Tectonic Deformation Characteristics Research Articles

Large-scale topography of the north Tibetan ranges as a proxy for contrasted crustal-scale deformation modes

Forming the northern margin of the Cenozoic Himalayan–Tibetan orogen, the area surrounding the Qaidam Basin is a key region to study the mechanisms that govern the long-term evolution of intracontinental orogenic processes. Indeed, tectonic deformation in this region involves newly formed and inherited crustal and lithospheric structures, partition between horizontal and vertical movements, and a strong influence from external factors such as climate and erosion. This study proposes a description of the topography and crustal structure of the north Tibet ranges as an insight into their tectonic deformation characteristics. The topographic study includes the integrated analysis of regional topographic profiles, river profiles, slope maps and thermochronology data. The available geophysical, geological and structural data are used to draw regional, crustal-scale geological sections across northern Tibet to describe the regional crustal structure. We show that three deformation modes are expressed (block uplift, distributed shortening and crustal buckling) in structural compartments that involve either complete mountain ranges or some specific regions inside those ranges. We propose that a new crustal structure may develop parallel to the Altyn Tagh fault, connecting the eastern tip of the Qimen Tagh with the Haiyuan fault, across the Qaidam Basin. Supplementary material : Supplementary figures are available at https://doi.org/10.6084/m9.figshare.c.5841461 Thematic collection: This article is part of the Fold-and-thrust belts collection available at: https://www.lyellcollection.org/cc/fold-and-thrust-belts

Primary discussion about tectonic deformation characteristics in thev east Yarlungzangbo suture and subsurface structure of the Yarlhashampo dome as revealed by a deep seismic reflection profile

Primary discussion about tectonic deformation characteristics in thev east Yarlungzangbo suture and subsurface structure of the Yarlhashampo dome as revealed by a deep seismic reflection profile

Characteristics of tectonic deformation of the melange zone in the Lachlan Orogen along eastern coast of Australia

ABSTRACT The Narooma-Batemans Bay (NBB) area along the southeast coast of Australia is a part of the eastern zone of the Early Paleozoic Lachlan Orogen. In the NBB, a set of rock association consisting of turbidites, siliceous rock, basic lava, and argillaceous melange zone is mainly developed. According to systematic field geological survey, the deformation of 3 stages (D1, D2, and D3) was identified in the NBB. At stage D1, with the original bedding S0 in a nearly east-west trending as the deformation plane, tight folds, isoclinal folds, and other structures formed in the NBB accompanied by structural transposition. As a result, crenulation cleavage developed along the axial plane of the folds and schistosity S1 formed. At stage D2, with north-south-trending schistosity S1 as the deformation plane, a large number of asymmetrical folds and rotated porphyroclasts formed owing to thrusting and shear. At stage D3, left-lateral strike-slip occurred along the main north-south-trending schistosity. Based on the analysis of the characteristics of tectonic deformation in the NBB and summary of previous research results, it is determined that the early-stage (D1) deformation is related to Ordovician Macquarie arc-continent collision and the deformation at stages D2 and D3 is the result of the westward subduction of Paleo-Pacific Plate. That is, it is not the continuous westward subduction of the Paleo-Pacific Plate that constitutes the evolution model of the NBB as previously considered.

Controlling Effect of Fault Structural Styles on Aquifer Water Abundance for Panxie Mining Area, Huainan, China

According to the hydrogeological conditions, dynamic characteristics of tectonic deformation and geometric features, the fault structures in the Panxie mining area were divided into seven types respectively were horst, graben, graben-horst combination, forward (reverse) thrust structure, imbricate thrust structure, strike-slip structure, and others. Meanwhile, the q-structural styles boxplot had been constructed to analyze the water abundance of the karst formation aquifer. It has been verified via the practical drilling core data. The final results were that the water-rich characteristics of the deep karst water controlled by the seven structural styles were different. The water abundance of graben-horst combination structure was strongest; the next was the horst in deep which was stronger than the graben. Then, the imbricate thrust structure, strike-slip fault, and other structural styles had low water abundance in deep karst aquifer. The results can be aimed at different structural styles to guide the prevention and control of karst water hazards on the floor of Group A coal mining.

Geometry and tectonic deformation of the seismogenic structure for the 8 August 2017 <i>M</i><sub>S</sub> 7.0 Jiuzhaigou earthquake sequence, northern Sichuan, China

To reveal the geometry of the seismogenic structure of the Aug. 8, 2017 MS 7.0 Jiuzhaigou earthquake in northern Sichuan, data from the regional seismic network from the time of the main event to Oct. 31, 2017 were used to relocate the earthquake sequence by the tomoDD program, and the focal mechanism solutions and centroid depths of the ML ≥ 3.5 events in the sequence were determined using the CAP waveform inversion method. Further, the segmental tectonic deformation characteristics of the seismogenic faults were analyzed preliminarily by using strain rosettes and areal strains (As). The results indicate: (1) The relocated MS 7.0 Jiuzhaigou earthquake sequence displays a narrow ~ 38 km long NNW-SSE-trending zone between the NW-striking Tazang Fault and the nearly NS-striking Minjiang Fault, two branches of the East Kunlun Fault Zone. The spatial distribution of the sequence is narrow and deep for the southern segment, and relatively wide and shallow for the northern segment. The initial rupture depth of the mainshock is 12.5 km, the dominant depth range of the aftershock sequence is between 0 and 10 km with an average depth of 6.7 km. The mainshock epicenter is located in the middle of the aftershock region, showing a bilateral rupture behavior. The centroid depths of 32 ML ≥ 3.5 events range from 3 to 12 km with a mean of about 7.3 km, consistent with the predominant focal depth of the whole sequence. (2) The geometric structure of the seismogenic fault on the southern section of the aftershock area (south of the mainshock) is relatively simple, with overall strike of ~150° and dip angle ~75°, but the dip angle and dip-orientation exhibit some variation along the segment. The seismogenic structure on the northern segment is more complicated; several faults, including the Minjiang Fault, may be responsible for the aftershock activities. The overall strike of this section is ~159° and dip angle is ~59°, illustrating a certain clockwise rotation and a smaller dip angle than the southern segment. The differences between the two segments demonstrate variation of the geometric structure along the seismogenic faults. (3) The focal mechanism solutions of 32 ML ≥ 3.5 events in the earthquake sequence have obvious segmental characteristics. Strike-slip earthquakes are dominant on the southern segment, while 50% of events on the northern segment are thrusting and oblique thrusting earthquakes, revealing significant differences in the kinematic features of the seismogenic faults between the two segments. (4) The strain rosettes for the mainshock and the entire sequence of 31 ML ≥ 3.5 aftershocks correspond to strike-slip type with NWW-SEE compressional white lobes and NNE-SSW extensional black lobes of nearly similar size. The strain rosette and As value of the entire sequence of 22 ML ≥ 3.5 events on the southern segment are the same as those of the MS 7.0 mainshock, indicating that the tectonic deformation here is strike-slip. However, the strain rosette of the entire sequence of 10 ML ≥ 3.5 events on the northern segment show prominent white compressional lobes and small black extensional lobes, and the related As value is up to 0.52, indicating that the tectonic deformation of this segment is oblique thrusting with a certain strike-slip component. Differences between the two segments all reveal distinctly obvious segmental characteristics of the tectonic deformation of the seismogenic faults for the Jiuzhaigou earthquake sequence.

Characteristics of tectonic deformation in the Daning-Jixian region, eastern Ordos Basin: Implications for the exploration and development of coalbed methane

Eastern Ordos Basin is an important region for the development of Carboniferous-Permian coalbed methane in China; however, there are significant differences of the coalbed methane exploration and development prospects among different regions within eastern Ordos Basin due to the multiple tectonic movements. In this study, the No. 5 coal of the Shanxi Formation of the Lower Permian in the Daning-Jixian region was selected for analysis. The influences of structures on coalbed methane content and permeability of coalbed methane reservoirs in the Daning-Jixian region were discussed and the favorable target areas for coalbed methane development were determined based on the analysis of tectonic characteristics and evolution. The results indicate that the main structures in this region extend in the NE–NNE direction with distinct E-W-trending zoning, which can be specifically divided into, from the east to the west, the fault depression zone in basin margins, the gentle fold zone in basin slopes, and the gentle slope zone. The formation and evolution of the structures in this area are primarily formed during the Indosinian, the Yanshanian, and the Himalayan movement, and the tectonic movement during the Middle Yanshan Period is critical for the formation of the structural frameworks. The coalbed methane contents in the No. 5 coal increase from the east to the west; therefore, low gas contents are found in the eastern margin zone, while the Yaoqu-Wucheng zone of middle slope belt displays high coalbed methane contents. The permeability is relatively high in the eastern margin zone and in the Mingti-Yangjiahe region of the middle slope zone, where there exist relatively strong structural deformations. The Guyi and Mingzhu blocks are selected as the favorable target areas for coalbed methane exploitation by a comprehensive analysis of burial depth, coalbed methane content, and the permeability.

Present-day crustal movement of the Chinese mainland based on Global Navigation Satellite System data from 1998 to 2018

A total of more than 260 continuous stations and 2000 campaign stations from the Crustal Movement Observation Network of China (CMONOC) project, covering the Chinese mainland and its surrounding areas during the period of 1998–2018, are processed using the Bernese Global Navigation Satellite System (GNSS) software via a state-of-the-art method. We obtain the coordinate time series of all the stations given in the reference frame ITRF2014, estimate the coseismic deformation, and remove outliers. Lastly, we present the latest, most complete, and most accurate contemporary horizontal velocity field with respect to the stable Eurasian plate, irrespective of the postseismic deformations. This study shows that the signal of tectonic movement in Western China is stronger than that in Eastern China particularly in the Tibetan Plateau, with a rate of 18–32 mm/a. Moreover, the signal decays sharply from south to north. However, North China and South China move coherently to the ESE direction mostly at a rate of 4–10 mm/a and have not experienced any abrupt velocity gradients in their interiors. Meanwhile, Northeast China has the lowest velocity of only 2–4 mm/a in addition to the coastal areas that have slightly larger velocities. The densified and continuous observation of GNSS stations are of great significance to the study of the present-day crustal movement and tectonic deformation characteristics of the Chinese mainland. This would help to provide better constraints on the kinematics and dynamics of the region.

Tectonic evolution and its control over deposition in fault basins: A case study of the Western Sag of the Cenozoic Liaohe Depression, eastern China

The main petroliferous basins in eastern China are Cenozoic fault basins, most of which have experienced two-stage tectonic evolution, i.e., rifting subsidence in the Paleogene and post-rifting thermal subsidence in the Neogene-Quaternary. The episodic tectonic evolution and syndepositional faulting had significant influence on the fault basins in terms of accommodation space, deposition rate, and depositional facies zones. In this study, the tectonic deformation characteristics and the tectonic-depositional evolution of the Western Sag of the Cenozoic Liaohe Depression were investigated by comprehensive analysis of the available geological and geophysical data using the modern theory of tectonic geology and the balanced section technique. The tectonic deformation of the Cenozoic fault basin was characterized by superimposed faults and depression. In addition, there existed relatively independent but still related extensional tectonic systems and strike-slip tectonic systems. The tectonic evolution of the fault basin involved five stages, i.e., initial rifting stage (E2s4), intense faulting stage (E2s3), fault-depression transition stage (E3s1–2), differential uplifting stage (E3d), and depression stage (N-Q). According to the characteristics of tectonic development and evolution of the Western Sag, the depositional evolution in the Cenozoic fault basin was divided into two stages, i.e., multi-episodic rifting filling in the Paleogene and post-rifting filling in the Neogene-Quaternary. The former rifting stage was further subdivided into four episodes with different characteristics of depositional development. The episodic faulting controlled the filling process and filling pattern of the Cenozoic Western Sag as well as the development and spatial distribution of associated depositional systems, whereas the syndepositional faults that developed in multiple stages in various tectonic positions controlled the development of depositional systems and sand bodies in the Western Sag. That is, the fault terraces on steep slopes controlled the development of sand bodies, the fault terraces on gentle slopes controlled the development of low-stand fan bodies, and the fault terraces or fault troughs in the central basin controlled the development of fluxoturbidite bodies.

A decade of GEONET: 1994–2003 —The continuous GPS observation in Japan and its impact on earthquake studies—

The dense continuous GPS network of Japan, now called GEONET, has been operated since 1994 by the Geographical Survey Institute. GEONET provides precise daily coordinates of all the stations, with which displacement rates and strain rates are calculated nationwide. Various characteristics of tectonic deformation in the Japanese Is-lands have been revealed. GEONET is also quite useful in earthquake studies, precisely detecting co-seismic, post-seismic, and inter-seismic deformation signals. These observations are utilized to infer physical processes at earthquake sources. Slow slip events on plate boundaries have been found from GPS data. Such slow events provide an important constraint on the mechanism of faulting. On the other hand, there has been no success in detecting pre-seismic deformation. Lack of a precursory signal before the 2003 Tokachi-Oki (M8.0) earthquake has posed a serious question to short-term earthquake prediction. GEONET enables a good linkage between monitoring and modeling studies, opening a possibility of practical data assimilation. For further contribution to earthquake studies, it is necessary to continue GEONET with high traceability on the details in observation and analysis.