Flow Strength and Acoustic Emissions of Earth Materials at High Pressures

地球上的动态地幔过程驱动着构造板块运动，使我们的星球成为太阳系中独一无二的星球。尽管实验室岩石变形研究取得了突破，但我们对板块运动背后机制的理解，在板块构造的框架内，主要由于实验的限制，仍然相当原始。对地壳和地幔岩石高温流动的实验测量始于20世纪60年代，但高度精确的应力-应变测量只能在地壳条件下进行。第二个重大发展发生在2000年代，当时多砧技术与原位同步加速器x射线衍射技术相结合，用于估计高压下受控变形过程中的样品应力。然而，由于缺乏理论认识和测量限制，应力估计仍然具有高达1gpa的不可接受的不确定性。这种精度的缺乏阻碍了对地幔岩石的流动（即粘度）进行可靠的测量。高压岩石物理领域的第三个突破是进一步发展的必要条件。在本项目中，将开发用于大体积高压装置的内部压电应力传感器，并在高压下精确测定橄榄石的粘度。此外，应力传感器还将用于岩石变形过程中与声发射检测和定位相结合的应力测量。初步工作表明，该技术具有明显的可行性和优越性。利用开发的仪器，两个主要的突出问题将在实验上得到解决。(1)测量导致岩石圈和软流圈之间流变特性转变的粘度变化的原因和幅度。2)利用声发射原位记录研究俯冲带地震的成因。上述目标的实现使未来与地球动力学家（例如在Bayerisches地质研究所）的合作能够使用数值模型将实验室中的过程扩展到地球。因此，Flac项目的预期结果对于建立对地球内部运作的正确理解至关重要。

Dynamic mantle processes in the Earth that drive tectonic plate motions have shaped our planet into one that is unique in the solar system. Despite breakthroughs in laboratory rock-deformation studies, our understanding of the mechanisms behind plate motions, within the framework known as plate tectonics, are still quite primitive due principally to experimental limitations. Experimental measurements on high temperature flow of crustal and mantle rocks commenced in the 1960s, but highly accurate stress-strain measurements could only be made at crustal conditions. A second major development occurred in the 2000s when multianvil technology was combined with in situ synchrotron X-ray diffraction techniques to estimate sample stresses during controlled deformation at high pressures. However, due to a poor theoretical understanding and measurement limitations, stress estimates still have unacceptable uncertainties of up to 1 GPa. This lack in accuracy prevents robust measurements on the flow, i.e. viscosity, of mantle rocks from being made.A third breakthrough in the field of high pressure rock physics is necessary to progress further. In this project an internal piezoelectric stress sensor for large volume, high pressure devices will be developed and the viscosity of olivine will be precisely determined at high pressures. In addition, the stress sensor will be used as an application for stress measurements in conjunction with acoustic emissions detection and localization during rock deformation. Preliminary work has shown the clear feasibility and superiority of this technology over other methods. Using the developed apparatus, two principal outstanding issues will be experimentally addressed. 1) The cause and magnitude of viscosity changes responsible for the transition in rheological properties between the lithosphere and asthenosphere will be gauged. 2) The origin of subduction-zone earthquakes by means of in situ acoustic emissions recordings will be studied. Achievement of the objectives above enables future collaborations with geodynamicists (e.g. at the Bayerisches Geoinstitut) to scale up processes in the laboratory to the Earth using numerical models. The expected outcomes of the Flac project are therefore crucial towards building up a sound understanding of the inner workings of the Earth.