HR: 1345h
AN: T22C-0932
TI: Multichannel Seismic Imaging of the Lower Slope Offshore Nicaragua
AU: * Ahmed, I
EM: ahmed@ig.utexas.edu
AF: Univ of Texas Inst for Geophysics, 4412 Spicewood Sprgs Rd, Bldg 600, Austin, TX 78759-8500 United States
AU: McIntosh, K D
EM: kirk@ig.utexas.edu
AF: Univ of Texas Inst for Geophysics, 4412 Spicewood Sprgs Rd, Bldg 600, Austin, TX 78759-8500 United States
AU: Silver, E A
EM: esilver@es.ucsc.edu
AF: Earth Sciences Department, Univ of California, Santa Cruz, A112 EMS Bldg, Santa Cruz, CA 95064 United States
AU: Ranero, C R
EM: cranero@geomar.de
AF: GEOMAR, Wischhofstrasse 1-3, Kiel, 24148 Germany
AB: In May-June 2000 we acquired a large seismic reflection data set off the Pacific coast of Nicaragua. Using these data we are creating seismic images of the plate boundary and subducting Cocos plate beneath the lower slope offshore Nicaragua. Our goal is to use these images to study the relationships between the upper and lower plates here, especially with regard to the influence of subducting plate structure on sediment subduction, subduction erosion and seismogenic characteristics. Because of the dramatic variation in geochemical sediment tracer signal along the Central American volcanic arc, we are particularly interested in documenting the efficiency of sediment subduction, its along strike variation, and to see if it corresponds with the geochemical anomalies. We have done standard processing through post stack time migration on of the MCS lines that we have acquired. Key features of the Cocos plate structure are fault blocks that rotate to form half grabens, rather than the more typical horst and graben structure, as it bends down into the Middle American Trench. On some of the lines we observe that the fault block rotation is preserved as the lower plate is subducted. In one of the lines we also observe a subducted seamount and the upper plate deformation that results from it. Although we acquired high quality data, it has remained difficult to image the lower slope and subducting plate structure in detail with conventional processing techniques. Several characteristics of this environment pose seismic imaging problems: the area is heavily faulted, adjacent reflection boundaries have contrasting dips, and the velocity structure changes rapidly both laterally and vertically. In this environment the common midpoint gathers do not represent a collection of true common subsurface reflection points. To get a clearer image of the lower slope, we are starting to do more rigorous prestack depth migration.
DE: 1030 Geochemical cycles (0330)
DE: 3640 Igneous petrology
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8123 Dynamics, seismotectonics
DE: 8180 Tomography
SC: T
MN: 2001 AGU Fall Meeting