摘要
尽管P_n波品质因子(P_nQ)对上地幔流变性质研究及核试验监测有着深刻含义,迄今它仍然是一个难以准确测定的地震参量.这是因为除了众所周知的影响所有短周期Q的干扰因素外,在所有主要的区域震相中,地震工作者对P_n波的传播模式及几何扩散函数G=d^(-k)中的扩散率指数k了解最少.不同的研究者任意地假定不同的常数k,因此常算出非常不同的P_nQ值(例如文献[1]、[2]).实际上,理论研究已表明,k随频率而变,变化的形式取决于上地幔的速度结构.本文介绍用一推广的逆向双台法同时测定加拿大东部的P_nQ和k值.我们的结果表明:1.加拿大东部的P_n波是由一系列的干涉潜波叠加而形成;2.视P_nQ(散射和固有非弹性的综合效应)随频率而增加,在15Hz处接近2000.
In spite of its profound implications on the upper mantle rheology and seismic verification of low-threshold nuclear test ban treaties, PnQ, the quality factor for Pn wave, remains an elusive parameter to quantify. This is because in addition to the familiar contaminants affecting all short-period Q measurements, the Pn propagation mode, and hence, the spreading rate coefficient k in its geometrical spreading function PnG=d-k is among the least understood of all major regional phases. Large differences in the estimated PnQ can simply arise from k being arbitrarily assumed to take different (frequency-independent) values (e.g.,[1,2]). Theoretical studies [3'4] have in fact shown that k is characterized by a frequency dependence which is a function of the upper mantle velocity structure. We report here the results of a first attempt at a simultaneous determination of the PnQ and the k in eastern Canada using an extended reversed two-station method. The results suggest: a) the Pn waves in eastern Canadian originate from the superposition of a series of interfering diving waves; and b) the apparent PnQ (the net combined effects due to scattering and intrinsic anelasticity) increases very rapidly with frequency, approaching 2000 at 15 Hz.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
1991年第5期563-568,共6页
Chinese Journal of Geophysics
关键词
PN波
衰减
地震
地震波
Pn attenuation, Frequency-dependent geometric spreading, Reversed two- station method.
