NSF/EAR-BSF:Aftershock Productivity in Context of Rupture Kinematics

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Aftershock studies have blossomed in the current data-rich era. Substantial progress has been made in empirically predicting how many aftershocks are produced in the aftermath of an earthquake. Although predicting the timing and size of aftershocks have received more attention historically, the expected total number of aftershocks is just as robust an observation. In general, a magnitude 7 earthquake produces 10 times as many aftershocks as a magnitude 6 and the pattern continues for all magnitudes, i.e., the number of aftershocks increases by a factor of 10 for each magnitude unit. The project asks why does aftershock production follow this pattern? What information does it contain about earthquake mechanics? Why do some earthquakes, like the 2017 Chiapas earthquake produce many aftershocks, while others, like the 2017 Mexico City earthquake produce only a few? And most importantly, can this information be used to anticipate the aftershock production in the critical days following a disaster? This project has broader implications for our understanding of earthquake hazards, and adds to the US-Israel scientific partnership. The work will also support graduate students and an undergraduate researcher to conduct research as part of the project. Significant effort has been spent on these questions utilizing tools from statistical seismology. Many studies have focused on regional earthquakes, where statistics are most robust. Separating out the causes of aftershock production can benefit from information of the slip patterns of individual mainshocks that can be derived using global seismic data. Previous studies have strived to attack this problem by combining aftershock data with information about the timing and distribution of slip. The studies have been insightful, but have generally lacked the number of mainshocks required for statistical analysis. This lack has been, in part, because until recently slip maps were sufficiently difficult that they were only available for a small number of cases. Therefore, it was difficult to ask questions about the relation between aftershocks and mainshock rupture since different models are biased in different ways. This situation has changed dramatically with recently published large compilations of rupture sequences done uniformly with a single method. This work exploits a new era of combining information from kinematic ruptures and their ensuing aftershocks. The researchers will capitalize on this capability and attack aftershock productivity by: (1) using the spatial distribution of aftershocks relative to well-resolved coseismic slip maps to clarify physical origins of the magnitude dependence, (2) investigating regional variations in productivity, and (3) examining the interrelationship between aftershock productivity, regional strength, and arrest criteria for mainshock rupturesThis 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.