Network locational testing and velocity variations in central Virginia

Abstract

Twenty-four blasts from three quarries operating in the central Virginia area were used, first to test the locational capabilities of the Central Virginia - North Anna Network and then to generate relative station delay suites for network stations.

Using two different methods of approximating blast origin times, the Closest Station Method (CSM) and the Single Iteration Method (SIM), station delays were derived for different areas within central Virginia. Application of these station delay suites reduced locational errors in the general area from an average of 3.0 ± 1.2 to 1.7 ± 0.6 km (95% confidence level). In both cases, the average equivalent radii, a linear measure of error ellipse size, were 1.3 km. However, this result depends primarily on the improvement at one of the three quarries, where the locational error was reduced from 6.5 km to 2.6 km.

Utilizing one of these methods (the SIM), lateral varational patterns in velocity were inferred and determined to be velocity banding similar to that observed in the Piedmont province in Georgia, North and South Carolina.