Observations of Gravity and Geomagnetic Field with Special Reference to Detection of Their Anomalies

Abstract

Observations of gravity and geomanetic field have recently been made, as a remote-sensing method, for investigations of active fault structure and also for studies of anomalous changes before earthquake occurrences. Anomalies in the distribution of gravity have often turned out to be closely associated with active faults, sometimes with faults which have not been identified by the geomorphological and geological methods. Anomalous changes in gravity were also found in association with crustal uplift. Anomalies in the geomagnetic field have been found in relation to active faults and the anomalies could be interpreted as indicating an anomalous magnetic structure near faults. Such information should be taken into account when observation sites are to be selected for monitoring of anomalous changes before earthquakes, because significant changes are expected to appear near earthquake faults, as demonstrated by a typical example.