Surprisingly, it is not known why inland earthquakes occur. In the Japanese Islands, it is believed that inland earthquakes are generated as strain energy is accumulated by the subduction of oceanic plates. However, inland earthquakes do not occur by this process alone, since the accumulated strain energy is released through the occurrence of large subduction zone earthquakes. In my research, I propose a hypothesis that continuous slow deformations beneath inland earthquake faults accumulate strain energy on the faults and I am examining this hypothesis using observation data. I have developed a new seismic observation system that enables continuous seismic recording at many stations of an order of ten thousands, which has never been done before. I have named it the Manten System, and I have installed approximately 300 stations in Japan and New Zealand. The project is based at the Abuyama observatory.