Colloborative Research: Monitoring Antarctic Ice Sheet Changes with Ambient Seismic Noise Methods

合作研究：利用环境地震噪声方法监测南极冰盖变化

• 批准号: 1643761
• 负责人: German Prieto
• 金额: $ 20.91万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-05-01 至 2019-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1643761&HistoricalAwards=false
• 关键词: Colloborative; Research; Monitoring; Antarctic; Ice

Non-technical description:Global sea-level rise is a significant long-term risk to human population and infrastructure. To mitigate and properly react to this threat, society needs accurate predictions of future sea-level variations. The largest uncertainty in these predictions comes from estimating the amount of ice that melts from polar ice sheets, especially from the West Antarctica ice sheet. Right now, scientists estimate the mass variations of ice sheets in two ways. The first way is using airplanes and repeated flybys to monitor the variation of ice sheet topography and estimate the gain or loss of ice. The second way is using satellite measurements to track gravity fluctuations that correlate with the variation of ice sheet volume. Both techniques work, but both have limitations including cost and resolution. This project uses a passive seismic monitoring method to estimate the change in weight of the ice pressing on the Earth's crust. One advantage of this seismic method is that vibrations are recorded continuously; therefore, it is possible to monitor the changes of the ice sheet with better temporal resolution. The sensitivity of the seismic waves also provides a picture of the structure of the interface between the ice and the rocks beneath the ice, where most of the dynamics and changes of the ice sheet take place. This information is difficult to obtain with other methods. In this project, the researchers will process and analyze previously acquired seismic data from the POLENET-ANET array, measuring variations in seismic wave speed through time to assess the amount of ice lost or gained. They will also determine important information about the mechanical properties at the ice-rock interface. The project will support a postdoctoral scholar to develop this new branch of seismological research and more generally the field of environmental seismology. This project will also support the education of a PhD student who will work in close collaboration with the postdoctoral scholar and the two researchers.Technical description:The researchers plan to monitor ice-mass variations in the West-Antarctic ice sheet by measuring and interpreting seismic velocity changes in crust beneath the ice sheet. This project will extend similar work already completed on the Greenland ice sheet, where ice-mass fluctuations were found to lead to poroelastic changes in the crust and modify the seismic-wave velocity. This investigation uses a passive seismology method, whereby repetitive seismic noise correlation functions are computed from records of Earth's ambient seismic noise field. Measurements of the temporal changes in the correlation functions are made and then related to variations of the poroelastic properties of the crust. The physical model for the relationship between ice-mass change and surface-wave velocity change has previously been verified using GRACE satellite data in Greenland. This project will specifically focus on the recent rapid ice loss in Western Antarctica using data from the POLENET-ANET seismic network. A comparison between the ice-sheet behaviors in Greenland and Antarctica will provide clarification about the underlying physical processes responsible for the observed seismic velocity changes. This new method will be a transformative approach to monitor ice sheets with the potential for much higher spatial and temporal resolution than existing methods. The fact that this method relies on seismic waves makes the approach completely independent from other modern ice-sheet monitoring techniques.

非技术性说明：全球海平面上升对人口和基础设施构成重大的长期风险。为了减轻这种威胁并做出适当的反应，社会需要对未来海平面变化进行准确的预测。这些预测中最大的不确定性来自对极地冰盖融化的冰量的估计，特别是来自南极洲西部冰盖的冰量。现在，科学家们从两个方面估计冰盖的质量变化。第一种方法是利用飞机和重复飞越来监测冰盖地形的变化，并估计冰的增加或减少。第二种方法是使用卫星测量来跟踪与冰盖体积变化相关的重力波动。这两种技术都有效，但都有成本和分辨率等限制。该项目使用被动地震监测方法来估计冰压在地壳上的重量变化。这种地震方法的一个优点是可以连续记录振动;因此，可以以更好的时间分辨率监测冰盖的变化。地震波的敏感性还提供了冰与冰下岩石之间界面结构的图像，冰盖的大部分动力学和变化都发生在那里。这些信息很难用其他方法获得。在这个项目中，研究人员将处理和分析以前从POLENET-ANET阵列获得的地震数据，测量地震波速度随时间的变化，以评估冰的损失或增加。它们还将确定有关冰-岩界面力学特性的重要信息。该项目将支持一名博士后学者发展地震学研究的这一新的分支，以及更广泛的环境地震学领域。该项目还将支持一名博士生的教育，该博士生将与博士后学者和两位研究人员密切合作。技术说明：研究人员计划通过测量和解释冰盖下地壳的地震速度变化来监测西南极冰盖的冰量变化。该项目将扩展已经在格陵兰冰盖上完成的类似工作，在那里发现冰团波动导致地壳中的孔隙弹性变化并改变地震波速度。本研究采用被动地震学方法，根据地球环境地震噪声场的记录计算重复地震噪声相关函数。测量的相关函数的时间变化，然后与地壳的孔隙弹性性质的变化。冰量变化和表面波速度变化之间关系的物理模型以前已在格陵兰使用GRACE卫星数据进行了验证。该项目将利用POLENET-ANET地震网络的数据，具体侧重于南极洲西部最近的快速冰损失。格陵兰岛和南极洲冰盖行为之间的比较将提供有关观测到的地震速度变化的基本物理过程的澄清。这种新方法将是监测冰盖的一种变革性方法，具有比现有方法高得多的空间和时间分辨率。这种方法依赖于地震波的事实使其完全独立于其他现代冰盖监测技术。