Earthquake Early Warning in Japan: Warning the General Public and Future Prospects

Abstract

INTRODUCTIONe earthquake early warning (EEW) information provided by the Japan Meteorological Agency (JMA) is designed to enable public o cials, key safety personnel, and the general public to take advance countermeasures against the e ects of earthquake strong motion. e goal of the early warning system is earliest -wave arrival time in each subprefectural area (about a quarter to a third of one prefecture) before the strong motion arrival. For the system to be e ective, it is essential that JMA publicize the principle and purpose of the warning messages, the technical limits of EEW, and the proper actions to be taken when a warning is received. is is particularly important given the very short warning times (a few to a few tens of seconds) so that EEW can be used e ectively without causing unnecessary confusion. In this article we outline the design of the EEW system in Japan and the necessary preparatory process to start providing EEW information to the general public, summarize the performance of the system since it was launched nationwide in DESIGN OF THE EEW SYSTEMe parameters that the EEW must determine are the estimated origin time, the hypocenter location, the magnitude (in the JMA intensity scale, http://www.jma.go.jp/jma/en/ Activities/earthquake.html#S_I), and earliest arrival time (in seconds) of the strong motion for each subprefectural area.In Japan, seismic intensity has been recorded by instruments designed speci cally for this task (called "seismic intensity meters") since 1996. Seismic intensity meters observe seismic intensity at representative sites for the purposes of disaster mitigation (i.e. collect are not used for hypocenter and magnitude calculation.the acceleration a er a lter with (1/ ) 1/2 amplitude response 1996). Physically, seismic intensity is proportional to the loga--tion site per unit time. JMA has been issuing seismic intensity subprefectural area within two minutes a er the earthquake occurrence when seismic intensity of 1 or over (in JMA scale) is observed. More detailed information (seismic intensity at each observation site) promptly follows this report. Although these are "post-disaster" reports, they have been used as trigger information to start emergency responses such as directing rescue resources to an area where strong motion was observed. To integrate strong motion disaster mitigation, EEW was developed to enable countermeasures of the strong motion arrival. For EEW, seismic intensities are evaluated at -out Japan. Estimation of the seismic intensity has three steps: 1) estimation of hypocenter, 2) estimation of magnitude, and -amplitude on engineering bedrock (Si and Midorikawa 1999), 2) multiplication by the ampli cation coe cient to account conversion from velocity to seismic intensity (Midorikawa 1999). e hypocenter is the starting point of the rupture and is the earthquake, i.e., the magnitude, is predictable at the starting time of the rupture is controversial (e.g., Iio Nakatani a method that is applicable in the real-time processing environment to forecas...

Anomalously large seismic amplifications in the seafloor area off the Kii peninsula

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Source Parameter Estimation Method for Assessment of Structural Resiliencies

“…In the case of the Wenchuan 8.0 mainshock, using the first 3-second P wave may underestimate the magnitude by about 0.8 to 1.0 unit with the investigated parameters ( MI Ref = 7.18, = 7.05, and Ref = 6.91); however, the proposed MI was of the best performance. To mitigate this problem, several methodologies use a longer time window of P wave to update magnitude estimates [17,19]. The evolutionary estimation of MI as a function of the time window shows that the existing methodologies and regression relationships can be extended to large earthquakes, and the saturation effect can be removed through the use of time windows of approximately 6-7 seconds with the investigated MI parameter.…”

Improvement in the accuracy of expected seismic intensities for earthquake early warning in Japan using empirically estimated site amplification factors

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“…The Japan Meteorological Agency (JMA) began providing earthquake early warning (EEW) services to the general public on 1 October 2007 with the aim of mitigating seismic disasters (Hoshiba et al, 2008;Kamigaichi et al, 2009;Doi, 2010). An EEW notification includes information on the expectation of strong ground motion immediately after an earthquake, but before destructive strong motion arrives, by processing real-time data obtained at one or a few seismometers positioned near the source region.…”