Applicability of On-Site P-Wave Earthquake Early Warning to Seismic Data Observed During the 2011 Off the Pacific Coast of Tohoku Earthquake, Japan

Abstract

In this study, the on-site P-wave earthquake early warning (EEW) based on the site-specific spectral ratio of S-wave to P-wave to efficiently incorporate the site characteristics, which can potentially issue the earthquake warning by the time of Ts-p, was developed. The spectral ratio of S-wave to P-wave that are related to the source effects, the path effects, and the site effects are significantly affected by the site effects contrast to the source effects and the path effects in practical. At first, the on-site P-wave EEW method which multiplies a site-specific spectral ratio of S-wave to P-wave prepared in advance by P-wave observed in the real-time at seismic stations is applied to seismic data for moderate-sized earthquakes with a magnitude (Mj) of 5.0–6.0, occurred in the eastern Japan, observed at both the sedimentary basin site and the rock site. As a result, this method predicted well the observed S-wave in the single indicator of SI within the logarithmic standard deviation of 0.25 as well as in the frequency of more than 0.5 Hz. It is, also, confirmed that the site-specific spectral ratio of S-wave to P-wave at a seismic station was stably retrieved from 20 data samples at least. To investigate the applicability of this method to earthquake ground motions induced by a large-scaled earthquake, finally, this method is applied to seismic data during the 2011 off the Pacific coast of Tohoku earthquake, Japan (Mw 9.0). The prediction of S-wave using a time-window of 10 s after P-wave arrived, could not reproduce the observation with the underestimation; however, the prediction of S-wave using a time-window of more than 20 s containing P-wave propagated from an area generating strong motions in the fault, could reproduce the observation. Even in the case of the large-scaled earthquake, the on-site P-wave EEW method based on the site-specific spectral ratio of S-wave to P-wave at a seismic station availably works by using the gradually increasing time-windows after P-wave arrived in the single indicator of SI as well as in the frequency content, avoiding the mixture of S-wave into a part of P-wave.

Application of the on-site P-wave earthquake early warning method based on site-specific ratios of S-waves to P-waves to the 2016 Kumamoto earthquake sequence, Japan

“…The method directly predicts S-waves by multiplying site-specific ratios of S-waves to P-waves with P-waves observed in real-time at a strong-motion station, as expressed by Eq. (1) in the frequency domain with a logarithm (Tsuno and Miyakoshi 2019;Tsuno 2021). The method using P-waves can significantly reduce the time difference between the arrivals of P-and S-waves (Ts-p) to issue warnings compared to previous methods that mainly use S-waves.…”

“…The EEW systems are globally installed in many fields based on their own concepts to provide a warning prior to the strength of ground shaking (Allen et al 2009). Recently, methods reflecting differences at sites in the strength of ground shaking based on empirical site characteristics have been developed (Miyakoshi and Tsuno 2015;Miyakoshi et al 2019;Tsuno and Miyakoshi 2019;Zhao and Zhao 2019;Tsuno 2021). Tsuno (2021) applied the EEW method based on the empirical spectral ratio of S-wave to P-wave to seismic data of the 2011 off the Pacific coast of Tohoku earthquake (Mw 9.0), as large-sized offshore earthquakes.…”

“…Recently, methods reflecting differences at sites in the strength of ground shaking based on empirical site characteristics have been developed (Miyakoshi and Tsuno 2015;Miyakoshi et al 2019;Tsuno and Miyakoshi 2019;Zhao and Zhao 2019;Tsuno 2021). Tsuno (2021) applied the EEW method based on the empirical spectral ratio of S-wave to P-wave to seismic data of the 2011 off the Pacific coast of Tohoku earthquake (Mw 9.0), as large-sized offshore earthquakes. However, the performance and accuracy of these methods when applied to large-sized inland earthquakes have not yet been investigated.…”

“…In this study, we focused on the performance and accuracy of the on-site P-wave EEW method based on the site-specific ratio proposed by Tsuno (2021), using strong-motion data from the 2016 Kumamoto earthquake sequence. Finally, the applicability of this method to strong-motion data from the foreshock, mainshock, and largest aftershock of the 2016 Kumamoto earthquake sequence in the operational use was investigated.…”

Estimating S-wave Amplitude for Earthquake Early Warning in New Zealand: Leveraging the First 3 Seconds of P-Wave

“…To ensure the relevancy and suitability of the data for the study, ground motion records are exclusively retained from stations situated within a 30-kilometre epicentral distance from each earthquake event, a selection criterion supported by previous research (Böse, Hauksson, Solanki, Kanamori, Wu, et al, 2009;Tsuno, 2021;Zollo et al, 2010). Two key considerations drove this strategy.…”