Active Faulting of Landforms along the Tuosuhu-Maoniushan Fault and Its Seismotectonic Implications in Eastern Qaidam Basin, China

The fold-and-thrust belt along the northern margin of the Qaidam basin is a typical active tectonic belt located in the northeast Tibetan Plateau. This belt is at a high risk of strong earthquakes with magnitudes larger than 6, as shown by multiple recorded events during 1962–2009. The lack of detailed late Quaternary surficial faulting data and systematic seismotectonic studies has posed difficulties in properly assessing the seismic risks and understanding the ongoing geodynamics in this region. In this study, we mapped the geomorphic features and fault traces from high-resolution satellite images and field investigations of the Tuosuhu-Maoniushan fault (TMF). Field photogrammetry was conducted to obtain deformation measurements using a DJI M300 real-time kinematic (RTK) drone. The TMF displaces the Holocene and late Pleistocene alluvial terraces in the eastern Qaidam basin. This fault dips to the south in the west and central segments (as a boundary of the Denan depression) and to the north in the eastern segment along the piedmont of the Maoniushan Mountains. The vertical slip rate is estimated to be 0.37 ± 0.08 mm/yr, which is similar to that of the active southern Zongwulongshan fault. By integrating our investigations with the previously published studies on deep structures and Cenozoic geology of the region, we propose a deep-seated thrust model for the seismotectonics of the northern margin of the Qaidam basin. The Aimunike, Tuosuhu-Maoniushan, southern Zongwulongshan, and Zongwulong faults, along with many folds, form an active compressional zone. The complex across-strike structures and along-strike segmentation could facilitate the release of strain through earthquakes of magnitude 6–7 in this broad seismotectonics belt, rather than through strong surface-rupturing events resulting from a single mature large fault.

On the seismicity and tectonic activity Of the Bengal basin

The tectonic activity of the Bengal basin for years 1850-1988 of seismicity and 16 years (1970-1985) of P-wave first motion data have been studied. The seismicity studies reveal three seismic belts such as Dhubri fault (striking N-S), Calcutta hinge zone (striking NE-SW) and the central region of the Bengal basin (striking NW-SE). Dauki fault is comparatively less seismically active than Dhubri fault. The seismicity of Dhubri fault and Calcutta hinge zone are confined to limited extension. The seismic activity along the central portion of the Bengal basin is extending from the Himalayan region (27°N, 88.5°E) to eastern plate margin (23.8°N, 92°E). .This appears to be a tectonic belt and is associated with the northeast drifting of Indian plate. The focal, mechanism studies reveal thrust faulting showing the stresses to be perpendicular to the proposed belt.

New Detrital Apatite Fission Track Thermochronological Constraints on the Meso-Cenozoic Tectono-Thermal Evolution of the Micangshan-Dabashan Tectonic Belt, Central China

The Micangshan-Dabashan tectonic belt, located in the southern Qinling-Dabie Orogen near the northeastern Tibetan Plateau, is a crucial area for understanding the processes and mechanisms of orogenesis. Previous studies have been focused on the cooling process via thermochronology and the mechanism and process of basement uplift have been investigated. However, the coupling process of basement exhumation and sedimentary cap cooling is unclear. The tectono-thermal history constrained by the detrital apatite fission track (AFT) results could provide valuable information for understanding crustal evolution and the coupling process. In this study, we provided new detrital AFT thermochronology results from the Micangshan-Dabashan tectonic belt and obtained nine high-quality tectono-thermal models revealing the Meso-Cenozoic cooling histories. The AFT ages and lengths suggest that the cooling events in the Micangshan area were gradual from north (N) to south (S) and different uplift occurred on both sides of Micangshan massif. The cooling in Dabashan tectonic zone was gradual from northeast (NS) to southwest (SW). The thermal histories show that a relatively rapid cooling since ca. 160 Ma occurred in the Micangshan-Dabashan tectonic belt, which was a response to the event of Qinling orogenic belt entered the intracontinental orogenic deformation. This cooling event may relate to the northeastward dextral compression of the Yangtze Block. The sedimentary cap of Cambriano-Ordovician strata responded positively to this rapid cooling event and entered the PAZ since ca. 63 Ma. The deep buried samples may be limited affected by climate and water erosion and the accelerated cooling was not obvious in the Late Cenozoic. Collectively, the cooling processes of basement and sedimentary cap in Micangshan-Dabashan tectonic belt were inconsistent. The uplift of the sedimentary area is not completely consistent with that of the basement under thrust and nappe action. The rigid basement was not always continuous and rapidly uplifted or mainly showed as lateral migration in a certain stage because of the different intensities and modes of thrust and nappe action, and the plastic sedimentary strata rapidly uplifted due to intense folding deformation.

Coal–rock damage characteristics caused by blasting within a reverse fault and its resultant effects on coal and gas outburst

In view of the coal and gas outburst accidents occur frequently caused by blasting in geological structural belt, in order to study the mechanical characteristics of coal rock in tectonic belt disturbance by blasting and blasting vibration effect influenced on the stability of surrounding rock, coal–rock damage and failure characteristics within a reverse fault caused by a blasting stress wave were investigated using numerical analyses and experiments. According to the experimental results, the causes of coal and gas outburst dynamic disasters within a reverse fault during blasting are analyzed. The outcomes indicated that the crushing circle created by the crack propagation near the blasting hole severely damaged the fault plane and floor rocks adjacent to the footwall of the reverse fault. Fractures also extended to the upper and lower coal seams of the reverse fault; this caused the surface of the coal seam to fall off and severe internal damage. According to theoretical analysis, the reflection of the blasting stress wave propagating to the reverse fault intensified the damage to coal and rock. Elastic strain energy accumulation within the reverse fault structural zone was accompanied by high-stress concentration. The reverse fault tectonic region was destroyed by blasting vibration. It increased gas pressure and caused a weak surface, which provided a channel for gas flow and a dynamic basis for the occurrence of coal and gas outburst. The research results have important theoretical value to reveal the mechanism of coal and gas outburst in tectonic belt induced by blasting.

Himalayan Tectonic Belt: Morlet Wavelet Variation and Seismic Harmony

Morlet wavelet analysis is a method of studying the periodic spectrum of non-stationary physical signals and is applied to the Himalayan Tectonic Belt to explore whether there is any seismic periodicity, and to explore the possibility of harmony or commonality of properties among the seismic activities of different zones. The earthquake sequence during 1951–2016 with magnitudes M ≥ 6.0 is analysed. Wavelet non-periodicity for the Centre zone suggests a non-uniform spatial–temporal distribution of earthquake movement between plates which may relate with the rare great earthquakes, while the periodicities for the west and east zones may suggest the concurrence with the adjustment of the tectonic movement of the east- and west-end regions of the Himalayan Tectonic Belt relative to its central core. These three zones collectively form the Himalayan Tectonic Belt. This contains a periodicity of about five years of seismic activity that tests successfully with a 95% confidence statistic. Borrowing from the concept of musical harmony, this is the significant seismic harmonic which reflects the Belt’s pervasive tectonic stress and an overall harmony of continent–continent plate convergence. Morlet wavelet analysis also reveals the Himalayan Tectonic Belt and the Pamir–Hindu Kush Tectonic Zone to be engaged as a big new family: the Himalayan Tectonic Belt Plus. It is demonstrated that this new whole also has seismic harmony with the common property again being the 5-year periodicity. This indicates a unified structure of pervading active stress and seismic harmony permeating the overall seismicity.