EVALUATION OF EFFECTS OF SCATTERED WAVE BY CRUSTAL INHOMOGENEITY ON SEISMIC EXPLORATION RECORDS

地壳不均匀性散射波对地震勘探记录的影响评价

• 批准号: 11650958
• 负责人: MATSUMOTO Satoshi
• 金额: $ 2.24万
• 依托单位: KYUSHU UNIVERSITY (2000)Akita University (1999)
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1999
• 资助国家: 日本
• 起止时间: 1999 至 2000
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11650958/
• 关键词: scattering; seismic exploration; active fault; seismic array observation; 不均質; 散乱

Recent seismic exploration in Japan is carried out in complex geological structure area. For instance the area is the exploration in and around active tectonic area such as active fault area and volcanic area. It can not neglect an effect of scattered wave by randomly distributed scatterers, which is difficult to identify by usual techniques in seismic reflection. In this study, we investigated effects of scattered energy by crustal inhomogeneity on records obtained in seismic reflection experiments. The study has carried out in two major approaches. One is detection of scattered waves in seismic reflection experiment. Another is investigation for characteristics of inhomogeneity as spatial distribution of scatterer and strength of inhomogeneity.An seismic reflection and refraction experiment has carried out in the Senya faults area. Displacement had appeared with reverse faulting on Rikuu Earthquake in 1896 (M7.2). By means of P-wave shallow seismic reflection survey across the outcro … More p of the earthquake fault and geological survey, New four faults are estimated in this area. These faults appear in the migration section down to four hundred meters depth. These five faults are reverse faults with east dip. Folded structure appear in the east of the earthquake fault. However, intermittend plane reflectors are observed in the west of the earthquake fault. The active fault is still migrating westward in this study area. In this experiment, strong reflected phases appear by earthquake faults. This suggests inhomogeneity is strong on the fault plane and generate scattered wave. The strength of reflected phase is depend on reflection point. This also suggests that the fault has strong inhomogeneity and spatial variation of inhomogeneity.We discuss the single scattering model by using seismic array data. By analyzing observed seismic array records, we found that coda energy level for slant-stacked record is smaller than that for single station record as expected from the single scattering model. The energy level of slant-stacked waveform is dependent on stacking direction. The difference between envelopes stacked in the direction of hypocenter and in the opposite one attributes to the area of scattering shell reflected by geometrical relationship among source, array, and lapse time. The energy level variation for different slant-stacking directions suggests that horizontally aligned scatterers predominate over vertical ones. The present analysis is probably useful to detect scattering anisotropy.Temporal variation of the scatterer distribution has been detected around the focal area of M6.1 earthquake, northeastern Japan, by applying semblance analysis to seismic array data. The variation was found in slant-stacked waveforms of two explosions detonated just above the focal area one month before and two months after the M6.1 earthquake. According to geodetic observations, a pressure source that might be magma reservoir exists beneath this region and its location changed during the observation period. Slant-stacked waveforms are slightly different between the two explosions. The difference suggests that a scatterer contributing to the coda part is shifted toward the east and to the deeper depth only after three months. In this region, seismic and volcanic activity was very active during the interval of the two explosions. Volcanic activity of Mt. Iwate just north of the M6.1 earthquake, which started several months before, continued during the period. It can be considered that scatterer change relates to seismic and/or volcanic activity in the studied area. Less

日本近年来的地震勘探是在地质构造复杂的地区进行的。如在活动断裂区、火山区等活动构造区及其周围进行勘探。随机分布的散射体的散射波的影响是不可忽略的，这是常规地震反射技术难以识别的。在这项研究中，我们研究了地壳不均匀性对地震反射实验记录的散射能量的影响。这项研究主要从两个方面进行。一是地震反射实验中散射波的检测。二是研究了非均匀性的特征，如散射体的空间分布和非均匀性的强度，并在森雅断裂带进行了地震反射和折射实验。1896年陆羽地震（M7.2）时，伴随逆断层活动出现了位移。利用P波浅层地震反射法， ...更多信息 通过对地震断层的研究和地质调查，估算出本区新的四条断层。这些断层出现在深达400米的迁移剖面中。这五条断裂均为东倾逆断层。地震断层东侧出现褶皱构造。而在地震断层西侧则观察到了倾斜的平面反射体。研究区的活动断裂仍在向西迁移。在本实验中，地震断层出现了强反射震相。这表明断层面上的不均匀性很强，并产生散射波。反射相位的强弱取决于反射点。利用地震台阵资料讨论了单次散射模型。通过对台阵实测记录的分析，发现倾斜叠加记录的尾波能量比单台记录的尾波能量小，这与单散射模型的结果一致。倾斜叠加波形的能级与叠加方向有关。震源方向和对向叠加包络的差异是由震源、排列和时差之间的几何关系所反映的散射壳面积决定的。不同的倾斜堆叠方向的能级变化表明，水平排列的散射体占主导地位的垂直的。本文对地震台阵资料进行了语义分析，发现了日本东北部6.1级地震震源区附近散射体分布的时间变化。在6.1级地震前一个月和震后两个月，在震源区上方引爆的两次爆炸的倾斜叠加波形中发现了这种变化。根据大地测量资料，该区域下方存在可能为岩浆库的压力源，且其位置在观测期间发生了变化。两次爆炸的倾斜叠加波形略有不同。这种差异表明，一个散射体的尾波部分是向东移动，并在三个月后向更深的深度。在这一地区，地震和火山活动在两次爆炸之间非常活跃。火山活动的山。几个月前开始的6.1级地震以北的岩手县在此期间仍在继续。可以认为，散射体的变化与研究区的地震和/或火山活动有关。少

项目成果

Satoshi Matsumoto,Kazushige Obara,Kazuo Yoshimoto,Tatsuhiko Saito,Akihiko Ito,Akira Hasegawa: "Temporal change in P-wave scatterer distribution associated with M6.1 earthquake near Iwate volcano.NE Japan"Geophysical Journal International. 145. 48-58 (2001

Satoshi Matsumoto、Kazushige Obara、Kazuo Yoshimoto、Tatsuhiko Saito、Akihiko Ito、Akira Hasekawa：“与岩手火山附近 M6.1 地震相关的 P 波散射体分布的时间变化。日本东北部”《国际地球物理杂志》。

松本聡,小原一成,吉本和生,斎藤竜彦,長谷川昭,伊東明彦: "短スパンアレイ観測による奥羽脊梁山地周辺の地殻不均質構造のイメージング"地震. 2,52. 283-297 (1999)

Satoshi Matsumoto、Kazunari Ohara、Kazuo Yoshimoto、Tatsuhiko Saito、Akira Hasekawa、Akihiko Ito：“利用短跨度阵列观测对 Ou 脊椎山脉周围的异质地壳结构进行成像”，地震 2, 52. 283-297 (1999)。

Satoshi Matsumoto,Kazushige Obara,Akira Hasegawa: "Characteristics of coda envelope for slant-stacked seismogram"Geophysical Research Letters. 28,6. 1111-1114 (2001)

Satoshi Matsumoto、Kazushige Obara、Akira Hasekawa：“斜叠地震图的尾波包络特征”地球物理研究快报。

S.Matsumoto, K.Obara, K.Yoshimoto, T.Saito, A.Hasegawa and A.Ito: "Imaging of inhomogeneous structure of the crust beneath Ou Backbone Range, Northeastern Japan, based on small aperture seismic array observation"Zisin. 2, 52. 283-297 (1999)

S.Matsumoto、K.Obara、K.Yoshimoto、T.Saito、A.Hasekawa 和 A.Ito：“基于小孔径地震阵列观测，对日本东北部奥羽骨干山脉下方地壳的不均匀结构进行成像”Zisin。