Collaborative Research: New Approaches to Earthquake Stress Drop Estimation and Understanding Variations in High-Frequency Seismic Radiation

Earthquakes of similar size vary in the strength of the damaging ground motion that they produce. Understanding why this variation occurs is important for making better predictions of future ground motions during earthquakes. One approach to describing these differences involves a quantity termed "stress drop," which is related to the amount of energy released during earthquakes. However, earthquake stress-drop estimates from different groups of scientists often show poor agreement, showing that there are problems in our understanding of earthquakes. This project will improve stress drop measurements and other measures of earthquake behavior, including providing error estimates. Work will focus on California and New Zealand, both regions of high seismic activity and hazard. It will use data from national networks of seismic stations in both countries. The project will improve collaboration between scientists in the United States and New Zealand, and provide training for students and early career researchers. This project will investigate outstanding issues related to earthquake physics by developing new, robust approaches to quantify variations in high-frequency radiation from earthquakes. Such variations have long been observed in stress-drop studies but are subject to large uncertainties owing to poorly constrained seismic attenuation and non-unique model parameterizations. This has inhibited progress in evaluating the true variability in stress release during rupture and its dependence, if any, on seismic magnitude, depth, time, and tectonic regime. Recent work comparing results from different groups has shown that relative values of stress drop among nearby earthquakes are more reliably resolved than their absolute values. This project will jointly perform systematic analyses of high-frequency radiation from earthquakes and develop new methods to quantify and reduce uncertainties while identifying any spatial or temporal variations. The project aims to investigate the origins of these variations, and to test whether similar features exist in other tectonic settings, by analyzing key aftershock and seismicity clusters in New Zealand and working with local seismologists there to understand their properties. 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.