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.

为了更好地理解造山作用过程，斯堪的纳维亚加里东造山带碰撞造山作用项目（COSC）重点研究了斯堪的纳维亚中古生代加里东造山带。斯堪的纳维亚的加里东山脉提供了一个保存完好的、被严重侵蚀的古生代喜马拉雅尺度的陆-陆碰撞的例子。目前的结构包括外来体和下伏的原地单元，以及浅的1-2度西倾滑脱面，该滑脱面将两个单元分开，并由寒武纪黑色页岩的薄皮组成。位于加里东山脉之下的芬诺斯堪的纳维亚地盾的基底主要是古元古代的结晶岩。基底构造反射性强，以加里东期或前加里东期镁铁质岩席或变形带为主。COSC项目将检查这些单元的结构和物理条件，特别是加里东推覆体和下伏基底，在耶姆特兰西部有两个约2.5公里深的钻孔。除此之外，这些钻孔还将提供加里东山脉目前的温度梯度、岩层的孔隙度和渗透率以及岩石深层的岩石物理特性等独特信息。2014年钻探的COSC-1钻孔调查了高级变质外来岩（Seve Rappe Complex）的就位情况。第二个钻孔COSC-2将调查下伏的下部异地冲断岩席、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，并进行了几次现场前地震反射勘测，以确定确切的钻探地点。2014年，通过由多个钻孔和地面基础实验组成的广泛的地质调查，对COSC-1钻井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进行类似的调查。这将通过使用井中地震检波器系统的地震透射和反射实验的组合来实现，并通过在地面配备3C地震检波器的两条长偏移线来补充。震源和地面接收器将在不同的方位角对准，并以井眼位置为中心。这些陆基调查将由邻近湖泊内的气枪和OBS剖面补充。两个补充实验，零偏移距VSP和高频步行VSP将有助于描述钻孔附近的特征。数据处理将采用最近发展起来的先进成像技术，并将侧重于各向异性效应的分析。我们的调查结果将是高分辨率的图像，井周围的精细结构，这是一个可靠的外推结构和岩石物理钻孔结果的重要信息.