14-32. Controls on Intraplate Earthquakes in the Central and Eastern U.S. (CEUS)
Go East Young Researcher! The science behind the cause of earthquakes in most of the CEUS is ripe for new discoveries. There are more earthquakes in the western U.S., but due in part to lower crustal attenuation and a more vulnerable building inventory in the east, the earthquake impact and consequences cover a much larger area in the CEUS. Our understanding of the Quaternary history of intraplate earthquakes has improved in small parts of the CEUS in recent decades (e.g., New Madrid, Wabash, and Charleston, SC, seismic zones), but there is still much uncertainty about what controls CEUS earthquakes.
For example, the 2011 Mw 5.8 intraplate earthquake in central Virginia, which was felt by more people in the U.S. than any other earthquake and caused about $200 million in damage, occurred in a previously identified zone of elevated seismic hazard in the USGS National Seismic Hazard Map―the Central Virginia seismic zone. As is the case with most intraplate earthquakes, however, the causative fault or faults were not singled out prior to the event as more likely to rupture than any neighboring fault, no surface rupture has been detected, and none of the ancient faults mapped at the surface have been shown to be active in the Quaternary.
Like the Central Virginia seismic zone much of the seismic hazard in the CEUS is characterized solely by earthquake activity during historical time (the last 300-400 years). In contrast, the western U.S. contains many active faults that are clearly expressed at the surface and that have detailed paleoseismic histories revealed by trenching. Therefore, a fundamental challenge of this Opportunity is tying a causal mechanism to earthquake records that extend into pre-historic time in regions of the CEUS that are seismically active. Other unanswered questions include: How do the areas that are currently seismically active differ from those that are historically quiet? And, is there an on-off record of episodic earthquake activity hidden in the landscape or in the faults themselves?
Many factors contribute to the challenge of assessing seismic hazard in intraplate regions like the eastern United States, including long recurrence intervals on active faults; blind ruptures; erosional processes that remove surface evidence of recent fault activity; evidence of temporal variations (clustering) in earthquake occurrence, which complicates earthquake hazard modeling; and an incomplete understanding of how strain accumulates and is released on intraplate structures that have been active in Quaternary time. Because of complicating factors like these, there is much uncertainty about whether larger quakes are possible or have occurred before during the Quaternary in the Central Virginia seismic zone or other areas closer to densely populated CEUS cities.
We invite applicants to propose projects that focus on geological and geophysical investigations that will contribute to an expanded understanding of the factors that control intraplate earthquakes and improve our characterization of the seismic hazard. It is generally thought that CEUS earthquakes occur on ancient geologic faults that have been re-activated by the modern stress conditions in the Earth’s crust. It is also generally accepted that historically active areas, such as the Central Virginia seismic zone, have higher seismic hazard than areas that are historically less active or aseismic. An assessment of these principles is a key driver for this Mendenhall research.
We invite candidates to submit research proposals on intraplate fault systems in the CEUS to identify regions where fault reactivation can be expected, to determine the connection, if any, between ancient surface faults and historical seismicity, to explore how intraplate fault systems evolve and respond to contemporary strain fields, to develop methods for detecting and characterizing intraplate faults using remote sensing (particularly using detailed surface topographic models developed from airborne LiDAR) or geophysical techniques, and to develop models and theories of the underlying physical processes that generate intraplate earthquakes.
Mendenhall postdoctoral research may also be proposed to examine the long-term paleoseismic record of historically seismic and aseismic regions of the CEUS to quantify their seismic behavior, to provide evidence for or against strain localization on active structures in intraplate settings, and to search for temporal changes in fault behavior that can be identified and utilized in probabilistic seismic hazard calculations.
Projects that concentrate on previously identified regions of elevated seismic hazard in the USGS seismic hazard maps are also welcome. For example, the August 23, 2011, M5.8 Virginia and the April 18, 2008, M5.4 Illinois earthquakes provide especially rich and relevant datasets for analysis. Investigations of fault behavior and neotectonic expression related to this event can be synthesized with global observations to provide the widest possible context for understanding this event. This is a multidisciplinary opportunity involving geology, geophysics, and seismology. A strong background in seismotectonics is desired.
Proposed Duty Station: Golden, CO
Areas of Ph.D.: Geology, geophysics, seismology (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 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 a Human Resources specialist).
Research Advisors: Robert Williams, (303)273-8636, firstname.lastname@example.org.; Rich Briggs, (303) 273- 8465, email@example.com.; Ryan Gold, (303) 273-8633, firstname.lastname@example.org
Human Resources Office Contact: Robert Hosinski, (916) 278-9397, email@example.com
|Summary of Opportunities|