Search

We considered various non‐uniformities such as branch faults, rotation of stress field directions, and changes in tectonic environments to simulate the dynamic rupture process of the 6 February 2023 Mw 7.8 Kahramanmaraş earthquake in SE Türkiye. We utilized near‐fault waveform data, GNSS static displacements, and surface rupture to constrain the dynamic model. The results indicate that the high initial stress accumulated in the Kahramanmaraş‐Çelikhan seismic gap leads to the successful triggering of the East Anatolian Fault (EAF) and the supershear rupture in the northeast segment. Due to the complexity of fault geometry, the rupture speed along the southeastern segment of the EAF varied repeatedly between supershear and subshear, which contributed to the unexpectedly strong ground motion. Furthermore, the triggering of the EAF reminds us to be aware of the risk of seismic gaps on major faults being triggered by secondary faults, which is crucial to prevent significant disasters. Plain Language Summary: On 6 February 2023, the south‐central Türkiye was hit by two major earthquakes with magnitudes of Mw 7.8 and Mw 7.6 respectively. Among them, the complex rupture process and unexpected ground motion of the Mw 7.8 event attracted the attention of seismologists. In this paper, the 3D dynamic rupture process of this mainshock is simulated based on complex multi‐fault system and heterogeneous initial stress. And the simulation results are in good agreement with the observations. Our results show that high initial stress is required for the EAF to be triggered. The supershear rupture occurred only in certain fault segments and is unable to sustain itself in a significant area on the fault due to the along‐strike variations in fault geometry and strength. More importantly, the dynamic model suggests that we must be alert to the risk of major fault being triggered by earthquakes on nearby small faults, especially when there are seismic gaps on the major fault. Key Points: The high initial stress accumulated in the seismic gap leads to the successful triggering of the East Anatolian FaultThe change of fault geometry in the southwest segment prevented the sustained supershear ruptureThe risk of earthquake nucleation on the secondary fault triggering the major fault rupture and the related disaster was highlighted [ABSTRACT FROM AUTHOR]

Abstract We considered various non‐uniformities such as branch faults, rotation of stress field directions, and changes in tectonic environments to simulate the dynamic rupture process of the 6 February 2023 Mw 7.8 Kahramanmaraş earthquake in SE Türkiye. We utilized near‐fault waveform data, GNSS static displacements, and surface rupture to constrain the dynamic model. The results indicate that the high initial stress accumulated in the Kahramanmaraş‐Çelikhan seismic gap leads to the successful triggering of the East Anatolian Fault (EAF) and the supershear rupture in the northeast segment. Due to the complexity of fault geometry, the rupture speed along the southeastern segment of the EAF varied repeatedly between supershear and subshear, which contributed to the unexpectedly strong ground motion. Furthermore, the triggering of the EAF reminds us to be aware of the risk of seismic gaps on major faults being triggered by secondary faults, which is crucial to prevent significant disasters.

Intersecting orthogonal strike‐slip faults with opposite senses of slip pose the question of what allows rupture to propagate through the junction and through both faults versus confining rupture to a single fault. I conduct dynamic rupture simulations on simplified orthogonal strike‐slip fault systems, to determine which conditions produce rupture on both component faults. In models with uniform initial tractions on both faults, slip on the first fault must reduce normal stress on the second fault for it to rupture. If the first fault ends at the cross fault, a stopping phase causes the cross fault to rupture. In models where I resolve a uniform regional stress field on the faults, only a narrow range of stress orientations allow multifault ruptures. These results will be helpful for evaluating hazard near orthogonal strike‐slip faults. Plain Language Summary: There are many examples around the world where two strike‐slip earthquake faults cross each other at nearly 90° angles. This is not remarkable when only one of the faults in a pair causes an earthquake, but it becomes notable when two or more crossing faults move at the same time. This raises the question of what causes the second fault to get involved, or not. To address this question, I use computer simulations of the physics of the earthquake process to test dozens of different fault configurations and earthquake starting points. I find that the location where the earthquake starts on the first fault controls whether the second fault is made stronger versus weaker, and therefore whether both faults can move together in one earthquake. These results can help us understand earthquake hazard around crossing faults. Key Points: Nucleation location effectively controls whether multifault rupture occurs on orthogonal strike‐slip fault systemsA stopping phase from rupture reaching the end of one fault is often required to initiate rupture on the cross faultOnly a narrow range of regional stress orientations allows both cross‐faults to rupture [ABSTRACT FROM AUTHOR]

Physics-based dynamic rupture models capture the variability of earthquake slip in space and time and can account for the structural complexity inherent to subduction zones. Here we link tsunami generation, propagation, and coastal inundation with 3D earthquake dynamic rupture (DR) models initialized using a 2D seismo-thermo-mechanical geodynamic (SC) model simulating both subduction dynamics and seismic cycles. We analyze a total of 15 subduction-initialized 3D dynamic rupture-tsunami scenarios in which the tsunami source arises from the time-dependent co-seismic seafloor displacements with flat bathymetry and inundation on a linearly sloping beach. We first vary the location of the hypocenter to generate 12 distinct unilateral and bilateral propagating earthquake scenarios. Large-scale fault topography leads to localized up- or downdip propagating supershear rupture depending on hypocentral depth. Albeit dynamic earthquakes differ (rupture speed, peak slip-rate, fault slip, bimaterial effects), the effects of hypocentral depth (25–40 km) on tsunami dynamics are negligible. Lateral hypocenter variations lead to small effects such as delayed wave arrival of up to 100 s and differences in tsunami amplitude of up to 0.4 m at the coast. We next analyse inundation on a coastline with complex topo-bathymetry which increases tsunami wave amplitudes up to ≈1.5 m compared to a linearly sloping beach. Motivated by structural heterogeneity in subduction zones, we analyse a scenario with increased Poisson's ratio of ν = 0.3 which results in close to double the amount of shallow fault slip, ≈1.5 m higher vertical seafloor displacement, and a difference of up to ≈1.5 m in coastal tsunami amplitudes. Lastly, we model a dynamic rupture “tsunami earthquake” with low rupture velocity and low peak slip rates but twice as high tsunami potential energy. We triple fracture energy which again doubles the amount of shallow fault slip, but also causes a 2 m higher vertical seafloor uplift and the highest coastal tsunami amplitude (≈7.5 m) and inundation area compared to all other scenarios. Our mechanically consistent analysis for a generic megathrust setting can provide building blocks toward using physics-based dynamic rupture modeling in Probabilistic Tsunami Hazard Analysis.

Abstract Elastic dislocation models require large near‐trench slip to explain large tsunamigenesis, which is probably best exemplified in the 2011 M9 Tohoku earthquake. However, it is puzzling that the largest Tohoku tsunami heights occurred about 100 km north of the largest slip zone, where bathymetric surveys indicate no large slip at the trench or submarine landslides. Here we show that coseismic yielding of plentiful sediments in the northern Japan Trench margin can induce large inelastic uplift landward from the trench and diminish slip near the trench. The scarcity of sediments in the south leads to nearly elastic response with large slip at the trench and mostly horizontal seafloor displacement. Thus, the variations of sediments along the Japan Trench and sediment yielding can explain the puzzling variations of tsunamigenesis and near‐trench slip in this earthquake. Inelastic wedge deformation can be an important mechanism of tsunamigenesis in accretionary and other sediment‐filled plate margins.

Fracture mechanics theory and seismological observations suggest that slip-rate is constantly changing during earthquake rupture, including dramatic acceleration from static conditions to high velocity sliding followed by deceleration and arrest. This slip history is partly determined by a complex frictional evolution, including overcoming peak friction, rapid weakening, and re-strengthening (or healing). Recent experimental developments have allowed friction evolution measurements under realistic slip histories reaching high co-seismic slip-rates of meters per second. Theoretical work has focused on describing the observed steady-state weakening at these high-velocities, but the transient behavior has only been fit by direct parameterizations without state variable dependence, needed to simulate arbitrary slip-histories. Commonly used forms of rate-state friction (RSF) are based on low-velocity, step-change experiments and have been shown to not fit the entire frictional evolution using a single set of realistic parameters. Their logarithmic form precludes zero fault slip-rate, assuming it is never truly static, thus does not capture slip initiation phenomena that might contribute to nucleation behavior. Inverting high slip-rate and friction data from different types of experiments, we show that RSF can work by using parameter ranges far from typical low-velocity values. In comparison, we introduce “bristle-state” friction (BSF) models, developed by control-system engineers to predict the transient frictional evolution during arbitrary stressing, especially reversals through static conditions. Although BSF models were also designed for low-velocities, we show that their form provides advantages for fitting frictional evolution measurements under high slip-rate, long-displacement, non-trivial slip histories, especially during the initial strengthening stage.

One crucial yet unanswered question about the 2011 M W 9.1 Tohoku-Oki earthquake and tsunami is what generated the largest tsunami (up to 40 m) along the Sanriku coast north of 39°N without large slip near the trench. A minimalist dynamic rupture model with wedge plasticity is presented to address this issue. The model incorporates the important variation of sediment thickness along the Japan Trench into the Japan Integrated Velocity Structure Model (JIVSM). By revising a heterogeneous stress drop model, the dynamic rupture model with a standard rate-and-state friction law can explain the GPS, tsunami, and differential bathymetry data (within data uncertainties) with minimum tuning. The rupture is driven by a large patch of stress drop up to ∼10 MPa near the hypocenter with significantly smaller stress drop (< 3 MPa) in the upper ∼10 km. The largest shallow slip reaches 75.67 m close to the trench north of hypocenter, which is caused by the large fault width, free surface, shallowly dipping fault geometry, and northwardly increasing sediment thickness, dominated by elastic off-fault response. North of large shallow slip zone, however, inelastic deformation of thick wedge sediments significantly controls the rupture propagation along trench, giving rise to slow rupture velocity (∼850 m/s), diminishing shallow slip, and efficient seafloor uplift. The short-wavelength inelastic uplift produces impulsive tsunami consistent with the observations off the Sanriku coast in terms of timing, amplitude, and pulse width. Wedge plasticity and variation of sediment thickness along the Japan Trench thus provides a self-consistent interpretation to the along-strike variation of near-trench slip and anomalous tsunami generation in the northern Japan Trench in this earthquake. • A minimalist dynamic rupture model reveals a more complete picture of the 2011 Tohoku-Oki rupture process. • Inelastic deformation of thick sediments can explain the large tsunamigenesis north of 39°N with diminishing shallow slip. • A slow rupture velocity ∼ 850 m/s in the northern Japan Trench explains the timing of the impulsive tsunami. • Sediment thickness variation along the Japan Trench plays an important role in the near-trench slip and tsunamigenesis. [ABSTRACT FROM AUTHOR]

Elastic dislocation models require large near‐trench slip to explain large tsunamigenesis, which is probably best exemplified in the 2011 M9 Tohoku earthquake. However, it is puzzling that the largest Tohoku tsunami heights occurred about 100 km north of the largest slip zone, where bathymetric surveys indicate no large slip at the trench or submarine landslides. Here we show that coseismic yielding of plentiful sediments in the northern Japan Trench margin can induce large inelastic uplift landward from the trench and diminish slip near the trench. The scarcity of sediments in the south leads to nearly elastic response with large slip at the trench and mostly horizontal seafloor displacement. Thus, the variations of sediments along the Japan Trench and sediment yielding can explain the puzzling variations of tsunamigenesis and near‐trench slip in this earthquake. Inelastic wedge deformation can be an important mechanism of tsunamigenesis in accretionary and other sediment‐filled plate margins. Plain Language Summary: The general consensus about the devastating 2011 Tohoku tsunami is that it was due to large slip at the trench. This can be somewhat misleading because the largest tsunami heights occurred about 100 km north of where the largest trench slip occurred. Using elastic dislocation theory, inversions of tsunami data require large trench slip ~30 m in the north (north of 39°N). However, the bathymetry data before and after the earthquake suggest no large trench slip or submarine landslides in the north. Here we present a mechanism that involves the yielding of sediments in the overriding wedge. Our inelastic wedge deformation model can explain the puzzling observations of large tsunami heights along the Sanriku coast in the north with no or small trench slip and small tsunami in the south with large trench slip. The amount of sediments in a subduction margin can be very important in evaluating tsunami hazard. Key Points: Inelastic wedge deformation can induce large seafloor uplift efficiently landward from trench and diminish near‐trench slip on the faultAlong‐arc variation of sediment thickness in the Japan Trench margin can lead to important along‐arc variations of tsunamigenesisThe large tsunami heights along the Sanriku coast in the 2011 Tohoku earthquake can be due to inelastic wedge deformation [ABSTRACT FROM AUTHOR]

Orientations of natural fault systems are subject to large variations. They often contradict classical Coulomb failure theory as they are misoriented relative to the regional Andersonian stress field. This is ascribed to local effects of structural or stress heterogeneities and reorientations of structures or stresses on the long term. To better understand the relation between fault orientation and regional stresses, we simulate spontaneous fault growth and its effect on the stress field. Our approach incorporates earthquake rupture dynamics, viscoelastoplastic brittle deformation and a rate‐ and state‐dependent friction formulation in a continuum mechanics framework. We investigate how strike‐slip faults orient according to local and far‐field stresses during their growth. We identify two modes of fault growth, seismic and aseismic, distinguished by different fault angles and slip velocities. Seismic fault growth causes a significant elevation of dynamic stresses and friction values ahead of the propagating fault tip. These elevated quantities result in a greater strike angle relative to the maximum principal regional stress than that of a fault segment formed aseismically. When compared to the near‐tip time‐dependent stress field the fault orientations produced by both growth modes follow the classical failure theory. We demonstrate how the two types of fault growth may be distinguished in natural faults by comparing their angles relative to the original regional maximum principal stress. A stress field analysis of the Landers‐Kickapoo fault suggests that an angle greater than ∼25° between two faults indicates seismic fault growth. Key Points: Numerical model, combining viscoelastoplasticity, rate and state friction, and elastodynamics, simulates the growth of strike‐slip faultsTwo distinct fault growth modes, seismic and aseismic, can be distinguished by their fault orientation relative to regional stressesThe model explains altered stress orientations during the genesis of the Landers‐Mojave fault system [ABSTRACT FROM AUTHOR]

Geological faults comprise large-scale segmentation and small-scale roughness. These multi-scale geometrical complexities determine the dynamics of the earthquake rupture process, and therefore affect the radiated seismic wavefield. In this study, we examine how different parameterizations of fault roughness lead to variability in the rupture evolution and the resulting near-fault ground motions. Rupture incoherence naturally induced by fault roughness generates high-frequency radiation that follows an ω decay in displacement amplitude spectra. Because dynamic rupture simulations are computationally expensive, we test several kinematic source approximations designed to emulate the observed dynamic behavior. When simplifying the rough-fault geometry, we find that perturbations in local moment tensor orientation are important, while perturbations in local source location are not. Thus, a planar fault can be assumed if the local strike, dip, and rake are maintained. We observe that dynamic rake angle variations are anti-correlated with the local dip angles. Testing two parameterizations of dynamically consistent Yoffe-type source-time function, we show that the seismic wavefield of the approximated kinematic ruptures well reproduces the radiated seismic waves of the complete dynamic source process. This finding opens a new avenue for an improved pseudo-dynamic source characterization that captures the effects of fault roughness on earthquake rupture evolution. By including also the correlations between kinematic source parameters, we outline a new pseudo-dynamic rupture modeling approach for broadband ground-motion simulation. [ABSTRACT FROM AUTHOR]

Accurate predictions of the intensity and variability of ground motions are essential in simulation-based seismic hazard assessment. Advanced simulation-based ground motion prediction methods have been proposed to complement the empirical approach, which suffers from the lack of observed ground motion data, especially in the near-source region for large events. It is important to quantify the variability of the earthquake rupture process for future events and to produce a number of rupture scenario models to capture the variability in simulation-based ground motion predictions. In this study, we improved the previously developed stochastic earthquake rupture modeling method by applying the nonparametric co-regionalization, which was proposed in geostatistics, to the correlation models estimated from dynamically derived earthquake rupture models. The nonparametric approach adopted in this study is computationally efficient and, therefore, enables us to simulate numerous rupture scenarios, including large events ( M > 7.0). It also gives us an opportunity to check the shape of true input correlation models in stochastic modeling after being deformed for permissibility. We expect that this type of modeling will improve our ability to simulate a wide range of rupture scenario models and thereby predict ground motions and perform seismic hazard assessment more accurately. [ABSTRACT FROM AUTHOR]

Dynamic propagation of shear ruptures on a frictional interface in an elastic solid is a useful idealization of natural earthquakes. The conditions relating discontinuities in particle velocities across fault zones and tractions acting on the fault are often expressed as nonlinear friction laws. The corresponding initial boundary value problems are both numerically and computationally challenging. In addition, seismic waves generated by earthquake ruptures must be propagated for many wavelengths away from the fault. Therefore, reliable and efficient numerical simulations require both provably stable and high order accurate numerical methods. We present a high order accurate finite difference method for: a) enforcing nonlinear friction laws, in a consistent and provably stable manner, suitable for efficient explicit time integration; b) dynamic propagation of earthquake ruptures along nonplanar faults; and c) accurate propagation of seismic waves in heterogeneous media with free surface topography. We solve the first order form of the 3D elastic wave equation on a boundary-conforming curvilinear mesh, in terms of particle velocities and stresses that are collocated in space and time, using summation-by-parts (SBP) finite difference operators in space. Boundary and interface conditions are imposed weakly using penalties. By deriving semi-discrete energy estimates analogous to the continuous energy estimates we prove numerical stability. The finite difference stencils used in this paper are sixth order accurate in the interior and third order accurate close to the boundaries. However, the method is applicable to any spatial operator with a diagonal norm satisfying the SBP property. Time stepping is performed with a 4th order accurate explicit low storage Runge–Kutta scheme, thus yielding a globally fourth order accurate method in both space and time. We show numerical simulations on band limited self-similar fractal faults revealing the complexity of rupture dynamics on rough faults. [ABSTRACT FROM AUTHOR]

In an attempt to explain the large shallow slip that occurred near the trench during the 2011 Tohoku-Oki earthquake, numerical simulations of earthquake dynamic rupture were carried out using a fault model with a subduction interface containing a bump-shaped asperity, which might result from subduction of an old submarine volcano or seamount. It was assumed that during the interseismic period, slip only occurs outside the bump area and that stress accumulates inside the bump, creating a seismogenic asperity. We roughly evaluated the amount of slip outside the bump during the interseismic period, assuming a constant long-term subduction rate. Then we could estimate the accumulated stress inside the bump. We constructed the initial stress distribution based on the stress change caused by the slip-deficit distribution. A constitutive relation was constructed based on a slip-weakening friction law and was used to compute spontaneous ruptures. The results indicate that a large slip can occur between the trench and the bump, even though a very small amount of stress is accumulated there before the rupture. This is due to an interaction between the free surface and the fault that causes slip overshoot. On the region of the fault below the bump, such overshoot cannot occur because the fault is pinned by the deeper un-slipped zone. However, on the shallower side, the edge of the fault becomes free when the rupture approaches the free surface. In this region, such a large slip can occur without releasing a large amount of stress. [ABSTRACT FROM AUTHOR]

Abstract: Supershear rupture propagation has been inferred from seismic observations for natural faults and observed in laboratory experiments. We study the effect of the free surface on the transition of earthquake rupture from subshear to supershear speeds using simulations of spontaneous dynamic rupture on vertical strike-slip faults. We find that locally supershear rupture near the free surface can occur due to (i) the generalized Burridge–Andrews mechanism, that is, a supershear loading field between P- and SV-wave arrivals generated by the main rupture front at depths, and (ii) the phase conversion of SV to P-diffracted waves at the free surface. Weaker supershear slip due to the generalized Burridge–Andrews mechanism is caused by the low strength at shallow portions of the fault relative to deeper ones. Dominant supershear rupture is supported by the additional supershear loading field produced by phase conversion. Locally supershear propagation at the free surface occurs regardless of the level of prestress and can cause transition to supershear propagation over the entire seismogenic depth. Such global supershear transition, which depends on prestress, can occur under prestress levels lower than the theoretical estimates for models with no free surface. Although the effectiveness of supershear transition due to the free surface can be diminished by several potentially important factors, it may play an important role on natural faults, at least in those strike-slip earthquakes that accumulate significant surface slip. [ABSTRACT FROM AUTHOR]

The 2016 Kaikoura (New Zealand) earthquake is characterized as one of the most complex multifault rupture events ever observed. We perform dynamic rupture simulations to evaluate to what extent relatively simple forward models accounting for realistic fault geometry can explain the characteristics of coseismic observations. Without fine parameter tuning, our model reproduces many observed features including the multifault rupture, overall slip distribution, and the locations of the maximum slip and rupture arrest. In particular, our model shows spontaneous arrest of dynamic rupture at the both ends of the ruptured fault system due to smaller prestress levels expected from a regional tectonic stress field. Both the simulated and the observationally inferred source time functions show similar double peaks with a larger second peak. The results illuminate the importance of the 3‐D fault geometry in understanding the dynamics of complex multifault rupture. Plain Language Summary: The 2016 Kaikoura earthquake in the northern South Island of New Zealand was one of the most complex faulting events ever observed. Previous studies identified surface ruptures along at least a dozen major faults extending over 150 km. Here we use computer simulations to investigate how the complex three‐dimensional geometry of faults plays a role in the rupture propagation and termination during the Kaikoura earthquake. We find that our model can explain a number of observations associated with the earthquake. In particular, the model suggests that the termination of propagating rupture at the ends of faults was caused by the unfavorable orientations of these faults with respect to regional tectonic stresses. The results illuminate the importance of three‐dimensional fault geometry in understanding the dynamics of multifault earthquakes. Key Points: Dynamic model considering realistic fault geometry and regional stress field reproduces multifault rupture during the Kaikoura earthquakeModel shows spontaneous rupture arrest on the western Humps and Needles faults, which are unfavorably oriented in a regional stress fieldDynamic triggering of fault slip may have played an important role in transferring the rupture from the southern to northern faults [ABSTRACT FROM AUTHOR]