scholarly journals Multiple remote sensing assessment of the catastrophic collapse in Langtang Valley induced by the 2015 Gorkha Earthquake

2016 ◽  
Author(s):  
Hiroto Nagai ◽  
Manabu Watanabe ◽  
Naoya Tomii ◽  
Takeo Tadono ◽  
Shinichi Suzuki
Keyword(s):  
Visual Interpretation ◽  
Snow Melting ◽  
Multiple Sources ◽  
Gorkha Earthquake ◽  
Water Stream ◽  
Array Type ◽  
River Bed ◽  
2015 Gorkha Earthquake ◽  
Surface Models ◽  
Hazardous Zone

Abstract. We demonstrated an assessment of the sediments caused by a catastrophic avalanche, induced by the main shock of the 2015 Gorkha Earthquake in Nepal. Calculation of decreasing coherence and visual interpretation of amplitude images by means of the Phased Array-type L-band Synthetic Aperture Radar-2 (PALSAR-2) have a high potential for delineating the hazardous zone. These delineated outlines area highly consistent with that from a high-resolution optical image of WorldView-3 (WV-3). The delineated sediment collapse areas were estimated as 0.63 km2 (PALSAR-2 coherence calculation), 0.73 km2 (PALSAR-2 visual interpretation), and 1.09 km2 (WV-3), respectively. In the WV-3 image, surface features were classified into 15 segments, with the flowing, scattering, and other characteristics implying different physical properties; the different features suggest sequential collapse from multiple sources. By means of satellite-derived pre- and post-event digital surface models, differences in the surface altitudes of the collapse events estimated the total volume of the sediments as 6229.1 x 103 m3, with an error possibility between 5363.3 x 103 to 7314.8 x 103 m3, most of which are distributed along the river bed and the water stream. Further altitude measurements after ice/snow melting would reveal a contained volume of melting ice and snow, which will contribute to numerical avalanche simulation and source considerations.

scholarly journals Multiple remote-sensing assessment of the catastrophic collapse in Langtang Valley induced by the 2015 Gorkha earthquake

2017 ◽  
Vol 17 (11) ◽  
pp. 1907-1921 ◽  
Author(s):  
Hiroto Nagai ◽  
Manabu Watanabe ◽  
Naoya Tomii ◽  
Takeo Tadono ◽  
Shinichi Suzuki
Keyword(s):  
Monsoon Season ◽  
Deposition Process ◽  
Visual Interpretation ◽  
Gorkha Earthquake ◽  
Water Stream ◽  
2015 Gorkha Earthquake ◽  
Himalayan Mountain ◽  
Hazard Process ◽  
Langtang Valley

Abstract. The main shock of the 2015 Gorkha Earthquake in Nepal induced numerous avalanches, rockfalls, and landslides in Himalayan mountain regions. A major village in the Langtang Valley was destroyed and numerous people were victims of a catastrophic avalanche event, which consisted of snow, ice, rock, and blast wind. Understanding the hazard process mainly depends on limited witness accounts, interviews, and an in situ survey after a monsoon season. To record the immediate situation and to understand the deposition process, we performed an assessment by means of satellite-based observations carried out no later than 2 weeks after the event. The avalanche-induced sediment deposition was delineated with the calculation of decreasing coherence and visual interpretation of amplitude images acquired from the Phased Array-type L-band Synthetic Aperture Radar-2 (PALSAR-2). These outline areas are highly consistent with that delineated from a high-resolution optical image of WorldView-3 (WV-3). The delineated sediment areas were estimated as 0.63 km2 (PALSAR-2 coherence calculation), 0.73 km2 (PALSAR-2 visual interpretation), and 0.88 km2 (WV-3). In the WV-3 image, surface features were classified into 10 groups. Our analysis suggests that the avalanche event contained a sequence of (1) a fast splashing body with an air blast, (2) a huge, flowing muddy mass, (3) less mass flowing from another source, (4) a smaller amount of splashing and flowing mass, and (5) splashing mass without flowing on the east and west sides. By means of satellite-derived pre- and post-event digital surface models, differences in the surface altitudes of the collapse events estimated the total volume of the sediments as 5.51 ± 0.09  ×  106 m3, the largest mass of which are distributed along the river floor and a tributary water stream. These findings contribute to detailed numerical simulation of the avalanche sequences and source identification; furthermore, altitude measurements after ice and snow melting would reveal a contained volume of melting ice and snow.

scholarly journals The Influence of Surface Topography on the Weak Ground Shaking in Kathmandu Valley during the 2015 Gorkha Earthquake, Nepal

Sensors ◽  
2020 ◽  
Vol 20 (3) ◽  
pp. 678
Author(s):  
Mark van der Meijde ◽  
Md Ashrafuzzaman ◽  
Norman Kerle ◽  
Saad Khan ◽  
Harald van der Werff
Keyword(s):  
Numerical Simulations ◽  
Surface Topography ◽  
Seismic Energy ◽  
Spectral Element ◽  
Kathmandu Valley ◽  
Ground Displacement ◽  
Gorkha Earthquake ◽  
Ground Shaking ◽  
Earthquake Scenarios ◽  
2015 Gorkha Earthquake

It remains elusive why there was only weak and limited ground shaking in Kathmandu valley during the 25 April 2015 Mw 7.8 Gorkha, Nepal, earthquake. Our spectral element numerical simulations show that, during this earthquake, surface topography restricted the propagation of seismic energy into the valley. The mountains diverted the incoming seismic wave mostly to the eastern and western margins of the valley. As a result, we find de-amplification of peak ground displacement in most of the valley interior. Modeling of alternative earthquake scenarios of the same magnitude occurring at different locations shows that these will affect the Kathmandu valley much more strongly, up to 2–3 times more, than the 2015 Gorkha earthquake did. This indicates that surface topography contributed to the reduced seismic shaking for this specific earthquake and lessened the earthquake impact within the valley.

Characterizing the Kathmandu Valley sediment response through strong motion recordings of the 2015 Gorkha earthquake sequence

2017 ◽  
Vol 714-715 ◽  
pp. 146-157 ◽  
Author(s):  
S. Rajaure ◽  
D. Asimaki ◽  
E.M. Thompson ◽  
S. Hough ◽  
S. Martin ◽  
...  
Keyword(s):  
Strong Motion ◽  
Earthquake Sequence ◽  
Kathmandu Valley ◽  
Gorkha Earthquake ◽  
2015 Gorkha Earthquake

scholarly journals Comparison of Earthquake-Triggered Landslide Inventories: A Case Study of the 2015 Gorkha Earthquake, Nepal

Geosciences ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 437 ◽  
Author(s):  
Meena ◽  
Tavakkoli Piralilou
Keyword(s):  
Risk Mitigation ◽  
Landslide Susceptibility Mapping ◽  
Gorkha Earthquake ◽  
Area Distribution ◽  
2015 Gorkha Earthquake ◽  
The World ◽  
Mapping Techniques ◽  
Event Based ◽  
The Impact

Despite landslide inventories being compiled throughout the world every year at different scales, limited efforts have been made to critically compare them using various techniques or by different investigators. Event-based landslide inventories indicate the location, distribution, and detected boundaries of landslides caused by a single event, such as an earthquake or a rainstorm. Event-based landslide inventories are essential for landslide susceptibility mapping, hazard modeling, and further management of risk mitigation. In Nepal, there were several attempts to map landslides in detail after the Gorkha earthquake. Particularly after the main event on 25 April 2015, researchers around the world mapped the landslides induced by this earthquake. In this research, we compared four of these published inventories qualitatively and quantitatively using different techniques. Two principal methodologies, namely the cartographical degree of matching and frequency area distribution (FAD), were optimized and applied to evaluate inventory maps. We also showed the impact of using satellite imagery with different spatial resolutions on the landslide inventory generation by analyzing matches and mismatches between the inventories. The results of our work give an overview of the impact of methodology selection and outline the limitations and advantages of different remote sensing and mapping techniques for landslide inventorying.

scholarly journals OVERALL FEATURES OF MULTIPLE LAND-SLIDES ALONG TRISHULI RIVER TRIGGERED BY THE 2015 GORKHA EARTHQUAKE, NEPAL

2019 ◽  
Vol 75 (4) ◽  
pp. I_554-I_561
Author(s):  
Alessandra Mayumi NAKATA ◽  
Hikaru TOMITA ◽  
Kazuo KONAGAI ◽  
Masataka SHIGA ◽  
Takaaki IKEDA ◽  
...  
Keyword(s):  
Gorkha Earthquake ◽  
2015 Gorkha Earthquake
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