用接收函数方法研究云南及其邻区地壳上地幔结构

Crustal structure in the Yunnan region determined by modeling receiver functions

利用云南和中国地震台网30个台站记录的远震资料,采用接收函数扫描法和线性反演方法对云南及其邻区的壳幔速度结构进行了研究,获得了研究区内地壳厚度、Vp/Vs以及壳幔速度的分布特征.利用接收函数扫描（H-k）法和线性反演方法获取的台站下方地壳厚度结果表明,研究区地壳厚度变化剧烈.速度结构研究结果表明,红河断裂以西的腾冲-保山地块和思茅地块,以及南华板块北部地区的台站（如攀枝花、丽江、东川、永胜等）下方地壳均存在下地壳低速层,且具有高的地壳平均Vp/Vs值.这些不仅暗示研究区的下地壳低速异常可能为高温甚至高温导致的部分熔融所致,同时,也意味着该区下地壳的物质易于发生塑性流动,为地壳的变形和增厚创造了条件.红河断裂带作为云南地区的一个主要边界断裂,其西侧地区地壳厚度变化较东侧剧烈,另一方面,红河断裂西侧的平均地壳Vp/Vs值较其东侧要高.综合前人关于研究区岩石圈速度结构、地热流值、重力场和上地幔各向异性等地球物理场的研究结果.我们推断,现今的思茅块体和保山-腾冲块体在大地构造上应归属于冈瓦纳板块.

We selected broadband teleseismic waveform data recorded by the Yunnan Seismic Network and CDSN to study the crustal structure in Yunnan and its adjacent region.The crustal thickness and Vp/Vs ratio are estimated by the grid-search method using crustal conversion and multiples,assuming an average P-wave velocity in the crust.Teleseismic P waveform modeling is carried out to investigate the S-wave velocity structure,assuming the fixed Vp/Vs value inferred from the grid-search method.The results from the two estimation techniques were consistent.Our results show strong lateral variations in crustal thickness in this area.Our results also indicate that there exist low velocity zones and high Vp/Vs beneath the Yunnan region,especially in western Yunnan.All these are the possible evidence of the crustal flow in middle-to-lower crust,which are responsible for the thickening of crust.The Vp/Vs and crustal thickness are different across the Red-river fault,which implies that the Red-river fault is one main boundary fault.Combining results from other geophysical investigations,we conclude that both the Simao terrane and Baoshan-Tengchong terrane belong to the Gondwana plate.