CASE STUDIES OF SHEAR-WAVE SPLllTlNG IN REFLECTION SURVEYS IN SOUTH TEXAS

Three lines of shear-wave reflection surveys are processed to show the variation of shear-wave splitting with azimuths and offset. Signal amplitudes and time delays between the split shear waves correlate with fracture density and related oil production in the sur-vey area. The three lines, 1 and 2 in Dimmit County and 3 in Frio and La Salle Counties, were, respectively, parallel, perpendicular and at about 40 ” to the regional fracture strike. The time delays of the split shear waves measured from the stacked sections of the faster (Sl) and slower (S2) split shear waves of Line 1 are small, and events in both Sl and 52 sections have strong amplitudes and show good con-tinuity. These features correspond to the absence of commercial oil production nearby. There is a trend of increasing time delays between split shear waves from the Sl and S2 stacked sections o