A Proposal for a Standardized Fault Description Format to Study Active Intraplate Tectonics in the Korean Peninsula

Intraplate faulting and the resultant earthquakes are not well understood because of their complex distribution, long period of seismic recurrence, and poor exposure of surface rupture. Pre-existing weaknesses should be studied to understand intraplate faulting and earthquakes. We are developing a long-term project to understand Korean-type intraplate fault behavior and recurrence intervals. As the first step, we will establish an integrated system for production, analysis, and management of fault data related to active crustal deformation. Here we propose a new format for fault data description and management

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Neotectonic transpressional intraplate deformation in eastern Eurasia: Insights from active fault systems in the southeastern Korean Peninsula

Transpression occurs in response to oblique convergence across a deformation zone in intraplate regions and plate boundaries. The Korean Peninsula is located at an intraplate region of the eastern Eurasian Plate and has been deformed under the ENE–WSW maximum horizontal compression since the late Pliocene. In this study, we analyzed short-term instrumental seismic (focal mechanism) and long-term paleoseismic (Quaternary fault outcrop) data to decipher the neotectonic crustal deformation pattern in the southeastern Korean Peninsula. Available (paleo-)seismic data acquired from an NNE–SSW trending deformation zone between the Yangsan and Ulleung fault zones indicate spatial partitioning of crustal deformation by NNW–SSE to NNE–SSW striking reverse faults and NNE–SSW striking strike-slip faults, supporting a strike-slip partitioned transpression model. The instantaneous and finite neotectonic strains, estimated from the focal mechanism and Quaternary outcrop data, respectively, show discrepancies in their axes, which can be attributed to the switching between extensional and intermediate axes of finite strain during the accumulation of wrench-dominated transpression. Notably, some major faults, including the Yangsan and Ulsan fault zones, are relatively misoriented to slip under the current stress condition but, paradoxically, have more (paleo-)seismic records indicating their role in accommodating the neotectonic transpressional strain. We propose that fluids, heat flow, and lithospheric structure are potential factors affecting the reactivation of the relatively misoriented major faults. Our findings provide insights into the accommodation pattern of strain associated with the neotectonic crustal extrusion in an intraplate region of the eastern Eurasian Plate in response to the collision of the Indian Plate and the subduction of the Pacific/Philippine Sea Plates

Near-surface termination of upward-propagating strike-slip ruptures on the Yangsan Fault, Korea

Abstract 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  σv > σHmin to σHmax > σHmin > σv at depth of a ~ 200 m; and the physical properties of unconsolidated sediment, which have low inter-granular cohesion, resulting in distributed deformation

Correlation of paleoearthquake records at multiple sites along the southern Yangsan Fault, Korea: Insights into rupture scenarios of intraplate strike-slip earthquakes

he construction of spatiotemporal models of earthquake occurrence for intraplate areas is challenging due to the low deformation rates in these areas. In this study, we conducted paleoseismological investigations along the southern Yangsan Fault (SYF), a typical low-deformation-rate fault, on the Korean Peninsula. The SYF is distinct from the northern Yangsan Fault (NYF), and the boundary between them is located at the junction between the NNE-striking YF and another major structure, the NNW-striking Ulsan Fault (UF), which branches off from the YF. Paleoseismological trenches at four sites along the SYF indicate that this fault section has not ruptured during the Holocene, in contrast to the NYF and UF. In detail, surface ruptures along the studied section of the SYF occurred during three different time periods, as inferred from stratigraphy and radiocarbon dating: 74 to 49 ka at two sites, 39 to 35 ka at another site, and 28,000 cal yr BP (or 30 ka considering the OSL age) to 16 ka at all sites. These results suggest two alternative rupture scenarios for the timing of paleoearthquakes along the studied fault section during the Late Pleistocene: (1) full rupture along the entire studied section during each earthquake event, or (2) multiple partial ruptures along the two structurally distinguishable parts of the studied fault section, that is, the Wolsan–Miho and Inbo north–Inbo sections. We conclude that geometric discontinuities of the long-lived YF system in the Korean Peninsula intraplate region have played an important role in controlling recent spatiotemporal rupture behavior