Composition and Structure of Gouge from the Focal Depths of Recent Earthquakes: Rupture Zones in South African Gold Mines

近期地震震源深度的凿岩成分和结构：南非金矿的破裂带

• 批准号: 0207847
• 负责人: Thomas Dewers
• 金额: $ 20万
• 依托单位: University of Oklahoma Norman Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-07-01 至 2005-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0207847&HistoricalAwards=false
• 关键词: Composition; Structure; Gouge; Focal; Depths

It is impossible to access the rupture zone of an earthquake at its focal depth, and thus the perception of earthquake rupture zones is inferred from indirect observations of surface rupture and exhumed fault-zones. A different approach is used here: direct observations in deep gold mines of South Africa where the PI recently mapped the rupture zones of three earthquakes. These mapped zones are associated with moderate earthquakes of magnitudes 3.7 to 5.1 that cut across the thick quartzite sequences of the western Witwatersrand basin. He found that a typical rupture zone of a single earthquake consists of 5-20 crosscutting gouge zones that were active during the earthquake. The gouge zones contain crushed, quartzitic powder, rock fragments or clay minerals; some of these zones are 15 cm thick. The PI proposes to analyze in detail the composition, microstructure and geochemical stability of the gouge found in these rupture zones. He plans to determine gouge mineralogy, high-pressure phases, gouge surface area and gouge solubility. He will examine the fragmentation processes at the microscopic scale and the transition from intact rock to gouge powder. The gouge material will be subjected to long term (1-3 months) cementation experiments at hydrothermal condition ( 500) to explore its stability and strengthening under mid-crust conditions. This study will resolve some central questions of earthquake processes and seismic hazard.1. Is the slip during the earthquake localized along a single frictional surface or is it distributed along many fractures?2. Do high-pressure and high-temperature mineralogical phases form during an earthquake (they could be unstable and not be found in exhumed faults)?3. Could pseudotachylites form during shallow earthquakes?4. How much gouge is formed during a single earthquake?5. What portion of the mechanical energy of the earthquake is invested in gouge formation?6. Is the formed gouge good starting material for fault-zone cementation during the interseismic stage?7. Which properties of ERZ are indicators of the seismic activity and could be used for distinguishing between an exhumed seismic fault and an exhumed creeping?8. How fast does gouge compact and cement (lithify), and how does that affect fault strength?

在震源深度不可能到达地震的破裂带，因此对地震破裂带的感知是从对地表破裂和挖掘出的断裂带的间接观测中推断出来的。这里使用了一种不同的方法：在南非的金矿深处进行直接观察，PI最近绘制了三次地震的破裂带。这些绘制的区域与3.7到5.1级的中地震有关，这些中地震穿过了威特沃特斯兰德盆地西部的厚石英岩层序。他发现，一次地震的典型破裂带由5-20个横切断层带组成，这些断层带在地震期间活跃。泥断层带含有破碎的石英粉、岩石碎片或粘土矿物；其中一些区域厚达15厘米。项目建议详细分析在这些破裂带中发现的断层泥的组成、微观结构和地球化学稳定性。他计划确定泥矿物学、高压相、泥表面积和泥溶解度。他将在微观尺度上研究破碎过程，以及从完整岩石到泥粉的转变。该泥料将在热液条件下进行长期（1-3个月）胶结实验（500），探索其在中地壳条件下的稳定性和强化。这项研究将解决地震过程和地震灾害的一些核心问题。地震时的滑动是局限在一个单一的摩擦面上，还是分布在许多裂缝上？在地震中是否会形成高压和高温的矿物学相（它们可能是不稳定的，在挖掘出来的断层中找不到）？在浅层地震中是否会形成伪水晶石？在一次地震中形成多少断层泥？地震的哪一部分机械能被用于断层泥的形成？在震间期，形成的断层泥是否是断裂带胶结的良好起始物质？8.震波带的哪些性质是地震活动的指标，可以用来区分地震断层和蠕变？断层泥压实和胶结（岩化）的速度有多快？这对断层强度有何影响？