Mode Conversion Technology Provides Lower-Cost Option For Multicomponent Imaging By Glenn Winters, Bob A. Hardage and Bruce Karr MIDLAND-While vertical vibrators, vertical impacts, and shot-hole explosives are regarded as "P-wave" (compressional) seismic sources, these sources produce robust vertical shear (SV) wave fields in addition to P-wave fields at the point they apply their force vectors to the earth. In fact, when a vertical impulse is applied to the earth's surface, P and SV wave fields radiate away from the impact point in all possible takeoff angles. Because SV displacement vectors are oriented in every azimuth direction around the point of vertical force application, a far-field geophone receives radial-S and transverse-S displacements, regardless where a sensor is positioned relative to a vertical force source station. These P-source SV displacements are called "direct-S modes" to distinguish them from SV events created by P-to-SV mode conversions at interfaces remote from a P-wave source station. Direct-S data acquisition with P-wave sources provides important advantages. 94 THE AMERICAN OIL & GAS REPORTER