Microearthquakes on the Endeavour Segment, Juan de Fuca Ridge: A Near Real Time Earthquake Catalog for the ONC Cabled Observatory and a Reanalysis of Historical Data

胡安德富卡山脊奋进段的微地震：ONC 有线观测站的近实时地震目录和历史数据的重新分析

• 批准号: 1833419
• 负责人: William Wilcock
• 金额: $ 13.14万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-09-01 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1833419&HistoricalAwards=false
• 关键词: Microearthquakes; Endeavour; Segment; Juan; de

Midocean ridge earthquakes, while not as large and damaging as subduction zone earthquakes, are nevertheless important for understanding the geological processes that form ocean crust. These earthquakes arise due to motion on faults associated with tectonic plate extension or from magmatic activity associated with seafloor volcanic processes. Earthquakes are also generated by crustal cracking that results from hydrothermal cooling of ocean crust. Ocean Networks Canada have operated a cabled observatory at the Endeavour midocean spreading center segment of the Juan de Fuca Ridge off the Pacific Northwest coast since 2011. Initially, the cabled observatory supported a variety of instruments in two hydrothermal vent fields, but just a single seismic station. In 2016, the seismic network expanded to four stations and several more are being added in summer 2018, together with more instruments to monitor the hydrothermal vent fields. This study will create an earthquake catalog for the Endeavour cabled observatory that will update in near real time. Seismicity from two prior experiments with autonomous ocean bottom seismometers will be relocated with three-dimensional seismic velocity models from recent a tomography. The scientific goals are to characterize how the seismicity has evolved as extensional stresses have accumulated since the segment last ruptured volcanically two decades ago, improve the interpretation of two complex earthquake swarms in 2005, constrain the linkages between hydrothermal seismicity and heat uptake above the magma chamber, and provide a public earthquake catalog that can be used by researchers to investigate temporal linkages between seismicity and variations in the hydrothermal fields. In terms of broader impacts, this project will train a postdoctoral researcher and foster an international collaboration with Canadian scientists studying the Endeavour hydrothermal fields.Long term observatories are an important tool for capturing the seafloor spreading events that form the upper oceanic crust and for understanding the evolution of hydrothermal systems and the chemosynthetic biological communities they support. About 1 meter of extensional strain has accumulated since the last non-eruptive diking event on the central Endeavour segment in 1999, and the rates of seismicity and level of tidal triggering are likely to evolve as the current spreading cycle approaches its culmination. The two swarms that occurred in 2005 on the northern Endeavour segment and West Valley propagator were difficult to interpret because of large systematic location errors. Relocating the earthquakes with an accurate three-dimensional model and the double-difference technique will allow earthquakes to be associated with morphological features and facilitate a better understanding of the magmatic and tectonic contributions to these swarms. Existing locations for the earthquakes above the axial magma chamber have absolute errors of several hundred meters and relocating these events with an accurate three-dimensional velocity model will contribute to the understanding of hydrothermal heat uptake by constraining the position of earthquakes relative to the axial magma chamber. It may also resolve changes in the configuration of the hydrothermal system as a result of deepening of the hydrothermal system as heat is mined from the axial magma chamber and/or the injection of fresh magma.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

洋中脊地震虽然没有俯冲带地震那么大，破坏力也不强，但对于理解形成海洋地壳的地质过程还是很重要的。这些地震是由与构造板块伸展有关的断层运动或与海底火山作用有关的岩浆活动引起的。地震也是由海洋地壳的热液冷却导致的地壳破裂引起的。自2011年以来，加拿大海洋网络公司一直在太平洋西北海岸的胡安德富卡山脊的奋进号洋中扩展中心部分运营一个电缆观测站。最初，有电缆的天文台在两个热液喷口支持各种仪器，但只有一个地震站。2016年，地震网络扩展到四个站点，2018年夏季将增加几个站点，以及更多的仪器来监测热液喷口场。这项研究将为奋进号电缆天文台创建一个地震目录，该目录将在接近实时的情况下更新。用自主海底地震仪进行的两次先前实验的地震活动性将用最近的层析成像的三维地震速度模型重新定位。科学目标是描述自20年前最后一次火山破裂以来，随着拉张应力的积累，地震活动是如何演变的，改进对2005年两个复杂地震群的解释，约束热液地震活动与岩浆室上方热量吸收之间的联系，并提供一个公共地震目录，供研究人员用来研究地震活动性和热液场变化之间的时间联系。就更广泛的影响而言，该项目将培养一名博士后研究员，并促进与研究奋进号热液领域的加拿大科学家的国际合作。长期观测是捕捉形成上层海洋地壳的海底扩张事件和了解热液系统及其支持的化学合成生物群落的演化的重要工具。自1999年奋进号中部最后一次非喷发性筑堤事件以来，已经积累了大约1米的拉伸应变，随着当前扩张周期接近顶峰，地震活动的频率和潮汐触发的水平可能会发生变化。2005年发生在奋进号北段和西谷传播器上的两个蝗群很难解释，因为有很大的系统定位误差。用精确的三维模型和双差技术重新定位地震将使地震与形态特征联系起来，并有助于更好地理解岩浆和构造对这些群的贡献。轴向岩浆库上方地震的现有位置有几百米的绝对误差，用精确的三维速度模型重新定位这些事件将有助于通过限制地震相对于轴向岩浆库的位置来理解热液热吸收。它还可以解释由于从轴向岩浆房开采热量和/或注入新鲜岩浆而使热液系统加深而导致的热液系统结构的变化。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。