Common geophysical characteristics of Campi Flegrei, Rabaul and Usu: Three volcanic events

Abstract

Volcanogenic deformations during periods of unrest are related to volcanic seismicity in various ways. Magmas or geothermal fluids intrude beneath volcanoes and cause deformations at the surface gradually or rapidly. Mechanical energies of the intrusions are converted to deformation energy, earthquakes, and also explosions under certain circumstances. Partition among the three kinds of energies provides information of the internal processes and yields a clue to their origin. From the above standpoint, deformations accompanying seismicity at Campi Flegrei, Rabaul and Usu are discussed with the aid of published data. To quantitatively correlate the deformations and the seismicity, we discuss the time-derivatives of uplift and release of seismic energy, which are energetically interrelated. The correlation between them is moderate at Campi Flegrei, somewhat higher at Rabaul and high at Usu, but the data sets are not always equal in quality. The deformation volumes are also different among the three volcanoes. In order to standardize the volumes, seismic energies released by unit volume of each deformation are compared. The specific seismic energy is found to increase from Campi Flegrei through Rabaul to Usu. Such different behavior in seismodeformations among the three volcanoes is interpreted as differences in the mechanism of volcanic activity, and in physical properties of the mediums involved.