More than 100 aftershocks have been recorded since the devastating Nepal earthquake on April 25, 2015. The 7.8 magnitude tremor hit 80 kilometres west of the capital of Kathmandu and has resulted in widespread damage to life and property. An estimated 9,000 are dead, 18,000 injured and 300,000 structures have been destroyed, many of which were ancient historical sites. The numbers of dead and injured will rise as more rubble is cleared and relief and rescue crews gain access to remote areas.
The Himalayan region, stretching from Afghanistan to Myanmar, is not new to large earthquakes that result in destruction. Seismicity in the region dominantly results from the continental collision of the Indian plate to the south and the Eurasia plate to the north. This collision has been ongoing for the past 65 million years and has resulted in the Himalayas, Karakoram and Hindukush mountain chains with some of the highest peaks in the world such as Mount Everest, K-2, Nanga Parbat, Rakaposhi and Tirich Mir. The conversion occurs along major thrust faults, which are the main central thrust, main boundary thrust and main frontal thrust, from north to south. Major tremors have occurred along these fault lines, including the devastating 2005 Kashmir earthquake, the 1934 Kathmandu earthquake and the 1950 Assam earthquake, which was 8.6 on the Richter scale, the largest recorded in this region.
The Indian and Eurasian plates are converging at a relative rate of 40 to 50 mm per year. The continued collision progressively stores potential energy in the rocks and once the tipping point is reached, energy is released in the form of seismic waves that partly travel inside the earth as P-waves and partly reach the surface as S-waves. This geologic process generates numerous earthquakes and consequently makes this area one of the most seismically hazardous regions on the planet. Shaking results in primary damage to the foundations but significant destruction can occur as a result of secondary effects such as avalanches, landslides, bridge collapses and dam breaks. The avalanches on nearby Mount Everest have killed hundreds and trapped many so far.
Foreshocks occur before a major tremor (main shock) and aftershocks follow the main event. The latest aftershock was recorded at magnitude 7.3, striking east of the capital on May 11. It has worsened the already fragile ground situation. Subsequently, the continuous seismic activity in and around Kathmandu is an indication that the stored energy has not been fully released and the possibility of more aftershocks cannot be ruled out. Even major earthquakes in the region elsewhere are also possible.
Foreshocks, therefore, can be used in earthquake prediction. Geologists issued predictive warnings ahead of the April 25 earthquake. Earthquake prediction is a nascent science and, despite a long history of devastation from earthquakes, it has not been entirely possible to accurately predict an earthquake. Animals change their behaviour before an earthquake but the predictive interval is so short that this tool has not resulted in much success. Seismic gap is another predictive tool; it is the interval between seismic events of a given magnitude. Geologists can predict when “the next big one” will come. The best available tool currently at hand is to use instruments to monitor seismic activity along fault lines. The entire Himalayan region, unfortunately, is investing minimally in placing sensitive instruments to monitor seismic activity.
Even less is invested in preparing to deal with a major seismic event. Nepal, being a developing country, was not prepared to deal with such large-scale devastation. The main airport in Kathmandu has only one landing strip and critical relief equipment and supplies could not be delivered in time to those who needed them the most. Consequently, relief workers had to dig through the rubble with bare hands and many remote parts have not received any relief thus far.
The San Andreas fault in southern California is the most seismically active region in the US and is laced with thousands of monitoring instruments such as creepmeters, pore pressure monitors, strainmeters and tiltmeters, yielding valuable data in real time. On the contrary, the entire Himalayan region has only a few seismic stations yielding sporadic data that cannot be used in real time.
Earthquakes are a natural occurrence that can neither be accurately predicted nor stopped. However, adequate measures can be undertaken to mitigate the damages. The best way to prepare for an earthquake is to secure old structures and build any future structures adhering strictly to building codes. There is no credible data to show that structures in Pakistan, Afghanistan, Nepal, India, Bhutan and Myanmar are built according to building codes that can withstand magnitude seven and higher seismic events. High-rise buildings in the region are a sure way to inflict unnecessary destruction on life and property. The region must invest in developing critical infrastructure to deal with natural and geologic disasters such as earthquakes, floods, tsunamis and landslides.
The writer is a geoscientist by training and a geo-political analyst at the University of Maryland. He is the author of the book Afghanistan: From Cold War to Gold War and tweets @asimusafzai