Spatial and temporal variations of the fluid signatures with regard to ongoing magmatic and different earthquake swarm activity beneath the Cheb basin/CZ
Final Report Abstract
In the Nový Kostel focal zone in October 2008 a strong earthquake swarm occurred. The swarm was exceptional by its intensity and rapidity. Focal mechanisms and activated fault planes of the 2008 swarm seem to be directly comparable to the 2000 swarm. At the surface close to the Nový Kostel epicentral area (e.g. Kopanina) mantle-derived fluid flow is reduced, but directly above the focal zone no gas emissions occurred. To find further indications for the interaction of ascending mantle derived fluids and the occurrence of earthquake swarms, gas- and isotope geochemical investigation was started from mid-October 2008 to April 2011 at locations close to the focal zone. For the first time seismically induced effects at degassing locations on Mariánské Láznĕ fault (MLF) were traced. After the beginning of the earthquake swarm 2008, anomalies of the fluid signature were observed at locations along the Počatky-Plesná fault zone (PPZ) as well at locations along the MLF. Differences were observed in the temporal and spatial occurrence as well in the strength of the anomalies probably due to the position of the faults zone in relation to the Nový Kostel focal zone and the fluid migration paths. It was surprising that the degassing behaviour at locations along the MLF reacts more sensitive on effects due to occurred seismicity. The recorded anomalies of 3He/4He ratios at the Bublák mofette indicate that the 2000 swarm as well the 2008 swarm seems to be linked with supply of fresh magma from a less degassed reservoir in the upper mantle. Altogether, similar isotope pattern were observed at Bublák and the Wettinquelle due to both earthquake swarms. In 2000 only at Bublák, 3He/4He ratios with the signature of the subcontinental mantle were found. At Hartoušov only an increase of mantle helium could be observed. At least since 2007 at all studied mofettes along the PPZ between Bublák and Hartoušov the 3He/4He ratios cover the range of the subcontinental mantle. The increase of mantle-derived helium at the mofettes along the PPZ correlates with an increase of the CO2 flow. The distribution pattern of detailed δ13C studies at Bublák between 2005 and 2011 let assume that the δ13C values may depict effects due to ongoing magma degassing as well as seismically induced variations of the δ13C signature. In the meantime it is undisputed that the monitoring of the isotope composition of degassing volatiles is an excellent tool for the evaluation of the geodynamic situation within a region and perfectly suited to trace fluid migration and processes due to variations of the fluid sources. On the basis of the 2008 earthquake swarm again attention was given due to the fluid studies in the Eger Rift area resulting in manifold media release.
Publications
- (2011). Monthly monitoring of gas and isotope compositions in the free gas phase at degassing locations close to the Nový Kostel focal zone in the western Eger Rift, Czech Republic. Chem. Geol. 290, 163-176
Bräuer K., Kämpf H., Koch U., Strauch G.
- (2012). CO2 discharge in an active, non-volcanic continental rift area (Czech Republic): Characterisation (δ13C, 3He/4He) and quantification of diffuse and vent CO2 emissions. Chem. Geol.
Kämpf H., Bräuer K., Schuhmann J., Hahne K., Strauch G.
(See online at https://doi.org/10.1016/j.chemgeo.2012.08.005)
