JpGU-AGU Joint Meeting 2020

Presentation information

[J] Poster

S (Solid Earth Sciences ) » S-GD Geodesy

[S-GD02] Geodesy

convener:Koji Matsuo(Geospatial Information Authority of Japan), Yusuke Yokota(Institute of Industrial Science, The University of Tokyo), Daisuke Oka(Geological Survey of Hokkaido, Environmental and Geological Research Department, Local Independent Administrative Agency, Hokkaido Research Organization)

[SGD02-P11] Performance assessment of the GNSS carrier phase to fault slip approach and its feasibility for seismic monitoring

*Yusuke Tanaka1, Yusaku Ohta1 (1.Tohoku University)

Seismic monitoring based on conventional positioning analysis requires huge computational cost and strongly depends on external precise orbit information. Additionally, using coordinate time series for observation prevents us from evaluating accuracy of separation between fault slip and other unknown parameters such as tropospheric delay. Regarding these problems, we investigate the feasibility of the GNSS carrier phase to fault slip approach for seismic monitoring in subduction zone. 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, computational costs for real-time seismic monitoring can be reduced. Tanaka et al. (GRL, 2019) applied the PTS method to the 2016 Kumamoto earthquake and they proposed that PTS can work without external high-quality orbit because it relies on relative changes in azimuthal site-to-satellite ranges.

Here we applied the PTS method to the sequence of the 2011 Tohoku-Oki earthquake. In the analysis, we used both precise orbit which is provided by International GNSS Service (IGS) and broadcast orbit submitted from satellite without any network connection. As a result, in the case of IGS orbit, we obtained coseismic slip distribution of the mainshock that well agree with estimation result using conventional positioning analysis time series, such as shown by Iinuma et al. (2011). Although the estimated moment magnitude 8.8 is slight smaller than those by previous studies, calculated displacement field shows good consistency with that derived from positioning analysis. Moreover, we could also detect coseismic slip of subsequent two large aftershocks that occurred in the off Iwate and the off Ibaraki region. These results suggest that we can make use of the PTS method for continuous seismic monitoring in subduction zone. In case of using broadcast orbit, the long-term stability of the estimated slip time series become much worse. However, if we focus on their relative change within 10 minutes after the earthquakes, we can obtain very similar slip behaviors compared to using IGS orbit. Differences between the slip distributions of two cases became just around one meter or less, which is smaller than the estimated standard deviation of fault slip. These results indicate that the PTS method can be useful as a supplementary system of current monitoring system, which does not depend on any external information.
In the presentation, we will describe detail of these results. Additionally, we will also evaluate O-C fitness and accuracy of parameter separation quantitatively in the dimension of carrier phase, which is used as observation in PTS analysis. Then, we will discuss characteristics of the PTS and future works for refined seismic monitoring using this method.