Seismological Investigations of Earthquakes and Deep Earth Structure

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Networks of global seismic stations now record vast amounts of data, which have a wealth of information about both earthquakes and deep Earth structure. However, analysis of these data has lagged because traditional methods are time-intensive and do not fully exploit the capabilities of modern computers. By applying automated methods to hundreds or thousands of seismograms, it is often possible to resolve new features in the data, or to perform more comprehensive analyses of problems that were previously addressed on smaller scales. This U.C. San Diego project develops and applies these new methods to examine a variety of topics. These include: (1) Using scattered seismic waves to understand the frequency and strength of small-scale structures in the deep Earth, (2) Comparing and testing different methods to image large earthquake ruptures, (3) Examining the frequency content of seismic waves to test whether large earthquakes differ in fundamental ways from smaller earthquakes, and (4) Studying sharp interfaces in the Earth's upper mantle using reflections of seismic waves off these boundaries. This research is likely to lead to improved models of Earth structure and earthquake rupture processes.The increasing availability of large numbers of high-quality digital records from the global seismic networks has made possible a variety of new ways to study earthquakes and deep Earth structure. By analyzing hundreds or thousands of seismograms, it is often possible to resolve new features in the data, or to perform more comprehensive analyses of problems that were previously addressed on smaller scales. This project will continue analyses of global seismic data at U.C. San Diego to examine a variety of geophysical issues. These include: (1) Observation and modeling of scattered energy between major body-wave seismic phases to constrain the statistical properties of mantle heterogeneity at scale lengths shorter than can be resolved using seismic tomography, (2) Exploration of the resolution limits of back-projection compared to finite-fault and multiple-CMT approaches for resolving complex ruptures, and systematic application of back-projection to study recent large earthquakes, (3) Analysis of teleseismic P-wave spectra to estimate stress drops and radiated energy from large earthquakes and address earthquake scaling issues, (4) Stacking global and USArray seismograms to resolve upper-mantle discontinuities using topside reflections. This project supports the educational program at U.C. San Diego by providing funds for graduate and postdoctoral students. This research is likely to lead to improved models of Earth structure and earthquake rupture processes, which will be of interest to the tectonics, geodynamics and mineral physics communities. Some of the results may help inform and contribute to future estimates of seismic risk from large earthquakes. Results will be widely disseminated through publications, conference presentations, and material provided to SIO?s education and outreach programs.