Crustal attenuation in the southern Tibetan Plateau by reverse two-station Lg-wave Q value tomography

Based on the seismic waveform data of 757 earthquakes recorded by 27 broadband stations of Tibet Autonomous Region seismic network from 2017 to 2019, it is for the first time that the reverse two-station method has been applied to 1 Hz Lg-wave Q value tomography study in the southern Tibetan Plateau. In this research, total 1 981 Lg-waves were intercepted from the velocity window of 3.5−2.4 km/s and the Q values of 13 543 paths were calculated. After testing the checkerboard recovery of 1°×1° and 0.5°×0.5° grids respectively, we got the tomography of the Lg-wave Q₀ value of the southern Tibetan Plateau with 0.5°×0.5° resolution. The inversion result shows that there exhibits high attenuation and low Q values of Lg-wave in the southern Tibetan Plateau crust, which is highly consistent with the negative anomaly of P-wave velocity, the geothermal distribution and two rift valleys in the east of the Tibet. Therefore it is inferred that there may be widespread molten material in the crust of the southern Tibetan Plateau and two fluid-melting channels. The main channel is located between the Yadong-Gulu rift and the Sangri-Cona rift, and the secondary channel flows out along the Yarlung Zangbo suture zone. By analyzing the differences of molten material distribution on both sides of the Yadong-Gulu rift, it is considered that there are different dynamical evolution models in the front-end of collision between Indian Plate and Eurasian Plate, the dynamical evolution to the west of Yadong-Gulu rift is in accordance with the theory of shortening and thickening, and that to the east of Yadong-Gulu rift is consistent with the “pump” mode.