Field Reconnaissance after the 25 April 2015 M 7.8 Gorkha Earthquake

Abstract

Fault scarps and uplifted terraces in young alluvium are frequent occurrences along the trace of the northerly dipping Himalayan frontal thrust (HFT). Generally, it was expected that the 25 April 2015 M 7.8 Gorkha earthquake of Nepal would produce fresh scarps along the fault trace. Contrary to expectation, Interferometric Synthetic Aperture Radar and aftershock studies soon indicated the rupture of the HFT was confined to the subsurface, terminating on the order of 50 km north of the trace of the HFT. We undertook a field survey along the trace of the HFT and along faults and lineaments within the Kathmandu Valley eight days after the earthquake. Our field survey confirmed the lack of surface rupture along the HFT and the mapped faults and lineaments in Kathmandu Valley. The only significant ground deformation we observed was limited to an ∼1 km-long northeast-trending fracture set in the district of Kausaltar within Kathmandu. This feature is interpreted not to be the result of tectonic displacement, but rather a localized extension along a ridge. Our survey also shows the ubiquitous presence of fallen chimneys of brick kilns along the HFT and within the Kathmandu Valley. Measurements of a small subset of fallen chimneys across the region suggest a degree of systematic fall direction of the chimneys when subdivided geographically.

Unearthed lessons of 25 April 2015 Gorkha earthquake (MW 7.8): geotechnical earthquake engineering perspectives

“…However, primary surface rupture was not observed as reported by Angster et al (2015). Ground failure affected the local road networks in Kathmandu and Lalitpur (Figure 18(a,b)).…”

“…Rapid dissemination of geological field investigation, accelerometric interpretation, some geotechnical effects, rapid seismo-tectonic characterization, structural performance and other aspects of Gorkha earthquake are reported by several researchers (e.g. Angster et al 2015;Bhattarai et al 2015;Hayes et al 2015;Martin et al 2015;Moss et al 2015;Ahmad & Singh 2016;Dutta et al 2016;Gautam & Chaulagain 2016;Gautam et al 2016a;Rai et al 2016;Gautam 2017) and some site-specific reconnaissance reports can be found elsewhere.…”

“…Moreover, the Araniko Highway that connects Nepal with China was obstructed by large-scale ground fissure in Bhaktapur and Sindhupalchowk districts. Ground failure occurred along the Araniko Highway in Bhaktapur was »1.5 km long with a depth of »1.28 m at most (for details, see Angster et al 2015) and affected hundreds of residential buildings (Figure 18(c)). Ground fissures in Dhading district were found to be occurring in many villages and the depth was measured to »3 m at most.…”

Detecting Landscape Disturbance at the Nasca Lines Using SAR Data Collected from Airborne and Satellite Platforms

“…resolution of better than 20 m over a strip 250 km wide [33]. Interferometric Sentinel-1 data is being used widely for the rapid imaging of surface displacements caused by earthquakes, subsidence, and landslides [35], as well as other applications at various spatial scales.…”

Common structural and construction deficiencies of Nepalese buildings

“…1d), such gap was measured up to 0.40 m. Reinforcement in infill walls were not found to be provided in residential constructions with exception to some apartments. Due to lack of reinforced walls in most of the brick kiln chimneys, almost all chimneys suffered from partial to complete collapse in Kathmandu valley [12]. More significantly, the connection between the structural components was also found to be poor.…”