Collaborative Research: Detection and mechanics of sinkhole activities in central Florida

佛罗里达州中部的天坑活动是一项重大的自然灾害。在过去的几年里，有两个事件特别引起了媒体的关注。2013年3月，塞夫纳一所房屋下的一个天坑坍塌，将卧室里的一个人“吞下”。2013年8月，天坑坍塌摧毁了迪士尼世界附近的一个度假区建筑群。然而，这些戏剧性的事件只是一些极端的例子，从每年稳定的约2亿美元的财产损失索赔中脱颖而出，在人为抽取地下水的时候，这些索赔会激增。探测早期的天坑活动是一项具有挑战性的任务，因为大多数活动发生在地下。然而，在某些情况下，天坑活动也会引起地面下沉，这可以通过天基干涉合成孔径雷达(InSAR)观测到。这个项目是NSF资助的一个概念验证项目的后续项目，在该项目中，研究人员证明了InSAR观测可以检测到佛罗里达州中部地表变化的局部模式。然而，使用更先进的InSAR时间序列技术检测缓慢下沉需要比在最初项目有限的持续时间内获得的更长的采集跨度。在这个更新项目中，我们提议继续对佛罗里达州中部的天坑活动进行基于InSAR的探测，将观察期再延长两年。较长的时间序列将使我们能够减少测量噪声的影响，并检测到由天坑活动引起的局部缓慢下沉。拟议的项目还包括在选定的实地进行地球物理勘测，绘制天坑结构图和土壤采样。此外，力学建模工作将检查现场InSAR探测到的沉降是否与粘性土的测量特性、现场数据和天坑沉降的简单模型相一致。这种建模方法可以用来评估观测到的下沉是否可能是坍塌的前兆。

Sinkhole activity in central Florida is a major natural hazard. Over the past several years, two events in particular attracted media attention. In March 2013, a sinkhole collapsed beneath a house in Seffner and "swallowed" a person from his bedroom. In August 2013 a sinkhole collapse destroyed a resort complex near Disney World. These dramatic events, however, are just extreme examples that stand out from a steady stream of about $200 million per year in property damage claims, which spike at times of anthropogenic groundwater withdrawals. Detecting incipient sinkhole activity is a challenging task, because most of the activity occurs in the subsurface. However, in some cases sinkhole activities also induce surface subsidence, which can be detected by space-based Interferometric Synthetic Aperture Radar (InSAR) observations. This project is a follow up of a proof-of-concept project funded by NSF, in which the researchers demonstrated that InSAR observations can detect localized patterns of surface changes in central Florida. However, the detection of slow subsidence using more advanced InSAR time series techniques requires longer span of acquisitions than obtained during the limited duration of the initial project. In this renewal project, we propose to continue the InSAR-based detection of sinkhole activity in central Florida by extending the observation period for two additional years. The longer time series will allow us to reduce the effect of measurement noise and detect localized slow subsidence induced by sinkhole activity. The proposed project also includes geophysical surveys to map sinkhole structure and soil sampling at selected field sites. In addition, a mechanical modeling effort will examine whether, at the field sites, InSAR-detected subsidence is compatible with measured properties of cohesive soils, field data, and simple models for sinkhole subsidence. This modeling method could be used to assess whether observed subsidence represents a likely precursor to collapse.