Decadal seafloor geodesy constrains frictionally locked areas along the Nankai Trough

Identifying the frictionally locked area of a plate boundary is an important geodetic issue in mitigating earthquake disasters, but slow slips make it impossible to understand the frictional state via temporally averaged geodetic data. This problem is particularly serious at sub-seafloor plate boundaries, where long-term geodetic observations are difficult. Here, we evaluated long-term slip deficit rate variations in the Nankai Trough, the only area in the world for which high-density data on horizontal and vertical components have been accumulated via seafloor observations with a sufficient frequency on the decadal scale. Consequently, we constrained the constantly locked areas and found that it was limited mainly to a depth of 10–20 km, with slow slips occurring throughout the entire shallow side adjacent to the locked area., , , # Decadal seafloor geodesy constrains frictionally locked areas along the Nankai Trough

[https://doi.org/10.5061/dryad.bcc2fqzs1](https://doi.org/10.5061/dryad.bcc2fqzs1)

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We have submitted GNSS-A position data (**Data S1: res.$site**), velocity data (**Data S2: $site.data_mvel**), coefficients in SDR inversions (**Data S3: slipcoef_disp_$year_ud**), O-C values in SDR inversions (**Data S4: OC_$year**), and average of standard deviation of coefficients (**Data S5: slipcoef_disp_std_ud**).

## Descriptions

### **Data S1: res.$site**

Time series of positions of each observation site in Fig. S1.

* *$site*: Site name
* *Year*: Observed date
* *EW[m]*: Eastward component [m]
* *NS[m]*: Northward component [m]
* *UD[m]*: Upward component [m]

### **Data S2: $site.data_mvel**

Time series of velocities of each observation site in Fig. S1. The time period used to calculate the velocity and its estimation accuracy (velocity ±1σ) are also listed.
The eastward, northward, and upward compo...