management information systems, c.a. brebbia & p. pascolo ... · these landslides are caused by...

Remote sensing and CIS based geological

mapping for assessment of landslide hazard

in Southern Kyrgyzstan (Central Asia)

H.-U. Wetzel% S. Roessner * & A. Sarnagoev^

* GeoForschungZentrum (GFZ) Potsdam, GermanyM̂inistry of Emergency and Civil Defence (MECD), Bishkek, KyrgyzRepublic

Abstract

Large landslides (up to more than one million cubic meters per event) arewidespread at the eastern rim of the Fergana basin (forelands of Tienshanmountains) which is situated in an area of an active plate boundary (collision ofIndian and Eurasian plates). In this situation a detailed understanding ofgeological structures and ongoing tectonic activity plays a key role in theassessment of landslide hazard. This requires an evaluation of recent fracturingzones (faults) by morphological and structural criteria. In the result, fault patternsof various regional orders and technically stable blocks are determined. In thisstudy the potential of combining information derived from satellite remotesensing data with information obtained from geological maps and fieldobservations are investigated in a GIS environment. For this purpose two testsites (region Maili-Sai and Karamat) of about 20 by 20 km were definedcharacterising typical geological situations of this region. The database consistsof multitemporal Landsat-TM and stereoscopic MOMS-2P satellite imagery,basic geological maps (scale 1:200.000) and topographic maps (scale 1:100.000).The available MOMS-2P (Modular Optoelectronic Multispectral Scanner) datarecorded in Mode D allowed generating a Digital Elevation Model (DEM) of thestudy area forming the basis for perspective visualisations and profiling ofcomplex geological structures incorporating satellite remote sensing andgeological map data.

Management Information Systems, C.A. Brebbia & P. Pascolo (Editors) © 2000 WIT Press, www.witpress.com, ISBN 1-85312-815-5

356 Management Information Systems

Introduction

The Pamir-Tienshan region in Central Asia is part of the active collision zonebetween the Eurasian and the Indian Plates (Fig. 1). This collision and theresulting active development of the Pamir-Tienshan orogen is one of the mostinteresting geo-scientific problems. In this connection earthquakes and massmovements (landslides, rock falls) are expressions of ongoing tectonic activity.Occurrence of landslides is concentrated at the eastern rim of the Fergana Basinwhich is inhabited by about five million people (Kyrgyzstan and Usbekistan).

investigatedlandslide areas

Figure 1: Main structural units of the Pamir-Tienshan region (after [1; 2])overlaid by investigated areas of landslides

These landslides are caused by complex interactions between endogenic andexogenic factors. Methods of satellite remote sensing in combination with GIStechniques are especially suitable for investigations of these interactions formingthe basis for hazard assessment in regard to people and infrastructure. During thelast 10 years an increase of landslide activity has been observed in this region


Management Information Systems 357

which emphasises the need for scientific investigations of landslide-causingfactors. This problem is subject of a collaboration between the Remote SensingSection of the GFZ Potsdam and the Ministry of Emergency and Civil Defencein Kyrgyzstan. One question is a detailed assessment of geological structures asan important landslide-causing factor based on remote sensing and GIStechniques. This paper presents first results of these investigations.

Geological and Tectonic Situation

In the area of interest (Fig. 1) the development of the Tienshan orogen issubdivided in several structural phases [3; 4]. The Northern Tienshan alreadyexperienced Caledonian folding and consolidation. Southwards, this region isfollowed by the Variscian structural zone of the Middle Tienshan, whereas thesouthernmost part of the Tienshan is formed by an Alpidic main regionalstructure. In this area of interest the Tienshan is structurally dominated by theTalas-Fergana Fault. All structural units contain older consolidated cores andblocks and are overlaid by Meso- and Cenozoic platform sediments and youngerbasin structures [4]. The formation of orogenic morpho-structures is of Alpidicage and has been going on up to recent times, whereas folding is spreading outinto the forelands and intramontanous basins [2].

For analysis of landslide activity, the youngest alpidic phase of structuraldevelopment of the Tienshan is of special importance. During this phase theformation of the Fergana Basin has been taking place accompanied by tectonicdeformation of Meso-and Cenozoic sediments and folding of alreadyconsolidated blocks of older orogens. These processes are going on up to recenttimes, whereas the existence of older core units led to complicated geologicalstructures especially at the eastern rim of the Fergana Basin.

OSMONBETOV et. al. [5] subdivided the Alpidic development into twostructural phases. Folding during the older one (up to the Oligocene) led todominating NE-SW striking fold axes. During the younger one which has beenreaching from the Upper Oligocene until today main folding has been takingplace along ENE-WSW axes and cross folding along NNW-SSE axes. In thisprocess the units of the older structural phase are also affected by the youngerfolding leading to a reactivation of these older structures.

Recent tectonic activity is recorded in high-accuracy geodetic GPSmeasurements [6] which have been carried out in Central Asia by the GFZ in1992, 1994, 1996 and 1998 [7, 8]. They show regionally differing movementdirections of plate subunits. Highest movement rates of 1.4 cm/a were obtainedin NNE-direction at the Pamir-Tienshan collision front. They are modified in thearea of the Talas-Fergana Fault into a NE-oriented direction. This indicates achange in the horizontal stress field in this region leading to complicatedinteractions between active tectonic structures and consolidated older blocks asone factor controlling landslide activity in this area.



Landslides

Every year landslide activity in Kyrgyzstan leads to extensive damage ofsettlements and infrastructure and also to loss of human lives. These landslidesare caused by a combination of factors including structural and engineeringgeology, relief, meteorology and climate, whereas the geological setting formsthe primary frame for complex interactions between these factors. Threegeologically determined main groups of landslides can be distinguished:

Landslides developing in loess units of the Lower, Middle and UpperQuaternary (QrQs)

Landslides developing in weakly consolidated Meso- and Cenozoicsediments (Jura up to Paleogene) consisting of sand- and siltstones withintercalated clays, loams, carbonates and sulfates

Landslides developing in older and younger sedimentary units at the sametime and event

Sediments of the Upper Neogene (N2) are rarely affected by landslides. Theseunits mainly consist of conglomerates and weakly consolidated gravels withinterbedded loess-type loams. High porosity and permeability of these units seemto prevent engineering-geological conditions which are critical to slope failure.

In case of the first type of landslides (QrQs) the actual mass movement canhappen within minutes and hours and affect thousands up to more than onemillion cubic meters in a very short period of time. In case of the other twotypes, active mass movement takes place in the range of days up to severalweeks. In the same area phases of landslides activity can alternate with inactivephases over longer periods of time. In general, landslides may occur in theelevation range between about 700 and 2000 meters representing the weaklyconsolidated sediments of the topographically rising rim of the Fergana basinbelow its transition into the high mountains.

Landslide activity has been documented by local authorities for many yearsbased on terrestrial mapping, engineering-geological investigations, aerialphotographs and general geological maps. Because of the local character of theseinvestigations and the subordinate importance of the youngest tectonicstructures within the existing general geological maps, these information onlypartially allow landslide-oriented geological interpretations in a regional scale.



horizontal movementvectors by CATS-GPS-campaigns(1992-94-96)

Figure 2: Main tectonic structures and areas of landslides (background subset ofLandsat-TM mosaic); Arrows indicate directions of recent plate move-ments -after [8]

The regional distribution of landslides (Fig. 2) indicates that the geological andstructural setting plays a major role in the activation of landslide processes. For abetter understanding of this setting satellite remote sensing is a key tool, becauseit allows the assessment of regional structures.

Satellite remote sensing

The regional and local interpretation of geological and tectonic structures inrelation to landslides is based on multitemporal optical satellite remote sensingdata (Landsat-TM and MOMS-2P). Emphasis of the interpretation is put oncharacteristic landslide-related indicators, such as depression within slopesanomalies in vegetation cover and related structural and tectonic features, suchas fracture or shear elements and faults. The goal is a genetic interpretation ofstructural elements influencing slope failure based on information about their



position, relative age difference and relation to the surrounding geologicalsetting. The interpretation of the satellite remote sensing data is supported bygeological map information and field investigations which were incorporated inthe analytical environment of a GIS.

Structural geological investigations based on the combination of satellite remotesensing data and thematic information requires the incorporation of a DigitalElevation Model (DEM) for visualisation and analysis of complex geologicalstructures [9]. For this purpose a comparable degree of morphological detail inthe DEM and the satellite remote sensing data is needed. Since large-scaletopographic maps (scale 1:50.000 and better) are not available for this area, aDEM of 50 by 50 meters pixel size was generated based on stereoscopic MOMS-IP (Modular Optoelectronic Multispectral Scanner) data. They were recorded instereo mode D combining two inclined stereo channels and two nadir lookingspectral channels in the blue and near infrared ranges. In the process ofphotogrammetric point determination by bundle block adjustment control pointsand independent check points were used. These points were determined bydifferential GPS measurements in the field after identification in the MOMS-imagery.

Geological interpretation - example Maili-Sai

The example area Maili-Sai (Fig. 3 and 4) is situated in the transitional zonebetween the Variscian consolidated basement block in the north (Arslan-Bob)and the Fergana Basin in the south. In the area of the town of Maili-Sai thenorthern rim of the Fergana Basin is formed by an anticline consisting of weaklyconsolidated sediments (Upper Cretaceous up to Paleogene) which is foldedalong an E-W axis.This fold structure of the older Alpidic structural phase forms a morphologicalsaddle. In the northwest this structure interlocks with a NE-SW syncline whichdeveloped during the later Alpidic structural phase.The interpretation of the optical satellite data shows that the older anticline is cutby WNW-ESE tectonic features. These elements are part of a complex right-sidestrike-slip fault whereas the direction of the shift can be derived from thestructural interpretation. Young shear elements run sub-parallel to the slope andcan be mapped as small morphological steps in the terrain. Recent activity of theshear zone is also indicated by its autonomy in regard to older folded structuresand by the offset of older loess units (Ch). This shear zone separates the olderconsolidated basement from the younger structure of the Fergana Basin. In thisshear zone young NW-SE structures have been developed which can beinterpreted as extensional elements. The perspective view based on the DEMderived from the MOMS-2P data (Fig. 4) shows very well the spatial connectionof these extensional elements with landslides which developed further downhill.



Kashgarta landslide(Status 1998)

Figure 3: Structural interpretation based on MOMS-2P data (above);derived geological model - simplified (below)



0 2 4 6 8 10km

Figure 4: Perspective view based on the MOMS-2P DEM showing thestructural control of the landslide regime (orientation of theview - see Fig. 3)



Start springtime 1994Status: 13.07.99

Figure 5: Landslide Kashgarta (region Maili-Sai), position see Fig. 3 and 4

A special example for this mechanism is the Kashgarta landslide (Fig. 5) whichdeveloped in spring of 1994. The width of its upper part amounts to about 800meters where the detached material consists of weakly consolidated Tertiarysediments. In the lower parts of the valley Mid-Quaternary loesses were affectedby the mass movement. Until the end of June 1998 a total mass of about 10million tons had been moved downhill along a distance of 4 km in a glacier-typeway. A determination of the position of the lowest part of the landslide in thefield in July 1999 resulted in an increase of this distance up to 5.5 km. In theupper part of the photograph the described extensional structures running into thevalley can be recognised.

Geological interpretation - example Karamat

This example (Fig. 6) shows a block which is predominantly formed by the olderAlpidic structural phase and mostly consists of Meso-Cenozoic sediments. Inthe eastern part (settlement Karamat) these structures are overlaid by an youngerN-S brachysyncline (dominating loess units of the Lower Quaternary - Qi).During the older structural development folding of the sediments along a NE-SWaxis took place first and was related to a cross-folding (NW-SE). Additionally,several NW-SE structural zones can be recognised which dissect the blockbetween the Kara-Unkyur valley in the northwest and the loess-filledbrachysyncline in the southeast, but do not completely cross these youngerstructures. They are interpreted as active right-side shear zones whose originalstructure dates back to the older Alpidic structural phase. In contrast to the Maili-Sai example, in this region older structural elements are reactivated due topresent deformation (see also movement vectors in Fig. 2).



A more detailed view (Fig. 7) shows how young N-S oriented fracture elementswith extensional function develop under the influence of this spatially extensiveshear zone (A). These elements are probably responsible for the structuralcontrol of landslide 1 (Fig. 7 - upper part). The influence of shear zone A ends atshear zone B. Interference of these N-S extensional elements with active featherelementsjn the internal structure of zone B seems to control the activity oflandslides 2 and 3. This effect is illustrated by the DEM of Fig. 7 (lower part). Inthe neighbouring loess depression in the east (settlement Karamat) the NE-SWfault systems corresponding to the shear zone B form the valleys and generatefeather structures along the slopes. In connection with the lithology (thick loessunits) this leads to an especially high intensity of landslide activity in this area.

Upper Quarter naryalluvial sediments

Kilometers10

0 44 field checking 1999

j} contours of main landslides

(geological basis data accordingto Kyrgyz Geol Map, 1: 200000)

further landslide localities

structural pattern andand geological /litholgicalbarriers (interpretation)

Figure 6: Structural interpretation of the example Karamat



1900

Figure 7: Landslide situation in Karamat (subset Akshaluu)

Conclusions

1. A combined interpretation of multitemporal optical satellite remote sensingdata (Landsat-TM, MOMS-2P) with a DEM of comparable spatialresolution (50 meters pixel size) generated from stereoscopic MOMS-2Pdata allows a detailed interpretation of various structural settings controllingdifferent types of landslides.

2. The previously existing geological information which can be obtained fromgeological and lithostratigraphical basemaps (scale 1:200.000) only providea general geological structural model. They do not show neotectonicallyrelevant structures which only can be derived by combined interpretation ofoptical satellite remote sensing data and DEM information due to theirdistinct geomorphological expressions. However, spatially extensive remote



sensing based structural interpretations have to be supported by local fieldinvestigations.

3. It seems to be possible to apply the presented methodology to other regionalunits at the rim of the Fergana Basin which are also affected by landslides.This opens up new opportunities for a differentiated assessment of structuralsettings which seem to influence landslide activity in a large area along therim of the Fergana Basin. Such an approach is the first step towards anevaluation of tectonic impulses controlling landslide activity and forms thebasis for an improved assessment of landslide hazard in this region.

References

[1] Gubin, I.E. Litosfera Tian-Shana, Nauka: Moskva, 157 pp., 1986<russ.>.

[2] Chedia, O. K. Morphostrukturi i noveishi tektogenes Tian-Shana, Him:Frunse, 313pp., 1986 <russ.>.

[3] Judachin, F.N. Geofisisheskije polja, glubinnoe stroenie i seismichnostTianShana, Him: Frunse, 247 pp., 1983 <russ>.

[4] Bakirov, L. B., Voitovivch, 1.1. Shukov, J. V., Samaletdinov, T. S. &Israeleva, R. M. Maps of geological formations, Sheets 1:500 000,K-43-A, K-43-C, K-J-43-A, Goskartografia: Frunse, 1988 <russ.>.

[5] Osmonbetov, K.O., Shukov, J. V., Samaletdinov, T. S. & Israeleva, R.M. Tectonical Maps, Sheets 1: 500 000, K-43-A, K-43-C, K-J-43-A,Goskartografia: Frunse 1989 <russ>.

[6] Reigber, C., Klotz, J, Angermann, D. &Trapeznikov, Y.A. Pamir-Tienshan GPS Project: Network, Observation Campaign 92 andAnalysis Strategy. Geodesy and physics of the Earth: geodeticcontributions to geodynamics, 7* International Symposium, p. 42-45,1992.

[7] Angermann, D., Klotz, J., Michel, G. W., Reigber, C. & Reinking, J.GroBraumige GPS-Netze zur Bestimmung der Krustenkinematik inZentralasien und Sudamerika. D VW- Schriftenreihe zum 41.Fortbildungsseminar: GPS-Anwendungen und Ergebnisse '96, p. 79-93,1997.

[8] Reigber, C., Klotz, J., Angermann, D., Michel, G., Galas, R., Chen, J.Y., Tsurkov, A., Papchev, M., Machmatgaziev, M. C. & Ichanov, C.Central Crustal deformation resulting from Space Geodeticobservations in Asia, WPGM '98, EOS Supplement, 97, w!2, 1998.

[9] Wetzel, H.-U. Use of multispectral MOMS-02 data for geologicalstructure and landuse interpretation in NW Ethiopia. Proceedings ofISPRS Joint workshop „ Sensors and Mapping from Space 1999, CD-Rom, Hannover, Germany and Veroff. Inst. Phot, und Ing. Verm.Universitat Hannover, 18, 10 pages,, 1999.


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