SCEC Award Number 11153 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Rupture and ground motions near an extensional stepover on the San Jacinto Fault with validation from precariously balanced rocks: Collaborative research with UC Riverside and San Diego State Univ.
Investigator(s)
Name Organization
David D. Oglesby University of California, Riverside Kim B. Olsen San Diego State University
Other Participants Julian Lozos
James Brune
SCEC Priorities A9, A10, B1 SCEC Groups GMP, FARM, SHRA
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
 We are using the most accurate nonplanar fault geometry and material parameterization to model the 3D fault dynamics in this region, and then using a new scattering methodology to produce broadband ground motion estimates. These ground motion estimates can be evaluated in light of the existence of various precariously balanced rocks in the region to both validate our method, and to look for preferred rupture scenarios. We have found that an intermediate fault in a stepover region can have an extremely strong effect on the ability of rupture to propagate through the stepover, as well as on the resultant near-source ground motion. In particular, an intermediate fault in an extensional stepover can significantly hinder rupture propagation through the stepover; in contrast, an intermediate fault in a compressional stepover typically aids in through-going rupture propagation. We also find that the ability of rupture to propagate through the stepover, as well as the resultant ground motion, are strongly affected by the nucleation location. The results may have important implications for seismic hazard in this area and other stepovers throughout Southern California and Beyond.
Intellectual Merit We have found that an intermediate fault in a stepover region can have an extremely strong effect on the ability of rupture to propagate through the stepover, as well as on the resultant near-source ground motion. In particular, an intermediate fault in an extensional stepover can significantly hinder rupture propagation through the stepover; in contrast, an intermediate fault in a compressional stepover typically aids in through-going rupture propagation. We also find that the ability of rupture to propagate through the stepover, as well as the resultant ground motion, are strongly affected by the nucleation location.
Broader Impacts The results may have important implications for seismic hazard in this area and other stepovers throughout Southern California and Beyond. This project has aided in the training of a graduate student, and the method developed herein will be of tremendous use in modeling ground motion in other regions with geometrically complex faults.
Exemplary Figure Figure 3. Peak horizontal ground motion for idealized fault stepover with intermediate fault segments of different length. Fault segments are in dashed white lines, with the nucleation point marked with a black star. Note that the intermediate fault serves to hinder rather than aid in through-going rupture for segment lengths between 5 and 10 km.