Start Date: May 15, 2008                                              Funding: NSF (Tectonics), USGS (NEHRP)

Project summary: 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.

As part of this seismic experiment we will acquire 300 km of high-resolution seismic reflection data and chirp data along the Mississippi river, from Helena, Arkansas, to Caruthersville, Missouri. The study area is located in the Mississippi embayment, south of the enigmatic New Madrid seismic zone (NMSZ), an extraordinarily active seismic area in the heart of the North American continent, 2000km from the nearest plate boundary. In this area the high level of historic and instrumental seismicity clashes with the flat topography of the Mississippi Embayment, minimal geodetic vectors and a puzzling lack of substantial deformation in the post Late-Cretaceous sedimentary deposit of the Mississippi embayment. To reconcile this apparent paradox it has been proposed 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 at the continental or regional scale.

In order to test these hypotheses and by exploiting the advantages of marine seismic acquisition (time effective, low cost) the project will carry out reconnaissance of a large portion of the embayment. In the targeted area earthquake-induced liquefaction features that do not correlate with the NMSZ events have been identified, suggesting that an additional seismic source has been active in the embayment. The seismic acquisition, calibrated to illuminate the shallow section, will provide unprecedented high-resolution images of the Mississippi river sediments and of the suspected faults concealed under the subdued topography, providing detailed information on the partitioning of the deformation among key structures beyond the limit of the NMSZ.