HR: 1340h
AN: S13B-1043    [Abstracts]
TI: DEEP BOREHOLE RECEIVER FUNCTIONS IN LONG VALLEY CALDERA, CALIFORNIA
AU: * Chavarria, J
EM: jac4@duke.edu
AF: Duke University - Earth and Ocean Sciences, 103 Old Chemistry B90229, Durham, NC 27708 United States
AU: Julia, J
EM: jordi@duke.edu
AF: Duke University - Earth and Ocean Sciences, 103 Old Chemistry B90229, Durham, NC 27708 United States
AU: Malin, P
EM: malin@duke.edu
AF: Duke University - Earth and Ocean Sciences, 103 Old Chemistry B90229, Durham, NC 27708 United States
AB: Receiver functions are now routinely calculated from teleseismic P-waveform records to investigate the subsurface geology. For these calculations broad-band seismometers are generally used since only the low end of the frequency spectrum (f $<$ 1.5 Hz) can be interpreted. With a number of ongoing efforts of deep drilling and monitoring of earthquakes, a number of short period seismometers has been installed in deep wells in various geologic settings. In this work we explore the use of these short period instruments in deep borehole environments for the analysis of high signal to noise ratio receiver functions. Receiver functions are obtained by deconvolving the vertical component from the corresponding radial component of the waveforms, which equalizes for the source effects in the original data. During the deconvolution process, the instrument response is also equalized regardless of the dynamic range of the recording sensors. It has been noted that the signal to noise ratio increases with depth and here we show that single stations, located in deep boreholes, have strong signals that allow for stable deconvolutions. We tested the receiver function technique with short-period instruments (fc = 4.5 Hz) located in two wells in the Long Valley Caldera in California. The first instrument is located in a ~200m deep geothermal well whereas the other one is in the 2.5km deep Long Valley Exploratory Well. A number teleseismic events (30 $<$ D $<$ 90) have been recorded over a few months of acquisition and with these data, stable receiver functions were computed. The deconvolved traces coherently show strong secondary waves that we have interpreted as a Ps conversion and a PpPhs multiple reverberberation on top of a feature that we interpret as the top of a magma body located about 10-12 km depth.
DE: 7230 Seismicity and seismotectonics
DE: 7280 Volcano seismology (8419)
DE: 7294 Instruments and techniques
DE: 7299 General or miscellaneous
DE: 7205 Continental crust (1242)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting