The interdependence of seismic and volcanic phenomena: Some space — Time relationships in seismicity and volcanism

Research is described aimed at detecting significant relationships between patterns of earthquakes and volcanic eruptions. A large data file of seismic and volcanic events has been assembled on punched cards, and two computer programmes used to relate earthquakes to active or potentially active volcanic centres, and deep earthquakes to succeeding shallower ones and volcanic eruptions after the manner suggested byBlot. It is concluded that recognisable sequences occur in some areas, but that the process is neither universal nor invariable. The presence of random events or events due to other causes almost always obscures patterns of seismicity which seem to be related to volcanic eruptions. The «Blot process» appears to operate in some cases but is probably a second order phenomenon: primarily, correlated sequences of seismic and volcanic events result from periods of tectonic instability and perhaps increased tensional conditions which affect very wide areas of the Earth’s surface for periods of several months to several years at a time.