DOI: 10.5061/dryad.wh70rxwxn
title: Migrating shallow slow slip on the Nankai trough megathrust, captured by borehole observatories

description: Patterns of strain accumulation and release offshore in subduction zones
 are directly linked to the potential for shallow coseismic slip and
 tsunamigenesis, but remain elusive. Here, we analyze formation pore
 pressure records from three offshore borehole observatories at the Nankai
 subduction zone, Honshu, Japan to capture detailed slip-time histories of
 two slow slip events (SSEs) along the outermost reaches of the plate
 boundary. Slip initiates ~30 km landward of the trench, migrates seaward
 at 1-2 km d-1 to within a few km of, and possibly breaching, the trench
 and coincides with the onset and migration of tremor and/or very-low
 frequency earthquakes (VLFE). The SSE source region lies in a zone of high
 pore fluid pressure and low stress, providing clear observational evidence
 linking these factors to shallow slow earthquakes.
description: Data collected from borehole observatories that were made
 possible through efforts of the Integrated Ocean Drilling Program (IODP),
 and through the DONET cabled observatory installed and supported by
 JAMSTEC. Funding: Observatory installation and data acquisition were
 founded by attributed NSF Awards.<br><br>Data presented are
 subseafloor pore pressure responses for 2 separate slow slip earthquakes,
 one in 2015, another in 2020. Oceanopgrahic tides have
 been removed. Data are linearly detrended. 
description: # Migrating shallow slow slip on the Nankai trough megathrust, captured by
 borehole observatories
 [https://doi.org/10.5061/dryad.wh70rxwxn](https://doi.org/10.5061/dryad.wh70rxwxn) ## Description of the data and file structure All files: Pressure in kPa (column 1). Time in UNIX format (column 2). Files are named as "site_year.txt" Data are from 2 slow slip earthquakes, one in 2015, another in 2020, recorded at IODP borehole observatories. ### Files and variables #### File: C0002G\_2015.txt **Description:** pore pressure time series at site C0002G during an SSE in 2015 ##### Variables * * column 1: time (UNIX format) * column 2: pore pressure (kPa) #### File: C0002G\_2020.txt **Description:** pore pressure time series at site C0002G during an SSE in 2020 ##### Variables * * column 1: time (UNIX format) * column 2: pore pressure (kPa) #### File: C0010A\_2015.txt **Description:** pore pressure time series at site C0010A during an SSE in 2015 ##### Variables * * column 1: time (UNIX format) * column 2: pore pressure (kPa) #### File: C0010A\_2020.txt **Description:** pore pressure time series at site C0010A during an SSE in 2020 ##### Variables * * column 1: time (UNIX format) * column 2: pore pressure (kPa) #### File: C0006G\_2020.txt **Description:** pore pressure time series at site C0006G during an SSE in 2020 ##### Variables * * column 1: time (UNIX format) * column 2: pore pressure (kPa) ## Code/software Any software can be used to view the data. We use Matlab R2023b for our analyses, however Python can also be used for viewing.  optimization_pub.mat is the matlab script used to perform the optimizations with the provided data and green's functions.