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.
Highlights
An earthquake with a magnitude of 7.8 (Mw) occurred at 11:56 Nepal Standard Time (NST), on 25 April 2015, in the central part of Nepal (Gorkha).The epicenter was east-southeast of Lamjung, 77 km south-west of Kathmandu, 28.15 at the north latitude and 84.71 at the east longitude, and the depth was 15 km (USGS)
It was reported that [5,000,000 buildings and houses were damaged and about half those which of had collapsed. This earthquake was officially named as The 2015 Gorkha, Nepal earthquake, since the hypocenter was located in the Gorkha region
We found traditional construction methods are stronger than imagined
Summary
An earthquake with a magnitude of 7.8 (Mw) occurred at 11:56 Nepal Standard Time (NST), (local time) on 25 April 2015, in the central part of Nepal (Gorkha). We surveyed to the affected area during 26 May to 3 June and 17 to 24 to investigate the damage and collect data The findings of this investigation undertaken by this team on the various aspects of the earthquake disaster in the Kathmandu valley. Surveys of building types and damage extent were conducted, for every house in Sankhu and Khokana, Kathmandu, after a second survey term. A high-resolution image from March 12 (before the disaster) was obtained from Google EarthTM prior to the survey This image was used to identify the position of each building before the earthquake, based on which the damage to each building was estimated in accordance with EMS-98. Vr 1⁄4 0:72 Á Vs ð2Þ where R Circular strong motion generation area, Tp Pulse period, Vr Rupture velocity, Vs Shear-wave velocity. Two SMGA might existed near the city of Kathmandu
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