Japan has experienced many destructive earthquakes. The prevention and mitigation of disasters are important aspects of seismology. Earthquakes have been elucidated through multiple studies, providing significant information for earthquake prediction. We review the new results obtained through the “Second Earthquake and Volcano Hazards Observation and Research Program.” The project advanced understanding in several key areas. GNSS-A observations were performed in the southern part of the Kuril subduction zone, the Japan Trench, and the Nankai Trough, revealing accurate data regarding movement at the plate boundary. GNSS-A observations in the Kuril subduction zone were successfully conducted. The data from the Japan Trench and the Nankai Trough showed that temporal changes and regional variations in crustal movement could be detected, enabling the monitoring of plate interface displacement. This knowledge will be valuable in evaluating the risk of plate boundary earthquakes. The technological advances in this project have significantly contributed to the acquisition of stable data. For instance, knowledge of the mechanism of intraslab earthquakes has improved. The fluids and fissures existing within the plate were found to be closely related to the cause of intraplate earthquakes. Earthquakes occurring on active faults cause severe disasters, making risk mitigation crucial. This project identified numerous cases in which earthquakes were associated with crustal fluids. A comprehensive understanding of these cases will help elucidate the phenomenon of earthquakes caused by active faults. Seismic experiments were conducted in a laboratory to understand fault slips and the mechanisms driving these earthquakes.

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