Fig. 1: Study area and the young Juan de Fuca (JdF) Plate.

a Regional map of the JdF Plate and Cascadia subduction zone. The inset globe shows the global location of the area marked with the yellow star. Our study area is outlined by a black box (close-up is shown in panel b). The locations of the seismic reflection profiles collected in 2002 (refs. ^21,53) crossing the Endeavour and Northern Symmetric segments are shown in white lines; the locations of the reflection seismic profiles collected in 2012⁴¹ are shown in white-black lines. Coloured areas bounded by black lines represent the magnetic anomalies with the corresponding age shown in the time scale below the panel⁵³. Grey shaded zones outline the extent of the propagator wakes⁵³. The red dots represent epicentres along plate boundaries (June 1995–June 2019, United States Advanced National Seismic System and Canadian National Seismic Network catalogues). b The close-up of the study area. Around the ridge axis, dashed and grey transparent contours outline zones with lower (∼0%) and higher (3%) melt fraction at 7.8-km depth²⁸. The remaining symbols are shown in Legend.