Application of the Modified PLUM Method to a Dense Seismic Intensity Network of a Local Government in Japan: A Case Study on Tottori Prefecture

Takao Kagawa

doi:10.3389/feart.2021.672613

Abstract

An application of the PLUM (Propagation of Local Undamped Motion) method to real-time seismic intensity distribution from a dense seismic intensity network maintained by a local government in Japan is demonstrated. The JMA (Japan Meteorological Agency) has employed the PLUM method from March 2018 as a supplement to the traditional EEW (Earthquake Early Warning) which requires hypocenter determination. A dense observation network is desirable for upgrading accuracy and immediateness of EEW including the PLUM method. Seismic intensity meters in Tottori Prefecture, Japan, are suitable for the purpose because they have been improved to broadcast packets with peak ground acceleration and JMA seismic intensity at every 1 s. Also, 34 seismic intensity meters are installed in the target area while only six observation sites are used for the EEW by the JMA. The packet data are received at Tottori University, and the modified PLUM method considers wave propagation with damping from not only the observation points but also all evaluating grid points at a 1 km mesh. Additionally, P-wave amplitudes in preliminary tremors are also introduced to estimate seismic intensities from an empirical relationship. Applying the methodology to past earthquake data, more detailed and rapid evaluations of seismic intensity distribution are achieved. We expect the system will be utilized for earthquake disaster mitigation measures of local governments.

Highlights

Real-time shake map estimation using seismic intensity meters maintained by local governments in Japan has been enhanced
The data are received at Tottori University, Japan, Modified PLUM for Dense Network and the PLUM (Propagation of Local Undamped Motion) method (Hoshiba, 2013) is applied to the data for estimating JMA seismic intensity distribution at 1 km grid points
In case of the 2016 Central Tottori Prefecture Earthquake, Japan, with MJMA 6.6, the seismic intensities around the observation sites were overestimated to use as a reference for initial response to the disaster, since the seismic intensities are assumed to propagate without attenuation with emphasis on issuing earlier warning at the expense of accuracy

Summary

INTRODUCTION

Real-time shake map estimation using seismic intensity meters maintained by local governments in Japan has been enhanced. The PLUM (Propagation of Local Undamped Motion) method (Hoshiba, 2013) is applied to the data for estimating JMA seismic intensity distribution at 1 km grid points. Intensity five lower is smaller than the JMA interpolation, especially in the southern and western part from the source area It is because there are few observation points maintained by Tottori Prefecture (Figure 1). The following equation is derived from least-squares approximation: IJMA 2.18 log(PGAP) + 0.77 where IJMA is the JMA seismic intensity and PGAP is the peak ground acceleration of the vertical P wave Both show a good correlation, but the number of data are not enough in large amplitude range.

DISCUSSION

CONCLUSION