The 17 January 1994 Northridge, California, Earthquake: A Retrospective Analysis

The 17 January 1994 Northridge, California, earthquake was a watershed event with far‐reaching societal and scientific impacts. The earthquake, which occurred in the early days of both broadband seismic networks and the Internet, spurred advances in seismic monitoring, real‐time systems, and development of data products. Motivated by the 30th anniversary of the earthquake, we present a brief retrospective of the earthquake and its impact, and reconsider both ground motions and the aftershock distribution using modern tools and the best‐available data. With improvements in instrumentation and analysis methodology, recent earthquakes continue to reveal the increasing complexity of ground motions, fault systems, and earthquake ruptures. Even in the absence of data from state‐of‐the‐art instrumentation, a retrospective consideration of ground‐motion data from the Northridge earthquake reveals complexities beyond what could be characterized (and modeled) 30 yr ago. Aftershock relocations for both the 1971 Sylmar and 1994 Northridge earthquakes also reveal an updated view of fault complexity. Our study does provide a cautionary tale regarding legacy data sets and research results that are not easily accessible, which can result in discrepancies between catalog data and products from the best available science. We also briefly describe outreach products produced as a part of the anniversary commemoration.

Outreach products for the Northridge earthquake, including the animation and photographs of the damage are available from https://www.usgs.gov/centers/earthquake-science-center/science/m67-january-17-1994-northridge-california-earthquake (last accessed March 2024). A social media post including the animation can be accessed at https://twitter.com/USGS/status/1747597181572280565 (last accessed March 2024). Posts (“tweets”) inviting the public to submit retroactive “Did You Feel It?” (DYFI) reports can be accessed at https://twitter.com/USGS_Quakes/status/1745240406122500171 and https://twitter.com/USGS_Quakes/status/1745508071504335049, for English and Spanish, respectively (both last accessed March 2024). The Southern California Earthquake Center (SCEC) Unified Community Velocity Model (UCVM) version 22.7 software distribution was downloaded from https://github.com/SCECcode/UCVMC (last accessed April 2024).