The Main Frontal Thrust is the major source of earthquakes in South Asia
THE recent earthquakes in Delhi and nearby places have possibly originated on a NE-SW trending active fault system that is 400 km long. And at north it could crosscut the Main Himalayan/Frontal Thrust, which is the megathrust fault and accounts for most of the earthquakes at the Himalayan front.
The earthquake distribution in the region (Figure on right) suggests a strong pattern that could reflect strain accumulation on ~NE-SW oriented fault system. It could host a major earthquake in the future, which is based on the extent and pattern of seismicity, and the existence of faults in the region. However, the earthquake prediction is not possible, and therefore the best remedy is to prepare for the worst case scenario, which is to prepare for a magnitude 7 and above.
The overall earthquake hazard in South Asia is mainly associated with the Main Himalayan/Frontal Thrust system, but occasionally earthquakes occur away from the front, which should be studied in greater details to understand the possible causes, and to avert the future destruction.
The Main Himalayan/Frontal Thrust (MHT/MFT) is the surficial expression of the megathrust fault where an abrupt topographic high marks the end of Indo-Gangetic plains and the start of frontal mountain ranges. This fault system, which is younger than the other faults system north of it, remind us of the continuous push of the India tectonic plate against the Eurasia plate that has resulted in the formation of series of faults including the megathrust fault since Eocene time.
The occurrence of earthquakes in this region is a result of this push that deform rocks and therefore accumulate strain over the geological past that eventually overcomes the strength of these rocks by nucleating fractures which becomes fault and host earthquakes. Most of the present-day earthquakes are reported on the frontal fault system, with some on the interior faults as well. Some of the prominent earthquakes that are associated with significant damage are: the 2005 Kashmir earthquake (Mw = 7.6), the 1905 Kangra earthquake (Mw = 7.7), the 2015 Nepal earthquake (Mw = 7.9), the 1934 Bihar-Nepal earthquake (Mw = 8.1), the 1879 Shillong earthquake (Mw = 8.1), and the 1950 Assam earthquake (Mw = 8.4). The measurement of interseismic strain is therefore one of the most important aspects to understand the seismic hazard to millions of people who live in the closer vicinity of this deadly fault system.
Progress in building of resilient infrastructure and communities to handle potential earthquake disasters
Undoubtedly, a large portion of population in Kashmir and also across Pakistan, India, Nepal, Bangladesh, Myanmar, Thailand, Malaysia, and Indonesia live on or nearby active fault systems. Unregulated urbanization, coupled with many folds increase in populations, particularly in the last few decades have put these regions at greater earthquake risk.
Indo-Gangetic plains in India abruptly rise at the foothills of Himalayas where Himalayan frontal fault system emerges at surface at certain regions but mostly runs blind. A series of devastating earthquake in the past are a reminder that earthquakes have greatly shaped the landscape and its history, and often some of the major or devastating earthquakes are recorded in the historical text. Surprisingly during the earlier periods of human settlements, including the latest British India, no standard seismic building codes were enforced or implemented. Past records show that during the later stages of British India seismic resistant building codes were planned after the devastating 1935 Quetta earthquake in Baluchistan. Similarly, strengthening techniques are reported to have been implemented after the 1941 Andaman Islands earthquake. It is important to note that Greater India achieved independence from British rule in 1947, but at the cost of regional instability that was marked by one of the most brutal partitions in the world. The entire region was torn on religious lines with the creation of Hindu dominated India and Muslim dominated Pakistan (both East and West Pakistan at that time). What is more, the seeds of partition sprouted again with the emergence of East Pakistan again on blood-filled notions, into an independent nation, Bangladesh. During this time these newly created nations witnessed deadliest riots, bloodshed, and total devastation from national and international wars. Therefore, any previous effort of planning or implementing of the earthquake resistant building codes, as was done in Quetta (read below), was delayed. This clearly suggests that political stability of a nation is paramount to its preparedness to face any kind of disaster, and thus India, Pakistan, and Bangladesh were unable to achieve objectives to safeguard its populations from disasters. All these countries are still struggling to get out of the ruins of partition to implement seismic code, and in India it again picked up in the late 1950s when India was fully independent. India started working towards the development of infrastructure for education and development but it is still struggling to implement the resistant seismic building codes in regions where it is required.
Unfortunately, it takes a devastating earthquake to research, plan, and implement strategy to counter future potential disasters. This was apparent in most of SE Asia after the deadly event of 2004. In Pakistan, the huge loss of life and property that followed the 2005 Kashmir earthquake (see below) reminded authorities that there is a serious need to address this issue (Pathier et al. 2006). Likewise, in India the “Republican Day” earthquake of January 2001, which devastated Bhuj (Gujarat) with more than 19000 casualties did exactly this. After this earthquake both authorities and scientists kick started a comprehensive planning to understand the causes of earthquakes, and to plan and implement the seismic resistant building codes and earthquake education at large. Therefore, the National Information Centre of Earthquake Engineering was established, and with it a widespread 4-year National Programme on Earthquake Engineering Education that is implemented at Indian Institutes of Technology and the Indian Institute of Science, and it has developed a large scale education and training framework in India (Jain, 2016). However, a large portion of work remains to be achieved, particularly in rural areas where implementation of strict building codes is not practiced.
Pakistan shares a similar political background as of India, rests on geological structures, and some of them are active and capable of producing deadly earthquakes. It was the devastating Quetta earthquake of May 30th 1935 that caused a large scale damage in Quetta, and resulted in 60,000 casualties. This perhaps forced the British authorities (who controlled it at that time) to enforce a strict building codes, Quetta Building Code, and it was subsequently adapted in 1937. The construction of unreinforced masonry buildings was forbidden. This standard practice is reported to have saved people and property during the 1941 earthquake. After independent from British India in 1947, British India was torn into two dominions of Pakistan and India on religious lines, resulting in one of the most bloody partitions of human history. These scars were fresh when another massacre unfolded, and the East Pakistan independence struggle heated up with the formation of a new country called Bangladesh. This explains the delay in preparation and implementation of seismic resistant building codes in these regions, and thus after a period of relatively calm political atmosphere Pakistan developed 1986 Pakistan Building Code, which however had many problems, and did not reflect the ground realities, and even earthquake hazard zoning was greatly flawed. And it failed litmus test in 2005 when the Moment magnitude (Mw) 7.6 earthquake devastated Muzafarabad in Pakistani side of Kashmir, and caused extensive damage and a loss of more than 80,000 lives. The country was violently shaken by the loss of people and started to rethink over the adaptation of strict building codes, and in 2007 Pakistan Building Code was adapted, which is mostly based on the 1997 Uniform Building Code. However, on ground the implementation measures will have to go a long way.
- Author is Assistant Professor in Structural Geology, Faculty of Science, Universiti Brunei Darussalam. He can be reached at: [email protected]
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