J-Rapid Final Workshop 21 June, 2016, Kathmandu Inventory mapping of landslides induced by the Gorkha earthquake 2015 and a proposal for hazard mapping of future landslides for making a plan of better reconstruction "Impact on infrastructure by Gorkha earthquake 2015 induced landslides" Masahiro CHIGIRA Masahiro CHIGIRA Professor, Disaster Prevention Research Institute, Professor, Disaster Prevention Research Institute, Kyoto University Kyoto University Vishnu DANGOL Vishnu DANGOL Professor, Department of Geology, Professor, Department of Geology, Tribhuvan University Tribhuvan University Objective 1. to make an inventory mapping on landslides, cracks, and landslide dams induced by the Nepal earthquake and to investigate their formative mechanisms 2. to detect displaced areas of slope surfaces, of which future susceptibility to landslides would be evaluated on the basis of geology, geomorphology, and groundwater conditions. 3. propose a methodology of hazard mapping for earthquake-induced landslides in Nepal. Members (Japan side) 1. Masahiro CHIGIRA (Kyoto Univ.) PI Applied Geology 2. Daisuke HIGAKI (Hirosaki Univ.) Landslide control 3. Hiroshi YAGI (Yamagata Univ.) Landslide susceptibility mapping 4. Akihiko WAKAI (Gunma Univ.) Geotechnical analysis of landslide 5. Hiroshi, P. SATO (Nihon Univ.) Remote sensing 6. Go, SATO (Teikyo Heisei Univ.) Geomorpholoｇy 7. Ching-Ying, TSOU (Hirosaki Univ.) GIS analysis 8. Akiyo YATAGAI (Res. Inst. Humanity and Nature) Meteorology Members (Nepali side) 1. Vishnu DANGOL (Tribhuvan Univ.) PI Applied Geology 2. Smajwal BAJRACHARYA (ICIMOD) Remote sensing 3. Shanmukhesh Chandra AMATYA (DWIDP) Hydrogeology 4. Tuk Lal ADHIKARI (ITECO-Nepal) Geotechnical Field survey • Trishuli River catchment from Trishuli to Syabrubesi (29 October to 1 November, 2015) • Sun Kosi and Bhote Kosi River catchments from Bansaghu to Kodari. (2 to 4 November, 2015) • Budhi Gandaki River catchment from Arughat to Litin (6 and 7 March, 2016) • Dauradi River catchment from Jhulunge Bajar to Barpak (7 and 8 March, 2016) Inventory mapping of landslides Inventory Complied Data Used Note Topographic classification Knickpoint ASTER GDEM Data contributed by METI and NASA Slope break AW3D DEM derived AW3D DEM of JAXA Constant Vertical Exaggeration Stereoscopic Map (CVES Map) Deep-seated landslide Deep-seated landslide Stereo-pair aerial photos Complied by Dr. Go Sato CVES Map Used for the area not covered by stereo-pair aerial photos Slope failure with scar The 2015 newly formed scar Pre-earthquake: Google Complied with the Earthquake- Earth Imagery (Dec. 12, reference inventory of the induced slope enlargement of a pre- 2014) Japan Landslide Society failure existing scar Post-earthquake: Google Earth Imagery (May. Pre-existing slope failure not enlarged by 3, 2015) & Presented as points the earthquake LANDSAT 8 satellite imagery (June 1, 2015/covering the upstream Trishuli River) Geological setting of the affected area Higher Himalaya MCT Lesser Himalaya Kathmandu Mapped landslides 6,527 new landslides 558 enlarged landeslides 5,159 (ICIMOD-NELS) Cumulative landslide frequency and the landslide size Data added to Chigira et al. (2010, Geomorphology) What type of landslides occurred? Shallow disrupted landslides in most cases No gigantic landslides like those induced by the 2009 Wenchuan earthquake Bhote Koshi catchment Rockfall 400m fall from a slope break Dadakateri From a river terrace (Kodari) Cracks Mostly have not developed after the quake Cracks on a sharp ridge in Barpak Cracks on debris slopes (Bhote Koshi catchment) Large landslides, which had been continually moving were not reactivated. Dahlan landslide Mica schist Where did they occur? Inner Inner valleys valley (valley in valley) Inner valley Landslides Inner valley development Loosening of the valley wall Rapid River incision River Incision Valley widening Loosened rock masses have been removed by the shaking Failure within a landslide body Trishuli River Steep infacing-slopes Slate, Bhote Koshi catchment Terrace scarps ghat Along a road Before the EQ Landslides & Geology Gneiss (Bhote Koshi catchment) Schist Malekhu Limestone Benighat Slate Roban phyllite Dhading Dolomite 4 km Fagfog Quartzite Pinkish phyllite Kuncha F. phyllite Number of landslides by each geological zone Occupancy ratio of landslides by each geological zone 500 400 300 200 100 0 Landslides are dominating in areas of gneiss, slate, dolomite, quartzite Rare in areas of schist, phyllite Geology & Landslides 100 150 200 250 50 0 1～5° 6～10° 11～15° 16～20° Landslide 21～25° ～ ° 26 30 Landslides 31～35° 36～40° numbers 41～45° 46～50° 51～55° 56～60° 61～65° and 100 % % 10 20 30 40 50 60 70 80 90 0 slope 1～5° 6～10° 11～15° Areal ratios of landslides of ratios Areal angles 16～20° 21～25° 26～30° 31～35° 36～40° 41～45° 46～50° 51～55° 56～60° 61～65° Subsequent rainfalls enlarged some landslide scars Large landslide bodies were not reactivated (Trishuli River) The 2015 Earthquake- induced slope failure newly formed scar enlargement of a pre-existing scar Pre-existing slope failure not enlarged by the earthquake Deep-seated landslide InSAR image to detect small displacements on the order of cm Second (after the EQ) observation Crustal deformation First (before the EQ) observation In the case of LoS shortened, Blue -> Yellow -> Red: The ground was uplifted or close to the satellite 29 http://vldb.gsi.go.jp/sokuchi/sar/index-e.html Comparing before and after the earethquake Mixture of noise and crustal displacement, But the red circle shows local surface displacement. Blue->Red->Yellow, away from the satellite In the red circle Bansaghu “Talus slope” New cracks but no development after the quake Transient adjustment of rock fragments Groundwater level was shallow but the slope was not seriously destabilized. After the quake No change was found in the red circle InSAR is very helpful to monitor displacements after an earthquake Quantitative seismic response analysis with FEM. Input waveform (near the base camp of Mt. Everest, Ev-K2-CNR Association) 7.0km 5.8km Discretized finite element meshes for the analytical area along the Trisuli River. Calculated maximum value of Calculated maximum value of shear horizontal acceleration at ground stress in surficial layer. surface. Landslides occurred on slopes with amplified acceleration and/or mobilized shear stress Annual precipitation and landslides 1000 2000 3000 0 1 for Daily precipitationand accumulated 12 23 2015 mean 34 45 1 Jan 56 67 Pokhara 78 89 100 a Pokhar 111 2015_accum mean_accum 122 – 133 a Simar 30 144 155 Kathmandu 166 177 2015 July, 188 a Okhaldhung 199 210 1000 500 0 1 12 2008 23 2015 mean - 2014 (7years) 34 45 56 67 Kathmandu 1000 200 400 600 800 78 0 89 1 100 mean 12 111 2015_accum mean_accum 23 122 34 133 45 144 mean_accum 155 56 Okhaldhunga 67 166 177 78 89 188 100 199 111 210 2015 122 133 144 155 2015_accum 166 177 188 199 210 Antecedent rainfall amounts Noto Hanto Chuetsu-oki Mid-Niigata 150 Gorkha earthquake 10 days before the quake Proposal of the methodology for the Hazard mapping of earthquake-induced landslides on the basis of Slope angles Inner valleys, infacing slopes, and terrace edges and Geology Mapped landslides 6527 new landslides 558 enlarged landeslides Slope angles Slope (35 – 45deg) Slope (35 – 45deg)+Inner Valley Slope (35 – 45deg)+Inner Valley+Carbonate Slope (35 – 45deg)+Inner Valley+Carbonate +Landslides Other carbonates, sandstone, gneiss, slate, terraces, infacing slopes are not shown Conclusions • Landslides induced by the 2015 Gorkha earthquake were mostly shallow disrupted landslides. • Landslide dams hardly caused serious threats • Landslides occurred mostly on steep slopes in inner valleys, on geologically controlled steep slopes like infacing slopes, and on terrace edges • Earthquake shaking was amplified on convex slope breaks on steep slopes • Most susceptible rocks to landslide were carbonate, sandstone, gneiss and slate, while phyllite may be not • Some earthquake-induced landslides were enlarged by subsequent rainfalls • Earthquake-induced cracks have not always developed by subsequent rainfalls • Deep-seated large landslide bodies were hardly reactivated • The effects of rainfalls before the earthquake were not clearly identified, but landslides would be much more when the earthquake occurred during a rainy season • We propose hazard mapping of earthquake-induced landslides on the basis of topographic features and geology Impact on Infrastructure by Gorkha Earthquake 2015 Induced Landslides D. Pathak1,3, S. R. Bajracharya1,2 and V. Dangol1,3 1 Tribhuvan University; 2 ICIMOD, and 3Nepal Landslide Society Background • The 7.6 (ML) magnitude Gorkha Earthquake of 25 April, 2015 followed by numerous aftershocks has affected 31 affected districts, among which the impact was quite serious in 17 districts. • This presentation describes some damages to infrastructure like road, bridge, hydropower, settlements due to earthquake induced landslides. • The work was carried out through the use of satellite imageries and field visits at selected sites by Nepal Landslide Society for ICIMOD. Study districts Damage to road from earthquake induced landslide in Dhading after earthquake before earthquake The earthquake triggered old landslide Landslide triggered by earthquake at the bend in Pasang Lhamu highway, Rasuwa after earthquake before earthquake Damaged Road Sections due to the EQ induced landslides Road Name Damaged length, m Araniko Highway 11,336.60 Pasang Lhamu Highway 4,944.00 Chanaute-Barpak 3,713.70 Mailung Bazar Road 3,282.40 Chaku to inner village 2,736.60 Chaku Khola HPP Access Road 2,064.80 Lamusangu-Ramechhap Highway 1,741.70 Charikot-Lamabagar Road 1,366.90 Singati-Bigu Road 1,189.80 BP Highway 899.00 Listi Road 894.40 Melamchi-Helmbu Road 744.50 Bhirkot-Hanwa Road 741.00 Besisahar-Chame Road 516.30 Dolalghat-Chautara Road 435.40 Namdu-Jugu Road 329.80 Bhitkot-Jhule Road 200.40 Helambu Road 170.10 Barpak-Gumda Road 157.20 Balephi-Jalbire Road 64.30 Gorkha-Ghyampesal Road 64.20 Busti-Mirge Road 34.70 Sipring HP Access Road 455.60 Mid Bhotekoshi Access Road Camp Area 90.70 Upper Hadi HPP Access Road 26.10 Total road damaged: 38 km Araniko Highway: 11.3 km.