Search

While understanding the long-term slip rate of active normal faults is essential for the comprehensive assessment of seismic activity, it is difficult due to the absence of age control in the erosional bedrock region. The preserved sequence of wave-cut platforms in granite allows exploration of the long-term slip rate in the footwall of some normal faults. We investigated wave-cut platforms in the southern Pearl River Delta (PRD), a coastal delta transected by the seismically active Littoral Fault Zone (LFZ) in the northern South China Sea, to derive slip rates and their impacts on the seismic hazard potential. We mapped a flight of four wave-cut platforms (T1–T4), dated the T2 and T4 platforms by 10Be cosmogenic nuclide dating, and used the absolute age to correlate the un-dated platform to global sea-level highstands. Our results allocate the ages of 128 ka, 197 ka, and 239 ka to the upper three wave-cut platforms and yield temporally various uplift rates ranging from 0.30 to 0.38 mm/a during 239–128 ka to 0.09 mm/a since 128 ka. A decrease in the uplift rate, which coincided with a decreased subsidence rate within the PRD in previous work, implied a weakened differential uplift onshore of the LFZ system. Our findings infer that the transgression event occurred as early as marine isotope stage (MIS) 7 in the PRD, consistent with the view that Pleistocene sedimentation began in MIS 5 or earlier in the PRD.

The arc-shaped tectonic belt, located in the northeastern margin of the Tibetan Plateau, is one of the leading edges of the plateau’s outward growth and uplift expansion, with a large number of active faults and frequent seismic activity. Researchers have carried out numerous studies on active faults in this region, and a wealth of reliable basic data has been accumulated. However, integrating multidisciplinary data to establish a 3D geometrical structure model that is concerned about seismogenic tectonics and can be tested, has become the key to restricting the regional seismic hazard evaluation. Based on a series of published active tectonic research, we analyze in detail the surface and deep coupling relationships of the major active faults in this region and establish three sets of 3D fault structure models, which are built respectively by active fault mapping and dip angles (the V1 model), 7 magnetotelluric profiles and 7 auxiliary profiles (the V2 model), and multi-source data (the V3 model) and continuously close to the real geological facts. From the model perspective, it is suggested that the controversial Haiyuan fault is a crustal-scale left-slip fault and the shape of the Liupanshan fault reflects the absorption of the left-slip component of the Haiyuan fault. Comparing the same fault plane of these three models, we find that the V3 model is more consistent with geological facts, showing that by assisting the multi-source data 3D geological modeling technique we can establish a 3D geological model closest to the real regional structure. Finally, combining the V3 model, the fault segmentation, and the empirical formulas of the moment magnitude-rupture parameters, we segment the faults and calculate the potential moment magnitudes of the major active faults in the study region. The faults with relatively higher seismic hazards are the Liupanshan fault, the southeastern segment of the Xiangshan-Tianjingshan fault, the westernmost segment of the Haiyuan fault, and the West Qinling fault, of which the estimated potential moment magnitudes are generally more than 7.0. Our study provides a referenced 3D geological model for exploring the deep structures of the region, regional geological research, and earthquake disaster prevention.

The Qilian Shan, located in the northeastern Tibetan Plateau, is an intraplate orogenic belt that underwent several episodes of fold and thrust deformation, particularly during the Mesozoic and Cenozoic. However, the deformation styles and relationships between the basin and mountains remain controversial. Therefore, in the current study, we conducted detailed field mapping of the sedimentary basins in Sunan and Huangcheng, and observed three episodes of compressive tectonic activity. We also restored a deformed section to determine the shortening rate of the Cretaceous sedimentary Sunan Basin. The first thrust episode, during the Paleogene, involved a southwestward thrust motion, comprising the Yumu Shan and Gaizhangdaban thrust systems. The second Neogene episode involved the northeastern thrust belt in the northern Qilian Shan, which comprises the Northern Qilian thrust system. The third episode produced NW-trending strike-slip activity that became the major tectonic deformation style; thus, the entire block rotated clockwise. Additionally, the restored section revealed that the Cretaceous strata have been shortened by ∼3.56%. Collectively, these results indicate that the Sunan and Huangcheng area on the northeastern Tibetan Plateau is influenced by the far-field effects of the collision between the Indian and Asian continents, as well as the effects of intraplate orogenic processes related to the collision of the Alashan Block and the Qilian Shan. Therefore, the current study has defined the deformation style in the northeastern Qilian Shan region, so we wish to give a clarification of the tectonic evolution and forecast the tectonic propagation in the Qilian Shan region.