Decadal seafloor geodesy constrains frictionally locked areas along the Nankai Trough

Yokota, Yusuke 1 ; Watanabe, Shun-ichi2 ; Nagae, Koya2 ; Nakamura, Yuto 2 ; Ishikawa, Tadashi3

Published Aug 22, 2025 on Dryad. https://doi.org/10.5061/dryad.bcc2fqzs1

Data files

Aug 22, 2025 version files 177.88 KB

dataset.zip

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README.md

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Abstract

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.

https://doi.org/10.5061/dryad.bcc2fqzs1

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 components are listed in order from top to bottom.

$site: Site name
Year: Center of the range in which the velocity is calculated
Vel[m/y]: Calculated velocity [m/y]
from: Start of the range for calculating the speed
to: End of the range for calculating the speed
σ-: Vel-1σ [m/y] (σ: standard deviation in velocity calculation)
σ+: Vel+1σ [m/y]

Data S3: slipcoef_disp_$year_ud

Coefficients in the “02” (first column) and “03” (second column) directions of each node of Green’s function library when estimating SDR for each period in Fig. 4.

1st column: "02" direction of Green’s function library
2nd column: "03" direction of Green’s function library

Data S4: OC_$year

The observed and calculated values used in the SDR inversion for each epoch in Fig. 5.

$year: Time range (ex: "2015" indicates the period from Jan 2013 to Dec 2016) for the SDR inversion
Lon: Site longitude
Lat: Site longitude
obs_E(cm/y): Eastward component in observed velocity [cm/y]
obs_N(cm/y): Northward component in observed velocity [cm/y]
obs_U(cm/y): Upward component in observed velocity [cm/y]
cal_E(cm/y): Eastward component in calculated velocity [cm/y]
cal_N(cm/y): Northward component in calculated velocity [cm/y]
cal_U(cm/y): Upward component in calculated velocity [cm/y]

Data S5: slipcoef_disp_std_ud

The average of standard deviation (Fig. S2) of coefficients in the “02” (first column) and “03” (second column) directions when estimating SDR for the periods.

1st column: "02" direction of Green’s function library
2nd column: "03" direction of Green’s function library