The Earthquake Early Warning of Japan Meteorological Agency
Abstract
We review the operation of nationwide Earthquake Early Warning (EEW) of JMA. Then we show its performance of the cases of the 2011 off the Pacific Coast of Tohoku Earthquake (Mw9.0) and its aftershocks. After that, we present some lessons from the experience and future plans to improve the system. JMA began to operate the EEW nationwide in October, 2007. We predict seismic intensities and arrival times of S waves after determining the hypocenter by a combination of several techniques; the magnitude by maximum displacement amplitudes. The main part of the system uses 220 stations. The JMA EEWs are updated repeatedly as available data increases with elapsed time. The JMA seismic intensity scale is based on instrumental measurements which consider not only the amplitude but also the frequency and duration of the shaking. The scale has 10 degrees. Intensities of 5 and 6 are divided into 2 degrees, namely 5-lower, 5-upper, 6-lower and 6-upper, respectively. Intensity 1 corresponds to the ground motion that people can barely detect and 7 is the upper limit. There are 2 categories for the JMA EEW. The first one is "forecast" for the limited users, and the other is "warning" for the public. We issue the forecast in the case where the estimated maximum intensity exceeds 2, or estimated magnitude is larger than 3.5. We announce the warning through TV and cell phones to the general public when we predict the maximum intensity 5-lower or larger to the areas where the estimated intensities exceed 3. The forecast is updated whenever it is necessary, but we provide the updated warning only when the estimated intensities become 5-lower or larger from less than 4 in some areas, and limit it within 60 s after the first detection. The warning of the EEW was disseminated 30 s after the Mw9.0 event occurrence, which was 8 s after the first detection. The estimated magnitude was 7.2 at the time and the warning was issued for Tohoku. We could provide the warning before the arrival of S-waves for all warning areas. However, the actual magnitude was 9.0 and the wide area was ruptured. The under estimate of the magnitude and the extent of the source region caused the under estimate of intensities. Especially, in Kanto, we observed 6-upper, but we couldn't provide the warning for the public. The warning was provided for the public only once, but the updated information was provided only to the limited users. We issued the EEW totally 15 times for the event. Finally the EEW estimated M8.1 105 s after the first detection. Aftershocks sometimes occurred simultaneously over the wide region. Then, the system became confused and did not always determine the hypocenter parameters correctly. In 49 days after the main shock to April 28, 2011, 70 EEWs were announced to the public, but actual observed intensities did not exceed 2 at any stations in 17 cases. To overcome those problems, we will introduce the real-time pseudo seismic intensity by Kunugi et al. (2008), by which we will be able to monitor the extent of the strong motion field and to evaluate the calculated hypocenter parameter. As mentioned above, the current JMA EEW system is based on the calculated hypocenter parameter. We have the idea of a hybrid method using the conventional method and the real-time intensities.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2013
- Bibcode:
- 2013AGUSM.S42A..01N
- Keywords:
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- 7212 SEISMOLOGY / Earthquake ground motions and engineering seismology;
- 7219 SEISMOLOGY / Seismic monitoring and test-ban treaty verification;
- 7294 SEISMOLOGY / Seismic instruments and networks;
- 7290 SEISMOLOGY / Computational seismology