Terrestrial phenomena disasters/Earthquakes/Geotechnical disasters. Geotechnical disasters/Crustal deformation.
Disaster name
1995 Hyogo-ken Nanbu Earthquake (January 17, 1995, M7.2; catastrophic damage in Awaji Island, city of Kobe, and the Hanshin region. More than 6,000 deaths.)
Authors of WEB conversion
Une Hiroshi and Tobita Mikio

Case Study

No. 24

1. Analysis objective

In order to understand the areal distribution of crustal deformation associated with the earthquake, we attempted to map crustal deformation using spaceborne SAR interferometry.

2. Analysis procedure Analysis flow chart

1) Satellite data used: JERS-1 (Fuyô 1) SAR images

Prior to earthquake: September 9, 1992
After earthquake: February 6, 1995

2) Summary of analysis

After we measured pixel offsets between identical pixels in the two images and coregister corresponding pixels, we calculated phase difference between the two images for each pixel to produce an interferogram. Then, spatial filters, the multi-look filter and the adaptive filter developed by Goldstein and Werner (GRL, 1998), were applied to the interferogram. This dropped pixel resolution to about 100m.

We remove the systematic phase and the topographic phase using orbit elements of the satellite and DEM, respectively. We then expressed the remaining phase by colors in an image (interferogram).

3.Analysis results

1) We discovered a crustal deformation zone about 20km long and several kilometers wide that stretches from Suma ward to Higashinada ward in the city of Kobe. This zone runs nearly parallel to the coast, with a change that moves away from the satellite on the coastal side that can be explained by the right strike-slip of the fault. Although the noise increases and indistinctness grows larger on the east side of the image, it can be noticed that the direction of the displacement changes from east-northeast to northeast.

This suggests that the fault does not run in a straight line.

2) In contrast to the above-mentioned deformation, in Tarumi ward, Kobe a movement that approaches the satellite on the coastal side is seen. The change in the pattern is discontinuous exactly at the Tarumi ward and Suma ward boundary, suggesting the existence of underground fault slip.

3) In Awaji Island, a concentric circle deformation can be noted centered on the Nojima fault, which we can explain by a right strike-slip of the Nojima fault and uplift on the southeast side.

4. Usefulness of the analysis results

The analysis of the Hyogo-ken Nanbu Earthquake is a typical example, which dramatically increases the quantity of information concerning crustal deformation through combining information from GPS, traditional geodetic survey techniques, such as leveling, and the Synthetic Aperture Radar.

Although the SAR interferometry, a crustal deformation measurement technique, has only recently been developed, it opens the way to new possibilities in the research of crustal deformation.

In particular, many analysis results of JERS-1 data have indicated that L-band SAR was very effective to detect crustal deformation in heavily vegetated land like Japan.

5. Analysts

Analysts: Tobita Mikio, Fujiwara Satoshi and Murakami Makoto