Youichiro Takada

Coseismic displacement due to the 2008 Iwate-Miyagi Nairiku earthquake detected by ALOS/PALSAR: preliminary results

Applying interferometric SAR (InSAR) analysis to the 2008 Iwate-Miyagi Nairiku earthquake, we detected notable ground displacements of several tens of centimeters to about 1.2 m that extend further south of the epicentral area. We explained the InSAR data by constructing a fault model consisting of four WNW dipping and one ESE dipping reverse faults. The residuals between observed and modeled deformation are less than 6 cm in most of the area, which is comparable to the errors caused by atmospheric effect. To fill the lack of InSAR data in the hypocentral area, we applied a pixel matching technique to the intensity images, which shows a shortening in range offsets by as much as ∼2 m along a narrow zone stretching along the eastern foot of Mt. Kurikoma, indicating a localized uplift. We also found remarkable contrasts in the range offsets around the low coherence area equivalent to a very large displacement gradient to the WNW of the hypocentral area as well as ESE. We conclude that the main faulting occurred on the WNW dipping reverse faults, but that the overall geometry of the fault system is quite complex including at least one conjugate faulting, as also supported by the hypocentral distribution of aftershocks.

Correction to “Locations and types of ruptures involved in the 2008 Sichuan earthquake inferred from SAR image matching”

1 We have detected detailed ground displacements in the proximity of the 2 Longmen Shan fault zone (LMSFZ) by applying a SAR offset-tracking method in the 3 analysis of the 2008 Sichuan earthquake. An elevation-dependent correction is 4 indispensable for achieving sub-meter accuracy. A sharp displacement discontinuity 5 with a relative motion of ~1-2 m appears over a length of 200 km along the LMSFZ, 6 which demonstrates that the main rupture has proceeded on the Beichuan fault (BF) 7 among several active faults composing the LMSFZ, and a new active fault is detected 8 on the northeastward extension of the BF. The rupture on the BF is characterized by a 9 right-lateral motion in the northeast, while in the southwest an oblique right-lateral 10 thrust slip is suggested. In contrast to the northeast, where a major rupture proceeded on 11 the BF only, in the southwest multiple thrust ruptures have occurred in the southeastern 12 foot of the Pengguan massif. 13

PALSAR InSAR Observation and Modeling of Crustal Deformation Due to the 2007 Chuetsu-Oki Earthquake in Niigata, Japan

On June 16 2007 (AM 10:13 in Japan Standard Time), an earthquake of magnitude 6.8 took place about 10 km offshore of Chuetsu area in Niigata, Japan.

Interseismic crustal deformation in and around the Atotsugawa fault system, central Japan, detected by InSAR and GNSS

The Atotsugawa fault system is one of the best-known active faults in Japan. However, revealing the interseismic velocity field in and around the Atotsugawa fault system with high spatial resolution is challenging because of dense vegetation, steep topography, and heavy snowfall in winter. To overcome these difficulties, we combined ALOS/PALSAR data and GNSS data from our original stations in addition to the nationwide station network (GEONET). First, we removed the height-dependent phase change in each interferogram using a digital elevation model. Next, we removed the long-wavelength phase trend using the GNSS velocity field. Finally, we applied an InSAR time-series analysis, known as small baseline subset analysis (SBAS), to all the corrected interferograms. The resultant mean velocity field shows a remarkable phase gradient around the Atostugawa fault system. We found a sharp velocity gradient across the Ushikubi fault, a major strand of the Atotsugawa faults system, rather than the main trace of the Atotsugawa fault. Using InSAR, we found that the interseismic deformation inside the strain concentration zone is spatially heterogeneous and different from what we expect from the fault traces.

Coseismic Deformations of the 2011 Tohoku, Japan, Earthquake and Triggered Events Derived from ALOS/PALSAR

The Tohoku earthquake on March 11, 2011, caused a remarkably large deformation on the island of Honshu, Japan. By analyzing ALOS/PALSAR data, a range increase of up to 3.6 m at the tip of the Oshika Peninsula, the closest point to the epicenter, was detected from ascending orbits. Combining ascending and descending interferograms, this peninsula was confirmed to have subsided and shifted eastward. This deformation may have been caused by a huge reverse slip on the plate interface near the trench axis.