Flow Strength and Acoustic Emissions of Earth Materials at High Pressures

地球中驱动构造板块运动的动态地幔过程将我们的星球塑造成太阳系中独一无二的星球。尽管在实验室岩石变形研究中取得了突破，但我们对板块运动背后的机制的理解，在称为板块构造的框架内，仍然非常原始，主要是由于实验的限制。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，但只有在地壳条件下才能进行高精度的应力-应变测量。第二个重大发展发生在21世纪初，当时多砧技术与原位同步加速器X射线衍射技术相结合，以估计高压下受控变形期间的样品应力。然而，由于理论认识不足和测量限制，应力估计仍然具有高达1 GPa的不可接受的不确定性。这种精度上的不足阻碍了对地幔岩石流动（即粘度）的可靠测量。高压岩石物理学领域的第三个突破是进一步发展的必要条件。本计画将研制一种适用于大体积、高压装置的内部压电式应力感测器，并精确测定高压下橄榄石的黏度。此外，应力传感器将被用作在岩石变形期间结合声发射检测和定位的应力测量的应用。初步工作表明，这项技术明显可行，优于其他方法。使用开发的设备，两个主要的悬而未决的问题将实验解决。1)将测量岩石圈和软流圈之间的流变性质的转变负责的粘度变化的原因和幅度。2)将通过现场声发射记录研究俯冲带地震的起源。上述目标的实现使得未来能够与地球动力学家（例如在Bayerisches Geoinstitut）合作，使用数值模型将实验室中的过程扩大到地球。因此，Flac项目的预期成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.