A NEW ALGORITHM TO DETERMINE TRUE SEISMIC VELOCITY VALUES FOR DIPPING LAYERS DIRECTLY FROM THE TIME-DISTANCE CURVE

Shallow refraction seismic technique is widely used to determine depths to subsurface layers by calculating the velocities of seismic waves travelling through these layers. Calculating seismic velocities is also useful in estimating depths and elastic moduli of these layers which are vital for engineering investigations. Calculating such velocities for dipping layers using conventional algorithms is problematic and usually yields inaccurate velocity estimates. Even slight dips in subsurface layers can impose significant errors in their velocities and hence errors in their depth and elastic moduli values.

This study presents a new algorithm to calculate true seismic velocity of dipping layers directly from time–distance curve. The new algorithm is based on the time differences between the forward and the reverse arrival times. Tests conducted on synthetic seismic data show that the seismic velocities calculated using the new algorithm match the actual model velocities while those calculated using the traditional methods have significant amount of error. Moreover, this new algorithm in general needs neither interpolation nor extrapolation, guaranteeing an accurate estimate of the true velocities of dipping layers.