Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (11) Citing Articles via Google Scholar Google Scholar Articles by Fisher, M. A. Articles by Calvert, A. J. Search for Related Content GeoRef GeoRef Citation

Geology of the Continental Margin beneath Santa Monica Bay, Southern California, from Seismic-Reflection Data

U.S. Geological Survey, MS 999
345 Middlefield Rd.
Menlo Park, California 94025
mfisher{at}usgs.gov
(M.A.F., W.R.N., R.G.B., R.W.S.)

Simon Fraser University
Burnaby, British Columbia, Canada V5A 1S6
(A.J.C.)

We interpret seismic-reflection data, which were collected in Santa Monica Bay using a 70-in³ generator-injector air gun, to show the geologic structure of the continental shelf and slope and of the deep-water, Santa Monica and San Pedro Basins. The goal of this research is to investigate the earthquake hazard posed to urban areas by offshore faults. These data reveal that northwest of the Palos Verdes Peninsula, the Palos Verdes Fault neither offsets the seafloor nor cuts through an undeformed sediment apron that postdates the last sea level rise. Other evidence indicates that this fault extends northwest beneath the shelf in the deep subsurface. However, other major faults in the study area, such as the Dume and San Pedro Basin Faults, were active recently, as indicated by an arched seafloor and offset shallow sediment. Rocks under the lower continental slope are deformed to differing degrees on opposite sides of Santa Monica Canyon. Northwest of this canyon, the continental slope is underlain by a little-deformed sediment apron; the main structures that deform this apron are two lower-slope anticlines that extend toward Point Dume and are cored by faults showing reverse or thrust separation. Southeast of Santa Monica Canyon, lower-slope rocks are deformed by a complex arrangement of strike-slip, normal, and reverse faults. The San Pedro Escarpment rises abruptly along the southeast side of Santa Monica Canyon. Reverse faults and folds underpinning this escarpment steepen progressively southeastward. Locally they form flower structures and cut downward into basement rocks. These faults merge downward with the San Pedro Basin fault zone, which is nearly vertical and strike slip. The escarpment and its attendant structures diverge from this strike-slip fault zone and extend for 60 km along the margin, separating the continental shelf from the deep-water basins. The deep-water Santa Monica Basin has large extent but is filled with only a thin (less than 1.5-km) section of what are probably post-Miocene rocks and sediment. Extrapolating ages obtained from Ocean Drilling Program site 1015 indicates that this sedimentary cover is Quaternary, possibly no older than 600 ka. Folds and faults along the base of the San Pedro Escarpment began to form during 8–13 ka ago. Refraction-velocity data show that high-velocity rocks, probably the Catalina Schist or Miocene volcanic rocks, underlie the sedimentary section. The San Pedro Basin developed along a strike-slip fault, widens to the southeast, and is deformed by faults having apparent reverse separation and by folds near Redondo Canyon and the Palos Verdes Peninsula.

This article has been cited by other articles:

				C. M. Brankman and J. H. Shaw Structural Geometry and Slip of the Palos Verdes Fault, Southern California: Implications for Earthquake Hazards Bulletin of the Seismological Society of America, June 1, 2009; 99(3): 1730 - 1745. [Abstract] [Full Text] [PDF]

				J. D. Chaytor, C. Goldfinger, M. A. Meiner, G. J. Huftile, C. G. Romsos, and M. R. Legg Measuring vertical tectonic motion at the intersection of the Santa Cruz-Catalina Ridge and Northern Channel Islands platform, California Continental Borderland, using submerged paleoshorelines Geological Society of America Bulletin, July 1, 2008; 120(7-8): 1053 - 1071. [Abstract] [Full Text] [PDF]

				J. R. Hein, W. R. Normark, B. R. McIntyre, T. D. Lorenson, and C. L. Powell II Methanogenic calcite, 13C-depleted bivalve shells, and gas hydrate from a mud volcano offshore southern California Geology, February 1, 2006; 34(2): 109 - 112. [Abstract] [Full Text] [PDF]

				M. A. Fisher, W. R. Normark, V. E. Langenheim, A. J. Calvert, and R. Sliter The Offshore Palos Verdes Fault Zone near San Pedro, Southern California Bulletin of the Seismological Society of America, April 1, 2004; 94(2): 506 - 530. [Abstract] [Full Text] [PDF]