The Itoigawa-Shizuoka Tectonic Line (ISTL) is a major geological boundary between NE and SW
parts of Japan ( or NE Japan and SW Japan). , which is one of active inland
fault systems with a high slip rate in the Japanese arc ( or Japan island)[(reference)]. The central
and northern parts of ISTL have
a slip rate of 8.6 - 9.5 mm/yr and 3.0 mm/yr, respectively[(reference)], while the southern
part is considered (to have ceased its activity) to be inactive inferred from some observation. The
recurrence interval (or time) (of major earthquake) in the area is estimated at approximately 1000
years inferred from (what???) [(reference)], however,
in spite of the relatively high slip rates, no large event is recorded historically and geologically in
this region over its recurrence interval (or for more than that time). Thus, ISTL is
believed to have now one of the highest probabilities of next earthquake
(occurrence) in Japan.
The objectives of this study are to (clarify and) understand the recent seismicity in and around
the ISTL and relationship between seismicity and the active faults of the
area. We will also try to explain the mechanism that is responsible for
the genesis of these events.
To do so, we selected specific three areas (North, Central, South) along
ISTL and conducted temporary seismic array observations. We deployed 4-9
stations in each area from Aug. to Nov. 2003 with a station interval of
approximately 5 km.