INVESTIGATION OF THE LITHOSPHERE OF THE GULF COAST PLAIN AND LLANO UPLIFT USING RECEIVER FUNCTIONS AND PN TOMOGRAPHY

The nature of the basement rock beneath the Gulf Coast Plain (GCP) is difficult to image as a result of a relatively thick sedimentary cover (up to 17 km thick). Thus models, describing the nature of the opening of the Gulf of Mexico (GoM) and development of the lithosphere of the Gulf Coast Plain (GCP), are poorly constrained. The EarthScope transportable array (TA) passed through this region between 2009 and 2011; during which, there were anomalously large earthquakes located in Texas, (near the cities of San Antonio, Victoria, Dallas, Nacogdoches, and Synder), Central Oklahoma and Arkansas. These events were recorded at distances great enough to enable a low resolution Pn tomographic study of the region.

By mapping variations in the Pn velocity, we may gain understanding as to the nature of the mantle beneath the Moho. This will help constrain the depth and nature of the Gulf Coast anomaly of high magnetic values that parallels the coast line. Recent receiver function work found no positively polarized phase from the Moho beneath the Balcones fault zone. Some of the receiver function imaging suggests a negative Ps phase from the Moho may be present in this region. The Pn tomography work in this study will enable us to determine the lateral extent and location of this anomalous Moho in relation to the transition from Gulf Coast rifted margin to the cratonic lithosphere of the Llano uplift. Teleseismic bodywave tomography results have also found anomalous Vp/Vs ratios beneath the GCP. This will be augmented with receiver function analysis to better constrain crustal thickness and Vp/Vs ratio within particular layers, at various depths. Gravity modeling will be used to interpolate the seismic results and provide a more continuous geologic interpretation of the region.