Mamoru Koarai

Satellite data gives snapshot of the 2005 Pakistan earthquake

While it is well-known that the collision of the Indian subcontinent with the Eurasian continent forms the Himalayas, the real-time spatial crustal movement of these plates is difficult to observe. However, scientists can witness a part of this process of the formation of the Himalayas through an eye in space: synthetic aperture radar (SAR). From the European Space Agencys Envisat, a satellite with SAR, the details of crustal deformation resulting from a major earthquake—a chance snapshot of the growth of the Himalayas—has been captured. Envisats SAR has provided important data about the northern Pakistan earthquake (M7.6) of 8 October 2005, which occurred in the Kashmir region in the northwestern part of the Himalayas.

InSAR-derived crustal deformation and fault models of normal faulting earthquake ( M j 7.0) in the Fukushima-Hamadori area

Applying interferometric SAR (InSAR) analysis using ALOS/PALSAR data to inland crustal earthquakes in the Fukushima-Hamadori area, we succeeded in mapping a ground displacement associated with the Mj 7.0 earthquake that occurred on 11 April, 2011. The most concentrated crustal deformation is located ~20 km west of the city of Iwaki, showing displacements away from the satellite with ~2.2 m at the maximum. Clear displacement discontinuities are recognized with an offset of ~1.6 m at the maximum, which are just on the Shionohira, Idosawa and Yunotake faults. From field surveys, we found that earthquake surface faults appeared with a vertical offset of ~1.9 m, consistent with the InSAR observation, and their locations correspond to the discontinuities in the interferogram. We inverted the InSAR data to construct slip distribution models, and our models show (1) nearly pure normal fault motions (2) on west-dipping planes (3) with moderate-dip-angles (50–65°). The inferred west-dipping normal fault motion on the Yunotake fault is correlated with the present-day topographic features, consistent with the idea that the historically-repeated normal faultings have developed the topography. On the other hand, for the Shionohira and Idosawa faults antithetical relationships are presented, maybe suggesting that large normal faultings have been infrequent historically.

Crustal deformation and a preliminary fault model of the 2007 Chuetsu-oki earthquake observed by GPS, InSAR, and leveling

The 2007 Chuetsu-oki earthquake occurred just west off the coast of Kashiwazaki in Niigata Prefecture, Central Japan on July 16, 2007. The permanent GPS network (GEONET) clarifies the coseismic displacement as a thrust faulting whose compressional axis lies in the NW-SE direction. Interferometric analysis of synthetic aperture radar (SAR) images acquired by “Daichi” satellite (ALOS) maps a detailed spatial pattern of the displacement toward the satellite for both ascending and descending orbits. Peak-to-peak displacement reaches approximately 400 mm in the descending orbit interferometric (In)SAR data. Repeated precise leveling shows uplift near the northeast part of the aftershock area and subsidence near the southwestern part. We construct a preliminary fault model by inverting the observed deformation. The preferred model consists of two segments of rectangular faults whose moment magnitude is 6.7 in total. From only the used geodetic data on land, it is difficult to determine which plane in two conjugate planes of the focal solution was ruptured. It is important to consider the effect of a heterogeneous medium and variable slip on the faults as well as other geophysical data to determine the fault model with confidence.

The DEM generation of a volcano using airborne SAR interferometry

The airborne interferometric SAR technique enables us to generate a digital elevation model (DEM). However, in the mountainous area with steep terrain, we cannot obtain some DEM data because of radar shadowing, layover, etc. To generate the complete DEM of the observed area, it is necessary to observe with different incident angles and directions, and compound some DEMs obtained from the data of different incident angles and directions. In addition, if we use a light airplane, which is much affected by turbulence, the generated DEM contains large height errors caused by the intense body motion. Therefore, in case of the map projection, location errors are caused. As a result, it is very difficult to compound the DEM with accuracy. The volcanic eruption of Miyake Island in Japan occurred in July 2000, caused large-scale cave-in. We observed the crater by airborne interferometric SAR with two different incident angles from four directions in order to generate the DEM of the inside of the crater. After data acquisition, we tried to improve the accuracy of the DEM. The method is to iterate the following process, namely motion compensation considered to the rough target height in the azimuth compression in time domain and the interferometric SAR processing. Then, we were able to generate a comparatively accurate DEM, which covers the whole of Miyake Island with the inside height information of the crater.

Detection of 2011 off the Pacific Coast of Tohoku Earthquake-Induced Landslide Deformation Using InSAR

Many researchers have reported the landslide triggered by the 2011 off the Pacific coast of Tohoku earthquake. However, these reports are mainly based on field surveys and interpretation of aerial photographs. In this study, we try to detect and analyze earthquake-induced landslide deformations from InSAR (synthetic aperture radar interferometry) images using Advanced Land Observing Satellite (ALOS)/Phased-array L band SAR (PALSAR) data. We explain this method of landslide detection and introduce examples of detected landslides. It is thought that these landslides do not cause serious, rapid damage because they caused only minor displacement. However, continual monitoring of detected landslides using InSAR is important to prepare for possible landslide reactivation caused not only by an earthquake but also by snowmelt and heavy rainfall.

The update of the 1/25, 000 topographical map by using simple type mobile survey system

As acquisition of the position coordinate data of 2 dimensions or 3 dimensions needs time and labor, recently some real time acquisition of the GIS data using electronic flat board and GPS has been introduced. However, because it is using GPS, there are many problems the system itself is quite expensive, and it is impossible to acquire data in the urban area.Therefore, to acquire the position data easily and rapidly in the urban area where the data acquisition is difficult, a simple type mobile interface system is developed. It consists of the laser, gyro, electronic compass (the magnetic azimuth sensor) and DGPS. It controls all the data with one personal computer and it acquires data.