8:30 AM - 8:45 AM
[J06-1-01] Numerical experiments on estimation of frictional properties and slip evolution on the Bungo Channel Long-term SSE fault with Ensemble Kalman Filter
Long-term Slow Slip Events (LSSEs) occur on the plate interface beneath the source regions of the interplate large earthquakes. The activity of SSEs possibly changes before large interplate earthquakes and SSEs may directly trigger them. Our final goal is to estimate slip evolution and frictional parameters with Ensemble Kalman Filter (EnKF), one of data assimilation methods. In this paper, we execute numerical experiments for the Bungo Channel LSSEs, southwest Japan, before analyzing the actual GNSS observation data.
Our previous experiments for the Yaeyama SSEs in the Ryukyu region showed that, for well recovery of parameters and slip evolution with EnKF, the conditions are: 1)SSEs have been observed more than once, 2)The duration of SSEs is long, 3)SSEs are observed at observation points with enough density and coverage. Hence, we target at the Bungo Channel LSSEs which have occurred several times with the duration of about 1 year.
We set a dipping fault in a homogeneous elastic half space and assume a rate-state friction law and the slowness law of state evolution. We set a circular velocity-weakening patch (radius R=40km) on the fault plane with frictional parameters so that R/Rc=0.9 (Rc: critical nucleation radius). We generate synthetic observed data by adding random numbers to the simulated surface displacement rates and performed EnKF estimations of the frictional parameters A and L on the fault plane and B-A on the patch along with the slip rates and the state variables.
The results show that if the duration of SSEs is sufficiently longer than the assimilation step, update is moderately performed and calculation does not stop. As long as we use a simple model, we can estimate the frictional parameters on the fault with considerable accuracy for the actual GNSS (GEONET) distribution.
In our current model, frictional parameters are uniform on the SSE patch. We need to perform numerical experiments with more complicated models.
Our previous experiments for the Yaeyama SSEs in the Ryukyu region showed that, for well recovery of parameters and slip evolution with EnKF, the conditions are: 1)SSEs have been observed more than once, 2)The duration of SSEs is long, 3)SSEs are observed at observation points with enough density and coverage. Hence, we target at the Bungo Channel LSSEs which have occurred several times with the duration of about 1 year.
We set a dipping fault in a homogeneous elastic half space and assume a rate-state friction law and the slowness law of state evolution. We set a circular velocity-weakening patch (radius R=40km) on the fault plane with frictional parameters so that R/Rc=0.9 (Rc: critical nucleation radius). We generate synthetic observed data by adding random numbers to the simulated surface displacement rates and performed EnKF estimations of the frictional parameters A and L on the fault plane and B-A on the patch along with the slip rates and the state variables.
The results show that if the duration of SSEs is sufficiently longer than the assimilation step, update is moderately performed and calculation does not stop. As long as we use a simple model, we can estimate the frictional parameters on the fault with considerable accuracy for the actual GNSS (GEONET) distribution.
In our current model, frictional parameters are uniform on the SSE patch. We need to perform numerical experiments with more complicated models.