Earthquake Focal Mechanisms in Yunnan and their Inference on the Regional Stress Field

2013 ◽  
Vol 103 (4) ◽  
pp. 2498-2507 ◽  
Author(s):  
L. Zhao ◽  
Y. Luo ◽  
T.-Y. Liu ◽  
Y.-J. Luo
Keyword(s):  
Stress Field ◽  
Focal Mechanisms ◽  
Regional Stress ◽  
Earthquake Focal Mechanisms ◽  
Regional Stress Field

scholarly journals Focal mechanisms in the southern Aegean from temporary seismic networks – implications for the regional stress field and ongoing deformation processes

Solid Earth ◽  
2014 ◽  
Vol 5 (1) ◽  
pp. 275-297 ◽  
Author(s):  
W. Friederich ◽  
A. Brüstle ◽  
L. Küperkoch ◽  
T. Meier ◽  
S. Lamara ◽  
...  
Keyword(s):  
Stress Field ◽  
Focal Mechanisms ◽  
Small Scale ◽  
Principal Stresses ◽  
Western Turkey ◽  
Regional Stress ◽  
Regional Stress Field ◽  
Principal Axes ◽  
Gps Velocities ◽  
Seismic Networks

Abstract. The lateral variation of the stress field in the southern Aegean plate and the subducting Hellenic slab is determined from recordings of seismicity obtained with the CYCNET and EGELADOS networks in the years from 2002 to 2007. First motions from 7000 well-located microearthquakes were analysed to produce 540 well-constrained focal mechanisms. They were complemented by another 140 derived by waveform matching of records from larger events. Most of these earthquakes fall into 16 distinct spatial clusters distributed over the southern Aegean region. For each cluster, a stress inversion could be carried out yielding consistent estimates of the stress field and its spatial variation. At crustal levels, the stress field is generally dominated by a steeply dipping compressional principal stress direction except in places where coupling of the subducting slab and overlying plate come into play. Tensional principal stresses are generally subhorizontal. Just behind the forearc, the crust is under arc-parallel tension whereas in the volcanic areas around Kos, Columbo and Astypalea tensional and intermediate stresses are nearly degenerate. Further west and north, in the Santorini–Amorgos graben and in the area of the islands of Mykonos, Andros and Tinos, tensional stresses are significant and point around the NW–SE direction. Very similar stress fields are observed in western Turkey with the tensional axis rotated to NNE–SSW. Intermediate-depth earthquakes below 100 km in the Nisyros region indicate that the Hellenic slab experiences slab-parallel tension at these depths. The direction of tension is close to east–west and thus deviates from the local NW-oriented slab dip presumably owing to the segmentation of the slab. Beneath the Cretan sea, at shallower levels, the slab is under NW–SE compression. Tensional principal stresses in the crust exhibit very good alignment with extensional strain rate principal axes derived from GPS velocities except in volcanic areas, where both appear to be unrelated, and in the forearc where compressional principal stresses are very well aligned with compressional principal strain rates. This finding indicates that, except for volcanic areas, microseismic activity in the southern Aegean is not controlled by small-scale local stresses but rather reflects the regional stress field. The lateral and depth variations of the stress field reflect the various agents that influence tectonics in the Aegean: subduction of the Hellenic slab, incipient collision with continental African lithosphere, roll back of the slab in the southeast, segmentation of the slab, arc volcanism and extension of the Aegean crust.

Two key switches in regional stress field during multi-stage deformation in the Carboniferous−Triassic southernmost Altaids (Beishan, NW China): Response to orocline-related roll-back processes

2021 ◽  
Author(s):  
Zhonghua Tian ◽  
Wenjiao Xiao ◽  
Brian F. Windley ◽  
Peng Huang ◽  
Ji’en Zhang ◽  
...  
Keyword(s):  
Stress Field ◽  
Large Scale ◽  
Electron Backscatter Diffraction ◽  
Volcanic Rocks ◽  
Structural Deformation ◽  
Regional Stress ◽  
Regional Stress Field ◽  
Multi Stage ◽  
Beishan Orogenic Collage ◽  
Roll Back

The orogenic architecture of the Altaids of Central Asia was created by multiple large-scale slab roll-back and oroclinal bending. However, no regional structural deformation related to roll-back processes has been described. In this paper, we report a structural study of the Beishan orogenic collage in the southernmost Altaids, which is located in the southern wing of the Tuva-Mongol Orocline. Our new field mapping and structural analysis integrated with an electron backscatter diffraction study, paleontology, U-Pb dating, 39Ar-40Ar dating, together with published isotopic ages enables us to construct a detailed deformation-time sequence: During D1 times many thrusts were propagated northwards. In D2 there was ductile sinistral shearing at 336−326 Ma. In D3 times there was top-to-W/WNW ductile thrusting at 303−289 Ma. Two phases of folding were defined as D4 and D5. Three stages of extensional events (E1−E3) separately occurred during D1−D5. Two switches of the regional stress field were identified in the Carboniferous to Early Permian (D1-E1-D2-D3-E2) and Late Permian to Early Triassic (D4-E3-D5). These two switches in the stress field were associated with formation of bimodal volcanic rocks, and an extensional interarc basin with deposition of Permian-Triassic sediments, which can be related to two stages of roll-back of the subduction zone on the Paleo-Asian oceanic margin. We demonstrate for the first time that two key stress field switches were responses to the formation of the Tuva-Mongol Orocline.

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