Geoelectrical measurements for natural hazard monitoring

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Abstract
In many cases landslide and landslide related phenomena are abetted or triggered by hydrological processes. Since variations in soil humidity and subsurface water content are reflected in time-variable subsurface resistivities, the geoelectric method could be an appropriate methodology to monitor such phenomena. Therefore in 2002 the Geological Survey of Austria started to develop a complex geoelectrical system optimized for monitoring applications. This equipment now fulfills the requirements of permanent maintenance access, rapid and reliable data acquisition and robust design and automated data transfer and processing. Within a follow-up test phase of several years, the system was optimized for long-time field operation. For instance a lightning protection device for multi-core cables had to be developed as well as durable cable configuration had to be sorted out. The system was applied to observe the mudflow of Rindberg in the area of Sibratsgfäll. There a correlation of increased occurrences of geoelectric and self potential anomalies were detected at times characterized by larger movement rates, recorded by time-lapse GPS measurements. Furthermore the geoelectric methodology was also tested for observation of permafrost phenomena at the observatory of Sonnblick at an altitude of 3106 m parallel to depth dependent temperature monitoring. A first test phase of the system showed that due to the predominant high subsurface resistivities several adoptions to the GEOMON4D system had to be developed. Amongst others, current injection had to be changed from applying a constant voltage to applying a constant current flow to compensate for polarization effects.