China’s first optical stereo mapping satellite with a sub-meter resolution, GaoFen-7 (GF-7), launched in November 2019, shows significant potential for providing high-resolution topographic and geomorphic data for quantitative research on active tectonics. However, no studies have evaluated the capability of the GF-7-generated digital elevation model (DEM) for quantitatively studying active tectonics. This study aimed to validate the accuracy of the DEMs extracted from GF-7 stereo imagery, with or without ground control points (GCPs), and evaluated the potential of applying GF-7 DEMs to active tectonics. First, GF-7 stereo images were processed to obtain DEMs with a spatial resolution of 2 m, utilizing three different methods, including block adjustment without GCPs, block adjustment with the aid of Google Earth images and SRTM DEM, and block adjustment with GCPs derived from the Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) data. These three generated DEMs were called GF-7 DEM_Method1, GF-7 DEM_Method2, and GF-7 DEM_Method3, respectively, and were verified by the airborne LiDAR data in the Hasishan section of the Haiyuan fault. Second, the capability of the GF-7 DEMs for identifying active faults, fault scarps, and horizontal offsets was evaluated. Finally, 8 vertical and 13 horizontal offsets were measured based on three different GF-7 DEMs, and airborne LiDAR data were used to verify the measurements’ accuracies. The results indicated that the accuracy of GF-7 DEM_Method1 was the worst and that of GF-7 DEM_Method3 was superior to that of GF-7 DEM_Method2. The GF-7 DEMs could effectively identify the apparent fault scarps and horizontal offsets. The RMSE values of the vertical offsets measured based on GF-7 DEM_Method1, GF-7 DEM_Method2, and GF-7 DEM_Method3 were 0.55 m, 0.55 m, and 0.41 m, respectively. The horizontal offsets yielded RMSE values of 3.98 m, 2.52 m, and 1.37 m, respectively. These findings demonstrated that vertical and horizontal offsets could be accurately measured using the DEMs generated from GF-7 stereo images. Meanwhile, our study indicated that the GCPs derived from ICESat-2 data could be utilized to improve the accuracies of the GF-7 DEM, and the measurements of vertical and horizontal offsets.

The Zheduotang fault (ZDTF) is located in the Kangding section of the Xianshuihe fault zone (XSHF). While the ZDTF plays an essential role in understanding the structural deformation pattern of the Kangding section. Little information is known about the paleoearthquake offsets and slip behavior of the ZDTF. It is therefore essential to analyze the seismic hazards in this area. Using UAV-based photogrammetry, high-resolution satellite images, and field observations, we mapped the surface trace of the fault in detail and measured the horizontal and vertical offsets geomorphological landforms along the fault. The binned cumulative offset probability density (COPD) distribution was calculated to analyze single-event and multievent cumulative offsets. We found that the ZDTF has scarps along its entire ~46 km length, and the offset distributions of its northwestern (NW) and southeastern (SE) sections feature different characteristics. The SE section follows a uniform slip model based on the relationship between cumulative and coseismic offsets. We estimated the maximum potential earthquake magnitudes of the NW section and SE section to be M6.6 and M7.0, respectively, from the measured offsets and empirical formulas. Finally, we discussed the seismic hazard of the ZDTF based on our findings and paleoearthquake data. The NW section is at risk of large earthquakes recurring in the future, whereas the SE section has a low risk of a >M7.0 earthquake recurring in the next 100 years. If these two sections rupture at the same event in the future, the maximum potential magnitude of the ZDTF is M7.2.

Detailed geological and geomorphological evidence has suggested that the Yilan-Yitong fault (YYF), one of the key branches of the Tancheng-Lujiang fault zone in northeastern China, has been an active fault since the Holocene that has extended from Liaoning Province to far-eastern Asia. However, there are no clear fault traces or late Quaternary active features northeast of Tangyuan County. In this study, we carried out shallow seismic reflection exploration, field geological investigation, and trench excavation across the YYF north of Tangyuan. The results revealed that the YYF is composed of two main branches: the west YYF branch is a late Pleistocene active fault, and the east one is a middle-to-early Pleistocene fault. In Heli Town, the west branch of YYF presents fault scarps with heights of ~0.6 m. Across the scarps, we excavated a trench, and we propose that the YYF displaced the late Pleistocene to Holocene deposits, as this was indicated by the geochronological data. The seismic reflection data and sedimentary sequence revealed that the YYF north of Tangyuan is composed of three tectonic belts: the western depression, the central bulge, and the eastern depression. Each tectonic belt is composed of several small folds formed from the end of the Paleogene to the beginning of the Neogene. After the Neogene, different subsidence and uplift events occurred in various parts of the YYF, and after the early Pleistocene, the fault showed a consistent subsidence.