What do Taiwan's (and Himachal's and New York's) earthquakes teach us about our preparedness?
Building codes, early warning systems, and most importantly, understanding plate movements are crucial if we want to mitigate the impact of future earthquakes
As we read this, the images of destruction from the powerful earthquake near Hualien city of Taiwan on April 3 are pouring in. The strongest to strike Taiwan in a quarter century, the magnitude 7.2 earthquake shook the buildings in Taipei for a minute or more, leaving over 1,000 people injured and at least 12 dead.
Not a decade in recent history has passed without extremely damaging earthquakes. In the last two decades alone, damaging earthquakes have occurred in Indonesia, Japan, China, Italy, Nepal, Afghanistan, Pakistan, Ecuador, Mexico and the Turkey-Syria border. The Taiwan is the latest in this series. Among these, three occurred in India’s vicinity — the 2004 earthquake and its transoceanic tsunami that hit Indian shores was unprecedented. The 2005 India-Pakistan earthquake devastated the Kashmir Valley. The Nepal earthquake of 2015 caused severe devastation in Kathmandu, but spared the Indian side of the Himalayas. More recently, on April 4, the Chamba region of Himachal Pradesh was hit by a magnitude 5.3 earthquake. Quite intriguing that a highly damaging earthquake of magnitude 7.8 hit the Kangra region in 1905, coincidentally on the same day. Perhaps a gentle reminder that history can repeat itself!
The science behind earthquakes
What do all these regions have in common? The answer to this question can be obtained from the global map of earthquakes, which makes it clear that earthquakes are not random, but are concentrated along certain narrow bands. This spatial distribution is justified by the theory of plate tectonics, which explains how the earth’s outermost 100-km-thick layer is fragmented as 15 major fragments or plates which are constantly moving. The source of energy for this motion comes from the earth’s interior where high temperatures keep the rocks in a molten state. As the molten material rises up, it oozes out through deep fractures between the plates. As the lava cools and forms denser rocks, they start to push sideways, creating horizontal motions of the plates. The movement varies from 0.1 cm to 10 cm per year, the Pacific plate being the fastest. Eventually, the moving plates collide with each other, forming mountain chains like the Himalayas, and deep trenches like the Japan Trench. These interacting plate boundaries are under increased stress, which are occasionally released as earthquakes. That explains why there is a pattern to the earthquakes.
Take the case of the Indian and Eurasian plates, which collided about 40 million years ago and created the Himalayas. The Indian plate continues to move to the northeast at roughly 5 cm/year, diving beneath the Eurasian Plate and pushing the Himalayas higher. The compressive forces deform the rocks and create weak zones called faults. As the plate motion continues, more stress accumulates and eventually it will be released by earthquakes.
What happened in Taiwan?
The April 2 earthquake that shook Hualien city occurred near the boundary between the Eurasian and Philippine plates. Here the Philippine plate is moving northwest with respect to the Eurasian plate at a velocity of about 7.8 cm/year, quite fast compared to the Indian plate's motion. Being a plate boundary, earthquakes are not new to this region. Over the last 50 years, six earthquakes of more than 7 magnitude have occurred here. The largest was in September 1999 (Chi-Chi earthquake), just 59 km west of Hualien City, with a magnitude of 7.7, which killed over 2,400 people. Although the new earthquake was as large as its predecessor, the reported death toll is only 10, thanks to the high level of preparedness, including the implementation of strict building codes. An effective early warning system is believed to have issued alerts and stopped the trains. The preparations at Taiwan make a stark contrast with the magnitude 7.8 earthquake that struck Turkey–Syria on February 6 last year, which killed 50,000 people and wiped-out entire stock of buildings.
India has many lessons to learn from these recent examples. The Turkey-Syria earthquake illustrates the need for strict implementation of safer building codes. Developmental projects need to consider the vulnerability of the Himalayan mountains. It is also very important to identify weak buildings, including the heritage structures and retrofit them. An equally important step is to increase the level of preparedness among the people living in the hills and the Gangetic plains. Constant monitoring of the region and a standard operating procedure in the post-earthquake scenario should help minimise the damage.
Experts believe that the Garhwal-Kumaon Himalayas is the most likely candidate for the next large Himalayan earthquake. This is an observation based on the long interval of time, i.e., about a thousand years that has elapsed since the last great earthquake here. If plates are still moving and if the stresses are building up, then earthquakes must occur. When, is the only question. The long silence itself is an alert and we start our preparation, before the signals turn red.
Kusala Rajendran has co-authored, The Rumbling Earth: The Story of Indian Earthquakes, with CP Rajendran. Rajendran was formerly professor of Earth sciences at the Indian Institute of Science, Bengaluru.
