4:45 PM - 5:00 PM
[SSS05-12] Possible overlap of coseismic slip and afterslip investigated by InSAR analysis
Keywords:InSAR, ALOS-2, Afterslip
According to previous studies using seismic waves and crustal deformation data, the afterslip area on a fault is often estimated around the coseismic slip area, which is theoretically understood in such a way that the stress concentration caused by the unstable coseismic slip induces the surrounding stable slip area to slip (e.g., Marone et al., 1991, Boatwright & Cocco, 1996 etc.). In this study, we report the results of the 20 May 2016 earthquake in central Australia, where the coseismic slip and the afterslip areas may largely overlap.
We used ALOS-2 ascending data of path 124, frame 6670. For the extraction of the coseismic deformation, the pair of 15 December 2015 and 14 June 2016 were used. For the extraction of the postseismic deformation, the pairs of 14 June 2016 and 13 December 2016 (about six months after the earthquake), and 14 June 2016 and 28 November 2017 (about a year and a half after the earthquake) were used. In both InSAR analyses, spatial patterns of deformation, dominantly LOS shortening consistent with the reverse faulting, were confirmed along the known active fault trace (figure). In these results, the deformed area is localized around the fault, suggesting that the mechanism of the postseismic deformation is dominantly afterslip. The maximum coseismic LOS shortening was about 60cm, and that of the postseismic period was about 3cm. The two interferograms of the postseismic deformation periods showed no temporal increase of the deformation. Preliminary inversion analysis using the coseismic and postseismic interferograms indicated that the slip occurred on similar areas on the fault. Here we assumed that the deformation in the postseismic interferograms was due to afterslip.
The coseismic interferogram was created using the SAR image taken 25 days after the main shock, so it may contain a considerable amount of postseismic deformation. Assuming that the actual coseismic slip is significantly larger than the afterslip, however, we can consider that the “coseismic” interferogram is dominated by actual coseismic deformation. If so, an identical spatial pattern in “coseismic” and postseismic interferograms indicates an identical slip area. Based on the above results and consideration, we infer that the coseismic slip and afterslip areas largely overlapped for the case of the 2016 Australia earthquake.
We used ALOS-2 ascending data of path 124, frame 6670. For the extraction of the coseismic deformation, the pair of 15 December 2015 and 14 June 2016 were used. For the extraction of the postseismic deformation, the pairs of 14 June 2016 and 13 December 2016 (about six months after the earthquake), and 14 June 2016 and 28 November 2017 (about a year and a half after the earthquake) were used. In both InSAR analyses, spatial patterns of deformation, dominantly LOS shortening consistent with the reverse faulting, were confirmed along the known active fault trace (figure). In these results, the deformed area is localized around the fault, suggesting that the mechanism of the postseismic deformation is dominantly afterslip. The maximum coseismic LOS shortening was about 60cm, and that of the postseismic period was about 3cm. The two interferograms of the postseismic deformation periods showed no temporal increase of the deformation. Preliminary inversion analysis using the coseismic and postseismic interferograms indicated that the slip occurred on similar areas on the fault. Here we assumed that the deformation in the postseismic interferograms was due to afterslip.
The coseismic interferogram was created using the SAR image taken 25 days after the main shock, so it may contain a considerable amount of postseismic deformation. Assuming that the actual coseismic slip is significantly larger than the afterslip, however, we can consider that the “coseismic” interferogram is dominated by actual coseismic deformation. If so, an identical spatial pattern in “coseismic” and postseismic interferograms indicates an identical slip area. Based on the above results and consideration, we infer that the coseismic slip and afterslip areas largely overlapped for the case of the 2016 Australia earthquake.