SCEC Award Number 15120 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Robust Quantification of Earthquake Clustering: Overcoming the Artifacts of Catalog Uncertainties
Investigator(s)
Name Organization
Ilya Zaliapin University of Nevada, Reno Yehuda Ben-Zion University of Southern California
Other Participants One Undergraduate Student at UNR (TBN); One Graduate Student at USC (TBN)
SCEC Priorities 2b, 2f, 4e SCEC Groups Seismology, EFP, CSEP
Report Due Date 03/15/2016 Date Report Submitted 03/09/2016
Project Abstract
 The project aimed at improving the ability to use seismicity clusters to clarify physical processes associated with faulting in the crust. Specific science targets included (i) understanding the effects of (space-time varying) errors in earthquake catalogs and distinguishing such errors from genuine changes of seismicity, and (ii) finding cluster signatures that can distinguish natural from human-induced seismicity. The project builds on the PIs results from previous SCEC projects on quantitative characterization of earthquake clustering in space and time in relation to different event sizes and physical properties of the lithosphere.
First, we document and quantify effects of catalog uncertainties on results of statistical cluster analyses of seismicity in southern California. We present statistical evidence for three artifacts: (1) Increased distance between offspring and parents. (2) Underestimated clustering. (3) Overestimated background rates. We also find that short-term incompleteness leads to (4) Apparent magnitude dependence and temporal fluctuations of b-values. Next, we analyze statistical features of background and clustered subpopulations of earthquakes in different regions in an effort to distinguish between human-induced and natural seismicity. Induced seismicity is shown to have (i) higher rate of background events, (ii) faster temporal offspring decay, (iii) higher rate of repeating events, (iv) larger proportion of small clusters, and (v) larger spatial separation between parent and offspring.
The results can inform a range of studies focused on small-magnitude seismicity patterns in the presence of catalog uncertainties, as well as to improve seismic hazards assessment related to induced earthquakes.
Intellectual Merit The study combines novel approaches to earthquake cluster identification/classification and high quality earthquake catalogs from different environments toward improved understanding of seismicity in relation to human-induced earthquakes. An ability to track the evolving response of the crust to different loadings may be used to monitor the build up of stress in a region. The developed tools and results can have transformative impact on analysis of seismic hazard in active tectonic environments, oil and other production areas, and regions containing both, such as California.
Broader Impacts The addressed problems on natural/induced seismicity have critical societal and economic importance. The research can inform and impact significantly various related studies on earthquake physics. The developed cluster framework can be applicable to other processes that develop in space-time-energy domains (e.g., river/subsurface flows, aerosol dynamics, chemical reactions, and fires).
Exemplary Figure Figure 3: Change of clustering style in Coso and Salton Sea geothermal fields after beginning of active geothermal production. Figure shows the distribution of the rescaled time to parent T for the offspring within one parent rupture length from the parent. (a,c) Coso geothermal field; production began in 1987. (b,d) Salton Sea geothermal field; production began during 1988-1992. (a,b) Offspring before geothermal production. (c,d) Offspring during geothermal production. After Zaliapin and Ben-Zion, BSSA (2016).