Methods of Data Processing for Debris Flow Seismic Warning

The output of the seismic devices commonly employed for the monitoring of debris flows, such as geophones and seismometers, is a voltage that is directly proportional to the ground vibration velocity. The output signal in analogical form is usually digitalized at a fixed sampling frequency to be opportunely processed. The processing is performed to both reduce the amount of data to be stored in a data-logger and to reveal the main features of the phenomenon that are not immediately detectable in the raw signal, such as its main front, eventual subsequent surges, the wave form and so on. The processing also allows a better and sounder development of algorithms, when seismic devices are employed for warning purposes. However, the processing of the raw signal alters in different ways the original raw data, depending on the processing method adopted. This may consequently limit or reduce the efficacy of the warning. Different methods of data processing can be found in literature, each with its own advantages and shortcomings. In this paper we will explore and discuss the effects of some of these latter on the efficacy of the algorithms employed for warning, applying them to the seismic recordings obtained in the instrumented basins of Gadria (Italy), Rebaixader (Spain) and Illgraben (Switzerland).