Measurement of Topographic variation by Hyogo-Nanbu Earthquake
with JERS 1STAR Interferometry
Yuichi Maruyama, Hiroji Tsu
Earthquake Remote Sensing Data Analysis Center (ERSDAC)
Forefront Tower, Kachidoki 3-12-1, Chuo-ku, Tokyo, JAPAN
Tel. 03-3533-9380,fax. 03-3533-9383
1. Introduction
The Hyogo-Nanbu Earthquake occurred on 17 January 1995 attacked the Kobe city and the Awaji island. More than 5,000 of human lives were lost under the collapsed houses and a fire.
The fault activity was observed on the several points in the area after the occurrence.
The fault displacements were measured in many places. The deformation of the topographic surface, however, was hardly measured on the surrounded area of the fault line.
The purpose of this study is to know the availability of the interferometric SAR for the deformation of topographic surface, by the earthquake with JERS-1 SAR data. Because, it can be very useful information for the study of active geological structure. In addition, it is also possible to apply for the natural disaster focusing such as landslide, volcanic hazards, etc.
For this purpose the area studied is selected in the northern part of Awaji island (Figure1), where the Nojima fault, one of the active faults had moved to rise sever hazar.
Figure 1: Location of Study Area
2.Method
2.1 Data Used
The data employed to carry out double difference interferogram analysis are shown as followed:
- JERS-1 SAR data
- acquired on 9 September 1992
- acquired on 6 February 1995
- DEM
It is 50m interval mesh data, that is based on 1:25,000 topographical maps.
2.2 Data Processing
The process to generate the interferogram and double difference interferogram image is shown in Figure 2. At the first step, phase preserved SAR imageries were created with the data from the 1992 and the 1995 scene, the interfered in them to create initial
Figure 2: Flow and sketch for process of double difference interferogram image preparation
Interferogram. Then, reference interferogram was generated with the virtual phase and the 1992 scene data. The virtual phase was generated from the satellite position of 1995's scene to the DEM (Digital Elevation Model) surfaces.
The subtraction of these two interferogram could realize to obtain a double difference interferogram. The process and data matching are schematically shown in Figure 2(B).
2.3 Double Difference Interferogram Imagery
The estimated phase difference was divided into three levels to assign them different colors (Figure 3), and the imagery divided into two levels is prepared additionally (Figure 4 ). These two kinds of imageries are prepared for the following purposes. The figure 3 is to understand total amount of topographic variation. JERS-1 SAR represent the topographic variation of 11.75 cm by single rotation. This value corresponds to a half of wavelength of JERS-1 SAR. The figure 4 is prepared as convenient imagery for the interpretation of small scale topographic deformation.
Figure 3: Double difference interferogram image (Divided into three levels)
Figure 4: Double difference interferogram image
