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We applied the g CAP algorithm to determine239 focal mechanism solutions 3:0 M We 6:0T with records of dense Chin Array stations deployed in Yunnan,and then inverted 686 focal mechanisms(including 447 previous results) for the regional crustal stress field with a damped linear inversion. The results indicate dominantly strike-slip environment in Yunnan as both the maximum(r1) and minimum(r3) principal stress axes are sub-horizontal. We further calculated the horizontal stress orientations(i.e., maximum and minimum horizontal compressive stress axes: S H and S h, respectively) accordingly and found an abrupt change near *26°N. To the north, S H aligns NW-SE to nearly E-W while S h aligns nearly N-S. In contrast, to the south, both S H and S h rotate laterally and show dominantly fan-shaped patterns. The minimum horizontal stress(i.e., maximum strain axis) S h rotates from NW-SE to the west of Tengchong volcano gradually to nearly E-W in west Yunnan, and further toNE-SW in the South China block in the east. The crustal strain field is consistent with the upper mantle strain field indicated by shear-wave splitting observations in Yunnan but not in other regions. Therefore, the crust and upper mantle in Yunnan are coupled and suffering vertically coherent pure-shear deformation in the lithosphere.
We applied the gc algorithm to determine 239 focal mechanism solutions 3: 0 M We 6: 0T with records of dense Chin Arrayations deployed in Yunnan, and then inverted 686 focal mechanisms (including 447 previous results) for the regional crustal stress field with a damped linear inversion. The results indicate dominantly strike-slip environment in Yunnan as both the maximum (r1) and minimum (r3) principal stress axes are sub-horizontal. We further calculated the horizontal stress orientations (ie, maximum and minimum horizontal compressive stress To the north, SH aligns NW-SE to nearly EW while S h aligns nearly NS. In contrast, to the south, both SH and S h, respectively) AND and found an abrupt change near * 26 ° N S h rotate laterally and show dominantly fan-shaped patterns. The minimum horizontal stress (ie, maximum strain axis) S h rotates from NW-SE to the west of Tengchong volcano gradually to nearly EW in west Yunnan, and further to NE-SW in the South Chi na block in the east. The crustal strain field is consistent with the upper mantle strain field indicated by shear-wave splitting observations in Yunnan but not in other regions. Thus, the crust and upper mantle in Yunnan are coupled and suffering vertically coherent pure- shear deformation in the lithosphere.