Search

To estimate the tectonic displacement history of the Yangsan Fault (YSF) in the Cretaceous Gyeongsang Basin (GB), SE-Korea, gravity field measurements were implemented and interpreted. A total of 8000 ground-measured gravity data were compiled and deployed to calculate the Bouguer and residual gravity field. The residual field shows that the mean value in the southern segment of the YSF is very similar to that of the northern segment, meanwhile that of the central segmentation is significantly lower than those of the other segmentations. This implies that the crustal structure and petrophysical properties of the central segment differ significantly from those of the other segments. Applying dip curvature analysis to enhance the image of the residual gravity field, we find that (1) the Gaum fault system (GF) in the western and middle part of the GB extends up to the YSF, where A-type granite outcrops are observed. (2) The middle- and eastern segments of the GF that formed before tectonic motion of the YSF are revealed in turn in areas east of the YSF, which were now covered by the younger sedimentary basin. (3) The middle segment of the GF which occupies between the YSF and the Yeonil tectonic line (YTL) has been displaced approximately 25 km southward from the main GF trace. (4) The easternmost segment is revealed buried in the eastern side of the YTL, which is displaced southward about 18 km from the main GF trace. Comparing all the available geoscientific data sets, we conclude that the right-lateral tectonic movement of the YSF, and the deeply buried middle segment of the GF remained stationary, while the most eastern segment of the GF is reversely moved to the north through left-lateral strike movement of the YTL. [ABSTRACT FROM AUTHOR]

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]