The M6.4 Ferndale earthquake of December 20, 2022, caused extensive damage in the city of Rio Dell, California (population 3,400), including impacts to buildings and critical lifeline systems such as water, sewer, natural gas, cell phone, and electric power. On‐site reconnaissance was conducted by the authors during three field visits from December 2022 to August 2024, supplemented by comprehensive damage assessments performed by the State of California staff. Notably, the earthquake's highest recorded free‐field peak ground acceleration (1.43g) occurred at a seismic station within Rio Dell, providing a rare opportunity to correlate strong shaking with detailed damage observations across nearly the entire building inventory. This paper summarizes the observed damage and ground motion data and develops empirical fragility functions for common residential structures (types W1 and MH). The findings offer insight into expected damage patterns for similar communities exposed to comparable seismic demands and provide practical lessons for future earthquake assessments.
Maison et al. (Sun,) studied this question.