Too-Late Warnings by Estimating Mw: Earthquake Early Warning in the Near-Fault Region

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

Earthquake early warning (EEW) systems aim to provide advance warnings of impending strong ground shaking. Many of EEW systems are based on a strategy in which precise and rapid estimates of source parameters, such as hypocentral location and moment magnitude (M_w), are used in a ground motion prediction equation to predict the strength of ground motion such as PGA and/or PGV. Strategy based on rapid estimation of M_w implicitly assume that precise estimation of M_w leads to precise prediction of the strength of ground motion and that this estimation can be done earlier than the arrival of strong ground motion. Are these assumptions true?

In some regions near the causative fault this approach leads to late warnings. The peak strong ground motions often occur during earthquake ruptures before the final M_w can be estimated in the near-fault region, where large PGA and PGV are usually recorded. The 2016 Kumamoto earthquake (M_w 7.1) actually indicated that the estimation of M_w is later than the arrival of peak ground motion in the near-fault region, where the strong ground motions were recorded by a dense observation network. This phenomenon is explained by a reason that the strong ground motion in the near-fault region is controlled by instantaneous strong radiation of seismic waves caused by the local process of rupture, while M_w is finally estimated at the end of rupture reflecting the whole process. An EEW strategy based on rapid estimation of M_w thus is not suitable for regions near faults where strong shaking is usually recorded. Approaches based on real-time monitoring of ground motion are more promising for these near-fault locations.

Presenting Author: Mitsuyuki Hoshiba

Authors