HR: 0830h
AN: S51C-0062    [PDF]
TI: A Rayleigh Wave Analysis at the DESERT Broadband Array
AU: * Laske, G
EM: glaske@ucsd.edu
AF: IGPP-0225 UC San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0225 United States
AU: The DESERT Team, .
AF: IGPP-0225 UC San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0225 United States
AB: A variety of geophysical experiments conducted in the 2000/2001 DESERT project in Israel, Palestine and Jordan provided a rich palette of datasets to examine the crust and uppermost mantle beneath one of Earth's most prominent fault systems, the Dead Sea Transform system (DST). As part of the passive seismic component, thirty broad--band sensors were deployed across the DST for roughly one year. During this deployment we recorded 115 teleseismic earthquakes that are suitable for a fundamental mode surface wave analysis at intermediate periods (20-120s). Analyzing arrival angle measurements we are able to determine the orientation of the horizontal components to within one degree. Some sensors were misaligned by nearly 10 degrees which is confirmed by the station operators (e.g. one station was oriented parallel to a road because the compass broke). The frequency--dependent Rayleigh wave phase at each station is measured with respect to each other rather than relative to a synthetic. This results in a much more precise dataset than what is common for global dispersion datasets. A preliminary analysis reveals a seismically fast but thin lid (about 80~km) to the west of the DST. Toward the east, shallow seismic velocities are low while a deeper low velocity zone is not detected. This contradicts the currently favored thermo-mechanical model for the DST that predicts lithospheric thinning toward the east. Unfortunately, the distribution of sensors at the array was not ideal for a surface wave analysis. The stations west of the DST were equipped with true broad-band sensors (Streckeisen STS-2 or Guralp CMT-3T), while the stations east of the DST were equipped with ''wideband'' Guralp-40T that are considerably noisy at periods longer than 40s. We we able to measure dispersion down to 80~s, sometimes below that, depending on the size of the earthquake, but not for all earthquakes. Dispersion at these periods are needed to trace the bottom of the lithosphere. The apparent absence of the low--velocity zone on the eastern side of the DST is therefore somewhat uncertain. A follow--up deployment of ten STS-2 sensors in Jordan should resolve this issue within the coming year.
UR: http://www.gfz-potsdam.de/pb2/pb22/projects/deadsea/ds-home.html
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 7255 Surface waves and free oscillations
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8180 Tomography
SC: Seismology [S]
MN: 2003 Fall Meeting