The next M6 Parkfield Earthquake: USGS science priorities and plans
Elizabeth H. HearnSubmitted August 30, 2026, SCEC Contribution #15281, 2026 SCEC Annual Meeting Poster #171
The San Andreas Fault at Parkfield, California is perhaps unique in the world as a site for in-depth study of earthquakes and their effects. It regularly hosts M6 earthquakes (with recurrence intervals of 12 - 38 years), displays a wide range of seismic and aseismic slip behaviors, and has been thoroughly characterized after decades of focused observational and modeling studies. The last M6 earthquake, in 2004, marked the culmination of the Parkfield Experiment, a period of focused observations designed to capture the M6 at close range and assess possible precursors.
Since 2004, the USGS, UC Berkeley, the California Geological Survey (CGS), and EarthScope have continued to operate seismic and geodetic monitoring networks in the region, but now is the time to strategize on readiness for another possible mainshock. The USGS Earthquake Hazards Program (EHP) is making preparations to maximize what can be learned from a future M6, given current budget and workforce constraints.
After an internal meeting in March 2026 and subsequent discussions, the EHP identified high-priority Parkfield science questions and observations needed to address these questions. Priority science topics fall into five categories:
- Repeatability of M6 coseismic slip patterns and radiating patch locations
- Physics of rupture propagation, stopping, and triggering
- Strong ground motion variability, uncertainty, and causes
- Geometric complexity and fault localization at depth
- Partitioning of slip throughout the seismic cycle and seismic gaps
Our immediate observational priorities, informed by the priority science questions, include high-precision LiDAR imaging to provide a detailed topographic baseline for the region, and upgrades to analog seismometers to better capture the southern extent of slip in a future rupture. We plan to co-locate accelerometers with the upgraded seismometers, and to install an accelerometer at Middle Mountain, near where CGS recorded extreme ground accelerations in 2004. Another goal is maintaining seismic and geodetic instrument coverage comparable to that in 2004, with our partners at CGS, Berkeley, and EarthScope. With additional observations based on newer techniques (e.g., NISAR, optical image correlation, DAS at SAFOD, and LiDAR), and advances in AI/ML and computation, these observations should prove transformative for the study of earthquake physics and forecasting of strong ground motions.
Key Words
seismic cycle, creep, LFEs, repeating earthquakes, monitoring, Parkfield
Citation
Hearn, E. H. (2026, 08). The next M6 Parkfield Earthquake: USGS science priorities and plans. Poster Presentation at 2026 SCEC Annual Meeting.
Related Projects & Working Groups
Seismology
