18-24. Using ocean bottom seismograph (OBS) data for natural hazard studies

Detailed seismic observations of subduction-zone related processes, including major hazards such as great subduction earthquakes, tsunamis, and island volcanic eruptions, require the use of ocean bottom seismographs (OBS) for accurate imaging and detailed earthquake localization. Passive margins like the U.S. Atlantic, the North Slope of Alaska, and the Gulf of Mexico, host major oil, gas, and hydrate reservoirs and are prone to submarine slope failures and potentially landslide-generated tsunamis. Shear-wave measurements, which can only be recorded directly by on-bottom instruments, provide valuable constraints on mechanical properties of marine sediments in situ, enabling us, for example, to model forearc deformation and tsunami generation during large subduction earthquakes, assess the potential for submarine slope failures, and measure natural gas hydrate concentrations. The advent of passive seismological techniques such as beam forming, seafloor compliance, and ambient noise imaging provide new tools to analyze data and learn new information about the seafloor and the hazards it contains. The USGS Woods Hole Science Center (WHSC), located within the campus of the Woods Hole Oceanographic Institution (WHOI), owns many of the short-period OBS in the academic fleet, and two intermediate-period seismographs, and has access to additional intermediate-period seismographs. It maintains a close working and technical relationship with the National OBS facility (OBSIC) located at WHOI. The USGS is also building jointly with WHOI a new fleet of light-weight, state-of-the-art OBS for rapid-response capability in response to earthquakes and volcanic events. Data from these short-term rapid-response deployments will also be available for analysis.

This Mendenhall project provides an opportunity to conduct independent innovative research on three passive seismology data sets collected by the OBS and to participate in the collection of new data sets. A high-quality data set was recorded for a year by six broad-band OBS arrayed close to the Puerto Rico Trench north in 2015-16 to augment data collected by the Puerto Rico seismic network. The OBS recorded over 4000 earthquakes, many of them occurring in seismic swarms. The data appears to be among the quietest data ever recorded by OBS due to the large water depth (~5,500 m) and lack of currents. First-order scientific questions that can be answered with this data set are, for example: Is the slab torn? What is the origin of the frequent seismic swarms that unnerve the citizens of Puerto Rico? Can the Puerto Rico trench produce a M9 earthquake and tsunami? The second data set consists of a cluster of intermediate-period OBS presently being deployed on the continental slope off Georges Bank to record ambient noise and teleseismic events. The goals there are to characterize the sediment properties of the failing slope and the deeper structure of the margin and understand the coupling between major storms and seismic energy traveling through the Earth. The teleseismic events may help define the crustal structure and tectonic evolution of this never-before studied portion of the U.S. margin, which has implications to potential energy resources in the area. A third OBS deployment is planned for 2020 along Queen Charlotte Fault, Alaska, to study fault-zone properties via the propagation of fault-guided waves. The Queen Charlotte Fault, connecting Vancouver Island and southern Alaska is perhaps the fastest moving strike-slip earthquake on Earth, with six M >7 during the past 100 years and a super-shear rupture, and is therefore a useful laboratory to study rupture along these types of faults.

The successful candidate will be part of the marine geohazards group at WHSC, which has been conducting geophysical research in the northeast Caribbean plate boundary, the Atlantic and Gulf of Mexico margins, and, most recently, along the Queen Charlotte Fault. The project has taken a multidisciplinary approach to studying earthquake, tsunami, and landslide hazards using methods including global tomography, earthquake detection and relocation, geodynamic models, active source seismology, geodesy, instrument building, the characterization of near-seafloor sediments by seismic, coring, and sampling methods, as well as direct observations using remotely operated vehicles (ROV). The candidate will have the opportunity to be trained at the Ocean Bottom Seismograph Instrument Center (OBSIC) at WHOI in all aspects of OBS instrumentation, from instrument engineering to instrument deployment and recovery.

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

Proposed Duty Station: Woods Hole, MA 

Areas of Ph.D.: Seismology, marine geophysics or related disciplines (candidates holding a Ph.D. in other disciplines but with 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