EMISSION OF CHARGED-PARTICLES FROM INDENTATION FRACTURE OF ROCKS

IT has long been realized that earthquakes are often associated with various kinds of anomalous electromagnetic phenomena. These phenomena might be caused by rock failure in the Earth's crust, but the details of the mechanisms are still unknown. Here we describe an attempt to measure the emission of charged particles from rocks undergoing indentation fracture under atmospheric conditions, using a specially designed indentation system. High electron and ion emission intensities could be detected during parts of the loading cycle when cracking occurred around the indent. The emission behaviour of feldspar and quartz in granite was different from that of the hygroscopic matrix of hornblende andesite; moisture in the hornblende andesite enhanced emission appreciably. The different behaviour observed may be attributable to two different mechanisms. © 1990 Nature Publishing Group.