DETECTION METHOD OF SLOPE FAILURES DUE TO THE 2009 SUMATRA EARTHQUAKE BY USING TERRASAR-X IMAGES Toyohashi University of Technology Makoto KAWAMURA Fukui National College of Technology ○ Kazuhiko TSUJINO Fukui National College of Technology Yuji TSUJIKO Andalas University Jafril TANJUNG 2011 IEEE International Geoscience And Remote Sensing Symposium July, Vancouver, Canada

Introduction Debris flow and slope failures typically occur on steep slopes and are often triggered by heavy rainfall or earthquake. In Japan, aerial photographs are usually used for the investigation immediately after the disaster. However, because the aerial photographs are not used for the developing country and a lot of time is necessary to grasp damaged area from the large area. We have proposed the detection method of slope failures by using the optical sensor image in such a situation. However, an optical sensor might not be able to observe the ground by the cloud. On the other hand, because of the SAR image uses the micro wave, the influence of the cloud is not received easily. Therefore, the SAR image can be used for an urgent observation when the disaster occurs.

Target of this study Motivation Large Earthquake To understand outline To understand details TimeImmediately after the disasterPeriod of Restoration Moreover, it is necessary to analyze, while obtained information is a little. Many Information Aerial photographs Other satellite images Field survey Geological type, terrain ・・・ It is demanded to find the large damage area, even if there are "miss" and "wrong extraction". It is necessary to collect many information, and analyze damage more in detail.

Three cases were prepared in this research. Interpretation of the slope failure occurring by using two time series TSX StripMap images （ color composite image of before and after EQ. ） Detection of the slope failures by using TSX StripMap image and local incidence angle. InSAR by using TDX images Methodology

2009 Sumatra Earthquake The 2009 Sumatra earthquake occurred just off the southern coast of Sumatra, Indonesia. The major shock hit at 17:16 local time on September 30, 2009 and had a moment magnitude of 7.6. The epicenter was 45 kilometres west- northwest of Padang, Sumatra. The situation of Sumatra is similar to the Honsyu (Mainland) in Japan. (Scale, Frequent occurrence zone of EQ. and Received the damage of TSUNAMI.) The TSUNAMI damage due to the 2004 sumatra earthquake was huge.

Used data in this study TSX StripMap(VV), Ascending Feb.8 th 2009.(Before EQ) TSX StripMap(VV), Ascending Oct. 8 th 2009.(After EQ) TSX StripMap(HH), Descending Mar. 12 nd 2010.(After EQ) TSX StripMap(HH), Ascending May 5 th (After EQ) Geological Map West SUMATRA (1:250,000) Digitized SPOT-5 image Oct.8 th SRTM 90m-mesh DEM ASTER GDEM 30m-mesh DEM © CNES 2009 © Infoterra GmbH, Distribution [PASCO] © Infoterra GmbH, Distribution [PASCO] © Infoterra GmbH, Distribution [PASCO] © Infoterra GmbH, Distribution [PASCO] Azimuth Range Azimuth Range Azimuth Range Azimuth Range

TamDEM-X (TDX) image Mar and Mar We requested TDX according to the field survey. ©Infoterra GmbH, Distribution[PASCO]

Padang Field survey area ： G.Tigo Field survey Pariaman About 50km About 20km Many building damage occurred in the Padang city. Many slope failures were generated in the mountainous district in the Padang Pariaman Pref. 1 st Field survey (Jan. 2010): Measurement concerning shape and size of slope failures 2 nd Field survey (Mar. 2011): Measurement concerning expansion of slope failures by squall in the rainy season

An example of color composite image ©Infoterra GmbH, Distribution[PASCO] Color composite image of TSX （ R,G,B ） = （ After EQ ， Before EQ ， Before EQ. ）

Comparison of TSX EEC color composite images and field survey result Backscatter strength is strong at the middle of slope before the earthquake. (Light blue) Backscatter strength is strong at the main scape after the earthquake.(Red) Before EQ.After EQ. Change in geographical features Main scape Movement region of soil Color composite image Field survey ©Infoterra GmbH, Distribution[PASCO] Microwave Main scape

Large scale circular slip The section of after collapses is divided into a rapid inclination part and a smoothness part. The width of the site A was about 200m. ©Infoterra GmbH, Distribution[PASCO] ©CNES 2009 (R,G,B)=(After EQ. ， Before EQ ， Before EQ.) Field survey (Site A, Jan ）

Site A Site A （ Mar. 15 th, 2011) The dam was constructed in this area. A part of the accretion sediment was cut out compared with the first investigation, and the unpaved road was constructed. There was no vegetation in the main scape.

(R,G,B)=(After EQ. ， Before EQ ， Before EQ.) The width of the center was about 150m. The shape of Site B similar to the Site A. Rapid inclination slope angle: 26°, Height is about 35m from the BM. Smoothness part slope angle:8°30′ ． In the top part, there was the tension crack (about 30cm). ©Infoterra GmbH, Distribution[PASCO] ©CNES 2009 Field survey (Site B, Jan ）

Field survey （ Site B, Mar ） ↑ These photographs were ← taken with the RC helicopter. (Bizworks Co.)

There was a rice field in the south of the site C. The width of Site C was abut 100m. The slope angle of top part from BM was about 17° ， and Rapid inclination slope angle was about 30° ． ©Infoterra GmbH, Distribution[PASCO] ©CNES 2009 Field survey (Site C, Jan ） (R,G,B)=(After EQ. ， Before EQ ， Before EQ.)

Site C (14 th Mar. 2011) There was no vegetation in steep slope ． The main scape had been eroded. Many stripe of erosion by the squall were able to confirm at the middle of slope. Remarkable growth of the grass was seen compared with the 1st investigation. → about 2m over.

Verification data （ SPOT-5 image （ Spatial resolution: about 10m ） Slope failure area ： Yellow polygon Decipherment of the color and field survey results → Forest area （ Red ） or Sediment （ Loess color ） ● Geological type: weathering Tuffs ● Combined Large slope failure area about 870,000m 2 ● Dashed line: G. Tigo district Three villages were swallowed to sediment at this district. © CNES 2009

An example of Detection results Color composite image of TSX image and cos(loc) R:1008TSX,G:1008TSX,B:cos(GIM) Multi-level slice Case aimed at dark part Average±1σ 1008TSX ： 41±21 Cos(GIM) ： ± Overlay with verification data ○ ： main scape was able to be detected by the accuracy of 65%. × ： main scape was not able to be detected ©Infoterra GmbH, Distribution[PASCO]

Results of InSAR analysis by using TDX pair （ coherence ） Coherence is high in artificial feature and slope failure area. The feature of x band can be confirmed. ©Infoterra GmbH, Distribution[PASCO]

Result of InSAR analysis by using TDX pair The interference fringe appears in the area where the coherence is high. ©Infoterra GmbH, Distribution[PASCO]

Comparison with the SPOT-5 image and InSAR analysis ©Infoterra GmbH, Distribution[PASCO] Site C Site B Site A ©CNES 2009 → Grass grow very quickly in the tropical zone.

Detection accuracy Because of vegetation area is changed, the detection accuracy cannot be compared directly. The detection results were compared with 2 nd field survey result (GPS survey) in March, Slope failures were detected by binarize processing of the coherence image. The GPS tracking was smoothed and the verification data was made newly. Site No. Detection results （ m 2 ） Verification data （ m 2 ） Accuracy (%) Site A Site B Site C

Summary In this research, the detection method of slope failures which used the TSX and TDX images was examined. The conclusions are shown as follows. The case of two time series TSX image was used, the main scape was possible to distinguish easily by using color composite image. When the TSX image after the earthquake and local incidence angle were used, the main scape was able to be detected by the accuracy of about 65%. InSAR analysis was done by using TDX image after the earthquake, and clear interference fringe appeared in slope failure area. Therefore, the InSAR analysis was effective to the detection of slope failures. Detection accuracy was about 70 to 98 %.

Future work To understand of the volume of slope failure area DEM of the collapse area is calculated based on the result of interference fringe.

Acknowledgement This work was supported by SAR technology and application committee in 2010 of PASCO Corporation.

Thank you for your attention DETECTION METHOD OF SLOPE FAILURES DUE TO THE 2009 SUMATRA EARTHQUAKE BY USING TERRASAR-X IMAGES 2011 IEEE International Geoscience And Remote Sensing Symposium July, Vancouver, Canada

Squall in the rainy season

Detection of expansion Due to the 2009 Sumatra earthquake Due to the squall after the earthquake Plane figure of slope failure expansion of collapse by squall