Overview
- The Science study by USGS, UC Davis and CU Boulder maps the junction using dense seismometer data on magnitude-zero, low-frequency events.
- The work identifies the Pioneer fragment translating north beneath western North America with an essentially horizontal, surface-invisible boundary.
- A broken piece of the North American plate is being pulled down with the Gorda plate at the southern end of the Cascadia subduction zone.
- The revised geometry explains the unexpected shallowness of the 1992 magnitude 7.2 Petrolia earthquake by placing the subducting surface higher than earlier models.
- Tidal modulation of tiny earthquake rates supports the model, and experts say it points to potential unaccounted hazard and a greater chance of Cascadia–San Andreas interaction without forecasting specific events.