Seismic trapped modes in the Oroville and San Andreas Fault zones

Journal Article · Fri Aug 17 04:00:00 EDT 1990 · Science (Washington, D.C.); (USA)

DOI:https://doi.org/10.1126/science.249.4970.763· OSTI ID:6262203

Li, Yong-Gang; Leary, P; Aki, K ^[1]; Malin, P ^[2]

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1. Univ. of Southern California, Los Angeles (USA)
2. Univ. of California, Santa Barbara (USA)

Three-component borehole seismic profiling of the recently active Oroville, California, normal fault and microearthquake event recording with a near-fault three-component borehole seismometer on the San Andreas fault at Parkfield, California, have shown numerous instances of pronounced dispersive wave trains following the shear wave arrivals. These wave trains are interpreted as fault zone-trapped seismic modes. Parkfield earthquakes exciting trapped modes have been located as deep as 10 kilometers, as shallow as 4 kilometers, and extend 12 kilometers along the fault on either side of the recording station. Selected Oroville and Parkfield wave forms are modeled as the fundamental and first higher trapped SH modes of a narrow low-velocity layer at the fault. Modeling results suggest that the Oroville fault zone is 18 meters wide at depth and has a shear wave velocity of 1 kilometer per second, whereas at Parkfield, the fault gouge is 100 to 150 meters wide and has a shear wave velocity of 1.1 to 1.8 kilometers per second. These low-velocity layers are probably the rupture planes on which earthquakes occur. 15 refs., 5 figs., 1 tab.

• DOE Contract Number: FG03-87ER13807
• OSTI ID: 6262203
• Journal Information: Science (Washington, D.C.); (USA), Journal Name: Science (Washington, D.C.); (USA) Vol. 249:4970; ISSN SCIEA; ISSN 0036-8075
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
BOREHOLES
CALIFORNIA
CAVITIES
DATA
EARTHQUAKES
EXPERIMENTAL DATA
FEDERAL REGION IX
GEOPHYSICAL SURVEYS
INFORMATION
MICROEARTHQUAKES
NORTH AMERICA
NUMERICAL DATA
SEISMIC EVENTS
SEISMIC SURVEYS
SURVEYS
USA