32. Exploring Tremor, Slow Slip, and Earthquakes in Alaska and the Aleutian Arc

We seek a postdoctoral fellow to study slow slip events, tremor, and earthquakes in Alaska and the Aleutian arc. This Opportunity promises to provide key observational constraints and insights related to perhaps the newest and most exciting discovery in solid earth science. While a few faults and other natural systems that relieve stress by slipping (for example, landslides, glaciers) are known to slip slowly (days to months), the abundance of slow slip has only recently been documented thanks to advances in geodetic measurement capabilities. Slow slip events commonly occur along subduction zones down-dip of the segments that produce large earthquakes. In addition to possibly changing the probability of the latter occurring, slow slip events hold the promise of delineating the boundaries of the earthquake-producing regions, which have been difficult to define otherwise. In roughly the same places where slow slip events occur, faults or some unknown process radiate seismic waves as tremor. Tremor likely arises from physical processes that differ from those governing earthquake-generated waves. While neither tremor nor slow slip is hazardous, they provide clues about the behaviors and properties of faults that fail as hazardous earthquakes. 

Alaska and the Aleutian arc are home to a 2500 km-long subduction zone, hosting one of the most prominent volcanic arcs in the world and frequent large earthquakes (for example, a magnitude >7 earthquake occurs in Alaska annually on average).  Several episodes of slow slip and tremor have been identified geodetically in Alaska; however, a wealth of existing seismic and GPS data simply have not been analyzed to document these phenomena. To understand the underlying mechanisms of slow slip events, tremor, and earthquakes we must know the range of physical properties under which these processes occur. The Aleutian megathrust is characterized by segments in various stages of the earthquake cycle and thus provides an unparalleled dataset to constrain this range. Moreover, the subduction zone in southern Alaska is unique among virtually all subduction zones in that it has a particularly large land area above the megathrust that can be monitored.

A first order challenge for this opportunity will be to quantify the occurrence and extent of tremor in Alaska and the Aleutian arc using data from the extensive seismic networks in the region. The postdoctoral fellow may also seek ties between tremor and slow slip using GPS data.  Datasets of unprecedented quality and quantity are now available through the University of Alaska Fairbanks, the Plate Boundary Observatory and Alaska Volcano Observatory. Once the spatial and temporal occurrence of non-volcanic tremor and slow slip has been ascertained, results will serve as a springboard for investigating relationships between these processes and earthquakes and potentially for exploring dynamically triggered tremor. Results can be compared to other locales (for example, Cascadia, Japan, New Zealand) to gain insight into how the physical properties of subduction zones, such as heat flow, convergence rate, and the earthquake cycle, influence the occurrence of these phenomena. The postdoctoral fellow may also investigate the as yet uncharted relationship between volcanic activity, slow slip, and tremor. While tremor is much more broadly distributed and often far from individual volcanic centers it shares many similarities with signals well documented on volcanoes; this opportunity may explore this commonality, posing the hypothesis that the only difference between volcanic and non-volcanic tremor is the stress source that leads to the failure and radiation of seismic energy.

Proposed Duty Station: Anchorage, AK, with possible extended visits to Fairbanks, AK and Seattle, WA

Areas of Ph.D.: Geophysics, geology, seismology, geodesy

Qualifications: Applicants must meet one of the following qualifications: Research Geophysicist , Research Geologist

(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.)

Research Advisor(s): Stephanie Prejean, (907) 786-7462, sprejean@usgs.gov; Joan Gomberg, (206) 616-5581, gomberg@usgs.gov; Doug Christensen (University of Alaska Fairbanks), (907) 474-7426, doug@giseis.alaska.edu; J. Jeffrey Freymueller (University of Alaska Fairbanks), (907) 474-7286, jeff@giseis.alaska.edu; Peter Haeussler (USGS), (907)786-7447, pheuslr@usgs.gov

Human Resources Office contact: Candace Azevedo, (916) 278-9393, caazevedo@usgs.gov

Summary of Opportunities