scholarly journals Crustal Density Structure of the Jiuzhaigou Ms7.0 Earthquake Area Revealed by the Barkam–Jiuzhaigou–Wuqi Gravity Profile

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1497
Author(s):  
Guangliang Yang ◽  
Chongyang Shen ◽  
Hongbo Tan ◽  
Jiapei Wang
Keyword(s):  
Tibet Plateau ◽  
Tectonic Activity ◽  
Moho Depth ◽  
Low Density ◽  
Density Structure ◽  
The West ◽  
West Qinling ◽  
Crustal Density ◽  
Bayan Har ◽  
Gravity Profile

The Barkam–Jiuzhaigou–Wuqi gravity profile extends across the Jiuzhaigou Ms7.0 earthquake (in 2017) zone and passes through several historical big earthquakes’ zones. We have obtained Bouguer gravity anomalies along the profile composed of 365 gravity observation stations with Global Positioning System (GPS) coordinates, analyzed the observed data and inverted subsurface density structure. The results show that the Moho depth has a big lateral variation from southwest to northeast, which shallows from 57 km to 43 km with maximum variation up to 14 km within 800 km. The most acute depth change of the Moho is in the boundary region between the Bayan Har block and West Qinling–Qilian block. According to our analysis, it is related to the eastward movement of the Bayan Har block. There are three main pieces of evidence that support it: (1) Density is higher in the east of the Bayan Har block and smaller in the west, which is the same as seismic activity; (2) Two thin low-density layers exist in the upper and middle crust of the Bayan Har block, which may promote inter-layer slip and the Jiuzhaigou Ms7.0 earthquake occurred in the boundary area of the two low-density layers, where the crustal density and Moho surface fluctuate sharply; (3) the GPS velocity field in the southwestern part gravity profile is significantly larger than that of the northeastern part, which is consistent with the density structure. Our studies also suggest that the large undulation of the Moho prevents the movement of the Bayan Har block, and strain is prone to accumulate here. The dynamic background analysis of the crust in this area indicates that the Moho surface uplifts in the West Qinling–Qilian block, which decelerates the eastern migration of material on the Qinghai–Tibet Plateau, and leads to the weak tectonic activity of the north part of the Bayan Har block.

Crustal density structure of the Antarctic continent from constrained 3-D gravity inversion

2020 ◽  
Author(s):  
Fei Ji ◽  
Qiao Zhang
Keyword(s):  
Gravity Inversion ◽  
Inversion Method ◽  
Rift System ◽  
Low Density ◽  
Density Structure ◽  
West Antarctica ◽  
The West ◽  
Antarctic Continent ◽  
Crustal Density ◽  
The Antarctic

<p>Crustal density is a fundamental physical parameter that helps to reveal its composition and structure, and is also significantly related to the tectonic evolution and geodynamics. Based on the latest Bouguer gravity anomalies and the constrains of 3-D shear velocity model and surface heat flow data, the 3-D gravity inversion method, incorporating deep weight function, has been used to obtain the refined density structure over the Antarctic continent. Our results show that the density anomalies changes from -0.25 g/cm<sup>3</sup> to 0.20 g/cm<sup>3</sup>. Due to the multi-phase extensional tectonics in Mesozoic and Cenozoic, the low density anomalies dominates in the West Antarctica, while the East Antarctica is characterized by high values of density anomalies. By comparing with the variations of effective elastic thickness, the inverted density structure correlates well with the lithospheric integrated strength. According to the mechanical strength and inverted density structure in the West Antarctic Rift System (WARS), our analysis found that except for the local area affected by the Cenozoic extension and magmatic activity, the crustal thermal structure in the WARS tends to be normal under the effect of heat dissipation. Finally, the low density anomalies features in West Antarctica extend to beneath the Transantarcitc Mountains (TAMs), however, we hypothesize that a single rift mechanism seems not be used to explain the entire TAMs range.</p>

Moho depth determination from waveforms of microearthquakes in the West Bohemia/Vogtland swarm area

2013 ◽  
Vol 118 (1) ◽  
pp. 120-137 ◽  
Author(s):  
Pavla Hrubcová ◽  
Václav Vavryčuk ◽  
Alena Boušková ◽  
Josef Horálek
Keyword(s):  
Moho Depth ◽  
The West ◽  
Depth Determination ◽  
West Bohemia

scholarly journals The syncollisional granitoid magmatism and crust growth during the West Qinling Orogeny, China: Insights from the Jiaochangba pluton

2018 ◽  
Vol 54 (6) ◽  
pp. 4014-4033
Author(s):  
Juanjuan Kong ◽  
Yaoling Niu ◽  
Meng Duan ◽  
Fengli Shao ◽  
Yuanyuan Xiao ◽  
...  
Keyword(s):  
The West ◽  
Granitoid Magmatism ◽  
West Qinling

scholarly journals A pilot seismo-stratigraphic study on the West Greenland continental shelf

1989 ◽  
Vol 142 ◽  
pp. 1-16
Author(s):  
J.A Chalmers
Keyword(s):  
Petroleum Industry ◽  
Source Rocks ◽  
Tectonic Activity ◽  
The West ◽  
West Greenland ◽  
Main Site ◽  
Half Graben ◽  
Greenland Basin ◽  
Seismic Sections ◽  
Structural Closure

Seismo-stratigraphic interpretation of seismic sections dating from the mid-1970s has disclosed the existence of four megasequences of sediments, the oldest of which has not previously been reported from West Greenland. The basins containing these sediments developed as a series of coalescing half graben, in which the main site of tectonic activity changed with time. A structural closure of sufficient size to contain interesting quantities of hydrocarbons, given suitable source rocks, reservoir and seal, is identified. The study has shown that the evaluation of the West Greenland Basin during the 1970s was inadequate, and that abandonment of exploration by the petroleum industry may have been premature.

Role of rigid block in tectonic transformation zone at east Tibet 

2021 ◽  
Author(s):  
Tuo Shen ◽  
Xiwei Xu ◽  
Shiyong Zhou ◽  
Shaogang Wei ◽  
Xiaoqiong Lei
Keyword(s):  
Tibet Plateau ◽  
Rigid Block ◽  
Strain Partitioning ◽  
Transformation Models ◽  
Transformation Zone ◽  
Northern Margin ◽  
Eastern Margin ◽  
Bayan Har ◽  
The Tibet Plateau

<p>In recent decades, plateau margins have attracted attention because the understanding of their dynamics and history provides insights into the modes of crustal deformation responsible for the plateau structure and morphology and more widely into the deformation of continental lithosphere. The slip transformation and strain partitioning mechanism at the eastern termination of the Kunlun fault system remain unclear. Geophysics investigations revealed the Ruoergai Basin as a rigid block; however, insufficient information is available on the role of this block in tectonic transformation zone at east Tibet. We employed the finite element method in our simulations to delimitate the presence of the Ruoergai block and determine how it affects the surrounding area. We found that the Ruoergai block moves independently to the east or northeast, and its motion differs from that of the Bayan Har block in the eastward escape process of this last-named block. The formation and behavior of Awancang fault and Longriba fault seems to impact by the Ruoergai block. The influence of the Ruoergai block in the east margin should not be ignored. The Awancang fault and Ruoergai block absorbed the north vector velocity of the Bayan Har block, after which the Bayan Har block started moving southeast. The strain partitioning at the eastern margin of the Tibet Plateau is progressively complete[A1]  from the Awancang fault, Ruoergai block, and Longriba fault area to the Longmenshan block. The presence of the Ruoergai block could decrease the strike-slip rate of the Maqin–Maqu section of the Kunlun fault. Given its influence in the region, the Ruoergai block should be incorporated in future studies on regional deformation and in deformation and tectonic transformation models. Then we compared the deformation and tectonic transformation models in the northern margin of the Tibet Plateau. Proposed a rigid block compression pattern unite the tectonic transformation and deformation issue, further explain most of the fault behaviors in the northern margin and eastern margin of Tibet.</p><p> </p>

Quantitative seismicity maps of India

1972 ◽  
Vol 62 (5) ◽  
pp. 1119-1132 ◽  
Author(s):  
K. L. Kaila ◽  
V. K. Gaur ◽  
Hari Narain
Keyword(s):  
Return Period ◽  
West Coast ◽  
Active Zone ◽  
East Coast ◽  
Indian Subcontinent ◽  
B Value ◽  
Tibet Plateau ◽  
The West ◽  
Period Map ◽  
A Value

Abstract Using the Kaila and Narain (1971) method, three quantitative seismicity maps have been prepared for the Indian subcontinent which are compared with regional tectonics. These are the A-value map, the b-value map and the return-period map for earthquakes with magnitude 6 and above where A and b are the constants in the cumulative regression curve represented by log N = A - bM. The A-value seismicity map shows that India can be divided into two broad seismic zones, the northern seismically highly active zone and the southern moderately active zone. In the northern active zone, a number of seismic highs have been delineated such as the Pamir high, the northwest-southeast trending Srinagar-Almora high, the Shillong massif high, the Arakan Yoma high and the West Pakistan highs. These seismic highs are consistent with the Himalayan tectonic trends. Contrary to this, two seismic highs fall in the Tibet plateau region which align transversely to the main Himalayan trend. In the southern moderately active zone, two seismic highs are clearly discernible, the east and the west coast high, the latter being seismically more active than the former. The least active zone encompasses the Vindhyan syncline and the areas of Delhi and Aravalli folding. Between this zone and the east coast high lies another moderately active zone which encloses the Godavari graben, western part of the Mahanadi graben and the Chattisgarh depression. The b-value seismicity map also demarcates the same active zones as are brought out on the A-value map. The return-period map of India for earthquakes with magnitude 6 and above shows a minimum return period of 100 years in the Pamirs, about 130 years in the various seismic highs in the northern active zone, 180 years on the west coast high, 200 years on the east coast high and about 230 years in the least active Vindhyan-Aravalli zone and the Hyderabad-Kurnool area. These quantitative seismicity maps are also compared with the seismic zoning map of Indian Standards Institution and seismicity maps of India prepared by other workers.

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