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

地球表面的三分之二是在大洋中脊形成的，然而这一基本过程的动力学还没有被很好地理解。从2003年至2006年，首次在海底地震仪上记录到了与海底扩张事件相关的微震特征。这些数据表明，在几年的时间里，火山喷发是一个逐渐积累的过程，这导致了未来喷发可能被预测的可能性。在导致喷发的微震数据中，埋藏着令人兴奋的对完整的热液环流单元结构的新见解。大洋中脊的热液环流贡献了全球热通量的10%和全球热流异常的30%。它还显著影响岩石圈和上覆海洋的化学，并支持非凡的化学合成生物群落。资料表明，下降流发生在轴线上，地震活动的精细尺度分段与化学和可能的岩浆体的精细尺度分段相匹配。在这个项目中，我们将继续定位和分析导致喷发的微震数据，并具体观察热液单元的地震活动如何随时间变化。例如，我们假设热液单元的形状基本保持不变，但地震活动的强度将增加，特别是在轴向岩浆室附近的地区，因为它接近喷发。我们还假设，与轴向岩浆室盖有关的地震活动深度不太可能随着时间而变化，直到喷发之前。一些研究表明，岩浆室在喷发前几个月或几年内将变浅，但2003-2004年部署(喷发前两年)的活动不支持这一点。通过挑选和定位2004-2005年部署期间记录的100,000次微震，我们将能够查明2003-2004年数据中显示的热液单元深度或性质的任何变化。这项研究对海底扩张的特征和大洋中脊的热液循环性质至关重要。我们的结果将与该站点正在进行的其他研究相联系，具有广泛的跨学科价值，并将有助于形成对这段大洋中脊从地幔到微生物的全面综合理解，正如最初的Ridge 2000科学计划中所概述的那样。这项工作有更广泛的影响，因为它支持对研究生和代表不足的群体(托尔斯泰)的成员的培训。托尔斯泰是该项目的带头人，他在与该项目相关的教育和外展工作方面也有很好的记录，包括Ridge 2000杰出讲师，为学校教师和学生做过多次讲座，并参与了教育电影《深海的外星人》。托尔斯泰预计将继续从事这类外展工作，并已承诺在未来几个月内进行3次与这项工作相关的教育演讲，包括2007年3月作为特邀演讲者参加的公共广播公司频道13“教学与学习的庆祝”。

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.