1994年北海道東方沖地震 (<i>M</i>_JMA=8.1) のCMT解: 広帯域強震計データを用いたインバージョン

• 長 郁夫

  北海道大学大学院理学研究科地球惑星科学専攻

• 中西 一郎

  京都大学大学院理学研究科地球物理学教室

• 今西 和俊

  弘前大学理学部地球科学教室

• 佐藤 魂夫

  弘前大学理学部地球科学教室

書誌事項

タイトル別名

• The CMT Solution of the 1994 October 4 Shikotan Island Earthquake (<i>M</i>_JMA=8.1) Recorded by Broad-band Strong-motion Seismographs
• 1994年北海道東方沖地震(MJMA=8.1)のCMT解--広帯域強震計データを用いたインバージョン
• 1994ネン ホッカイドウ トウホウオキ ジシン MJMA 8.1 ノ CMT

抄録

The great Hokkaido Toho-Oki earthquake (M_JMA=8.1) occurred at 13h 23m on October 4, 1994 (GMT), in the region off the Shikotan Island. Since all STS-1 seismographs in Eastern Japan were saturated by the earthquake, broad-band strong-motion seismographs (velocity response is flat from 0.015s to 600s) installed at two stations in the region of the northern end of the main land of Japan, where the seismic intensity of 4 was reported by JMA, were used to make a long-periods (≥70s) moment tensor inversion. Our solution in terms of best double couple is (strike, dip, slip)=(69°, 67°, 119°), M_c=1.8×10²¹ Nm (M_w=8.0), and centroid depth=42km. This depth of 42km and aftershock distribution determined by the Research Center for Earthquake Prediction of Hokkaido University may suggest that the earthquake occurred within the Pacific plate.<br>Since the data of this great Hokkaido Toho-Oki earthquake are recorded at epicentral distances of about 5 to 6°, the spatiotemporal source finiteness must affect our estimate of moment tensor even at long-periods (≥70s). Our numerical experiments using finite sources (e. g., unilateral moving line source) show that the source finiteness has a small influence on the source mechanism estimate, but causes the seismic moment to be underestimated. The moment reduction rate depends on the mode of moment release (moving source) and is about 50% in the case of the October 4 earthquake. This result may suggest that our estimation of the moment of the October 4 earthquake should be multiplied by a factor of about 2. The experiments also show that the source finiteness effect can be reduced by using data of longer periods when the station coverage is good.

収録刊行物

• 地震　第２輯

  地震　第２輯 48 (3), 353-364, 1995

  公益社団法人 日本地震学会

詳細情報

• CRID: 1390282679283059840
• NII論文ID: 130006788049
• NII論文ID: 10002499906
• NII書誌ID: AN00305741
• DOI: 10.4294/zisin1948.48.3_353
• ISSN: 18839029
• ISSN: 2186599X
• ISSN: 00371114
• NDL書誌ID: 3636495
• Web Site: https://ndlsearch.ndl.go.jp/books/R000000004-I3636495
• Web Site: https://www.jstage.jst.go.jp/article/zisin1948/48/3/48_3_353/_pdf
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