SEISMIC ALERT SYSTEM OF MEXICO CITY
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BACKGROUND
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Historical information from the beginning of XX century and some studies about the seismic activity of Guerrero's coast, recorded between 1984
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and 1987, shows that it exists a condition of seismic silence between Zihuatanejo and Acapulco ports, within a region where a movement must take place with proportions similar to the one that caused big damages in 1985 to Mexico city. In 1986, It has been recommended to CONACyT, to develop a technical and social feasibility study to instrument a seismic alert system with sensors in Guerrero's coast to reduce the size of the damages of a future seismic disaster that may occur in the valley of Mexico.
The seismic alert system SAS, operates in a continuous way since August of 1991 and its objective is to give seismic anticipated warning to Mexico city, in case of an earthquake occurs in the region that is covered with sensor stations in Guerrero.
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Epicenters of earthquakes, 1985 through June 1987, which yielded one or more accelerogram on the Guerrero array. Source: Earthquake Spectra, August 1988 pp.635-646
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DESCRIPTION
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The seismic alert system has 12 seismic sensing stations in Guerrero's coast that value the forecast of the local seismic activity magnitude and send it by radio to the central station in Mexico city.
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Distribution of the Stations Sensors of SAS
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Sensor Station of SAS
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FUNCTIONING
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SAS can emit seismic warning in the valley of Mexico when it recognizes the beginning of the big
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earthquakes that occurs in Guerrero's coast. In the city, with a distance bigger than 320 km to Guerrero's coast, the most destructive effect can be warned with an approximated opportunity of 60 sec, thanks to distance and to the difference between the propagation speed of seismic and radio waves. The fastest face of a seismic wave travels at 8 Km/s. Fortunately the slowest but strongest is propagated at 4 Km/s.
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Zone of capture of SAS and the aproximated distance between the coast of Gerrero and City.
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WHAT IT IS ABLE TO DO
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The seismic alert is automatically activated when the sensor stations inform and confirm the beginning of a great magnitude earthquake. The early warning of the start of a strong earthquake with an approximated time of 60 sec. before the impact reaches the valley of Mexico and Toluca, gives us the opportunity to do procedures and actions that increases our advantage to reduce the possibility of suffering a new seismic disaster. A seismic early warning sign is powerful when preventive simulacrums are practiced, for people protection and also to secure risk industrial processes. Since it started, the seismic early warning system has gone through a continuous program of activities to secure its strategic service. It is essential, spite of the routinish performance of the activities of conservation and operation, to evaluate daily its function and to analyze
the results to improve its efficacy, to essay solutions for different technical problems that may end in failures, as to perfection its procedures and integrate new technologies to assure its future viability.
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What to do when the seismic alert system sounds.
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WHAT IT IS NOT ABLE TO DO
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The seismic alert system is not activated when the earthquake's magnitude is smaller than 5. SAS can not give a prognostic of magnitude that corresponds with the right warning notice out of the capture zone neither, even though it can detect an earthquake out of it. Nevertheless, facing the experiences occurred during the second semester of 1999, the convenience of extending the covering of the sensing stations to other regions that generates strong earthquakes that may affect Mexico city, is discussed now.
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STATISTICS
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For more than 12 years of continuous operation SAS has achieved to determine more than 58 earthquakes with magnitudes between 4 and 7.3. From these events SAS has detected 47 moderated range events and 11 strong range. Table shows the number of earthquakes recordered by SAS, which 46 of them generated "preventive warning" and 11 generated " public warning".
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USERS
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Since August 1993, SAS gives a public warning service to people in the valley of Mexico and Toluca. In 2007 the cities of
Acapulco and
Chilpancingo
were added like users of the system.
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Among the users of the
Mexico city,
it is remarkable the Secretaría de Educación Pública, who recommends schools to listen to the radio transmissions of the broadcasting stations that belong to Radiodifusores del valle de México. SAS warning is used in: subway, Protección Civil of Mexico city and Mexico state, in Tv channels 11 and 22, la Secretaria de Obras y Servicios del DF, UNAM, UAM, the habitational unit "El Rosario", among others.
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Subway, schools, radio stations and TV, habitational units, hospitals and public in general. |
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All the users except radio, television and subway. |
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Information kept like event. |
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