著者
和田 博夫 伊藤 潔 大見 士朗 岩岡 圭美 池田 直人 北田 和幸
出版者
京都大学防災研究所
雑誌
京都大学防災研究所年報. B = Disaster Prevention Research Institute Annuals. B (ISSN:0386412X)
巻号頁・発行日
vol.42, no.B-1, pp.81-96, 1999-04-01

1998年8月7日飛騨山脈上高地付近において群発地震が発生した。衛星通信システムの導入によって周辺観測網のデータが得られるようになった最初のイベントであり, 8カ月間に10, 000個以上の震源を求めることができた。活動は, 上高地付近の東西に帯状の地域, 穂高岳から槍ヶ岳にかけての南北の帯状の地域及び野口五郎岳付近の南北に帯状の地域に発生し, これらの活動域を移動, 再帰する現象が見られた。決められたH・2以上の地震約300個のメカニズム解は北西-南東方向に主圧力軸をもつ横ずれ型が卓越し, 群発地震の南北, 東西の並びと調和的である。また隣接する焼岳の火山活動との関連が注目されたが, 火山活動を示す現象は観測されなかった。なお, 今回の活動に関するデータを, 地元岐阜県上宝村へ随時提供して災害対策の基礎資料とした。
著者
和田 博夫 伊藤 潔 梅田 康弘 角野 由夫
出版者
京都大学防災研究所
雑誌
京都大学防災研究所年報. B = Disaster Prevention Research Institute Annuals. B (ISSN:0386412X)
巻号頁・発行日
vol.36, no.B-1, pp.291-303, 1993-04-01

Earthquake swarm activities have been occurring since January 1990 in the vicinity of Mount Yake-dake volcano in central Honshu, Japan.The volcano erupted frequently but it has been 30years since the last eruption in 1962.Temporary observation of microerarthquakes was conducted -near the volcano to survey the seismic activity.A station was set at about 1.5 km away from the summit crater in September, 1990 and five temporary stations were installed in the surrounding area of the volcano during the period from July to September, 1992. After that, three stations have been maintained to monitor the seismic activity.Although only a few events were located in the volcano during the period from July to September, 1992, the focal depths of the events were found to be very shallow as less than 3 km.In October and December, earthquake swarms occurred right beneath Yake-dake volcano.Earthquake swarms were also found in northeast, north and southeast of the volcano.Reviews of the studies on the volcano activity and earthquake swarms near the volcano are also given in this paper.
著者
尾池 和夫
出版者
京都大学防災研究所
雑誌
京都大学防災研究所年報. A = Disaster Prevention Research Institute Annuals. A (ISSN:0386412X)
巻号頁・発行日
vol.13, no.A, pp.133-140, 1970-03-01

The mechanism of earthquake swarm that occurred at Mt. Yakedake on November 8, 1968, have been studied. The swarm began at Olh3Om and terminated at 14h51m. 43 shocks wererecorded at Kamitakara by the vertical component seismograph for the observation of micro-earthquakes. The frequency distribution of the P-IS interval times of the swarm corresponds toone of four peaks in that distribution which were observed at the station during four monthsbefore the occurrence of the earthquake swarm.The foci of these shocks have been determined from the P-IS times observed at the near micro-earthquake observation stations. They are confined within a small volume whose dimensionis about 500 meters.The time variation of the S/P which means the ratio of the maximum amplitudes of P and Swaves have been investigated. The push-pull distributions of the initial P motions have beenalso studied. The results show that the focal mechanism changes in relation to the activityof the earthquake swarm and seems to approach the stationary state at the end of the swarm.It is supposed that the occurrence of the main shocks disturbed the stress field around theirfoci and gave the great influences upon the mechanism of the smaller shocks.This earthquake swarm is separated into four sequences. In the first sequence the large shockof M=~3.4 occurred in isolation. The main shock of M=3.3 and many aftershocks took placein the second sequence, the main shock of M =03.1 with some foreshocks and aftershocks occurredin the third one and the swarm of some smaller shocks occurred in the fourth one. This variationof the characteristics of the activity of each sequence seems to be related to the development ofthe fractures in the focal region.
著者
西田 良平 中尾 節郎 石賀 崇 西上 欽也
出版者
京都大学防災研究所
雑誌
京都大学防災研究所年報. B = Disaster Prevention Research Institute Annuals. B (ISSN:0386412X)
巻号頁・発行日
vol.41, no.B-1, pp.1-9, 1998-04-01

鳥取県東部は1943年9月10日に鳥取地震が発生し、1083名の人が亡くなる大きな被害を出している。この時、地震断層として吉岡・鹿野断層が出現した。1969年から、鳥取観測所での微小地震観測が開始されると、断層に伴う地震活動が観測され、鳥取地震を発生させた地殻応力が現在も作用していることが判っている。最近、地震活動が活発化し、それらの地震活動で左横ずれ断層の整列化が見られた。しかし、鳥取県東部地域は低地震活動が続き、隣接している兵庫県北西部では、右横ずれ断層である湯村断層周辺で、1995年兵庫県南部地震前後で地震活動、地殻応力の変化が観測され、西南日本の広い範囲で地殻応力の変化があったことが判った。