Microtremor Array Data from the Skagit River Delta, Washington State, 2025

This data release contains seismic waveform data collected using nodal seismometers in the Skagit River Delta, WA. These data were acquired between July 21 and July 26, 2025 using SmartSolo IGU-16HR 3-component seismometers with a natural frequency of 5 Hz. Depending on site conditions, instruments were buried, partially buried, or placed on the ground surface (covered with a traffic cone) to record ambient seismic data for between 2-9 hours. These ambient (i.e., passive-source) data were collected to estimate horizontal-vertical spectral ratios (HVSR), which complement a concurrent active-source seismic reflection survey taking place in the same vicinity (Stephenson et al., 2026). The sites are arranged in four intersecting lines; the first (SL1-SL8) is a north-south line along Skagit City Rd.; the second (SL21-SL28) is a north-south line along Dry Slough Rd.; the third (SL31 and SL32) is an east-west line along Polson Rd.; and the fourth (SL33 and SL34) is an east-west line along Moore Rd.

Waveform data are archived as GNU-zipped tar directories and are saved in Miniseed (mseed) format. Each mseed file contains the 3-component (north, east, vertical) time series sampled at 2 ms (500 Hz) in units of counts. Nodes were programmed with a pre-amplifier gain of 12db, and a linear-phase anti-alias filter. Data polarity is positive values for motion to the north, east, or upward. Mseed file names are in the format "SiteName_InstrumentID_UTCStartDate_counts.mseed". Station details are included in "station_info.csv". These include the site name ("site"); the record start and end times in UTC ("tstart" and "tend"); the site latitude and longitude in decimal degrees ("latitude" and "longitude"); the site elevation in meters ("elevation"); the burial status of the seismometer ("burial"); and the associated mseed file name ("filename"). Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.