EAR-PF: Are large earthquakes like small earthquakes? Using synthetic earthquakes to resolve discrepancies in observations of earthquake stress drop magnitude-invariance

Neely, James Scott, Evanston IL

Investigators

Abstract

Dr. James Neely has been awarded an NSF EAR Postdoctoral Fellowship to assess whether small and large earthquakes release energy in the same way. This work will be conducted at the University of Chicago in collaboration with Dr. Sunny Park and Dr. Annemarie Baltay of the U.S. Geological Survey. Larger earthquakes release more energy than smaller earthquakes, but how earthquakes release that energy is not as well understood, despite having important implications for seismologists’ understanding of earthquake processes and, crucially, the seismic hazards that earthquakes pose. Specifically, the way that a given earthquake releases energy determines, at least in part, how strong the shaking will be (which should, in turn, inform building safety standards, etc.). Using computer simulations, Dr. Neely will examine assumptions about how earthquakes release energy and assess whether insights from small earthquakes can help us better understand the hazards posed by rarer, large earthquakes. Additionally, Dr. Neely will work on an initiative to foster knowledge-sharing relationships between Illinois state legislators and researchers within the state. In this project, Dr. Neely will examine the question of whether earthquake stress drop—the decrease in stress along a fault due to an earthquake—is magnitude-invariant. Earthquake stress drop is thought to control the levels of high-frequency shaking that damages buildings, and it may provide insight into earthquake rupture dynamics. Some studies suggest that earthquake stress drop is constant with earthquake magnitude, while others indicate that it varies systematically with magnitude. Because seismologists cannot directly measure stress drop, they cannot compare estimates to the true value, so it is not known which methods are most accurate. Dr. Neely will overcome this issue by generating a large dataset of synthetic earthquakes with known stress drops and then apply four commonly used stress drop estimation methods to this dataset. To simulate real earthquake data, Dr. Neely will generate earthquakes that differ from the simple earthquake models assumed by the stress drop methods and examine how well the stress drop estimates match the true values. Dr. Neely will identity which stress drop method is most accurate and then examine a large dataset of real earthquakes to determine whether stress drop is or is not magnitude-invariant. If stress drop magnitude-invariance is true, seismologists can measure the stress drops of a region’s past small earthquakes to gain insight into the stress drops, and potential shaking levels, of future large earthquakes. But if stress drop magnitude-invariance is false, then seismological models—and as a result policy preparations, including building codes—for this future shaking may be wrong and need major revisions. In addition to this stress drop analysis, Dr. Neely will work to expand the Science One-Pager Initiative (SOPI), an Illinois-based program where graduate students and post-doctoral researchers provide short analyses of scientific topics to state legislators. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.