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

非技术描述：全球海平面上升对人口和基础设施是一个重大的长期风险。为了减轻和适当应对这种威胁，社会需要准确预测未来海平面的变化。这些预测中最大的不确定性来自对极地冰原，特别是南极洲西部冰原融化冰量的估计。目前，科学家们用两种方法来估计冰盖的质量变化。第一种方法是利用飞机和重复飞行来监测冰盖地形的变化，并估计冰的增加或减少。第二种方法是利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，但都有成本和解决方案方面的限制。本项目采用被动地震监测方法，估算地壳冰压重量的变化。这种地震方法的一个优点是振动是连续记录的；因此，有可能以较好的时间分辨率监测冰盖的变化。地震波的灵敏度还提供了冰与冰下岩石之间界面结构的图像，大部分冰盖的动力学和变化都发生在这里。这一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先前从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。它们还将确定冰岩界面的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个新分支，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名研究人员密切合作。技术描述：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南极西部冰盖的冰质量变化。该项目将扩展已经在格陵兰冰盖上完成的类似工作，在那里发现冰质量波动导致地壳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记录计算重复地震噪声相关函数。测量相关函数的时间变化，然后将其与地壳孔隙弹性特性的变化联系起来。冰质量变化与表面波速度变化之间关系的物理模型先前已在格陵兰使用GRACE卫星数据进行了验证。该项目将利用POLENET-ANET地震台网的数据，特别关注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的比较将澄清造成观测到的地震速度变化的潜在物理过程。这种新方法将是监测冰盖的一种变革性方法，具有比现有方法更高的空间和时间分辨率的潜力。这种方法依赖于地震波的事实使该方法完全独立于其他现代冰盖监测技术。

Non-technical description:Global sea-level rise is a significant long-term risk for 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.