Abstract

The location and geometry of seismogenic faults are fundamental to understanding the regional seismic hazard; however, surface evidence for active faults in the seismically active central United States is rare, thus contributing to the uncertainty in the hazard estimation. Multicomponent S‐wave reflection energy was acquired near the northern boundary of the New Madrid Seismic Zone across a well‐constrained N61°E‐oriented fault that extends above the top of Paleozoic bedrock and into near‐surface Quaternary sediment in order to evaluate the effectiveness of shear‐wave splitting measurements for determining azimuthal orientation of fault‐deformed unlithified sediment that lack a surface manifestation. The data were analyzed within the shear‐wave window (i.e., without wide‐angle distortion) using orthogonal source–receiver orientations. Normalized reflection energy spectra of the main and cross‐diagonal elements were rotated in 5° increments to determine fast (S1) and slow (S2) S‐wave directions associated with the azimuthally anisotropic inclusion. The resultant natural coordinate system was N60°E and N30°W for S1 and S2, respectively. The S1 orientation correlated with the established N61°E fault strike. In addition, there was an average dynamic mistie of 11.3 ms that suggests 3.6% azimuthal anisotropy between the top of bedrock and ground surface. These results suggest that shear‐wave birefringence can be a useful tool for defining azimuthal orientation of neotectonic inclusions that lack surface or geomorphic expression, as well as for areas that may have limited accessibility (i.e., urban environments) for deploying multiple widespread geophysical surveys.

You do not currently have access to this article.