Characterizing shallow fault zones by integrating profile, borehole and array measurements of seismic data and distributed acoustic sensing

IF 1.1 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS Near Surface Geophysics Pub Date : 2024-04-01 DOI:10.1002/nsg.12293
Nikolaus Rein, Marius P. Isken, Dorina Domigall, Matthias Ohrnberger, Katrin Hannemann, Frank Krüger, Michael Korn, Torsten Dahm
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Abstract

Within the framework of the Intercontinental Scientific Drilling Programme (ICDP) ‘Drilling the Eger Rift’ project, five boreholes were drilled in the Vogtland (Germany) and West Bohemia (Czech Republic) regions. Three of them will be used to install high‐frequency three‐dimensional (3D) seismic arrays. The pilot 3D array is located 1.5 km south of Landwüst (Vogtland). The borehole, with a depth of 402 m, was equipped with eight geophones and a fibre optic cable behind the casing used for distributed acoustic sensing (DAS) measurements. The borehole is surrounded by a surface array consisting of 12 seismic stations with an aperture of 400 m. During drilling, a highly fractured zone was detected between 90 m and 165 m depth and interpreted as a possible fault zone. To characterize the fault zone, two vertical seismic profiling (VSP) experiments with drop weight sources at the surface were conducted. The aim of the VSP experiments was to estimate a local 3D seismic velocity tomography including the imaging of the steep fault zone. Our 3D tomography indicates P‐wave velocities between 1500 m/s and 3000 m/s at shallow depths (0–20 m) and higher P‐wave velocities of up to 5000 m/s at greater depths. In addition, the results suggest a NW–SE striking low‐velocity zone (LVZ; characterized by = 1500–3000 m/s), which crosses the borehole at a depth of about 90–165 m. This LVZ is inferred to be a shallow non‐tectonic, steep fault zone with a dip angle of about . The depth and width of the fault zone are supported by logging data as electrical conductivity, core recovery and changes in lithology. In this study, we present an example to test and verify 3D tomography and imaging approaches of shallow non‐tectonic fault zones based on active seismic experiments using simple surface drop weights as sources and borehole chains as well as borehole DAS behind casing as sensors, complemented by seismic stand‐alone surface arrays.
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通过整合地震数据的剖面、钻孔和阵列测量以及分布式声学传感,确定浅断层带的特征
在洲际科学钻探计划(ICDP)"埃格尔裂谷钻探 "项目框架内,在沃格特兰(德国)和西波希米亚(捷克共和国)地区钻探了五个钻孔。其中三个将用于安装高频三维(3D)地震阵列。试验性三维阵列位于 Landwüst(沃格特兰)以南 1.5 公里处。钻孔深度为 402 米,配备了 8 个检波器,套管后方的光纤电缆用于分布式声学传感 (DAS) 测量。钻探过程中,在 90 米至 165 米深度之间发现了一个高度断裂带,被解释为可能的断层带。为了确定该断层带的特征,在地表进行了两次垂直地震剖面(VSP)试验,使用了落锤震源。垂直地震剖面试验的目的是估算当地的三维地震速度层析,包括陡峭断层带的成像。我们的三维地震层析显示,浅层(0-20 米)的 P 波速度介于 1500 米/秒和 3000 米/秒之间,更深处的 P 波速度高达 5000 米/秒。此外,研究结果表明,有一个西北-东南走向的低速带(LVZ;特征为 = 1500-3000 m/s),在约 90-165 米深处穿过钻孔。电导率、岩心回收率和岩性变化等测井数据为断层带的深度和宽度提供了支持。在本研究中,我们以主动地震实验为基础,以简单的地表落锤为震源,以井眼链和套管后的井眼 DAS 为传感器,辅以地震独立地表阵列,对非构造浅断层带的三维层析成像方法进行了测试和验证。
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来源期刊
Near Surface Geophysics
Near Surface Geophysics 地学-地球化学与地球物理
CiteScore
3.60
自引率
12.50%
发文量
42
审稿时长
6-12 weeks
期刊介绍: Near Surface Geophysics is an international journal for the publication of research and development in geophysics applied to near surface. It places emphasis on geological, hydrogeological, geotechnical, environmental, engineering, mining, archaeological, agricultural and other applications of geophysics as well as physical soil and rock properties. Geophysical and geoscientific case histories with innovative use of geophysical techniques are welcome, which may include improvements on instrumentation, measurements, data acquisition and processing, modelling, inversion, interpretation, project management and multidisciplinary use. The papers should also be understandable to those who use geophysical data but are not necessarily geophysicists.
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