Spatio-temporal Permafrost Monitoring on Mt. Zugspitze (Germany) with Seismic Interferometry and Wavefield Gradients

利用地震干涉测量和波场梯度对德国楚格峰多年冻土进行时空监测

• 批准号: 464282872
• 负责人: Dr. Fabian Lindner
• 金额: --
• 依托单位: Sektion Geophysik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/464282872?language=en
• 关键词: Spatio; temporal; Permafrost; Monitoring; Mt.

Permafrost crucially affects the stability of rock walls. In particular, globally rising temperatures promote permafrost degradation potentially resulting in hazardous failure of rock walls. Thus, various techniques including electrical resistivity tomography and borehole temperature logging have been employed to monitor permafrost. However, the commonly used methods are typically laborious, expensive, and are limited in the spatial extent and/or temporal resolution. In contrast, by continuously sampling the ground motion, seismology yields high temporal resolution and spatial insights, as the seismic waves travel through the subsurface. This has been extensively harvested for the monitoring of various subsurface processes through seismic interferometry. Yet, only a few exploratory experiments were conducted in the realm of permafrost monitoring.In this project, we aim to monitor and image permafrost on Mt. Zugspitze (Germany) with seismic interferometry. From a seismological perspective, the occurrence of permafrost strongly affects seismic velocities of the subsurface, hence, we expect spatial velocity contrasts (from frozen to unfrozen rock) and temporal velocity variations due to permafrost dynamics (thaw and refreeze). We will install three seismic arrays along the permafrost affected ridge, which will consist of standard seismometers allowing to derive also rotational ground motions. In addition, we will periodically (at least once per quarter year for one week) add a rotational motion sensor to each array and measure ground-motion induced strain every few meters along a fiber-optic cable to be deployed along the ridge. Rotations and strains, the wavefield gradients, constitute new observables with new opportunities for seismology.We plan to extract continuous time series of seismic velocity variations between the arrays for at least two years. In addition, the unprecedented spatial sensor coverage of strain sensing along the fiber-optic cable will allow us to locate the velocity variations and to image the spatial extent of permafrost. The wavefield gradients will help to better detect the permafrost boundaries, as they are more affected by near-receiver structure than the classically measured translations, i.e. the wavefield. As wavefield gradients just start to be incorporated in common seismic deployments, experience is limited. We will therefore develop the methodology with numerical modeling of seismic wavefields and their gradients, thereby establishing a close connection between theory and field experiments allowing to optimally exploit the advantages of wavefield gradients. The objective of this project is to decipher permafrost dynamics, i.e. thaw, refreeze and general degradation, through improved spatio-temporal monitoring. This will help to better detect rock instabilities caused by permafrost degradation and to improve our understanding of the dynamic interplay between the atmosphere and the Earth.

永久冻土对岩壁的稳定性有着至关重要的影响。特别是，全球气温上升会促进永久冻土退化，可能导致岩壁的危险破坏。因此，包括电阻率断层扫描和钻孔温度测井在内的各种技术已被用来监测永久冻土。然而，常用的方法通常费力、昂贵，并且在空间范围和/或时间分辨率方面受到限制。相比之下，通过连续采样地面运动，当地震波穿过地下时，地震学可以产生高时间分辨率和空间洞察力。这已被广泛收集，用于通过地震干涉测量来监测各种地下过程。然而，在永久冻土监测领域只进行了一些探索性实验。在这个项目中，我们的目标是利用地震干涉测量技术对楚格峰（德国）的永久冻土进行监测和成像。从地震学的角度来看，永久冻土的出现强烈影响地下的地震速度，因此，我们预计由于永久冻土动力学（融化和再冻结）造成的空间速度对比（从冻结到未冻结的岩石）和时间速度变化。我们将沿着受永久冻土影响的山脊安装三个地震阵列，其中包括标准地震仪，还可以导出旋转地面运动。此外，我们将定期（至少每季度一次，持续一周）向每个阵列添加一个旋转运动传感器，并沿着沿着山脊部署的光纤电缆每隔几米测量地面运动引起的应变。旋转和应变、波场梯度构成了新的可观测值，为地震学带来了新的机遇。我们计划提取阵列之间地震速度变化的连续时间序列至少两年。此外，沿光纤电缆的应变传感的前所未有的空间传感器覆盖范围将使我们能够定位速度变化并对永久冻土的空间范围进行成像。波场梯度将有助于更好地检测永久冻土边界，因为它们比传统测量的平移（即波场）更容易受到近接收器结构的影响。由于波场梯度刚刚开始纳入常见的地震部署中，因此经验有限。因此，我们将开发地震波场及其梯度数值模拟的方法，从而在理论和现场实验之间建立密切联系，从而能够最佳地利用波场梯度的优势。该项目的目标是通过改进的时空监测来破译永久冻土动态，即解冻、重新冻结和总体退化。这将有助于更好地检测由永久冻土退化引起的岩石不稳定性，并提高我们对大气与地球之间动态相互作用的理解。