四川地区的地震层析成像

由四川地震台网的P波数据所进行的层析成像研究得到了该区地壳及上地幔速度图像的新信息(结果表明:1.20^-km深度处的速度图像与地表构造特征密切有关,反映了地壳的岩性分布,呈现为断块结构;龙门山、鲜水河主要断裂及南北构造带和四川盆地清晰地成像在图上.一直被认为是隐伏存在的华蓥山断裂则鲜明地展现在20-85km深度的速度图像上.2.50±km深度处的速度图像则反映了该区的莫霍面深度明显起伏;四川盆地、徽（县）成（县）盆地和汉中盆地的地壳厚度小于50km,上地幔顶部速度约8.1km/s.龙门山以104°E为界,北段地壳厚度与四川盆地一样,中南段与川西相近.康滇地轴为四川地区地壳由东向西增厚的过渡地带.3.岩石层厚度显著变化,扬子准地台为比较活动的褶皱区,具有较厚的岩石层.4.速度结构与地震活动性存在一定的联系,该区1930年以来M≥6.0的强震震中在20^-km深度（上地壳）上的投影大都分布在速度梯度带上,成条带分布.考虑到强震的余震区大都偏高速体一侧,似乎表明,高速体有高于周围介质的剪切强度,它可能起沿断裂带凹凸体的作用.强震震中在50⁺km深度（上地幔顶部）上的投影几乎都分布在低速区及其边缘,那里壳幔间速度呈过渡关系,是软流层顶部较浅地区.

SEISMIC TOMOGRAPHY OF SICHUAN

New information of velocity images of the crust and upper mantle of Sichuan area has been obtained from tomography using P arrival time data of Sichuan seismic network. The results are:1.Velocity image of the section of 20^- km depth is correlate with the tectonic characters of crust surface, reflecting lithological distribution, showing block structure; Longmen mountains, Xianshui river main faults and s'outh-north tectonic belt and Sichuan basin splendly are showed on the pictures. The Huayin mountain covered fault clearly displayed on the velocity images from the section of depth 20 km down to the section of depth 85 km.2.The velocity images of sections 50± km reflect the topography of Moho interface: The Moho depth of Sichuan basin, Huei conty basin, Chen conty basin are less 50 km, the velocity of top of their upper mantale is 8.1km/s. From 104°E the Moho depth of north section of Longmen mountains is the same with Sichuan basin, middle south section similar to the west part of Sichuan. Kangdian earth's axis is' transition zone of thickening of Sichuan area from. east to west. .3.Lithosphere of Yangzi metaplatform is thicker than the active fold areas.4.It seems that there is link between seismic activity and velocity structure; Hypocen-ters of strong earthquakes M≥6.0 since 1930 mostly located at the velocity gradient belt, of 20 ^- km depth image, and down to the 50⁺ km image distributed in the low velocity area and it's edges where in velocity between crust and upper mantle gradual change pattern appears and asthernosphere bumps.