Characteristics of Shallow Subsurface Faults on Texas Inner Shelf: ABSTRACT

Abstract

Faults mapped on the Texas inner shelf from high-resolution sparker profiles show diverse densities, continuities, orientations, displacements, and degrees of recent activity. Potentially active faults either intersect or are near the seafloor at the upper limit of detection on geophysical records, whereas inactive faults are usually overlain by continuous seismic reflectors. Fault characteristics are broadly defined by geologic age, depositional history, and degree of tectonic subsidence. Faults of greatest density and lateral continuity (< 27 km) are peripheral to the Rio Grande delta, an area of active Holocene deposition. Faults are equally dense and less continuous (< 16 km) near the Brazos-Colorado delta, whereas presently active faults are rare between the de tas except near Corpus Christi. Faults are least continuous (< 5 km) and dense along the upper coast which has remained relatively stable during the late Quaternary. Displacements at depths of 150 m range from 3 to 30 m; most displacements, however, are between 3 and 10 m when rollovers are discounted. These en echelon growth End_Page 498------------------------------ faults coincide with the regional onshore (Willimar) trend oriented subparallel with the coast. Most are down-to-basin faults, but up-to-basin faults also occur. Some topographic highs on the seafloor apparently formed by differential erosion of zones preferentially cemented by fluids migrating along fault planes. Seafloor expression of diapiric structures with radial faults is negligible; however, surface sediments near these structures exhibit subtle changes, which suggests minor differences in slope. Quaternary sediments, specially fluvial sediments, were also locally controlled by faulting. End_of_Article - Last_Page 499------------