GENERATION OF SEISMIC WAVES BY WEIGHT DROPS

Abstract

A series of experiments designed to evaluate the weight‐drop technique was conducted in West Texas. These tests demonstrated the general nature of the seismic waves generated by a weight drop and the effectiveness of compositing drops in providing useful reflection information. At the first of two test sites discrete waves from single drops consisted of a refracted wave, an air‐earth coupled wave, reflected wave segments, and fragmentary waves which were likely dispersive surface waves. A 72-seismometer array provided appreciably more reflected wave segments on records from single drops and also on records from the composite of these drops than did a single seismometer. Additional testing revealed that records prepared from weight drops along three parallel lines 100 ft apart recorded at the same seismometer station are appreciably different. Compositing of the drop lines in general did not provide reflections superior to the best on individual lines. At the second test site record quality appeared significantly superior to that at the first site. Discrete waves on records from single drops recorded by a 36-seismometer array were of the same types as those observed previously. However, the air‐earth coupled wave, prominently developed at the first site, did not appear. Compositing of drops provided two prominent reflections which were correlatable over a 5-mile traverse.