A Digital Recording Field System for Geomagnetic-Telluric-Array Studies

Geomagnetic-array studies in the westem United States have identified a number of geomagnetic induction anomalies that are associated with regions of enhanced geothermal heat flow. In 1974, the U. S. Geological Survey began development of geomagnetic-array instrumentation in order to investigate the sources of these geomagnetic induction anomalies in greater detail. The instruments used in these arrays are capable of digital data acquisition, which facilitate handling of the large volumes of data gathered in a geomagnetic-array study, and have a magnetotelluric capability for depth control in the interpretation of such studies. Geomagnetic variations recorded during field studies in central New Mexico illustrate a case of anomalous induction caused by a lateral variation in the conductivity of the earth´s crust.