利用远震P波接收函数研究中国福建地区地壳厚度和泊松比

地壳厚度和泊松比是反映地壳结构和内部物质组成的重要参数,能够为区域构造和动力学研究提供重要依据.本文基于福建地区分布相对均匀的88个测震台2014—2017年的远震波形数据提取P波接收函数,采用H-κ叠加获得台站下方的地壳厚度和泊松比,并与该地区已有的研究结果进行对比、分析及整合,最终获得了研究区117个观测台站下方的地壳厚度和泊松比,揭示了中国福建地区地壳结构和泊松比变化特征.结果显示:(1)研究区内地壳厚度整体较薄,在27.4~34.3 km之间,平均值为31.4 km.地壳厚度从西北往东南减薄,具有明显条带和块状特征,与地壳主要深大断裂的分布有一定相关性.本文以更为密集的台站结果进一步验证了研究区具有由陆壳向洋壳逐渐减薄的过渡特征,并揭示了地壳新的局部起伏.这也意味着福建地区从内陆到沿海并非线性减薄,存在小尺度横向非均匀性.(2)研究区内泊松比平均值为0.25,范围为0.20~0.30,北部整体偏高,南部整体较低,泊松比分布特征与该区地壳物质组成和矿物含量密切相关.沿海地区泊松比明显高于内陆地区,推测与沿海地区较高的热流值和幔源物质底侵过程有关.(3)地壳厚度与泊松比成负相关,推测在地壳伸展背景下,古太平洋板块俯冲华南大陆,幔源物质进入地壳,在造成莫霍面抬升的同时提高了泊松比.

Analysis of the crustal thickness and Poisson's ratio in Fujian,Southeast China,from teleseismic P-wave receiver functions

Crustal thickness and Poisson′s ratio are important parameters for understanding the crustal structure and the material composition of the Earth,which can provide an important basis for regional structure and dynamics research.Based on the teleseismic waveform data of 88 seismic stations with relatively uniform distribution in Fujian Province from 2014 to 2017,we calculated P-ware receiver functions.For each station,we estimated crustal thicknesses and average Poisson′s ratio using the H-κstacking.We also collected and compared the existing results,and finally integrate our results with the previous results obtained by the receiver function method to obtain crustal thickness and Poisson′s Ratio under 117 seismic stations in Fujian,which revealed the crustal structure and Poisson′s ratio variation characteristics of the Fujian,southeast China.The results show that:(1)the overall thickness of the crust in the study is relatively thin,ranges from 27.4 km to 34.3 km,with an average number of 31.4 km.Further,the crustal thickness gradually decreases from the northwest to the southeast.The crustal thickness in the study exhibits significant small-scale transversal variation,showing obvious zonal and massive characteristics,which is related to the distribution of major deep faults in the crust.In this paper,the results of more intensive stations further verified that the crustal thickness in the study had a transitional characteristic of gradual thinning from the continental crust to the oceanic crust,and reveals new local crustal undulation.It also implied that the crustal thickness is nonlinear thinning from inland to coastal areas,and there is small-scale transversal heterogeneity in Fujian Province.(2)The average Poisson′s ratio is 0.25,ranges from 0.20 to 0.30.It is quite high in the north and low in the south.The distribution of Poisson′s ratio is closely linked to the material composition and mineral content of the crust.The Poisson′s ratio in coastal areas is higher than that in inland areas,which may be related to the higher heat flow in the coastal area and the process of mantle-derived material underplating.(3)The crust thickness is negatively correlated with the Poisson′s ratio.It is speculated that under the background of crustal extension,the paleo Pacific plate subducted the South China continent,and the mantle-derived materials entered the crust.Which caused the uplift of Moho interface and the increase of Poisson′s ratio.