对山东莒县地声极微震观测系统的初步研究

A PRELIMINARY STUDY OF GEOSOUND ANDNANO-EARTHQUAKE OBSERVATION SYSTEM AT JUXIAN COUNTY, SHANDONG PROVINCE

一般情况下都是采用深井系统观测地声和极微震,但却很少有人研究井系统对记录的影响。本文首先从理论上探讨了深井中能够存在的波型。在轴对称条件下有四种波:P、S首波、stoneley波和简正波;在非轴对称条件下,存在非对称的stoneley波、简正波、液体波和S首波。频率较低时,仅存在对称和非对称的stoneley波。其次计算了浅井系统对计录的影响,浅井中记录的信号与原始波形非常接近,可近似作为原始信号。比较深井和浅井的理论和观测结果可知,深井系统能降低噪声,提高信噪比,但使信号发生较大的畸变;而浅井系统的环境噪声较高,但获得的信号非常接近原始波形。最后介绍了在上述结果的指导下所建立的山东省莒县地声台网。

Geosound and nano-earthquake are usually observed by a deep-well system, but the effect of a well system itself on the recordings is seldom studied. In this paper, first the wave forms that might exist in a deep-well are theoretically Studied. There are four wave forms under an axial-symmetric condition: P and S first wave, Stoneley wave, and hamonic wave. But under a non-axisymmetric condition, there are non-axisymmetric Stoneley wave, hamonic wave, liquid wave and S first wave. At lower frequency there exist only symmetric and asymmetric Stoneley waves. Secondly, the effect of a shallow-well system on recordings is calculated. Signals recorded in a shallow well are very much approximate to the original ones, which can be taken as the original signals. It can be seen from a comparison between both theoretical and observational results in deep and shallow wells that, a deep-well system can decrease noise and increase the signal noise ratio, but making signals produce larger distortion; though the environmental noise of a shallow-well system is higher, the obtained signals are very much close to the original wave forms. Lastly, the geosound network set up at Juxian County, Shandong Province, under the guidance of the above mentioned results is introduced briefly.