The 1993 seismic swarm and volcanic eruption on the CoAxial segment of the Juan de Fuca Ridge was the first verified mid-ocean ridge accretion event monitored by the National Oceanic and Atmospheric Administration/U. S. Navy Sound Surveillance System (SOSUS). Ambiguity in the location of the initial seismicity resulted in an uncertainty as to whether the dike intruded from the summit and north rift zone of the adjacent Axial Volcano or whether it arose locally within the CoAxial segment. However, analyses of multibeam, side-scan sonar, towed camera, submersible, and geochemical data show that the CoAxial segment is morphologically, structurally, and geochemically distinct from the north rift zone of Axial Volcano. There is no geologic or geochemical evidence that dike injections from Axial Volcano have extended north of 46°18N in the past, whereas the 1993 eruption site is at 46°31N. Furthermore, all seafloor manifestations of the 1993 dike injection lie along the central neovolcanic zone of the CoAxial segment. Analyses of repeat SeaBeam surveys combined with seafloor observations show that two other eruptions of approximately the same volume as the 1993 eruption occurred along the CoAxial segment in the 19811991 interval. These three diking events may have relieved decades of accumulated stress over ~35 km or more of this segment. The spatial pattern and hydrothermal history of the 1993 event is consistent with a dike with a significant lateral component of injection.
2. Sources of Data
2.1. Multibeam Bathymetry
2.2. Side-Scan Sonar
2.3. Submersible and Camera Tow Data
3. The Structural and Volcanological
Context of the Central Juan de Fuca Ridge
4. CoAxial Segment and Its Relation to Axial Volcano
5. The 1993 Eruption Site ("Flow Site")
6. The 19821991 Lava Flow at the Flow Site
7. Floc Site
8. The 19811991 Lava Flows at the "Floc Site"
9. Southern CoAxial Segment and the "Source Site"
10.1. Relationship of T Wave Seismicity to Seafloor Structure and Geologic Observations
10.2. Implications for Stress Release During Accretion Events on the Mid-Ocean Ridge
10.3. Implications for Magma Delivery Systems at Intermediate Spreading Rates
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