OBN转换横波分裂分析刻画东海西湖凹陷裂缝分布*

doi:10.11978/2024056

摘要/Abstract

摘要：

裂缝方位和发育强度是各向异性研究的重要参数, 通过常规纵波地震数据难以辨识。相比之下, 裂缝引起的横波分裂现象更加明显。为研究中国东海西湖凹陷探区裂缝发育情况, 本文利用四分量海底节点(ocean bottom nodes, OBN)地震数据中记录的转换横波信息进行了横波分裂分析。研究发现: 浅层(0~3000ms)快慢横波时间延迟3~5ms, 平均裂缝方向约111°—117°, 裂缝方位相似度高达80%~90%, 裂缝发育比较集中; 深层(大于3000ms)裂缝分布较复杂, 快慢横波时间延迟主要集中于6~8ms, 主要方位集中于119°, 但裂缝方位相似度低(低于50%), 方位不集中, 出现约20°—40°方位的裂缝。研究区浅层主要发育NW(西北)向裂缝, 深层主要发育NW(西北)和NE(东北)向裂缝, 与研究区断层发育方向基本一致; 横波分裂时间延迟量从浅部到深部逐渐增大, 表明越往深层, 裂缝发育强度越强; 研究区南侧时间延迟明显高于北侧, 表明南侧裂缝发育强度高于北侧。

关键词: 东海, 横波分裂, OBN转换横波, 各向异性, 裂缝特征

Abstract:

The orientation and intensity of fracture are important information for studying anisotropy, but they are difficult to identify through the conventional compression wave (P) of seismic data. In contrast, the shear wave splitting (SWS) caused by azimuth anisotropy in the converted seismic wave (PS) is helpful to characterize the strength and azimuth of fractures. In order to study the distribution characteristics of fractures in the Xihu Sag of East China Sea, the converted shear wave information recorded in four-component submarine nodes (ocean bottom nodes, OBN) was used to conduct SWS analysis. First, the principle of SWS and the layer-stripped method were introduced in detail. Then, the SWS analysis with the seismic data in the study area was carried out. The results show that in the shallow layer (0~3000 ms), the time delay of fast and slow shear waves is 3~5 ms, the average fracture direction is about 111°-117°, and the fracture similarity is as high as 80%~90%, which indicates that the fracture orientation is relatively concentrated. However, in the deep layer, the distribution of fracture is rather complex, for which the time delay is about 6~8 ms and the main azimuth is concentrated at 119°, but the fracture similarity is low (less than 50%) and the fracture direction is about 20°−40°, which indicates that the azimuth is not concentrated. The results show that NW-trending fractures are mainly developed in the shallow layer of the study area, and NW- and NE-trending fractures are mainly developed in the deep layer, which is consistent with the fault development directions obtained from the P results in the study area. The time delay gradually increases from the shallow to the deep part, indicating that the deeper the layer, the more intense the fracture develops. The time delay in the south of the study area is significantly higher than that in the north, indicating that the intensity of fracture in the south is higher than that in the north.

Key words: East China Sea, shear wave splitting, OBN converted shear wave, anisotropy, fracture characterization

中图分类号:

P315

李亚清, 刘苗, 赵秀莲, 陈茂根, 朱宝衡, 陈琳枝, 李振伟. OBN转换横波分裂分析刻画东海西湖凹陷裂缝分布*[J]. 热带海洋学报, 2025, 44(1): 189-199.

LI Yaqing, LIU Miao, ZHAO Xiulian, CHEN Maogen, ZHU Baoheng, CHEN Linzhi, LI Zhenwei. OBN converted shear wave splitting analysis depicts the fracture distribution in the Xihu Sag in the East China Sea*[J]. Journal of Tropical Oceanography, 2025, 44(1): 189-199.

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内容	参数
记录道数/道	133
最小炮检距/m	25.67
最大炮检距/m	6482.12
面元尺寸/(m×m)	12.5×25
覆盖次数	8横×80纵=640次
道距/m	50
横向炮间距/m	50
纵向炮间距/m	37.5
横向滚动距/m	300
接收线方位角	120°