REAL-TIME MONITORING FOR EMERGENCY RESPONSE: THE CONUNDRUM OF ACTION THRESHOLDS

Monitoring involves a multitude of techniques and analysis methods suitable for systematically understanding landslide phenomena, determining the parameters of a specific landslide event, or evaluating the performance of mitigation measures (De Graff, 2011). Landslide researchers use monitoring to collect data showing change or lack of change over a period of time in an effort to yield rates of movement, clarify the relationship to triggering mechanisms, and other time-dependent variables. An important result can be the identification of a threshold where the measured value changes significantly. Such thresholds may or may not be anticipated, but they generally need not be identified or known prior to initiation of the research study. In contrast, real-time monitoring of landslides during an emergency response can necessitate identifying a threshold value for undertaking an evacuation or similar action to protect lives and property. Such action thresholds must be identified in anticipation of their occurrence rather than by observing changes within incoming monitored data. This is a conundrum because an action threshold presumes what our data might show rather than being what our monitoring data has shown. Three strategies for developing action thresholds protective of health and safety are illustrated by real-time monitoring in the aftermath of the 2006 Ferguson rock slide near El Portal, California. The first strategy is to directly monitor the potentially affected feature rather than the landslide activity threatening it. A second approach would be to evaluate a similar, existing dataset to establish a threshold for a comparable monitoring measure. Finally, action thresholds with incremental degrees of risk can be calibrated to initial monitoring values. These incremental thresholds can create warning and watch stages prior to the final action threshold triggering a full emergency response action; e.g., evacuation of residents from a threatened area.