|Long Term Deformation in the Mississippi
University of Memphis (CERI), University of Texas at Austin (UTIG)
Start Date: May 15, 2010 Funding: NSF (Tectonics), USACE
End Date: May 14, 2013
Project Summary: The debate regarding the significance of seismicity in the Mississippi embayment has recently seen increased interest due to the release of new GPS data showing geodetic vectors of < 0.2 mm/yr, which clearly suggest that the area is deforming slowly (if at all) and that resulting repeat times for large earthquakes should be on the order of 10,000-100,000 years. This observation clashes with the puzzling high levels of seismicity and with the established paleoseismological record which shows repeat times of ~500 yr at least for the Holocene. The hypotheses proposed to reconcile the controversial observations propose that the seismicity in the NMSZ is either 1) episodic, 2) very young (at least in its present incarnation), or 3) migrates throughout a broad region.To test these hypotheses and capitalizing on the success of the Phase I pilot project, we will acquire 580 km of high-resolution, marine seismic reflection and chirp data along the Mississippi river across the New Madrid Seismic Zone (NMSZ), and in the southern Mississippi embayment, across a series of inferred faults suspected to be responsible for earthquake induced liquefaction features predating the seismic activity of the NMSZ. We will take advantage of the presence of the Mississippi river, which runs through the NMSZ and across many of the suspected faults, to acquire marine seismic data during two acquisition campaigns, exploiting the advantages of the marine seismic method (low cost, time effective) to cross a large section of the continent. Thanks to the experience gained during the Phase I pilot project, we are now confident that the seismic data will clearly image the Paleozoic to Quaternary sedimentary section with unprecedented high-resolution and will provide critical information to decipher the timing and location of deformation in this area, therefore discriminating among the proposed hypotheses.
The U.S. Army Corps of Engineers – Memphis District, will continue to support the project by hosting our team on one of their vessels during both seismic acquisition campaigns, therefore alleviating a substantial part of the costs of fieldwork.
Intellectual Merit: Although the theory of plate tectonics revolutionized our understanding of earthquake processes, it does not explain why earthquakes occur in regions distant from plate boundaries where deformation rates are low and where plate motions supply insufficient driving energy. The proposed research will primarily provide observational constraints on theoretical models proposed to explain the timing and magnitude of continental intraplate seismicity in the Central U.S. Models that involve localization of central U.S. strain within the NMSZ do not predict additional fault zones in the region with comparable levels of strain accommodation, whereas models that involve a broad zone of intraplate deformation predict the presence of central U.S. active fault systems in addition to the NMSZ. This area provides a prime opportunity to investigate seismicity in stable continental regions and to develop tectonic models applicable to similar areas around the globe.
Broader Impacts: The high-resolution seismic data collected as part of this study will be suitable to diverse applications. The most important application will be in earthquake hazard assessment and earthquake loss and risk reduction in the mid-continent. The data will be also valuable for understanding the impact of a seismic event on the Mississippi River navigation by evaluating the riverbed and slope stability. In addition, the data will be critical for ground water sustainability and water quality studies in large metropolitan areas (e.g., Memphis). Finally, this research will form the core of one or more Master’s degree projects for University of Memphis graduate students.
Guo Lei Xenia Fave
CERI - UofM CERI - UofM