利用远震P波质点运动检核区域地震计水平分量方位

Component Azimuths of Regional CEArray Stations Checked by Teleseismic P-wave Particle Motion

摘要:

地震计三分量方位的准确性对现代地震学研究具有很重要的意义。文献[1]利用P波偏振原理和多地震事件加权叠加方法计算表明,中国"十五"数字地震网络台站中有近三分之一的台站存在地震计水平方位偏差大、极性接反或分量互换等方面的问题。本文选取鄂尔多斯地块周缘地区24个代表性台站,利用2007年8月至2011年3月期间73个M≥7远震事件的P波资料,对台站分量方位等问题进行了检核计算。考虑到期间地震仪的可能重新安装因素,应用单地震事件的反演方位时间序列变化来计算分量方位偏差及其可能的方位校正。研究结果表明,反演的方位与文献[1]的结果基本一致,表明中国＂十五＂数字地震网络确实存在部分台站方位偏差较大等方面问题。因此,在SKS横波分裂等现代地震学研究中应充分考虑台站地震计方位不准和变动等因素的影响。

Abstract:

Orientation accuracy of three components of station seismometers is very important for modern seismology research.Many aspects of modern seismic studies require rotating the BHN,BHE,and BHU as three-dimensional orthogonal coordinate components of particle motion;that is,radial(horizontal direction of incidence),horizontal(in the horizontal plane perpendicular to the incident direction),and vertical.If the station seismometer's BHN component direction and the true north direction N are really larger than the azimuth deviation,then the radial and transverse components will have a greater system deviation,which is based on the back azimuth value.This will affect the authenticity and reliability of modern seismic studies,such as shear-wave splitting SKS results,and also confuse seismic interpretation.For many years,seismic workers at home and abroad have attached great importance to the seismometer azimuth＇s accuracy and correction testing for basic research.If P-waves are compressed through horizontal layered anisotropic media to seismic stations,then the particle trajectories will be in the large in-plane circle composed of the seismic focus,the seismostation,and the geocentre.Seismic P-waves in the plane incident to station direction(radial or station azimuth direction)were also determined tohave radial(plane incident)P-waves with the greatest polarization energies in the plane perpendicular to the incident direction of landscape orientation with the lowest vibrational energy.If BHN coincides with the north direction N (BHE direction coincides with the East direction E),the rotation angle from BHN to the P-wave plane incident direction(energy maximum polarization direction)will be the seismostation to seismic focus＇s back azimuth.If the seismometer station BHN direction and the North direction N slightly deviate,the rotation angle from BHN to Pwave plane incident direction(polarization energy maximum)will not equal the seismostation to seismic focus＇s back azimuth.From the seismostation-seismic focus back azimuth angle and the rotation angle determined from the BHN/BHE components to the maximum polarization energy＇s direction,the seismometer BHN component＇s azimuth deviation could be obtained.Using an SNR-weighted multievent method and teleseismic P-wave particle motions,Niu(2011)found that about one-third of the CEArray stations have some sort of problems,including misorientation of the two components,mislabeling of BHN and BHE components,as well as polarity reversal in one or more components,all of which were brought to the attention of the China Earthquake Administration and seismic data users.In this study,we rechecked the component azimuths of the circum-Ordos block of CEArrays from P-wave particle motions of 73 M >7teleseismic events from August 2007through March 2011.Considering possible seismometer re-installation,we estimated the north-component azimuth for each station by analyzing the time series of the calculated azimuths of each individual event.Our calculated azimuths are very consistent with the results of Niu(2011),which implies that the CEArray does have a problem with misorientation.The teleseismic P-wave particle motion method can be used to effectively check the seismometer stations＇ horizontal azimuth deviations.Therefore,in modern seismology research such as SKS splitting with CEArray data,users should pay particular attention to component misorientation,polarity reversal,and mislabeling problems.