| 講演要旨(和文) | | 地震防災の観点から見た深部構造探査においては,内陸地震を引き起こす活断層(震源断層)に関して,地震基盤以深から脆性-延性境界に相当する地震発生層下限までの震源断層の形状把握が重要な課題である.こうした観点から,制御震源による地殻深部イメージング技術の向上を目的として,北上低地西縁断層帯を構成する出店断層(岩手県奥州市)を対象として反射法地震探査による深部地殻構造探査実験をおこなった.反射法,広角反射法および屈折法データ解析の結果,奥羽脊梁山地側への西傾斜を示す出店断層の深部延長,および深度約10-14kmに分布する地震発生層下限に相当する深部反射波群が明瞭に捉えられた.また,併せて実施された高分解能反射法結果からは鮮新世以降の活動に伴う浅層部の変形が明瞭に再現され,深部反射法結果と併せて,出店断層の地表直下浅部から地震発生層下限に至る詳細な形状が明らかにされた. |
|
|
| | 講演要旨(英文) | | To investigate the deeper extension of active faults within the seismogenic layer, we conducted a seismic reflection profiling experiment across the western marginal faults of Kitakami Lowland{KL}, northeast Japan. The KL is located at the eastern edge of the Miocene rift system of northern Honshu Island. The western marginal faults of KL are commonly recognized as active reverse faults re-activated after crustal stretching during Miocene back arc spreading and subsequent lithospheric cooling. In the seismic reflection survey, four vibrator trucks and 100kg explosives were used. Along an EW oriented 42km-long seismic line with 25-50m geophone spacing, approximately 500 vibrator shots, 15 higher energy vibrator shots up to 100 stationary sweeps at each point, and 2 explosive shots were carried out. Near the western marginal faults of KL, additional high-resolution seismic reflection data were acquired by dense spatial sampling. The seismic reflection profile clearly shows the geometry of west dipping listric faults and the east dipping mid-crustal detachment, suggesting that the deeper extension of the western marginal faults of KL converges on the mid-crustal detachment at the base of seismogenic layer. The high-resolution reflection profile documents the detailed process of reverse reactivation of pre-existing normal faults along the Kitakami fault system. |
|
|
|
| |
|