Long-Living Earthquake Swarm and Intermittent Seismicity in the Northeastern Tip of the Noto Peninsula, Japan

The factors controlling earthquake swarm duration are remain unclear, especially in the long-living ones. A severe earthquake swarm struck the tip of the Noto peninsula, Japan. Ten M > 4.0 earthquakes occurred, and the sequence has continued more than 4 years. We investigated the spatiotemporal characteristics of the swarm using relocated hypocenters to elucidate the factors causing this long duration. The swarm consists of four seismic clusters-northern, northeastern, western, and southern-the latter of which began first. Diffusive hypocenter migrations were observed in the western, northern, and northeastern clusters with moderate to low diffusivities, implying a low-permeability environment. Rapid diffusive migration associated with intermittent seismicity deep within the southern cluster suggests the presence of a highly pressurized fluid supply. We conclude that the nature of this fluid supply combined with intermittent seismicity from the southern cluster and a low-permeability environment are the key causes of this long-living swarm.

Automated summary

The factors controlling the duration of earthquake swarms, especially long-living ones, remain unclear. A severe earthquake swarm occurred on the Noto peninsula in Japan, lasting for more than 4 years and including ten M > 4.0 earthquakes. The swarm consisted of four seismic clusters, with diffusive hypocenter migrations observed in three clusters and rapid diffusive migration associated with intermittent seismicity in the southern cluster. The nature of the fluid supply, intermittent seismicity, and low-permeability environment are identified as the key causes of this long-living earthquake swarm.