Japan was hit by the largest earthquake ever recorded in the region on Friday, 11 March 2011. The original magnitude of moment magnitude (Mw) 8.9 has been now revised to Mw 9.0, making it globally the fifth largest recorded earthquake. This great mega thrust earthquake occurred at 05:46 Coordinated Universal Time (UCT), 130 km off the east coast of the Oshika Peninsula. The earthquake caused a massive tsunami, which hit the Japanese coast within minutes. The heights of the waves reached 10 m and the water reached up to 10 km inland. There was heavy damage to houses, roads, railways, airports and ports. Live coverage of the tsunami waves destroying and moving buildings, roads, aircrafts, ships and cars were heart wrenching. Japanese Prime Minister, Naoto Kan declared, “In the 65 years after the end of the World War II, this is the toughest and the most difficult crises for Japan”.
As far as earthquake research is concerned, Japan is considered one of the most advanced countries. The Sendai earthquake tragedy would have been several times more severe, but for the scientific and technological interventions and implementation of the defensive mechanism by Japanese scientists, engineers and administration. For example, the Earthquake Early Warning systems are operational in Japan. These systems determine the location and magnitude of an earthquake based on the recording of the longitudinal (P) waves, which travel at a velocity of about 7 km per sec. Maximum damage in an earthquake is done by transverse (S) waves that are slower and travel with a velocity of about 4 km per sec. About a minute prior to effects of the Sendai earthquake being felt in Tokyo, the Earthquake Early Warning System, connected to over 1000 seismometers in Japan, sent out a warning message on television to millions about the anticipated accelerations in the Tokyo region. It is believed that this early warning saved many thousands of lives.
Earthquakes in Asia Pacific Region
The Asia Pacific region accounts for half of the global population and about 80 per cent of all losses due to natural hazards. Earthquakes and the resultant tsunamis are one of the worst natural hazards and the impact is seen within a very short time. The secondary effects can continue to distress a region for months. The maximum human lives lost in any natural disaster were in the 23 January 1556 Shanxi Province, China earthquake (M 8.0) which claimed 830,000 lives. The Kanto earthquake (M 8.1) of 1 September 1923 claimed 142,800 lives mostly in Tokyo and Yokohama, Japan. A 12 m high tsunami was generated, horizontal displacements of up to 4.5 m were recorded and the fires continued for weeks. The official loss of human lives in the 27 July 1976 Tangshan earthquake (M 7.5) of China is 255,000, although some believe that as many as 655,000 lives were lost. The 26 December 2004 Sumatra earthquake was of Mw 9.2. This earthquake and the resultant tsunami claimed an estimated 228,000 human lives. The total number of lives lost in the Sendai Mw 9.0 earthquake is not likely to exceed 30,000. The credit goes to the Japanese scientists, engineers, administration and disciplined citizens in limiting the loss of human life.
Setting up An Earthquake Early Warning System in India
After the 26 December 2004 disaster, India has successfully set up a modern Tsunami and Storm Surge Warning Centre, which was made functional in a record time of 30 months and has been performing successfully for the past three and half years. With its success, the required steps can be taken to warn the citizens about the anticipated high accelerations in the big Indian cities when a major earthquake occurs in a nearby region.
As of now, earthquake forecast is not available for practical application. However, it is known that major damage by an earthquake is due to transverse and surface waves compared to the longitudinal waves. If a major earthquake occurs about 300 km away from a big city, and there is a good network of seismic stations in the vicinity of the epicentre, its focal parameters can be determined in 15 to 20 seconds. This would provide a lead time of about a minute to warn the public. For example, a source of major earthquakes in north India are the central Himalaya, which are about 200 to 300 km away from the National Capital Region (NCR). Thus, the Earthquake Early Warning system could effectively be deployed for the NCR with respect to earthquakes originating in the central Himalaya. The efficacy of such a system has been proved in the recent Sendai earthquake. Such systems are already operating in many parts of the world such as Japan, Mexico, Romania and Taiwan. To implement such a scheme, extensive infrastructure and training will be required. However, the results of successful implementation are overwhelming, as seen in case of the recent Sendai earthquake.
Adapted by the author from ‘The Mw 9 Sendai, Japan Earthquake of 11 March 2011’ by Harsh Gupta, News and Notes, Journal of Geological Society of India, April 2011, Vol.77, No.4, pg 388.