HR: 0800h
AN: S41A-03    [Abstracts]
TI: A Study of Dispersion and Directionality Using Ambient Seismic Noise in Pakistan
AU: * Foster, A E
EM: anna.foster@marist.edu
AF: Marist College, Department of Mathematics 3399 North Road, Poughkeepsie, NY 12601, United States
AU: Frank, S D
EM: scott.frank@marist.edu
AF: Marist College, Department of Mathematics 3399 North Road, Poughkeepsie, NY 12601, United States
AU: Ferris, A
EM: aferris@westongeophysical.com
AF: Weston Geophysical, 181 Bedford St. Ste. 1 , Lexington, MA 02420, United States
AU: Johnson, M
EM: shellyj@optonline.net
AF: Weston Geophysical, 181 Bedford St. Ste. 1 , Lexington, MA 02420, United States
AB: As suggested by recent theoretical and observational studies, the long-time average cross-correlation of the ambient noise field between two seismographs approximates the inter-station Green's function. Using data from a PASSCAL deployment of 9 broadband seismographs in NE Pakistan (1992), we examine estimates of the longitudinal, radial and transverse Green's functions between all station pairs. The seismic stations have separation distances ranging from 40 to 160 km, and in most cases 73 days of continuous data are cross- correlated for each pair. Dispersion characteristics of the time-averaged correlation functions are analyzed using Hilbert transform filtering. Preliminary results show group velocities between 1 and 4 km/s for the period band between 2 and 20 seconds. Asymmetry between the causal and acausal portions of the cross-correlation functions is interpreted as preferred directionality of the ambient noise field. By comparing peak energy at causal and acausal delay times, the field appears to propagate from the north-northeast over the time period of interest. This may indicate that noise field propagation is related to the regional tectonics at short periods.
DE: 7200 SEISMOLOGY
DE: 7255 Surface waves and free oscillations
SC: Seismology [S]
MN: 2007 Joint Assembly