HR: 13:45h
AN: S23C-01 INVITED     [Abstracts]
TI: A 35-40% Likelihood of a Highly Damaging Tokyo Earthquake in Next 30 Years
AU: * Stein, R S
EM: rstein@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, MS 977, Menlo Park, CA 94025 United States
AU: Toda, S
EM: s-toda@aist.go.jp
AF: Active Fault Research Center, Geological Survey of Japan, AIST, Site 7, Higashi 1-1-1, Tsukuba, 305-8567 Japan
AU: Parsons, T
EM: tparsons@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, MS 977, Menlo Park, CA 94025 United States
AU: Bozkurt, S B
EM: sbozkurt@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, MS 977, Menlo Park, CA 94025 United States
AB: Tokyo and its outlying cities are home to one-quarter of Japan's 127 million people. Highly destructive earthquakes struck the capital in 1703, 1855 and 1923, the last of which took 105,000 lives. Reoccurrence of any of these shocks today would cost about one trillion dollars, of which perhaps 10% is insured. Fueled by Tokyo's rich data trove but hindered by its complexity, we carried out a new hazard assessment. We used the prehistoric record of great earthquakes preserved in uplifted marine terraces and tsunami deposits (17 M~8 shocks in the past 7,000 years), historical shaking (10,000 intensity observations in the past 400 years), the dense modern seismic network (300,000 earthquakes in the past 30 years), and the world's best geodetic array (150 GPS vectors spanning the past 10 years). We propose that a dislodged block of the Pacific plate is jammed between the Pacific, Philippine Sea and Eurasian plates beneath Tokyo, and controls much of Tokyo's seismic behavior for M≤7.5 shocks, including the damaging 1855 M~7.3 Ansei-Edo shock. On the basis of frequency-magnitude curves, earthquakes similar to the Ansei-Edo event should be quite frequent (25-35% likelihood in an average 30-yr period), and so such events dominate the combined probabilities. In contrast, our renewal model for the great 1703 and 1923 type plate boundary shocks yields a ~1% probability for the next 30 yr, with a time-averaged 30-yr probability of ~8%. The resulting net likelihood for severe shaking in Tokyo, Kawasaki, and Yokohama for the next 30 years is 25%-40%, but how can it be validated? The long historical record in Kanto affords a rare opportunity to calculate the probability of shaking in an alternative manner, based almost exclusively on intensity observations. This approach permits robust estimates for the spatial distribution of shaking, even for sites with few observations. The resulting probability of severe shaking over an average 30-yr period is ~35% in the Tokyo, Kawasaki, and Yokohama and ~10% in Chiba, in good agreement with our independent estimate, and thus bolstering our view that Tokyo's hazard looms large.
UR: http://quake.wr.usgs.gov/~tokyo/
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Seismology [S]
MN: Fall Meeting 2005