HR: 0800h
AN: S21A-0267    [Abstracts]
TI: Improvement of 3-D Automatic Surface-Wave Tomography Picks Using Windows Defined by the 1-D Refraction-Microtremor Method
AU: * Abbott, R E
EM: reabbot@sandia.gov
AF: Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185-1168 United States
AU: Bartel, L C
EM: lcbarte@sandia.gov
AF: Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185-1168 United States
AU: Engler, B P
EM: bpengle@sandia.gov
AF: Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185-1168 United States
AU: Pullammanappallil, S
EM: satish@optimsoftware.com
AF: Optim, UNR Seismology Lab 1664 N. Virgina St., Reno, NV 89557-0141 United States
AB: We present a method to improve the automatic arrival-time picking of small source-receiver-offset surface waves. We use very narrow bandpass filters and the Hilbert transform to find the instantaneous amplitude at discrete frequencies. We then make the assumption that the maximum instantaneous amplitude of the waveform represents the fundamental mode surface-wave arrival at that frequency. This assumption can be violated in a number of ways, chiefly when a mode other than the fundamental is dominant over a given frequency range. To better recognize subsurface geometries that give rise to these situations, we first gather the data from all source-receiver pairs, sort by offset, and process them using the Refraction-Microtremor (ReMi) method. In this way, we make a 1-D approximation over the entire region sampled by the tomography data. The resulting ReMi slowness-frequency plot allows us to simultaneously identify not only fundamental-mode, but also higher-mode, surface waves. We then define windows representing an acceptable range of slownesses for each mode for each frequency. If the automatic tomography picks fall outside these windows, the value is not used and is flagged for further analysis. This process has been tested on a 330-element seismic array near Albuquerque, New Mexico, and resulted in better agreement when compared to body-wave tomography of the same site.
DE: 7255 Surface waves and free oscillations
DE: 7299 General or miscellaneous
DE: 0910 Data processing
DE: 0935 Seismic methods (3025)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting