Seismic trapped modes in the Oroville and San Andreas fault zones
Li Y, Leary P, Aki K, Malin P. 1990. Seismic trapped modes in the Oroville and San Andreas fault zones. Science. 249(4970):763-766
Three-component borehole seismic profiling of the recently active Oroville, California, normal fault and microearthquake even recording with a near-fault three-compoenent 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 plances on which earthquakes occur.
- Type
- Journal Article
- Authors
- Li, Yong-Gang; Leary, Peter; Aki, Keiiti; Malin, Peter
- Units
- PINN
- Keywords
- Active Faults, boreholes, Butte County California, California, Elastic Waves, Fault Zones, Faults, Geology, guided waves, Interpretation, low velocity zones, microearthquakes, Monterey County California, normal faults, Oroville California, Oroville Fault, Pacific Coast, Parkfield California, Propagation, Rupture, San Andreas Fault, seismic logging, Seismology, Strike Slip Faults, three component seismographs, Velocity, vertical seismic profiles, wave guides, waveforms, well logging, Western U.S.