11:00 AM - 1:00 PM
[SGD01-P05] Detection of unsteady GNSS displacements by removing the postseismic displacements of an earthquake
Keywords:slow slip event, Nankai Trough, GNSS
We developed a prototype method to estimate and correct the postseismic displacements of a large earthquake using GNSS daily coordinates. Only one logarithmic function was adopted as the approximation function for the postseismic displacements at this time. The initial conditions to be given are the start and end dates of the correction factor calculation, logarithmic time constant range, number of fitting calculations, and convergence judgment criteria. For each station, the time constant is determined using the east-west and north-south components, and then the coefficients for the amplitude of each component are determined. The SCE-UA method (Duan et al., 1992), which is one of the global search methods, was used to minimize the difference between the observed and theoretical displacements. Since fitting with the same weights for all periods would not fit the changes in the early stages of the postseismic displacements, we used more data from the early stages to estimate.
While correcting for the postseimic displacements of an earthquake, we confirmed the detection of subsequent unsteady crustal displacements. The earthquake to be corrected is the M7.2 earthquake off Miyagi Prefecture on August 16, 2005. The detection targets are the postseismic displacements of the M7.0 earthquake off Ibaraki Prefecture on May 8, 2008 and the M6.9 earthquake off Fukushima Prefecture on July 19, 2008. We applied the GNSS long-term slow slip objective detection method (Kobayashi, 2017) to the Tohoku region. As a result, a range of correlation coefficients above 0.6 began to appear in the process until the end of August 2008, and was clearly detected in the process until the end of September 2008. In the future, we plan to verify the phenomena with shorter time constants.
The GNSS F5 coordinate data and offset data were provided by the Geospatial Information Authority of Japan.
While correcting for the postseimic displacements of an earthquake, we confirmed the detection of subsequent unsteady crustal displacements. The earthquake to be corrected is the M7.2 earthquake off Miyagi Prefecture on August 16, 2005. The detection targets are the postseismic displacements of the M7.0 earthquake off Ibaraki Prefecture on May 8, 2008 and the M6.9 earthquake off Fukushima Prefecture on July 19, 2008. We applied the GNSS long-term slow slip objective detection method (Kobayashi, 2017) to the Tohoku region. As a result, a range of correlation coefficients above 0.6 began to appear in the process until the end of August 2008, and was clearly detected in the process until the end of September 2008. In the future, we plan to verify the phenomena with shorter time constants.
The GNSS F5 coordinate data and offset data were provided by the Geospatial Information Authority of Japan.