S21D-01
Provision of Earthquake Early Warning to the General Public and Necessary Preparatory Process in Japan
Earthquake early warning of JMA is to enable advance countermeasures to the strong motion disaster by providing expected seismic intensity and arrival time of the strong motion, as well as estimated hypocenter parameters, before the S wave arrival. However, due to its very short available time period, it is essential to well publicize the principle and technical limit of EEW, and proper actions to be taken when it is seen or heard, to utilize EEW effectively without causing unnecessary confusion. Accordingly, JMA decided to provide EEW in two steps. Namely, JMA started to provide EEW to a limited number of users who understand the technical limit of EEW and can utilize it effectively, such as for automatic control from August 2006. At that moment, EEW was not well known to the general public, so JMA started to provide it to the general public in October 2007, after publicizing the principle and proper actions to be taken. EEWs are issued basically several times for one earthquake improving the accuracy as available data increases as time passes, securing the promptness of the first issuance at the same time. On line connected computer can utilize such multiply issued information for automatic control. But, when they are transmitted to a public, it is impossible to respond properly, and also it is impossible to transmit all by characters and voice. So, JMA considered the issuance criterion and contents of EEW when it is issued to the general public to meet the following conditions. 1) Should be issued on the best timing, to avoid the false alarm, to secure the promptness as much as possible, and to make the revised issuance as few as possible. 2) Should be issued when really a strong motion is expected, and it should be made clear where the safety actions should be taken. As a result, - Issuance criterion : when the maximum seismic intensity 5 lower(JMA scale) or over is expected by using seismic records from more than one station. - EEW contents : Origin time, epicentral region name, and names of areas(unit is about 1/3 to 1/4 of one prefecture) where seismic intensity 4 or over is expected. Expected arrival time is not included because it differs substantially even in one unit area. Considering the gravity of EEW which can save lives, JMA is considering the framework to clearly define the responsibility of JMA, and to assure the technical standard of EEWs that will be issued from private companies to provide expected seismic intensity and arrival time at individual house and building, which is beyond the national agencyfs service. In the meeting, some examples of the actual issuance will be introduced. EEW system has been developed by JMA, Railway Technical Research Institute, and National Research Institute for Earth Science and Disaster Prevention.
S21D-02
Integrated System for Earthquake Early Warning and Quick Response Against Strong Motion - In Case of the Tokyo Metro Company
In July 2005, an earthquake of M6.0 attacked the Tokyo metropolitan area. This earthquake occurred at 35.5N and 140.2E with about 73km in depth, and the maximum JMA intensity was 5+ corresponding to MMI VIII approximately. This earthquake occurred at north-west of Chiba prefecture and caused a traffic disturbance widely in Tokyo metropolitan area. All the train operation had been stopped for a long time after the earthquake, although a severe damage was not caused even in the area of high intensity. The longest down time for the train operation was more than seven hours. After the earthquake, we proposed a new system for early warning and quick response. Tokyo Metro Company accepted our proposal, and we replaced and built the new early warning/quick response system as followed. The system consists of two seismometer networks. One is the early warning system FREQL network with six seismometers to control or stop the train operation immediately after the earthquake occurrence. And the other is the portable digital seismometer AcCo network distributing 33 seismometers in every about three kilometers mesh to grasp more detailed seismic motion on their service area. The information from both FREQL network and AcCo network are gathered to the operation center and displayed on the individual monitoring system. The monitoring system for AcCo can indicate the integrated information from AcCo and FREQL on the subway network image. The AcCo monitoring system is also installed on the control table for each subway line. At the time of the earthquake, the early warning system detects at first the earthquake immediately and then the 33 local seismometers inform the actual earthquake motion of each site independently and rapidly. This system realized quick response and restart of the train operation because the early warning became faster and checking zone after earthquake was optimized. This updated system is expected to realize quicker response during and after. For the large system as the train operation, it is necessary for the control against the earthquake to equip the system not only to issue the early warning but also to support the quick and rational recovery work after the earthquake.
S21D-03
Home Seismometer
We have developed an automated system for analyzing Hi-net seismograms for earthquake early warning (EEW) in Japan. Because of limitations imposed by station spacing, our system generally cannot issue an EEW to areas within about 30 km distance of the earthquake's hypocenter. We estimate that about 10 times the number of stations would be needed to issue an EEW in these areas, but the overhead would be cost prohibitive for governmental agencies. The practical deployment of EEW in Japan has started in October, 2007 and millions of people are expected to purchase and install the receiving/alarm unit of EEW. Since most of these units are connected to internet and equipped with a CPU and memory, we realized that the addition of an inexpensive seismometer and digitizer would transform the receiver into a real-time seismic observatory, which we are calling a home seismometer; these modifications only cost about $20. The home seismometer can help to generate alerts at the time of the occurrence of a large local earthquake by using locally observed data. Also, home seismograms can be used to estimate the amplification factor in sedimentary layers, which will be used to determine the site correction for shaking intensity by comparing the waveform data from the home seismometer against those from nearby Hi-net or K-NET stations. This amplification factor, which is essentially the basis of a shake-map with very-high spatial resolution, will help to establish a safety index of houses/buildings for large earthquakes, since a structure located at a site with large seismic amplification can be damaged more seriously than those with small amplification factors. The installation of home seismometers will create an extremely dense seismic network that is without precedence. We are developing an automatic system that collects waveform data from all home seismometer installations, calculates earthquake parameters in real-time, and then sends back alarms signals based on computed results in order to provide an accurate estimate of the expected shaking level at each house or building. http://www.bosai.go.jp/e/index.html
S21D-04
Istanbul Earthquake Early Warning System
As part of the preparations for the future earthquake in Istanbul a Rapid Response and Early Warning system in the metropolitan area is in operation. For the Early Warning system ten strong motion stations were installed as close as possible to the fault zone. Continuous on-line data from these stations via digital radio modem provide early warning for potentially disastrous earthquakes. Considering the complexity of fault rupture and the short fault distances involved, a simple and robust Early Warning algorithm, based on the exceedance of specified threshold time domain amplitude levels is implemented. The band-pass filtered accelerations and the cumulative absolute velocity (CAV) are compared with specified threshold levels. When any acceleration or CAV (on any channel) in a given station exceeds specific threshold values it is considered a vote. Whenever we have 2 station votes within selectable time interval, after the first vote, the first alarm is declared. In order to specify the appropriate threshold levels a data set of near field strong ground motions records form Turkey and the world has been analyzed. Correlations among these thresholds in terms of the epicenter distance the magnitude of the earthquake have been studied. The encrypted early warning signals will be communicated to the respective end users. Depending on the location of the earthquake (initiation of fault rupture) and the recipient facility the alarm time can be as high as about 8s. The first users of the early warning signal will be the Istanbul gas company (IGDAS) and the metro line using the immersed tube tunnel (MARMARAY). Other prospective users are power plants and power distribution systems, nuclear research facilities, critical chemical factories, petroleum facilities and high-rise buildings. In this study, different algorithms based on PGA, CAV and various definitions of instrumental intensity will be discussed and triggering threshold levels of these parameters will be studied. More complex algorithms based on artificial neural networks (ANN) can also be used [Boese et al., 2003]. ANN approach considers the problem of earthquake early-warning as a pattern recognition task. The seismic patterns can be defined by the shape and frequency content of the parts of accelerograms that are available at each time step. ANN can extract the engineering parameters PGA, CAV and instrumental intensity from these patterns, and map them to any location in the surrounded area. Boese M., Erdik, M., Wenzel, F. (2003), Artificial Neural Networks for Earthquake Early Warning, Proceedings AGU2003 Abstracts, S42B-0155
S21D-05
Perspectives on the use of Active Structural Control Systems for Seismic Early Warning
In thinking about feasibility of earthquake early warning systems (EEWS), the actual question to ask is if they have a potential as tools for real-time seismic risk mitigation, which implies seismology to converge alongside earthquake engineering to real-time loss reduction. In fact, although the evacuation of buildings requires warning time not available in many urbanized areas threatened by seismic hazard, if they may still be used for the real- time protection of critical facilities using automatic systems is the focus of a great deal of research. To this aim, possible interaction between EEWS and semi-active structural control is to be investigated. As a matter of fact, real-time seismology, via the rapid estimation of earthquake's features based on measurements made on the first seconds of the P-waves, allows to predict peak ground motion features of earthquake engineering interest, as the response spectrum at a site, before the quake strikes. This opens new prospects for the adoption of feed-forward control algorithms able to adapt the dynamic features of the structure to better withstand the ensuing ground motion. Nonetheless, feasibility analysis of such EEWS requires the assessment of the risk reduction and cost efficiency due to the security action. An important point, in respect to classical risk assessment, is related to the uncertainties in the estimation of the event and ground motion features, as well as their evolution in time and space. In fact, the performance target of this kind of systems is no longer only related to the maximization of the warning time. The key issue is the calibration, in a full probabilistic approach, of the alarm thresholds and of the decisional rules in order to maximize the loss reduction following the decision, which should account for costs due to false alarms. In this paper these issues, in respect of structural control for seismic early warning in the performance-based earthquake engineering framework, are discussed. http://www.saferproject.net/
S21D-06
Early Warning System: a juridical notion to be built
Early warning systems (EWS) are becoming effective tools for real time mitigation of the harmful effects arising from widely different hazards, which range from famine to financial crisis, malicious attacks, industrial accidents, natural catastrophes, etc. Early warning of natural catastrophic events allows to implement both alert systems and real time prevention actions for the safety of people and goods exposed to the risk However the effective implementation of early warning methods is hindered by the lack of a specific juridical frame. Under a juridical point of view, in fact, EWS and in general all the activities of prevention need a careful regulation, mainly with regards to responsibility and possible compensation for damage caused by the implemented actions. A preventive alarm, in fact, has an active influence on infrastructures in control of public services which in turn will suffer suspensions or interruptions because of the early warning actions. From here it is necessary to possess accurate normative references related to the typology of structures or infrastructures upon which the activity of readiness acts; the progressive order of suspension of public services; the duration of these suspensions; the corporate bodies or administrations that are competent to assume such decisions; the actors responsible for the consequences of false alarm, missed or delayed alarms; the mechanisms of compensation for damage; the insurance systems; etc In the European Union EWS are often quoted as preventive methods of mitigation of the risk. Nevertheless, a juridical notion of EWS of general use is not available. In fact, EW is a concept that finds application in many different circles, each of which require specific adaptations, and may concern subjects for which the European Union doesn't have exclusive competence as may be the responsibility of the member states to assign the necessary regulations. In so far as the juridical arrangement of the EWS, this must be brought back to the general normative context predisposed by every state for the accomplishment of the service of civil protection. In synthesis: EWS are one of the activities engaged in disaster mitigation. Apart from the situation of trans national events, in which case the European Union has an important function in coordination, the activities of prevention are developed in individual states by their own civil protection systems. They are based on the principle of collaboration between the central government and the regional and local authorities, as these are the forms administration organization that are closer to the people and to emergency territorial needs. That being stated, the configuration of the EWS as typology having juridical importance is the result of an reconstructing operation based on elements of positive law and on an interpretative and researching activity able to furnish de iure condendo alternative solutions to the problems that the application of the typology can involve.