Fault zones in crystalline rocks generally possess a relatively narrow (<50-cm-thick) fault core (i.e., a fault gouge layer/zone). However, the Geumwang Fault, a major strike-slip fault developed in granitic rocks in Korea, has a wider (∼24-m-thick) fault core with several gouge layers. Here we conduct detailed field and microanalytical investigations on the fault core of the Geumwang Fault. Results showed that some of the gouges are primary gouges in which seismic slip was localized as the principal slip zones (PSZs), whereas others are secondary gouges that formed by the injection of fluidized gouge material into fractures. Within the PSZs, the presence of amorphous carbon and graphite implies that frictional heat generated by coseismic slip triggered siderite decomposition. It was likely the consequence of gouge fluidization induced by thermal pressurization under fluid drained conditions. In addition, the gouge fluidization seems to neutralize the foliation of the PSZ. This process, together with weakening of the damage zone by long-term alteration, may facilitate subsequent seismic slip occurred along foliated breccia or the fault core boundary rather than the former neutralized PSZs, thereby widening the Geumwang Fault. We propose that coseismic fluidization of PSZ by thermal pressurization can act as a potential mechanism to widen the fault core and generate multiple gouge layers in crystalline rocks.

结晶岩中的断层带通常具有相对较窄（<50 厘米厚）的断层核心（即断层泥层/带）。然而，在韩国花岗岩中发育的主要走滑断层Geumwang断层具有更宽（~24米厚）的断层核心和几个泥层。在这里，我们对金旺断层的断层核心进行了详细的现场和微观分析调查。结果表明，一些泥是初级泥，其中地震滑动被定位为主滑动区（PSZ），而另一些泥是通过将流化泥材料注入裂缝中形成的次生泥。在 PSZ 内，无定形碳和石墨的存在意味着同震滑移产生的摩擦热引发菱铁矿分解。这可能是在排液条件下由热加压引起的过切流化的结果。此外，过切流化似乎中和了 PSZ 的叶状结构。这一过程，再加上长期蚀变造成的破坏区弱化，可能会促进随后沿叶状角砾岩或断层核心边界发生地震滑动，而不是先前中和的PSZ，从而扩大金旺断层。我们提出通过热加压对 PSZ 进行同震流化可以作为一种潜在的机制来扩大断层核心并在结晶岩中产生多个凿层。可能有助于随后沿叶状角砾岩或断层核心边界发生地震滑动，而不是先前中和的 PSZ，从而扩大金旺断层。我们提出通过热加压对 PSZ 进行同震流化可以作为一种潜在的机制来扩大断层核心并在结晶岩中产生多个凿层。可能有助于随后沿叶状角砾岩或断层核心边界发生地震滑动，而不是先前中和的 PSZ，从而扩大金旺断层。我们提出通过热加压对 PSZ 进行同震流化可以作为一种潜在的机制来扩大断层核心并在结晶岩中产生多个凿层。