Component Azimuth Checking Of The Circum-ordos Block Seismographic Network

Orientation accuracy of three components of station seismometers is veryimportant for modern seismology research. Establishment and operation of global andregional three-component broad-band digital seismic network, have greatly promotedthe research and development of modern seismology. For many years, seismicworkers at home and abroad have always attached great importance to theseismometer azimuth’s accuracy and correction testing of basic research. Modernbroadband seismographs have better and more stable instrument parameters, and arewidespread adoption of integrated structural design, the orthogonality betweenthree-component sensor (set) is guaranteed (deviation less than1o), However, due tothe influence of human factors, environmental and other aspects, three components ofstation seismometers might be some deviations. Using an SNR-weighted-multi-eventmethod and from telseismic P-wave particle motions, Niu(2011) found that about onethird of the CEArray stations have some sort of problems, including misorientation ofthe two components, mislabeling of BHN and BHE components as well polarityreversal in one or more components. In this paper, we recheck the componentazimuths of the circum-Ordos block CEArrays from P wave particle motions of73M>7teleseismic events during August2007through March2011. Considering thepossible seismometer re-installation, we estimate north-component azimuth for eachstation by analyzing the time series of the calculated azimuths of each individualevents. Through comparing the different authors’s SKS anisotropy results, wediscussed the effects of seismometer azimuth’s deviations on SKS anisotropicresearch results. Recheked results have shown that8stations with suspected polarconfusion reverse or component identification presented in Niu (2011) do have theproblem of misorientation, but Hanzhong(HZHG) station do not.Our calculated azimuths are well consistent with the results of Niu (2011), whichimplies that the CEArray do have the problem of misorientation. Using teleseismicp-wave particle motion method can effectively check seismometer stations’ horizontalazimuth deviations.Through the time series of the calculated azimuths results of Ledu(LED) station,we can see that seismometer had a sudden change of azimuth in2009, then wecontacted with Qinghai provincial Seismological Bureau monitoring center, got thatthe station had a transformation in the first half of2009, and original digitalseismographs were shifting and do a new correction of the three components ofstation seismometers. This is a effective way to prove that using the time series of thecalculated azimuths method to monitoring station seismometers’s operation ispractical. This provides a more reliable and practical techniques for national andregional digital seismic network’s accurate operation and maintenance monitoring.Different SKS anisotropy results of different authors revealed that SKS fastpolarization directions are reliable on the whole of this area and the seismometerazimuthal deviations effect on SKS anisotropic, which characterized bycomprehensive change of two parameters rather than by a single parameter change independently. so in modern seismology research such as SKS splitting with CEArraydata, users should pay attention to the component misorientation, polarity reversal andmislabeling problems.