HR: 10:35h
AN: T12B-02 INVITED     [Abstracts]
TI: Earthquake Potential Inferred From Recurrence Intervals of Turbidites in the Southeastern Margin of the Japan Sea
AU: * Nakajima, T
EM: takeshi.nakajima@aist.go.jp
AF: Institute for Geo-Resources and Environment, Geologocal Survey of Japan/AIST, Cite 7, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AB: The eastern margin of the Japan Sea, situated along the western coast of the northeast Japan, has been regarded as a new plate boundary. Several damaging earthquakes whose magnitudes were 7.5-7.8 took place along the eastern margin of the Japan Sea during the last century. However, the recurrence intervals of earthquakes in this margin have been poorly known since they were too long to have been covered by historic records. Although several attempts have been made to evaluate earthquake potential using recurrence intervals of deep-sea turbidites in the northern half of this margin, southern half has remained uninvestigated. Assessment of seismicity in this part of the Japan Sea has been urgently required, as a part of this portion (i.e. Sado Ridge) has been suspected to be a seismic gap. In this study, the earthquake potential in the southeastern margin of the Japan Sea was studied based on the recurrence intervals of turbidites. The average recurrence interval of turbidites was estimated around 1000, 500 and 250 years in the southern Sado Ridge (38-39deg.N, 138-139deg.E), the northern Sado Ridge (39-40deg.N, 138-139deg.E) and the northernmost, hypocenter region of 1983 earthquake (40-41deg.N, 139deg.E), respectively. In the Sado Ridge, the last event was estimated at A.D.1200-1600 in the southern part and A.D.1500-1800 in the northern part, respectively. These results suggest that the earthquake potential in the southeastern margin of the Japan Sea is higher than in the northeastern margin where turbidite recurrence intervals of 500-3000 years have been reported. The results also support the notion that the Sado Ridge is a seismic gap and a high-risk area of near future earthquake/tsunami hazards. However, more study is required to reveal the exact seismicity of the eastern margin of the Japan Sea since fault systems there are complex and segmented.
DE: 4863 Sedimentation
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
DE: 1744 Tectonophysics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting