Continuous gas monitoring in the West Bohemian earthquake area, Czech Republic: First results

Abstract

Two stations monitoring concentrations of carbon dioxide and radon in soil gas (Oldřišská and Nový Kostel) and one station monitoring flow of carbon dioxide at a mofette (Soos) have been operated in the area of the West Bohemian earthquake swarms. We present preliminary results obtained on the base of four-year observations. We found that data are not influenced considerably by barometric pressure. Although the CO 2 concentration varies greatly, the long-term trends at stations Oldřišská and Nový Kostel are similar, which indicates that the CO 2 flow is controlled by common geogenic processes. Also temporal trends of CO 2 and Rn concentrations in soil gas at individual stations are analogous. We found diurnal variations of both CO 2 concentration in soil gas and the CO 2 flow at mofettes due to the earth tides. A response to tides of semi-diurnal period is insignificant in CO 2 concentration and only weak in the CO 2 flow. We also examined possible pre-seismic, co-seismic and post-seismic effects of the intensive 2008 earthquake swarm on the CO 2 concentration at Oldřišská and Nový Kostel, and on the CO 2 flow at Soos. However, all potential indications were insignificant and there has not been proven any influence of the swarm on the CO 2 concentration as well as on the CO 2 flow. Nevertheless, a gradual decrease of amplitudes of diurnal variations before the swarm and the lowest amplitudes during the swarm is a noteworthy phenomenon, which might indicate the strain changes of the rock associated with earthquake swarm.

Some possible correlations between electro-magnetic emission and seismic activity during West Bohemia 2008 earthquake swarm

“…As an example, observations of CO 2 gas emanation (e.g. Faber et al, 2009), gravimetric measurements (Mrlina and Seidl, 2008;Kämpf, et al, 2008), GPS measurements (Schenk et al, 2009), micro-network observation (Häge and Joswig, 2008). We made an attempt to record the electromagnetic emission (here after EME) excited by seismic activity.…”

Earthquake impact on iron isotope signatures recorded in mineral spring water

“…The swarm was located in the southern part of the main Nový Kostel focal zone, where the fault plane is striking 168°N and dipping 80° westward, Figure [ Fischer and Horálek , ]. Previous studies suggested a connection between the common occurrence of deep‐seated fluids (mostly mantle‐derived CO 2 ‐rich fluids) and seismicity, where the observed anomalies may reflect a seismically induced release of fluids and/or changes in fluid migration pathways [ Bachura and Fischer , ; Bräuer et al, ; Bräuer et al, ; Faber et al, ; Horálek and Fischer , ; Koch et al, ; Koch and Heinicke , ; Kämpf et al, ].…”

Tasks and challenges of geochemical monitoring

“…). Secular variations of environmental tracer concentrations in groundwater, such as 3 H, 85 Kr and SF 6 are used for groundwater dating. Spontaneous changes have been reported and related to seismic activity …”