First break refraction methods to calculate statics

Abstract

The methods which calculate weathering statics from first break refraction data often involve the determination of the intercept time Ti and an estimate of the velocity of the consolidated formation V1, with the weathering velocity obtained from an uphole or Low Velocity Layer (LVL) survey. It is erroneous to extract the intercept time Ti on the x-t graph for determination of the delay time Td (from Td, = 1/2 Ti), or to estimate the consolidated formation velocity V1 from the gradient of the line of best fit through the x, t points, on the basis of refraction first breaks obtained from individual seismic shot records. However, the iterative method minimises the error in estimation of the intercept time T1 for the calculation of weathering statics, and obtains the consolidated formation velocity as a by-product, which is then used to compute the elevation statics.