Geophysical constraints on the location and geometry of the Las Vegas Valley Shear Zone, Nevada

We model the basin configuration beneath Las Vegas Valley, Nevada, on the b asis of gravity, drillhole, and seismic reflection data. We locate and char acterize the various strands of the Las Vegas Valley Shear Zone (LVVSZ) by variations in basin thickness beneath the valley. The pre Tertiary bedrock surface is complex, with subbasins buried beneath the flat alluvial surface of the valley. We suggest that these basins are formed from transtensional strain. Subbasins elongated N70(0)W and N50(0)W are interpreted as strike- slip basins. The deepest subbasin is 5 km west of Frenchman Mountain and st rikes N40(0)E. This basin probably formed by combined movement on nonparall el strands of the LVVSZ and an earlier episode of normal faulting. The basi n thickness map constrains the minimum depth of the inferred detachment fau lt beneath Las Vegas Valley to at least 4 km. Seismic reflection data do no t image a detachment fault in the upper 10 km beneath Las Vegas Valley. Our results also illustrate the utility of gravity in determining basinal stru ctures and providing a three-dimensional perspective in areas with limited seismic reflection control.