Research in Fiscal Year 1998 Findings of Active Fault Survey Projects

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The followings are main results of active fault and paleoearthquake researches in the 1998 fiscal year. They are published in the Geological Survey of Japan Interim Report no. EQ/99/3 (Interim Report on Active Fault and Paleoearthquake Researches in the 1998 Fiscal Year).Map of the Studied Area
Summarized survey result and earthquake potential of major active faults in the Kinki Triangle, central Japan [PDF 24KB]
Authors: Yuichi Sugiyama, Koichi Shimokawa, Yasuo Awata, Kenji Satake, Kiyohide Mizuno, Toshikazu Yoshioka, Taku Komatsubara, Futoshi Nanayama, Yoshihiko Kariya, Takashi Azuma, Yuichiro Fusejima, Eikichi Tsukuda, Akira Sangawa and Toshihiko Sugai (Univ. Tokyo)

Abstract:
After the 1995 Kobe earthquake, the Geological Survey of Japan is conducting systematic study of major active faults in the Kinki Triangle, a central part of Japan containing Osaka and Nagoya metropolitan areas. We have studied 25 active faults, about 75% faults in this region, by the end of the 1998 fiscal year. We rearranged these faults into 18 seismogenic faults based on the criteria proposed by Matsuda (1990) for grouping and dividing faults. We next divided the seismogenic faults into 31 behavioral segments, using 2-km distance, difference in rupture history, and a value of 20,000×displacement per event as criteria for segmentation.
Earthquake potential of each segment was assessed based on the elapsed time ratio and probability for rupture in the coming 100 years. It is made clear that the 24-km-long Aibano segment with 3 to 5 m unit slip, on the west coast of Lake Biwa, has 12 to 38% probability of an M≧7 earthquake within the next 100 years. The 44-km-long Uemachi fault traversing Osaka has 5% probability of a big earthquake in the coming 100 years at the maximum.
On the other hand, at least 14 behavioral segments including the Hokudan which produced the Kobe earthquake have relatively low earthquake potential. Their probabilities for rerupturing in the next century are less than 0.2%. Most of them proved to be causative faults of disastrous historical earthquakes such as the 1325 Shochu, 1586 Tensho, 1596 Keicho and 1662 Kanbun earthquakes.

Seismogenic faults and behavioral segments in the Kinki Triangle and their elapsed time ratios.

Seismogenic faults and behavioral segments in the Kinki Triangle and their probability for an earthquake in the next 100 yr.

	Contents
1	Behavioral segments and their cascades for the earthquake occurrence in the Japanese surface ruptures -Tentative Study-
2	Sedimentological study of postulated tsunami deposits along the Kuril subduction zone, eastern Hokkaido, northern Japan: preliminary study around the Kiritappu marsh land
3	1998 rupturing andpaleoseismicity of northern Shizukuishi-bonchi seien fault
4	Subsurface structure of the Fukaya fault and its southeastern extension as perceived on seismic reflection profiles
5	Reevaluation of the displacement per event along the Tsukioka fault, central Japan, based on the fault geometry in the shallow depth
6	P-wave seismic reflection survey of the Kakuda-Yahiko fault group in Niigata Prefecture, central Japan
7	Detailed structure of the shallow part of the Kakuda-Yahiko fault group revealed by high-resolution S-wave eflection survey and seismic cone penetration tests
8	900,000-year cyclostratigraphic record from a 600m core, GS-NB-1, the Nobi Basin, central Japan
9	Basin dynamics and subsidence history of the Nobi plain, central Japan, revealed by 600m-deep core analyses and deep seismic reflection survey
10	Late Holocene paleoseismicity of the Yoro fault system, central Japan－geologic evidence of the last two historical large (M7.8 to 8) earthquakes of Tensyo jishin (earthquake) in 1586 and Tenpyo jishin (earthquake) in 745
11	Paleoseismological study of the Kizugawa fault system
12	Segmentation of the surface ruptures associated with the 1891 Nobi earthquake, central Honshu, Japan, based on the paleoseismic investigations
13	Tectonic microforms and the latest activity of the Nagataki fault, the Nobi active fault system in central Honshu, Japan
14	High-resolution aeromagnetic survey in the Fukui plain, central Japan
15	High-resolution gravity survey in the Fukui plain, central Japan
16	High-resolution gravity survey of the south extension of the Yanagase fault on the northeastern coast of Lake Biwa
17	Paleoseismological study of the Daguchi fault in Fukui Prefecture
18	Sonic prospecting and boring surveys of the Mikatagoko basins, Fukui Prefecture
19	Trenching study of the Mikata fault and reconstruction of crustal movements during the 1662 Kambun earthquake by historical records
20	Supplementary study of the Katata fault on the west coast of Lake Biwa and sublacustrine faults off Imazu to Takashima, Shiga Prefecture
21	Paleoseismological study of the Mitoke and Tonoda faults in Kyoto Prefecture
22	Paleoseismological study of the Tomogashima-suido fault, Median Tectonic Line active fault system, during the Holocene, at the eastern side of the Kitan Straits, central Japan
23	Paleoseismicity and activity study of the Hinagu fault system
24	GSJ-MTA international cooperative research on the Anatolian paleoseismicity