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The Jeokjung-Chogye Basin (JCB) is the first impact crater discovered in the Korean peninsula. The geometric centre of the exterior crater rim is demarcated by an elevation high surrounding the JCB, exceeding 200 m. The diameter of the exterior ring is approximately 6500 m, and its centre is located about 1000 m southwest of the basin centre. Using terrestrial measured gravity field interpretations such as dip curvature and Z -derivative analysis of the residual anomaly field, we calculated the diameters of the peak ring and uplift ring to be about 4000 and 1500 m, respectively. The centre of the peak ring is located approximately 350 m to the west of the centre of the exterior ring; meanwhile, the centre of the uplift ring is located about 300 m to the east from the exterior ring's centre. Application of the Euler deconvolution method indicates that the depth discrepancy between the peak and uplift rings is approximately 200 m. This discrepancy indicates that the bedrock under the uplift ring has risen about 200 m following the meteorite impact. The offsets of the peak and the uplift ring's centres, relative to the diameter of the crater centre, allow us to conclude that the JCB was formed by steeply inclined impact (∼50–60° to the horizontal) from the eastern direction. [ABSTRACT FROM AUTHOR]

An earthquake (2016M5.8_GY) occurred on 2016 September 12 due to the SW−NE movement of the Yangsan fault in the Gyeongsang Basin in the southeastern part of the Korean Peninsula and caused more than 600 aftershocks within a 1-yr period. To find out the causes and process of the 2016M5.8_GY and its aftershocks, we conducted 3-D underground structural modelling of the Gyeongju area using a combined interpretation of geological, petrophysical and potential field data and hence calculated the density- and magnetic-field distribution along the Yangsan fault. The results of the 3-D modelling indicate that the 2016M5.8_GY occurred in the ductile region of the fault, which is tectonically very unstable, and is therefore highly likely to be significantly affected by any future seismological stress. The crustal structure most affected by the 2016M5.8_GY is the Cretaceous Granite, which has a vertical relief of approximately 12 km with a relatively lower density material than the surrounding country rock and rests on highly ductile material. Therefore, the lower part of the granite is enough unstable that it was probably crushed by the main shock. That is also the reason, why so many aftershocks occurred beneath the granites. [ABSTRACT FROM AUTHOR]