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类人口和基础设施是一个重大的长期风险。为了缓解和妥善应对这一威胁，社会需要对未来海平面变化的准确预测。这些预测中最大的不确定性来自对极地冰盖，特别是西南极冰盖融化冰量的估计。目前，科学家们通过两种方法估计了冰盖的质量变化。第一种方式是利用飞机和重复飞行来监测冰盖地形的变化，估计冰层的得失。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压在地壳上的冰的重量变化。这种地震方法的一个优点是连续记录振动；因此，有可能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的结构图，冰盖的大部分动力学和变化都发生在那里。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以前从POLENET-ANET阵列获得的地震数据，测量地震波速随时间的变化，以评估冰块的损失或增加的数量。它们还将确定有关冰-岩石界面的力学性质的重要信息。该项目将支持一名博士后学者发展这一新的地震学研究分支，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，他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西南极冰盖的冰块变化。该项目将扩展已经在格陵兰冰盖上完成的类似工作，在格陵兰冰盖上，冰块波动被发现会导致地壳中的孔洞弹性变化，并修改地震波速度。这项研究使用被动地震学方法，即根据地球周围地震噪声场的记录计算重复的地震噪声相关函数。测量了相关函数的时间变化，并将其与地壳孔隙弹性性质的变化联系起来。关于冰块变化和表面波速度变化之间关系的物理模型此前已经使用格陵兰岛的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，特别关注最近南极西部冰层的快速融化。格陵兰岛和南极洲冰盖行为的比较将澄清导致观测到的地震速度变化的潜在物理过程。这一新方法将是一种监测冰盖的变革性方法，其空间和时间分辨率可能比现有方法高得多。这种方法依赖于地震波，这一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.