18-8. Novel crustal deformation models for characterizing deformation rates with application to the Uniform California Earthquake Rupture Forecast

The mission of the USGS Earthquake Science Center is to conduct basic and applied research on earthquakes, especially as related to quantifying seismic hazard and mitigating the effects of earthquakes in the United States and elsewhere.  Crustal deformation models are a key component of many of the USGS’s most important earthquake hazard products. Such models provide estimates of present-day fault slip rates for the 3rd Uniform California Earthquake Rupture Forecast (UCERF3) and the U.S. National Seismic Hazard Model (NSHM). Crustal deformation models constrained by surface-based geodetic observations are used after damaging earthquakes to quantify coseismic and post-seismic deformation, including fault afterslip and off-fault deformation as well as stress and strain transfer to nearby, potentially hazardous faults.  Owing in part to the difficulties in separating long-term fault slip rates from short-term, geodetically observed transients, crustal deformation models have been underutilized in UCERF. However, there is great potential for leveraging geodetic crustal deformation models to provide critical constraints on fault slip rates and strain rates that will complement the geologic slip-rate data that is now primarily used in calculating earthquake rupture probabilities in UCERF3.

UCERF3 requires characterization of long-term slip rates on regional faults combined with instrumental and paleoseismic data on frequency and slip per event of past earthquakes to calculate earthquake rupture probabilities; the NSHM then combines this information with ground motion models to generate probabilistic seismic hazard maps. Crustal deformation data are well-suited to characterize both long-term slip rates on known faults and rates of more diffuse deformation in the adjacent crust in order to constrain the additional hazard posed by distributed (or unknown) faults. There is a wealth of geodetic data that can be brought to bear on deformation models that inform fault slip rates, including continuous and survey-mode Global Positioning System (GPS); interferometric processing of synthetic aperture radar (InSAR), and Mobile Laser Scanning (MLS).  These constitute large data sets that yield contemporary crustal strain rates and contribute to other models that help quantify long-term deformation rates, allowing us to determine which areas of a fault are likely to have relieved their accumulated strain in an earthquake, how much of the deformation budget is released aseismically, and how crustal strain transients evolve after an earthquake due to ongoing surface slip, deep afterslip, and/or viscoelastic relaxation. Models based on these types of data can contribute to subsequent UCERF models by providing estimates of long-term slip rates on known faults, the sense of slip on faults (e.g., strike slip or thrust), `off-fault’ deformation rates in areas of diffuse seismicity where multiple slowly-slipping faults exist (or a dominant fault has not been identified), and information on the distribution of interseismic creep. 

Possible avenues of research for this Mendenhall position include, but are not limited to, leveraging time-independent block models to provide slip rates on block-bounding faults and estimates of distributed deformation rates within selected blocks; exploring both fault-based and continuum models to estimate deformation rates on known faults and/or areas of diffuse deformation; evaluating the influence of time-dependent earthquake-cycle effects in block models or fault-based and continuum models in order to better quantify the uncertainties in fault slip rates; investigating how transient, earthquake cycle effects might create discrepancies between geologic and geodetic slip rates and what impact the uncertainties and biases in each have on UCERF3 and the NSHM; and better characterizing aseismic fault slip, either by improved observational constraints or via an improved understanding of how this influences effective rupture area and/or slip rates.  Deformation modeling approaches that include robust estimation of uncertainties are especially encouraged in order to better quantify how regional deformation rates can best be used to constrain spatial and temporal variations in fault loading in the seismogenic crust for robust determination of earthquake rupture probabilities.

Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.

Proposed Duty Station: Moffett Field, CA

Areas of PhD: Geophysics, seismology, or related fields (candidates holding a Ph.D. in other disciplines, but with extensive knowledge and skills relevant to the Research Opportunity may be considered).

Qualifications: Applicants must meet the qualifications for: Research Geophysicist

(This type of research is performed by those who have backgrounds for the occupations stated above.  However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Human Resources Office Contact: Audrey Tsujita, 916-278-9395, atsujita@usgs.gov