Landslide Characteristics and Observations

Transcription

1 Landslide Characteristics and Observations Lecture at the Summer School Alpbach 2006 by Helmut Rott Dept. of Meteorology & Geophysics, Univ. of Innsbruck & ENVEO IT GmbH, Innsbruck AUSTRIA Contents of Lecture Overview of landslide types and characteristics Factors for slope stability Overview of in situ observation methods Landslide mapping by optical sensors Satellite-borne interferometric SAR (InSAR) for slope deformation, applications examples in mountains and inhabited areas InSAR application for landslide susceptibility mapping Conclusion on satellite methods for landslide monitoring Aplbach_2006 H. Rott 1

2 Landslide Types Classification of Landslides according to type of material and movement. After Varnes (1978) Major Landslide Types - 1 Source: USGS Aplbach_2006 H. Rott 2

3 Major Landslide Types - 2 Source: USGS Landslide Type: Debris Avalanche Volume 80 x 10 6 m 3 Earthquake triggered Landslide - Pakistan Satellite Image: Digital Globe QuickBird II, 27 Oct 05 Source: USGS Report Aplbach_2006 H. Rott 3

4 Vajont Landslide Volume 270 x 10 6 m 3 D. Petley, Volcanoclastic Mudflow triggered by Intense Rain Sarno, Campania, 5 May 1998 Ref: NEDIS Report Aplbach_2006 H. Rott 4

5 Features observed in high resolution imagery: drainage patterns gully erosion marks transversal and radial cracks scarps transverse ridges changes in vegetation cover Landslide - Geomorphological Features Characterization of Landslides for Stability Assessment Failure surfaces (shape, roughness, defects) Surface topography (precision digital maps, morphology) Depositional area Type of movement Rate of movement Size and properties of material (structure, strength, friction angle) Age of failure Subsurface water level, pore pressure Trigger mechanisms Aplbach_2006 H. Rott 5

6 GEO-Information Tools for Landslide Risk Analysis Ref: Van Westen, 2004 Landslide Stability Analysis Equilibrium of Forces Normal stress across contact surface σ n = (W cosα)/a Shear strength on sliding surface τ = c + tanφ W cosα/a Resisting shear force R = τa = ca + W cosα tanφ Limiting block equilibrium condition (Mohr-Coulomb Criterion: Linear relationship between normal and shear stresses) W sin α = c + W cosα tanφ W block weight force A area of the block base c cohesion strength (stress) φ friction angle φ Key landslide triggering factors Changes of water level (intense rain; water level fluctuations of reservoirs) Excavation by construction activities and mining Deforestation, erosion Glacier and permafrost retreat Earthquakes Volcanic activities Aplbach_2006 H. Rott 6

7 Landslide Zonation Methods Source: LESSLOSS Landslide Exploration Techniques Surface Observations Mapping by airborne and spaceborne imagers: extent, morphology, topogr. Geologic field surveys: morphology, shape, roughness, structure, lithology Airborne laser scanning: precise topographic mapping Ground based geodesy (GPS etc.): surface displacement Ground-based SAR, GB laser scanner: surface displacement, topography Spaceborne SAR: surface displacement, topography Extensiometers: surface deformation Sub-surface Exploration Rock coring, test pits: material properties, characteristics of failure surface Refraction and reflection seismics: depth and characteristcis of discontinuities Ground penetrating radar (GPR); depth and type of discontinuity Electromagnetics, geoelectrics: subsurface discontinuities; ground water Inclinometers, tiltmeters, accelerometers in boreholes: Subsurface movements Time domain reflectometry TDR in borehole: depth of shear plane; water Aplbach_2006 H. Rott 7

8 Example of Geophysical Exploration: Seismic Monitoring Atemkopf, Kaunertal Measurement Campaign Aug Microseisimic Stations Location of seismic events ISDR-IDNDR Project of ÖAW Project Lead: E. Brückl, TU Wien Ground-based InSAR for Continuous Monitoring Eiblschrofen near Schwaz LISA (Linear SAr), developed at IPSC-JRC Stepped frequency CW radar, 500 MHz - 18 GHz Aplbach_2006 H. Rott 8

9 LISA Measurements at Eiblschrofen Time period: 7 days Time period: 2 months LOS Displacement on slope Ku-band measurements in 2001 Landslide Monitoring by Optical Remote Sensing 28/09/1988 Tessina Landslide Belluno 7/10/1994 Ref: Hervas et al., 2003 Red: new soil outcrops Yellow; new vegetation growth Aplbach_2006 H. Rott 9

10 Mapping Small-Scale Earthflows Landsat-7 TM 13/09/1999 Band 4,3, 2 Gerlostal (Zillertal) Ikonos 15/08/2000 Band 4,3, 2 Resolution: 4 m Comparison of Techniques for Landslide Mapping Tsaoling Landslide, Taiwan A AIRSAR L-band polarimetry B C-band VV C Landsat 7 TM D IRS Pan (5 m) Ref: Czuchlewski et al., 2004 Aplbach_2006 H. Rott 10

11 Measurement of Surface Displacement by InSAR φ dis = (4π/λ) R = (4π/λ)( y sin θ - z cos θ) InSAR measures the displacement in LOS of the radar beam C-band SAR (λ = 5.66 cm): φ (2π) R = 2.83 cm y = 7.24 cm, z = 3.07 cm (23 ) L-band SAR (λ = 25 cm): φ (2π) R = cm (23 ) Requirement for DInSAR Processing: Coherence Coherence Image 1-year Time Spans Tyrolean Alps Degree of Coherence Aplbach_2006 H. Rott 11

12 Coherence in Alpine Area over Annual Intervals Data: ERS SAR, descending pass Basin Zillertal, Eastern Alps, 1618 km 2 Criteria: 15 θ 80 γ 0.3 Mass Waste above the Gepatsch Reservoir Aplbach_2006 H. Rott 12

13 The Unstable Slope above Gepatsch Reservoir Landsat-7 image 13/09/1999 View from the dam Aplbach_2006 H. Rott 13

14 SAR Amplitude Image in Radar Geometry One-Year Coherence c o h e r e n c e Aplbach_2006 H. Rott 14

15 Interferogram topo and motion phase 25/9/95-12/9/96 B n = -12m H a = 920 m Annual Surface Motion by ERS InSAR Displacement in mm/a with surface-parallel assumption Aplbach_2006 H. Rott 15

16 Profiles of Surface Motion, Integration of InSAR Motion Map with GIS Motion contours on Orthophoto Aplbach_2006 H. Rott 16

17 Modelling Displacement and Stability of the Mass Waste Gepatsch Objectives: - Interpretation of observed InSAR displacements - Simulations of conditions for failure Diagram: Setup with zones of base Gneiss, weak Gneiss and Moraine Arrows: Total displacement after reducing angle of inner friction Model Code: UDEC Universal Distinct Element Code, Itasca Inc. Ancona Landslide Analysis by Permanent Scatterers Radar Data: ESA ERS-1/2 Processing: POLIMI 1 2 Descent Front Ascent Front Aplbach_2006 H. Rott 17

18 Average Displacement Rate of Permanent Scatterers Jesi Chiaravalle Average LOS Displacement Rate Falconara Landslide Harbour Aspio Ancona [mm/yr] Analysis of Surface Displacement in Mountain Village Topographic Phase ERS Tandem Data Schellen berg Bodensee Walgau 14/13 Jan 1996 Bper = 89 m Ha = 110 m Triesen berg L F Aplbach_2006 H. Rott 18

19 One-year Coherence and Interferogram 1996 Jul Aug 31 blue green yellow Coherence Interferogram (incl. topographic phase contribution): B n = 31 m Slope Motion retrieved from Single SAR Image Pair >25mm/a <1mm/a N Triesenberg, Lichtenstein Interferometric motion 7 July Aug 1997 surface-parallel assumption (on Orthophoto ) Aplbach_2006 H. Rott 19

20 DInSAR Slope Motion from Single Image Pair Triesenberg Comparison of one-year motion InSAR ) vs. GPS (mean ) RMSE = 3.5 mm/year Comparison GPS - Permanent Scatterer Motion Aplbach_2006 H. Rott 20

21 DinSAR Analysis in Forested Areas using Reflectors Multi-temporal Envisat ASAR image, IS2 VV Aplbach_2006 H. Rott 21

22 Specular Reflectors 1 x 1 m 2 σ max = 35.9 dbm 2 for 5.3 GHz Reflector P4 Impulse Response of Reflector (Amplitude) Envisat ASAR IS2 VV Aplbach_2006 H. Rott 22

23 Displacement of Reflectors Kerschbaumsiedlung, Navis ASAR IS2 VV SLCI slant range image Landslide Mapping at Regional Scale using InSAR Landslides (in red) in the Arno river basin (Umbria, Toscana) Superimposed to DEM Project SLAM Service for Landslide Monitoring (funded by ESA DUP) Aplbach_2006 H. Rott 23

24 SLAM - Landslide Displacement Monitoring SLAM - Landslide Susceptibility Mapping Aplbach_2006 H. Rott 24

25 SLAM - Landslide Susceptibility Map Arno Basin Data Base: InSAR (350 SAR images) DEM Geomorphological maps Geology & soil properties Etc. InSAR Applicability for Landslide Motion Monitoring InSAR: AE Area extended; PS Permanent Scatterer; GB Ground-Based Landslide Motion Monitoring Requirements INSAR Tools Resolution Motion range Accuracy Repeat interval Rapid slides ca. 50 m > 1 m/d 10 % of velocity 10 min 2 h GB Moderate motion ca. 50 m 0.5 m/a 1 m/d 0.1 m/a 0.1 m/d 1 20 d AE, GB Slow slides 50 m 100 m m/a m/a a PS, AE, GB Aplbach_2006 H. Rott 25

26 Satellite Capabilities for Landslide Monitoring Optical imagery and SAR amplitude images provide basic information on landslide areas and surface morphology useful for landslide zonation at regional scale InSAR provides very accurate information on LOS displacement of slopes, a very important indicator of slope stability Slope movements (on the order of mm/a to m/a) can be detected and mapped by means of satellite-borne SAR interferometry InSAR is an economic tool for regional landslide surveys and monitoring, but constraints related to vegetation, observation geometry and landslide type need to be taken into account 15 years of archived SAR data are useful to study temporal variations of motion, important for assessing slope stability, complementary to other information New SAR systems (in particular TanDEM-X) will acquire high resolution DEMs, key information for landslide characterization Needs for Ground Instability Information Source: IGOS Geohazards Report Aplbach_2006 H. Rott 26

27 References Czuchlewski K.R., Y. Kim and J.K. Weissel Assessing natural disaster impacts and recovery using multi-frequency, fully polarimetric SAR. Proc. POLinSAR 2005, Colesanti, C., Ferretti, A., Prati, C. et al Monitoring landslides and tectonic motions using the Permanent Scatterer Technique. Engineering Geology 86, IGOS Integrated Global Observing Strategy Geohazards Theme Report. Hervas J. et al Monitoring landslides form optical remotely sensed imagery: the case history of Tessina landslide, Italy. Geomorphology 54, Rott H., Scheuchl, B., Siegel, A et al. Monitoring very slow slope movements by means of SAR interferometry: a case study from a mass waste above a reservoir in the Ötztal Alps, Austria. Geophys. Res. Let., 26, Rott, H., Nagler, T., Rocca, F., et al MUSCL - Monitoring Urban Subsidence, Cavities and Landslides by remote sensing, Final Report, EC project EVG1-CT , Inst. for Meteorology and Geophysics, Univ. of Innsbruck, Austria. Rott, H. and T. Nagler. The Contribution of Radar Interferometry to the Assessment of Landslide Hazards. Adv. Space Research, 37, Strozzi, T., Wegmüller, U., Werner, C.L., et al., JERS SAR interferometry for land subsidence monitoring. IEEE Trans. Geosc. Rem. Sens,. 41(7), Van Westen, C.J Geo-information tools for landslide risk assessment. Proc. 9th Int. Symp. on Landslides, Balkema, pp Relevant Web Sites LESSLOSS - Risk Mitigation for Earthquakes and Landslides, EC-FP6, MUSCL - Monitoring urban subsidence, cavities and landslides by remote sensing, EC-FP5 EU-MEDIN - European Mediterranean Disaster Information Network. LEWIS - Landslide Early-Warning Integrated System, EC-FP-5, GLALAHAD - Advanced Remote Monitoring Techniques for Glaciers, Avalanches & Landslides Hazard Mitigation NEDIS Natural Environmental Disaster Information Exchange System, USGS Landslide Hazards Program, SLAM InSAR Conference Aplbach_2006 H. Rott 27