The October 2008 Novy Kostel earthquake swarm and its gas geochemical precursor

0472828 - ÚSMH 2017 RIV US eng J - Článek v odborném periodiku
Weinlich, F. H. - Gaždová, Renata - Teschner, M. - Poggenburg, J.
The October 2008 Novy Kostel earthquake swarm and its gas geochemical precursor.
Geofluids. Roč. 16, č. 5 (2016), s. 826-840. ISSN 1468-8115. E-ISSN 1468-8123
Institucionální podpora: RVO:67985891
Klíčová slova: CO2 * earthquake precursor * earthquake swarm * gas monitoring * water table fluctuations
Kód oboru RIV: DD - Geochemie
Impakt faktor: 2.687, rok: 2016

A gas geochemical precursor anomaly was identified prior to the October 2008 Novy Kostel (Czech Republic) earthquake swarm with a peak magnitude ML of 3.8. This anomaly was observed as a deviation of CO2 concentrations from the long-term annual CO2 concentration trend in the gas extracted from the scree at the Novy Kostel and Oldrisska gas monitoring stations, which are directly above the Plesna valley-Pocatky and Marianske Lazne fault systems. Both sites are located within the major focal zone of the NW Bohemian swarm earthquake region at the northern edge of the Cheb Basin. A decrease in CO2 concentration started at Novy Kostel in September 2008, 17 days before the swarm, opposite to the usually increasing annual trend in the autumn period, and ended with a nearly coseismic drop immediately prior to the onset of the first swarm. The CO2 concentrations at Oldrisska, deviating from the annual trend, did not further increase after August 2008. The calculated horizontal strain field, based on the data of two permanent Global Navigation Satellite Systems stations, proved there was horizontal compression in this period. The increasing compression along the Plesna valley-Pocatky and Marianske Lazne fault systems during the stress build-up reduced the fault permeability prior to this earthquake swarm as indicated by the decrease in CO2 concentration. The 17-day duration of the earthquake precursor at Novy Kostel and about 65 days at Oldrisska lie within the range of the precursor times that are hypothesized worldwide for an M-L = 3.8 earthquake. The nature of earthquake precursors and their origin are discussed, for example, as an indication of changed fault permeability by stress build-up in the case of the Novy Kostel swarm earthquake precursor or as fault opening in other cases.
Trvalý link: http://hdl.handle.net/11104/0270048