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Wide Area Sounders are the critical final component of disaster warning systems

04 July 2016

The 26 December 2004 Indian Ocean tsunami killed 230,000 people in 14 countries, swamping coastal communities in 14 countries with waves up to 30m high.

System schematic
System schematic

The 11 March 2011 Japanese tsunami with 40m high waves was the result of the fourth most powerful earthquake in the world. It killed 16,000 people, a relatively low number compared with the Indian Ocean disaster, attributable in part to the presence of sophisticated monitoring systems set up in the region in the aftermath of the Indian Ocean event.

Following the 2004 disaster, the UN set up the Indian Ocean Tsunami Warning System and although the country was not directly affected by the 2004 tsunami, the Philippines set up a similar early warning system to protect inhabitants of the west coasts of the islands. This area, which faces the 5,400m deep Manila trench located between the Philippines and Vietnam, is particularly exposed to tsunami. Earthquakes frequently occur in the Manila trench; the last major event was in 2006, and the probability of a major tsunami at some time in the future is very high.

London-based E2S Warning Signals supplies the high output wide area sounders that provide the critical audible messages and tones in the Philippines system, which is being progressively rolled out from the densely populated coastal towns and cities to the rest of the region. The components of the alerting system include detection sensors, a GSM data communication system, data visualisation, interpretation, local tsunami emergency decision tools and multiple local tsunami warning stations equipped with GSM-activated E2S A121 AX Appello sounders. Ultrasonic tide gauge sensors, which detect sudden rise and fall of sea level, and ‘dry’ and ‘wet’ sensors, detecting post-earthquake receding waters, are placed offshore on up to 15m high poles. Information generated by the sensors is sent in real time to the Philippine Institute of Volcanology and Seismology, PHIVOLCS, Data Receiving Centre. Satellite activation backup is provided in case the GSM-GPRS communication network is down. For sustainability, both the sensors and the tsunami warning stations are solar powered.

If the earthquake is strong enough to cause a tsunami, the PHIVOLCS will activate the network of local warning stations to alert the population to give them sufficient time to prepare and flee their homes following designated evacuation paths leading to higher ground. 

The solar powered local tsunami warning stations rely on E2S Warning Signals’ A121AX Appello 126 dB(A) output user-recordable alarm horns, which have a 300m effective range, to generate the audible alarms to alert the population to an impending emergency. The A121AX can store up to 2 minutes (4 x 30 seconds) of custom messages that can be played with or without the 45 embedded alarm tones. Three units per station, spaced at 120° intervals, ensure all-round audibility, and the units generate warning alert tones followed by recorded messages to ensure that the warning is unambiguous. 

Tsunami warning is one example of the use of wide area sounders; closer to home, E2S have also supplied sounders for use in Chesil Beach flood warning systems and RNLI lifeboat launch warning systems. Wide area sounders are primarily intended for use in quarries, on large industrial and petrochemical sites and for civil defence requirements. Outputs range from 120 to 140 dB(A), giving effective ranges of 300 to 750m from the sounder. The devices typically generate multiple internationally recognised alarm tones including fire, security, civil defence, alert, COMAH (SEVESO II) toxic gas alarms and disaster warnings for flood, tsunami, tornado and other severe bad weather conditions. To learn more about the Appello X family of products watch the video

In 2011 E2S provided sounders for a Tsunami Evacuation Alert System at Penco, Chile. As part of UNESCO’s and the European Commission Humanitarian Aid Department’s (ECHO) project to provide tsunami preparedness and risk reduction, a number of sirens and backup systems were installed to Penco's coastal areas to alert the 40,000 plus population in case a tsunami was likely to occur. The battery backed up system comprises A131 131 dB(A) alarms. The A131 alarm system can be initiated through radio communications from the Hydrographic and Oceanographic Service of the Chilean Navy (SHOA) whenever they consider the population of Penco need to be warned of a possible tsunami.

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