Zhongtai He

As the Tibetan Plateau expands, its outskirts suffer significant seismic hazards. Remotely affected by the expansion of the Tibetan Plateau, the northwestern Ordos area develops an extensional tectonic setting. The occurrence of destructive earthquakes, such as the 1739 Yinchuan‐Pingluo M 8.0 earthquake, reflects serious tectonic activities in this area. Therefore, studying the activity of the boundary normal faults is crucial. This study calculated the vertical slip rate of the Langshan Piedmont Fault (LPF) and integrated it with the parameters of other faults to develop a quantitative tectonic model of the sub‐blocks in the northwestern Ordos area. Using high‐precision unmanned aerial vehicles, drilling, and two Quaternary dating methods (¹⁴C and optically stimulated luminescence), the vertical displacement of the LPF was constrained by the same lacustrine layer in a footwall outcrop and in a hanging wall borehole. The vertical slip rate of the LPF since 51 ka was calculated to be 3.14 ± 1.14 mm/a. The northwestern Ordos area primarily includes parts of the Alxa and Ordos blocks, with the Alxa Block further divided into the Northern Alxa, Bayanhot, and Helanshan sub‐blocks. The LPF is the boundary of the Northern Alxa and Ordos blocks. The Ordos, Bayanhot and Helanshan Sub‐blocks move relative to the Northern Alxa Sub‐block at 1.36 ± 0.30 mm/a (N138.04°), 0.24 ± 0.33 mm/a (N65.34°), 0.26 ± 0.15 mm/a (N133.78°), respectively. Therefore, under the northeastward growth and extrusion of the Tibetan Plateau, the tectonic deformation in northwest Ordos area mainly manifested as the relative movement between the Alxa and Ordos blocks.

High-resolution topographic and geomorphic data are important basic data for the study of active structures. Here, multisource remote sensing data were used to reinterpret the active faults in the northern segment of the Red River Fault (China). First, we obtained airborne light detection and ranging (LiDAR) data, high-resolution GaoFen-7 (GF-7) remote sensing image data, and historical aerial photographs, and a high-resolution digital elevation model (DEM) was generated based on the airborne LiDAR data and GF-7 data. According to the remote sensing interpretation, the main active faults were identified. We subsequently verified the faults in the field and constrained the geographic locations. The current activity was confirmed to be dominantly normal faulting, with some dextral strike-slip components, and the latest active age was the Late Holocene. It reflects the coordination of structural deformation between the rotation of the secondary block and the sliding of the boundary fault within the Sichuan–Yunnan Block. The results show that airborne LiDAR and GF-7 remote sensing data have a great application value in providing high-resolution topographic and geomorphologic data for the study of active structures. The comprehensive application of multisource remote sensing data can greatly improve the reliability of active fault interpretations and provide a reference for follow-up research within the study area.

The Sichuan-Yunnan block is a tectonically active region in China, with frequent large earthquakes occurring in and around it. Despite most earthquakes being concentrated along boundary faults, intraplate faults also have the potential to generate damaging earthquakes. Remote sensing makes it possible to identify these potential earthquake source faults. During an active fault investigation in the Liangshan area, a distinct lithological boundary named Caimashui fault was found. The geometric distribution and kinematic parameter of the fault is crucial for assessing seismic hazards and understanding the deformation pattern within the Sichuan-Yunnan block. The Caimashui fault is mapped with remote sensing interpretation, a field survey, and UAV measurement. Through trenching and Quaternary dating, the Late Quaternary active characteristics of the fault are studied. The fault is a Holocene active dextral strike-slip fault with a reverse component, exhibiting a dextral strike-slip rate of ~0.70 ± 0.11 mm/a. Paleoseismic investigation shows that the last surface rupture event of the Caimashui fault occurred later than 4150 ± 30a BP, with a magnitude of M ≥ 7.0. The fault may act as a secondary splitting fault, absorbing the deformation caused by various sinistral strike-slip rates of the boundary faults and the potential energy from the counterclockwise rotation of the Central Yunnan micro-block.

The tectonic deformation of the southeastern margin of the Tibetan Plateau underwent significant changes before and after the Miocene, which led to the change of the deformation characteristics of the Sichuan‐Yunnan block, and some local areas in the block also showed structural patterns inconsistent with the macroscopic clockwise rotation deformation. Moreover, the Chenghai fault (CF) in the Sichuan‐Yunnan block was the seismogenic fault of the M 7³/₄ Yongsheng earthquake in 1515. However, the dense vegetation impeded the acquisition of surface deformation characteristics and small‐scale horizontal offsets along the fault, resulting in its misty kinematic properties, roughly determined geometric distribution, and the highly controversial rupture parameters of the Yongsheng earthquake. Therefore, we used airborne light detection and ranging, which can penetrate vegetation to obtain high‐resolution surface topography, to map the CF within 120 km. Combined with satellite images and field investigations, we determined that the CF consists of a series of secondary faults with simple geometric structures. Continuous offset linear landforms were preserved along the fault. 102 offsets below 30 m were statistically analyzed and the result revealed that the CF has a characteristic displacement of ∼6 m and it may rupture as a united rupture segment in each large earthquake or its two rupture segments cascade rupture to generate large earthquakes. The magnitude of the Yongsheng earthquake in 1515 was estimated at 7.7. Finally, based on this study, the kinematic characteristics of the Dali terrane and Sichuan‐Yunnan block, where the CF is located are discussed.

The middle segment of the Kalawenguquan fault has been active since the Holocene, with a maximum credible earthquake magnitude of M_S 7.5. We established two source models based on empirical relationships, as well as geological, geomorphological, and seismic characteristics. Taking into account the uncertainties of simulation parameters, we adopted the stochastic finite-fault method to calculate all combinations of a multi-scheme simulation. The effects of different source models, initial rupture points, and site locations on the prediction of ground motion parameters were analyzed. The results indicate that when a site is located on a smaller asperity and is a certain distance from the largest asperity, the simulation results are higher. For different sites, when the initial rupture point is located near the smaller rather than the larger asperity, the acceleration response spectra are higher. Our results show that the relationships between the initial rupture points, asperities, and sites have a significant impact on the simulation results. Therefore, our study highlights the relevance of determining the initial rupture point and source model to obtain a reasonable evaluation for near-field strong ground motion simulations at major infrastructures.

The quantity and quality of remote sensing measurements of tectonic deformation have increased dramatically over the past two decades, improving our ability to observe active geomorphological tectonic processes. High-precision and high-resolution topography is the basis for the quantitative study of active geomorphological and tectonic processes. Recently, with the rapid development of computer visual science and the growing application of light detection and ranging (LiDAR), small unmanned aerial vehicles (UAVs) and structure from motion (SfM) photogrammetry have shown great potential in providing high-resolution and high-precision topographic information. In this Special Issue, we focus on the tectonic activity of active faults and the geomorphic processes in various global tectonic regimes that are related to remote sensing measurements. This Special Issue covers major earthquake hazards and seismogenic structures, new methods in seismological studies using high-resolution data sets, and the tectonic and geomorphic application of high-resolution data sets worldwide and, in particular, in the Eastern Tibetan Plateau and Tian Shan. These contributions will provide new insights into the remote sensing perspectives of geomorphological and tectonic processes.

Long paleoearthquake series are crucial for understanding the recurrence patterns of active faults and evaluating the seismic hazards of faults. In this study, the first semiquantitative evaluation of paleoearthquake events from trenches was applied to normal faults, and classification criteria for identifying paleoearthquakes in trenches on normal faults are proposed to demonstrate the feasibility of semiquantitative evaluations of paleoearthquake events on normal faults. In this study, 72 paleoearthquake trench sites on normal faults around the world were analyzed, and the main indicators for identifying paleoearthquakes on normal faults include the presence of vertical offset (VO), collapse wedge (CW), fissure (FIS), buried paleosol (BP), angular unconformity (AU), upward termination (UT), and sand liquefaction (LF) features. To describe and apply this semiquantitative evaluation method for paleoearthquake events on normal faults, 33 trenches for paleoearthquakes on a fault system in the northern margin of the Hetao Basin were comprehensively analyzed to determine Holocene paleoearthquake events on the Sertengshan, Wulashan, and Daqingshan piedmont faults, and the reliability of paleoearthquake events is discussed. The integrity of the paleoearthquake events obtained was tested by the displacement limit method. The Holocene paleoearthquake recurrence on the three faults was quasiperiodic; the coefficients of variation (COVs) were 0.44, 0.58, and 0.4.