Blind Shear-Wave Velocity Comparison of remi and masw Results with Boreholes to 200 m in Santa Clara Valley: Implications for Earthquake Ground-Motion Assessment

Abstract

Multichannel analysis of surface waves (masw) and refraction microtremor (remi) are two of the most recently developed surface acquisition techniques for determining shallow shear-wave velocity. We conducted a blind comparison of masw and remi results with four boreholes logged to at least 260 m for shear velocity in Santa Clara Valley, California, to determine how closely these surface methods match the downhole measurements. Average shear-wave velocity estimates to depths of 30, 50, and 100 m demonstrate that the surface methods as implemented in this study can generally match borehole results to within 15% to these depths. At two of the boreholes, the average to 100 m depth was within 3%. Spectral amplifications predicted from the respective borehole velocity profiles similarly compare to within 15% or better from 1 to 10 Hz with both the masw and remi surface-method velocity profiles. Overall, neither surface method was consistently better at matching the borehole velocity profiles or amplifications. Our results suggest masw and remi surface acquisition methods can both be appropriate choices for estimating shear-wave velocity and can be complementary to each other in urban settings for hazards assessment.