On: “Search for Geothermal Siesmic Noise in the East Mesa Area, Imperial Valley, California,” by H. M. Iyer (GEOPHYSICS, December 1975, p. 1066–1072)

Abstract

Dr. Iyer rightfully points out that cultural noise sources (e.g., traffic, canals) tend to mask smaller amplitude geothermally generated microtremors. These problems have been recognized by other investigators as well. However, we take exception to his conclusions questioning the validity of groundnoise surveys as a geothermal exploration tool based solely on this study or his other survey in Long Valley, California where he had 1000 head of cattle nibbling on his geophones. Areas adjacent to cultural noise generators are not meant to be surveyed by this technique, as he points out. But what of the hundreds of other areas that are culturally silent? Results from these areas have yet to be weighed. Preliminary results from suitably applicable areas appear to have favorable indications. One prospect drilled on a groundnoise anomaly has been confirmed as a major geothermal find. Crustal inversion techniques applied to groundnoise spectra have been used to interpret geological structure. Gravity and resistivity profiles, and well log information over the same areas, have verified the groundnoise interpretations. As with many other geophysical methods, groundnoise should be used as a reconnaissance tool or in conjunction with other surveys.