Seismic site characterization in and around the COSC-2 drillhole

COSC-2 钻孔内及其周围的地震现场特征

• 批准号: 456669297
• 负责人: Professor Dr. Stefan Buske
• 金额: --
• 依托单位: Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum (GFZ)
• 依托单位国家: 德国
• 项目类别: Infrastructure Priority Programmes
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/456669297?language=en
• 关键词: Seismic; site; characterization; around; COSC

The project COSC (Collisional Orogeny in the ScandinavianCaledonides) focuses on the mid Paleozoic Caledonide Orogen inScandinavia in order to better understand orogenic processes. TheScandinavian Caledonides provide a well preserved deeply erodedexample of a Paleozoic continent-continent collision of Himalayandimensions. The current structure consists of the allochthons and theunderlying autochthonous units, and the shallow 1-2 degreeswestdipping décollement surface that separates the two units andconsists of a thin skin of Cambrian black shales. The basement of theFennoscandian Shield, underlying the Caledonides is dominated bycrystalline rocks of Paleoproterozoic age. The structure of thebasement is highly reflective and dominated by either mafic sheets ordeformation zones of Caledonian or pre-Caledonian age. The COSCproject will examine the structure and physical conditions of theseunits, in particular the Caledonian nappes and the underlyingbasement, with two approximately 2.5 km deep boreholes, located inwestern Jämtland. In addition to that, the boreholes will provideunique information about the present temperature gradient in theCaledonides, the porosity and permeability of the rock formations, andthe petrophysical properties of the rocks at depth. The boreholeCOSC-1, drilled in 2014, investigated the emplacement of high-grademetamorphic allochthons, the Seve Nappe Complex. The secondborehole COSC-2 will investigate the character of the underlyinglower allochthonous thrust sheets, the main Caledonian décollementand the Precambrian basement. Existing regional seismic andmagnetotelluric data have imaged the geometry of the upper crust,and several pre-site seismic reflection surveys were performed inorder to define the exact drill site locations. The surrounding of theCOSC-1 drill site was characterized 2014 through an extensiveseismic survey consisting of several borehole and surface basedexperiments. The goal of this current proposal is to perform similarinvestigations around the new COSC-2. This will be achieved by acombination of seismic transmission and reflection experiments usinga borehole geophone system and complemented by two long offsetlines at the surface equipped with 3C geophones. Sources andsurface receivers will be aligned at different azimuths and centredaround the borehole location. These land-based investigations will be complemented by an airgun and OBS profile within the adjacent lake.Two supplementary experiments, a zero-offset VSP and ahighfrequency walkaway VSP will help to characterize the directvicinity of the borehole. The data processing will employ recentlydeveloped advanced imaging techniques and will focus on theanalysis of anisotropic effects. The results of our investigations will behigh-resolution images of the fine-scale structures around the boreholewhich is vital information for a reliable extrapolation of structural andpetrophysical borehole findings.

COSC（斯堪的纳维亚喀里多尼亚碰撞造山运动）项目重点研究斯堪的纳维亚半岛中古生代喀里多尼亚造山带，以便更好地了解造山过程。斯堪的纳维亚喀里多尼亚山脉提供了一个保存完好、深度侵蚀的喜马拉雅维度古生代大陆与大陆碰撞的例子。目前的结构由异地体和下面的本土单元以及浅层西倾 1-2 度的滑脱面组成，该滑脱面将两个单元分开，并由一层薄薄的寒武系黑色页岩皮组成。芬诺斯坎迪亚地盾的基底位于喀里多尼德山脉下方，主要由古元古代的结晶岩组成。地下室的结构具有高度反射性，主要由加里东或前加里东时代的镁铁质片或变形区主导。 COSC项目将检查这些单元的结构和物理条件，特别是喀里多尼亚推覆体和底层基底，以及位于耶姆特兰西部的两个约2.5公里深的钻孔。除此之外，钻孔还将提供有关喀里多尼德山脉当前温度梯度、岩层的孔隙度和渗透率以及深层岩石的岩石物理性质的独特信息。 2014 年钻探的 COSC-1 钻孔调查了高级变质异地岩（Seve Naappe Complex）的就位情况。第二个钻孔 COSC-2 将研究底层下异地冲断层、主要加里东滑脱和前寒武纪基底的特征。现有的区域地震和大地电磁数据已经对上地壳的几何形状进行了成像，并且进行了几次现场地震反射勘测，以确定确切的钻探地点位置。 2014 年，通过由多个钻孔和地面实验组成的广泛地震勘测，对 COSC-1 钻探现场的周围环境进行了表征。当前提案的目标是围绕新的 COSC-2 进行类似的研究。这将通过使用钻孔地震检波器系统进行地震传输和反射实验相结合来实现，并辅以地面上配备 3C 地震检波器的两条长偏移线。源和地面接收器将在不同的方位角上对齐并以钻孔位置为中心。这些陆基调查将得到邻近湖内气枪和 OBS 剖面的补充。两个补充实验（零偏移 VSP 和高频无人 VSP）将有助于表征钻孔的直接邻近区域。数据处理将采用最近开发的先进成像技术，并将重点放在各向异性效应的分析上。我们的调查结果将是钻孔周围精细结构的高分辨率图像，这是可靠地推断结构和岩石物理钻孔结果的重要信息。