Earthquake early warning (EEW) systems are one of the most effective ways to reduce earthquake disaster. Earthquake magnitude estimation is one of the most important and also the most difficult parts of the entire EEW system. In this paper, based on 142 earthquake events and 253 seismic records that were recorded by the KiK-net in Japan, and aftershocks of the large Wenchuan earthquake in Sichuan, we obtained earthquake magnitude estimation relationships using the s c and P d methods. The standard variances of magnitude calculation of these two formulas are ±0.65 and ±0.56, respectively. The P d value can also be used to estimate the peak ground motion of velocity, then warning information can be released to the public rapidly, according to the estimation results. In order to insure the stability and reliability of magnitude estimation results, we propose a compatibility test according to the natures of these two parameters. The reliability of the early warning information is significantly improved though this test.
In this paper, real‐time location methods applied in earthquake early warning system are first summarized, then combined with the actual situation of seismic monitoring network in our country, a complete set of location methods that continuously locate earthquake from the triggering of only one monitoring station to four stations is proposed. The method used in this paper is tested by means of the actual observatory data from the 68 earthquakes over magnitude 3.0 recorded by Fujian earthquake monitoring networks. Results show that for earthquakes within the network, the location error for one‐station method is all less than 50km, the location error for two stations is less than 35 km, the location error for three stations is about 15 km, and the location error for four stations is about 6 km; for earthquakes outside the network, the location error for three or four stations is all less than 30 km. Then the location error formula for earthquake early warning is deduced by means of the information from first three and four stations. And location error distributions are obtained separately under the current condition of seismological observatory network in Fujian province and under the condition of observatory network after the “Eleventh Five‐Year Plan” construction. Based on these analyses, the location results can be judged in advance, which will contribute to improving the reliability of the whole earthquake early warning system.
Ground motion prediction is important for earthquake early warning systems, because the region's peak ground motion indicates the potential disaster. In order to predict the peak ground motion quickly and precisely with limited station wave records, we propose a realtime numerical shake prediction and updating method. Our method first predicts the ground motion based on the ground motion prediction equation after P waves detection of several stations, denoted as the initial prediction. In order to correct the prediction error of the initial prediction, an updating scheme based on real-time simulation of wave propagation is designed. Data assimilation technique is incorporated to predict the distribution of seismic wave energy precisely. Radiative transfer theory and Monte Carlo simulation are used for modeling wave propagation in 2-D space, and the peak ground motion is calculated as quickly as possible. Our method has potential to predict shakemap, making the potential disaster be predicted before the real disaster happens. 2008 M S 8.0 Wenchuan earthquake is studied as an example to show the validity of the proposed method.
In this article, we systematically introduce the latest progress of the earthquake early warning (EEW) system in Fujian, China. We focus on the following key technologies and methods: continuous earthquake location and its error evaluation; magnitude estimation; reliability judgment of EEW system information; use of doubleparameter principle in EEW system information release threshold; real-time estimation of seismic intensity and available time for target areas; seismic-monitoring network and data sharing platform; EEW system information release and receiving platform; software test platform; and test results statistical analysis. Based on strong ground motion data received in the mainshock of the Wenchuan earthquake, the EEW system developed by the above algorithm is simulated online, and the results show that the system can reduce earthquake hazards effectively. In addition, we analyzed four earthquake cases with magnitude greater than 5.5 processed by our EEW system since the online-testing that was started one year ago, and results indicate that our system can effectively reduce earthquake hazards and have high practical significance.
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