scholarly journals Centroid moment tensor inversions of offshore earthquakes using a three-dimensional velocity structure model: slip distributions on the plate boundary along the Nankai Trough

2020 ◽  
Vol 222 (2) ◽  
pp. 1109-1125 ◽  
Author(s):  
Shunsuke Takemura ◽  
Ryo Okuwaki ◽  
Tatsuya Kubota ◽  
Katsuhiko Shiomi ◽  
Takeshi Kimura ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Seismic Wave ◽  
Velocity Structure ◽  
Nankai Trough ◽  
Moment Tensor ◽  
Plate Boundary ◽  
Seismic Wave Propagation ◽  
Structure Model ◽  
Centroid Moment Tensor ◽  
Heterogeneous Distribution

SUMMARY Due to complex 3-D heterogeneous structures, conventional 1-D analysis techniques using onshore seismograms can yield incorrect estimation of earthquake source parameters, especially dip angles and centroid depths of offshore earthquakes. Combining long-term onshore seismic observations and numerical simulations of seismic wave propagation in a 3-D model, we conducted centroid moment tensor (CMT) inversions of earthquakes along the Nankai Trough between April 2004 and August 2019 to evaluate decade-scale seismicity. Green's functions for CMT inversions of earthquakes with moment magnitudes of 4.3–6.5 were evaluated using finite-difference method simulations of seismic wave propagation in the regional 3-D velocity structure model. Significant differences of focal mechanisms and centroid depths between previous 1-D and our 3-D catalogues were found in the solutions of offshore earthquakes. By introducing the 3-D structures of the low-velocity accretionary prism and the Philippine Sea Plate, dip angles and centroid depths for offshore earthquakes were well-constrained. Teleseismic CMT also provides robust solutions, but our regional 3-D CMT could provide better constraints of dip angles. Our 3-D CMT catalogue and published slow earthquake catalogues depicted spatial distributions of slip behaviours on the plate boundary along the Nankai Trough. The regular and slow interplate earthquakes were separately distributed, with these distributions reflecting the heterogeneous distribution of effective strengths along the Nankai Trough plate boundary. By comparing the spatial distribution of seismic slip on the plate boundary with the slip-deficit rate distribution, regions with strong coupling were clearly identified.

Simulation of induced seismic ground motions using coupled geomechanical and seismic wave propagation models

2019 ◽  
Author(s):  
Bob Paap ◽  
Dirk Kraaijpoel ◽  
Brecht Wassing ◽  
Jan-Diederik van Wees
Keyword(s):  
Wave Propagation ◽  
Seismic Wave ◽  
Ground Motions ◽  
Moment Tensor ◽  
Seismic Wave Propagation ◽  
Fault Reactivation ◽  
Dynamic Rupture ◽  
Propagation Models ◽  
Earthquake Nucleation ◽  
Spatio Temporal

Summary Numerical simulations of seismic wave propagation usually rely on a simple source model consisting of an idealized point location and a moment tensor. In general, this is a valid approximation when the source dimensions are small relative to the distance of points at which the seismic wave motions are to be evaluated. Otherwise, a more realistic spatio-temporal source representation is required to accurately calculate ground motions at the position of monitoring stations. Here, we present a generic approach to couple geomechanical simulations to seismic wave propagation models using the concept of the equivalent force field. This approach allows the simulation of seismic wave propagation resulting from the spatio-temporal dependent earthquake nucleation and rupture processes. Within the geomechanical package two separate geomechanics codes are used to simulate both the slow loading stage leading to earthquake nucleation as well as the successive dynamic rupture stage. We demonstrate the approach to a case of induced seismicity, where fault reactivation occurs due to production from a natural gas reservoir.

scholarly journals Seismic Wave Propagation and Inversion with Neural Operators

2021 ◽  
Vol 1 (3) ◽  
pp. 126-134
Author(s):  
Yan Yang ◽  
Angela F. Gao ◽  
Jorge C. Castellanos ◽  
Zachary E. Ross ◽  
Kamyar Azizzadenesheli ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Wave Equation ◽  
Seismic Wave ◽  
Automatic Differentiation ◽  
Velocity Structure ◽  
Waveform Inversion ◽  
Seismic Wave Propagation ◽  
Source Location ◽  
Velocity Models ◽  
Reverse Mode

Abstract Seismic wave propagation forms the basis for most aspects of seismological research, yet solving the wave equation is a major computational burden that inhibits the progress of research. This is exacerbated by the fact that new simulations must be performed whenever the velocity structure or source location is perturbed. Here, we explore a prototype framework for learning general solutions using a recently developed machine learning paradigm called neural operator. A trained neural operator can compute a solution in negligible time for any velocity structure or source location. We develop a scheme to train neural operators on an ensemble of simulations performed with random velocity models and source locations. As neural operators are grid free, it is possible to evaluate solutions on higher resolution velocity models than trained on, providing additional computational efficiency. We illustrate the method with the 2D acoustic wave equation and demonstrate the method’s applicability to seismic tomography, using reverse-mode automatic differentiation to compute gradients of the wavefield with respect to the velocity structure. The developed procedure is nearly an order of magnitude faster than using conventional numerical methods for full waveform inversion.

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