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Imaging faults at depth: the seismic transport properties of fault zones

深度断层成像：断层带的地震传输特性

基本信息

批准号：
NE/F019920/1
负责人：
Daniel Faulkner
金额：
$ 58.69万
依托单位：
University of Liverpool
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2008
资助国家：
英国
起止时间：
2008 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FF019920%2F1
关键词：
Imaging faults depth seismic transport

项目摘要

Earthquakes and fault slip are still relatively poorly understood phenomena. One of the principal reasons for this is that fault zones, at the crustal levels where earthquakes nucleate, are very difficult to observe. Field mapping of large faults at the surface can provide valuable information, but they are often incompletely exposed and/or have suffered continued slip and hence overprinting during exhumation. As a consequence seismology is one of the key tools used to investigate fault zone structure and properties at depth. It has the potential to show fault zone structure and dimensions, slip distributions, fracture damage, stress orientations and fault fluid pressures. However the seismic data have to be inverted to decipher fault zone structure and properties and these inversions often yield non-unique answers. In this research we aim to combine field mapping, laboratory measurements and seismic experiments on an exceptionally well-exposed and characterized fault zone in southern Spain in order to understand the sensitivity of the seismic signals to the observed surface structure and physical properties of the fault rocks as determined from detailed mapping and laboratory seismic measurements. As part of a tied studentship, we will also measure the seismic properties of rocks recovered from 3km depth on the San Andreas fault in California as part of the San Andreas Fault Observatory at Depth (SAFOD) project that recently drilled a scientific borehole through the fault near Parkfield. Natural seismicity recorded on borehole instruments will provide comparison with laboratory measurements and allow us to broaden the scope of the work by detailed analysis of another major fault zone. The combination of all these data will provide a greatly improved understanding of the controls on fault zone seismology leading to a clearer picture of fault zones at depth. Specifically, we will map in detail part of the Carboneras fault in southeastern Spain; a major strike-slip fault with 40km offset that has been exhumed from 4 to 6km depth. Samples from the fault zone will have their seismic properties measured in the laboratory, including the P and S wave velocity, the attenuation of the seismic waves, and the degree of the polarization the S waves. The field and laboratory data will be combined to create a synthetic 3D model of the fault zone in which earthquake events may be 'created' and the resultant seismic signals predicted. We will additionally conduct 'active' seismic experiments on the fault zone where controlled seismic sources from explosions will excite seismic waves that we can then measure with a carefully positioned seismic network within and around the fault zone. The signals from these experiments will help characterize the subsurface structure of the fault and can be compared with predicted signals from the detailed mapping and laboratory measurement program. The project will provide information on fault zone structure from direct observation of a major fault, measurements of the physical properties of a range of fault zone materials and direct seismic measurements of the fault zone that can be directly compared with the surface structure. These data will not only provide key insights in understanding fault zone structure and properties from seismic data, but they will also be of significant interest to the hydrocarbon and mining industries, as faults control the movement of subsurface fluids, leading to problems in the recovery of oil and gas, and also distribution of hydrothermally /transported, fault hosted ore deposits.

地震和断层滑动仍然是人们对现象知之甚少的现象。造成这种情况的主要原因之一是，地震发生的地壳层面的断层带很难观察到。地表大型断层的现场测绘可以提供有价值的信息，但它们通常不完全暴露和/或在挖掘过程中遭受持续滑动并因此叠印。因此，地震学是用于研究深部断层带结构和性质的关键工具之一。它有可能显示断层带结构和尺寸、滑移分布、裂缝损伤、应力方向和断层流体压力。然而，必须对地震数据进行反演才能破译断层带的结构和特性，而这些反演通常会产生非唯一的答案。在这项研究中，我们的目标是将现场测绘、实验室测量和地震实验结合起来，对西班牙南部一个异常暴露和特征化的断层带进行分析，以了解地震信号对观察到的断层岩石表面结构和物理性质的敏感性，这些是通过详细测绘和实验室地震测量确定的。作为固定学生项目的一部分，我们还将测量从加利福尼亚州圣安德烈亚斯断层 3 公里深度处回收的岩石的地震特性，这是圣安德烈亚斯断层深度观测站 (SAFOD) 项目的一部分，该项目最近在帕克菲尔德附近的断层上钻了一个科学钻孔。钻孔仪器记录的自然地震活动将与实验室测量进行比较，并使我们能够通过对另一个主要断层带的详细分析来扩大工作范围。所有这些数据的结合将大大提高对断层带地震学控制的理解，从而更清晰地了解断层带的深度。具体来说，我们将详细绘制西班牙东南部卡沃内拉斯断层的部分地图；一个偏移 40 公里的主要走滑断层，已从 4 至 6 公里深度挖掘出来。来自断层带的样本将在实验室中测量其地震特性，包括纵波和横波速度、地震波的衰减以及横波的偏振程度。现场和实验室数据将结合起来创建断层带的综合 3D 模型，在该模型中可以“创建”地震事件并预测由此产生的地震信号。我们还将在断层带上进行“主动”地震实验，其中爆炸产生的受控震源将激发地震波，然后我们可以使用断层带内部和周围精心定位的地震网络进行测量。这些实验的信号将有助于表征断层的地下结构，并可以与详细测绘和实验室测量程序的预测信号进行比较。该项目将通过直接观察主要断层、测量一系列断层带材料的物理特性以及可直接与表面结构进行比较的断层带直接地震测量来提供断层带结构信息。这些数据不仅将为通过地震数据了解断层带结构和特性提供重要见解，而且对碳氢化合物和采矿业也具有重大意义，因为断层控制地下流体的运动，导致石油和天然气的回收问题，以及热液/运输、断层矿床的分布。