Near Real-Time Automated Classification of Seismic Signals of Slope Failures with Continuous Random Forests

Abstract. In mountainous areas, mass movements such as rockfalls, rock avalanches, and debris flows constitute a risk to prop- erty and human life. Seismology has evolved into a standard tool to study temporal and spatial variability of mass movements in recent years. Increasing data volumes and the demand for near real-time monitoring call for automated techniques to detect and classify seismic signals generated by such events. Ideally, a large-aperture seismic array recording a significant number of events is available for such applications. This is, however, rarely the case, as a result of cost and time constraints. For most sites, the number of previously recorded slope failures is low, which impedes a reliable application of classification algorithms. Here, we use supervised random forest to classify windowed seismic data on a continuous data stream of a small seismic array, that was installed as a post-event intervention measure after a major rock avalanche. The presented method aims to facilitate data evaluation for stakeholders to detect an increase in slope activity in a near real-time manner. We define three different classes: Noise, slope failures, and earthquakes. Due to the sparsity of slope failures, the training data set is highly imbalanced. We find that several standard techniques to handle such data sets do not increase prediction accuracy. However, a lowering of the prediction threshold for slope failures leads to a prediction accuracy of 80 % for slope failures, 90 % for earthquakes, and 99 % for noise. The classifier is then used to classify 176 days of seismic recordings in 2019 containing four slope failure events. In total, the model classifies eight events as slope failures, of which three are actual slope failures. The other events are very local to regional earthquakes with relatively large magnitudes. One slope failure that has been reported by hikers is not classified as an event. This can be attributed to the small volume of the slope failure and thus low signal to noise ratio. We conclude that the method is suitable for continuous near real-time seismic monitoring.