On April 25th, 2015, Nepal experienced a devastating magnitude earthquake, which measured Mw7.8 on the Richter scale and had its epicenter 80km northwest of Kathmandu at Lumjung. The shocks were intense enough to be felt in northern India, China, Tibet, and Bangladesh. This sample geography essay will explore the natural disaster and relief efforts.
The MHT Fault and Nepal's earthquake
The MHT fault is a 2200km-long zone, running by the southern border of Tibet, and along this fault line, the Indian subcontinent is being pushed underneath Asia (Hand 2015). This collision of earth at the Indian and Eurasian plates is pushing the world’s tallest mountain range, the Himalayans, upwards (Aydan and Ulusay 2015). The MHT fault is divided into three parts:
- The Himalayan Frontal Thrust (HFT)
- Main Boundary Thrust (MBT)
- Main Central Thrust (MCT)
Researchers had for some time reported the presence of active faults in the southwestern areas of the Kathmandu basin as they were displacing Late Pleistocene sediments at a rate of 1mm per year (Aydan and Ulusay 2015).
The International GPS service measures the crustal deformation in order to track and predict the motions of the crustal plates at these faults, but the measurements carried out at GPS stations are not always continuous (Aydan and Ulusay 2015). Therefore, approximate measurements of crustal straining are used to figure annual deformation rates in the hopes of estimating the risk for an earthquake along these faults (Aydan and Ulusay 2015).
The 2015 Gorkha-Nepal earthquake experienced ground motion during the main shock was less than the peak ground acceleration estimates that are used to express the probability of seismic hazard (Goda et al. 3). The earthquake, according to post-analyses, was less destructive than what was expected by predictive modeling and the significant Richter reading (Hand 2015).
Nepal's geography's impact on the earthquake
One factor that affected the ground motion intensity is the situation of Kathmandu on a basin, which is composed of soft sediments at a depth of 550-650m to bedrock (Goda et al. 5). These soft sediments aid in the amplification of low-frequency waves, which tend to be more destructive to taller buildings (Hand 2015). The Kathmandu Valley is a similar setting to that of Mexico City, which has soft lakebed deposits that also amplify ground motions and caused damage to higher buildings in the 1985 Michoacán earthquake (Goda et al. 5).
High-frequency waves cause more damage to lower buildings, while the low-frequency waves abetted and intensified by underlying soft deposits have a more destructive effect on higher buildings, such as the nine-story Dharahara tower in Kathmandu (Hand 2015). This building was rendered into rubble by the 2015 quake, despite the fact that one- and two-story structures remained intact (Hand 2015).
Land type causes destruction
The foundation of the soft sediment is one explanation for this disparity, but slow beginning to the quake’s rupture also lessened the higher frequency seismic waves moving through the ground (Hand 2015). However, some researchers remained mystified by the longer, five-second period waves since they may not be explained fully by the composition of Kathmandu’s basin (Hand 2015).
The amplification of the lower-frequency waves might have been due in part to the particular characteristics of the slip since the quake happened closer to a plastic zone where there are higher temperatures located deeper in the crust (Hand 2015). A rupture in such an area is not as brittle as those occurring in faults not dipping toward the earth, and this difference may account for the gentler character of the quake (Hand 2015).
Damage caused by the quake
Despite some uncertainty about the exact reasons for this, there is still general agreement that the earthquake was smoother than expected in its onset and less destructive than it perhaps should have been as a Mw7.8 event (Hand 2015). The destructive effects of the Nepal earthquake did not depend only on the intensity measurements of the Richter scale; rather, the specific geology of the site crust, building design, and the pressure of population also contributed to the levels of damage (Dey 30).
For example, buildings in Nepal are not constructed to withstand seismic activity, and these structural inadequacies contributed to the number of deaths during the sequence of shocks and aftershocks (Goda et al. 8). Mud-bonded and masonry buildings with wood frames are the most prevalent structures in all areas in Nepal, and such buildings have a low strength factor, which makes them susceptible to seismic waves (Goda et al. 8).
Buildings not built to withstand disaster
The urban areas of the Kathmandu Valley typically have buildings with a cement-bonded, brick or stone basis, and those, along with the more modern, reinforced concrete buildings, are not engineered to withstand earthquakes (Goda et al. 8). As a result, Kathmandu’s urban areas were severely damaged by the April earthquake, and the older buildings in the population-dense valley were completely destroyed (Dey 31). Habitat for Humanity attributed much of Th hindrances during their humanitarian mission was caused by delapidated buildings.
On the other hand, scientists were surprised that the death toll was not greater, considering the density of the population, the vulnerability of the buildings, and the nearness of the epicenter to Kathmandu (Zielinski 2015). Less than one percent of Kathmandu’s structures were collapsed in the earthquake, and however devastating, the damage was nowhere near what scientists would have predicted given the power of the quake (Zielinski 2015).
Nepal's research to prevent future earthquakes
Researchers, however, predict that the western portion of the fault is still facing a high risk for seismic hazard, especially since the last huge quake, estimated at Mw8.5, in that segment happened long ago in 1505 (Zielinski 2015). This region has historically seen tremendous earthquakes, and built-up strain, accumulating over 510 years, is locked and loaded for a potentially massive rupture (Hand 2015).
This has many worried that the failure to detect slow, precursor slips in the locked fault through careful monitoring may pose a serious problem for Nepal (Hand 2015). It is difficult to predict how severe a future quake might be in the country or when it will occur, but recent geophysical studies of the Nepalese landscape hold some promising insights. Studies supported by NASA’s satellite radar imagery and enhanced by the work of the Institute of Earth and Environmental Science may have opened up a new window onto the future movements of the ground in Nepal (CIT 2015).
Conclusion
Nepal remains vulnerable to an even more massive and destructive earthquake and other hazards in the future because of its relatively young geology, its changing climatic conditions, and its unplanned settlements (Poudel et al. 2015). Its increased urbanization in some of its most vulnerable areas will likely pose serious humanitarian challenges in the case of such an event.
The World Bank has ranked Nepal as the eleventh most vulnerable country in the world to earthquakes, and Geo-Hazards International puts Kathmandu as one of the world’s most threatened cities in terms of seismic activity (Poudel et al. 2015). Fortunately, with the advent of new GPS monitoring stations in the country, along with a more detailed analysis of satellite imagery, researchers have much more data to build a dynamic and comprehensive map of the 2015 earthquake (Zielinski 2015).
Works Cited
Aydan, Ömer, and Ulusay, Resat. “A Quick Report on the 2015 Gorkha (Nepal) Earthquake and Its Geo-engineering Aspects.” 2015. Web. 25 March 2016. http://www.iaeg.info/wp-content/uploads/QuickRepot_2015NepalEarthquake_Aydan_Ulusay_IAEG.pdf.
California Institute of Technology. “Studies of Recent and Ancient Nepal Quakes Yield Surprises.” Jet Propulsion Laboratory. 16 December 2015. Web. 25 March 2016. http://www.smithsonianmag.com/science-nature/why-nepal-earthquake-was-especially-bad-historic-cultural-sites-180956184/?no-ist.
Dey, Sourav. “A Devastating Disaster: A Case Study of Nepal earthquake and Its Impact on Human Beings.” IOSR Journal of Humanities and Social Science 20.7 (2015): 28-34.
Goda, Katsuichiro, Kiyota, Takashi, Pokhrel, Rama, Chiaro, Gabriele, Katagiri, Toshihiko, Sharma, Keshab, and Wilkinson, Sean. “The 2015 Gorkha Nepal Earthquake: Insights from Earthquake Damage Survey." Frontiers in Built Environment 1 (2015): 1-15.
Hand, Eric. “Why the Nepal Earthquake was Far Less Damaging than Feared.” Science Magazine. 6 August 2015. Web. 25 March 2016. http://www.sciencemag.org/news/2015/08/why-nepal-earthquake-was-far-less-damaging-feared.
Poudel, Bharat, Fitzgerald, Gerry, Clark, Michele, Mehta, Amisha, and Poudyal, Meen. “Disaster Management in Nepal: Media engagement in the Post-2015 Framework for Disaster Risk Reduction.” GRF Davos Planet@Risk 3.2 (2015): 209-221.
Zielinski, Sarah. “Why the Nepal Earthquake was Especially Bad for Cultural Sites.” The Smithsonian Magazine. 6 August 2015. Web. 25 March 2016. http://www.smithsonianmag.com/science-nature/why-nepal-earthquake-was-especially-bad-historic-cultural-sites-180956184/?no-ist.