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Application of polarization analysis in correcting the orientation error of a downhole seismometer
Author(s) -
Chiu HungChie,
Huang HueyChu,
Leu ChunLong,
Ni SheanDer
Publication year - 1994
Publication title -
earthquake engineering and structural dynamics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.218
H-Index - 127
eISSN - 1096-9845
pISSN - 0098-8847
DOI - 10.1002/eqe.4290231003
Subject(s) - seismometer , geology , geodesy , polarization (electrochemistry) , orientation (vector space) , waveform , tilt (camera) , vertical orientation , horizontal plane , seismology , azimuth , optics , acoustics , physics , geometry , mathematics , chemistry , quantum mechanics , voltage
This paper shows that the polarization analysis of later arrivals could be used to estimate the orientation error and the tilt of the downhole accelerometers in the Dahan downhole strong‐motion array. This four‐level array is located to the north of Hualien city in eastern Taiwan. Polarization analysis of a windowed signal which includes significant phases (e.g. primary S wave) can give a stable major polarization axis. This axis can then be used as the reference direction for correcting the orientation error and the tilt of the downhole seismometers. If the surface instrument is chosen as the reference, the angle between the major polarization axes of the surface and any downhole recordings will be the orientation error needed to be corrected for the downhole accelerograph. This angle is a combination of the tilt and the orientation errors which correspond to the dip and strike of maximum polarization, respectively. At the Dahan downhole strong‐motion array, the orientation errors of the seismometers at the depth of 50, 100 and 200 m were 1°, 90° and 84°. These orientation errors were consistent with the horizontal particle‐motion analysis. The errors of horizontal plane (tilt) were almost zero. After correction, the coherency of the waveforms between the surface and the downhole recordings was significantly improved.