Constraining Compression Wave Velocity Profiles Using Incidence Angles of P Waves

Abstract

This study proposes a method of constraining compression (P) wave velocity (VP) profiles (up to a depth of 1700 m) using P-wave seismograms recorded on the ground surface. The relationship between the incidence angle of P waves near the ground surface and the ratio of the radial to vertical components of P-wave seismograms on the surface is developed based on 895 seismograms recorded at 630 Kiban-Kyoshin network (KiK-net) stations in Japan. The incidence angles for the underlying layers with hypothesized VP values are estimated using Snell's law. The epicentral distance is estimated using these incidence angles and layer thicknesses. The processes of estimating the incidence angles and the epicentral distance are repeated using a new hypothesis on VP profiles, until the misfit between the estimated epicentral distance and the known epicentral distance is smaller than the predefined tolerance. This methodology is validated using the measured VP profiles at eight KiK-net stations that exceed a depth of 800 m. When predefined layer thicknesses are used, the standard deviations of the between-site residuals for various depth intervals vary from, approximately, 0.11 to 0.22, indicating good agreement between the measured and estimated VP profiles. For the cases of known layer thicknesses, the standard deviations of between-site residuals vary from 0.11 to 0.19.