Detection of precursory relative quiescence before great earthquakes through a statistical model 论文

摘要

Relative quiescence is defined as a significant decrease of earthquakes compared with the occurrence rate expected from a point‐process model for ordinary seismic activity. This definition is linked with the idea that aftershocks, as a useful signal for the investigation of seismicity, should not be removed from original occurrence data. The Epidemic Type Aftershock‐Sequences (ETAS) model is proposed to identify patterns in an earthquake sequence in an area, using occurrence time and magnitude data. Even in an active stage of seismicity, a decrease from the expected level can take place, and the significance and size of such a quiescence can be graphically shown using time‐changed occurrence data which are transformed based on the estimated ETAS model. This procedure permits detection of a clear, relatively quiet stage before great earthquakes in Japan and elsewhere in the world. Such relative quiescence lasts a number of years prior to the occurrence of great earthquakes, which occasionally take place in the recovering stage. No significant relative quiescences were seen in the current seismicity of a few wide regions, in and around Japan, including several source regions of expected great earthquakes.