Surface Rupture Earthquakes and the Mechanics of Earthquake Faulting

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The proposed work will develop new observations and data from historical groundrupturing earthquakes to improve understanding of the earthquake rupture process. Priorobservations have worked to define the role of fault geometry in rupture propagation, addressedand discounted self-similarity in the description of surface rupture slip distributions, shownclearly that fault rupture is not consistently uni- or bi-lateral, that earthquakes do not consistentlyinitiate on the section of fault ultimately recording maximum slip, and thatthe relationshipbetween average coseismic slip and rupture length for large strike-slip earthquakes appears torequire coseismic slip at progressively greater depths below the seismogenic layer as a functionof rupture length. Previous work was been limited by time and funding to a set of about threedozen large continental earthquakes which shared the characteristics that there existed (1) mapsof 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 thesurface slip distribution. The resulting compilation has already become a heavily cited andwidely used resource for the larger earthquake physics community. This work will extendprevious analyses to a list of more than twice as many earthquakes that have produced surfaceruptures but for which documentation may not simultaneously satisfy all three criteria. Thepremise of this proposal is that many observations and insights are yet to be gained in followinga 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 earthquakeprocess is at the heart of quantifying earthquake hazard imposed by mapped active faults; this isthe broadest and most practical impact of the proposed research. Other researchers havedeveloped numerical models of earthquake rupture behavior, but knowing how well they predictreal earth behavior depends on observational data from real ground ruptures. Research questionsinclude how far a rupture can jump from one fault to another, how angle deviations in a faulttrace affect rupture, how deep into the crust rupture extends, and how surface rupture correlateswith expected ground motions. As a practical example, the empirical observations will improvetools 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.