Kazushige Obara

Various types of slow earthquakes have been detected on plate interfaces near the seismogenic zones of megathrust earthquakes. We investigated long-term changes of deep very low frequency earthquake (VLFE) activity over a period of 13 years in Shikoku region, southwest Japan. VLFEs can be categorized as slow earthquakes. VLFE activity is expected to be a proxy of interplate slip.

Deep tectonic tremor, which is extremely sensitive to small stress variations, could be used to monitor fault-zone processes during large earthquake cycles and aseismic processes before large earthquakes.

Slow earthquakes are characterized by a wide spectrum of fault slip behaviors and seismic radiation patterns that differ from those of traditional earthquakes. However, slow earthquakes and huge megathrust earthquakes can have common slip mechanisms and are located in neighboring regions of the seismogenic zone. The frequent occurrence of slow earthquakes may help to reveal the physics underlying megathrust events as useful analogs.