SCEC Award Number 16170 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Physical and observational reasons for the lack of conspicuous induced seismicity in Central California
Investigator(s)
Name Organization
Emily Brodsky University of California, Santa Cruz Thomas Goebel University of California, Santa Cruz
Other Participants
SCEC Priorities 2f, 4a, 2a SCEC Groups SDOT, FARM, Seismology
Report Due Date 03/15/2017 Date Report Submitted 07/06/2017
Project Abstract
 California is the third largest oil producing state in the United States with a history of oil extraction that dates back more than 100 years. Many hydrocarbon reservoirs in California require invasive injection methods to mobilize trapped oil and boost production. One of the unintended site effects of such injection activity are induced earthquakes triggered by waste fluid injection and hydraulic fracturing (e.g. Keranen et al. 2013; Holland 2013). Fluid injection is common practice throughout California oilfields yet no significant increase in seismicity rates has been detected (Goebel 2015).
This project focuses on the apparent absence of large-scale induced seismicity in California oilfields. We investigate two primary contributors that may explain the lack of induced seismicity: 1) limitations within the seismic record due to instrumental constraints; 2) physical contributions related to reservoir characteristics, stress distributions and local geology.
Our results highlight that instrumental issues significant limit the ability to detect small earthquakes in California sedimentary basins. In addition, location uncertainties are high especially in regions between Northern and Southern California further complicating the statistical association of earthquake activity and injection wells.
In addition, we find that reservoir characteristics significantly differ between Oklahoma, the state with the most severe increase in induced seismicity and California. The relatively homogeneous vertically stratified sedimentary basins in Oklahoma allow for efficient large-scale poroelastic stressing to distances of more than 40 km (Goebel et al, 2017). Such large-scale induced stress changes are likely absent in highly compartmentalized California oil fields.
Intellectual Merit The study addresses four SCEC science objectives, i.e.,
2f: Improved understanding of induced seismicity and induced seismicity potential in different geologic and tectonic regions.
4a & 4b: by improving our understanding of crustal heterogeneity and the role of faults as fluid conduits or barriers;
2a: by assessing the quality of earthquake catalogs in small regions and by extending earthquake catalogs using template matching and joint-event-relocation methods.

In addition, induced seismicity sequences allow for the study of foreshocks and systematic event migration prior to the largest magnitude event of a sequence (EFP) which is rarely observed for tectonic earthquake sequences.
Broader Impacts Our study addressed some fundamental questions about fault zone hydrology and the connection between crustal heterogeneity and induced poroelastic stresses.
A more in-depth understanding of conditions that lead to more severe seismogenic consequences to fluid injection activity may also help guide future seismic hazard mitigation strategies.
Exemplary Figure

The Fairview earthquake sequence which occurred in Northwestern Oklahoma between 2014 to 2016, provides evidence for long-range poroelastic stressing in Oklahoma. The figure shows the expected extent and amplitude of pore pressure perturbation (see color-bar) as a result of fluid injection into wastewater disposal wells (blue triangles) based on a semi-analytical model of radial flow in the Arbuckle formation (from Goebel et al. 2017). The significant difference in geological setting in California likely prevents such large-scale poroelastic stresses to unfold.
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