11:45 AM - 12:00 PM
[SGD01-11] Early afterslip of the 2011 Tohoku-Oki sequence estimated by the GNSS carrier phase to fault slip approach
Time scale of few minutes to half day is remained shadow zone of current GNSS analysis. This is mainly due to difficulty of separation between deformation and other error factors such as atmospheric delay. And, actually very few previous studies analyzed deformation and/or fault slip with this time scale, for example early postseismic process. Using coordinate time series for observation is also obstruction for quantitative evaluation of parameter separation, since positioning analysis is originally independent from source of deformation, i. e. fault slip. Regarding these problems, we are developing broadband fault slip monitoring based on alternative approach, the GNSS carrier phase to fault slip approach. This method, which we call PTS (Phase To Slip), relates fault slip directly to relative change of GNSS carrier phase. As PTS method estimates all unknown parameters in parallel, we can evaluate their separation and discuss its improvement comprehensively.
In this study, we tried to continuously estimate coseismic and early postseismic slip of the 2011 Tohoku-Oki sequence. In the analysis, we used 1 Hz carrier phase data of 66 GEONET sites around east Japan. Then we estimated spatio-temporal evolution of slip from 05:00 to 06:56 (UTC) on 2011 March 11. As a result, PTS estimated aseismic slip increase in time after the mainshock. We obtained slip areas around downdip side of the assumed fault zone, which is below coastal region of Iwate, Miyagi, Fukushima and Ibaraki. We also obtained slip area around off Iwate and Aomori. All of them is adjacent to the mainshock rupture, and well intersect with early afterslip area estimated by normal positioning such as Munekane (2012). On the other hand, slip amount is about 0.4 to 0.5 m in maximum and equivalent seismic moment reached Mw7.47 in 33 minutes after the mainshock. These amounts seem to be slight larger than estimations by normal positioning. Additionally, our results show earlier slip increase around Fukushima and Ibaraki. This is also an unprecedented characteristic.
Our results indicate capability of the PTS method for broadband fault slip monitoring, which includes early postseismic process. In the presentation, first we will discuss robustness and reliability of our results. Then, we will focus on comparison of the estimations based on the PTS and normal positioning. Additionally, we evaluate O-C fitness and accuracy of parameter separation quantitatively in the dimension of carrier phase, which is used as observation in the PTS.
In this study, we tried to continuously estimate coseismic and early postseismic slip of the 2011 Tohoku-Oki sequence. In the analysis, we used 1 Hz carrier phase data of 66 GEONET sites around east Japan. Then we estimated spatio-temporal evolution of slip from 05:00 to 06:56 (UTC) on 2011 March 11. As a result, PTS estimated aseismic slip increase in time after the mainshock. We obtained slip areas around downdip side of the assumed fault zone, which is below coastal region of Iwate, Miyagi, Fukushima and Ibaraki. We also obtained slip area around off Iwate and Aomori. All of them is adjacent to the mainshock rupture, and well intersect with early afterslip area estimated by normal positioning such as Munekane (2012). On the other hand, slip amount is about 0.4 to 0.5 m in maximum and equivalent seismic moment reached Mw7.47 in 33 minutes after the mainshock. These amounts seem to be slight larger than estimations by normal positioning. Additionally, our results show earlier slip increase around Fukushima and Ibaraki. This is also an unprecedented characteristic.
Our results indicate capability of the PTS method for broadband fault slip monitoring, which includes early postseismic process. In the presentation, first we will discuss robustness and reliability of our results. Then, we will focus on comparison of the estimations based on the PTS and normal positioning. Additionally, we evaluate O-C fitness and accuracy of parameter separation quantitatively in the dimension of carrier phase, which is used as observation in the PTS.