California nFI
Quantifying relative high-frequency enrichment of earthquakes
Earthquakes of similar size can produce strikingly different amounts of high-frequency shaking — the rapid jolts most responsible for damage to buildings and infrastructure. What controls this variability remains an open question, and answering it has direct implications for how we forecast ground motion and assess seismic hazard.
This project applies the normalized frequency index (nFI), a recently developed metric that measures the relative high-frequency content of an earthquake’s seismic radiation, to 30 years of seismicity across California (1995–2024). The result is the first statewide map of relative high-frequency source variability, which we use to investigate how factors like fault maturity, heat flow, faulting style, tectonic region, and pore pressure influence earthquake shaking.
Below are the interactive preliminary results. Navigating the entire dataset is a bit difficult, so I have also broken up the results into different regions. All results begin with North (green arrow) up. Fault traces are from the USGS Quaternary Faults database.
Mobile: Tap & drag to rotate, double finger tap & drag to pan, pinch to zoom.
Desktop: Click & drag to rotate, shift + click & drag to pan, scroll to zoom.
Refresh to reset to original view.
Want to take a look at the data yourself? Send me an email!
Full results
Regional results