Low-frequency earthquakes track the motion of a captured slab fragment

• 成果类型: Article
• 署名作者: Shelly, David R.; Thomas, Amanda M.; Materna, Kathryn Z.; Skoumal, Robert J.
• 署名单位: United States Department of the Interior; United States Geological Survey; University of California System; University of California Davis; University of Colorado System; University of Colorado Boulder; United States Department of the Interior; United States Geological Survey
• 刊物名称: SCIENCE
• ISSN/ISSBN: 0036-8075; 1095-9203
• DOI: 10.1126/science.aeb2407
• 发表日期: 2026-01-15
• 页码: 294-299
• 关键词: MENDOCINO TRIPLE JUNCTION; san-andreas fault; NON-VOLCANIC TREMOR; CAPE MENDOCINO; TIDAL MODULATION; seismic evidence; subduction zone; episodic tremor; FRANCISCO BAY; california

摘要

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.