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

日本最近的地震探索是在复杂的地质结构区域进行的。例如，该区域是主动构造区域及其周围的探索，例如活动断层面积和火山区域。它无法通过随机分布的散射器来忽略散射波的影响，这在地震反射中很难通过通常的技术识别。在这项研究中，我们研究了地壳反射实验中获得的记录的散射能量的影响。这项研究以两种主要方法进行了。一种是在地震反射实验中检测散射波。另一个是研究不均匀性的特征，作为散射器的空间分布和不均匀性的强度。在Senya断层区域进行了地震反射和折射实验。 1896年的Rikuu地震发生了位移的反向断层（M7.2）。通过在OUTCRO上进行的P波浅地震反射调查……地震断层和地质调查的更多P，在该地区估计了新的四个断层。这些断层出现在迁移部分下降到400米的深度。这五个故障是东倾角的反向断层。折叠结构出现在地震断层的东部。但是，在地震断层的西部观察到了间歇平面反射器。在该研究区域，主动断层仍在向西迁移。在此实验中，地震断层出现了强反射阶段。这表明在断层平面上的不均匀性很强并产生散射波。反射阶段的强度取决于反射点。这也表明该断层具有强大的不均匀性和不均匀性的空间变化。我们使用地震阵列数据讨论单个散射模型。通过分析的观察到的地震阵列记录，我们发现倾斜堆积记录的CODA能级小于单个站记录，如单个散射模型所预期的。倾斜波形的能级取决于堆叠方向。堆叠在降压器方向的包络与相反的属性与散射壳区域的相反属性之间的差异，这些区域是由源，阵列和衰减时间之间的几何关系反射的散射壳区域。不同倾斜方向的能级变化表明，水平对齐的散射器占主导地位以于垂直方向。目前的分析可能对于检测散射各向异性很有用。通过将外表分析应用于地震阵列数据，已经检测到日本东北部M6.1地震的焦点区域周围的散射器分布变化。在M6.1地震发生前一个月和两个月的两个月前，两次爆炸爆炸的倾斜波形发现了这种变化。根据大地观测，可能是岩浆晶状体的压力源存在于该地区的下方，其位置在观察期间发生了变化。两次爆炸之间的倾斜堆积波形略有不同。差异表明，仅在三个月后才向东方和更深的深度移动一个散射器。在该地区，在两次爆炸的间隔内，地震活动和火山活性非常活跃。在M6.1地震以北的Iwate山的火山活动开始于几个月前，在此期间一直持续。可以认为，散射器的变化与Studiod区域中的地震和/或火山活动有关。较少的

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》。

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。

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)。