Crustal and Uppermost Mantle Structure of Texas-Gulf of Mexico from Surface Wave Dispersion and Migrated Ps Receiver Functions.

Abstract:

The seismic velocity structure beneath Texas Gulf Coastal Plain (GCP) is imaged by fitting of surface wave dispersion and velocity analysis of Ps receiver functions. The GCP is a portion of an ocean-continental transition zone, or "passive margin", which have only been subject to a few seismic investigations that are capable of revealing 2-D structure. Seismic data from a linear array of 22 broadband stations, spaced 16-20 km apart along a ~330-km-long profile across the Texas-Gulf of Mexico passive margin, were employed to construct a coherent image of the crust and uppermost mantle. A Common Conversion Point (CCP) stacking technique is applied to teleseismic earthquake data to improve the signal-to-noise ratios of receiver functions and to map Ps phases to their conversion points to produce a 2-D image.

Using an incorrect velocity model for time-to-depth migration of a stacked CCP image may produce an inaccurate image of the subsurface, especially in the presence of substantial lateral velocity variations. To find accurate P- and S-velocity models, we first apply a nonlinear modeling technique to fit Rayleigh wave group velocity dispersion curves via Very Fast Simulated Annealing (VFSA), a global optimization method. We use ambient noise cross-correlation to compute Rayleigh wave group velocity dispersion curves. Based on our results, the Moho disappears in the vicinity of the Balcones Fault System and outboard, which suggests that the Balcones is a through-going fault system. The RF CCP results suggest that tectonic events in the study area have created pathways for fluids to penetrate to the uppermost mantle, which reduces the impedance contrast across the Moho by serpentinization of the mantle.