Continuous Monitoring of Potential Geochemical and Geomagnetic Earthquake Precursors: Lessons Learned

Abstract:

In the last decades different studies have addressed short-term earthquake precursors by focusing on the observation of a wide variety of physical phenomena that can precede strong earthquakes. This includes anomalous seismicity patterns, ground water level changes, gas emissions, geochemical changes in groundwater, seismo-electromagnetic phenomena, seismo-ionospheric coupling, surface deformations etc. Some cases of the potential precursors observed in the past where later found as an artifact of sensor-system malfunctioning. Therefore, such monitoring needs to be long-term, time-stamped and continuous, with a professional quality assurance procedure. Moreover, it is important to correlate data recorded with multi-sensor systems. We present a case study of running a multi-sensor system in Valais, Switzerland. The Valais is the area of highest seismic hazard in Switzerland and has experienced a magnitude 6 or larger event every 100 years on average. The system consists of seismic, geodetic (GPS), geochemical and geomagnetic instruments. Here we focus on the latter two. In particular, the observation of possible geochemical earthquake precursory signals is carried out by the installation of two instruments: 1) field fluorometer for monitoring of the fluorescence spectral analysis of water, which can monitor 3 different wavelength bands, temperature and turbidity; 2) geochemical gas concentration sensors, which monitor radon, CO2, and CH4 gases. The geomagnetic observations are performed by three component coil magnetometers. All instrument are designed to run in continuous mode and stream data in real-time. In this presentation we focus mainly on operational aspects of such system. We discuss problems faced during operation, feasibility of the installation, and in general lessons learned for potential future applications.