THE ANISOTROPY BENEATH SOUTHEASTERN UNITED STATES: INFLUENCES OF MANTLE FLOW AND TECTONIC EVENTS

The southeastern United States is the area that includes the states West Virginia, Arkansas, Florida and so on. In this project, the study area is defined with a range of 90°~75°W, 40°~24°N.

The main purpose of the research is to ascertain the interior structure under the certain area, by using seismological data to investigate the influence of the mantle flow to the anisotropy in the Southeastern United States.

Simple shear originated from the gradient of the mantle flow in the asthenosphere can lead to a fast direction of the anisotropy that is parallel to the mantle flow direction. Another issue believes that the lithospheric compression results in the anisotropy with a fast direction parallel to the strike of mountain belts. Southeastern US experienced a significant amount of deformation while there is mantle flow traveling beneath. By applying Shear Wave Splitting (SWS) origin of the anisotropy could be constrained from the results.

The project was conducted by using Shear-wave splitting (SWS), which is one of the most commonly used techniques in structural seismology. Two resulting splitting parameters indicate the orientation and strength of seismic anisotropy accumulated along the ray path, the polarization direction of the fast wave (fast direction) and the arrival time difference between the fast and slow waves (splitting time). The P-to-S converted waves at the core-mantle boundary (XKS, including SKS , SKKS, and PKS ) are ideal for SWS analysis, due to the fact that the initial polarization direction is along the radial direction and thus any energy in the XKS window on the transverse component is an indicator of azimuthal anisotropy.

In this research, I observed special features by comparing data in figures and by analyzing geological history. With reliable observations, I developed explenations and possible model related to the formation of anisotropy of this area.