The Suryum fault is an active fault in southeast Korea crosscutting the Quaternary sediment deposit. We conducted outcrop-scale to microscale observations of the fault slip zone and performed shear experiments on the fault gouge at subseismic (3–30 µm/s) and seismic slip rates (0.53 m/s). The gouge is rich in clay minerals (> 58%), particularly in expandable clay minerals (40%). In the gouge zone, a very narrow (20–150 µm thick) principal slip zone (PSZ), identified by the strong alignment of clay minerals, was developed. At several places along the fault, the gouge is observed to have been injected into the Quaternary wallrock sediments. The development of the narrow PSZ is incompatible with the velocity-strengthening behavior of the Suryum fault gouge observed in the shear tests, and it may indicate that seismic rupture could be propagated along the PSZ in the clay-rich gouge. Slip localization into the PSZ was presumably possible because of significant dynamic fault weakening due to thermal pressurization (or buildup of pore pressure caused by frictional heating) in the low-permeability clay gouge during fast slip. The gouge injections along the Suryum fault may be the geological record of gouge fluidization caused by thermal pressurization. This idea is supported by observations of very low friction of the Suryum fault gouge when sheared experimentally at the seismic slip rate and of the gouge injections in the sheared gouge. The dynamic weakness of the Suryum fault implies that large displacement and low-frequency ground motion at near-surface depths would be possible when it is reactivated.

中文翻译：

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沿着活动断层横切未固结第四纪沉积物的地震滑移的结构记录和力学特征：韩国苏留姆断裂

Suryum断层是活跃的断层，在韩国东南部横穿第四纪沉积物。我们对断层滑动带进行露头到微观的观测，并在亚地震（3–30 µm / s）和地震滑动速率（0.53 m / s）下对断层泥进行了剪切实验。凿子富含粘土矿物（> 58％），尤其是可膨胀粘土矿物（40％）。在气刨区，开发了一个非常狭窄（20-150 µm厚）的主滑带（PSZ），该带由粘土矿物的强烈排列确定。在沿断层的几个地方，观察到该断层已注入第四纪围岩沉积物中。窄PSZ的发展与剪切试验中观察到的Suryum断层泥的速度强化行为不兼容，这可能表明地震破裂可能在富含粘土的凿岩中沿PSZ传播。滑移定位到PSZ中是可能的，因为在快速滑移过程中，低渗透性黏土中的热增压（或由摩擦加热引起的孔隙压力的增加）会导致动态断层显着减弱。沿Suryum断层注入的胶泥可能是热加压导致胶泥流化的地质记录。当以地震滑移率进行实验剪切时，Suryum断层泥的摩擦非常低，并且在剪切过的泥中注入了泥，这一观点得到了支持。Suryum断层的动态弱点意味着重新激活后，可能会在近地表深度发生大位移和低频地震动。