| 講演要旨(和文) | | 有珠昭和新山屋根山で反射法地震探査を行い, 溶岩ドーム基部の地下構造を推定した. 昭和新山ではこれまで様々な調査研究が行われており, その形成過程やマグマの供給経路について議論されてきた. しかし屋根山の構造については未解明な部分が多い. 本研究では溶岩ドーム東側でほぼ東西方向に2測線(Y17, Y18), 溶岩ドーム南東側のグレン谷で2測線(G17, G18) 計4測線での探査を行った. 測線Y17, G17では震源にかけやを用いた. 測線Y18, G18では震源にタンピングランマーを用いた. 解析によって, 全ての測線で深度断面を得た. これにより溶岩ドームに対して接線方向となる測線では溶岩ドームから離れるほど深部に水平な反射面が表れ, 放射方向となる測線では, 溶岩ドームから離れるほど深くなる傾斜構造が見られた. |
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| | 講演要旨(英文) | | Seismic reflection surveys at Usu-Showashinzan-Yaneyama was conducted in order to, estimate the shallow structure of the lava-dome base. Four seismic 4 lines were conducted in 2017 and 2018 with 2 lines each two survey lines (Y17 and Y18) were set in the radial direction from the east foot of the lava dome and two (G17 and G18) in tangential direction in the Gurendani on the southeast foot of the lava dome. Both survey lines (Y17, G17) were conducted in 2017 with 24 receivers with using a hammer as the seismic source. The others (Y18, G18) conducted in 2018 with 48 receivers with using a tamping rammer as the seismic source. Split-spread method was applied in all survey lines. The receiver interval was 4m for Y lines and 3m for G lines. As a result of reflection analysis, migrated sections were obtained for all survey lines. The radial sections show an inclined structure that becomes deeper as it moves away from the lava dome, and the tangential sections show a horizontal reflecting surface deeper as it moves away from the lava dome. |
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