Your search within this document for 'Nepal' resulted in 13 matching pages.
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“...Observations of Landslides Caused by the April 2015 Gorkha, Nepal, Earthquake Based on Land, UAV, and Satellite Reconnaissance Dimitrios Zekkos,a) m.eeri, Marin Clark,b) Michael Whitworth,c) William Greenwood,a) s.m.eeri, A. Joshua West,d) Kevin Roback,b) Gen Li,d) Deepak Chamlagain,e) John Manousakis,^ Paul Quackenbush,d) William Medwedeff,b) and Jerome Lynch,a) m.eeri Thousands of landslides occurred during the April 2015 Gorkha earthquake in Nepal. Previous work using satellite imagery mapped nearly 25,000 coseismic landslides. In this study, the satellite-based mapping was analyzed in three areas where field deployment was also conducted—the Budhi Gandaki, Trishuli, and Indrawati river valleys—to better characterize the landslides. Unmanned aerial vehicles (UAVs) were deployed to map the three-dimensional (3-D) geometry of failed slopes using photogrammetry, as well as to characterize rock structure and strength. The majority of landslides were rock slides along the ridges and the steeper...”
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“...OBSERVATIONS OF LANDSLIDES CAUSED BY THE APRIL 2015 GORKHA, NEPAL, EARTHQUAKE S97 April 25th Mw7.8 Elev (nr mainshock # May 12th Mw7.2 aftershock e; • co-seismic landslide □ landslide mapping extent Machhakhok 28 ^andaki > Fig.HB 'rishuliR. ndrawati/ lamchi R. - 86°E Kathmandu 50 Kilometers Figure 1. Area strongly affected by landsliding during the April-May Gorkha earthquake sequence in Nepal. Black line = northern limit of landslide mapping from high-resolution satellite images (Roback et al. 2017); white shading = basin areas studied (these areas do not cover the entire Trishuli and Budhi Gandaki drainage basins); red outline = areas surveyed by manned vehicle or UAVs; black arrows = “physiographic transition” from Lesser to High Himalaya topography in central Nepal, defined by the prominent break in hillslope gradient between the arrows (Wobus et al. 2003). - NEPAL 1 v. study area \Kathmandu ( weeks at a time. The geology of the study area primarily comprised various metamorphic rocks...”
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“...S98 ZEKKOS ET AL. 28 N 0.4g 50 km Budhi Gandaki R. wkholagon 0.2g Trishuli R. ^ nSyabru Besi j&Qriche# Kathmandu Geologic Units of Nepal Tethwn Himalaya k»er Himplwm tegwKe Mi Mesozoics Carbonate Rand Paleozoics Other Sed. Rocks High Himalayan Sequence Quartzite Band ■■Two - Mica Leucogranite 1 1 Other Meta. Rocks ■11Paleozoic Granites Paleocene - ^Hlllqh Himalayan Gneisses Miocene Rocks Neoproterozo* Nepheline Syanite Cambrian Rocks of Gorklra ■ : Proterozoic Lime-Silicates Paleoproterozolc HOther Proterozoic Rocks Gneisses • landslide locations PGA(g) Plto-Pleislocene Sediments S* April 26th epicenter Neogene Siwaliks May 12lhepicener Indrawati/ Melamchi R. 86°E Figure 2. Geologic map (Dhital 2015), PGA (Shake Map v. 9, released 2 July 2015; USGS 2015b), and landslides (Roback et al. 2017). Study areas highlighted by saturated colors. BUDHI GANDAKI BASIN Machhakholagaon, lying at the intersection of a number of important routes to the north, is usually accessed either by four-w...”
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“...OBSERVATIONS OF LANDSLIDES CAUSED BY THE APRIL 2015 GORKHA, NEPAL, EARTHQUAKE S99 at a resolution of less than 1 m, supplemented with Astrium’s Pleiades submeter-resolution satellite data accessed via Google Earth and used where DigitalGlobe data were cloud-covered or distorted. Mapping involved the creation of landslide polygons with separate identification of source area and total landslide area. Shuttle radar topography mapping (SRTM) digital topography at 30-m horizontal resolution was used to derive elevation (Farr et al. 2007). In total, 24,915 landslides, with a total landslide area of 86 km2, were identified in a mapped area of 28,345 km2. Results and first-order regional interpretations were presented by Roback et al. (2017), whose data set was used in this study to provide more detailed insights into regional landslide patterns in the selected basins. • In situ land-based observations during field deployment, which allowed for site-specific assessment of landsliding. Accessibility...”
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“...OBSERVATIONS OF LANDSLIDES CAUSED BY THE APRIL 2015 GORKHA, NEPAL, EARTHQUAKE SIOI affected by the level of detail as well as the accuracy required in the developed model. Development of the 3-D model required SfM methodology, as presented by Westoby et al. (2012), using Pix4d and Agisoft Photoscan software. Detailed discussion of the procedures used in this study is found in Greenwood et al. (2016) for two selected landslides. In addition to computation and data analysis time, a significant amount of time was invested in obtaining permission from the Nepalese government to fly the UAVs in the specific areas. The statistics reported in Table 1, especially those related to ground-based and UAV-based assessments, are the estimates for this specific expedition; they generally vary depending on the conditions in the field, the type of data required, the UAV and imagery technology used, and the experience of the deployment team members. FIELD OBSERVATIONS Numerous landslides were observed in...”
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“...OBSERVATIONS OF LANDSLIDES CAUSED BY THE APRIL 2015 GORKHA, NEPAL, EARTHQUAKE SI03 Figure 5. (a) Landslide along a ridgeline in the Budhi Gandaki region; (b) tension crack behind the failed ridge line. (Figure 3) and indicative of the failure of a broken-up rock mass mechanically characterized as Hoek and Brown strength material (Hoek and Brown 1980). A 3-D overview of the rock-slide is shown as a UAV-derived point cloud in Figure 6a. The outlined debris cone is sloping at approximately 35°. The landslide scarp exposes the rock mass structure over an area approximately 40 m high and 45 m wide. Ground control points were placed only in accessible locations at the toe of the landslide, and laser measurements were used to appropriately scale the entire model. An annotated cross section derived from the point cloud is shown in Figure 6b. An annotated close-up of the back-scarp of the rock slide is shown in Figure 6c. The geological strength index (GSI) is a critical parameter for the geomechanical...”
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“...OBSERVATIONS OF LANDSLIDES CAUSED BY THE APRIL 2015 GORKHA, NEPAL, EARTHQUAKE SI05 Table 2. Indicative Hoek and Brown cohesion and friction angle for landslide ground units near Melamchi Ground unit Cohesion (kPa) Friction angle (°) Unweathered, GSI = 45—65 rock 2,000 59 Weathered, GSI = 25—45 rock 570 42 Highly weathered with built-up soil 180 24 rock blocks downhill (Figure 7), these rock falls were a significant hazard in the area. One of the most characteristic examples of coseismic rockfall is the rock fall that damaged the construction site of a water supply tunnel near Timbu in the Melamchi study area (Figure 8). Several large (>10-m3) rock blocks detached from higher slopes and impacted the construction site during the earthquake. The workers were in the tunnel and remained safe; however, one student, who was part of a group of 30 students visiting the construction site, was killed. SOIL TERRACE SLOPE FAILURES The Trishuli, Melamchi, and Indrawati rivers cut into fill terraces that...”
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“...OBSERVATIONS OF LANDSLIDES CAUSED BY THE APRIL 2015 GORKHA, NEPAL, EARTHQUAKE SI07 Figure 10. Pre-monsoon (May 2015) and Post-monsoon (January 2017) satellite images: (a) UAV-enabled orthophoto; (b) DEM of monsoon-induced debris flow near Timbu (shown in Figure 11) caused by coseismic landslide debris. its blocks as shown in the inset of Figure 10c. In comparison, the satellite imagery was on average 2.5 m/pixel. The UAV was subsequently flown to the east to investigate the potential relationship between the debris flow and coseismic landslides. UAV footage confirmed that the debris flow originated at a higher elevation and was connected to the debris from a number of rock slides, as shown in Figure 11, highlighting the influence of the earthquake not only on coseismic landslides but also on subsequent geologic hazards. Figure 11 shows the UAV-inspected area and the landslides that occurred and contributed not only to sediment transport downstream but also, in some cases, to the debris...”
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“...OBSERVATIONS OF LANDSLIDES CAUSED BY THE APRIL 2015 GORKHA, NEPAL, EARTHQUAKE SI09 Figure 12. (a) Frequency distribution and cumulative density function of landslide size in each study area and in all areas combined; (b) normalized landslide frequency as a function of distance to channel in the three study areas (inset: main channels). (a) (b) (c) Figure 13. (a) Budhi Gandaki, (b) Trishuli, and (c) Indrawati overlaying slope angle, PGA, and mapped landslides showing mapped landslides concentrated in steep-slope areas. Red outline = field reconnaissance areas. different common drainage area thresholds were considered, 50,000 m2 was the maximum that captured the trunk river system in all three catchments; however, this also included some portions of major tributaries. Because smaller drainage area thresholds would have increased the percentage of landslides with close proximity to streams (Roback et al. 2017), decreasing the threshold size increased the similarity of the three study basins...”
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“...OBSERVATIONS OF LANDSLIDES CAUSED BY THE APRIL 2015 GORKHA, NEPAL, EARTHQUAKE S Figure 14. Relationship between landslide source area and total landslide area for the three study areas. Landslide source areas and total areas were identified separately, allowing for an investigation of the relationship between the two. Overall, as shown in Figure 14, all three study regions showed similar trends between source area (Asource) and total areas (Atotal), with larger source areas being correlated with larger total landslide areas. Regression analyses resulted in Equation 1 with R2 = 0.896, which is consistent with the regional equation proposed by Roback et al. (2017): Atotal = 5.736 xAsoJ" (1) Thus despite differences in total landslide area between the three basins studied here (Figure 12a), the ratio between source and full areas is statistically constant. SUMMARY AND CONCLUSIONS The April 2015 Gorkha earthquake in Nepal caused thousands of landslides and significant associated damage. The...”
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“...their assistance during the 2015 field expedition to Nepal. Site reconnaissance in the Budhi Gandaki river basin was undertaken as part of the Earthquake Field Evaluation Team (Wilkinson et al. 2015) mission to Nepal, in conjunction with the UN Office for the Coordination of Humanitarian Affairs (UNOCHA). REFERENCES Athanasopoulos-Zekkos, A., Pence, H., and Lobbestael, A., 2016. Ground motion selection for seismic slope displacement evaluation analysis of earthen levees, Earthquake Spectra 32(1), 217-237. Bilham, R., 2004. Earthquakes in India and the Himalaya: tectonics, geodesy, and history, Annals of Geophysics 47, 839-858. Bray, J. D., and Rathje, E. M., 1998. Earthquake-induced displacements of solid-waste landfills, Journal of Geotechnical and Geo environmental Engineering 124(3), 242-253. Collins, B. D., and Jibson, R. W., 2015. Assessment of Existing and Potential Landslide Hazards Resulting from the April 25, 2015 Gorkha, Nepal, Earthquake Sequence, U.S. Geological Survey Open-File...”
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“...OBSERVATIONS OF LANDSLIDES CAUSED BY THE APRIL 2015 GORKHA, NEPAL, EARTHQUAKE SI 13 small unmanned aerial vehicles and structure from motion computer vision following the April 1, 2014 Chile earthquake, Journal of Geotechnical and Geoenvironmental Engineering 143(5), 04016125. Gong, J., Wang, D., Li, Y., Zhang, L., Yue, Y., Zhou, J., and Song, Y., 2010. Earthquake-induced geological hazard detection under hierarchical stripping classification framework in the Beichuan area, Landslides 7(2), 181-189. Hashash, Y. M. A., Tiwari, B., Moss, R. E. S., Asimaki, D., Clahan, K. B., Kieffer, D. S., Dreger, D. S., Macdonald, A., Madugo, C. M., Mason, H. B., Pehlivan, M., Rayamajhi, D., Acharya, I., and Adhikari, B., 2015. Geotechnical Field Reconnaissance: Gorkha (Nepal) Earthquake of April 25 2015 and Related Shaking Sequence, GEER Association Report No. GEER-040. Hoek, E., and Brown, E. T., 1980. Empirical strength criterion for rock masses, Journal of Geotechnical Engineering Division 106(GT9)...”
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“...Merchel, S., Rugel, G., Fort, M., and Korup, O., 2015. Repeated catastrophic valley following medieval earthquakes in the Nepal Himalaya, Science 351, 147-150. doi: 10.1126/science.aac9865. Turner, D., Lucieer, A., and de Jong, S. M., 2015. Time series analysis of landslide dynamics using an unmanned aerial vehicle, Remote Sensing 7(2), 1736-1757. U.S. Geological Survey (USGS), 2015a. PAGER estimates for M 7.8-36km E of Khudi, Nepal, available at http://earthquake.usgs.gov/earthquakes/eventpage/us20002926”\l”pager. U.S. Geological Survey (USGS), 2015b. ShakeMap for M 7.8-36km E of Khudi, Nepal, available at https://earthquake.usgs.gOv/earthquakes/eventpage/us20002926#shakemap. Wesnousky, S. G., Kumahara, Y., Chamlagain, D., Pierce, I. K., Karki, A., and Gautam, D., 2017. Geological observations on large earthquakes along the Himalayan frontal fault near Kathmandu, Nepal, Earth and Planetary Science Letters 457, 366-375. Westoby, M. J., Brasington, J., Glaser, N. F., Hambrey, M. J., and Reynolds...”