Understanding of rupturing patterns or fault segmentations for long active fault systems is one of the most intriguing research subjects to evaluate scale of cascade-type earthquakes. Many researchers have proposed segmentation models for long active fault systems, based on various fault activity data. But there are not sufficiently considered the stress condition through its entire length in these segmentation models. As a whole, many long active fault systems in the world might not indicate a uniform static stress condition through it's entire length, but heterogeneous. Therefore, we, at first, need to clear the heterogeneity of static stress condition of a long active fault system derived from the relative plate motion around it, and, then, divide into some stress condition segments based on the heterogeneous static stress condition, in order to consider segmentation models for long active fault systems. The Median Tectonic Line active fault system (hereafter MTLAFS), one of the longest and most active arc-parallel fault systems in Japan, is located in Southwest Japan, and the right-lateral strike-slip movement of this fault system is related to the oblique subduction of the Philippine Sea (PHS) plate. The MTLAFS has ruptured repeatedly during the last 10,000 years, and has high seismic potential both now and in the future. In recent, various kinds of geological and geomorphological researches are conducted for the MTLAFS, providing the detailed fault distribution and fault activity data. There evolve some extensional structures along the MTLAFS in the western Shikoku and Kyushu, while linear trend in the eastern Shikoku. Furthermore, the average horizontal and vertical slip rate along the MTLAFS become lower and higher from east to west, respectively. These facts suggest that the active environment of the MTLAFS changes through the eastern Shikoku to the western Shikoku and Kyushu. On the basis of geological and geophysical, we could divide the MTLAFS into three¡¡stress condition segments, East Shikoku, West Shikoku, and Kyushu segment. The East Shikoku segment and the Kyushu segment are under compressional and tensional stress conditions in N¡ªS direction, respectively. The West Shikoku segment locating between the East Shikoku segment and the Kyushu segment, is under a mixed stress condition (or a transitional stress condition) of compression and tension. Here, the MTLAFS corresponds to the northern tectonic boundary of the Nankai forearc sliver. The principle driving force of the Nankai forearc sliver is the NW subduction of the PHS plate. In addition to this, the SE pulling force derived from the back arc spreading in the Okinawa trough effects to the stress condition of the MTLAFS in the western Shikoku and Kyushu. As the results, the Nankai forearc sliver rotates counterclockwise relative to the Amurian plate, occurring this heterogeneous static stress condition of the MTLAFS. This regional stress condition and active environment around the MTLAFS is analogy with that of the North Anatolian Fault, however scale is different in comparison of these two fault systems.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 8118 Dynamics and mechanics of faulting (8004);
- 8122 Dynamics: gravity and tectonics;
- 8123 Dynamics: seismotectonics