| Popis: |
Amplitude tomography of Lg waves at frequencies from 1 to 5 Hz are investigated in this work to reveal the lateral attenuation heterogeneities of the study area, the Xinjiang Uygur Autonomous Region of China and its adjacent regions, by using a large set of broadband seismic waveform data. First, we inverted the average Q Lg at each of 10 frequencies from 0.5 to 5 Hz. Then, the study area was divided into evenly spaced 1°×1° grid cells after conducting both a checkerboard test and a resolution test. Finally, the high-resolution Q Lg tomographic images at the 10 frequencies were obtained. The moment magnitudes of the events and the site terms of the stations we used were obtained simultaneously. The attenuation pattern of Q Lg at each frequency shows obvious lateral heterogeneities in Xinjiang and its adjacent regions, which are coincident with the geological features of the area. The Tarim basin and the middle and the eastern part of the southern Tian Shan belong to high- Q regions. The northeastern margin of the Pamir Plateau, the northwestern margin of the Tibetan Plateau, the western part of the southern Tian Shan and northern Tian Shan are prominent low- Q areas. The attenuation pattern of Lg waves shows that large-scale tectonic boundaries, zones with rapid topographic or crustal thickness gradient, are in good accordance with the boundaries of the high and low Q Lg . Most of the historical strong earthquakes occurred on the interior or edge of low- Q Lg areas. |
