Using the teleseismic waveform data recorded by the seismic station Bachu （hereafter referred to as station BCH ） in the Tarim Basin and the seismic station Taxkorgan （hereafter referred to as station TAG ） in the...Using the teleseismic waveform data recorded by the seismic station Bachu （hereafter referred to as station BCH ） in the Tarim Basin and the seismic station Taxkorgan （hereafter referred to as station TAG ） in the west Kunlun Mountains for years, we applied the receiver function H - K stacking method to study the crustal structure beneath stations BCH and TAG. The results showed that there are obvious differences in the crustal thickness beneath stations BCH and TAG, and the regional crustal thickness and terrain have a very good corresponding relationship. There are high crustal average Vp/Vs values beneath the two stations. The crustal thickness is 44km, and the crustal average wave velocity ratio is 1. 849 beneath station BCH. There is a sharp discontinuity in the middle of the crust beneath station BCH at a depth of 21km. There is a low average P wave velocity and low Vp/Vs from the surface to the discontinuity beneath station BCH. The depth of the discontinuity is consistent with the lower interface of the focal depth from accurate location in the Jiashi earthquake source area adjacent to station BCH; and may be the crustal brittle-ductile conversion boundary. The crustal thickness is 69km, and the crustal average wave velocity ratio is 1. 847 beneath station TAG, a thicker crust and high Vp/Vs may indicate that materials in the lower crustal are prone to plastic flow, which is responsible for the thickening of the crust.展开更多
Detailed information about the crustal structure is essential for better understanding the occurrence and mechanisms of earthquakes and volcanoes.Here we present a study of the upper crustal P-wave velocity structure ...Detailed information about the crustal structure is essential for better understanding the occurrence and mechanisms of earthquakes and volcanoes.Here we present a study of the upper crustal P-wave velocity structure of two seismically and volcanically active areas in northern Iran using the two-dimensional Pg travel time tomography method.The imaging results suggest low velocities in the upper crust beneath the Damavand and Sahand-Sabalan volcanic areas in the central and western parts of northern Iran,respectively.The upper crustal low velocities in these two areas roughly coincide with previously imaged low Pn velocity anomalies,suggesting that the Late Cenozoic volcanic activity was probably caused by the upwelling of hot materials from the mantle.The image feature of the Pg velocity structure beneath the Sahand-Sabalan volcanic area further indicates that the hot materials stored in the upper crust beneath Sahand may be larger in size than those stored beneath Sabalan.Comparison of the Pg velocity images with the earthquake distribution in north Iran suggests that earthquakes mainly occur at moderately low velocity or low to high velocity boundary areas instead of significantly low or high velocity regions.The anisotropy results show that the Pg wave fast direction is consistent with the GPS direction at high Pg velocity areas and the fast direction is inconsistent with the GPS direction but consistent with the strike direction of faults at low velocity areas.Our new upper crustal structural images provide the basic observation for better understanding of the regional seismicity and volcanism,and link the surface geological phenomena to deep crustal and mantle processes associated with the active tectonics in northern Iran.展开更多
基金sponsored by the Seismic Networks Young Junior Training Project(20130216)the Earthquake Science and Technology Spark Program from China Earthquake Administration(XH15046)
文摘Using the teleseismic waveform data recorded by the seismic station Bachu （hereafter referred to as station BCH ） in the Tarim Basin and the seismic station Taxkorgan （hereafter referred to as station TAG ） in the west Kunlun Mountains for years, we applied the receiver function H - K stacking method to study the crustal structure beneath stations BCH and TAG. The results showed that there are obvious differences in the crustal thickness beneath stations BCH and TAG, and the regional crustal thickness and terrain have a very good corresponding relationship. There are high crustal average Vp/Vs values beneath the two stations. The crustal thickness is 44km, and the crustal average wave velocity ratio is 1. 849 beneath station BCH. There is a sharp discontinuity in the middle of the crust beneath station BCH at a depth of 21km. There is a low average P wave velocity and low Vp/Vs from the surface to the discontinuity beneath station BCH. The depth of the discontinuity is consistent with the lower interface of the focal depth from accurate location in the Jiashi earthquake source area adjacent to station BCH; and may be the crustal brittle-ductile conversion boundary. The crustal thickness is 69km, and the crustal average wave velocity ratio is 1. 847 beneath station TAG, a thicker crust and high Vp/Vs may indicate that materials in the lower crustal are prone to plastic flow, which is responsible for the thickening of the crust.
基金supported by the Strategic Priority Research Program(B) of the Chinese Academy of Sciences(Grant No.XDB03010800)the National Natural Science Foundation of China (Grant Nos.41225016,41304065 & 41674066)
文摘Detailed information about the crustal structure is essential for better understanding the occurrence and mechanisms of earthquakes and volcanoes.Here we present a study of the upper crustal P-wave velocity structure of two seismically and volcanically active areas in northern Iran using the two-dimensional Pg travel time tomography method.The imaging results suggest low velocities in the upper crust beneath the Damavand and Sahand-Sabalan volcanic areas in the central and western parts of northern Iran,respectively.The upper crustal low velocities in these two areas roughly coincide with previously imaged low Pn velocity anomalies,suggesting that the Late Cenozoic volcanic activity was probably caused by the upwelling of hot materials from the mantle.The image feature of the Pg velocity structure beneath the Sahand-Sabalan volcanic area further indicates that the hot materials stored in the upper crust beneath Sahand may be larger in size than those stored beneath Sabalan.Comparison of the Pg velocity images with the earthquake distribution in north Iran suggests that earthquakes mainly occur at moderately low velocity or low to high velocity boundary areas instead of significantly low or high velocity regions.The anisotropy results show that the Pg wave fast direction is consistent with the GPS direction at high Pg velocity areas and the fast direction is inconsistent with the GPS direction but consistent with the strike direction of faults at low velocity areas.Our new upper crustal structural images provide the basic observation for better understanding of the regional seismicity and volcanism,and link the surface geological phenomena to deep crustal and mantle processes associated with the active tectonics in northern Iran.
