HR: 0830h
AN: S41A-05    [Abstracts]
TI: Detailed Three-Dimensional P and S Wave Velocity Models for the New Madrid Seismic Zone
AU: * Powell, C
EM: capowell@memphis.edu
AF: Center for Earthquake Research and Information, University of Memphis 3876 Central Ave., Ste 1, Memphis, TN 38152 United States
AU: Withers, M
EM: mwithers@memphis.edu
AF: Center for Earthquake Research and Information, University of Memphis 3876 Central Ave., Ste 1, Memphis, TN 38152 United States
AU: Vlahovic, G
EM: gvlahovic@nccu.edu
AF: Department of Geography and Earth Sciences, North Carolina Central University, Durham, NC 27707 United States
AB: Detailed P and S wave velocity models and Vp/Vs values have been determined for the New Madrid Seismic Zone (NMSZ) based upon arrival times recorded by the New Madrid seismic network and by PANDA stations. The combined data set consists of 11,778 P wave arrivals and 8,579 S wave arrivals recorded by 97 stations. We used a modified version of the Benz et al., 1996 algorithm that inverts simultaneously for both P and S velocities and hypocentral locations (Tryggvason et al., 2002). The ability to specify independent P and S wave starting velocity models, rather than an S wave model linked to the P wave model via a constant Vp/Vs ratio, is particularly important for the NMSZ because the surface sediments have highly variable Vp/Vs ratios. Block size was reduced to 2x2x2 km, yielding the most detailed image of the NMSZ ever obtained. Inversion results were tested using chessboard models, spike tests and reconstruction techniques. Intrusions are imaged in great detail. Low P wave velocity and high S wave velocity appear to be correlated with earthquake occurrence; this results in distinct regions of low Vp/Vs values that correspond to the major arms of seismicity. The unusual low Vp/Vs values could be due to lithology variations but may be related to fluid saturation and porosity variations.
DE: 7205 Continental crust (1242)
DE: 7230 Seismicity and seismotectonics
DE: 8123 Dynamics, seismotectonics
DE: 8180 Tomography
SC: Seismology [S]
MN: 2005 Joint Assembly