Active Tectonics Research Center, Korea Institute of Geoscience and Mineral Resources, Daejeon, 34132, South Korea.
Department of Geological Sciences, Pusan National University, Busan, 46241, South Korea.
Sci Rep. 2023 Jun 19;13(1):9869. doi: 10.1038/s41598-023-37055-7.
We present a new example of the termination of strike-slip paleoearthquake ruptures in near-surface regions on the Yangsan Fault, Korea, based on multi-scale structural observations. Paleoearthquake ruptures occur mostly along the boundary between the inherited fault core and damage zone (N10-20°E/> 75°SE). The ruptures propagated upward to the shallow subsurface along a < 3-cm-wide specific slip zone with dextral-slip sense, along which the deformation mechanism is characterized mainly by granular flow in near-surface region. The ruptures either reach the surface or are terminated in unconsolidated sediment below the surface. In the latter case, the rupture splays show westward bifurcation, and their geometry and kinematics show a change to NNW-strike with low-angle dip and dextral-reverse oblique-slip sense in the strata. We suggest that the upward termination of the contractional strike-slip ruptures is controlled by the inherited fault geometry that is unfavorable with respect to the stress field (ENE-WSW σ) at basement depths in terms of movement on the fault, and the lack of extension of the fault into shallow subsurface; a depth-dependent change in stress from σ > σ > σ to σ > σ > σ at depth of a ~ 200 m; and the physical properties of unconsolidated sediment, which have low inter-granular cohesion, resulting in distributed deformation.
我们提出了一个新的例子，即在韩国牙山断层近地表地区，走滑古地震破裂的终止，基于多尺度结构观测。古地震破裂主要发生在继承性断层核和破坏带（N10-20°E/>75°SE）之间的边界上。破裂沿着一条宽约 3 厘米的右旋走滑特定滑动带向上浅部扩展，其变形机制主要以近地表区的颗粒流为特征。破裂要么到达地表，要么在地表以下的未固结沉积物中终止。在后一种情况下，破裂分叉呈向西分叉，其几何形状和运动学显示在近地表地层中向 NNW 走向、低角度倾斜和右旋逆斜滑的变化。我们认为，收缩性走滑破裂的向上终止受继承性断层几何形状的控制，该几何形状不利于基底深度处的应力场（ENE-WSW σ）相对于断层上的运动，以及断层没有延伸到浅部；在深度为 a~200m 处，应力从σ>σ>σ 到 σ>σ>σ 的深度依赖性变化；以及未固结沉积物的物理性质，其颗粒间凝聚力低，导致分布式变形。
