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Analysis of the two-dimensional effect in the H/V spectral ratio method for bedrock depth estimation on bedrock depth estimation by the H/V seismic method

Lanbo Liu (Lanbo.Liu@UConn.edu)
Department of Civil and Environmental Engineering, University of Connecticut, Storrs, CT 06269, USA

Lieyuan Zhu
Department of Civil and Environmental Engineering, University of Connecticut, Storrs, CT 06269, USA

John W. Lane, Jr. (jwlane@usgs.gov)
U.S. Geological Survey Office of Ground Water, Branch of Geophysics, Storrs, CT 06269, USA

Abstract

The horizontal-to-vertical spectral ratio (H/V) method for analysis of microtremor surveys is widely used as a practical and economical way to obtain bedrock depth information for hydrogeological studies and to assess potential site effects for earthquake damage. This method is effective because it relies on the frequency of vibration of the sedimentary layers, even when there are uncertainties in the amplitude. Because of its ease of use, many scientists use the H/V method as an exploration tool since, in the one-dimensional case, the resonance frequency is linked to the shear-wave velocity and the sediment thickness. The accuracy of the H/V method suffers, however, when the sediment-bedrock interface has small-wavelength undulations because the method assumes a horizontally layered earth. To investigate the effect of unevenness of the bedrock interface on the H/V value and to quantify the applicability of this method for estimation of depth to bedrock at a watershed scale, we conducted a series of tests using a finite-difference time-domain numerical model. The general conclusion is that when the wavelength of the bedrock undulation is less than three times the depth to bedrock, there can be a significant effect on the estimate of the fundamental frequency as determined by the H/V method.

Final copy as submitted to the American Geophysical Union for publication as: Liu, Lanbo; Zhu, Lieyuan; and Lane, J.W., Jr., 2007, Analysis of the two-dimensional effect in the H/V spectral ratio method for bedrock depth estimation on bedrock depth estimation by the H/V seismic method: EOS Transactions, American Geophysical Union, v. 88, no. 52, Fall Meeting Supplement, Abstract H21A-0187.