Low-frequency earthquakes track the motion of a captured slab fragment
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Abstract
Accurate tectonic models are essential for assessing seismic hazard and fault interactions. However, the plate configuration at the complex Mendocino triple junction, where the San Andreas Fault and the Cascadia subduction zone meet, remains uncertain. We analyzed fault slip associated with a recently identified zone of tectonic tremor and low-frequency earthquakes (LFEs) near the southern edge of the subducting Gorda slab. Based on tidal sensitivity and P-wave first motions, we show that the LFEs are generated by dipping, strike-slip motion. This suggests that a former Farallon slab fragment, now captured by the Pacific plate, is translating northward beneath westernmost North America. This geometry effectively extends the slab interface fault, challenging prevailing interpretations of slab window formation and creating a potential unaccounted earthquake hazard in this region.
Suggested Citation
Shelly, D.R., Thomas, A.M., Materna, K.Z., Skoumal, R.J., 2026, Low-frequency earthquakes track the motion of a captured slab fragment: Science, v. 391, no. 6782, p. 294-299, https://doi.org/10.1126/science.aeb2407.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Low-frequency earthquakes track the motion of a captured slab fragment |
| Series title | Science |
| DOI | 10.1126/science.aeb2407 |
| Volume | 391 |
| Issue | 6782 |
| Publication Date | January 15, 2026 |
| Year Published | 2026 |
| Language | English |
| Publisher | American Association for the Advancement of Science |
| Contributing office(s) | Geologic Hazards Science Center - Seismology / Geomagnetism |
| Description | 6 p. |
| First page | 294 |
| Last page | 299 |