Does the subducted ridge impede large shallow slow earthquakes?
Does the subducted ridge impede large shallow slow earthquakes?
hunsuke Takemura1, Suguru Yabe2, Kentaro Emoto3 and Satoru Baba3
1ERI UTokyo, 2AIST, 3Kyushu Univ.
Takemura, S., Yabe, S.., Emoto, K., Baba, S. (2025). Along-dip variations in source characteristics of shallow slow earthquakes controlled by topography of subducted oceanic plate, J. Geophys. Res., 130, e2024JB030751, https://doi.org/10.1029/2024JB030751
Shallow slow earthquakes occur in regions adjacent to or at the shallower extension of the megathrust zones. How will the shallow slow earthquake zone behave in future megathrust earthquakes? It is an important issue for earthquake physics and disaster mitigation from megathrust earthquakes. To obtain slip behaviors in the shallow slow earthquake zone of the Nankai subduction zone, we investigate source characteristics of shallow very low frequency earthquakes (VLFEs). Shallow VLFEs are a kind of slow earthquake and often occur around the plate boundary at depths ≤ 10 km. We found a notable characteristic change in shallow VLFEs due to the Paleo-Zenisu ridge (Figure 1c), the subducted seamount beneath our target region.
Our results imply that large-scale topographic features of the subducted oceanic plate could control a slip behavior around the shallow plate boundary fault (Figure 2). The subducted Paleo-Zenisu ridge may impede large shallow VLFEs.
Figure 1. Spatial variations of source characteristics of shallow VLFEs. (a) Cumulative moments of shallow VLFEs from April 2015 to March 2021. The diamonds represent the station locations of DONET. The dashed gray line is the Nankai Trough. Cumulative moments were evaluated via the gridding algorithm (Wessel et al., 2013) within each 0.05º-grid cell. The gray-shaded area represents the subducted Paleo-Zenisu ridge (Park et al., 2004). (b) Along-strike and (c) dip variations of moment rates of shallow VLFEs. The intersection point in (a) represents along-strike and dip distances of 0 km in (b) and (c). The shallow VLFEs with along-strike distances of 10-30 and 40-60 km are used in the along-dip dependency of KMD-KMC and KMB profiles. The blue dotted lines in (b) and (c) are the detectability of VLFEs in this region (Fig. 11 of Takemura, Baba, et al., 2024).Figure 2. Schematic figure of shallow VLFE moment rates along the (a) KMD-KMC and (b) KMB profiles. The subducted Philippine Sea plate along the KMD-KMC and KMB profiles is referred to as line 5 of Park et al. (2002) and line D7 of Park et al. (2004), respectively. The locked zone is referred from the spatial distribution of the shear-stress change rate on the Philippine Sea Plate (Noda et al., 2018, 2021). We considered the zones with large (≥ 5 kPa/y) shear stress change rates as frictionally locked zones. The blue shaded area in Figure 5b represents the area of stress shadow or fracture network due to a seamount subduction referred from previous studies (e.g., Chesley et al., 2021; Ruh et al., 2016; Wang & Bilek, 2011).
