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Earthquakes, tsunamis and lessons learn from the world

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The horrific shakings from beneath the Earth

The year 2010 starts with two destructive earthquakes consecutively occurred within less than two months. The Haiti earthquake on Jan. 12 and the Chilean earthquake on Feb. 27 once again raise an alarm to the World about the threat of horrible shakings from beneath the earth.

The Haiti earthquake on January 12, 2010

A massive earthquake of magnitude 7.0 struck Haiti at 4:53 p.m., and soon followed by two aftershocks with magnitudes of 5.9 and 5.5. The quake’s epicenter was located about 10 miles southwest of Port-au-Prince, the country's capital and at the depth of 8 km under the sea.

The quake was the worst in the region in more than 200 years. The whole country was shuck, huge swaths of the capital, Port-au-Prince, lay in ruins, and thousands of people lay trapped or dead in the rubble of government buildings, foreign aid offices and shantytowns. Survivors squatted in the streets, some hurt and bloody, many more without food and water, close to piles of covered corpses and rubble. Limbs protruded from disintegrated concrete, muffled cries emanated from deep inside the wrecks of buildings - many of them poorly constructed in the first place.


The Haiti earthquake on January 12, 2010. (Source: Reuters)

At the CARICOM meeting on February 21, Haiti's president, René Préval, called the destruction "unimaginable". The quake left the country in shambles, without electricity or phone service. With little food and water to be had, thousands of residents of the capital, Port-au-Prince, where the destruction was centered, fled the city to seek refuge with relatives in the countryside. A study by the Inter-American Development Bank estimates that the cost could be between $7.2 billion to $13.2 billion, based on a death toll from 200,000 to 300,000.


The disastrous Haiti earthquake on January, 2001 causes thousands of collapsed building and more than 200.000 casualties. Photo: Reuters

The Chilean earthquake on February 27, 2010

The disastrous 8.8 moment magnitude earthquake occurred off the coast of the Maule Region of Chile on February 27, 2010, at 03:34 local time (06:34 UTC). The epicenter of the earthquake was offshore from the Maule Region, approximately 317 km southwest of the capital Santiago and 100 km  north-northeast of Chile's second largest city, Concepción. In Santiago, during 10-30 minutes of shaking, many buildings collapsed and there were power outages and lost of communication in parts of the city. The USGS estimated that the earthquake has focal depth of 35 km.

An aftershock of 6.2 was recorded 20 minutes after the initial quake offshore Chile, 210 km West-Southwestward of Concepción. Two more aftershocks of magnitudes 5.4 and 5.6 followed within an hour of the initial quake in a city named Valparaiso, located 84 km westward of Santiago.


Epicenter of the Chilean earthquake on February 27, 2010. Source: BBC

After earthquake at least 795 people were reported killed, although later reports from Chilean officials indicated that the death toll was significantly overestimated, with the actual identified death toll being 486 as of March 8, 2010.

A tsunami amplitude of up to 2.6 m high was recorded in the sea at Valparaiso. A wave amplitude of 2.34 m was recorded at Talcahuano in the Biobío Region causing damages along  200 km of the Maule coastal zone, which has  250 000 residents. In many places, the tsunami’s runner up area spreads to 2000 km landward. The local authorities predicted the casualties might reach the number 1000.

A boat was “thrown” by tsunami on the shore at Talcahuano, Chile - Photo: AP

Lessons learned

Despite of the fact that both Haiti and Chilean earthquakes are the destructive ones, there are significant differences in their occurrence mechanism and magnitudes. The Haiti earthquake registered at 7 on the moment magnitude scale, is much smaller than the magnitude 8.8 Chilean earthquake. According to the seismologists, the energy produced by the Chilean earthquake is approximately 1000 time bigger than the energy produced by the Haiti event. However, the damage caused by these two earthquakes is far not proportional to their magnitudes. Why?

From scientific point of view, it can be explained that the Haiti earthquake occurred at very shallow depth (8 km) from the Earth’s surface, with epicenter located just several kilometers from the capital city. Meanwhile, the Chilean earthquake was originated at the depth of 35 km, with an off-shore epicenter, affecting a littoral area with low population density.

Another undeniable and very important fact is that the awareness of the risk caused by earthquakes and tsunamis in these two countries are quite different. It is worldwide recognized that Chile has been prepared much better for the response to earthquakes. Being located in a high seismicity area in the World, Chile has been shaken many times by earthquakes, including the 9.5 magnitude event in 1960, which was considered to be largest in the World’s history. As a matter of fact, in Chile school children are trained how to response during earthquake. The Chilean law requests all the constructions in the country to follow anti-seismic design standards. In the first hour after earthquake the Chilean president Michelle Bachelet appeared in public, taken the rescue responsibility in the country.

Meanwhile, earthquakes have never been felt in Haiti since the 19 century. The majority of buildings in the country is made of masonry and unreinforced concrete. These structures usually become the death traps when large earthquakes occur. Therefore, the 7 magnitude Haiti earthquake caused at least 230,000 deaths to that country, making it the 6th deadliest earthquake in recorded history.

Earthquake information and tsunami warning in Vietnam

Two largest earthquakes with magnitude of 6.7 – 6.8 occurred in the Northeastern Vietnam are the Dien Bien earthquake (1935) and the Tuan Giao earthquake (1983). Although there were only slight buildings damage and no casualties reported, the magnitudes of these earthquakes are comparable to Kobe earthquake of January 17, 1995. With epicenter located 20 km from Kobe city and the focal depth of 16 km, the Kobe earthquake caused 6434 death tolls and a loss of aproximately 102 billions USD.

In the southern part of the country the maximum earthquake magnitude recorded reaches 6.1 Richter scale (the Hon Tro earthquake of 1923). More recently, on November 8, 2005, a 5.1 magnitude earthquake occurred offshore Vung Tau city. In the same day a larger 5.5 magnitude earthquake occurred out the coast of Southern Central Vietnam. Regardless the fact that these medium events caused  the shaking intensity (in MSK-64) of 5 in Vung Tau city and of 3 in the Ho Chi Minh city, their effects on urban communities were considerable. In Ho Chi Minh city, shaking from the earthquakes shook the highrise buildings, causing panic in public. Seismic shakings were felt within a large area in Central and South Vietnam territory and offshore. In Phu Quy island windows broken of the houses, while in White Tiger oil field, the 6th well was rocking back and forth under the seismic load.

Up to now no official reports on damage and casualties caused by tsunamis in Vietnam are published. However, the impact of the most destructive in recorded history in December 26, 2004 Indian Ocean tsunami has changed the viewpoint and awareness on earthquake and tsunami threats of many countries in the Southeast Asia. After this event the whole World has gathered in a common effort to build and manipulate an Early Tsunami Warning System (ETWS) for regions, adjacent to the Oceans of the World. The system’s mechanism is based on the linkage between some leading International Tsunami Warning Centers (TWC) and satelite National Tsunami Warning Centers. In case of emergency, the  data and information on the occurrence, travel time of tsunamis are disseminated from leading TWCs to all National TWCs in the region. In results, many National TWCs has been established in the countries adjacent to the World’s Oceans like the Indian and the Pacific Oceans. The National TWCs play an important role in receiving international consultancy and real time information from the regional ETWS and are responsible for the earthquake information and tsunami warning procedure within each country.

Nowadays, coupled with flood and storm, earthquake and tsunami are added in the list of the most destructive natural disasters in Vietnam. Following the disastrous 2004 Indian Ocean tsunami, the Vietnamese Government led immediate efforts to establish a response plan against these natural disasters, including promulgation of the two Prime-Minister’s decisions on Earthquake Information and Tsunami Warning (November 11, 2006) and on Earthquakes and Tsunamis Preparedness (May 29, 2007). The Earthquake Information and Tsunami Warning Centre (EITWC) was established shortly afterward, in September 4, 2007 under the Institute of Geophysics, VAST as the only organization responsible for observing, processing and warning earthquakes and tsunamis information in Vietnam. At EITWC, a 24x7 on-duty operational regime is maintained in order to timely detect the earthquake and tsunami threats. Based of the real-time earthquake data received directly from the national and partly from the regional earthquake monitoring systems, all events with magnitude exceeding 3.5 Richter scale occurring within Vietnamese territory and the adjacent sea areas will be informed to various organisations, responsible for natural disaster response within the country, among which, the first to be informed are VTV, VOV, the Standing Committee for Flood and Storm and National Committee for Search and Rescue.

Soon after its establishment, the EITWC as representative of Vietnam became an official member of the regional and World’s Early Tsunami Warning System. In Asia-Pacific region, the ETWS’s coordinating ETWCs are the Pacific Tsunami Warning Center of the US, which based in Hawaii, and the Northwest Pacific Tsunami Advisory Center (NWPTAC) which belongs to the Japan Meteorological Agency. Tsunami warning activities are carried out between the leading ETWCs and the National ETWCs. As many other countries in the South East Asia, Vietnam still can not afford to equipe the measurment and observational facility in the middle of the ocean to detect tsunamis. Therefore, the tsunami warning messages are issued and directly disseminated from the leading ETWCs to the National ETWCs in the Pacific Ocean region, including Vietnam. This warning procedure is carried out continuously during the transmission of the tsunami and is canceled only when the threat is gone. The warning messages describe all information on comming tsunami as the magnitude, coordinates and depth of earthquake originating tsunami, and also indicate the countries, of which the coasts is probably be affected by the tsunami, the tsunami wave high and travel time, etc. Starting from this point, the tsunami warning is carried out within each country acording to the governmental regulation. Thus, Vietnam is well and on time informed about any tsunami, affecting its coasts on the international standard bases.


Processing of earthquake data at the Earthquake Information and Tsunami Warning Centre

 

Vietnam Centre for Earthquake Information and Tsunami Warning
Nguyen Hong Phuong, Le Huy Minh

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