HR: 1340h
AN: S33A-1037    [Abstracts]
TI: The Lithospheric Velocity Structure in New Madrid Seismic Zone from Teleseismic Travel Time Data
AU: * Zhang, Q
EM: qz9n9@missouri.edu
AF: University of Missouri-Columbia, 101 Geology Building, Columbia, MO 65211,
AU: Sandvol, E
EM: sandvole@missouri.edu
AF: University of Missouri-Columbia, 101 Geology Building, Columbia, MO 65211,
AB: Totally 2664 teleseismic P arrivals have been used to invert the 3D velocity fluctuations in New Madrid Seismic Zone (NMSZ). These new teleseismic dataset were manually collected from 122 earthquakes (magnitude >= 5.0 Mb) and 105 stations through the period 1999-2005. Teleseismic travel times were determined by a semi- automated method of Multi-Channel Cross-Correlation (MCCC). We used a shorter correlation window for impulsive arrivals and a longer correlation window for un-impulsive ones to achieve high quality readings. Using the measured travel times we tomographically mapped the 3D P wave velocity structure in NMSZ in a space of 500 x 500 x 200 km. The tomographic model shows that a consistent low velocity anomaly is strongly correlated with three main NMSZ faults, where dense seismicity concentrates. This low anomaly extends down to the bottom of the model (200 km) with a decreasing magnitude of perturbation. It is also oriented parallel to the major trend of NMSZ faults, or the Realfoot Rift Zone (RRZ). Our observed anomaly of relatively low velocity lies within a much larger anomaly of faster Pn velocity that spans entire NMSZ and surrounding regions. It requires that the absolute velocity of this relatively slow anomaly is more close to the average velocity in the uppermost mantle whereas the surrounding regions are substantially faster. The low velocity anomaly in the crust seems to correlate with both the active faults and high gravity in NMSZ. It suggests that a fault zone may extend throughout much of the crust.
DE: 7203 Body waves
DE: 7205 Continental crust (1219)
DE: 7218 Lithosphere (1236)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7270 Tomography (6982, 8180)
SC: Seismology [S]
MN: 2007 Fall Meeting