Techniques for Interpreting and Improving Vp/Vs Measurements When Assuming a Layered Geothermal Model

Abstract

If a geothermal area is modeled as a layered earth and elastic constants vary only with depth, then measured Vp/Vs ratios will depend on microearthquake positions relative to the array as well as focal depths. Vp/Vs ratios obtained from microearthquake data are relationships of apparent P and S phase velocities. An apparent Vp/Vs ration can represent a medium Vp/Vs value if rays to all stations are through one medium, or if arrivals are critical refractions from a layers at depth. Improved measurements can be obtained when factors contributing to errors in measuring Vp/Vs are understood. In additional to P and S timing precisions, the error in measuring Vp/Vs depends on epicenter position relative to an array with particular configuration, and the P and S apparent velocities.