Loma Prieta earthquake: Lessons for applied geology
Conference
·
· AAPG Bulletin (American Association of Petroleum Geologists); (United States)
OSTI ID:5210945
- Univ. of California, Santa Cruz (United States) Smith-Evernden Associates, Davenport, CA (United States)
On October 17, 1989, a magnitude 7.1 earthquake took place on the San Andreas fault. The fault break was 40 km long in the Santa Cruz Mountains. California. the hypocenter was at 18 km depth (deep) and was followed by many aftershocks. The pattern of hypocenter/epicenter distribution and geodetic measurements demonstrated that (1) fault rupture extended upward from approximately 19 km to 4-6 km depth, but not to the ground surface; (2) the fault slip was 1.7 m right lateral and 1.3 reverse ({approximately} vertical = thrust); (3) this section of the San Andreas fault is not vertical but inclines southwest at {approximately} 75{degree}. Main shock horizontal and vertical ground accelerations and shaking intensities were high; effects including liquefaction and structural damage were pronounced locally and extended considerable distances on bad ground.' Distribution of effects reinforced some preexisting ideas, for example, that saturated sediments of certain grain sizes will liquefy widely and that unreinforced masonry construction and homes/structures with inadequate horizontal shear support will fail where ground shaking is intensified. Previously unrecognized, however, was that (narrow) ridge tops focus or intensify ground accelerations, leading to ground shattering and structural damage. Directional characteristics of seismic wave propagation, often in combination with topography, can markedly affect intensity. Also previously unrecognized was that San Andreas fault breaks may not extend to the surface (in particular earthquakes). This calls into question the standard geological practice of looking for paleoseismic histories (by ground trenching) at sites in Alquist-Priolo (earthquake hazard) zones proposed for development.
- OSTI ID:
- 5210945
- Report Number(s):
- CONF-9103128--
- Conference Information:
- Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States) Journal Volume: 75:2
- Country of Publication:
- United States
- Language:
- English
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