Experimental rock physics: fundamental and applied studies in the laboratory and the field

岩石是复杂而耐人寻味的物质。在地球上，它们的物理性质随矿物成分、流体含量、构造应变和温度而变化。地球物理学家利用地震和电磁波远程探测地球；但对实地观测的知情评估需要了解岩石特性与现场条件之间的关系。岩石物理学家努力了解更多关于这些关系的知识，并将它们应用于野外数据。由施密特博士领导的实验地球物理小组在实验室中研究这些特性，并通过现场测量进行独特的研究。这项研究使用了从微型超声波换能器到大型车载地震能源的各种工具。一个问题是，比方说，由这些不同的测量得出的地震波速度的值可能会有很大不同。例如，在地震频率下的地震波速度通常会比使用超声波获得的速度小得多。我们将通过两种方式解决这个问题。首先，我们将在实验室使用“强迫振荡”方法来限制这种地震频散，这种方法将部分利用我们实验室正在建造的一种新仪器。其次，我们将继续对地震波在液体饱和的多孔介质中传播时的行为进行基本测量，以测试现有理论的局限性。这项研究的第三部分研究了控制雷达波传播的因素，雷达波用于探测近地结构。这项工作将尽可能与与科学钻探、近地表危险描述和延时监测有关的平行实地地球物理研究相结合。在实验地球物理学小组工作的学生接触到广泛的地球科学问题，预计所有人都将通过参加实地项目来扩大他们的接触；在过去的几年里，这些项目遍及四大洲和两个极地地区。

Rocks are complex and intriguing materials. In the earth, their physical properties vary with mineral composition, fluid content, tectonic straining, and temperature. Geophysicists probe the earth remotely with seismic and electromagnetic waves; but informed assessments of the field observations require knowledge of the relation between rock properties and in situ conditions. Rock physicists strive to learn more about these relationships and to apply them to field data. The Experimental Geophysics Group led by Dr. Schmitt studies these properties in the laboratory and, uniquely, by field measurements. This research uses tools that range from tiny ultrasonic transducers to large truck mounted seismic energy sources. One problem is that the values of, say, a seismic wave speed given by these varied measurements can be quite different. For example, a seismic wave speed at seismic frequencies will often be substantially less than that obtained using ultrasonic waves. We will address this problem two ways. First, we will constrain this seismic dispersion in the laboratory using 'forced oscillation' methods that will partly employ a new instrument being constructed in our laboratory. Second, we will continue to make fundamental measurements of the behaviour of seismic waves as they travel through a liquid-saturated porous medium in order to test the limits of existing theories. A third component of the research studies the factors controlling the propagation of radar waves that are used to probe near earth structure. This work will be integrated as much as possible with parallel field geophysical studies related to scientific drilling, near-surface hazard characterization, and time-lapse monitoring. Students working in the Experimental Geophysics Group are exposed to a wide range of geoscience problems and all are expected to broaden their exposure by participation in field projects; in the last few years these have ranged over 4 continents and both polar regions.