large-scale 3-d simulations of spontaneous rupture and wave propagation in complex, nonlinear media...
TRANSCRIPT
Large-scale 3-D Simulations of Spontaneous Rupture and Wave Propagation in Complex, Nonlinear Media
Roten, D.1, Olsen, K.B.2, Day, S.M.2, Dalguer, L.A.1 and Fäh, D.1
1 Swiss Seismological Service / ETH Zürich2 San Diego State University
Annual Meeting of the Seismological Society of America17-19 April, Salt Lake City, UT
Annual Meeting of the Seismological Society of America, April 17-19 2013, Salt Lake City, UT
Introduction
2
• Advances in computer codes and increases in computational resources enable numerical prediction of ground motions at increasingly higher frequencies, e.g.:- M8 up to 2 Hz (Cui et al., 2010)- Chino Hills EQ up to 5 Hz
• Nonlinear behavior of soft soils should be taken into account when predicting ground motions at frequencies above ~1 Hz
• Nonlinear material behavior may also occur in the damage zone around the fault (on- and off-fault plasticity; e.g. Andrews (2005), Ma (2008).
3Annual Meeting of the Seismological Society of America, April 17-19 2013, Salt Lake City, UT
Implementation of damage rheology in AWP-ODC
Non-associative Drucker-Prager plasticity with yielding in shear (based on guidelines from SCEC/USGS Spontaneous Rupture Code Verification Project):
4Annual Meeting of the Seismological Society of America, April 17-19 2013, Salt Lake City, UT
Implementation of damage rheology in AWP-ODC
Return map algorithm:
Time-dependent relaxation (Andrews, 2005):
5Annual Meeting of the Seismological Society of America, April 17-19 2013, Salt Lake City, UT
• Staggering of grid requires interpolation of missing elements in stress tensor and initial stresses from adjacent nodes
• Optimization that reduces number of interpolations results in significantly reduced computational cost
Material model CPU time per iteration Normalized CPU time
Elastic 0.18 s 100%
Elastoplastic 0.68 s 378%
Elastoplastic optimized 0.29 s 161%
Computational aspects
6Annual Meeting of the Seismological Society of America, April 17-19 2013, Salt Lake City, UT
Verification against SCEC/USGS TPV13
• Spontaneous rupture on a planar, dipping fault (approximated by vertical fault in AWP-ODC)
c = 5 Mpa
tan(φ) = 0.85
Tv = 0 s
7Annual Meeting of the Seismological Society of America, April 17-19 2013, Salt Lake City, UT
Convergence test (vertical strike-slip fault)
8Annual Meeting of the Seismological Society of America, April 17-19 2013, Salt Lake City, UT
ShakeOut Earthquake Scenario
• Based on kinematic source description (Graves et al., 2008)• visco-elastic medium
9Annual Meeting of the Seismological Society of America, April 17-19 2013, Salt Lake City, UT
ShakeOut Earthquake Scenario with Plasticity
10
Annual Meeting of the Seismological Society of America, April 17-19 2013, Salt Lake City, UT
QuickTime™ and aMotion JPEG OpenDML decompressor
are needed to see this picture.
11
Annual Meeting of the Seismological Society of America, April 17-19 2013, Salt Lake City, UT 11
ShakeOut Earthquake Scenario with Plasticity
Visco-elasto-plasticVisco-elastic
12
Annual Meeting of the Seismological Society of America, April 17-19 2013, Salt Lake City, UT
ShakeOut Earthquake Scenario with PlasticityFinal Principal Plastic Strain η at surface
13
Annual Meeting of the Seismological Society of America, April 17-19 2013, Salt Lake City, UT
ShakeOut Earthquake Scenario with PlasticityFinal Principal Plastic Strain η at z = 600 m
14
Annual Meeting of the Seismological Society of America, April 17-19 2013, Salt Lake City, UT
Conclusions
• We have implemented damage rheology based on the Drucker-Prager yield condition into the highly scalable 3D finite difference code AWP-ODC
• The method has been validated against four finite element codes in the framework of the SCEC/USGS Spontaneous Rupture Code Verification Project
• Computational cost of modeling plasticity amounts to an additional ~60% of the CPU time required for an elastic simulation
• We simulate the ShakeOut-K earthquake scenario for a visco-elasto-plastic material, assuming that cohesions range from ~50 kPa in low-velocity sediments near the surface to several MPa at depth
• Our results suggest that long-period (< 2 s) ground motion in the Los Angles area, amplified by a wave guide of interconnected sedimentary basins, could be significantly reduced as compared to visco-elastic solutions
• Improved calibration of additional parameters (cohesion C and friction angle ϕ is required to reliably predict off-fault plasticity and nonlinear behavior of near-surface deposits