Wadati method as a simple tool to study seismically active fault zones: a case study from the West-Bohemia/Vogtland region,central Europe

The ratio of P- to S-wave velocities, V_P/V_S, is an important parameter characterizing rock composition and fluid saturation. We have studied properties of the ratio in the West-Bohemian seismically active region, using data from the earthquake swarm which occurred here in 2008. The earthquake swarm was well recorded by 23 seismic stations from epicentral distances less than 25 km. We selected a subset of 158 events with local magnitudes between 1.5 and 3.8. Applying the Wadati method to the measured arrival times of P and S waves, we arrived at an average value of V_P/V_S =1.68 ± 0.01. This differs a little from the value of V_P/V_S = 1.70, which is routinely used for earthquake locations in the region at present. Moreover, it was recognized that the points in the Wadati graphs for some stations were systematically deviated from the mean straight lines. In particular, the stations with the largest positive deviations (above the mean straight lines) are situated close to the Mariánské Lázně Fault and to some intensive mofettes. Further analyses revealed reduced P- and S-wave velocities along the seismic rays toward these anomalous stations. In our opinion, the seismic waves arriving at the anomalous stations probably propagated along a fault or another zone of weakness. In this way, our results support the hypothesis that the Mariánské Lázně Fault is a deep-seated fault continuing down to the seismically active zone of local earthquakes. From a general point of view, this study demonstrates that even some narrow structural anomalies in the crust, such as fault zones, can be recognized by the simple Wadati method if data from a dense seismic network are available.     

The deviation of the total geomagnetic field direction from the dipole field direction as a manifestation of the non-dipole field

Summary The angle between the total geomagnetic field direction and the axial dipole field direction was computed for the whole of the Earth's surface for the epoch 1945. It was supposed that the dipole field exerts a latitude-dependent influence on the surface manifestation of the non-dipole field. A modifying function of latitude was estimated to eliminate this influence. The isolines of the resulting quantity were plotted.     

Post-glacial diatom and geochemical records of ecological status and water level changes of Lake Vorota,Western Beringia

Journal of Paleolimnology - In this study, radiocarbon-dated geochemical and diatom records from Lake Vorota located within the informal meteorological ‘pole of cold’ of the northern...     

Seismically induced variations in Mariánské Lázně fault gas composition in the NW Bohemian swarm quake region, Czech Republic — A continuous gas monitoring

A continuously operated gas monitoring station was emplaced within the epicentral area of the NW Bohemian swarm earthquakes overlying directly the active Mariánské Lázně fault. The recordings of 8-month continuous monitoring period are presented. The variations in radon concentrations are similarly to variations in CO₂, i.e. CO₂ is considered to be the carrier gas for radon. Very small diurnal variations in gas concentration are caused by the earth tides, as daily variations in meteorological conditions cannot explain a short daily minimum at midday times. Sudden changes in gas concentration, which clearly exceed these diurnal variations occur and are always linked with seismic activities. Decreased gas concentration may indicate compression resulting in reduced fault permeability as is implied by negative peaks following local earthquake swarms. A sudden increase in CO₂ and Rn concentration may indicate an increased fault permeability caused by stress redistribution, giving rise to opening of migration pathways. This implies a repeatedly sudden rise in gas concentration before local earthquake swarms. Several variations in gas concentration were monitored linked with remote earthquakes of ground motion amplitudes  >1 μm. These seismic events are accompanied by an interference of the diurnal gas concentration–stress-cycle along the Mariánské Lázně fault. However, if shocks of remote earthquake can alter properties of the migrating fluids or the fault properties it can be suggested that these are able to trigger local seismicity, as indicated in the case of the Slovenia earthquake on 12th July 2004.     

Documentary proxies and interdisciplinary research on historic geomorphologic hazards: a discussion of the current state from a central European perspective

During the last two decades, documentary data (written and iconographic sources) have been increasingly employed in geomorphologic research aiming at reconstruction of territorial distribution, temporal occurrence and social and economic impacts of various geomorphologic hazards. The goal of this paper is to broaden the previous discussion (Glade et al. The use of historical data in natural hazard assessments. Kluwer, Dordrecht, 2001) of the methodological constraints on the use of documentary data for geomorphologic hazard research. Using the interdisciplinary approach of geomorphology, historiography and medial studies, we firstly summarise the major finding of papers that have employed various types of documentary data sources to study geomorphologic hazards in different regions. In the second section, we present case studies from the Czech Republic resulting from the ongoing research project that is devoted to the assessment of the potential of documentary data to reconstruct past occurrences of and mitigation strategies for geomorphologic hazards. Finally, we discuss three main methodological issues emerging from our research: (a) problems emerging from the positivist approach to documentary data sources and the necessity for critical analyses of documentary data sources based on modern historiographic approaches, (b) constraints arising from the combination of documentary data from different spatiotemporal scales and (c) lacks in the use of documentary data to study local-based adaptation strategies to cope with geomorphologic hazards.     

Domesticating neo-liberalism: Everyday lives and the geographies of post-socialist transformations

This paper examines the ways in which neo-liberalism is both constructed and made ‘more tolerable’ through everyday practices and livelihoods in post-socialist cities. It argues that existing conceptualisations of neo-liberalism centre too fully on the role of powerful global forces and institutions in constructing marketisation processes, and consequently neglect the ways in which everyday lives are embroiled in the formation of neo-liberal worlds. Through an exploration of the experience of neo-liberalism in the Slovak Republic and drawing upon research with households in one large housing estate in Bratislava, the paper examines the ways in which everyday lives construct neo-liberal possibilities in the attempt to make them ‘more tolerable’. In particular, the paper explores the postponement of the future by some members of the middle-aged generation failing to reap the benefits of economic reform, the role of economic practices ‘outside’ of market-based capitalist relations in constructing engagements with the formal market, and the role of domestic food production in sustaining household networks and social reproduction for some of the most marginal households in the context of low-wage employment and state benefit reductions.     

The <Emphasis Type="Italic">M</Emphasis><Subscript>w</Subscript> 4.3 January 17, 2014, earthquake: very rare seismic event on the Siberian platform

We described the 2014 January 17 earthquake (M _w?=?4.3) occurred on the Siberian platform in the area of sublongitudinal part of the Angara river in the zone of possible influence of two large reservoirs—Ust-Ilimsk and Boguchan. This is the first event of such magnitude recorded in this previously aseismic area during the whole period of instrumental observations. A seismic moment, a moment magnitude, a hypocentral depth, and a focal mechanism of the event were calculated on the basis of surface wave amplitude spectra. Analysis of the geological and geophysical data showed that the earthquake origin is connected with high-velocity gradient zone located at the border of the Late Proterozoic cover and the Precambrian basement of the Siberian platform. Some evidences for a natural character of the earthquake were considered.