11:15 AM - 11:30 AM
[SCG61-21] Interplate coupling distribution along the Nankai trough in southwest Japan estimated by the block motion model on the basis of onshore and seafloor geodetic observation data
Keywords:Interplate coupling, Onshore and seafloor geodetic observation data, Block motion model, Optimization of estimation error
In the block motion model, observed crustal deformation dkObs is assumed that the sum of rigid
block motion vikRigid and elastic deformation due to coupling at block boundaries vijkElastic as follows:
dkObs=vikRigid +vijkElastic =ωi×rk+GklCl(ωi-ωj)×rl
(ω, Euler pole; r, position; G, Green function of elastic half-space; C, Coupling ratio (0-1);
i, j, k, site; l, subfault).
This is a non-linear equation; thus, we estimate the probability density function (PDF) of ω and C simultaneously to minimize the sum of squared residuals between observed and calculated crustal deformation vectors, using the Markov Chain Monte Carlo (MCMC) method. The estimation error is optimized to be homogeneously in space, using the method of Kimura et al. (2016, 126th meeting of the Geodetic Society of Japan). The input data are onshore GNSS (GEONET, 2006-2009; ZENISU, 2005-2010) and seafloor GNSS/A observation conducted by Nagoya University and Japan Coast Guard (2004-2016); the total number of data is 887. The tectonic models are made based on the active fault trace and spatial epicenter distribution. We select the best tectonic model, which consists of 12 blocks, based on the Akaike's Information Criterion.
We show the estimated coupling distribution and some examples of PDF of coupling ratio obtained by MCMC in the Figure. Variances of PDFs are nearly equal in all the subfaults, meaning that the coupling is estimated with homogeneously in space for almost all the subfaults by optimization of estimation error.
We find that the spatial distribution of interplate coupling along the Nankai Trough is heterogeneous along the strike of the trough axis, although plate interface shallower than 25 km is strongly coupled overall. This spatial heterogeneity of shallow interplate coupling is an important feature obtained by using the seafloor GNSS/A observation data.
Although Yokota et al. (2016) has estimated the strong coupling on the plate interface deeper than 40 km, we estimate that the down-dip limit of strong coupling is about 30 km in depth, by applying the block motion model. Our estimation coincides with the down-dip limit of locking area estimated from the thermal and deformation model (e.g., Hyndman et al., 1995).