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Investigation of the earthquake sequence off Miyagi prefecture with historical seismograms

Kanamori, Hiroo and Miyazawa, Masatoshi and Mori, Jim (2006) Investigation of the earthquake sequence off Miyagi prefecture with historical seismograms. Earth Planets and Space, 58 (12). pp. 1533-1541. ISSN 1343-8832.

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We investigated the old seismograms of several earthquakes which occurred offshore of Miyagi prefecture in 1933 (June 18, 21:37 UT), 1936 (Nov. 2, 20:45 UT), 1937 (July 26, 19:56 UT), 1978 (June 12, 08:14 UT), and 2005 (Aug. 16, 02:46 UT). A characteristic earthquake model for the sequence of the 1936, 1978, and several other earlier events is the basis of the recent forecast by the Earthquake Research Committee (2003) that “The probability of the occurrence of another similar earthquake in the next 30 years is 99%”. To assess the validity of the characteristic earthquake model, we compared the waveforms, size and other characteristics of these earthquakes recorded at Pasadena, DeBilt, Abuyama, Aso, Weston, Strasbourg, and Christchurch. We conclude that (1) The 1978 event is 3 to 4.5 times larger (in seismic moment) than the 2005 event; (2) The 1936 and the 2005 events are about the same size and are fairly close in location; (3) The 1937 event is smaller than the 1936 event, and is significantly deeper, possibly as deep as 90 km. In contrast, the 1933 event is significantly shallower than the 1936 event. The differences between these events are too large to justify the use of a simple characteristic earthquake model for the probabilistic forecast. The seismic slip rate in this area and along the adjacent subduction zone to the south is about 1/4 of the plate convergence rate, which has an important implication for the long-term seismic hazard in this area.The 2005 West Off Fukuoka Prefecture earthquake caused serious damage to and on Genkai Island as well as to downtown Fukuoka City. There were no strong motion instruments on the island, therefore no one knows how the strong ground motion occurred during the mainshock. The ground motion simulation on Genkai Island is very important to our understanding of earthquake damage at the near-source region. We have conducted an aftershock observation on the island in order to verify site amplification due to steep topography and to record aftershocks for reproducing ground motion during the mainshock by the empirical Green’s function method. The observed records of aftershocks show small variations in the input motions in the island, indicating that the amplification due to the topography seems to be small below 2 Hz. We first estimated the strong motion generation area for the mainshock using the observation records at stations surrounding the source region. We then carried out broadband ground motion simulation on Genkai Island by using the aftershock records as empirical Green’s functions. The simulated ground velocities exceed 1 m/s with a dominant period of 1–2 s due to the forward rupture directivity, and the instrumental seismic intensity reaches 6.6.

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Kanamori, Hiroo0000-0001-8219-9428
Additional Information:© 2005 The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB. Received January 6, 2006; Revised March 30, 2006; Accepted April 23, 2006; Online published February 2, 2007. We thank Katsuyuki Abe for providing us with key information on the old Japanese events. We thank Bernard Dost (DeBilt), Luis Rivera (Strasbourg), Brian Ferris (Christchurch), and John Ebel and Dina Smith (Weston) for locating and sending us the copies of the seismograms used in this study. Anthony Guarino helped us find old seismograms from the Caltech seismogram archive. The copies of the pages of the Gutenberg notepad used in this study were provided by the Archives of the California Institute of Technology. For the study of the 2003 and 2005 events, we used the Japanese F-Net seismograms, and the Global Seismic Network seismograms of the Incorporated Research Institutions for Seismology. We thank Luis Rivera, Toru Matsuzawa, and Keiko Kuge for careful and thoughtful reviews. Hiroo Kanamori acknowledges the support of the Japan Society of Promotion of Science under its Eminent Scientists Award program, which allowed his visit to the Disaster Prevention Research Institute, Kyoto University.
Funding AgencyGrant Number
Japan Society for the Promotion of Science (JSPS)UNSPECIFIED
Subject Keywords:Miyagi-Oki earthquakes, characteristic earthquake, probabilistic forecast, asperity
Issue or Number:12
Record Number:CaltechAUTHORS:20141111-094855637
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51556
Deposited By: Tony Diaz
Deposited On:11 Nov 2014 21:48
Last Modified:09 Mar 2020 13:18

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