Investigation of Damage in and Around Kathmandu Valley Related to the 2015 Gorkha, Nepal Earthquake and Beyond

Abstract

An earthquake with a magnitude of 7.8 (M w) occurred at 11:56 NST (local time) on 25 April 2015, in the central part of Nepal (Gorkha).We organized a damage survey team and dispatched it to the affected area for several periods following the earthquake (May 26 to June 3: first trip, June 17 to 24: second trip, August 16 to 21: third trip and October 27 to November 2: forth trip) to investigate the damage and collect data. We found traditional construction methods are stronger than imagined. Many traditional earthquake-resistance technologies exist in Nepal. The first and second surveys were to collect timely statistical information on the damage to brick and stone masonry buildings and to confirm the availability of data and their sources for subsequent surveys. We also carried out a first-hand building damage survey in selected areas. The investigation of the strong-motion data set from the USGS Center for Engineering Strong Motion Data includes information from stations in Nepal that continued to function throughout the main shock and the several subsequent strong aftershocks of the 2015 earthquake. The third and fourth surveys were to collect the every building damage survey in selected areas. The motivation behind the survey was to obtain ground truth data for the calibration and improvement of a wide-area damage estimation system that uses satellite data; the system is currently under development by National Research Institute for Earth Science and Disaster Prevention (NEID) and the Japan Aerospace Exploration Agency (JAXA). A survey of the degree of damage was conducted for every house in Sankhu and Khokana by the European Macroseismic Scale (EMS)-98. This report outlines the findings of this investigation team into various aspects of the earthquake disaster in the Kathmandu Valley. The motivation behind the survey was to obtain ground truth data for the calibration and improvement of a wide-area damage estimation system that uses satellite data. Field surveys confirmed that the severely damaged urban area was well detected by the decrease derived from the ALOS-2 satellite SAR data. The higher classification accuracy for non-damaged area helps to detect the damaged urban area using this technique, immediately after a disaster. Keywords Gorkha Á Nepal earthquake Á Kathmandu Á Masonry Á Ground truth 1 Introduction An earthquake with a magnitude of 7.8 (M w) occurred at 11:56 Nepal Standard Time (NST), (local time) on 25 April 2015, in the central part of Nepal (Gorkha).

Damage Reconnaissance of Unreinforced Masonry Bearing Wall Buildings after the 2015 Gorkha, Nepal, Earthquake

“…During the reconnaissance, the observed damage was classified per the criteria introduced by Grunthal (EMS, 98), which defined six damage levels associated to a numerical score, D, which ranges from 0 (undamaged structures) to 5 (maximum damage), according to the descriptions provided in Table 1. The same type of investigation was carried out by other researchers in other zones of Nepal (Ohsumi et al 2016).…”

Detection of damaged urban areas using interferometric SAR coherence change with PALSAR-2

“…Grade 2 or 3 indicates partial damage. Details about the building damage surveys have been described by Ohsumi et al (2016). Building damage surveys were also conducted in the areas, where the decrease in coherence was observed in Kathmandu, Bhaktapur, and Madhyapur Thimi; photographs and videos were taken.…”

Building Damage Assessment in the 2015 Gorkha, Nepal, Earthquake Using Only Post-Event Dual Polarization Synthetic Aperture Radar Imagery

“…Finally, images were projected to WGS 1984, UTM 45 N reference. In this study, we obtained ground-truth data (GTD) by referring to the damage map of Nepal provided by Ohsumi et al (2016) and UNOSAT (2015). The details of our study area and the GTD are shown in Figure 1.…”