Active fault detection has an important significance for seismic disaster prevention and mitigation in urban areas. The high-density station arrays have the potential to provide a microtremor survey solution for shallow seismic investigations. However, the resolution limitation of the nodal seismometer and small-scale lateral velocity being inhomogeneous hinder their application in near-surface active fault exploration. Distributed acoustic sensing (DAS) has been developed rapidly in the past few years; it takes an optical fiber as the sensing medium and signal transmission medium, which can continuously detect vibration over long distances with high spatial resolution and low cost. This paper tried to address the issue of near-surface active fault exploration by using DAS. We selected a normal fault in the southern Datong basin, a graben basin in the Shanxi rift system in north China, to carry out the research. Microtremor surveys across the possible range of the active fault were conducted using DAS and nodal seismometers, so as to obtain a shallow shear wave velocity model. Meanwhile, we applied a Brillouin optical time domain reflectometer (BOTDR) and distributed temperature sensing (DTS) to monitor the real-time fluctuation of ground temperature and strain. Our results show that the resolution of the deep structures of the fault via the microtremor survey based on DAS is lower than that via the seismic reflection; whereas, their fault location is consistent, and the near-surface structure of the fault can be traced in the DAS results. In addition, both the BOTDR and DTS results indicate an apparent consistent change in ground temperature and strain across the fault determined by the DAS result, and the combination of surface monitoring and underground exploration will help to accurately avoid active faults and seismic potential assessment in urban areas.

The Dunhua-Mishan fault is a component of the Tanlu fault zone, and it is also a major regional fault structure in Liaoning area. The study area is located in Fushun area of the Dunhua-Mishan fault. In order to study the crustal velocity structure in this region, we used 60 sets of three-component short-period seismographs and lay out two temporary profiles in Fushun, Liaoning from Nov. 3 to 25, 2019. Each temporary profiles is about 12km long that is composed of 30 seismometers, which nearly vertically cross the Dunhua-Mishan fault where the survey lines are 6km apart. The installation stations spacing distance from 200 to 400m use the external GPS time service to record frequency range of 0.2 to 150Hz in the instrument. The crustal structure characteristics of the fault zone are studied by ambient noise cross-correlation method. In order to efficiently extract high and low frequency surface wave dispersion signals at the same time, we adopt the Extended Range Phase Shift (ERPS) method. Finally, we use ERPS method to process the collected data and invert the S-wave velocity structure. We initially obtained the S-wave velocity structure of the upper crust below 5 km in the area, which matches well with the local geological data. The S-wave velocity structure has significant lateral inhomogeneity of the Dunhua-Mishan fault in Fushun area. The S-wave velocity is obviously lower on the Dunhua-Mishan fault, while with the existence of ancient mixed granite the velocity on both sides of the fault is obviously higher.

The Yanzhou Coal Mining area in North China has experienced a significant increase in shallow depth (<2 km) seismic activity in recent years, particularly following the 2017 M 4 lower crust earthquake. However, the relationship between deep tectonic earthquakes and shallow seismicity remains poorly understood. This study employs seismic tomography to resolve a high-resolution 3D crustal velocity structure and inverts the source parameters of the 2017 M 4 event (22 km depth) to calculate static Coulomb stress changes. By integrating these analyses, we investigated the mechanical relationship between the lower crustal and shallow seismicity. The 2017 earthquake, which is spatially correlated with a low-velocity anomaly and the westward migration of the hypocenters in the lower crust, suggests that fluid-driven fault activation occurred where deep fluids from the upper mantle led to increased seismicity rates. In contrast, Coulomb stress changes generated by this event are insufficient to induce stress-triggering effects and lack a direct causative relationship with shallow seismic activity. Although our analysis rules out static stress transfer associated with the 2017 M 4 event, the possibility of remote dynamic triggering remains and cannot be definitively excluded. Instead, the statistically significant increase in shallow seismicity correlated temporally with extended subsurface resource extraction and the post-2017 use of new deep-mining methods under conditions of high stress and elevated temperatures, highlighting anthropogenic production behaviors as a primary driver. The study demonstrates that lower crustal seismicity and shallow mining-induced activity operate within distinct mechanical frameworks. Although deep fluids influence tectonic earthquakes by reducing the effective normal stress along the fault plane, shallow seismicity is dominantly controlled by the intensity of coal mine extraction. These findings highlight the necessity of distinguishing between tectonically driven and mining-induced seismic hazards.