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Research about Nepal

Source-linked reports with geographic coverage including Nepal.

35 records · Page 2Linked to original sources
USGS2016

Building damage survey and microtremor measurements for the source region of the 2015 Gorkha, Nepal, earthquake

We performed a damage survey of buildings and carried out microtremor observations in the source region of the 2015 Gorkha earthquake. Our survey area spans the Kathmandu valley and areas to the east and north of the valley. Damage of buildings in the Kathmandu valley was localized, and the percentage of the totally collapsed buildings was less than 5 %. East of the Kathmandu valley, especially in Sindhupalchok district, damage of buildings was more severe. In the center of Chautara and Bahrabise, towns in Sindhupalchok district, the percentage of the totally collapsed houses exceeded 40 %. North of the Kathmandu valley, the damage was moderate, and 20–30 % of the buildings were totally collapsed in Dhunche. Based on the past studies and our microtremor observations near the strong motion station, the H/V spectrum in Kathmandu has a peak at around 0.3 Hz, which reflects the velocity contrast of the deep sedimentary basin. The H/V spectra in Bahrabise, Chautara, and Dhunche do not show clear peaks, which suggests that the sites have stiff soil conditions. Therefore, the more severe damage outside the Kathmandu valley compared with the relatively light damage levels in the valley is probably due to the source characteristics of the earthquake and/or the seismic performance of buildings, rather than the local site conditions.

Earth, Planets and Space↗
USGS2016

Introduction to the special issue on the 25 April 2015 Mw 7.8 Gorkha(Nepal) earthquake

On April 25, 2015, a moment magnitude (M w ) 7.8 earthquake struck central Nepal, breaking a section of the broader Himalayan Front that had been largely quiescent in moderate-to-large earthquakes for much of the modern seismological era. Ground shaking associated with the event resulted in a broad distribution of triggered avalanches and landslides. The ensuing aftershock sequence was punctuated by a Mw 7.3 event 17 days after the mainshock. The combined effects of these earthquakes and secondary hazards have led to the Gorkha earthquake becoming the worst natural disaster in Nepal since the 1934 Nepal-Bihar earthquake, causing close to 9000 deaths and severely injuring over 21,000 people ( OCHA, 2015 ). Despite the devastating effects of this earthquake, the convergent margin that hosted it is thought to be capable of much larger ruptures—perhaps as large as Mw 9 ( Feldl and Bilham, 2006 ). The 2015 Gorkha rupture lies just to the west of the 1934 M 8.0–8.4 event ( Sapkota et al., 2013; Bollinger et al., 2014 ). Unlike the 1934 event, which has been documented in paleoseismic trenches along the Himalayan Front (e.g., Sapkota et al., 2013 ), and other large ruptures along the arc (e.g., Lavé et al., 2005; Kumar et al., 2006 ), the 2015 event did not rupture to the surface (e.g., Galetzka et al., 2015 ). As a result, some researchers have suggested that the Gorkha earthquake was not as large, or as damaging, as might have been expected based on our (albeit limited) understanding of historic earthquakes, seismic hazard and risk (e.g., Bilham, 2015; Hough, 2015 ). Important questions surrounding the earthquake and its regional setting thus arise. What were the detailed characteristics of the rupture and the aftershock sequence, and what is the relationship between mainshock slip and subsequent seismicity? Why did this event not rupture to the surface? Was damage less than should have been expected; and if so, why? What role did path effects, such as basin amplification, play? Do details of the earthquake sequence allow us to better understand regional seismotectonics, and in turn, future risk? Discussion of these and other issues has been ongoing since the earthquake; a large body of literature already exists that characterizes details of the earthquake sequence and its effects. This special issue attempts to gather a wide variety of detailed studies that wholly characterize this event to a degree that has not yet been possible. The studies herein provide an improved understanding of the Gorkha earthquake, its impact on the region, and its place in the broader seismotectonic history of the Himalayan Front.

Gorkha↗
USGS2016

Geomorphic and geologic controls of geohazards induced by Nepal’s 2015 Gorkha earthquake

The Gorkha earthquake (magnitude 7.8) on 25 April 2015 and later aftershocks struck South Asia, killing ~9000 people and damaging a large region. Supported by a large campaign of responsive satellite data acquisitions over the earthquake disaster zone, our team undertook a satellite image survey of the earthquakes’ induced geohazards in Nepal and China and an assessment of the geomorphic, tectonic, and lithologic controls on quake-induced landslides. Timely analysis and communication aided response and recovery and informed decision-makers. We mapped 4312 coseismic and postseismic landslides. We also surveyed 491 glacier lakes for earthquake damage but found only nine landslide-impacted lakes and no visible satellite evidence of outbursts. Landslide densities correlate with slope, peak ground acceleration, surface downdrop, and specific metamorphic lithologies and large plutonic intrusions.

Science↗
USGS2016

Buildings (EERI Earthquake Reconnaissance Team Report: M7.8 Gorkha, Nepal Earthquake on April 25, 2015 and its Aftershocks)

The most common building typologies in Nepal are reinforced concrete (RC) frame buildings with masonry infill walls, unreinforced masonry (URM) bearing wall buildings, and wood frame buildings (Figure 5-1). The RC frames with masonry infills are commonly constructed in urban and semi-urban areas. Most of these buildings are three to five stories high, and most privately owned buildings are non-engineered. High rise buildings (up to 17 stories high) are also found in Kathmandu, but their number is limited. Burnt clay bricks are widely used as masonry infill walls; external walls are generally one full brick thick (~ 230 mm), and internal walls are one half brick thick. URM bearing wall buildings are an obvious choice for the population in rural areas and the outskirts of cities, primarily to limit the material expenses. Such buildings are generally two to four stories high and constructed using burnt clay brick masonry or stone masonry with cement, lime, or mud mortar. In some of the older constructions, a different mortar known as Vajra (a mix of lime and brick dust) is also observed. These buildings have either wooden or reinforced concrete flooring. A hybrid type of construction also prevails in semi-urban and rural areas, where wood frames are used in the ground story front façade, and rest of the house is made of unreinforced masonry bearing walls. Wood frame houses (generally two to three stories high) are also observed in rural areas where the material for such construction is easily available.

Kathmandu Valley↗
USGS2015

Ground motions from the 2015Mw 7.8 Gorkha, Nepal, earthquake constrained by a detailed assessment of macroseismic data

To augment limited instrumental recordings of the M w 7.8 Gorkha, Nepal, earthquake on 25 April 2015 (Nepali calendar: 12 Baisakh 2072, Bikram Samvat), we collected 3831 detailed media and first-person accounts of macroseismic effects that include sufficiently detailed information to assign intensities. The resulting intensity map reveals the distribution of shaking within and outside of Nepal, with the key result that shaking intensities throughout the near-field region only exceeded intensity 8 on the 1998 European Macroseismic Scale (EMS-98) in rare instances. Within the Kathmandu Valley, intensities were generally 6–7 EMS. This surprising (and fortunate) result can be explained by the nature of the mainshock ground motions, which were dominated by energy at periods significantly longer than the resonant periods of vernacular structures throughout the Kathmandu Valley. Outside of the Kathmandu Valley, intensities were also generally lower than 8 EMS, but the earthquake took a heavy toll on a number of remote villages, where many especially vulnerable masonry houses collapsed catastrophically in 7–8 EMS shaking. We further reconsider intensities from the 1833 earthquake sequence and conclude that it occurred on the same fault segment as the Gorkha earthquake.

Gorkha↗
USGS2015

Rapid characterization of the 2015 M w 7.8 Gorkha, Nepal, earthquake sequence and its seismotectonic context

Earthquake response and related information products are important for placing recent seismic events into context and particularly for understanding the impact earthquakes can have on the regional community and its infrastructure. These tools are even more useful if they are available quickly, ahead of detailed information from the areas affected by such earthquakes. Here we provide an overview of the response activities and related information products generated and provided by the U.S. Geological Survey National Earthquake Information Center in association with the 2015 M 7.8 Gorkha, Nepal, earthquake. This group monitors global earthquakes 24  hrs/day and 7  days/week to provide rapid information on the location and size of recent events and to characterize the source properties, tectonic setting, and potential fatalities and economic losses associated with significant earthquakes. We present the timeline over which these products became available, discuss what they tell us about the seismotectonics of the Gorkha earthquake and its aftershocks, and examine how their information is used today, and might be used in the future, to help mitigate the impact of such natural disasters.

Seismological Research Letters↗
USGS2015

Strong-motion observations of the M 7.8 Gorkha, Nepal, earthquake sequence and development of the N-shake strong-motion network

We present and describe strong-motion data observations from the 2015 M 7.8 Gorkha, Nepal, earthquake sequence collected using existing and new Quake-Catcher Network (QCN) and U.S. Geological Survey NetQuakes sensors located in the Kathmandu Valley. A comparison of QCN data with waveforms recorded by a conventional strong-motion (NetQuakes) instrument validates the QCN data. We present preliminary analysis of spectral accelerations, and peak ground acceleration and velocity for earthquakes up to M 7.3 from the QCN stations, as well as preliminary analysis of the mainshock recording from the NetQuakes station. We show that mainshock peak accelerations were lower than expected and conclude the Kathmandu Valley experienced a pervasively nonlinear response during the mainshock. Phase picks from the QCN and NetQuakes data are also used to improve aftershock locations. This study confirms the utility of QCN instruments to contribute to ground-motion investigations and aftershock response in regions where conventional instrumentation and open-access seismic data are limited. Initial pilot installations of QCN instruments in 2014 are now being expanded to create the Nepal–Shaking Hazard Assessment for Kathmandu and its Environment (N-SHAKE) network.

Seismological Research Letters↗
USGS2015

Geotechnical effects of the 2015 magnitude 7.8 Gorkha, Nepal, earthquake and aftershocks

This article summarizes the geotechnical effects of the 25 April 2015 M 7.8 Gorkha, Nepal, earthquake and aftershocks, as documented by a reconnaissance team that undertook a broad engineering and scientific assessment of the damage and collected perishable data for future analysis. Brief descriptions are provided of ground shaking, surface fault rupture, landsliding, soil failure, and infrastructure performance. The goal of this reconnaissance effort, led by Geotechnical Extreme Events Reconnaissance, is to learn from earthquakes and mitigate hazards in future earthquakes.

Gorkha↗
USGS2015

Introduction to the focus section on the 2015 Gorkha, Nepal, earthquake

It has long been recognized that Nepal faces high earthquake hazard, with the most recent large ( M w >7.5) events in 1833 and 1934. When the 25 April 2015 M w 7.8 Gorkha earthquake struck, it appeared initially to be a realization of worst fears. In spite of its large magnitude and proximity to the densely populated Kathmandu valley, however, the level of damage was lower than anticipated, with most vernacular structures within the valley experiencing little or no structural damage. Outside the valley, catastrophic damage did occur in some villages, associated with the high vulnerability of stone masonry construction and, in many cases, landsliding. The unexpected observations from this expected earthquake provide an urgent impetus to understand the event itself and to better characterize hazard from future large Himalayan earthquakes. Toward this end, articles in this special focus section present and describe available data sets and initial results that better illuminate and interpret the earthquake and its effects.

Gorkha↗
USGS2015

Assessment of existing and potential landslide hazards resulting from the April 25, 2015 Gorkha, Nepal earthquake sequence

Introduction On April 25, 2015, a large ( M 7.8) earthquake shook much of central Nepal and was followed by a series of M >6 aftershocks, including a M 7.3 event on May 12, 2015. This earthquake and aftershocks, referred to as the “Gorkha earthquake sequence,” caused thousands of fatalities, damaged and destroyed entire villages, and displaced millions of residents. The earthquakes also triggered thousands of landslides in the exceedingly steep topography of Nepal; these landslides were responsible for hundreds of fatalities, and blocked vital roads and trails to affected villages (fig. 1). Landslides caused by the Gorkha earthquake sequence continue to pose both immediate and long-term hazards to villages and infrastructure within the affected region. Some landslides blocked rivers and thus created another potential concern for villages located downstream. With the support of the United States Agency for International Development (USAID), Office of Foreign Disaster Assistance (OFDA), and in collaboration with earthquake-hazard organizations from both the United States (for example, U.S. National Science Foundation Geoengineering Extreme Event Reconnaissance [GEER] Team) and Nepal (International Centre for Integrated Mountain Development [ICIMOD]), the U.S. Geological Survey (USGS) responded to this crisis by providing landslide-hazard expertise to Nepalese agencies and affected villages. In addition to collaborating with an international group of remote-sensing scientists to document the spatial distribution of landsliding in the first few weeks following the earthquake, the USGS conducted in-country landslide hazard assessments for 10 days beginning May 24, 2015. Much of the information obtained by the USGS during their time in Nepal was conveyed directly to affected villages and government agencies as opportunities arose. Upon return to the United States, data organization, interpretation, and synthesis began immediately to provide a rapid assessment of landslide hazards for use by Nepalese agencies during the 2015 summer monsoon (typically occurring from June through September). This report provides a detailed account of assessments performed in May and June 2015 and focuses on valley-blocking landslides because they have the potential to pose considerable hazard to many villages in Nepal. First, we provide a seismological background of Nepal and then detail the methods used for both external and in-country data collection and interpretation. Our results consist of an overview of landsliding extent, a characterization of all valley-blocking landslides identified during our work, and a description of video resources that provide high resolution coverage of approximately 1,000 kilometers (km) of river valleys and surrounding terrain affected by the Gorkha earthquake sequence. This is followed by a description of site-specific landslide-hazard assessments conducted while in Nepal and includes detailed descriptions of five noteworthy case studies. Finally, we assess the expectation for additional landslide hazards during the 2015 summer monsoon season.

Open-File Report↗
USGS2015

Slip pulse and resonance of Kathmandu basin during the 2015 Mw 7.8 Gorkha earthquake, Nepal imaged with space geodesy

Detailed geodetic imaging of earthquake rupture enhances our understanding of earthquake physics and induced ground shaking. The April 25, 2015 Mw 7.8 Gorkha, Nepal earthquake is the first example of a large continental megathrust rupture beneath a high-rate (5 Hz) GPS network. We use GPS and InSAR data to model the earthquake rupture as a slip pulse of ~20 km width, ~6 s duration, and with peak sliding velocity of 1.1 m/s that propagated toward Kathmandu basin at ~3.3 km/s over ~140 km. The smooth slip onset, indicating a large ~5 m slip-weakening distance, caused moderate ground shaking at high >1Hz frequencies (~16% g) and limited damage to regular dwellings. Whole basin resonance at 4-5 s period caused collapse of tall structures, including cultural artifacts.

Gorkha↗
USGS2011

Fine-scale spatio-temporal variation in tiger Panthera tigris diet: Effect of study duration and extent on estimates of tiger diet in Chitwan National Park, Nepal

Attempts to conserve declining tiger Panthera tigris populations and distributions have experienced limited success. The poaching of tiger prey is a key threat to tiger persistence; a clear understanding of tiger diet is a prerequisite to conserve dwindling populations. We used unpublished data on tiger diet in combination with two previously published studies to examine fine-scale spatio-temporal changes in tiger diet relative to prey abundance in Chitwan National Park, Nepal, and aggregated data from the three studies to examine the effect that study duration and the size of the study area have on estimates of tiger diet. Our results correspond with those of previous studies: in all three studies, tiger diet was dominated by members of Cervidae; small to medium-sized prey was important in one study. Tiger diet was unrelated to prey abundance, and the aggregation of studies indicates that increasing study duration and study area size both result in increased dietary diversity in terms of prey categories consumed, and increasing study duration changed which prey species contributed most to tiger diet. Based on our results, we suggest that managers focus their efforts on minimizing the poaching of all tiger prey, and that future studies of tiger diet be of long duration and large spatial extent to improve our understanding of spatio-temporal variation in estimates of tiger diet.

Chitwan National Park↗
USGS2010

Current status of brown bears in the Manasalu Conservation Area, Nepal

Although brown bears ( Ursus arctos ) are rare in the Himalayan region, populations have been documented in alpine habitats of Pakistan and India. Brown bears were once known to exist in both Nepal and Bhutan, but current information on their numbers and distributions was lacking. We document the presence of brown bears in the Manasalu Conservation Area (MCA) in Nepal using field surveys and interviews with local people. We were able to confirm the existence of a remnant population based on finding bear scat and locations where bears excavated for Himalayan marmots ( Marmota himalayana ). Based on interviews with local people, it appeared that the presence of brown bears in the area is relatively recent and likely a result of immigration of bears from the Tibetan Autonomous Region. Interviews with local herders also indicated that livestock losses from brown bear predation amounted to approximately 318,000 Nepali rupees (US $4,240) from February 2006 through July 2008.

Manasalu Conservation Area↗
USGS2006

Landscape response to deglaciation in a high relief, monsoon-influenced alpine environment, Langtang Himal, Nepal

Significant glacial fluctuations and rapid paraglacial reworking of glacigenic sediments characterize the Middle and Late Holocene of the Langtang Khola Valley, Central Nepal Himalaya. Geomorphic mapping and beryllium-10 cosmogenic radionuclide (CRN) dating of moraines and paraglacial fans were undertaken to test the existing paraglacial fan, terrace and moraine chronologies. The new dating compares favorably with prior studies that utilized radiocarbon, adding additional support to the assumption that fan and terrace formation are strongly linked to deglaciation. Fan and terrace denudation rates are so rapid in this region, averaging ∼33 mm/yr, that no depositional landforms older than 5 ka are preserved within 250 m of the valley floor. In this region, high rates of denudation during the Late Quaternary are driven by a combination of rapid tectonic uplift, numerous glacial fluctuations and intense weathering driven by an active monsoon climate. Extensive reworking of glacigenic sediments in Langtang during the latter half of the Holocene is consistent with studies completed in other areas of the Himalaya that are strongly influenced by the monsoon.

Langtang Himal↗
USGS1998

Use of a subsurface plankton layer to benefit a cage-culture fishery in Lake Phewa, Nepal

The Nepalese government and some 225 families in the private sector are engaged in an expanding aquaculture program in lakes Phewa, Begnas and Rupa in the Pokhara Valley, Nepal (Swar & Pradhan 1992). Bighead carp ( Aristichthys nobilis ) and silver carp ( Hypopthalmichthys molitrix ) are propagated in hatchery ponds and are raised to market size in mesh enclosures (having sides, tops and bottoms) suspended to a depth of 2 m. Some 300 cages are presently in use, with annual production varying from 3.4 kg/m 3 Lake Phewa to about 5 kg/m 3 in lakes Begnas and Rupa (Swar & Pradhan 1992). These cage-reared fish are an important source of animal protein and revenue (Swar 1981). Tourism in the region provides growers a continuous market for their fish.

Lake Begnas, Lake Phewa, Lake Rupa↗