Seismic waves of the 10 December 2020 M6.6 Yilan earthquake observed by interferometric fiber-optic gyroscope

A newly developed cost-effective fiber-optic gyroscope (FOG) and an existing seismometer co-locating at the campus of National Central University (NCU) recorded seismic waves of a M6.6 Yilan earthquake and aftershock events occurring at around 24.74° N 122.03° E (88 km away from NCU) during 10–11 December 2020. Two nearest accessible broadband seismographs located in Hsinchu have also been employed as measurement references for facilitating the analysis of the detected seismic signals. Conventional seismometers usually detect the translational components of the seismic waves, while the FOG observes the rotational component. The recorded FOG data exhibit high-resolution details of the rotational component of shockwaves, which provides additional information of seismic waves. The shock waveforms of the translational and rotational components, analyzed under the conservation of the shock wave energy density received by FOG and seismograph, are found to be significantly correlated. The correlation coefficients of 60-s data are > 0.85 for the main shock and > 0.86 for the aftershock, while those of the 10-s peak periods are as high as 0.9064 and 0.8953, respectively. The highly correlated data imply that the energy registered by the two devices are equivalent. The optical interference-based rotation senor of the cost-effective FOG provides a high sensitivity of better than 3.6 deg/h and an extended dynamic sensing range as high as 55 dB with the fully sensing ability from ± 3.6 deg/h to ± 720,000 deg/h. The FOG seismometer sheds some light on building an earthquake six-degree-of-freedom observation array to have a bettering on the understanding of the seismicity.