华北地区地壳上地幔三维P波速度结构

利用华北地震科学台阵和首都圈地震台网记录的4511次近震和625次远震的P 波到时数据,采用纬度和经度方向分别为0.5deg;times;0.5deg;的网格划分,反演得到了华北北部地区（111deg;E——120deg;E,37deg;N——42deg;N）深至400km 的地壳上地幔三维P 波速度结构.层析成像结果表明,研究区的速度存在明显的横向不均匀性,随着深度增加横向不均匀性总体呈现减弱趋势.燕山隆起带在60——120km 深度内存在明显的高速异常,这与较大的岩石圈厚度有关;山西裂陷盆地、华北平原下方60km 深度存在明显低速异常,与软流圈的出现有关.燕山隆起带岩石圈厚度在120km 以上,明显比太行山隆起的岩石圈厚度大,与稳定大陆地区的岩石圈厚度一致.太行山山前断裂已切穿莫霍面,贯入岩石圈.研究区上地幔顶部大范围的低速异常反映了软流圈上隆的特点.在华北平原及燕山隆起下方200——300km 存在高速异常可能与太古代大陆板块岩石圈的残留体有关.

3-D P wave velocity structure of crust and upper mantle beneath North China

3-D P wave velocity structure of the crust and upper mantle beneath North China (37°N-42°N, 111°E-120°E) down to a depth of 400 km has been studied by tomographically inverting P arrival times from 4512 local events and 625 telesiesmic events recorded by the North China Seismic Array and the Capital Circle Seismic Network. With a resolution of grid spacing of 0.5°×0.5°, the latreral velocity heterogeneity is obviously seen though it attenuates with increasing depth. Prominent high velocity anomalies are imaged beneath Yanshan uplift in the depth range of 60-120 km, possibly inplying a thick lithosphere there. Remarkable low velocity anomalies beneath Shanxi orogenic belt and North China basin around the depth of 60 km may indicate the appearance of asthenosphere. The thickness of lithosphere may be beyond 120 km depth beneath Yanshan uplift, which is thicker than Taihangshan uplift. Taihangshan-frontal fault may reach the lower lithosphere. Low velocity anomalies in uppermost mantle may be related to the upwelling of hot materials from asthenosphere. High velocity anomalies beneath North China basin and Yanshan uplift in the depth range of 200-300 km may be an indication of the detached Archaean continental lithosphere.