26. Studying Slow Earthquakes in Cascadia with Borehole Strainmeter Data

The U.S. Geological Survey is the agency with authority to issue geologic hazards warnings with respect to earthquakes and volcanoes, and, to exercise this authority, conducts research aimed at assessing earthquake hazards and developing earthquake forecast methodologies. An important aspect of this research entails determining rates of aseismic deformation on and around faults with high earthquake potential, as well as the variation of these rates in space and in time. This information is used to help estimate the magnitudes and recurrence intervals of future earthquakes, important information in estimating the seismic hazard that the built environment must be designed to withstand.

USGS scientists utilize a variety of geodetic techniques to monitor the aseismic deformation of active faults. Beginning in 2004, the Plate Boundary Observatory (PBO), part of the National Science Foundation Earthscope Initiative, will deploy a large number of continous GPS receiving stations and borehole strainmeters in the western United States, greatly expanding the crustal deformation data set available to study earthquake and volcano hazards. We are particularly interested in research to enhance the utilization of borehole strainmeter data because these instruments provide a means of observing transient slip on active seismogenic faults. A unique opportunity is presented by PBO's plan to install twelve borehole strainmeters, with co-located downhole seismometers, in northwestern Washington during 2004 and 2005, to record "slow earthquakes" on the Cascadia subduction zone, which last a few weeks, recur every 13-16 months, and are accompanied by slip comparable to a magnitude 6.5 or greater earthquake as well as associated low-frequency deep seismic tremor. We anticipate that these first deployments of borehole strainmeters in the Cascadia setting will add considerable information about the slow slip events beyond what can be learned from GPS and existing surface-based seismological networks.

Although promising results have already been obtained using borehole strainmeter data, the PBO Cascadia strainmeter deployments are also designed to help answer certain remaining questions about these instruments. It is especially critical to understand how conditions in the borehole and immediately surrounding fluid-saturated rock influence the relationship between borehole strainmeter data and tectonic deformation. Additional research is also needed to understand the response of the strainmeters at frequencies as high as 20 Hz, which overlaps with the frequency band monitored by seismic instrumentation. The postdoctoral fellow will have access to a large pre-existing USGS borehole strainmeter data set from California and Hawaii, and can also plan field tests to address the research issues. The research results can be applied to data from strainmeters currently being operated by the USGS, as well as strainmeters being installed by Earthscope, the goal being to improve site selection, installation, and data processing practices.

In addition to having a Ph.D. or an equivalent degree, the applicant must be knowledgeable about crustal deformation and seismological data, and familiar with computer-based data analysis techniques. The applicant need not have experience working with borehole strainmeter data.

Proposed Duty Station: Vancouver, Washington

Areas of Ph.D.: Crustal deformation, seismology, solid earth geophysics, tectonophysics

Qualifications: Applicants must meet one of the following qualifications: Research Geologist, 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 Personnel specialist.)

Research Advisor(s): Evelyn Roeloffs, (360) 993-8937, evelynr@usgs.gov; Seth Moran, (360)993-8934, smoran@usgs.gov

Personnel Office contact: Marie Guillory, (650) 329-4112, guillory@usgs.gov

Summary of Opportunities