Collaborative Research: Developing a Methodology for Imaging Stress Transients at Seismogenic Depth

合作研究：开发震源深度应力瞬变成像方法

• 批准号: 0352134
• 负责人: Fenglin Niu
• 金额: $ 0.45万
• 依托单位: William Marsh Rice University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-05-01 至 2006-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0352134&HistoricalAwards=false
• 关键词: Collaborative; Research; Developing; Methodology; Imaging

EAR-0352134NiuWe seek to develop a robust methodology for directly measuring temporal variations in subsurface tectonic stress by exploiting the stress dependence of seismic velocity. The dependence of crustal seismic velocities on crack properties and in turn, the dependence of crack properties on stress, means that seismic velocity exhibits stress dependence. This dependence constitutes, in principle, a powerful instrument for studying subsurface transient changes in stress. While these relationships and their scientific potential have been known for several decades, the use of time-dependent seismic imaging, has not yet developed into a reliable means of measuring subsurface seismogenic stress changes. There are two primary reasons for this: 1) lack of sufficient time-delay precision to detect small changes in stress, and 2) the difficulty in establishing a reliable calibration between stress and seismic velocity. These two problems are coupled because the best sources of calibration are the solid-earth tides and barometric pressure, both of which produce weak stress perturbations of order 102-103 Pa. Detecting these sources requires measurement of fractional velocity changes on the order of 10-5-10-6, based on laboratory experiments. We propose to conduct a cross-well experiment in the Parkfield area of the San Andreas Fault, with the goal of successfully measuring delay-time variations induced by tides and barometric pressure, as a means of demonstrating that known stress changes can be reliably measured. By exploiting advances in the characteristics of artificial seismic sources (such as rapid and reliable repeatability), dramatic advances in computational power (allowing massive stacking of seismic waveforms), it will be possible to measure variations in seismic velocity with unprecedented precision that meet the requirement noted above. This will permit a meaningful stress calibration of this method. The proposed experiment consists of two phases: a test phase to take place at two locations at and near Lawrence Berkeley National Laboratory, and an experimental phase at Parkfield on the site of the 2-km-deep SAFOD Pilot Hole, where progressively more realistic geometries will be utilized. Ultimately, we will shoot to receivers in the Pilot Hole, which will allow us to retrieve stress information at seismogenic depths.***

EAR-0352134Niu我们寻求开发一种稳健的方法，通过利用地震速度的应力依赖性来直接测量地下构造应力的时间变化。地壳地震速度对裂缝性质的依赖性以及裂缝性质对应力的依赖性意味着地震速度表现出应力依赖性。 原则上，这种依赖性构成了研究地下应力瞬态变化的强大工具。 虽然这些关系及其科学潜力几十年来已为人所知，但与时间相关的地震成像的使用尚未发展成为测量地下地震应力变化的可靠方法。造成这种情况的主要原因有两个：1）缺乏足够的时滞精度来检测应力的微小变化，2）难以在应力和地震速度之间建立可靠的校准。 这两个问题是耦合的，因为最好的校准源是固体地球潮汐和气压，两者都会产生 102-103 Pa 量级的弱应力扰动。检测这些源需要测量 10- 量级的分数速度变化。 5-10-6，基于实验室实验。 我们建议在圣安德烈亚斯断层的帕克菲尔德地区进行跨井实验，目的是成功测量潮汐和气压引起的延迟时间变化，作为证明可以可靠测量已知应力变化的一种手段。 通过利用人工震源特性的进步（例如快速可靠的重复性）、计算能力的巨大进步（允许地震波形的大量叠加），将有可能以前所未有的精度测量地震速度的变化，满足要求如上所述。 这将允许对该方法进行有意义的应力校准。 拟议的实验由两个阶段组成：测试阶段将在劳伦斯伯克利国家实验室及其附近的两个地点进行，实验阶段将在帕克菲尔德 2 公里深的 SAFOD 先导孔现场进行，其中的几何形状逐渐变得更加真实将被利用。 最终，我们将向导向孔中的接收器进行射击，这将使我们能够检索地震发生深度的应力信息。***