[S-CG45] Science of slow-to-fast earthquakes

[SCG45-05] New slip deficit rate model and slow earthquakes at the Nankai subduction zone

*Raymundo Omar Plata Martinez¹, Takeshi Iinuma¹, Fumiaki Tomita², Takuya NISHIMURA^1,3, Yasuyuki Nakamura¹, Takane Hori¹ (1.JAMSTEC, 2.International Research Institute of Disaster Science, Tohoku University, 3.DPRI, Kyoto University)

Keywords:Geodesy, Slip deficit rate, Slow earthquakes

The last two important earthquakes occurring at the Nankai subduction zones were the Tonankai and Nankaido magnitude 8 earthquakes in 1944 and 1946, respectively. A repeating interval of 100-150 years has been estimated for these types of large earthquakes in the region. Furthermore, slow earthquakes at the shallow and deep plate interface are another important phenomenon occurring at Nankai. Slip from large earthquakes and slow earthquakes originate from different types of frictional characteristics, mostly driven by an accumulation of interplate slip deficit. To continue the monitoring of the Nankai subduction zone, here we present a new model of slip deficit rate at the plate interface. We invert the slip deficit rate using a new trans-dimensional reversible jump Markov Chain Monte Carlo method (Tomita et al. 2021) with onshore and offshore geodetic data (Nishimura et al., 2016). Additionally, we used elastic Green Functions estimated from a 3D heterogeneous structure of the Nankai region (Hori et al., 2021), instead of a homogeneous medium as previously done. We obtained a new model of slip deficit rate that agrees and adds to previous ones to maintain updated models. Regions with high slip deficits, or high coupling, agree with the rupture areas of historic large earthquakes that might have been stopped by adjacent uncoupled areas. The spatial occurrence of slow earthquakes matches with intermediate values of the slip deficit rate and defines the transition between a locked and unlocked plate interface. Moreover, the occurrence of shallow slow earthquakes at a coupled plate interface can be explained by the presence of subducting seamount.