RAPID: Seismic Monitoring of Post-Fire Debris Flows Associated with the Museum Fire, Northern Arizona

在美国西部，野火的频率和强度正在增加。当这些事件发生时，它们会焚烧植被和烘烤土壤，从而减少降水进入地面的渗透和地表的稳定性。由于这些对土壤的影响，当降水事件发生时，野火往往会紧随其后的是泥石流。这些泥石流对人类生命财产构成重大威胁。位于亚利桑那州北部的弗拉格斯塔夫市上方的山上目前正在燃烧一场主要的野火--博物馆大火。这场大火的规模和距离城市很可能是美国西部未来野火的特征。在亚利桑那州北部，大部分年降雨量以夏末季风暴雨的形式出现，目前该地区正开始出现这种暴雨。由于最近的一场野火和暴雨的结合，预计该市部分地区将出现泥石流和洪水。越来越多的研究表明，地震仪可以根据泥石流下坡时产生的振动能量来监测泥石流。在这个项目中，调查人员将在博物馆火灾和下坡排水沟附近部署一个地震仪网络，以监测来自烧毁地区的泥石流并确定其特征。这些地震观测将与流域的水流测量、灾后地表观测、雨量计数据和下游泥石流沉积的观测相结合，以更好地了解泥石流如何发起和向下传播。这项工作还将用于评估使用地震阵列作为泥石流预警系统的有效性。由于越来越多的人生活在荒地-城市交界处，这项工作的结果对保护人类生命和财产免受未来自然灾害具有重要影响。该项目还将支持研究生和本科生的培训。最近的一场重大野火和季节性季风的爆发相结合，使亚利桑那州弗拉格斯塔夫周围的山脉成为未来两个月(2019年7月至9月)泥石流和洪水的地点。为了更好地了解泥石流的起因和泥石流向下移动的特征，私人投资者将部署一个由15台地震仪组成的小型网络，以记录与这些事件相关的地震信号。该阵列收集的地震数据将与地面观测进行比较，包括水流测量、冲刷河道的震后地面观测和下游泥石流沉积。这将使调查人员能够校准地震观测，以估计泥石流的体积、颗粒大小和速度，并扩大以前使用地球物理数据评估泥石流的努力。这项工作的广泛目标是：1)利用地震信号确定泥石流事件向下移动时的特征；2)确定部署地震监测网作为未来泥石流预警系统的有效性。从该阵列收集的数据将与科学界和公众共享，目的是鼓励和扩大地震数据用于泥石流监测。最终，这项工作将有助于建立一个利用地震数据对泥石流进行快速评估的框架，这对保护人类生命和财产具有长期影响。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Within the western United States, the frequency and intensity of wildfires are increasing. When these events occur, they burn vegetation and bake the soil, which reduces the infiltration of precipitation into the ground and the stability of the land surface. Due to these effects on soil, wildfires are often followed by debris flows when precipitation events occur. These debris flows pose a major risk to human lives and property. A major wildfire, the Museum fire, is currently burning in the hills above the city of Flagstaff, located in northern Arizona. The scale and proximity of this fire to the city is likely characteristic of future wildfires in the western US. Within northern Arizona, much of the annual precipitation comes in the form of intense late-summer monsoonal rain storms, which are currently starting to occur across the region. Due to this combination of a recent wildfire and intense rain, debris flows and flooding are anticipated in parts of the city downslope from the fire.There is a growing body of research showing that seismometers can be used to monitor debris flows based on the vibrational energy they produce as they travel downslope. In this project, the investigators will deploy a network of seismometers in the vicinity of the Museum fire and downslope drainages to monitor and characterize debris flows originating from the burned region. These seismic observations will be combined with flow measurements in drainages, post-event surface observations, rain gauge data, and observations of downstream debris flow deposits to better understand how debris flows initiate and travel downslope. This work will also be used to assess the effectiveness of using seismic arrays as early warning systems for debris flows. Due to the increasing number of people living at the wildland-urban interface, the results of this work have important implications for protecting human lives and property from future natural disasters. This project will also support the training of graduate and undergraduate students.The combination of a recent major wildfire and the onset of seasonal monsoons make the mountains surrounding Flagstaff, Arizona a location where debris flows and flooding are expected over the next two months (July to September, 2019). In order to better understand debris flow initiation and characterize their downslope travel, the PIs will deploy a small network of fifteen seismometers to record seismic signals associated these events. Seismic data collected by this array will be compared to surface observations including flow measurements, post-event surface observations of scoured channels, and downstream debris flow deposits. This will allow the investigators to calibrate seismic observations to estimates of debris flow volume, grain size, and velocity and expand upon previous efforts to assess debris flows using geophysical data. The broad objectives of this effort are 1) to use seismic signals to characterize debris flows events as they travel downslope and 2) to determine the effectiveness of deploying a seismic monitoring network to serve as an early warning system for debris flows in the future. The data collected from this array will be shared with the scientific community and general public with the goal of encouraging and expanding the use of seismic data for debris flow monitoring. Ultimately, this work will help establish a framework for the rapid assessment of debris flows using seismic data, which has long-term implications for protecting human life and property.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.