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Seismic site characterization in and around the COSC-1 drillhole

COSC-1 钻孔内及其周围的地震现场特征

基本信息

批准号：
235844139
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
财政年份：
2013
资助国家：
德国
起止时间：
2012-12-31 至 2018-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/235844139?language=en
关键词：
Seismic site characterization around COSC

项目摘要

The project COSC (Collisional Orogeny in the Scandinavian Caledonides) focuses on the mid Paleozoic Caledonide Orogen in Scandinavia in order to better understand orogenic processes, both in the past and in recent active mountain belts (Gee et al., 2010). The Scandinavian Caledonides provide a well preserved example of Paleozoic plate collision, where the surface geology in combination with geophysical data provide control of the geometry of the Caledonian structure, both of the allochthon and the underlying autochthon, including a shallow W-dipping décollement surface on a thin skin of Cambrian black shales beneath the Caledonian thrust sheets. The structure of the basement underneath the décollement is highly reflective and apparently dominated by mafic sheets intruded into either late Paleoproterozoic granites or Mesoproterozoic volcanics and sandstones. The COSC project will examine the structure and physical conditions of these units, in particular the Caledonian nappes ("hot" allochthon) and the underlying basement, with two approximately 2.5 km deep drillholes, located near Åre and Mörsil in western Jämtland (http://www.sddp.se/COSC). In addition to that, the drillholes will provide unique information about the present temperature gradient in the Caledonides, the porosity and permeability of the rock formations, and the petrophysical properties of the rocks at depth. Existing regional seismic and magnetotelluric data have imaged the geometry of the upper crust, and pre-site seismic reflection survey were preformed in 2010 and 2011 to better define the exact drill site locations (Hedin et al., 2012). This present proposal is dedicated to complement these surface seismic measurements by drillhole-based investigations to better resolve and define the small-scale structures (including lithological boundaries, steeply dipping fault segments, fracture sets, etc.) around the drillhole COSC-1. This will be achieved by a combination of seismic transmission and reflection experiments using a 3C borehole geophone system and complemented by 3C geophones at the surface, where sources and surface receivers will be aligned at different azimuths and centred around the borehole location. The data processing will employ recently developed advanced imaging techniques and will focus on, amongst other things, the analysis of anisotropic effects caused by aligned fractures and faults and their relation to the stress regime. The results of our investigations will be high-resolution images of the fine-scale structure of faults and fractures around the borehole. This information is vital not only for a reliable spatial extrapolation of the structural and petrophysical properties observed in the borehole, but also for a thorough understanding of the tectonic and geodynamic setting, including, but not limited to, the past and present stress regime.

COSC（斯堪的纳维亚加里东造山带碰撞造山）项目的重点是斯堪的纳维亚中古生代加里东造山带，以便更好地了解过去和最近活动的造山带的造山过程（Gee等人，2010年）。斯堪的纳维亚的加里东山脉提供了一个保存完好的古生代板块碰撞的例子，在那里，地表地质与地球物理数据相结合，提供了加里东构造的几何形状的控制，无论是外来岩和下面的原地岩，包括一个浅W倾斜的滑脱表面上的一个薄皮的寒武纪黑色页岩下的加里东逆冲岩席。滑脱层下的基底结构具有高度反射性，明显地以侵入晚古元古代花岗岩或中元古代火山岩和砂岩的镁铁质岩片为主。COSC项目将研究这些单元的结构和物理条件，特别是加里东推覆体（“热”外来岩）和下面的基底，并在耶姆特兰西部的Mörsil和Alzere附近进行两个约2.5公里深的钻孔（http：//www.sddp.se/COSC）。除此之外，钻孔将提供有关加里东山脉目前温度梯度、岩层孔隙度和渗透率以及岩石深部岩石物理特性的独特信息。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，并且在2010年和2011年进行了现场前地震反射勘测，以更好地确定确切的钻探现场位置（Hedin等人，2012年）。本提案致力于通过基于钻孔的调查来补充这些地面地震测量，以更好地解析和定义小规模结构（包括岩性边界、陡倾断层段、断裂组等）。在COSC-1钻孔周围这将通过使用3C钻孔地震检波器系统并辅以地面3C地震检波器的地震透射和反射实验相结合来实现，其中震源和地面接收器将在不同的方位角对准，并以钻孔位置为中心。数据处理将采用最近开发的先进成像技术，除其他外，将侧重于分析对齐的裂缝和断层及其与应力状态的关系所造成的各向异性效应。我们的调查结果将是钻孔周围断层和裂缝的精细结构的高分辨率图像。这一信息不仅对于可靠地对钻孔中观察到的结构和岩石物理特性进行空间外推至关重要，而且对于彻底了解构造和地球动力学背景，包括但不限于过去和现在的应力状况也至关重要。