SCEC Award Number 11010 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Study of the origin of shallow slip deficit in strike-slip earthquakes through simulations of earthquake sequences in elasto-plastic media
Name Organization
Yoshihiro Kaneko University of California, San Diego
Other Participants Fialko, Yuri
SCEC Priorities A7, A9, A10 SCEC Groups FARM, Seismology, Geodesy
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
Using simulations of spontaneous dynamic rupture with off-fault yielding, we have investigated whether the occurrence of inelastic deformation can account for shallow slip deficit inferred from slip inversions of several well-documented M7 earthquakes. Our results suggest that shallow slip deficit due to coseismic inelastic deformation occurs under a wide range of parameters that characterize strength of the uppermost crust and can account for some, but not all of, the slip deficit inferred from kinematic inversions of geodetic data. The goals of the project described in the 2011 proposal were (1) to estimate the amount of `artificial deficit' in a geodetic inversion procedure that is based on a purely elastic model, and (2) To quantify interseismic inelastic deformation and its contribution to coseismic shallow slip deficit. We have accomplished goal (1) and published the results in Geophysical Journal International (Kaneko and Fialko, 2011). Inelastic deformation in the shallow crust reduces coseismic strain near the fault, introducing an additional `artificial' deficit of up to 10 percent of the maximum slip in inversions of geodetic data that are based on purely elastic models. The largest magnitude of slip deficit in our models combined with the bias in inversions accounts for up to 25 percent of shallow slip deficit, which is comparable to those inferred from kinematic inversions. We also show that unresolvable interseismic creep may account for some of the remaining discrepancy. Currently, we have been working on (2), and so far, we have been testing several implicit numerical algorithms for interseismic inelastic deformation.
Intellectual Merit One of the SCEC science objectives is to determine the origin, evolution and implications of on- and off-fault damage. Our research project has resulted in an improved understanding of how inelastic deformation (or off-fault damage) in the vicinity of active faults influences the coseismic slip distribution in large strike-slip earthquakes. The results have also impacted interpretations of fault slip based on geodetic data, as inversions of geodetic data based on purely elastic models may lead to an artificial slip deficit.
Broader Impacts Determining the origin of the shallow slip deficit is important for estimating seismic hazard, as suppression of shallow rupture could influence strong ground motion in the vicinity of active faults. Our project has linked advances in earthquake source physics, crustal deformation, earthquake geology, and computational science. Results from our research have been broadly disseminated through conference presentations, seminars, and publications in peer-reviewed literature.
Exemplary Figure Figure 2. (a) An earthquake sequence in an elastic model with a velocity-strengthening shallow layer and a slower plate loading rate of 1 mm/yr. Solid lines show slip accumulation every 200 years, whereas dashed lines are plotted above 18-km depth every second during the simulated earthquakes. The surface creep rate during the interseismic period is ~0.15 mm/yr and the recurrence interval is 4800 years. (b) Coseismic slip distributions for the elastic case shown in panel a and the corresponding elasto-plastic case with rock cohesion of 0 MPa and internal friction of 0.98. The amount of coseismic slip deficit in the elasto-plastic and elastic simulations is 25% and 15%, respectively. Minor shallow creep during interseismic periods leads to a larger coseismic slip deficit. From Kaneko and Fialko (2011).