Deformed submarine terraces in Puget Sound, Pacific Northwest indicate only one M > ~7.5 earthquake on the Seattle fault zone in the past 11,000 years

Seafloor terraces around ~50 m depth are abundant beneath Puget Sound. These terraces have been attributed to a sea-level lowstand ca. 11 ka. Depths to the terraces across upper plate faults in Puget Sound can be used as a record for tectonic deformation since that time.  

The data consist of bathymetric and seismic reflection data from Puget Sound, Washington, USA. They have been interpreted to show an upward offset in bathymetric terraces across the Seattle fault zone. This data repository includes the following files necessary to reproduce these results:

basemap.pdf: Bathymetric and topographic map of the study area (central Puget Sound, USA) showing the location of bathymetric profiles and fault zones used in the study.

bathymetric_datasets.xlsx: Spreadsheet describing all public bathymetric datasets used in the study.

profiles.zip: Text files of bathymetric profiles used in the study. Each profile consists of a distance and depth extracted from the bathymetric files listed in dataset 2.

picks.xlsx: Spreadsheet that identifies each bathymetric profile, the x-y coordinate location and measured depth for each profile's bathymetric terrace and the uncertainties and propagated error for each depth.

images.pdf:  PDF document showing locations and images for the two seismic reflection profiles used in the study, plus explanations for each image. See the Methods section for a description of the collection of these profiles.

Methods
Dataset 5 (images.pdf) shows images from two seismic reflection surveys collected in Puget Sound, USA:

2019 CHIRP seismic reflection survey

This survey was collected by the authors in October, 2019 aboard the R/V Weelander, a 15 ft vessel operated by the University of Washington School of Oceanography. The survey was collected with an ultra-high resolution, 2-16 kHZ Edgetech 216s CHIRP system and crossed Elliott Bay, the Duwamish Waterway, and terraces offshore Bainbridge Island. Data were processed using a standard CHIRP processing workflow that included heave correction and conversion to envelope. After processing, the data were collected in an interpretation project along with complementary datasets using the IHS Kingdom Suite software. Two-way travel time in seconds was converted to depth using a constant velocity of 1500 m/s. Depths were not tide-corrected, and we do not use absolute depths in this study.

1982 minisparker legacy data

This survey was collected in 1982 by Dr. Mark Holmes and others aboard the R/V Onar at the University of Washington School of Oceanography. A cruise map and paper scrolls showing the data were produced and were encountered by the authors in the files of the University of Washington School of Oceanography.