Earthquake loss estimation for the Kathmandu Valley

Abstract

The capital city, Kathmandu, is the most developed and populated place in Nepal. The majority of the administrative offices, headquarters, numerous historical monuments, and eight World Heritages sites are in the Kathmandu Valley. However, this region is geologically located on lacustrine sediment basin, characterized by a long history of destructive earthquakes. The past events resulted in great damage of structures, losses of human life's and property, and interrupted the social development. Therefore, earthquake disaster management is one of the most serious issues in highly seismically active regions such as the Kathmandu Valley. In recent years, the earthquake risk in this area has significantly increased due to uncontrolled development, poor construction practices with no earthquake safety consideration, and lack of awareness amongst the general public and government authorities. In this context, this study explores the realistic situation of earthquake losses due to future earthquakes in Kathmandu Valley. To this end, three municipalities: (a) Kathmandu metropolitan city (KMC), (b) Lalitpur Sub-Metropolitan City (LSMC) and (c) Bhaktapur Municipality (BMC) are selected for study. The earthquake loss estimation in the selected municipalities is performed through the combination of seismic hazard, structural vulnerability, and exposure data. For what concerns the seismic input, various earthquake scenarios considering four seismic sources in Nepal were adopted. Regarding the exposure, data about the type of existing buildings, population, and ward level distribution of building typologies is estimated from the recent national census survey of 2011. The economic losses due to the scenario earthquakes are determined using fragility functions. The commonly used standard fragility curves are adopted for adobe, brick/stone with mud mortar buildings, and brick/stone with cement mortar buildings. For the reinforced concrete structures, a new fragility model was derived considering four construction typologies: i) current construction practices (CCP), ii) structures according to the Nepal buildings code (NBC), iii) structures according to the modified Nepal building code (NBC+) and iv) well designed structures (WDS). In this study, a set of fragility functions is converted into a vulnerability model through a consequences model. Finally, the ward level distribution of damage for each building typology, building losses and the corresponding economic loss for each scenario earthquake is obtained using the OpenQuake-engine. The distribution of damage within the Kathmandu Valley is currently being employing in the development of a shelter model for the region, involving various local authorities and decision makers.

Seismic Vulnerability of Urban Vernacular Buildings in Nepal: Case of Newari Construction

“…In Bhaktapur, above 80% building stocks were the vernacular Newari buildings and most of the remaining buildings were substandard RC buildings (for details see: Chaulagain et al [2013]). During Gorkha earthquake, relatively lower value of PGA and short duration of shaking may have resulted low damage statistics and hence previous loss estimation models depicted by Chaulgain et al [2016] were not able to represent the actual damage scenario.…”

“…For instance, at 0.4 g PGA, existing curve depicts 60% probability of collapse whereas newly derived curve highlights 30% collapse probability only. It should be carefully noted that the comparison is made between broadly comparable building classes; however, brick masonry class used by Chaulgain et al [2016] does not exhaustively represent vernacular Newari buildings. Hence, the discrepancies are obviously expected in fragility functions.…”

Structural performance and associated lessons to be learned from world earthquakes in Nepal after 25 April 2015 (MW 7.8) Gorkha earthquake

“…For example: the seismic hazard assessment by Chaulagain et al [15]) depicts the possibility of higher hazard level near the epicenter of 2015 Gorkha earthquake, apart from this, Chaulagain et al [13]) delineated the high vulnerability of non-engineered to poorly engineered masonry structures however no attentions were paid for such findings. Similarly, the seismic loss estimated by Chaulagain et al [16]) and site effects and structural damage analysis performed by Gautam and Chamlagain [27]) and Gautam et al [30]) significantly correlate the damage pattern and losses along with damage distribution during 2015 Gorkha earthquake. So, due account of the novel findings and associated precautions will be significant to reduce the losses due to earthquakes in Nepal.…”

Strong-Motion Characteristics and Visual Damage Assessment Around Seismic Stations in Kathmandu after the 2015 Gorkha, Nepal, Earthquake

“…We compared the Fragility Curve for load bearing masonry-cement mortar and RC infill frame structures of Nepal (JICA 2002) with the damage ratio ( Figure 12). We also considered the fragility curve for moderate damage of load bearing masonry-cement mortar and RC infill frame structures (Chaulagain et al 2016). The difference in values of fragility curves for the same type of buildings from two different research studies can be attributed to difference in method of fragility curve construction.…”