SCEC Award Number 19071 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Data-driven characterization of spatio-temporal aftershock evolution and consequences for earthquake source processes
Investigator(s)
Name Organization
Egill Hauksson California Institute of Technology
Other Participants Men-Andrin Meier, Associate Staff Seismologist
SCEC Priorities 1d, 3a, 2c SCEC Groups Seismology, FARM, CXM
Report Due Date 03/15/2020 Date Report Submitted 03/30/2020
Project Abstract
 We have used high quality seismicity catalogs from California and from Japan to develop a novel method for characterizing individual earthquake ruptures and seismicity sequences, in a data-driven, objective and fully automatable way. The core of the method is an eigenvalue decomposition of earthquake hypocenter clusters to characterize the evolution of event sequences in space and time.
We have been able to use this method i) to derive novel earthquake source scaling relationships that span an unprecedented magnitude range and cover the medium and small magnitude events, which are usually outside the applicability window of existing methods; ii) to gain data-driven insights into various aspects of earthquake triggering processes and statistics, including for on-fault versus off-fault triggering; iii) to test various source physics hypotheses, such as the rupture aspect ratio would change above a threshold magnitude; anomalous Brune-type stress drops would represent untypical rupture sizes; the rupture area would be devoid of seismicity because of complete or near-complete stress drop; iv) to perform fully automated, rapid source dimension estimates during an ongoing earthquake sequence in near-real time and can be used for fault plane identification, as well as for association with known faults. Because of the constantly improving detection sensitivities of our seismic network and monitoring methods, the small events that the method uses and characterizes become increasingly important for a wide range of seismological research domains, including hazard estimates and fault characterization.
Intellectual Merit The project relates to the basic questions no. 1) and 2) in the 2019 SCEC Science Plan in that the seismicity characterizations offer a window into the on- and off-fault structure and behavior of faults, not just at the scale of the few large earthquakes for which we have a wide range of observations, but also for the plethora of smaller events that are harder to characterize. The insights on earthquake triggering will allow us to address questions of earthquake predictability (basic question no. 5), and to provide yet another brick for the house of effective real-time seismic risk reduction.
Broader Impacts In earthquake seismology we are interested in the physical processes that play out when earthquake ruptures unfold. In all but the rarest cases, the place of rupture is entirely inaccessible and we can only use indirect information to infer the rupture processes. Most earthquake source properties are therefore inherently under-constrained from an observational perspective (Kaneko and Shearer, 2015). In this context, aftershock observations provide an invaluable source of information, since their occurrence, and the patterns with which they occur, are directly or indirectly related to the source processes we wish to infer. Since we can locate aftershocks with high precision (e.g. Trugman and Shearer, 2017; Hauksson et al., 2012; Waldhauser and Schaff, 2008), aftershock catalogs are among the sharpest tools that we can use to map inaccessible source processes.
Exemplary Figure Figure 5. Best fit regression relations between rupture dimensions of mainshocks and their respective magnitudes for southern California re-located seismicity; Meier et al., in preparation; Meier et al, in preparation.