scholarly journals The Community Code Verification Exercise for Simulating Sequences of Earthquakes and Aseismic Slip (SEAS)

2020 ◽  
Vol 91 (2A) ◽  
pp. 874-890 ◽  
Author(s):  
Brittany A. Erickson ◽  
Junle Jiang ◽  
Michael Barall ◽  
Nadia Lapusta ◽  
Eric M. Dunham ◽  
...  
Keyword(s):  
Ground Deformation ◽  
Benchmark Problems ◽  
Physical Factors ◽  
Code Verification ◽  
Aseismic Slip ◽  
Dynamic Rupture ◽  
Earthquake Physics ◽  
Spontaneous Nucleation ◽  
Fault Behavior ◽  
Antiplane Problem

Abstract Numerical simulations of sequences of earthquakes and aseismic slip (SEAS) have made great progress over past decades to address important questions in earthquake physics. However, significant challenges in SEAS modeling remain in resolving multiscale interactions between earthquake nucleation, dynamic rupture, and aseismic slip, and understanding physical factors controlling observables such as seismicity and ground deformation. The increasing complexity of SEAS modeling calls for extensive efforts to verify codes and advance these simulations with rigor, reproducibility, and broadened impact. In 2018, we initiated a community code-verification exercise for SEAS simulations, supported by the Southern California Earthquake Center. Here, we report the findings from our first two benchmark problems (BP1 and BP2), designed to verify different computational methods in solving a mathematically well-defined, basic faulting problem. We consider a 2D antiplane problem, with a 1D planar vertical strike-slip fault obeying rate-and-state friction, embedded in a 2D homogeneous, linear elastic half-space. Sequences of quasi-dynamic earthquakes with periodic occurrences (BP1) or bimodal sizes (BP2) and their interactions with aseismic slip are simulated. The comparison of results from 11 groups using different numerical methods show excellent agreements in long-term and coseismic fault behavior. In BP1, we found that truncated domain boundaries influence interseismic stressing, earthquake recurrence, and coseismic rupture, and that model agreement is only achieved with sufficiently large domain sizes. In BP2, we found that complexity of fault behavior depends on how well physical length scales related to spontaneous nucleation and rupture propagation are resolved. Poor numerical resolution can result in artificial complexity, impacting simulation results that are of potential interest for characterizing seismic hazard such as earthquake size distributions, moment release, and recurrence times. These results inform the development of more advanced SEAS models, contributing to our further understanding of earthquake system dynamics.

Towards simulating sequences of seismic and aseismic slip across scales: Initial benchmarks and future directions

2020 ◽  
Author(s):  
Luca Dal Zilio ◽  
Meng Li ◽  
Ylona van Dinther ◽  
Casper Pranger
Keyword(s):  
Elastic Half Space ◽  
Plate Motion ◽  
Tectonic Deformation ◽  
Fault Mechanics ◽  
Inertial Effects ◽  
Aseismic Slip ◽  
Dynamic Rupture ◽  
Earthquake Physics ◽  
Dynamic Propagation ◽  
Antiplane Problem

<p>Numerical simulations of the earthquake cycle have made great progress over the past decades to address important questions in earthquake physics and fault mechanics. However, significant challenges in bridging multiscale interactions between long-term tectonic deformation, aseismic fault slip, earthquake nucleation, and dynamic rupture still remain. In this study, we present results from GARNET, a newly-developed numerical library to simulate sequences of seismic and aseismic slip across scales. This finite difference code utilizes a fully staggered spatially adaptive rectilinear grid. Furthermore, it incorporates an automatic discretization algorithm and combines different physical ingredients, including a visco-elasto-plastic rheology and quasi- and fully dynamic formulation of inertial effects into one algorithm. While PETSc and Kokkos libraries are included for parallel computing, an adaptive time stepping is integrated into the algorithm to resolve both long- and short-time scales, ranging from years to milliseconds during the dynamic propagation of earthquake rupture.</p><p> </p><p>Here we present results from two benchmarks (BP1 and BP3) based on the community code-verification effort for Sequences of Earthquakes and Aseismic Slip (SEAS) by the Southern California Earthquake Center (SCEC). BP1 benchmark is a 2D antiplane problem, with a 1D planar vertical strike-slip fault obeying rate-and-state friction, embedded in a 2D homogeneous, linear elastic half-space. The fault has a shallow seismogenic region with velocity-weakening friction and a deeper velocity-strengthening region, below which a relative plate motion rate is imposed. A periodic sequence of spontaneous, quasi-dynamic earthquakes and slow slip are simulated in the model. In the BP3 benchmark we consider full inertial effects during the dynamic rupture and we investigate its influence on earthquake behaviour and patterns. Results from these two benchmarks represent the first step towards more advanced seismic cycle models, which will help to enhance our understanding in earthquake physics.</p>

scholarly journals Deformation associated with sliver transport in Costa Rica: seismic and geodetic observations of the July 2016 Bijagua earthquake sequence

2019 ◽  
Vol 220 (1) ◽  
pp. 585-597 ◽  
Author(s):  
Maria C Araya ◽  
Juliet Biggs
Keyword(s):  
Surface Deformation ◽  
Ground Deformation ◽  
Surface Displacement ◽  
Strike Slip ◽  
Central American ◽  
Earthquake Sequence ◽  
Fault System ◽  
Aseismic Slip ◽  
Volcanic Arc ◽  
Forearc Sliver

SUMMARY Tectonic slivers form in the overriding plate in regions of oblique subduction. The inner boundaries of the sliver are often poorly defined and can consist of well-defined faults, rotating blocks or diffuse fault systems, which pass through or near the volcanic arc. The Guanacaste Volcanic Arc Sliver (GVAS) as defined by Montero et al., is a segment of the Central American Forearc Sliver, whose inner boundary is the ∼87-km-long Haciendas-Chiripa fault system (HCFS), which is located ∼10 km behind the volcanic arc and consists of strike slip faults and pull apart steps. We characterize the current ground motion on this boundary by combining earthquake locations and focal mechanisms of the 2016 Bijagua earthquake sequence, with the surface ground deformation obtained from Interferometric Synthetic Aperture Radar (InSAR) images from the ALOS-2 satellite. The coseismic stack of interferograms show ∼6 cm of displacement towards the line of sight of the satellite between the Caño Negro fault and the Upala fault, indicating uplift or SE horizontal surface displacement. The largest recorded earthquake of the sequence was Mw 5.4, and the observed deformation is one of the smallest earthquakes yet detected by InSAR in the Central American region. Forward and inverse models show the surface deformation can be partially explained by slip on a single fault, but it can be better explained by slip along two faults linked at depth. The best-fitting model consists of 0.33 m of right lateral slip on the Caño Negro fault and 0.35 m of reverse slip on the Upala fault, forming a positive flower structure. As no reverse seismicity was recorded, we infer the slip on the Upala fault occurred aseismically. Observations of the Bijagua earthquake sequence suggests the forearc sliver boundary is a complex and diffuse fault system. There are localized zones of transpression and transtension and areas where there is no surface expression suggesting the fault system is not yet mature. Although aseismic slip is common on subduction interfaces and mature strike-slip faults, this is the first study to document aseismic slip on a continental tectonic sliver boundary fault.

scholarly journals Sequences of seismic and aseismic slip on bimaterial faults show dominant rupture asymmetry and potential for elevated seismic hazard

2021 ◽  
Author(s):  
Mohamed Abdelmeguid ◽  
Ahmed Elbanna
Keyword(s):  
Seismic Hazard ◽  
Normal Stress ◽  
Nucleation Site ◽  
Rupture Propagation ◽  
Aseismic Slip ◽  
Earthquake Physics ◽  
Slip Rates ◽  
Seismicity Pattern ◽  
Sequence Of Events ◽  
Material Contrast

We perform numerical simulations of sequences of earthquake and aseismic slip on planar rate and state faults separating dissimilar material within the 2-D plane strain approximation. We resolve all stages of the earthquake cycle from aseismic slip to fast ruptures while incorporating full inertia effects during seismic event propagation. We show that bimaterial coupling results in favorable nucleation site and subsequent asymmetric rupture propagation. We demonstrate that increasing the material contrast enhances this asymmetry leading to higher slip rates and normal stress drops in the preferred rupture propagation direction. The normal stress drop, induced by the bimaterial effect, leads to strong dynamic weakening of the fault and may destabilize the creeping region on a heterogeneous rate and state fault, resulting in extended rupture propagation. Such rupture penetration into creeping patches may lead to more frequent opening of earthquake gates, causing increased seismic hazard. Furthermore, bimaterial coupling may lead to irregular seismicity pattern in terms of event length, peak slip rates,and hypocenter location, depending on the properties of the creeping patches bordering the seismogenically active part of the fault . Our results highlight robust characteristics of bimaterial interfaces that persist over long sequence of events and suggest the need for further exploration of the role of material contrast in earthquake physics and models of seismic hazard.

Episodic fluid pressure cycling controls earthquake sequences on subduction megathrusts

2021 ◽  
Author(s):  
Luca Dal Zilio ◽  
Taras Gerya
Keyword(s):  
Fluid Flow ◽  
Finite Difference Methods ◽  
Fluid Pressure ◽  
Seismogenic Zone ◽  
Slow Slip ◽  
Aseismic Slip ◽  
Earthquake Physics ◽  
Megathrust Earthquakes ◽  
Pressure Cycling ◽  
Crustal Stresses

<p>A major goal in earthquake physics is to derive a constitutive framework for fault slip that captures the dependence of friction on lithology, sliding velocity, temperature, and pore fluid pressure. Here, we present a newly-developed two-phase flow numerical model — which couples solid rock deformation and pervasive fluid flow — to show how crustal stresses and fluid pressures within subducting megathrust evolve before and during slow slip and fast events. This unified 2D numerical framework couples inertial mechanical deformation and fluid flow by using finite difference methods, marker-in-cell technique, and poro-visco-elasto-plastic rheology. An adaptive time stepping allows the correct resolution of both long- and short-time scales, ranging from years to milliseconds during the dynamic propagation of dynamic rupture.</p><p>We investigate how permeability and its spatial distribution control the interseismic coupling along the megathrust interface, the interplay between seismic and aseismic slip, and the nucleation of large earthquakes. While a constant permeability leads to more regular seismic cycles, a depth dependent permeability contributes substantially to the development of two distinct megathrust zones: a shallow, locked seismogenic zone and a deep, narrow aseismic segment characterized by slow-slip events. Furthermore, we show that without requiring any specific friction law, our models reveal that permeability, episodic stress transfer and fluid pressure cycling control the predominant slip mode along the subduction megathrust. Furthermore, we analyze how rate dependent strength and dilatation affect rupture propagation and arrest. Our preliminary results show that fluid-solid poro-visco-elasto-plastic coupling behaves similarly to rate- and state-dependent friction. In this context, fluid pressure plays the role of state parameter whose time evolution is governed by: (i) the short-term elasto-plastic collapse of pores inside faults during the rupture (coseismic self-pressurization of faults) and (ii) the long-term pore-pressure diffusion from the faults into surrounding rocks (post- and interseismic relaxation of fluid pressure). This newly-developed numerical framework contributes to improve our understanding of the physical mechanisms underlying large megathrust earthquakes, and demonstrate that fluid play a key role in controlling the interplay between seismic and aseismic slip.</p>

Induced seismicity associated with fluid injection into a fractured rock mass

2020 ◽  
Author(s):  
Brice Lecampion ◽  
Federico Ciardo ◽  
Alexis Saèz Uribe ◽  
Andreas Möri
Keyword(s):  
Rock Mass ◽  
Percolation Threshold ◽  
Pore Pressure ◽  
Finite Volume ◽  
Fractured Rock ◽  
Fluid Injection ◽  
Aseismic Slip ◽  
Dynamic Rupture ◽  
Fractured Rock Mass

<p>We investigate via numerical modeling the growth of an aseismic rupture and the possible nucleation of a dynamic rupture driven by fluid injection into a fractured rock mass. We restrict to the case of highly transmissive fractures compared to the rock matrix at the scale of the injection duration and thus assume an impermeable matrix. We present a new 2D hydro-mechanical solver allowing to treat a large number of pre-existing frictional discontinuities. The quasi-static (or quasi-dynamic) balance of momentum is discretized using boundary elements while fluid flow inside the fracture is discretized via finite volume. A fully implicit scheme is used for time integration. Combining a hierarchical matrix approximation of the original boundary element matrix with a specifically developed block pre-conditioner enable a robust and efficient solution of large problems (with up to 10<sup>6</sup> unknowns). In order to treat accurately fractures intersections, we use piece-wise linear displacement discontinuities element for elasticity and a vertex centered finite volume method for flow.</p><p>We first consider the case of a randomly oriented discrete fracture network (DFN) having friction neutral properties. We discuss the very different behavior associated with marginally pressurized versus critically stressed conditions. As an extension of the case of a planar fault (Bhattacharya and Viesca, Science, 2019), the injection into a DFN problem is governed by the distribution (directly associated with fracture orientation) of a dimensionless parameter combining the local stress criticality (function of the in-situ principal effective stress, friction coefficient and local fracture orientation) and the normalized injection over-pressure. The percolation threshold of the DFN which characterizes the hydraulic connectivity of the network plays an additional role in fluid driven shear cracks growth. Our numerical simulations show that a critically stressed DFN exhibits fast aseismic slip growth (much faster than the fluid pore-pressure disturbance front propagation) regardless of the DFN percolation threshold. This is because the slipping patch growth is driven by the cascades of shear activation due to stress interactions as fractures get activated. On the other hand, the scenario is different for marginally pressurized / weakly critically stressed DFN. The aseismic slip propagation is then tracking pore pressure diffusion inside the DFN. As a result, the DFN percolation threshold plays an important role with low percolation leading to fluid localization and thus restricted aseismic rupture growth.</p><p>We then discuss the case of fluid injection into a fault damage zone. Using a linear frictional weakening model for the fault, we investigate the scenario of the nucleation of a dynamic rupture occurring after the end of the injection (as observed in several instances in the field). We delimit the injection and in-situ conditions supporting such a possibility.</p>

Untangling the dynamics of the 2019 Ridgecrest sequence by integrated dynamic rupture and Coulomb stress modeling across an immature 3D conjugate fault network

2020 ◽  
Author(s):  
Alice-Agnes Gabriel ◽  
Taufiqurrahman Taufiqurrahman ◽  
Sara Carena ◽  
Alessandro Verdecchia ◽  
Bo Li ◽  
...  
Keyword(s):  
Dynamic Stress ◽  
Ground Deformation ◽  
Fluid Pressure ◽  
Stress Factors ◽  
Initial Stresses ◽  
Fault System ◽  
Coulomb Stress ◽  
Rupture Directivity ◽  
Dynamic Rupture ◽  
Fault Network

<p>We present combined 3D dynamic rupture scenarios of the 2019 M<sub>w</sub>6.4 Searles Valley and M<sub>w</sub>7.1 Ridgecrest earthquakes closely constrained by observations, incorporating complex subsurface material properties, high-resolution topography and off-fault plastic deformation empowered by supercomputing. A detailed 3D non-vertical fault model of the active quasi-orthogonal intersecting fault network is built by integrating relocated aftershocks and surface ruptures constrained by space geodesy and field observations. All faults are exposed to a 3D SCEC community stress model as well as long- and short-term static and dynamic stress transfers, which impact rupture dynamics, particularly in the vicinity of complexities in fault geometry.</p><p>By assuming apparently weak faults due to the effect of rapid velocity-weakening friction and elevated fluid pressure, we determine initial stresses and fault strength. Multi-fault rupture directivity and velocity of both events are constrained by aftershock calibrated back-projection. In the presented scenario two conjugate faults simultaneously rupture in the M<sub>w</sub>6.4 event, while only the SW-segment breaks the surface. The M<sub>w</sub>7.1 event experiences the full final state of stress (dynamic plus static effects) of the Searles Valley scenario, leading to complex rupture including re-activation of the conjugate M<sub>w</sub>6.4 segment, mixed crack and pulse-like propagation, tunneling beneath the fault intersection and choosing one Southern branch only. Both events exhibit a high dynamic stress drop reflecting the immature fault system. The foreshock induces a considerable Coulomb stress change in the M<sub>w</sub>7.1 hypocentral region; however, not enough to trigger rupture across the stress-shadowed main fault. Both scenarios match key observations including magnitude, rupture speed, directivity, off-fault damage, slip distribution from kinematic inversion, teleseismic waveforms, GPS, and InSAR ground deformation; while shedding light on geometric, strength and stress factors governing the complex rupture evolution and interaction of the Ridgecrest sequence.</p>

A geodetic exploration of the behavior of aseismic slip along the central section of the North Anatolian fault

2020 ◽  
Author(s):  
Jorge Jara ◽  
Alpay Ozdemir ◽  
Angelique Benoit ◽  
Romain Jolivet ◽  
Ziyadin Çakir ◽  
...  
Keyword(s):  
Time Series ◽  
Ground Deformation ◽  
North Anatolian Fault ◽  
Slow Slip ◽  
Aseismic Slip ◽  
Central Section ◽  
Slow Slip Events ◽  
The North ◽  
Aseismic Deformation ◽  
Over Time

<p>Many geodetic evidence suggest aseismic slip along active faults is more common than previously thought. Furthermore, aseismic slip during the interseismic period seems to be made of intermittent slow slip events, corresponding to episodes of loading and releasing of tectonic stress over time. However, although our capabilities of detection and location of aseismic deformation have significantly increased together with the growth in available geodetic data, the physical mechanisms governing slow slip remain unknown.</p><p>We explore the spatial and temporal behavior of aseismic deformation in the vicinity of the small town of Ismetpasa, located along the central section of the North Anatolian Fault (Turkey). We combine InSAR and GNSS data acquired over the last 10 years to locate and quantify aseismic slip in the subsurface. We process SAR images (ALOS and Sentinel-1) acquired from 2007 to 2018 to build time series of ground deformation and maps of ground velocity. We confirm the presence of a 100 km-long creeping section, at rates of 10-20 mm/yr. Along this section, slip is not constant and decreases over time as formerly observed over the last 60 years. Furthermore, via a detailed analysis of our geodetic time series, we detect 3 major episodes of aseismic slip between 2015 and 2018, with durations ranging from 6 months to 1 year and magnitudes between 4.6 - 5.2. These results are compared with time series obtained from a network of GNSS permanent stations we have installed in the region (17 stations, period 2016 - 2019). As a conclusion, aseismic slip along this section of the North Anatolian Fault is characterized by slow slip events rather than by a constant, steady-state aseismic slip rate. We discuss the potential implications in terms of mechanics of slow slip along the NAF.</p>

A Crosslink Constraint Method for Modeling Episodic Dynamic Rupture on Intersecting Faults

2020 ◽  
Vol 91 (2A) ◽  
pp. 1030-1041 ◽  
Author(s):  
Chunfang Meng ◽  
Bradford Hager
Keyword(s):  
Finite Element ◽  
Open Source ◽  
Benchmark Problems ◽  
Finite Element Code ◽  
Dynamic Rupture ◽  
Slip Direction ◽  
Constraint Equations ◽  
Main Fault ◽  
Constraint Method ◽  
Dynamic Slip

Abstract We present a crosslink constraint method for numerically modeling dynamic slip on intersecting faults, without prescribing slip (dis-)continuation directions. The fault intersections are constrained by crosslinked split nodes, such that the slip can only be continuous on one of the two intersecting faults at a time and location. The method resolves the episodic intersection offset by examining the dynamic fault traction resulting from two sets of constraint equations, one for each slip direction. To verify this method, we modify two benchmark problems, hosted at Southern California Earthquake Center (SCEC), by allowing a branching fault to step across a main fault. The modified SCEC problem results agree with our expectations that the intersection offset scenarios are dictated by the nucleation patch location and initial fault traction. This new method comes with an open-source finite-element code Defmod.

scholarly journals The Community Code Verification Exercise for Simulating Sequences of Earthquakes and Aseismic Slip (SEAS)

2019 ◽  
Author(s):  
Brittany Erickson ◽  
Junle Jiang ◽  
Michael Barall ◽  
Nadia Lapusta ◽  
Eric Dunham ◽  
...  
Keyword(s):  
Code Verification ◽  
Aseismic Slip

The State of Stress on the Fault Before, During, and After a Major Earthquake

2020 ◽  
Vol 48 (1) ◽  
pp. 49-74 ◽  
Author(s):  
Emily E. Brodsky ◽  
James J. Mori ◽  
Louise Anderson ◽  
Frederick M. Chester ◽  
Marianne Conin ◽  
...  
Keyword(s):  
Stress Drop ◽  
Tohoku Earthquake ◽  
Static Friction ◽  
Japan Trench ◽  
Dynamic Friction ◽  
Earthquake Physics ◽  
Stress Reversal ◽  
Fault Resistance ◽  
Fault Behavior

Earthquakes occur by overcoming fault friction; therefore, quantifying fault resistance is central to earthquake physics. Values for both static and dynamic friction are required, and the latter is especially difficult to determine on natural faults. However, large earthquakes provide signals that can determine friction in situ. The Japan Trench Fast Drilling Project (JFAST), an Integrated Ocean Discovery Program expedition, determined stresses by collecting data directly from the fault 1–2 years after the 2011 Mw 9.1 Tohoku earthquake. Geological, rheological, and geophysical data record stress before, during, and after the earthquake. Together, the observations imply that the shear strength during the earthquake was substantially below that predicted by the traditional Byerlee's law. Locally the stress drop appears near total, and stress reversal is plausible. Most solutions to the energy balance require off-fault deformation to account for dissipation during rupture. These observations make extreme coseismic weakening the preferred model for fault behavior. ▪  Determining the friction during an earthquake is required to understand when and where earthquakes occur. ▪  Drilling into the Tohoku fault showed that friction during the earthquake was low. ▪  Dynamic friction during the earthquake was lower than static friction. ▪  Complete stress drop is possible, and stress reversal is plausible.

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