NEHRP Clearinghouse
- Title
- Marine Geology and Earthquake Hazards of the San Pedro Shelf Region, Southern California.
- File
- PB2006105344.pdf
- Author(s)
- Fisher, M. A.; Normark, W. R.; Langenheim, V. E.; Calvert, A. J.; Sliter, R.
- Source
- January 2005, 46 p.
- Identifying Number(s)
- USGS/PP-1687
- Abstract
- High-resolution seismic-reflection data have been combined with a variety of other geophysical and geological data to interpret the offshore structure and earthquake hazards of the San Pedro Shelf, near Los Angeles, California. Prominent structures investigated include the Wilmington Graben, the Palos Verdes Fault Zone, various faults below the western part of the shelf and slope, and the deep-water San Pedro Basin. The structure of the Palos Verdes Fault Zone changes markedly southeastward across the San Pedro Shelf and slope. Under the northern part of the shelf, this fault zone includes several strands, but the main strand dips west and is probably an oblique-slip fault. Under the slope, this fault zone consists of several fault strands having normal separation, most of which dip moderately east. To the southeast near Lasuen Knoll, the Palos Verdes Fault Zone locally is a low-angle fault that dips east, but elsewhere near this knoll the fault appears to dip steeply. Fresh sea-floor scarps near Lasuen Knoll indicate recent fault movement. The observed regional structural variation along the Palos Verdes Fault Zone is explained as the result of changes in strike and fault geometry along a master strike-slip fault at depth. The shallow summit and possible wavecut terraces on Lasuen knoll indicate subaerial exposure during the last sea-level lowstand. Modeling of aeromagnetic data indicates the presence of a large magnetic body under the western part of the San Pedro Shelf and upper slope. This is interpreted to be a thick body of basalt of Miocene age.
- Keywords
- Wilmington Graben; Marine geology; San Pedro Shelf Region; Offshore structures; Regional geology; Structural belt; California; Earthquake faults; Seismic-reflection data; Structural variation; Tectonic evolution; Hazards; Palos Verde Fault Zone; Regional structure; Geophysical data; Earthquakes