Published reports attribute the 1978 Santa Barbara earthquake to a north-dipping reverse fault supported in part by first-motion studies. Surface geology augmented by oil-well and trench logs shows a predominance of late Quaternary reverse faults which dip steeply south, suggesting that the alternate nodal plane determined from first-motion studies is preferred. A steep fault would better explain the narrow rectangular map pattern of aftershocks. The Santa Barbara region has a high historical seismicity compared to the onshore Ventura basin to the east, where late Quaternary displacements on seismically active north-dipping faults are much higher, a paradox if the 1978 event were also produced by a north-dipping fault. On the other hand, the tectonic subprovince characterized by steeply south-dipping faults is much better developed at Santa Barbara, where the historical seismicity is higher, than in the onshore Ventura basin.

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.