Strategies for measuring geologic slip rates

Ryan Gold

Submitted September 7, 2025, SCEC Contribution #14526, 2025 SCEC Annual Meeting Poster #TBD

Geologic slip rates are a primary input for probabilistic seismic hazard analyses,
which forecast ground shaking in future earthquakes. In the presentation, I examine sources of uncertainty in measuring geologic slip rates along strike-slip faults. These slip-rate measurements are derived from geomorphic features that record fault displacement, along with age constraints obtained from chronologic data. Key sources of uncertainty associated with displacement include measurement errors, ambiguities in feature reconstructions, and the effects of distributed faulting. Conversely, age constraint uncertainties arise from factors such as analytical uncertainties, inheritance in the sample material, post-depositional contamination, and most critically, ambiguity in correlating samples ages with the landforms or deposits from which they were collected. Additional sources of uncertainty associated with slip-rate measurements include the number of earthquake cycles over which geologic slip rates are sampled and the impact of secular variation in slip. To illustrate these uncertainties, I examine case studies from western North America, New Zealand, and Asia. I emphasize practices that can document slip rate uncertainties, including bracketing the age of faulted landforms using numerous geochronometers, documenting multiple offset landforms, and sampling a range of magnitudes of slip within a probabilistic framework. As an example, individual faulted terrace risers along the Honey Lake fault in California yield slip rates ranging from 0.3 to 7.1mm/yr; however, a slip rate of 1.6 mm/yr (1.4–1.9 mm/yr at 95%) satisfies the observations when combining numerous faulted landforms while honoring a full treatment of the various sources of uncertainty.

Key Words
fault, slip rate, uncertainty

Citation
Gold, R. (2025, 09). Strategies for measuring geologic slip rates. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology