Detailed gravity profiles across linear gravity gradients 20 to 30 km long indicate 1 to 2 km of structural relief in zones more than 5 km wide. The gravity anomaly is attributed to low-density alluvial basin fill, the density of which is assumed to decrease basinward from the fault as a result of blending of piedmont-slope alluvial with fluvial sedimentary facies. A direct inverse solution of gravity for lateral density variation is derived. The gravity data are compatible with a single large fault and a density contrast increasing from 0 to 0.4 g/cm3 in a 5-km-wide zone. The data are also compatible with a constant density contrast and a gently dipping fault, although this seems unlikely, geologically, because most observed faults are high angle. Geologic and gravity data considered together suggest the presence of a relatively few, widely spaced, long, steeply dipping (at shallow levels), mostly buried “master” faults, to which most observed faults are secondary and sympathetic.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not have access to this content, please speak to your institutional administrator if you feel you should have access.