HR: 1340h
AN: T13A-0436    [Abstracts]
TI: Lithospheric Structure Beneath Northern California
AU: Li, X
EM: li@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AU: * Yuan, X
EM: yuan@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AU: Kind, R
EM: kind@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AB: The coast range of northern California is a tectonically very active region. Many of the tectonic features are directly related to the northward migration of the Mendocino triple junction (MTJ) along the western edge of North America during the past 30 million years. South of the MTJ the Farallon slab has completely subducted beneath the North American plate, leaving a slab window which is thought to be filled by the upwelling asthenospheric materials. Accurate knowledge of the thickness of the lithosphere is crucial to understand the tectonic evolution of northern California. High temperature in the upper mantle estimated from seismic tomography and xenolith data indicates a thin (<100 km) thermal lithosphere. A zone of low shear wave velocity is imaged down to a depth of 300 km by surface wave tomography. Receiver function technique is one of the most powerful tools to detect seismic discontinuities in the crust and upper mantle. Here we jointly use P and S receiver function methods for 24 permanent broadband seismic stations of the Berkley Digital Seismic Network in northern California. The P receiver functions reveal complicated crustal structures. A strong intra-crustal interface at a depth of ~20 km effectively masks the converted signals from the Moho and lithospheric interfaces at many sites. The S receiver function method overcomes this problem, as the direct S-to-P converted waves arrive earlier than the S waves and thus consequently separated from the multiples that arrive later. We calculated S receiver functions from waveform data of S and SKS phases for all the stations. A significant phase with negative amplitudes is observed in the S receiver functions at ~8 s, indicating a low velocity interface in the upper mantle at a depth of ~70 km. We interpret this phase as the S-to-P conversion at the base of the lithosphere. Waveform modeling shows that the lithosphere-asthenosphere boundary here is ~10 km sharp.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7218 Lithosphere (1236)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8104 Continental margins: convergent
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Tectonophysics [T]
MN: Fall Meeting 2005