| 摘要: | 岩石變形試驗可以用來探討地震蘊生與擴展時的行為和機制。其中，地震斷層破裂的行為與機制，多使用可大滑移距離與高滑移速度實驗條件的旋剪儀進行岩石變形試驗。一般來說，斷層帶物質多為無內聚力岩石(斷層泥)，所以探討斷層行為時，旋剪儀的岩石變形試驗也以天然的斷層泥或合成的岩石粉末為主。目前，高速變形的斷層泥變形試驗，多以鐵氟龍環的包覆為圍壓。而此種包覆，只能使用較低正向應力(約0.5到3百萬帕)進行岩石變形試驗，過程中有斷層泥溢出與化學汙染等議題。我們設計一金屬壓力閥，成功增強包覆能力，並提升可執行之正向應力(高達18 百萬帕)，且實驗過程中無高嶺土(試驗材料)或水溢出的情形。實驗結果顯示，壓力閥的摩擦阻力(金屬接觸之摩擦)非常小(摩擦係數≈0.02)，而且於低正向應力飽和水條件獲得之高嶺土的實驗數據與前人發表的數據相似，說明壓力閥的數據可信。另外，我們發現，分別於室濕與飽和水條件下變形之高嶺土(高速高正向應力)有迥異之摩擦行為(室濕條件有較小之破裂能、較短之弱化距離與較高之穩態摩擦係數，飽和水條件則相反)。我們推測閃熱作用於室濕條件下升溫速度快，迅速產生熔融(熱崩解)弱化並達到摩擦穩態。相反的，因為水的存在(吸熱膨脹與不可壓縮)，閃熱作用於飽和水條件下被抑制，所以產生較長之弱化距離與較大破裂能。目前我們無法確定相關之弱化機制(液壓、蒸氣弱化，或是水彈性動力弱化)，未來還需要相關實驗對這方面多著墨。簡而言之，新設計的壓力閥可以擴增實驗條件，並可讓我們對斷層(或山崩)變形有更多的瞭解。
;Rock deformation experiments are utilized to investigate the frictional behaviors and the associated mechanism of a fault during earthquake nucleation and ruptures. In particular, rotary shear apparatuses, characterizing with the deformation of large displacement and high velocities, are allowed to determine the fault behavior and its mechanism operated during earthquake propagation. In general, incohesive materials (fault gouges) are the dominant component within a fault core. Therefore, the studying materials, including both natural and synthetic gouges, are widely utilized with rotary shear apparatuses. So far, experiments on gouges deformed at seismic rates are confined with Teflon rings and at low normal stresses (0.5 to 3 MPa), sometimes with the issues of gouge extrusion and chemical contamination. Here we develop a metal pressure vessel which allows to deform gouges at high normal stresses (up to 18 MPa) and at seismic rates and, importantly, without gouge and/or fluid extrusion. The results show (1) the resistance of the pressure vessel (metal-to-metal contact) is extremely low (friction coefficient≈0.02) and (2) similarity to the previously published data, suggesting the data of the pressure vessel is convincing. In particular, deformed at seismic rates, significantly different frictional behaviors of kaolinite between room humidity and water-saturated conditions are observed (small fracture and short dynamic weakening distance is observed under room humidity condition, and the opposite is observed under water-saturated condition). It suggests that under room humidity flash heating can rapidly increase temperature and facilitate frictional melting (thermal decomposition) on gouges to promptly reach steady state of friction. Instead, under water-saturated condition, because water can absorb frictional heat and be incompressible, flash heating is inhibited, displaying a large fracture energy and large dynamic weakening distance. The dynamic weakening is still unclear (fluid pressurization, thermal pressurization, or elastohydrodynamic lubrication) and further experiments are required for the determination. In summary, the designed pressure vessel could expand the experimental conditions and allows to enrich the understanding of fault (landslide) deformation. |
