Abstract
The recent development of a dense seismic observation network in Japan enables the detection of various slow earthquakes around the upper boundary of the Philippine Sea Plate, which is subducting beneath Southwest Japan at the Nankai Trough. At the deeper extension of the seismogenic zone, a narrow belt with a length of 600 km is marked by short-term, slow slip events (representing stick-slip at the plate interface with a duration of several days), deep very-low-frequency earthquakes with a predominant period of 20 seconds, and deep low-frequency tremors with a predominant frequency of around 2 Hz. These areas of deep, slow earthquakes can be divided into segments in which events occur with recurrence intervals of 3 or 6 months. Shallow, very-low-frequency earthquakes with a predominant period of 10 seconds occur within the accretionary prism, landward of the Nankai Trough. Shallow, deep slow earthquakes may be related to deformation of the accretionary prism above the subducting plate or metamorphism and dehydration of the subducting plate at depths of around 30 km.
