Multicycle Simulation of Strike-Slip Earthquake Rupture for Use in Near-Source Ground-Motion Simulations

2021 ◽  
Author(s):  
Percy Galvez ◽  
Anatoly Petukhin ◽  
Paul Somerville ◽  
Jean-Paul Ampuero ◽  
Ken Miyakoshi ◽  
...  
Keyword(s):  
Ground Motion ◽  
Stress Drop ◽  
Slip Rate ◽  
Rupture Process ◽  
Earthquake Rupture ◽  
Rupture Velocity ◽  
Source Inversion ◽  
Dynamic Rupture ◽  
Wide Range ◽  
Source Scaling

ABSTRACT Realistic dynamic rupture modeling validated by observed earthquakes is necessary for estimating parameters that are poorly resolved by seismic source inversion, such as stress drop, rupture velocity, and slip rate function. Source inversions using forward dynamic modeling are increasingly used to obtain earthquake rupture models. In this study, to generate a large number of physically self-consistent rupture models, rupture process of which is consistent with the spatiotemporal heterogeneity of stress produced by previous earthquakes on the same fault, we use multicycle simulations under the rate and state (RS) friction law. We adopt a one-way coupling from multicycle simulations to dynamic rupture simulations; the quasidynamic solver QDYN is used to nucleate the seismic events and the spectral element dynamic solver SPECFEM3D to resolve their rupture process. To simulate realistic seismicity, with a wide range of magnitudes and irregular recurrence, several realizations of 2D-correlated heterogeneous random distributions of characteristic weakening distance (Dc) in RS friction are tested. Other important parameters are the normal stress, which controls the stress drop and rupture velocity during an earthquake, and the maximum value of Dc, which controls rupture velocity but not stress drop. We perform a parametric study on a vertical planar fault and generate a set of a hundred spontaneous rupture models in a wide magnitude range (Mw 5.5–7.4). We validate the rupture models by comparison of source scaling, ground motion (GM), and surface slip properties to observations. We compare the source-scaling relations between rupture area, average slip, and seismic moment of the modeled events with empirical ones derived from source inversions. Near-fault GMs are computed from the source models. Their peak ground velocities and peak ground accelerations agree well with the ground-motion prediction equation values. We also obtain good agreement of the surface fault displacements with observed values.

Dynamic Rupture and Ground Motion Modeling of the 2016 M6.2 Amatrice and M6.5 Norcia, Central Italy, Earthquakes Constrained by Bayesian Dynamic Source Inversion

2020 ◽  
Author(s):  
Taufiq Taufiqurrahman ◽  
Alice-Agnes Gabriel ◽  
Frantisek Gallovic ◽  
Lubica Valentova
Keyword(s):  
Ground Motion ◽  
Dynamic Models ◽  
Central Italy ◽  
Foot Wall ◽  
Source Inversion ◽  
Dynamic Rupture ◽  
Highly Efficient ◽  
Starting Point ◽  
Dynamic Source ◽  
Strong Ground

<p>The complex evolution of earthquake rupture during the 2016 Central Italy sequence and the uniquely dense seismological observations provide an opportunity to better understand the processes controlling earthquake dynamics, strong ground motion, and earthquake interaction. </p><p>We here use fault initial stress and friction conditions constrained by a novel Bayesian dynamic source inversion as a starting point for high-resolution dynamic rupture scenarios. The best-fitting forward models are chosen out of ~10<sup>6</sup> highly efficient simulations restricted to a simple planar dipping fault. Such constrained, highly heterogeneous dynamic models fit strong motion data well. Utilizing the open-source SeisSol software (www.seissol.org), we then take into account non-planar (e.g., listric) fault geometries, inelastic off-fault damage rheology, free surface effects and topography which cannot be accounted for in the highly efficient dynamic source inversion. SeisSol is based on the discontinuous Galerkin method on unstructured tetrahedral meshes optimized for modern supercomputers. </p><p>We investigate the effects of including the realistic modeling ingredients on rupture dynamics and strong ground motions up to 5 Hz. Synthetic PGV mapping reveals that specifically fault listricity decreases ground motion amplitudes by  ~50 percent in the extreme near field on the foot-wall. On the hanging-wall shaking is increased by ~150 percent as a consequence of wave-focusing effects within 10 km away from the fault. Dynamic modeling thus suggests that geometrical fault complexity is important for seismic hazard assessment adjacent to dipping faults but difficult to identify by kinematic source inversions.</p>

Global catalog of earthquake rupture velocities shows anticorrelation between stress drop and rupture velocity

2018 ◽  
Vol 733 ◽  
pp. 148-158 ◽  
Author(s):  
Agnès Chounet ◽  
Martin Vallée ◽  
Mathieu Causse ◽  
Françoise Courboulex
Keyword(s):  
Stress Drop ◽  
Earthquake Rupture ◽  
Rupture Velocity

scholarly journals Surface Displacement and Ground Motion from Dynamic Rupture Models of Thrust Faults with Variable Dip Angles and Burial Depths

2020 ◽  
Vol 110 (6) ◽  
pp. 2599-2618
Author(s):  
Sirena Ulloa ◽  
Julian C. Lozos
Keyword(s):  
Ground Motion ◽  
Stress Drop ◽  
Ground Motions ◽  
Ground Surface ◽  
Surface Displacement ◽  
Initial Stresses ◽  
Thrust Faults ◽  
Dynamic Rupture ◽  
Blind Thrust ◽  
Dip Angle

ABSTRACT Thrust-fault earthquakes are particularly hazardous in that they produce stronger ground motion than normal or strike-slip events of the same magnitude due to a combination of hanging-wall effects, vertical asymmetry, and higher stress drop due to compression. In addition, vertical surface displacement occurs in both blind-thrust and emergent thrust ruptures, and can potentially damage lifelines and infrastructure. Our 3D dynamic rupture modeling parameter study focuses on planar thrust faults of varying dip angles, and burial depth establishes a physics-based understanding of how ground motion and permanent ground surface displacement depend on these geometrical parameters. We vary dip angles from 20° to 70° and burial depths from 0 to 5 km. We conduct rupture models on these geometries embedded in a homogeneous half-space, using different stress drops but fixed frictional parameters, and with homogeneous initial stresses versus stresses tapered toward the ground surface. Ground motions decrease as we bury the fault under homogeneous initial stresses. In contrast, under tapered initial stresses, ground motions increase in blind-thrust faults as we bury the fault, but are still the highest in emergent faults. As we steepen dip angle, peak particle velocities in the homogeneous stress case generally increase in emergent faults but decrease in blind-thrust faults. Meanwhile, ground motion consistently increases with steepening dip angle under the stress gradient. We find that varying stress drop has a considerable scalar effect on both ground motion and permanent surface displacement, whereas changing fault strength has a negligible effect. Because of the simple geometry of a planar fault, our results can be applied to understanding basic behavior of specific real-world thrust faults.

3D simulation of near-field strong ground motion based on dynamic modeling

1998 ◽  
Vol 88 (6) ◽  
pp. 1445-1456
Author(s):  
Tomohiro Inoue ◽  
Takashi Miyatake
Keyword(s):  
Ground Motion ◽  
Stress Drop ◽  
Strong Ground Motion ◽  
Source Parameters ◽  
Peak Ground Velocity ◽  
Crack Model ◽  
Rupture Velocity ◽  
Ground Acceleration ◽  
Fault Trace ◽  
Strong Ground

Abstract We simulate the strong ground motion generated from the earthquake rupture process on a shallow strike-slip fault using a 3D finite-difference method. The faulting process is modeled using a crack model with fixed rupture velocity. The variability of peak ground velocity patterns, correlated with fault location and source parameters such as stress drop or rupture velocity, is investigated. Our findings suggest that these patterns are strongly affected by rupture directivity and the uppermost depth of the fault or that of the asperity. When a fault breaks the ground surface, the peak ground velocity and the peak ground acceleration show a narrow region of strong motion. When a fault is buried under the ground, the high peak ground velocity zone of the fault-parallel component is apart from the fault trace by a distance comparable to the fault depth. On the other hand, the fault-normal peak ground velocity is a maximum along the fault trace. The fault length (or asperity length) is not so effective for peak ground velocities. The effect of heterogeneity in stress drop and rupture velocity on strong ground motion is also investigated. When stress drop is not uniform but increases linearly with depth from zero at the uppermost depth, the peak ground velocity is reduced. These results help better predict the strong ground motion generated from a potential fault.

scholarly journals A convolutional neural network approach to estimate earthquake kinematic parameters from back-projection images

2021 ◽  
Author(s):  
Marina Corradini ◽  
Ian McBrearty ◽  
Claudio Satriano ◽  
Daniel Trugman ◽  
Paul Johnson ◽  
...  
Keyword(s):  
Neural Network ◽  
Convolutional Neural Network ◽  
Rise Time ◽  
Rupture Process ◽  
Large Set ◽  
Rupture Velocity ◽  
Back Projection ◽  
Source Inversion ◽  
Kinematic Parameters ◽  
Finite Fault

The retrieval of earthquake finite-fault kinematic parameters after the occurrence of an earthquake is a crucial task in observational seismology. Routinely-used source inversion techniques are challenged by limited data coverage and computational effort, and are subject to a variety of assumptions and constraints that restrict the range of possible solutions. Back-projection (BP) imaging techniques do not need prior knowledge of the rupture extent and propagation, and can track the high-frequency (HF) radiation emitted during the rupture process. While classic source inversion methods work at lower frequencies and return an image of the slip over the fault, the BP method underlines fault areas radiating HF seismic energy. HF radiation is attributed to the spatial and temporal complexity of the rupture process (e.g., slip heterogeneities, changes in rupture speed and in slip velocity). However, the quantitative link between the BP image of an earthquake and its rupture kinematics remains unclear. Our work aims at reducing the gap between the theoretical studies on the generation of HF radiation due to earthquake complexity and the observation of HF emissions in BP images. To do so, we proceed in two stages, in each case analyzing synthetic rupture scenarios where the rupture process is fully known. We first investigate the influence that spatial heterogeneities in slip and rupture velocity have on the rupture process and its radiated wave field using the BP technique. We simulate different rupture processes using a 1D line source model. For each rupture model, we calculate synthetic seismograms at three teleseismic arrays and apply the BP technique to identify the sources of HF radiation. This procedure allows us to compare the BP images with the causative rupture, and thus to interpret HF emissions in terms of along-fault variation of the three kinematic parameters controlling the synthetic model: rise time, final slip, rupture velocity. Our results show that the HF peaks retrieved from BP analysis are better associated with space-time heterogeneities of slip acceleration. We then build on these findings by testing whether one can retrieve the kinematic rupture parameters along the fault using information from the BP image alone. We apply a machine learning, convolutional neural network (CNN) approach to the BP images of a large set of simulated 1D rupture processes to assess the ability of the network to retrieve from the progression of HF emissions in space and time the kinematic parameters of the rupture. These rupture simulations include along-strike heterogeneities whose size is variable and within which the parameters of rise-time, final slip, and rupture velocity change from the surrounding rupture. We show that the CNN trained on 40,000 pairs of BP images and kinematic parameters returns excellent predictions of the rise time and the rupture velocity along the fault, as well as good predictions of the central location and length of the heterogeneous segment. Our results also show that the network is insensitive towards the final slip value, as expected from a theoretical standpoint.

Characterization of Shallow Rupture Kinematics in Strong Ground Motion Simulations of Strike-Slip Earthquakes Constrained by Dynamic Rupture Modeling

2020 ◽  
Author(s):  
Arben Pitarka ◽  
Robert Graves
Keyword(s):  
Ground Motion ◽  
Strong Ground Motion ◽  
Broad Band ◽  
Slip Rate ◽  
Dynamic Rupture ◽  
Weak Zone ◽  
Frictional Properties ◽  
Rupture Kinematics ◽  
Strong Ground

<p>The objective of our study is the improvement of shallow rupture characterization in kinematic rupture models used in strong ground motion simulations. Based on geological investigations, earthquake stress drop, depth-variation of seismicity, as well as recorded near-fault ground motion, there is clear evidence for depth variation of frictional properties of crustal materials. The material ductility in the weak zone (upper 3-5 km of the crust) and the transition from ductile state to brittle state in the upper seismogenic zone, determine how the fracture energy is consumed by the earthquake rupture, and  how generated seismic energy is distributed in space and time.</p><p> </p><p>Using plausible stress models for crustal ruptures, we performed dynamic rupture simulations on vertical strike slip faults that break the free surface. We used a 3D staggered-grid finite-difference method (Pitarka and Dalguer, 2009) and regional 1D velocity model. The stress drop as a function of slip was modeled using a linear slip weakening frictional law that reflects the depth and lateral variations of frictional properties of crustal materials. Through dynamic rupture modeling we were able to extract kinematic rupture characteristics, such as changes in the shape of slip rate functions, rupture velocity, and peak slip  rate across the weak zone, and in the slip asperity areas. These results were then used to refine our existing rupture generating model (Graves and Pitarka, 2016) for crustal  earthquakes. The modifications to the rupture generator code include changes to the shape of slip-rate function at shallow depths, rise time variation with depth and stronger correlation with slip at shallow depths.</p><p> </p><p>The effects of the new characterization of shallow rupture kinematics on simulated ground motion was thoroughly investigated in broad-band (0-10Hz) simulations of the M7.1 2019 Ridgecrest California earthquake. The ground motion time histories were computed using the hybrid method of Graves and Pitarka (2010. In our simulations we considered several slip distributions, including two that were obtained by inverting recorded velocity and displacement ground motion, respectively.  Finally, through comparisons with recorded data, we analyzed the sensitivity of computed near-fault broad-band ground motion characteristics, including amplitude of ground motion velocity pulse, peak acceleration, and response spectra, to shallow slip characterization and location of strong motion generation areas for each rupture model. The proposed modifications to kinematic rupture models of crustal earthquakes provide improved simulation of broadband strong ground motion and seismic hazard assessment.</p><p><em>This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344</em></p>

Six Degree-of-Freedom Broadband Ground-Motion Observations with Portable Sensors: Validation, Local Earthquakes, and Signal Processing

2020 ◽  
Vol 110 (3) ◽  
pp. 953-969 ◽  
Author(s):  
Shihao Yuan ◽  
Andreino Simonelli ◽  
Chin-Jen Lin ◽  
Felix Bernauer ◽  
Stefanie Donner ◽  
...  
Keyword(s):  
Ground Motion ◽  
Central Italy ◽  
Rigid Base ◽  
Small Scale ◽  
Volcano Seismology ◽  
Source Inversion ◽  
Motion Sensitivity ◽  
Rotation Sensor ◽  
Wide Range ◽  
Portable Sensors

ABSTRACT The additional observation of three components of rotational ground motions has benefits for tilt-seismometer coupling (e.g., ocean-bottom seismometry and volcano seismology), local site characterization, wavefield separation, source inversion, glacial and planetary seismology, as well as the monitoring of structural health. Field applications have been mostly hampered by the lack of portable sensors with appropriate broadband operation range and weak-motion sensitivity. Here, we present field observations of the first commercial portable broadband rotation sensor specifically designed for seismology. The sensor is a three-component fiber-optic gyro strictly sensitive to ground rotation only. The sensor field performance and records are validated by comparing it with both array-derived rotation measurements and a navigation-type gyro. We present observations of the 2018 Mw 5.4 Hualien earthquake and the 2016 central Italy earthquake sequence. Processing collocated rotation and classical translation records shows the potential in retrieving wave propagation direction and local structural velocity from point measurements comparable to small-scale arrays of seismic stations. We consider the availability of a portable, broadband, high sensitivity, and low self-noise rotation sensor to be a milestone in seismic instrumentation. Complete and accurate ground-motion observations (assuming a rigid base plate) are possible in the near, local, or regional field, opening up a wide range of seismological applications.

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