Earthquake Cycle Simulations Research Articles

Paleoseismology of the Northern Kongur Shan Extensional System, NE Pamir: Implications for Potential Irregular Earthquake Recurrence

AbstractThe intricate and changing stress conditions within complex fault networks pose challenges in understanding earthquake recurrence and seismic hazards. The Kongur Shan Extensional System (KSES) in the northeastern Pamir, characterized by complex fault geometries and potentially variable surface loads in its surroundings, offers an ideal research area. Here we investigate three paleoseismic sites in the northern KSES, including lacustrine seismites in the Muji Basin, secondary fault scarps of the northern Kongur Shan Fault (KSF), and an exposure of the eastern Muji Fault. The seismites, as a regional record, indicate two Mw 6–7.3 paleoearthquakes occurring 720–680 and 1030–940 cal yr BP, with an interval of 230–330 years. The other two on‐fault sites reveal paleoearthquakes with compatible magnitudes but much longer average time intervals (ATI). Secondary fault scarps of the northern KSF indicate four Mw 6.9–7.2 paleoearthquakes since 4.8 ± 0.8 ka, with an ATI of 1,000–1,870 years. The fault exposure of the eastern Muji Fault indicates two Mw 6.8–7.3 paleoearthquakes since 2.7 ± 0.3 ka, with an ATI of 1,200–3,000 years. Using its previously constrained long‐term slip rate of ∼6.3 mm/yr and a simple Monte Carlo simulation of earthquake cycles, the observed ATI of the eastern Muji Fault suggests a “clustered” earthquake recurrence behavior. Such potential irregular earthquake recurrence is likely due to the low maturity and fault interaction in the northern KSES, and climate‐related changes in surface loads of paleolakes and glaciers.

The role of heterogeneous stress in earthquake cycle models of the Hikurangi-Kermadec subduction zone

Summary Seismic and tsunami hazard modelling and preparedness are challenged by uncertainties in the earthquake source process. Important parameters such as the recurrence interval of earthquakes of a given magnitude at a particular location, the probability of multi-fault rupture, earthquake clustering, rupture directivity and slip distribution are often poorly constrained. Physics-based earthquake simulators, such as RSQSim, offer a means of probing uncertainties in these parameters by generating long-term catalogues of earthquake ruptures on a system of known faults. The fault initial stress state in these simulations is typically prescribed as a single uniform value, which can promote characteristic earthquake behaviours and reduce variability in modelled events. Here, we test the role of spatial heterogeneity in the distribution of the initial stresses and frictional properties on earthquake cycle simulations. We focus on the Hikurangi-Kermadec subduction zone, which may produce Mw > 9.0 earthquakes and likely poses a major hazard and risk to Aotearoa New Zealand. We explore RSQSim simulations of Hikurangi-Kermadec subduction earthquake cycles in which we vary the rate and state coefficients (a and b). The results are compared with the magnitude-frequency distribution (MFD) of the instrumental earthquake catalogue and with empirical slip scaling laws from global earthquakes. Our results suggest stress heterogeneity produces more realistic and less characteristic synthetic catalogues, making them particularly well suited for hazard and risk assessment. We further find that the initial stress effects are dominated by the initial effective normal stresses, since the normal stresses evolve more slowly than the shear stresses. A heterogeneous stress model with a constant pore-fluid pressure ratio and a constant state coefficient (b) of 0.003 produces the best fit to MFDs and empirical scaling laws, while the model with variable frictional properties produces the best fit to earthquake depth distribution and empirical scaling laws. This model is our preferred initial stress state and frictional property settings for earthquake modelling of the Hikurangi-Kermadec subduction interface. Introducing heterogeneity of other parameters within RSQSim (e.g. friction coefficient, reference slip rate, characteristic distance, initial state variable, etc) could further improve the applicability of the synthetic earthquake catalogues to seismic hazard problems and form the focus of future research.

Toward quantitative characterization of simulated earthquake-cycle complexities

Earthquake cycle simulations based on the rate-and-state friction formulation are evolutions of nonlinear dynamical systems (NDS). The term “cycle” implies an overall stable structure that is a phase-space attractor naturally traced out by trajectories of NDS as it evolves. Quantitatively characterizing these attractors should be a basis for measuring complexities of the simulated earthquake cycles, i.e. to determine if and how regular or chaotic they are. I first revisit the textbook-standard quasi-dynamic spring-slider system from an NDS perspective, explicitly showing the attractors, their relationship with the parameters of the NDS, and how they can be characterized taken advantage of their low-dimensionality while aiming to extend the analysis to high-dimensionality. I evaluate two approaches, computing the Lyapunov exponents (LEs) and measuring correlation dimensions, with the simple spring-slider and earthquake-cycle examples whose phase-space attractors can be visually verified. I conclude LEs are too inconvenient and computationally expensive to use whereas measuring correlation dimensions is an easy and effective approach even with highly non-uniform time sampling present in all simulations. For earthquake-cycle simulations, an attractor reconstruction is performed based on Taken’s theorem to corroborate my correlation-dimension results. The current method is limited in its ability to detect chaos in a dichotomous manner, which illuminates the direction for future study. An improving ability to quantitatively characterize earthquake-cycle simulations as an overall stable structure offers new opportunities to understand exotic seismic observations such as slow-slip events and enables more informative comparison with real data, particularly from paleoseismology, which could have far-reaching implications in earthquake forecasting.

The effects of precursory velocity changes on earthquake nucleation and stress evolution in dynamic earthquake cycle simulations

Seismic velocity changes in earthquake cycles have been observed over a wide range of timescales and may be a good indicator of the onset of future earthquakes. Understanding the effects of precursory velocity changes right before seismic and slow-slip events could potentially elucidate the onset and timing of fault failure. We use numerical models to simulate fully dynamic earthquake cycles in 2D strike-slip fault systems with antiplane geometry, surrounded by a narrow fault-parallel damage zone. By imposing S-wave velocity changes inside fault damage zones, we investigate the effects of these precursors on multiple stages of the seismic cycle, including nucleation, coseismic, postseismic, and interseismic stages. Our modeling results show a wide spectrum of fault slip behaviors including fast earthquakes, slow-slip events, and variable creep. One primary effect of the imposed velocity precursor is on the earthquake nucleation phase, and earlier onset of precursors causes earthquakes to nucleate sooner with a smaller nucleation size that is not predicted by theoretical equations. Furthermore, such precursors affect the nucleation of dynamic earthquakes and slow-slip events. Our results highlight the importance of short- and long-term monitoring of fault zone structures for better assessment of regional seismic hazard.

A proxy implementation of thermal pressurization for earthquake cycle modelling on rate-and-state faults

SUMMARY The reduction of effective normal stress during earthquake slip due to thermal pressurization of fault zone pore fluids is a significant fault weakening mechanism. Explicit incorporation of this process into frictional fault models involves solving the diffusion equations for fluid pressure and temperature outside the fault at each time step, which significantly increases the computational complexity. Here, we propose a proxy for thermal pressurization implemented through a modification of the rate-and-state friction law. This approach is designed to emulate the fault weakening and the relationship between breakdown energy and slip resulting from thermal pressurization and is appropriate for fully dynamic simulations of multiple earthquake cycles. It preserves the computational efficiency of conventional rate-and-state friction models, which in turn can enable systematic studies to advance our understanding of the effects of fault weakening on earthquake mechanics. In 2.5-D simulations of pulse-like ruptures on faults with finite seismogenic width, based on our thermal pressurization proxy, we find that the spatial distribution of slip velocity near the rupture front is consistent with the conventional square-root singularity, despite continued slip-weakening within the pulse, once the rupture has propagated a distance larger than the rupture width. An unconventional singularity appears only at shorter rupture distances. We further derive and verify numerically a theoretical estimate of the breakdown energy dissipated by our implementation of thermal pressurization. These results support the use of fracture mechanics theory to understand the propagation and arrest of very large earthquakes.

Recurrence intervals for M > 7 Miyagi-ken-Oki earthquakes during an M ~ 9 earthquake cycle

The 2011 Tohoku-Oki great earthquake increased the difficulty of evaluating the long-term probability of seismic activity along the Japan Trench because of the unknown impact of the unprecedentedly large slip. In this study, the long-term activity of “Miyagi-ken-Oki earthquakes”, an M > 7 earthquake sequence off Miyagi Prefecture, located at the edge of the source area of the Tohoku-Oki earthquake was simulated. We conducted numerical simulations of earthquake generation cycles based on the rate- and state-dependent friction law representing the stress accumulation and release process on the plate interface. We also validated the results based on analyses of observational data, including time intervals and afterslip distributions for the previous Miyagi-ken-Oki earthquakes. The simulation results were then compared with repeating-earthquake-derived interplate slip observations over 30 years. The results showed that the spatial and temporal characteristics of aseismic slips on the plate interface near the M > 7 Miyagi-ken-Oki source were qualitatively reproduced. The time interval between the M ~ 9 earthquake and the first M > 7 earthquake is shorter than the average recurrence interval of M > 7 earthquakes during the latter stage of each M ~ 9 earthquake cycle. In contrast, the interval between the first and the second M > 7 earthquakes is the longest in each M ~ 9 earthquake cycle. The time intervals of the M > 7 earthquakes fluctuated in the early stage compared to those in the latter stage of the M ~ 9 earthquake cycle. These characteristics were associated with the extent of the locked and afterslip areas in and around the source. Hence, monitoring the spatio-temporal distribution of the slip rate in and around the source area during the preparation process of earthquakes occurring in the downdip area off Miyagi Prefecture is very important to assess whether the next M > 7 earthquake is approaching. Furthermore, earthquake cycle simulations combined with earthquake and slow slip monitoring can provide meaningful insights for long-term assessments of great interplate earthquakes.

Numerical Simulation of Episodic Aseismic Slip Events as Incomplete Nucleation of Seismic Slip Due to Heterogeneous Stress Distribution

ABSTRACT Shear stress concentration at the deeper edge of a locked fault affects detachment of the fault, such as upward propagation of aseismic sliding, episodic aseismic slip events, and partial seismic rupture. Numerical simulations of earthquake cycles on a strike-slip fault were conducted using a rate- and state-dependent friction law to investigate the occurrence conditions of episodic aseismic slip events within a fault having uniform velocity-weakening friction. When the velocity-weakening zone is much wider than the critical nucleation zone size, a rupture that seismically or aseismically breaks a part of the velocity-weakening zone occurs during the interseismic period between large earthquakes. The partial seismic rupture results in a small earthquake, and the partial slow rupture results in an episodic aseismic slip event. The seismic or aseismic rupture is arrested in a low-shear-stress area, which is caused by the preceding large earthquake. The episodic aseismic slip events may be regarded as incomplete nucleation of an earthquake, because the rupture is arrested before acceleration to seismic slip, and this process may explain episodic aseismic slip events at seismogenic depths. The width of the area of preseismic sliding immediately before a simulated large earthquake is similar to that of episodic aseismic slip.

Modeling earthquake cycles and wear on rough faults with the mortar finite element method

SUMMARYThis paper presents a mortar-based finite element formulation for modelling earthquake cycles and wear on rough faults governed by rate and state friction. The method allows large sliding on the fault and accounts for all stages in the earthquake cycle, using a variable time step size with a transition between quasi-static and fully dynamic time discretizations. Wear laws with linear and power law forms are discretized and implemented into the mortar method, as well as a minimum level of normal traction constraint to treat fault opening. We examine the effect of wear laws on the slip behaviour and near-fault stresses during simulations of earthquake cycles on rough faults. The simulations demonstrate that the implementation of wear allows more realistic modelling of the earthquake cycle without the development of unrealistically large stresses and with less reduction of earthquake magnitude with total fault slip. Moreover, the method enables to study the effects of roughness and fault slip on the gouge zone thickness.

Dynamic Simulations of Earthquake Cycles in Strike-Slip Fault Zones

Dynamic Simulations of Earthquake Cycles in Strike-Slip Fault Zones

Fully Dynamic Earthquake Cycle Simulations on a Nonplanar Fault Using the Spectral Boundary Integral Element Method (sBIEM)

ABSTRACT One of the most suitable methods for modeling fully dynamic earthquake cycle simulations is the spectral boundary integral element method (sBIEM), which takes advantage of the fast Fourier transform (FFT) to make a complex numerical dynamic rupture tractable. However, this method has the serious drawback of requiring a flat fault geometry due to the FFT approach. Here, we present an analytical formulation that extends the sBIEM to a mildly nonplanar fault. We start from a regularized boundary element method and apply a small-slope approximation of the fault geometry. Making this assumption, it is possible to show that the main effect of nonplanar fault geometry is to change the normal traction along the fault, which is controlled by the local curvature along the fault. We then convert this space–time boundary integral equation of the normal traction into a spectral-time formulation and incorporate this change in normal traction into the existing sBIEM methodology. This approach allows us to model fully dynamic seismic cycle simulations on nonplanar faults in a particularly efficient way. We then test this method against a regular BIEM for both rough-fault and seamount-fault geometries and demonstrate that this sBIEM maintains the scaling between the fault geometry and slip distribution.

Propagation of a precursory detachment front along a seismogenic plate interface in a rate–state friction model of earthquake cycles

SUMMARYA numerical simulation of earthquake cycles at the subduction zone of a plate interface was conducted, using a rate- and state-dependent friction law, to examine aseismic sliding processes propagating into a locked plate interface. In the model, a reverse fault is assumed in a 2-D uniform elastic half-space, and relative plate motion is imposed with a constant velocity. Simulated earthquakes occur repeatedly at a shallower seismogenic plate interface with a velocity-weakening frictional property, while stable sliding occurs in the deeper part, in which a velocity-strengthening frictional property is assumed. During interseismic periods, deep stable sliding causes shear stress to concentrate at the deeper edge of the locked plate interface, and a partial drop in stress occurs, resulting in plate detachment. The resulting detachment front propagates upwards along the seismogenic plate interface until an earthquake occurs, causing aseismic sliding with a sliding velocity significantly lower than the imposed relative plate velocity. The propagation velocity of the detachment front is almost constant in each case, and it is proportional to the relative plate velocity and inversely proportional to the effective normal stress. Episodic events of increased slip velocity occur in the latter half of an interseismic period when the characteristic slip distance is small. Updip propagation of episodic slip is arrested by a low stress barrier, and episodic slips backpropagate downdip. During the final few years of the simulation cycle, the average sliding velocity is approximately inversely proportional to the time to occurrence for a large interplate earthquake.

Pulsed carbon export from mountains by earthquake-triggered landslides explored in a reduced-complexity model

Abstract. In mountain ranges, earthquakes can trigger widespread landsliding and mobilize large amounts of organic carbon by eroding soil and vegetation from hillslopes. Following a major earthquake, the landslide-mobilized organic carbon can be exported from river catchments by physical sediment transport processes or stored within the landscape where it may be degraded by heterotrophic respiration. The competition between these physical and biogeochemical processes governs a net transfer of carbon between the atmosphere and sedimentary organic matter, yet their relative importance following a large landslide-triggering earthquake remains poorly constrained. Here, we propose a model framework to quantify the post-seismic redistribution of soil-derived organic carbon. The approach combines predictions based on empirical observations of co-seismic sediment mobilization with a description of the physical and biogeochemical processes involved after an earthquake. Earthquake-triggered landslide populations are generated by randomly sampling a landslide area distribution, a proportion of which is initially connected to the fluvial network. Initially disconnected landslide deposits are transported downslope and connected to rivers at a constant velocity in the post-seismic period. Disconnected landslide deposits lose organic carbon by heterotrophic oxidation, while connected deposits lose organic carbon synchronously by both oxidation and river export. The modeling approach is numerically efficient and allows us to explore a large range of parameter values that exert a control on the fate of organic carbon in the upland erosional system. We explore the role of the climatic context (in terms of mean annual runoff and runoff variability) and rates of organic matter degradation using single pool and multi-pool models. Our results highlight the fact that the redistribution of organic carbon is strongly controlled by the annual runoff and the extent of landslide connection, but less so by the choice of organic matter degradation model. In the context of mountain ranges typical of the southwestern Pacific region, we find that model configurations allow more than 90 % of the landslide-mobilized carbon to be exported from mountain catchments. A simulation of earthquake cycles suggests efficient transfer of organic carbon out of a mountain range during the first decade of the post-seismic period. Pulsed erosion of organic matter by earthquake-triggered landslides is therefore an effective process to promote carbon sequestration in sedimentary deposits over thousands of years.

Bayesian Parameter Estimation for Space and Time Interacting Earthquake Rupture Model Using Historical and Physics-Based Simulated Earthquake Catalogs

ABSTRACTThis article introduces a framework to supplement short historical catalogs with synthetic catalogs and determine large earthquakes’ recurrence. For this assessment, we developed a parameter estimation technique for a probabilistic earthquake occurrence model that captures time and space interactions between large mainshocks. The technique is based on a two-step Bayesian update that uses a synthetic catalog from physics-based simulations for initial parameter estimation and then the historical catalog for further calibration, fully characterizing parameter uncertainty. The article also provides a formulation to combine multiple synthetic catalogs according to their likelihood of representing empirical earthquake stress drops and Global Positioning System-inferred interseismic coupling. We applied this technique to analyze large-magnitude earthquakes’ recurrence along 650 km of the subduction fault’s interface located offshore Lima, Peru. We built nine 2000 yr long synthetic catalogs using quasi-dynamic earthquake cycle simulations based on the rate-and-state friction law to supplement the 450 yr long historical catalog. When the synthetic catalogs are combined with the historical catalog without propagating their uncertainty, we found average relative reductions larger than 90% in the recurrence parameters’ uncertainty. When we propagated the physics-based simulations’ uncertainty to the posterior, the reductions in uncertainty decreased to 60%–70%. In two Bayesian assessments, we then show that using synthetic catalogs results in higher parameter uncertainty reductions than using only the historical catalog (69% vs. 60% and 83% vs. 80%), demonstrating that synthetic catalogs can be effectively combined with historical data, especially in tectonic regions with short historical catalogs. Finally, we show the implications of these results for time-dependent seismic hazard.

Fault‐Zone Damage Promotes Pulse‐Like Rupture and Back‐Propagating Fronts via Quasi‐Static Effects

AbstractDamage zones are ubiquitous components of faults that may affect earthquake rupture. Simulations show that pulse‐like rupture can be induced by the dynamic effect of waves reflected by sharp fault zone boundaries. Here we show that pulses can appear in a highly damaged fault zone even in the absence of reflected waves. We use quasi‐static scaling arguments and quasi‐dynamic earthquake cycle simulations to show that a crack turns into a pulse after the rupture has grown larger than the fault zone thickness. Accompanying the pulses, we find complex rupture patterns involving back‐propagating fronts that emerge from the primary rupture front. Our model provides a mechanism for back‐propagating fronts recently observed during large earthquakes. Moreover, we find that slow‐slip simulations in a highly compliant fault zone also produce back‐propagating fronts, suggesting a new mechanism for the rapid tremor reversals observed in Cascadia and Japan.

Dynamic Earthquake Cycle Simulations Considering Changes in Dominant Deformation Mechanisms of a Fault Slip

Dynamic Earthquake Cycle Simulations Considering Changes in Dominant Deformation Mechanisms of a Fault Slip

Crack to pulse transition and magnitude statistics during earthquake cycles on a self-similar rough fault

Faults in nature demonstrate fluctuations from planarity at most length scales that are relevant for earthquake dynamics. These fluctuations may influence all stages of the seismic cycle; earthquake nucleation, propagation, arrest, and inter-seismic behavior. Here I show quasi-dynamic plane-strain simulations of earthquake cycles on a self-similar and finite 10 km long rough fault with amplitude-to-wavelength ratio α=0.01. The minimum roughness wavelength, λmin, and nucleation length scales are well resolved and much smaller than the fault length. Stress relaxation and fault loading is implemented using a variation of the backslip approach, which allows for efficient simulations of multiple cycles without stresses becoming unrealistically large. I explore varying λmin for the same stochastically generated realization of a rough fractal fault. Decreasing λmin causes the minimum and maximum earthquakes sizes to decrease. Thus the fault seismicity is characterized by smaller and more numerous earthquakes, on the other hand, increasing the λmin results in fewer and larger events. However, in all cases, the inferred b-value is constant and the same as for a reference no-roughness simulation (α=0). I identify a new mechanism for generating pulse-like ruptures. Seismic events are initially crack-like, but at a critical length scale, they continue to propagate as pulses, locking in an approximately fixed amount of slip. I investigate this transition using simple arguments and derive a characteristic pulse length, Lc=λmin/(4π4α2) and slip distance, δc based on roughness drag. I hypothesize that the ratio λmin/α2 can be roughly estimated from kinematic rupture models. Furthermore, I suggest that when the fault size is much larger than Lc, then most space-time characteristics of slip differ between a rough fault and a corresponding planar fault.

A Novel Hybrid Finite Element‐Spectral Boundary Integral Scheme for Modeling Earthquake Cycles: Application to Rate and State Faults With Low‐Velocity Zones

AbstractWe present a novel hybrid finite element‐spectral boundary integral (SBI) scheme that enables efficient simulation of earthquake cycles. This combined finite element‐SBI approach captures the benefits of finite elements in modeling problems with nonlinearities, as well as the computational superiority of SBI. The domain truncation enabled by this scheme allows us to utilize high‐resolution finite elements discretization to capture inhomogeneities or complexities that may exist in a narrow region surrounding the fault. Combined with an adaptive time stepping algorithm, this framework opens new opportunities for modeling earthquake cycles with high‐resolution fault zone physics. In this initial study, we consider a two‐dimensional antiplane model with a vertical strike‐slip fault governed by rate and state friction in the quasi‐dynamic limit under the radiation damping approximation. The proposed approach is first verified using the benchmark problem BP‐1 from the Southern California Earthquake Center sequence of earthquake and aseismic slip community verification effort. The computational framework is then utilized to model the earthquake sequence and aseismic slip of a fault embedded within a low‐velocity fault zone (LVFZ) with different widths and compliance levels. Our results indicate that sufficiently compliant LVFZs contribute to the emergence of subsurface events that fail to penetrate to the free surface and may experience earthquake clusters with nonuniform interseismic time. Furthermore, the LVFZ leads to slip rate amplification relative to the homogeneous elastic case. We discuss the implications of our results for understanding earthquake complexity as an interplay of fault friction and bulk heterogeneities.

A computational method for earthquake cycles within anisotropic media

SUMMARYWe present a numerical method for the simulation of earthquake cycles on a 1-D fault interface embedded in a 2-D homogeneous, anisotropic elastic solid. The fault is governed by an experimentally motivated friction law known as rate-and-state friction which furnishes a set of ordinary differential equations which couple the interface to the surrounding volume. Time enters the problem through the evolution of the ordinary differential equations along the fault and provides boundary conditions for the volume, which is governed by quasi-static elasticity. We develop a time-stepping method which accounts for the interface/volume coupling and requires solving an elliptic partial differential equation for the volume response at each time step. The 2-D volume is discretized with a second-order accurate finite difference method satisfying the summation-by-parts property, with boundary and fault interface conditions enforced weakly. This framework leads to a provably stable semi-discretization. To mimic slow tectonic loading, the remote side-boundaries are displaced at a slow rate, which eventually leads to earthquake nucleation at the fault. Time stepping is based on an adaptive, fourth-order Runge–Kutta method and captures the highly varying timescales present. The method is verified with convergence tests for both the orthotropic and fully anisotropic cases. An initial parameter study reveals regions of parameter space where the systems experience a bifurcation from period one to period two behaviour. Additionally, we find that anisotropy influences the recurrence interval between earthquakes, as well as the emergence of aseismic transients and the nucleation zone size and depth of earthquakes.

Earthquake Cycle Modelling of Multi-segmented Faults: Dynamic Rupture and Ground Motion Simulation of the 1992 Mw 7.3 Landers Earthquake

We perform earthquake cycle simulations with the goal of studying the characteristics of source scaling relations and strong ground motions in multi-segmented fault ruptures. The 1992 Mw 7.3 Landers earthquake is chosen as a target earthquake to validate our methodology. The model includes the fault geometry for the three-segmented Landers rupture from the SCEC community fault model, extended at both ends to a total length of 200 km, and limited to a depth to 15 km. We assume the faults are governed by rate-and-state (RS) friction, with a heterogeneous, correlated spatial distribution of characteristic weakening distance Dc. Multiple earthquake cycles on this non-planar fault system are modeled with a quasi-dynamic solver based on the boundary element method, substantially accelerated by implementing a hierarchical-matrix method. The resulting seismic ruptures are recomputed using a fully-dynamic solver based on the spectral element method, with the same RS friction law. The simulated earthquakes nucleate on different sections of the fault, and include events similar to the Mw 7.3 Landers earthquake. We obtain slip velocity functions, rupture times and magnitudes that can be compared to seismological observations. The simulated ground motions are validated by comparison of simulated and recorded response spectra.

Slow‐Slip Recurrent Pattern Changes: Perturbation Responding and Possible Scenarios of Precursor toward a Megathrust Earthquake

AbstractAdvances in geodetic techniques enable us to detect “slow‐earthquake” transients (e.g., slow‐slip events, SSEs) with improving accuracy and coverage. Recent observations reveal intriguing changes of SSE behavior before and/or after earthquakes. However, the physics behind these observations remain largely unknown. How does SSE pattern change during megathrust earthquake super‐cycle? How do SSEs respond to “external” tectonic perturbations such as stress perturbation from earthquakes, or nontectonic forces such as tidal modulation and seasonal loading? Can SSE pattern changes shed light on the onset of a large earthquake? To address these questions, we employ laboratory‐based rate‐and‐state frictional law on subduction zone faults with realistic frictional properties incorporating megathrust earthquake and SSE regions. We conduct 2‐D/3‐D quasi‐dynamic earthquake cycle simulations to study the “intrinsic” SSE pattern changes as how it evolves at different stages of the earthquake cycle, versus the changes in SSE pattern responding to external stress perturbations. Our results suggest that, despite both intrinsic and perturbation models are capable to introduce large variability in SSE pattern, there are considerable observable characteristics that can be used to differentiate these two models. Without external perturbation the SSE patterns change intrinsically during the super‐cycle. The recurrence interval and peak slip rate of SSEs decrease significantly right before megathrust earthquake and could be used as a potential warning sign. Whereas SSE patterns can vary significantly when perturbed by an earthquake or other tectonic/nontectonic sources. Recurring SSEs can be advanced or delayed by external perturbations, and multiple SSEs can be affected if perturbation is long‐lasting.