Application Of The Method Of Damped Stress Tensor Inversion In New Britain And Pamir-Gindu Kush Areas Based On The Focal Mechanisms

Tectonic stress field plays a key role on the plate movement and the mechanism of subduction zone intraction.In this study,crustal stress fields are estimated and analyzed in New Britain Areas and the Pamir-Hindu Kush subduction zone using the damped stress field inversion method.1.There occurred a series of earthquakes in New Britain,Papua New Guinea,from March 30 to May 15,2015.It is significance to determine the stress field in the source region and analyze earthquake preparation mechanism.The focal mechanism data in the source region and its adjacent area is collected from Global CMT catalogue.The tectonic stress field is determined by using the focal mechanism data.The result shows:(1)The boundary zone of the north and south Bismarck micro-plate is in strike-slip stress regime with the compressive stress of SWW.(2)The subduction zone of the Solomon Sea in the trend of NW and NE direction is under compression.The bending portion of the Solomon Sea block subducting under the New Britain and Solomon Islands is in extension state.(3)Under the NS compression of the subduction zone,extrusion caused by the clockwise rotation of the South Bismarck block,and the influence of the west motion of the Pacific plate,the stress field in the joint region of New Britain and New Ireland is extremely heterogeneous.(4)The strike-slip and thrust type focal mechanism in this earthquake sequence are produced by both the subduction of the Solomon Sea plate and the EW compression of the South Bismarck micro-plate and the Pacific Plate.2.255 focal mechanisms with depth larger than 70 km in Pamir-Hindu Kush are collected from Global CMT catalogue between January,1976 to June,2016.By using the method of regional damped stress field inversion provided by Hardebeck and Michael,the tectonic stress field in the depths of70-170 km and 170-280 km are determined individually.The results show: in the depth between 70 km to 170 km,(1)Subduction zone in the north of Pamir is right lateral slip,owing to the NW-SE compression of Pamir Plateau and Northern Tien Shan.(2)The direction of the compressive stress is along NNW direction in Hindu Kush region,counter-clockwise rotation from west to east,which may be probably resulted from the combined effect of the thermal convection to the north below the Indian Plate and upper mantle flow along NW direction under Tibetan Plateau.(3)The Pamir and Hindu Kush are collided nearby 37°N,which causing more complicated stress regime.The plunge of the principal extensional stress is nearly 80° in the Hindu Kush region in the depth of 170-280 km.(4)The direction of the compressive stress is nearly N-S in the west to 70.85°E,which probably caused by compression to the subduction plate along NS direction by north flow of the India plate stemed thermal convection below it.(5)The direction of the compressive stress is along NW-SE driection in the east to 70.85°E,which probably caused by upper mantle flow along NW direction under Tibet Plateau.