Post-Eruption Seismic Monitoring at 9N: Toward Capturing a Full Volcanic Cycle

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Two-thirds of the surface of our planet is formed at mid-ocean ridges, and yet the dynamics of this fundamental process are not well understood. From 2003-2006 the microearthquake character of the build-up to, and eruption associated with, a seafloor spreading event were recorded for the first time on ocean bottom seismometers. These data showed that there is a gradual build-up to an eruption, over several years, leading to the possibility that future eruptions may be predicted. Buried within the microearthquake data leading up to the eruption was exciting new insight into the structure of a full hydrothermal circulation cell. Hydrothermal circulation at mid-ocean ridges is responsible for 10% of global heat flux and 30% of the global heat flow anomaly. It also is significantly influences the chemistry of the lithosphere and overlying ocean, and supports extraordinary chemosynthetic biological communities. The data show that down-flow occurs on-axis and that fine scale segmentation of the seismicity matches fine scale segmentation of the chemistry and likely the magma body. In this project we will continue location and analysis of the microearthquake data leading up to the eruption, and specifically will look at how the seismicity of the hydrothermal cell changes with time. For instance, we hypothesize that the shape of the hydrothermal cell will stay essentially the same, but that the intensity of the seismicity will increase, particularly in areas close to the axial magma chamber as it nears eruption. We also hypothesize that the depth of seismicity associated with the axial magma chamber lid is unlikely to change with time until immediately prior to the eruption. Some studies have suggested that the magma chamber will shallow in the months or years preceding an eruption, but activity in the 2003-2004 deployment (2 years prior to the eruption) do not support this. By picking and locating the 100,000 microearthquakes recorded during the 2004-2005 deployment we will be able to identify any changes in the depth or character of the hydrothermal cell imaged in the 2003-2004 data. This research is fundamental to the character of seafloor spreading and to the nature of hydrothermal circulation at mid-ocean ridges. Our results will be of broad interdisciplinary value by linking to the other on-going studies at this site, and will help to shape a full integrated understanding of this section of mid-ocean ridge, from the mantle to the microbe, as outlined in the original Ridge 2000 science plan. The work has broader impacts in that it supports the training of graduate students, and a member of an underrepresented group (Tolstoy). Tolstoy, the lead-PI, also has a strong record of education and outreach work associated with this project including the Ridge 2000 distinguished lectureship, numerous lectures to school teachers and students, and participation in the educational film 'Aliens of the Deep'. Tolstoy anticipates continuing to do this type of outreach work, and is already committed to 3 educational presentations associated with this work in the coming months, including the PBS-Channel 13 'Celebration of Teaching and Learning' as an invited featured speaker in March 2007.