Spatial patterns of seismogenic faulting in northeastern Asia

A combination of 60 years of seismicity, over 45 years of fault plane solutions of moderate-sized to large earthquakes, and recent databases of high-resolution topography delineate spatial patterns of seismogenic faulting in northeastern Asia. Here I synthesize new knowledge with known features in a regional context. Strike -slip faulting characterizes active deformation along the northern and southeastern margins, as well as the interior of this vast region; while normal and reserve faulting dominate its northwestern/southwestern and eastern margins, respectively. Consistent patterns of transpressive and reverse seismogenic faulting persist along the Sakhalin-Hokkaido shear zone and the Eastern Japan Sea fold-and-thrust belt over lengths of over 1000 km each, respectively, but not as throughgoing faults. The latter transitions into strike-slip faulting farther south along the North Chugoku shear zone in southwestern Japan and continues southward into Kyushu. Meanwhile, the true intra-continental, strike-slip Tanlu fault zone reaches an uninterrupted length of about 2000 km. Fault plane solutions, including one from a recent event near the great intra-continental earthquake of 1668, provided much-needed new evidence for the dextral-slip nature of this long fault and a paleo-seismic study confirmed that the entire fault is seismogenic. Meanwhile, active segments of strike-slip faults elsewhere in the North China basin, of lengths less than about 200 km, have been responsible for devastating earthquakes. These observations are noteworthy as the current speed of the ground, based on Global Navigation Satellite System (GNSS) measure-ments, is only 3-4 mm/yr over a length-scale of 3000 km in the entire area of study. Regions of particular concern include: 1) The east coast of South Korea where recent, moderate earthquakes ruptured small sections of an active fault system that has a set of sharp fault scarps extending southward near the metropolitan area of Busan; and 2) the North China basin where intense historical seismicity contrasts with quiescence that persisted since 1976. Overall, no continental block, including the Amurian microplate, is well defined and only the oceanic Japan Sea exhibits little internal deformation.