Clay–clast aggregates in fault gouge: An unequivocal indicator of seismic faulting at shallow depths?
Clay–clast aggregates in fault gouge: An unequivocal indicator of seismic faulting at shallow depths?
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DOI：
10.1016/j.jsg.2012.07.008
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发表时间：
2012-10
影响因子：
3.1
通讯作者：
R. Han;T. Hirose
中科院分区：
文献类型：
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作者：
R. Han;T. Hirose
一个常见的问题，在天然断层断层泥轴承的研究是很难确定所观察到的断层泥是否剪切地震或抗震;这个问题的出现，因为断层滑动率断层泥的指标的稀缺。最近，粘土碎屑聚集体（CCA; CCA包括由超细颗粒的边缘覆盖的碎屑核）被提出作为地震断层泥中的滑动的可能指标，在地震滑动率的断层泥剪切实验的基础上。为了研究CCA形成的过程和条件，我们在正常应力（0.3-3.0 MPa）和滑动速率（0.0005-1.3 m s-1）下，以及在室内湿度（室内干燥）和水饱和（湿）条件下，对石英和石英-膨润土泥进行了旋转剪切实验。我们发现，即使在最低的滑动率，这是相当慢，比实际的地震滑动率，CCA可以产生在室内干燥的断层泥。这一发现表明，热加压和流化在高温地震滑动过程中不一定需要的CCA的形成，与以前的观点相反。鉴于在很宽的滑动速率范围内发生CCA，我们认为CCA的存在并不是地震滑动速率下断层滑动的明确指标。
A common problem encountered in studies of gouge-bearing natural faults is the difficulty of ascertaining whether the observed gouge was sheared seismically or aseismically; this problem arises because of the scarcity of indicators of fault slip rates for gouge. Recently, clay–clast aggregates (CCAs; a CCA comprises a clastic core mantled by a rim of ultrafine particles) were proposed as a possible indicator of seismic slip in gouge, on the basis of shear experiments on gouge at seismic slip rates. To examine the processes and conditions of CCA formation, we conducted rotary shear experiments on quartz and quartz–bentonite gouges under normal stresses (0.3–3.0 MPa) and slip rates (0.0005–1.3 m s−1), and in both room-humidity (room-dry) and water-saturated (wet) conditions. We found that CCAs could be produced in room-dry gouges even at the lowest slip rates, which are considerably slower than actual seismic slip rates. This finding demonstrates that thermal pressurization and fluidization at elevated temperature during seismic slip are not necessarily needed for the formation of CCAs, contrary to previous views. Given the occurrence of CCAs over a wide range of slip rates, we suggest that the presence of CCAs is not an unequivocal indicator of fault slip at seismic slip rates.