CONSTRAINTS ON OCEANIC LITHOSPHERE STRUCTURE FROM DEEP-FOCUS REGIONAL RECEIVER FUNCTION INVERSIONS

We extend teleseismic P wave receiver function techniques to include regional P waveforms from deep-focus earthquakes and document a new data source for the study of oceanic lithosphere structure. High microseismic noise in oceanic environments strongly contaminates waveform recordings for moderate teleseisms. The use of high-amplitude deep-focus regional body waves significantly improves signal-to-noise ratio. Deep sources can generate body waves that propagate as direct waves or turning waves at regional distances which have ray parameters similar to the teleseismic body waves. The amplitudes of these regional body waves may be 10 to 20 times that of the teleseismic body waves for constant magnitude and same radiation pattern effects simply due to large differences in the geometrical spreading and attenuation along the propagation path. To demonstrate the feasibility of utilizing deep-focus regional waveform data in studying oceanic lithosphere structure, we examine body wave recordings collected at the seismic station GUMO (Guam, Mariana Islands). The oceanic lithosphere structure under the island is resolved using a jumping inversion approach that includes a singular-value decomposition procedure along with the Tikhonov regularization. The thickness of the crust appears to be about 15.0 km. The shallow structure has large positive velocity gradients, and the Moho is a broad crust-mantle transition zone. Velocity complexity occurs in the middle crust.