HR: 1330h
AN: T42D-0968
TI: Preliminary Results from Integration of 2D PSDM and ODP Leg 196 LWD Velocity Data in the Nankai Accretionary Prism
AU: * Hills, D J
EM: djhills@soest.hawaii.edu
AF: SOEST, U. Hawaii, Dept. of Geology and Geophysics 1680 East West Rd. , Honolulu, HI 96822
AU: Moore, G F
AF: SOEST, U. Hawaii, Dept. of Geology and Geophysics 1680 East West Rd. , Honolulu, HI 96822
AU: Bangs, N L
AF: UTIG, 4412 Spicewood Springs Rd., Bldg. 600, Austin, TX 78759
AU: Gulick, S S
AF: UTIG, 4412 Spicewood Springs Rd., Bldg. 600, Austin, TX 78759
AB: The Nankai Trough "Muroto Transect" has been extensively studied, with 3 Ocean Drilling Program (ODP) legs (Legs 131, 190, and 196), numerous multichannel seismic (MCS) reflection surveys, including a 3D survey in 1999, and several refraction studies. As ODP sites only provide point measurements of structure and physical properties, it is necessary to use other methods, such as MCS reflection studies, to interpolate between sites. 2D prestack depth migration (PSDM) velocity analyses have been carried out on several lines extracted from the 3D MCS data set. Initial lines were chosen to intersect the latest ODP sites (Sites 1173-1175,1178, Leg 190; Sites 808 and 1173, Leg 196). Primary results of these 2D PSDM analyses include more accurate depth sections along the Muroto transect, that are vital for accurate interpretation of physical property and structural information between the ODP sites. Additionally, strucutres have been made clearer through the 2D PSDM, including brightening of the proto-thrust and several backthrusts, as well as bringing out the decollement reflector more continuously. Our PSDM velocities roughly correlate with the core and wireline velocity measurements collected on ODP Legs 131 and 190. As core and wireline velocity measurements are made long after the hole has been drilled, they may not represent in situ values. However, PSDM-calculated velocities have been shown to closely approximate in situ velocities; this may explain the misfit. During ODP Leg 196, Logging-While-Drilling (LWD) measured in situ physical properties at Sites 1173 and 808. With the ISONIC tool, in situ seismic velocities were be accurately measured. The PSDM velocities are shown to correlate significantly better with the ISONIC velocities from Leg 196 than with the core and wireline velocities from previous legs. This confirms that the PSDM velocities calculated are representative of in situ velocities in the prism. Therefore, we can interpolate other physical property measurements (e.g., porosity) between the drill sites, using our PSDM velocities for calibration.
DE: 3025 Marine seismics (0935)
DE: 8150 Plate boundary--general (3040)
SC: T
MN: 2001 AGU Fall Meeting