Surface Rupture Earthquakes and the Mechanics of Earthquake Faulting

Board Of Regents, Nshe, Obo University Of Nevada, Reno, Reno NV

Investigators

Abstract

The proposed work will develop new observations and data from historical ground rupturing earthquakes to improve understanding of the earthquake rupture process. Prior observations have worked to define the role of fault geometry in rupture propagation, addressed and discounted self-similarity in the description of surface rupture slip distributions, shown clearly that fault rupture is not consistently uni- or bi-lateral, that earthquakes do not consistently initiate on the section of fault ultimately recording maximum slip, and thatthe relationship between average coseismic slip and rupture length for large strike-slip earthquakes appears to require coseismic slip at progressively greater depths below the seismogenic layer as a function of rupture length. Previous work was been limited by time and funding to a set of about three dozen large continental earthquakes which shared the characteristics that there existed (1) maps of the surface rupture trace, (2) maps of the nearby active faults that did not rupture, and (3) measurements of coseismic offset at many points along the strike of the rupture to define the surface slip distribution. The resulting compilation has already become a heavily cited and widely used resource for the larger earthquake physics community. This work will extend previous analyses to a list of more than twice as many earthquakes that have produced surface ruptures but for which documentation may not simultaneously satisfy all three criteria. The premise of this proposal is that many observations and insights are yet to be gained in following a similar approach and extending the analysis to these additional surface rupturing earthquakes. Broader Significance: Placing observational bounds on our efforts to understand the physics of the earthquake process is at the heart of quantifying earthquake hazard imposed by mapped active faults; this is the broadest and most practical impact of the proposed research. Other researchers have developed numerical models of earthquake rupture behavior, but knowing how well they predict real earth behavior depends on observational data from real ground ruptures. Research questions include how far a rupture can jump from one fault to another, how angle deviations in a fault trace affect rupture, how deep into the crust rupture extends, and how surface rupture correlates with expected ground motions. As a practical example, the empirical observations will improve tools to define the expected endpoints and thus rupture lengths of earthquakes in California. Funding will also contribute to the training of a graduate-level geoscience student.