Joint Shear‐Wave Analysis Using MASW and Refraction Traveltime Tomography

Abstract

We use the multichannel analysis of surface waves (MASW) and SH‐wave refraction traveltime tomography to constrain each method's starting layer‐model at a site located at the Yuma Proving Ground, AZ. Our treatment resulted in a more stratified, higher‐resolution MASW S‐wave velocity (Vs) model that deviated from the tomographic SH‐wave solution by approximately 15%. The top 12 m were our target at the test site, which is comprised of roughly 30 m of unconsolidated sediments overlying bedrock. A bungee‐assisted drop‐weight source was used for MASW and a hammer and block were used for the refraction survey. A preliminary MASW profile served as the starting model for refraction inversion. The resultant Vs tomogram contained slightly higher velocity ranges and imaged a highvelocity layer not apparent with initial MASW results. Using this a priori information, along with density values from well logs, more layers were added to an updated Vs model for MASW inversion. The subsequent higher‐resolution MASW profile moved toward the tomographic solution. The use of two inversion schemes allowed a more constrained Vs model of the site, while limiting resolution uncertainties for the MASW Vs section. Moreover, the possible over‐parameterization problem seen with increased layers is defended through refraction comparison. We recommend the combined approach as a means to constrain MASW inversion and increase confidence in future Vs appraisals.