This data release provides supplementary information supporting our study on seismic intensities, ground motions, and basin amplification during the Mw 6.4 Ferndale, California earthquake of December 20th, 2022. A field survey was conducted between January 9-12 and March 6-9 in 2023 to assess the damage and shaking intensity experienced across the affected areas. During this survey, 17 sites in Northern California were visited. The sites include cities, towns, unincorporated communities, and census-designated places that fall within 150km of the earthquake epicenter. The data collected at each site includes qualitative observations of structural damage to homes and urban infrastructure, descriptions of damage to interior spaces and publicly accessible facilities, as well as reports of earthquake shaking intensity. Observations were made at multiple sub-localities within a designated site and were later summarized in order to assign a Modified Mercalli Intensity (MMI) Index to each site. The journal article accompanying this data release integrates the calculated MMI values with seismic waveform data from seismometers to characterize strong ground motion regionally and to better constrain the hazards associated with subduction zone earthquakes in Northern California.
