Seismic Sensor Misorientation Measurement Using P-Wave Particle Motion: An Application to the NECsaids Array

Seismic sensor orientation is one of the most critical parameters for modern three-component seismological observation. However, this parameter is easily subject to error imposed by strong magnetic anomalies near the station or by human error in declination calibration. It is therefore very important to inspect and correct for sensor misorientation before utilizing three-component waveform data. In this study, we measured the epoch-dependent sensor misorientation for our temporary seismic array (NorthEast China Seismic Array to Investigate Deep Subduction, or NECsaids) by analyzing P-wave particle motions. We applied principal component analysis and the minimizing transverse energy method to study earthquakes with epicentral distance between 5 degrees and 90 degrees to estimate the sensor misorientation. Our results show high consistency with the direct gyrocompass measurements, with a correlation coefficient of 0.95. Our statistical analysis suggests that we can estimate robust sensor misorientation utilizing 10 earthquakes with high signal-to-noise ratio records and highly linear P-wave polarizations. We also find that the influence of anisotropy or a dipping interface produces a periodical pattern with back azimuth and is relatively small for our misorientation estimation. By analyzing the amplitude change of synthetic seismograms due to misorientation and taking into account the influence of anisotropy and dipping interfaces, as well as the measurement errors, we expect engineers to be able to orient seismic sensors with error smaller than 3 degrees.