Multiple remote sensing assessment of the catastrophic collapse in Langtang Valley induced by the 2015 Gorkha Earthquake
Hiroto Nagai1, Manabu Watanabe2, Naoya Tomii3, Takeo Tadono1, and Shinichi Suzuki11Earth Observation Research Center, Japan Aerospace Exploration Agency, 2-1-1 Sengen, Tsukuba, Ibaraki, 305-8505, Japan 2School of Science and Engineering, Tokyo Denki University, Ishizaka, Hatoyama-machi, Hiki-gun, Saitama, 305-0394, Japan 3Satellite Applications and Operations Center, Japan Aerospace Exploration Agency, 2-1-1 Sengen, Tsukuba, Ibaraki, 305-8505, Japan
Received: 29 Aug 2016 – Accepted for review: 14 Sep 2016 – Discussion started: 16 Sep 2016
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.
Nagai, H., Watanabe, M., Tomii, N., Tadono, T., and Suzuki, S.: Multiple remote sensing assessment of the catastrophic collapse in Langtang Valley induced by the 2015 Gorkha Earthquake, Nat. Hazards Earth Syst. Sci. Discuss., doi:10.5194/nhess-2016-285, in review, 2016.