![]() ![]() The Tohoku-Oki earthquake and subsequent intense seismic activity also had shed light on technical limitations of the Japanese nationwide earthquake early warning (EEW) system, which afterwards led to further developments of the system. The resulting strong ground shaking and large tsunami caused severe damage in a large part of eastern Japan. ![]() It has been 10 years since the 2011 off the Pacific coast of Tohoku earthquake (Tohoku-Oki earthquake), a M w9.0 megathrust event in the Japan Trench, occurred on March 11, 2011. Those findings indicate that the JMA EEW system has made substantial progress both on software and hardware aspects over the 10 years after the Tohoku-Oki earthquake. The detection time analysis for the S-net incorporation suggested that S-net enabled the system to issue the first EEW report earlier than before the S-net incorporation for earthquakes around the Japan and Kuril trenches. PLUM made the system less likely to underpredict strong ground motions and improved the warning issuance timeliness. The prediction accuracy and warning issuance performance analysis for the updated JMA EEW system showed that IPF improved the source-based ground motion prediction accuracy and reduced the risk of issuing overpredicted warnings. Another notable update was the incorporation of new observation facilities including S-net, a large-scale ocean bottom seismometer network deployed along the Japan and Kuril trenches. IPF is a robust point-source algorithm based on the Bayesian inference, and PLUM is a wavefield-based algorithm that predicts ground motions directly from observed shakings. One of significant improvements in the JMA EEW system was the implementation of two new ground motion prediction methods: the integrated particle filter (IPF) and propagation of local undamped motion (PLUM) algorithms. In addition, we evaluate how the system performance was influenced by the updates. In this paper, we summarize major system developments after the Tohoku-Oki event to overcome the limits of the standard point-source algorithms and to enhance the EEW performance further. The point-source algorithms successfully provided ground motion predictions with high accuracy during the initial operation however, the 2011 M w9.0 Tohoku-Oki earthquake and the subsequent intense aftershock and triggered earthquake activities underscored the weaknesses of the source-based approach. ![]() In the beginning of the operation, the system ran based mainly on standard source-based algorithms with a point-source location estimate and ground motion prediction equation. In Japan, the nationwide earthquake early warning (EEW) system has been being operated by the Japan Meteorological Agency (JMA) since 2007, disseminating information on imminent strong ground motion to the general public and advanced technical users.
0 Comments
Leave a Reply. |