ALBERT

Description: Mofettes are gas emission sites where high concentrations of CO2 ascend through conduits from as deep as the mantle to the Earth’s surface and as such provide direct windows to processes at depth. The Hartoušov mofette, located at the western margin of the Eger Graben, is a key site to study interactions between fluids and swarm earthquakes. The mofette field (10 mofettes within an area of 100 m × 500 m and three wells of 28, 108, and 239 m depth) is characterized by high CO2 emission rates (up to 100 t/d) and helium signatures with (3He/4He)c up to 5.8 Ra, indicating mantle origin. We compiled geological, geophysical, geochemical, and isotopic data to describe the mofette system. Fluids in the Cheb basin are mixtures between shallow groundwater and brine (〉40 g/L at a depth of 235 m) located at the deepest parts of the basin fillings. Overpressured CO2-rich mineral waters are trapped below the mudstones and clays of the sealing Cypris formation. Drilling through this sealing layer led to blow-outs in different compartments of the basin. Pressure transients were observed related to natural disturbances as well as human activities. External (rain) and internal (earthquakes) events can cause pressure transients in the fluid system within hours or several days, lasting from days to years and leading to changes in gas flux rates. The 2014 earthquake swarm triggered an estimated excess release of 175,000 tons of CO2 during the following four years. Pressure oscillations were observed at a wellhead lasting 24 h with increasing amplitudes (from 10 to 40 kPa) and increasing frequencies reaching five cycles per hour. These oscillations are described for the first time as a potential natural analog to a two-phase pipe–relief valve system known from industrial applications.

Description: The ionospheric manifestations of geohazards of earthquakes and tsunamis are well documented based on the radio sounding of the medium.In particular, Global Navigation Satellite Systems (GNSS) based ionospheric monitoring provided more insights towards understanding the dynamic coupling between the lithosphere-atmosphere-ionosphere (LAI) during earthquakes and tsunamis. The present paper will brief the concept of LAI coupling and discuss that how the ionospheric signals produced by earthquakes can be inverted to infer the seismic source characteristics of large earthquakes to envisage the propagation time of tsunami waves. The paper concludes by demonstrating that ionosphere based monitoring of earthquakes and tsunamis may facilitate further advancement of existing tsunami warning systems.

Description: Nowadays, many sites are considered waste, due to high potentially toxic metal (PTM) concentration. Recycling of globally critical metals requires development of environmentally friendly processes for metal recovery. To study plants response to elevated Zn and Cu concentration in soil, a greenhouse experiment was designed using hyperaccumulator Brassica juncea. Plants were irrigated daily with PTM solutions, with final mass of both Zn and Cu added to the soil reaching 104.5, 209, 313.5, and 330 mg. After 8 weeks, samples were harvested, dried, weighed, and elemental analysis was conducted using atomic emission spectrometry (Agilent Technologies 4210 MP-AES). Phytotoxicity was determined based on visual observation, biomass, and chlorophyll measurements. The highest accumulation of Zn and Cu was found in the stem and leaf material, with observed concentrations of Zn in the leaf being 16.750 mg kg−1 and 7.170 mg kg−1 of Cu in the stem. The highest allocated in the biomass mass of Zn and Cu was in T4 treatment reaching 25.8 mg and 9.5 mg, respectively. Treatment with 330 mg Zn and Cu application displayed a 62.3% decrease in stem mass, a 25% decrease in average root mass (LD30 reached), and a 59% decrease in leaf mass when compared with the control. With increasing PTM concentration, root, biomass (from about 0.4 to 0.1 g; from about 3.8 to 2.0 g, respectively) and chlorophyll “a” (from about 24 to 19 μg/cm2) decline was observed, which correlates with observed chlorosis. This study reaffirmed the capabilities of B. juncea to bioaccumulate Zn and Cu from an enriched soil and provided further understanding as to how Zn and Cu translocate within plant tissues.

Description: The 2021 Fagradalsfjall volcanic eruption in the Reykjanes Peninsula, Iceland, was preceded by a M〈sub〉L 〈/sub〉5.3 earthquake of 24 February 2021, which was followed by an intensive earthquake swarm lasting one month. Precise relocations show two hypocenter clusters in the depth range of 1-6 km. The swarm and later eruption occurred in the area which was the place of several swarms in the period of 2017-2020. We analyze the spatiotemporal characteristics of the activity, the Coulomb stress change caused by the ML 5.3 earthquake and by the magmatic dyke and the moment tensors of previous swarms to better understand the stress transfer between seismic and magmatic activity. Our analysis shows a coincidence of several phenomena which could have contributed to driving the seismic and volcanic activity. The stress change analysis suggests that the forming magmatic dyke has increased the Coulomb stress on the M〈sub〉L 〈/sub〉5.3 earthquake fault. The following earthquake rupture resulted in unclamping of the fissure where the dyke formed and in Coulomb stress increase in the area of aftershocks and the following earthquake swarm. The WSW-ENE trending cluster of the 2021 and previous swarms show a stepover, forming an extension structure at the intersection with the dyke. And the moment tensors of the 2017 swarm events show that volumetric components vary along the cluster. Interestingly, the 2021 eruption occurred in the extension structure, suggesting that magma erupted at the place of crustal weakening.

Description: The new in situ geodynamic laboratory established in the framework of the ICDP Eger project aims to develop the most modern, comprehensive, multiparameter laboratory at depth for studying earthquake swarms, crustal fluid flow, mantle-derived CO2 and helium degassing, and processes of the deep biosphere. In order to reach a new level of high-frequency, near-source and multiparameter observation of earthquake swarms and related phenomena, such a laboratory comprises a set of shallow boreholes with high-frequency 3-D seismic arrays as well as modern continuous real-time fluid monitoring at depth and the study of the deep biosphere. This laboratory is located in the western part of the Eger Rift at the border of the Czech Republic and Germany (in the West Bohemia–Vogtland geodynamic region) and comprises a set of five boreholes around the seismoactive zone. To date, all monitoring boreholes have been drilled. This includes the seismic monitoring boreholes S1, S2 and S3 in the crystalline units north and east of the major Nový Kostel seismogenic zone, borehole F3 in the Hartoušov mofette field and borehole S4 in the newly discovered Bažina maar near Libá. Supplementary borehole P1 is being prepared in the Neualbenreuth maar for paleoclimate and biological research. At each of these sites, a borehole broadband seismometer will be installed, and sites S1, S2 and S3 will also host a 3-D seismic array composed of a vertical geophone chain and surface seismic array. Seismic instrumenting has been completed in the S1 borehole and is in preparation in the remaining four monitoring boreholes. The continuous fluid monitoring site of Hartoušov includes three boreholes, F1, F2 and F3, and a pilot monitoring phase is underway. The laboratory also enables one to analyze microbial activity at CO2 mofettes and maar structures in the context of changes in habitats. The drillings into the maar volcanoes contribute to a better understanding of the Quaternary paleoclimate and volcanic activity.

Description: Important effects of mesoscale eddies in eastern boundary upwelling systems (EBUS) are offshore transport of coastal water and vertical exchange between the mixed layer and below. In our contribution we reconstruct the 3-D structure of several cyclonic eddies and anticyclonic modewater eddies in the Canary EBUS from in situ velocity observations, based on different survey patterns of different durations. The reconstructions include derived dynamic properties such as vorticity and divergence, so that trapping radii and shallow secondary circulation can be estimated. Common features of the eddies are used to extrapolate on the offshore transport and vertical exchange caused by EBUS eddies. Some collateral insights from these investigations include that (i) a few inertial periods of observation time are needed to estimate vertical velocity, and (ii) all observed eddies have a radius very similar to the Rossby radius, as opposed to the larger variability in size that satellite products suggest.

Description: Maar-diatreme volcanoes are small volcanic structures with a funnel-shaped crater surrounded by a tephra-ring. They are usually formed by the explosive phreatomagmatic eruptions when groundwater comes into the contact with magma. We focus on such a structure in the geodynamically active western Eger Rift (Czech Republic) and present results from multidisciplinary geophysical investigation calibrated by drilling in the newly discovered Pleistocene Bažina maar. We evaluated morphological (LiDAR-based DEM) data and confirmed the existence of a maar-diatreme structure by combined geophysical methods. In the map view, they revealed circular negative gravity anomaly, funnel-shape low-resistivity anomaly, and strong magnetic anomaly. These results allowed for the optimal location of two boreholes in the maar crater, which evinced its contact with country rocks and lithologies of the maar-diatreme filling. The drilling revealed coherent volcanic rocks and volcaniclastic deposits, moreover, it revealed a presence of a pyroclastic cone with the olivine nephelinite feeding conduit. Further investigations disclosed maar structure and subsequent pyroclastic cone(s) with several generations of eruptions and systematic decrease of water influence on the eruption style. Different eruption styles suggest a unique evolution of two volcanoes, one inside the other. The age of the Bažina maar eruption, estimated from the reverse polarity of the detected magnetic anomaly, implies that the effusion and solidification of the lava during the eruption must be older than 0.78 Ma (Pleistocene). This points to an active volcanism in the western Eger Rift in a span of ∼0.5 Ma, where Bažina represents the oldest (maybe opening) phase.

Description: Reykjanes Peninsula (SW Iceland) is extraodrinary place from the geophysical perspective. Lying on the on-shore part of the Mid-Atlantic Ridge, interlaced by volcanic systems and hosting sevral high temperature geothermal areas the seismic activity on Reykjanes Peninsula is generally persistent often on a microseismic level but occasionally reaching up to ML~5-6. Throughout the years many temporary seismic stations or small to medium size local seismic networks have beed deployed there for various purposes from geothermal prospection monitoring to short time passive seismic experiments. We analyzed 10 years period of recording of the natural seismicity recorded at the stations of the semi-permanent local seismic network REYKJANET (in operation since 2013) together with several permanent stations of SIL network present in the area of interest. This timespan contained times of relative rest, several small earthquake swamrs associated with purely tectonic origin as well as very turbulent and active periods with magnitudes up to ML=5.4 related to volcanic eruptions. We study the distribution of foci of the background seismicity as well as for the several seismically active periods with consistent set of stations. We compare different automatically derived earthquake catalogs and their common features like the aseismic zones or upper and lower limit of the foci occurence, seismogenic faults and void areas. The dataset contains also Fagradalsfjall volcanic system dyke intrusions related events in 2021-2022. We deal with several tens of thousands of foci with high quality stable location imaging the subsurface beneath Reykjanes Peninsula.

Description: The hypocentres of natural earthquake swarms and injection-induced seismicity usually show systematic migration, which is considered to be a manifestation of their triggering mechanism. In many of these cases, the overall growth of the earthquake distribution is accompanied by short episodes of rapid migration, the origin of which is still not sufficiently clarified. We review the possible triggering mechanisms of these migrating episodes and propose a graphical method for distinguishing internal and external triggering forces. We also analyse the theoretical relationship between the evolution of the cumulative seismic moment and the rupture area and propose two models, the crack model and the rupture front model, which can explain the spreading of hypocentres. We developed an automatic algorithm for detecting fast migration episodes in seismicity data and applied it to relocated catalogues of natural earthquake swarms in California, West Bohemia, and Iceland, and to injection-induced seismicity. Fast migration episodes is shown to be relatively frequent during earthquake swarms (8–20 per cent of all events) compared to fluid-induced seismicity (less than 5 per cent of the events). Although the migration episodes were detected independently of time, they grew monotonically with time and square-root dependence of radius on time was found suitable for majority of sequences. The migration velocity of the episodes of the order of 1 m s−1 was found and it anticorrelated with their duration, which results in a similar final size of the clusters scattering around 1–2 km. Comparison of seismic moment growth and activated fault area with the predictions of the proposed models shows that both the rupture front model and the crack model are able to explain the observed migration and that the front model is more consistent with the data. Relatively low estimated stress drops in the range of 100 Pa to 1 MPa suggest that aseismic processes are also responsible for cluster growth. Our results show that the fast migrating episodes can be driven by stress transfer between adjacent events with the support of aseismic slip or fluid flow due to dynamic pore creation.

Description: Successful utilization of geothermal energy is conditioned by sufficient permeability of the rock formation as a heat exchanger. We present results of hydraulic injection tests carried out in 2020 in the pilot geothermal borehole PVGT-LT1 in Litoměřice, Czech Republic, which samples 800 m of Paleozoic and Mesozoic sediments on the top of a crystalline basement. The low hydraulic conductivity on the order of 10−11 m/s obtained by recovery tests was verified by large-scale injection tests monitored by DTS temperature logging. During the first test, 24 m3 of water were injected and a permeable fracture was created at 880 m depth, breaking through the ignimbrite layer. The opening pressure of 12.55 MPa corresponds to the lower estimate of the minimum stress at this depth. The second injection was performed 7 months later and 202 m3 were injected at flow rates reaching 50 l/min. It showed that the fracture had been preserved since the first injection, which was documented by a non-zero flow rate at the smallest injection pressures and also by a stabilized water level in the borehole, which dropped immediately after the fracture formation. No induced seismicity accompanied the injection, which indicates a possibly low seismogenic potential of this area of the Bohemian Massif. The model of finite conductive fracture fitted to the pressure decay curve during shut-in intervals gives an estimate of a fracture half-length exceeding 100 m.