INVESTIGATING THE ANISOTROPY IN THE UPPER CRUST OF THE NEW MADRID SEISMIC ZONE

In this study we investigate crustal anisotropy due to presence of micro cracks within the New Madrid seismic zone (NMSZ), by analyzing shear wave splitting from local earthquake data. The NMSZ is centrally located in the United States, spanning portions of western Tennessee, northeastern Arkansas, and southeastern Missouri. The NMSZ is also the location in which three of the largest known earthquakes took place in North America, occurring in 1811-1812. Although many seismic studies have been performed in this region, there is no consensus about seismotectonic model that could satisfy both the current observations, as well as the historical seismicity. Therefore, it is important to continue investigating the NMSZ, to gain a better understanding of its seismicity, and the possible mechanisms that drive it. The automated technique developed by Savage et al. (2010) is used to perform the shear wave splitting measurements at 120 seismic stations within the NMSZ. The Center for Earthquake Research and Information (CERI) at the University of Memphis provided waveform data for 1151 earthquakes spanning the years 2003-2011. The results of this study will provide information about orientation of microcracks in the upper portion of the crust; future work will include analysis for temporal and spatial variations in order to assess the state of stress in the region.