A study of deep structure of volcanoes and crustal earthquakes by seismic observations

地震观测研究火山深层结构和地壳地震

• 批准号: 04452061
• 负责人: HASEGAWA Akira
• 金额: $ 3.33万
• 依托单位: TOHOKU UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (B)
• 财政年份: 1992
• 资助国家: 日本
• 起止时间: 1992 至 1993
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-04452061/
• 关键词: crustal earthquake; deep structure of volcano; seismic tomography; seismic velocity structure; S-wave reflector; seismicity; 地震波トモグラフィ; 地震; 火山; マグマ; 地震波散乱体; 地震波減衰構造; 地震波反射面; 地殻不均質構造

Possible evidence for manmatic activity in the crust and the uppermost mantle beneath northern Japan has been obtained from seismic observations. Tomographic image of the 3-D seismic velocity structure clearly delineate low-velocity zones, which are continuously distributed from the upper crust just beneath active volcanoes to the upper mantle. They are inclined to the west and nearly parallel to the dip of the subducted oceanic plate. Exceptionally deep (22-40km), low-freqyebcy micro earthquakes have been found at 12 locations around the low-velocity zones beneath volcanoes, suggesting a close relation to the deep magmatic activity. At shallower depth (10-15km) in or around the low-velocity zones, there exist distinct S-wave reflectors. Observed amplitude spectral rations of reflected to direct S-wave show that the reflector has a strong velocity contrast to the surrounding medium and its thickness is in the order of 100m, which suggests that the reflector body is a thin layr filled with partially molten materials. A detailed seismicity study reveals that the cutoff depth for shallow crustal seismicity changes with location and becomes shallow beneath active volcanoes. These observations appear to shed some light on the state of magma at depths and its close relation to shallow seismic activity in subduction zones.

日本北方地壳和上地幔中的地幔活动可能是由地震观测获得的。三维地震速度结构的层析成像图像清楚地描绘出低速带，这些低速带从上地壳到上地幔连续分布。它们向西倾斜，几乎与俯冲洋板块的倾角平行。在异常深（22- 40 km）的火山低速带周围的12个地点发现了低频微震，表明与深部岩浆活动有密切关系。在低速带内或其周围较浅的深度（10- 15 km），存在明显的S波反射。反射横波与直达横波振幅谱比的观测结果表明，反射体与周围介质有很强的速度对比，反射体厚度约为100 m，反映了反射体是一个充满部分熔融物质的薄层。详细的地震活动研究表明，地壳浅层地震活动的截止深度随位置而变化，在活火山下方变浅。这些观察似乎揭示了岩浆在深处的状态及其与俯冲带浅层地震活动的密切关系。

项目成果

A.Hasegawa: "Deep structure of arc volcanoes as inferred from seismic observations" Phil.Trans.Roy.Soc.London. 342. 167-178 (1993)

A.Hasekawa：“根据地震观测推断的弧火山的深层结构”Phil.Trans.Roy.Soc.London。

A.Hasegawa: "Seismic structure of the northeastern Japan convergent margin : a synthesis." J.Geophys. Res.in press.

A.Hasekawa：“日本东北部辐合边缘的地震结构：综合”。

長谷川 昭: "地震波でみた島弧火山の根" 地球惑星科学関連学会1992年合同大会予稿集. 237- (1992)

Akira Hasekawa：“从地震波中看到的岛弧火山的根源”1992 年地球与行星科学协会联合会议记录 237- (1992)。

S.Horiuchi: "Seismic scatter distribution near focal area of the 1931 Oguni Earthquake, Iwate Prefecture, northeastern Japan, as derived from P coda wave observations of an explosion by a dense seismic array network." J.Seism. Soc. Japan. 46. 75-84 (1993)

S.Horiuchi：“1931 年日本东北部岩手县小国地震震源区附近的地震散射分布，源自密集地震阵列网络对爆炸的 P 尾波观测。”

T.Kono: "Microearthquake activity in the focal area of 1962 Northern Miyagi Earthquake (M6.5)." J.Seism. Soc. Japan. 46. 85-93 (1993)

T.Kono：“1962 年宫城北部地震 (M6.5) 震源区的微地震活动。”