SCEC Award Number 16001 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Nonlinear attenuation of strong seismic waves, intact rock as a fragile geological feature, and modulation of tectonic strain by strong ground motions
Investigator(s)
Name Organization
Norman Sleep Stanford University
Other Participants
SCEC Priorities 6e, 6b, 2d SCEC Groups Geology, GMP, Seismology
Report Due Date 03/15/2017 Date Report Submitted 03/08/2017
Project Abstract
Strong seismic waves bring the subsurface beyond its elastic limit. In particular, surface waves produce strain that varies slowly with depth. The dynamic stress is strain times the stiffness. Failure occurs when this stress exceeds the frictional strength, cracking the rock and reducing the stiffness. The stiffness self-organizes with depth in the damaged zone so that failure is just reached in strong events, yielding an estimate of past shaking. We have used borehole data to confirm the predicted effects on stiffness from finite past water table depth and coefficients of friction depending on clay content occur. We have numerically modeled strong vertical S-waves at shallow depths. We used scaling relationships to study the rupture tip and the near fault environment of large earthquakes. We documented nonlinear interaction of S-waves with Rayleigh waves, which constrains three-dimensional frictional failure criteria.