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Defining Earthquake Source Zones and Onland Hazards Posed by Earthquakes in the California Borderland: Shirley Baher

Project Title: Defining Earthquake Source Zones and Onland Hazards Posed by Earthquakes in the California Borderland
Mendenhall Fellow: Shirley Baher, sbaher@usgs.gov
Duty Station: Menlo Park, California
Start Date: January 1, 2003
Education: Ph.D. Geophysics, Seismology, University of California, Los Angeles, 2001
Research Advisors: Gary Fuis, (650) 329-4758, fuis@usgs.gov; William Normark, (650) 329-5200, wnormark@usgs.gov; Mike Fisher, (650) 329-5158, mfisher@usgs.gov; Tom Parsons, (650) 329-5074, tparsons@usgs.gov; Dan Ponti, (650) 329-5679, dponti@usgs.gov; Homa Lee, (650) 329-548, hjlee@usgs.gov; Bob Bohannon, (303) 236-1235, bbohannon@usgs.gov

Project Description: The historical seismicity of offshore and near coastal earthquakes such as Santa Barbara (1925, Ml 6.3) and Long Beach (1933, Mw 6.4) has provided insight to the seismic hazard and economic impact on near coastal communities. The goal of this project is to better quantify this hazard by analyzing high-resolution shallow seismic reflection data acquired by the Coastal Marine Group along with the onshore and offshore crustal structure data acquired by the Earthquake Hazards Team as part of the Los Angeles Region Seismic Experiment. The later inclusion of industry data (seismic-reflection and borehole data) along with on-land geologic mapping, crustal tomography, geodesy and potential fields would result in these specific goals to: 1) define structures that are continuous offshore to onshore; 2) define the location and geometry of offshore faults and potential tsunamigenic landslides; and 3) image faults from the surface to seismogenic depths.

Map of multi-beam and bathymetry with relocated epicenter locations of the diffuse seismicity of the area.

Map of multi-beam and bathymetry with relocated epicenter locations of the diffuse seismicity of the area (adapted from Marlow et al., 2000). The seismicity of the San Pedro Shelf region is highlighted in red. The seismicity generally correlates with certain fault locations (black lines) and inferred locations (dashed lines).


Color contoured version of the final velocity model developed from theoretical ray tracing of the P arrival times and final velocity model with vertical exaggeration of 2:1 which is a closer representation of fault dip.

a), Color contoured version of the final velocity model developed from theoretical ray tracing of the P arrival times. The black lines are certain faults and dotted lines represent inferred faults. Well logs taken from Wright (1991) see reference for well name. Catalog seismicity obtained from the Southern California Earthquake Center database for the year 1975-2003 (red dots). Results of the survey from Shor and Raitt (1976) the orange crosses show locations where the two surveys were closer together and yellow crosses show the surveys some distance apart. The diffuse region shows the region of unconstrained velocity. b). Final velocity model with vertical exaggeration of 2:1 which is a closer representation of fault dip.

Map of central and southern California showing the Transverse Ranges and the Continental Borderland and map of multi-beam and bathymetry of the study area near Palos Verdes, California.

a), Map of central and southern California showing the Transverse Ranges and the Continental Borderland SB= Santa Barbara, V=Ventura, LA=Los Angeles. b), Map of multi-beam and bathymetry of the study area near Palos Verdes, California. Triangles are OBS locations, Green line is LARSE line 1 streamer line that is coincident with air gun shots until OBS A1, red dotted line shows the continuation of the air gun shots to the coastline (orange), and black lines are faults (adapted from Jennings, 1977).

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