Your search within this document for 'Earthquake' resulted in 18 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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“...ET AL. were injured during this event. The earthquake also resulted in an estimated 35% loss of the country’s gross domestic product (GDP) (USGS 2015a). A significant portion of these losses have been attributed to landsliding. One avalanche on Mount Everest reportedly killed 21 people, making April 25 the deadliest day in the mountain’s history; another avalanche in Langtang valley resulted in 250 casualties. The earthquake occurred in one of the most active tectonic environments in the world, where the Indian and Asian tectonic plates converge at a rate of 45 mm/yr (Sella et al. 2002). A portion of this convergence (20 mm/yr) is accommodated by the Main Himalayan Thrust (MHT), which has been responsible for historical Mw 8.0—8.5 earthquakes and, based on paleoseismic records, great medieval earthquakes (Bilham 2004, Wesnousky et al. 2017). Major pulses of sedimentation followed these events, presumably associated with large-scale, earthquake-triggered landsliding and subsequent debris...”
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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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“...along the route from Soti Khola in the south. At the time of the site reconnaissance (June 2015), both routes were cut off by landslides and the only access was by helicopter. The field focus for this study area was a series of landslides 10 km east of the epicenter along a 10-km section of the Budhi Gandaki River near Machhakholagaon. Based on interviews conducted with villagers, 24 people (out of a population of 350-500) were killed by landslides, with no reported deaths directly from the earthquake and associated building collapses. The geology of the study area comprises a series of phyllites, quartzites, schists, and gneiss of the Greater Himalyan Cystalline Zone in the north and the Lesser Himalayan units in the south (Figure 2). According to the USGS ShakeMap (USGS 2015b), the study area experienced PGAs of 0.23-0.77 g, as shown in Figure 2. METHODS EMPLOYED AND DATA COLLECTED Landslide assessment was conducted with the following methodologies: • High-resolution, high-quality satellite...”
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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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“...permitting identification of landslides that were at least 10 m2 in dimension. Ground-based assessment, conducted from four-wheel-drive vehicles (as well as on foot) can cover approximately tens to hundreds of square kilometers per day depending on field conditions. It generates primarily qualitative observations with the focus more on greater area coverage and less on detail. Quantitative measurements are time-consuming and affect a team’s ability to investigate larger areas. Road conditions, earthquake damage, and lack of resources also reduce the ability to cover ground. However, ground-based assessments provide the opportunity to understand landslide mechanisms and assess the geomechanical characteristics of rock masses. In this project, approximately 10 days in the field were required to inspect a 326-km2 area in the Trishuli and Indrawati basins and to investigate approximately 30 landslides more closely. Empirically, the hours of additional office work just to organize the data collected...”
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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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“...had fresh, unweathered, and locally rough surface discontinuities. These observations indicate that the rock masses, already weakened by weathering, failed as a result of earthquake shaking and associated seismic stresses. For example, damage to the rock mass and tension cracks with widths varying between 0.2 m and a few centimeters running parallel to the ridgeline were observed for a landslide in the Budhi Gandaki area, as shown in Figure 5. This damage was common for many of the landslides and preconditioned the remaining slopes for subsequent gravity or monsoon-induced failures. An example of a rock slide on a 75-m-high mica schist and granitic gneiss slope, located near Melamchi, is shown in Figure 6. Figure 6d shows the location of the landslide as observed in the satellite imagery before and after the earthquake. The landslide is clearly visible, but very limited additional information beyond its total area could be collected from these satellite images alone. The slope was, on average...”
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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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“...S104 ZEKKOS ET AL. weathered, disintegrated rock wm Less weathered, blocky rock Pre-Earthquake Residual soil Post-Earthquake More weathered disintegrated rock Jr? \ GSI=25-45 Less weathered blocky rock, GSI=45-65 Figure 6. Landslide near Melamchi (3-D point cloud): (a) overview; (b) cross section; (c) closer view (6-cm/pixel mean resolution) of back-scarp with annotated layers and GSI parameters (from Marinos et al. 2005); (d) pre- and post-earthquake satellite images (from Roback et al. 2017). Debris cone m Residual soil parameters for the different units observed in Figure 6c is shown in Table 2. These strength parameters could be used for subsequent back-analysis of failed slopes, although it should be recognized that the failed material might have been weaker (more weathered and fractured) than the material observed on the back-scarp. ROCK FALLS There was clear evidence of rock falls in all three study areas. In many cases, these rock falls were difficult to discern in the satellite...”
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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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“...the predominant lithology in each basin. The observations for these basins were consistent with the inferences from Roback et al. (2017) for the entire study area—that there was no systematic lithological dependence of landslide occurrence for this event. Other rock mass factors, such as rock structure, fracturing, and weathering patterns, also influence landslide trends, but they are not considered here. Contrary to observed PGA-landslide density correlations shown for several other large earthquake-landsliding events (Meunier et al. 2007, Li et al. 2017), landslide density for the Gorkha event correlated poorly with PGA (Martha et al. 2017, Galien et al. 2017, Roback et al. 2017), likely because PGA is not generally strongly correlated with landsliding compared to other ground motion characteristics (Rathje and Antonakos 2011, Bray and Travasarou 2007, Athanasopoulos-Zekkos et al. 2016) but also because ground motion intensities (including PGA) are poorly known for this event given the...”
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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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“...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 Report. doi:10.3133/off20151142. Dhital, M. R.,...”
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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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“...Reynolds, J M., 2012. ‘Struc-ture-ffom-motion’ photogrammetry: a low-cost tool for geoscience applications, Journal of Geomorphology YTf 300-314. Wilkinson, S., Whitworth, M., DeJong, M., Ghosh, B., Burton, P., Tallet-Williams, S., Novelli, V., Franco, G., White, T., Trieu, A., Datla, S., Lloyd, T., and Goda, K., 2015. Earthquake impacts on mountain communities—observations and lessons from the Mw 7.8 Gorkha earthquake of 25 April 2015, Proceedings of the Tenth Pacific Conference on Earthquake Engineering: Building an Earthquake-Resilient Pacific, 6-8 November 2015, Syndey, Australia, The Australian Earthquake Engineering Society and the New Zealand Society for Earthquake Engineering. Wobus, C. W., Hodges, K. V., and Whipple, K. X., 2003. Has focused denudation sustained active thrusting at the Himalayan topographic front?, Geology 31(10), 861-864. (Received 16 December 2016; accepted 8 August 2017)...”