primarily impact rupture speed, which then may affect other rupture parameters. We find a negative correlation between slip and peak slip-rate, unlike simpler dynamic rupture models. Mean peak ground velocities decrease faster with increasing shear-zone half-width than with increasing hydraulic diffusivity, whereas ground-motion variability is similarly affected by both the parameters. Our results show that shear-zone half-width affects rupture dynamics, kinematic rupture properties, and ground shaking more strongly than hydraulic diffusivity. We interpret the importance of shear-zone half-width based on the characteristic time of diffusion. Our findings may inform pseudodynamic rupture generators and guide future studies on how to account for thermal-pressurization effects.

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.

Source process of two Mw 6.9 aftershocks of the 2015 Mw 8.3 Illapel earthquake

The rupture of the September 16, 2015, Mw 8.3 Illapel earthquake extended over 200 km length along strike, where the southern portion of the rupture area is controlled tectonically by the collision of the Juan Fernandez Ridge at ∼32.5°S. On November 11th, two large aftershocks occurred in less than an hour, at shallow depths and epicenters closely located. Both events occurred beyond, but nearby, the northern limit of the Illapel rupture. We inverted kinematic rupture models by joint inversion of strong-motion and teleseismic body waves datasets. The Akaike's Bayesian Information Criterion (ABIC) was used to estimate the relative weighting between datasets, as well as the weighting of spatial and temporal constraints. The rupture of the first event propagated updip from the hypocenter, and later in a bilateral mode, with large slip to the south. The slip solution yields a total seismic moment of 4.44 × 1019 N m (Mw 7.0), and peak-slip of 0.82 m. The epicenter of the second event relocates 15 km southwest with respect to the first one. The rupture of the second event propagated mainly southwards and updip to the trench, re-rupturing an area already broken by the first event. The estimated seismic moment is 3.11 × 1019 N m (Mw 6.9), with a maximum slip of 0.59 m. The source durations from their respective moment-rate functions are 35 s, in both models. The spatial slip distribution retrieved for the two events suggests that the upper portion of the megathrust slipped, a region that is usually thought to behave aseismically, controlled by velocity-strengthening friction. We also relocated the earthquake catalog using a double-difference algorithm. The spatial distribution of seismicity shows clusters that are analyzed in different groups, and the most remarkable feature being a strip running parallel - and close by - to the trench region with very low seismicity. The majority of regional moment tensor solutions are thrust faulting mechanisms, and given the centroid depths retrieved, these events are consistent with interplate seismicity.

Simultaneous Rupture Propagation Through Fault Bifurcation of the 2021 Mw7.4 Maduo Earthquake

AbstractFault geometric complexity plays a critical role in earthquake rupture dimension. Fault bifurcations are commonly observed in earthquake geology, yet, robust kinematic rupture processes on bifurcated fault branches are largely missing, limiting our understanding of rupture dynamics and seismic hazard. Here, we holistically study the fault geometry and bilateral rupture of the 2021 Mw7.4 Maduo, China earthquake, that shows clear fault bifurcation near its eastern terminal. We integrate space geodesy imaging, back‐projection of high‐frequency teleseismic array waveforms, multiple point source and finite fault inversions, and constrain in detail the rupture process, in particular, through its fault bifurcation. Our models reveal a stable rupture speed of ∼2.5 km/s throughout the entire rupture and a simultaneous rupture through fault branches bifurcated at 20°. The rupture on bifurcated faults radiated more high‐frequency waves, especially from the stopping phases. The stopping phase on the southern branch likely stopped the rupture on the northern branch.