No abstract

The time series of two continuously operating gas monitoring stations at Old ri ssk a and Nov y Kostel located along seismoactive faults in the epicentral area of the NW Bohemian swarm earthquakes (Czech Republic) are compared with water level fluctuations in two boreholes positioned along these faults and with gas flux variations of a mofette at the Soos mofette field at 9 km distance. The seasonal trend of the monitored CO 2 concentration with a maximum in November and a minimum in March/April is governed by groundwater temperatures, superimposed in spring by soil temperatures. CO 2 concentration variations identified at Old ri ssk a are also reflected in gas flux variations in the Soos mofette and/or water level fluctuations of two boreholes. Variations in the gas monitoring recordings of station at Nov y Kostel are also linked with variations at Old ri ssk a. In all data sets, diurnal variations generated by earth tides occur, reflecting a daily stress -fault permeability cycle. Additional stress interferes with this cycle. Significant, abrupt changes are attributed to geodynamic processes linked with seismic events, as revealed by local seismicity or by the transient of waves of a strong remote earthquake. Simultaneous variations of the gas concentrations in the Nov y Kostel area and in the gas flux in the Soos point to an interconnected hydraulic conductive fault systems present in the northern part of the Cheb Basin. Sharp falls in gas concentration, during or subsequent to, earthquake swarms may reflect fault compression associated with impeded gas migration. However, gas variations also occur in periods without seismic activity, indicating changes in fault permeability were caused by local aseismic fault movements, as revealed by events with opposite trends in the gas recordings at Old ri ssk a, Nov y Kostel and the Soos. Therefore, a mathematical approach to establish a correlation between seismicity and gas geochemical variations is not possible.

No 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.

Investigations presented in this paper were aimed at defining the alterations of n-alkane composition in cases of oil-polluted alluvial sediments. Therefore, oil-polluted groundwater samples, taken in five different time intervals during a period of 28 months, were investigated. Samples of alluvial sediments were taken from two boreholes within an oil refinery at Pancevo, Yugoslavia. In both boreholes significant alterations with characteristic degradation of "oil" n-alkanes with no odd-or even-member predominance were observed, as well as subsequent synthesis of new ones with pronounced even-member predominance, and with maxima at C 16 and C 18 . Since no additional contamination of boreholes was observed by analyses of steranes and triterpanes, the observed changes can only be attributed to microbial activity. It is assumed that for the degradation of oil n-alkanes, as well as for the synthesis of "new" n-alkanes, algae such as dinoflagellates are responsible. This assumption was confirmed by identification of n-alcohols with even-member predominance (C 14 -C 20 ), by identification of cholesterol, as well as of n-fatty acids with even-member predominance (C 14 -C 18 ) in the extract with n-alkane even-member predominance.