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.

洋中脊地震虽然不像俯冲带地震那样规模大、破坏性大，但对于了解形成洋壳的地质过程非常重要。 这些地震是由于与构造板块延伸相关的断层运动或与海底火山过程相关的岩浆活动而引起的。 地震也是由海洋地壳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在太平洋西北海岸胡安德富卡海岭的 Endeavour 洋中扩张中心段运营了一个有线观测站。最初，该有线观测站支持两个热液喷口场的各种仪器，但只支持单个地震车站。 2016 年，地震网络扩展到四个台站，2018 年夏季又增加了几个台站，同时还增加了更多监测热液喷口场的仪器。 这项研究将为奋进有线观测站创建一个地震目录，该目录将近实时更新。 先前两次使用自主海底地震仪进行的实验的地震活动将通过最近层析成像的三维地震速度模型进行重新定位。科学目标是描述自该段二十年前最后一次火山破裂以来，随着伸展应力的积累，地震活动如何演变，改进对 2005 年两次复杂地震群的解释，限制热液地震活动与岩浆房上方吸热之间的联系，并提供一个公共地震目录，研究人员可以使用该目录来研究地震活动与热液场变化之间的时间联系。 就更广泛的影响而言，该项目将培训一名博士后研究员，并促进与研究奋进热液田的加拿大科学家的国际合作。长期观测站是捕捉形成上洋壳的海底扩张事件和了解海底扩张事件的重要工具。热液系统及其支持的化学合成生物群落的演化。 自 1999 年奋进中部段最后一次非喷发堤防事件以来，已经积累了约 1 米的拉伸应变，随着当前扩张周期接近其顶峰，地震活动率和潮汐触发水平可能会发生变化。 由于系统定位误差较大，2005 年发生在奋进号北部和西谷传播区的两起蝗群很难解释。 使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相关联，并有助于更好地了解岩浆和构造对这些群的贡献。轴向岩浆房上方地震的现有位置具有数百米的绝对误差，使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房的位置来了解热液吸热。 它还可以解决由于从轴向岩浆室开采热量和/或注入新鲜岩浆而加深热液系统而导致的热液系统配置的变化。该奖项反映了 NSF 的法定使命，并被认为是值得的通过使用基金会的智力优势和更广泛的影响审查标准进行评估来获得支持。