HR: 10:50h
AN: S42A-03    [Abstracts]
TI: Complications in Receiver Function Analysis on the Ocean Floor: Water and Sediment Reverberations
AU: * Harmon, N
EM: Nicholas_Harmon@brown.edu
AF: Brown University Department of Geologic Sciences, Box 1846 324 Brook St., Providence, RI 02912 United States
AU: Forsyth, D W
EM: Donald_Forsyth@brown.edu
AF: Brown University Department of Geologic Sciences, Box 1846 324 Brook St., Providence, RI 02912 United States
AU: Webb, S C
EM: SCW@LDEO.COLUMBIA.EDU
AF: Lamont-Doherty Earth Observatory Seismology Geology and Tectonophysics , 61 Route 9W - PO Box 1000, Palisades, NY 10964 United States
AB: Receiver function analysis of ocean bottom seismometer (OBS) data provides a unique opportunity for high resolution imaging of subsurface seismic discontinuities. However, because the OBS is located at the fluid solid boundary of the seafloor, reverberations from both the water column above and the oceanic crust below complicate the deconvolved signal. In addition, ultra slow sediment layers (ƒ < 400 m/s) of varying thickness, which create extremely high amplitude (S/P > .5) converted phases from the crust-sediment boundary, reverberate in the sediment column. Using the 11 month OBS deployment of the Gravity Lineations Intraplate Melting Petrology and Seismologic Expedition (GLIMPSE) we observe both the water column reverberations on the pressure record of the instruments as well as the sediment layer reverberations on the radial component from teleseismic events. We use this data to parameterize both types of reverberations to enhance the interpretation of receiver functions. Synthetic seismograms indicate that the amplitudes of water reverberations dominate the pressure record with a more subtle effect on the vertical record. Using reflection coefficient and the two way travel times determined from the observed pressure records we deconvolved the reverberation signal from the pressure and vertical component of our data, reducing the amplitudes of the water column reverberations in both records for up to 25 s before the effects of focusing and defocusing of the reverberation signal by heterogeneities render the assumption of simple reflections on a flat plane invalid. Similar analysis of synthetic seismograms indicates that sediment reverberations dominate the high frequency spectra of the radial component. We determined the S-P amplitude and delay time for the P-S conversion from the crust-sediment boundary from a suite of events at different slownesses. As expected the delay times are constant and on the order of a few tenths of a second because of the near vertical incidence caused by the sudden drop in shear velocity, and the S-P amplitudes increase with increasing slowness. With these two parameters we are able to invert for sediment layer thickness and shear velocity, and perhaps more importantly provide a minimum station correction for S delay times for use in body wave tomography.
DE: 7220 Oceanic crust
DE: 7245 Mid-ocean ridges
SC: Seismology [S]
MN: Fall Meeting 2005