Large Earthquakes Along the Mendocino Oceanic Transform Fault Hardly Have Any Foreshocks

Abstract Compared to continental strike‐slip faults, oceanic transform faults (OTFs) are thought to mainly slip aseismically and host significantly more foreshocks triggered by precursory aseismic slip which enhance the mainshocks' short‐term predictability. However, long‐term high‐resolution observational constraints remain limited. In December 2024, one of the largest ever OTF earthquakes occurred offshore California on the Mendocino OTF. Here we show that foreshock activity is very limited within the rupture zone of this moment magnitude ( M w ) 7.0 earthquake and does not indicate accelerating aseismic slip in the preceding month. The 2016 M w 6.6 and 1994 M w 7.0 Mendocino OTF earthquakes share similar characteristics. The 15 historical M w ≥ 5.5 mainshocks also have significantly fewer foreshocks on average compared to continental strike‐slip earthquakes. Therefore, there is no clear evidence of aseismic‐nucleation‐related seismicity preceding large Mendocino OTF earthquakes. Our results further demonstrate that enhanced foreshock activity is not a general characteristic of OTFs despite prevalent aseismic slip.