Measurement of seismometer misorientation based on P-wave polarization: application to dense temporary broadband seismic array in the epicentral region of 2016 Gyeongju earthquake, South Korea

Abstract

In this study, we probe the misalignment of 200 temporary broadband seismometers based on the polarization of P waves from regional and teleseismic earthquakes. The seismometers were deployed in the epicentral region of 2016 M-L 5.8 Gyeongju earthquake, South Korea, and this unprecedented dense array provided a unique opportunity for investigating fault structures from microseismicity. For the full use of three-component seismic records, we estimate and provide time-dependent misorientation angles of the 200 seismometers from June 2018 to March 2021 with uncertainty assessments. Two methods based on the principal component analysis and the minimization of transverse P-wave energy are applied. Our estimates are characterized by small uncertainty (average median absolute deviation of 3.14 degrees). Moreover, periods of suspected temporal changes in misorientation angles mostly coincide with periods of reported technical operations, which demonstrates reliability of our methods to precisely detect the temporal variation of misorientation angles. We expect our misorientation angles to serve as an essential metadata for further seismological researches utilizing the dense array data.