Formation of left-lateral fractures within the Summit Ridge shear zone, 1989 Loma Prieta, California, earthquake
- Purdue Univ., West Lafayette, IN (United States)
The 1989 Loma Prieta, California, earthquake is characterized by the lack of major, throughgoing, coseismic, right-lateral faulting along strands of the San Andreas fault zone in the epicentral area. Instead, throughout the Summit Ridge area there are zones of tension cracks and left-lateral fracture zones oriented about N45 deg W, that is, roughly parallel to the San Andreas fault in this area. The left-lateral fractures zones are enigmatic because their left-lateral slip is opposite to the right-lateral sense of the relative motion between the Pacific and North American plates. We suggest that the enigmatic fractures can be understood if we assume that coesiesmic deformation was by right-lateral shear across a broad zone, about 0.5 km wide and 4 km long, beneath Summit Ridge. Contrary to most previous reports on the Loma Prieta earthquake, which assert that coseismic, right-lateral ground rupture was restricted to considerable (greater than 4 km) depths in the epicentral area, we find that nearly all the right-lateral offset is represented at the ground surface by the Summit Ridge shear zone.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 79464
- Journal Information:
- Journal of Geophysical Research, Vol. 98, Issue B12; Other Information: PBD: Dec 1993
- Country of Publication:
- United States
- Language:
- English
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