Real-Time Prediction of Impending Ground Shaking: Review of Wavefield-Based (Ground-Motion-Based) Method for Earthquake Early Warning

Mitsuyuki Hoshiba

doi:10.3389/feart.2021.722784

Abstract

Earthquake early warning (EEW) systems aim to provide advance warning of impending ground shaking, and the technique used for real-time prediction of shaking is a crucial element of EEW systems. Many EEW systems are designed to predict the strength of seismic ground motions (peak ground acceleration, peak ground velocity, or seismic intensity) based on rapidly estimated source parameters (the source-based method), such as hypocentral location, origin time, magnitude, and extent of fault rupture. Recently, however, the wavefield-based (or ground-motion-based) method has been developed to predict future ground motions based directly on the current wavefield, i.e., ground motions monitored in real-time at neighboring sites, skipping the process of estimation of the source parameters. The wavefield-based method works well even for large earthquakes with long duration and huge rupture extents, highly energetic earthquakes that deviate from standard empirical relations, and multiple simultaneous earthquakes, for which the conventional source-based method sometimes performs inadequately. The wavefield-based method also enables prediction of the ongoing seismic waveform itself using the physics of wave propagation, thus providing information on the duration, in addition to the strength of strong ground motion for various frequency bands. In this paper, I review recent developments of the wavefield-based method, from simple applications using relatively sparse observation networks to sophisticated data assimilation techniques exploiting dense networks.

Highlights

Earthquake early warning (EEW) aims to prevent/mitigate earthquake disasters by providing people with enough time to take appropriate safety measures in advance of impending strong ground motion
Because seismic motion is a wave propagation phenomenon, the physics of wave propagation, which have been well studied in many research fields, is the basis of real-time prediction of ground motion
In history of EEW research, in the source-based method many authors have focused on rapidly estimating source parameters, from which peak ground motions (PGA, PGV or seismic intensity) are estimated using a ground motion prediction equation (GMPE)

Summary

Introduction

Earthquake early warning (EEW) aims to prevent/mitigate earthquake disasters by providing people with enough time to take appropriate safety measures in advance of impending strong ground motion. The wavefield-based method enables prediction of the ongoing seismic waveform itself using the physics of wave propagation, providing information on the duration, in addition to the strength of strong ground motion for various frequency bands. It is relatively easier to take high-frequency waves in the boundary integral equation method than in the finite difference method, information on the time-dependent propagation direction (θ) is required.

Results

Conclusion