A tale of two seafloor eruptions: Comparing seismic data from the 2006 East Pacific Rise and 2015 Axial Seamount eruptions

Abstract:

In January 2006 at 9°50’N on the East Pacific Rise, a three-OBS array captured the first in situ seismic data from a mid-ocean ridge eruption. The data show a steady build up in seismicity over the preceding 2+ years leading to a seismic crisis on January 22^nd2006 that lasted approximately 6 hours, with one particularly intense hour interpreted as a rising dike (Tolstoy et al., 2006). This was followed by approximately 10 days of dwindling activity.

In April-May 2015, at the ridge-hotspot Axial Seamount, an eight-OBS array captured the second in situ seismic data, and first real-time data, from a mid-ocean ridge eruption. This eruption was also preceded by high seismicity rates, though data were only available for ~6 months prior to the eruption. An ~10 hr seismic crisis on April 24^thwas followed by almost a month of dwindling activity. Immediately following the end of the crisis, previously unknown impulsive waterborne signals were observed coming from two sites along the north rift of Axial Seamount (Wilcock et al., this meeting; Garcia et al., this meeting). The signals were interpreted as being associated with lava reaching the seafloor, and subsequent multibeam mapping and an ROV dive confirmed the presence of fresh lava at these sites (Kelley et al., this meeting).

Re-examination of the East Pacific Rise eruption data has shown that the same impulsive waterborne signals were also observed there starting ~3 hrs after the beginning of the 2006 seismic crisis (Tan et al., this meeting). The locations of these signals track the mapped lava flow associated with this eruption (Soule et al., 2007), further supporting their association with lava extrusion onto the seafloor.

These two eruptions show similar characteristics including ~6-10 hr seismic crises, and lava likely reaching the surface within ~3 hrs (EPR) and ~10 hrs (Axial) of the initiation of seismic crisis activity. They also show similar tremor activity, likely suggesting similar magma movement processes at depth. However, all phases of the Axial activity lasted longer, and it appears that the magma may have migrated some distance, whereas the EPR lava appear more likely to have erupted primarily above existing axial magma lenses, with thinner flow over a larger area. Seismic and acoustic characteristics of these two eruptions will be compared.