SCEC Award Number 20065 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Space-time variations of background seismicity in southern California
Name Organization
Ilya Zaliapin University of Nevada, Reno Yehuda Ben-Zion University of Southern California
Other Participants Graduate Student @ UNR, Graduate student @USC
SCEC Priorities 2e, 3d, 1d SCEC Groups Seismology, EFP, FARM
Report Due Date 03/15/2021 Date Report Submitted 03/15/2021
Project Abstract
The project is aimed at developing methodology and analyzing the dynamics of seismicity in relation to preparation processes of large earthquakes and long-term evolution of seismic patterns. The project particularly focused on examining a special form of non-stationary behavior – evolving localization of background seismicity. The project resulted in refined techniques for analyzing localization of seismicity with a focus on the complex plate-boundary region in Southern California (SoCal) and Alaska. The research on localization of background seismicity combined current efforts in earthquake declustering, coalescent representation of seismicity, and a novel technique for quantifying time-dependent spatial localization of earthquakes. The research used the current updated version of the Hauksson et al. [2012] relocated catalog, and other catalogs for California and Alaska. The project trained graduate students and facilitate cross-disciplinary collaboration between UNR and USC.
Intellectual Merit The project developed a methodology for robust quantification of space-time localization of earthquakes – one of the principal mechanisms of generation of large earthquakes. The methodology has been applied to (i) Quantifying regional localization of raw and background seismicity in Southern California, and (ii) Quantifying time-dependent localization associated with preparation processes of large earthquakes in Southern California and Alaska. The project contributed to the general theory of random self-similar trees that are used to represent earthquake flow and are the essential element of nearest-neighbor cluster analyses (including earthquake declustering). The project also examined environmental earthquake triggering in Southern California.
Broader Impacts The project results have an impact on research areas outside of the immediate project scope. The project develops a novel method for localization of earthquake damage and coalescence of fractures prior to a large earthquake, and contributed to the general theory of random self-similar trees that has applicability beyond seismology.
Exemplary Figure Figure 1
Localization of background seismicity in Southern California. (Top) Relative localization with respect to a previous time interval. Its positive values indicate that the current spatial background distribution is a localized version of the earlier one – it has the same support and co-located yet more prominent peaks. (Bottom) Absolute localization. Its higher values indicate stronger deviation from the uniform spatial measure, or spikiness. The localization is estimated using square cells with linear size  = 0.4, windows w1 = 3yr (current distribution), w2 = 5yr (earlier distribution), and threshold P0 = 10 (minimal number of events in a cell). The four large earthquakes with M > 7 are marked by red vertical lines. Every target event occurred within 4 years after the localization peak. The blue arrows indicate the lead time from localization peak to a large event.