分析P、S波接收函数得到的云南岩石圈结构

Contrasting the lithospheric structure beneath Yunnan region revealed by P and S receiver functions

P波接收函数通过分离间断面上产生的P-to-S转换波来测量间断面的深度,由于地壳多次相的干扰,导致这一方法用于测岩石圈—软流圈界面(LAB)受到了很大的限制.不过,S波接收函数可以克服这一问题,因为它分离S-to-P转换相,而这一转换相比入射S波提前到达台站,于是避开了迟到的地壳S波振荡相.然而,由于S波的频率比P波低,这将导致S波接收函数的分辨率较P波接收函数的低.为了作对比分析,本文利用云南地区13个固定台站记录的远震三分量资料,分离出台站下方的P、S波接收函数,而且这些接收函数被校正到67°的参考震中距处,以便进行叠加增强信噪比.最后将时间域的叠加信号转换到深度域,分别获取台站下方的地壳和岩石圈的厚度.结果表明:P波接收函数得到的地壳厚度在32~56 km之间,S波接收函数得到的地壳厚度在41~54 km之间,S波接收函数得到地壳厚度系统地偏大8~9 km;P波接收函数得到的LAB深度在65~110 km之间,S波接收函数得到的LAB深度在66~135 km之间,S波接收函数得到的LAB深度偏大15~20 km,最大偏差达到了25 km.

The receiver function technique has been developed into one of the most powerful tools to observe seismic discontinuities in the crust and upper mantle,in which source,far field path,and instrument effects are removed by deconvolving the vertical component from the radial components. The resulting receiver function waveform is an estimate of the ground＇s impulse response.The P receiver functions isolates the P-to-S converted waves generated at seismic discontinuities,the timing of converted arrivals in a receiver function place constraints on the depth of the horizon that produced them. The technique isolates the P-to-S converted waves from the P-wave coda generated at seismic discontinuities（ P receiver function）. Although there are successful applications of the P receiver function for observation of the LAB, the method is generally limited for detecting interfaces in the mantle lithosphere due to interference of the primary conversions with strong crustal reverberations. Fortunately, the recently developed S receiver function technique appears to be able to overcome this problem,because it analyses S-to-P converted phases,which arrive earlier than the incident S phase and are consequently separated from the later arriving S reverberations. Nonetheless,there are a number of technical challenges specific to S-to-P conversions compared to P-toS conversions since S waves are generally characterized by lower frequencies than P waves,resulting in a lower spatial resolution.In the study,the P and the S receiver functions are isolated from three-component seismic data recorded by 13 permanent broadband stations deployed in Yunnan,and are move-out corrected to the reference epicentral distance of 67° before stacking into one trace. Then the stacked receiver functions are converted to the depth domain to obtain the crustal and lithospheric thickness beneath each station. The crustal thicknesses from the P-wave Receiver Functions（ PRFs） and from the S-wave Receiver Functions（ SRFs） are in the ranges of 32 ~ 56 km,and of 41 ~ 54 km,respectively. Our results show that the crustal thicknesses from SRFs are 8 ~ 9 km regionally larger than those from PRFs. Additionally,the depths of LAB from the PRFs and from the SRFs are in the ranges of 65 ~ 110 km,and of 66 ~ 135 km,respectively. The depths of LAB from the SRFs are 15 ~ 20 km larger than those from the PRFs,with a maximum deviation of 25 km.