著者

長宗 留男

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.40, no.3, pp.417-423, 1987-09-25 (Released:2010-03-11)

参考文献数

11

被引用文献数

2 2

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The minute investigation of the spatial distribution of intermediate-depth earthquakes reveals that the deep earthquake zone beneath the Kyushu-Ryukyu region is dislocated transversely and changes its strike under the Tokara Channel.Left-lateral dislocations of the isobaths of intermediate-depth earthquakes amount to 70-80km and 30-40km at depths of 80km and 150km, respectively. The isobath of the depth of 200km, however, is scarcely dislocated. The change in strike of the deep earthquake zone comes up to about 30° there.The discontinuity of the zone appears to be related closely to the surface geology. The Tokara Channel represents the left-lateral geological fault offsetting by 80-100km the tectonic belts in the pre-Miocene basement rocks running parallel to the island arc. In this region, there are a few left-lateral faults including the Tokara Channel, which traverse the Ryukyu Islands and divide the pre-Miocene tectonic belts into segments of 200 to 400km in strike length. But the other transverse discontinuities of the deep earthquake zone corresponding to the surface geological structure can not be found from the present analyses.

著者

長宗 留男

出版者

鹿児島大学

雑誌

鹿児島大学理学部紀要 地学・生物学 (ISSN:03854019)

巻号頁・発行日

no.21, pp.p23-33, 1988-12

被引用文献数

1

著者

長宗 留男 横山 博文 福留 篤男

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.37, no.1, pp.1-8, 1992-04-01 (Released:2017-03-20)

参考文献数

16

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Earthquake swarms which have frequently occurred off the east coast of the Izu Peninsula since 1978 are investigated, and the relationships between the swarms and the submarine volcanic eruption at Teisi Knoll in 1989 are discussed. The results are summarized as follows: 1) Shapes of epicentral areas of the earthquake swarms can be classified into the following two types, Type I and Type II. The former is an ellipse elongated NE-SW; the latler, an eilipse elongated approximately NW-SE. The swarms in the early years are of Type I, and those in the later stage (in particular, since 1984), for the most part, are of Type II.2) The largest earthquakes in the respective swarms for Type I are located along a straight line in the NE-SW direction, and those for Type II, along a curve line in the E-W to NW-SE directions. These two lines are probably indicative of active tectonic lines. 3) The epicentral areas for Type I and Type II, migrate periodically with a recurrece time of 6-7 years along the tectonic line in the NE-SW direction, and with a recurrence time of about 3.7 years along the tectonic line in the E-W to NW-SE directions, respectively. 4) Teisi Knoll where the submarine volcanic eruption took place on July 13, 1989, is situated in the northwestern part of the tectonic line trending E-W to NW-SE. The eruption was triggerd by the largest shock in the swarm which occurred around the northwestern end of the line.

著者

長宗 留男 横山 博文 福留 篤男

出版者

特定非営利活動法人日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.37, no.1, pp.1-8, 1992-04-01

被引用文献数

2

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Earthquake swarms which have frequently occurred off the east coast of the Izu Peninsula since 1978 are investigated, and the relationships between the swarms and the submarine volcanic eruption at Teisi Knoll in 1989 are discussed. The results are summarized as follows: 1) Shapes of epicentral areas of the earthquake swarms can be classified into the following two types, Type I and Type II. The former is an ellipse elongated NE-SW; the latler, an eilipse elongated approximately NW-SE. The swarms in the early years are of Type I, and those in the later stage (in particular, since 1984), for the most part, are of Type II.2) The largest earthquakes in the respective swarms for Type I are located along a straight line in the NE-SW direction, and those for Type II, along a curve line in the E-W to NW-SE directions. These two lines are probably indicative of active tectonic lines. 3) The epicentral areas for Type I and Type II, migrate periodically with a recurrece time of 6-7 years along the tectonic line in the NE-SW direction, and with a recurrence time of about 3.7 years along the tectonic line in the E-W to NW-SE directions, respectively. 4) Teisi Knoll where the submarine volcanic eruption took place on July 13, 1989, is situated in the northwestern part of the tectonic line trending E-W to NW-SE. The eruption was triggerd by the largest shock in the swarm which occurred around the northwestern end of the line.

著者

長宗 留男

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.33, no.1, pp.71-78, 1980-03-25 (Released:2010-03-11)

参考文献数

7

被引用文献数

1

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The epicentral distribution of aftershocks shows that the source region of the Izu-Oshima-Kinkai Earthquake of January 14, 1978 (origin time: 12h 24m 38.6s, 34°46′N, 139°15′E, depth: 0km), consisted of two areas, i. e., the area in the sea between Izu-Oshima and the Izu-Peninsula, spreading to the west from the epicenter of the main shock, and the one in the Izu-Peninsula, extending to the westnorthwest direction from the east coast of the peninsula.On the other hand, it has been pointed out that the earthquake was a multiple shock, and that the second event took place about 6sec after the occurrence of the main shock (first event). The location of the second event, however, was somewhat undefinitely.The records of the JMA 59-type electromagnetic seismographs were examined for locating the origin of the second event.From the readings of the first arrivals of P-waves, the origin for the second event was estimated as follows:Origin time: 12h 24m 44.5s (5.9sec after the occurrence of the main shock), Location: 34°46′N, 139°00′E (approximately 23km west of the epicenter of thee main shock), Depth: 0km.It appears that the second event occurred at a place linking two source areas mentioned above, when the rupture which started at the origin of the main shock and propagated westwards, deviated its direction of propagation to the westnorthwest.