Analysis of the 2012–2013 Torreperogil-Sabiote seismic swarm

This study analyses the temporal clustering, spatial clustering, and statistics of the 2012–2013 Torreperogil-Sabiote (southern Spain) seismic swarm. During the swarm, more than 2200 events were located, mostly at depths of 2–5 km, with magnitude event up to m_bLg 3.9 (M_w 3.7). On the basis of daily activity rate, three main temporal phases are identified and analysed. The analysis combines different seismological relationships to improve our understanding of the physical processes related to the swarm's occurrence. Each temporal phase is characterized by its cumulative seismic moment. Using several different approaches, we estimate a catalog completeness magnitude of m_c≅ 1.5. The maximum likelihood b-value estimates for each swarm phase are 1.11 ± 0.09, 1.04 ± 0.04, and 0.90 ± 0.04, respectively. To test the hypothesis that a b-value decrease is a precursor to a large event, we study temporal variations in b-value using overlapping moving windows. A relationship can be inferred between change in b-value and the regime style of the rupture. b-values are indicators of the stress regime, and influence the size of ruptures. The fractal dimension D₂ is used to perform spatial analysis. Cumulative gamma and beta functions are used to analyse the behaviour of inter-event distances during the earthquake sequence.     

Time–Frequency–Wavenumber Analysis of Surface Waves Using the Continuous Wavelet Transform

A modified approach to surface wave dispersion analysis using active sources is proposed. The method is based on continuous recordings, and uses the continuous wavelet transform to analyze the phase velocity dispersion of surface waves. This gives the possibility to accurately localize the phase information in time, and to isolate the most significant contribution of the surface waves. To extract the dispersion information, then, a hybrid technique is applied to the narrowband filtered seismic recordings. The technique combines the flexibility of the slant stack method in identifying waves that propagate in space and time, with the resolution of f–k approaches. This is particularly beneficial for higher mode identification in cases of high noise levels. To process the continuous wavelet transform, a new mother wavelet is presented and compared to the classical and widely used Morlet type. The proposed wavelet is obtained from a raised-cosine envelope function (Hanning type). The proposed approach is particularly suitable when using continuous recordings (e.g., from seismological-like equipment) since it does not require any hardware-based source triggering. This can be subsequently done with the proposed method. Estimation of the surface wave phase delay is performed in the frequency domain by means of a covariance matrix averaging procedure over successive wave field excitations. Thus, no record stacking is necessary in the time domain and a large number of consecutive shots can be used. This leads to a certain simplification of the field procedures. To demonstrate the effectiveness of the method, we tested it on synthetics as well on real field data. For the real case we also combine dispersion curves from ambient vibrations and active measurements.     

Asymmetry of Sunspot Distribution in Solar Cycles 12–24 and the Gnevyshev–Ohl Rule

Geomagnetism and Aeronomy - The nonaxisymmetric component of the sunspot distribution (longitudinal asymmetry) is considered based on the Greenwich–USAF/NOAA data for 1874–2016. Vector...     

Polar Activity of the Sun and Latitudinal Activity Drifts in Cycles 15–24

Geomagnetism and Aeronomy - The solar activity at different latitudes is analyzed based on daily observations at Kodaikanal, Mount Wilson, Sacramento Peak, and Meudon observatories in the CaIIK...     

On the Connection between the 2008–2009 Activation of the Koryakskii Volcano and Deep Magmatic Processes

Izvestiya, Physics of the Solid Earth - Abstract—The last activation of the Koryakskii volcano in 2008–2009 was accompanied by intense fumarolic and seismic activity. Volcanic activity...     

A Study of Fog Characteristics Using a Coupled WRF–COBEL Model Over Thessaloniki Airport, Greece

An attempt is made to couple the one dimensional COBEL-ISBA (Code de Brouillard à l’échelle Locale-Interactions Soil Biosphere Atmosphere) model with the WRF (Weather Research and Forecasting)–ARW (Advanced Research WRF) numerical weather prediction model to study a fog event that formed on 20 January 2008 over Thessaloniki Airport, Greece. It is the first time that the coupling of COBEL and WRF models is achieved and applied to a fog event over an airport. At first, the performance of the integrated WRF–COBEL system is investigated, by validating it against the available surface observations. The temperature and humidity vertical profiles were used for initializing the model. The performance of WRF–COBEL is considered successful, since it realistically simulated the fog onset and dissipation better than the WRF alone. The COBEL’s sensitivity to initial conditions such as temperature and specific humidity perturbations was also tested. It is found that a small increase of temperature (~1°C) counteracts fog development and results in less fog density. On the other hand, a small decrease of temperature results in much denser fog formation. It is concluded that the integrated model approach for aviation applications can be useful to study fog impact on local traffic and aviation.     

The Composition of Volcanic Ash and the Dynamics of the 2013–2016 Zhupanovsky Volcano Eruption

This paper presents the results from a study of ash compositions that were erupted in 2013–2016. The juvenile component has been identified in the ejecta using data on the morphology and textural features of ash particles and the composition of volcanic glasses. The data set suggests that the activity of the volcano was phreatomagmatic.     

Monitoring the Processes of Interseismic Accumulation and Coseismic Release of Stresses in the Medium Nearby Earthquake Sources Based on the Analysis of Tidal Response of the Earth’s Surface

Izvestiya, Physics of the Solid Earth - Abstract—The Global Seismographic Network (GSN) incorporating more than 150 seismic stations all over the world allows recording not only...     

Latitudinal Profiles of the Photospheric Magnetic Field in Solar Cycles 19–21

For various groups of photospheric magnetic fields differing in strength, averaged synoptic maps have been obtained from the data of the Kitt Peak National Solar Observatory (1976–2003). The latitudinal profiles of magnetic field fluxes are considered individually for each 5-G field strength interval. Changes in the maxima of the latitude profiles and their localization in the latitude are studied. The results are evidence that the latitudinal distribution of the magnetic fields changes significantly at field strengths of 5, 15, and 50 G. The magnetic flux for groups of fields differing in strength decreases monotonically as the strength increases, starting from B > 5 G; the fluxes of the southern hemisphere exceed those of the northern hemisphere. A very special group is formed by the weakest fields with B < 5 G, which are opposite in phase to stronger fields in terms of localization and time changes.     

Rotation of the Solar Corona from Observations of Radio and X-Ray Solar Emission for Solar Activity Cycles 22–24

Geomagnetism and Aeronomy - The values of the radio and X-ray solar flux over the last three cycles of solar activity were studied for the presence of quasi-periodic oscillations via the...     

Space–Time Analysis of Hydrochemical Composition and Pollution of Water in the Northern Dvina Basin

Water Resources - Water quality dynamics along the Northern Dvina River is analyzed under the conditions of anthropogenic impact. Overall, river water is classified as very polluted. The cases of...     

Analysis of STCC eddies using the Okubo–Weiss parameter on model and satellite data

The North Pacific Subtropical Counter Current (STCC) is a weak zonal current comprising of a weak eastward flow near the surface (with speeds of less than 0.1 m/s and a thickness of approximately 50–100 m) and westward flow (the North Equatorial Current) beneath. Previous studies (e.g., Qiu J Phys Oceanogr 29: 2471–2486, 1999) have shown that the STCC is baroclinically unstable. Therefore, despite its weak mean speeds, nonlinear STCC eddies with diameters ~300 km or larger and rotational speeds exceeding the eddy propagation speeds develop (Samelson J Phys Oceanogr 27: 2645–2662, 1997; Chelton et al. Prog Oceanogr 91: 167–216, 2011). In this study, the authors present numerical experiments to describe and explain the instability and eddy-generation processes of the STCC and the seasonal variation. Emphasis is on finite-amplitude eddies which are analyzed based on the parameter of Okubo (Deep-Sea Res 17: 445–454, 1970) and Weiss (Physica D 48: 273–294, 1991). The temperature and salinity distribution in March and April offer the favorable condition for eddies to grow, while September and October are unfavorable seasons for the generation of eddies. STCC is maintained not only by subsurface front but also by the sea surface temperature (SST) front. The seasonal variation of the vertical shear is dominated by the seasonal surface STCC velocity. The SST front enhances the instability and lead to the faster growth of STCC eddies in winter and spring. The near-surface processes are therefore crucial for the STCC system.     

Thermal regimes and degradation modes of permafrost along the Qinghai-Tibet Highway

Permafrost on the Qinghai-Tibet Plateau (QTP) is widespread, thin, and thermally unstable. Under a warming climate during the past few decades, it has been degrading extensively with generally rising ground temperatures, the deepening of the maximum summer thaw, and with lessening of the winter frost penetration. The permafrost has degraded downward, upward and laterally. Permafrost has thinned or, in some areas, has totally disappeared. The modes of permafrost degradation have great significance in geocryology, in cold regions engineering and in cold regions environmental management. Permafrost in the interior of the QTP is well represented along the Qing-hai-Tibet Highway (QTH), which crosses the Plateau through north to south and traverses 560 km of permafrost-impacted ground. Horizontally, the degradation of permafrost occurs more visibly in the sporadic permafrost zone in the vicinity of the lower limit of permafrost (LLP), along the margins of taliks, and around permafrost islands. Downward degradation develops when the maximum depth of seasonal thaw exceeds the maximum depth of seasonal frost, and it generally results in the formation of a layered talik disconnecting the permafrost from the seasonal frost layer. The downward degrada- tion is divided into four stages: 1) initial degradation, 2) accelerated degradation, 3) layered talik and 4) finally the conversion of permafrost to seasonally frozen ground (SFG). The upward degradation occurs when the geothermal gradient in permafrost drops to less than the geothermal gradients in the underlying thawed soil layers. Three types of permafrost temperature curves (stable, degrading, and phase-changing transitory permafrost) illustrate these modes. Although strong differentiations in local conditions and permafrost types exist, the various combinations of the three degradation modes will ultimately transform permafrost into SFG. Along the QTH, the downward degradation has been proceeding at annual rates of 6 to 25 cm, upward degradation at 12 to 30 cm, and lateral degradation in the sporadic permafrost zone at 62 to 94 cm during the last quarter century. These rates exceed the 4 cm per year for the past 20 years reported for the discontinuous permafrost zone in subarctic Alaska, the 3 to 7 cm per year reported in Mongolia, and that of the thaw-stable permafrost in subarctic Yakutia and Arctic Alaska.     

Spatial and Spectral Analysis of Refined Gravity Data for Modelling the Crust–Mantle Interface and Mantle-Lithosphere Structure

We analyse spatial and spectral characteristics of various refined gravity data used for modelling and gravimetric interpretation of the crust–mantle interface and the mantle-lithosphere structure. Depending on the purpose of the study, refined gravity data have either a strong or weak correlation with the Moho depths (Moho geometry). The compilation of the refined gravity data is purely based on available information on the crustal density structure obtained from seismic surveys without adopting any isostatic hypothesis. We demonstrate that the crust-stripped relative-to-mantle gravity data have a weak correlation with the CRUST2.0 Moho depths of about 0.02. Since gravitational signals due to the crustal density structure and the Moho geometry are subtracted from gravity field, these refined gravity data comprise mainly the information on the mantle lithosphere and sub-lithospheric mantle. On the other hand, the consolidated crust-stripped gravity data, obtained from the gravity field after applying the crust density contrast stripping corrections, comprise mainly the gravitational signal of the Moho geometry, although they also contain the gravitational signal due to anomalous mass density structures within the mantle. In the absence of global models of the mantle structure, the best possible option of computing refined gravity data, suitable for the recovery/refinement of the Moho interface, is to subtract the complete crust-corrected gravity data from the consolidated crust-stripped gravity data. These refined gravity data, that is, the homogenous crust gravity data, have a strong absolute correlation of about 0.99 with the CRUST2.0 Moho depths due to removing a gravitational signal of inhomogeneous density structures within the crust and mantle. Results of the spectral signal decomposition and the subsequent correlation analysis reveal that the correlation of the homogenous crust gravity data with the Moho depths is larger than 0.9 over the investigated harmonic spectrum up to harmonic degree 90. The crust-stripped relative-to-mantle gravity data correlate substantially with the Moho depths above harmonic degree 50 where the correlation exceeds 0.5.     

Study of the Activity and Segmentation of Active Faults Using Measurements of Radon and Mercury Gases

In this paper,measurements of gaseous radon and gaseous mercury densities were conducted for the first time along the Haiyuan active fault zone,including three longer secondary shear faults from Biangou to Shaokou,faults in the Ganyanchi pull-apart basin,and the Biangou push-up structure as well as the thrust fault at the eastern pediment of Liupanshan Mountain in the terminal compressional area.Then relations between fracture gas densities and faulting activity were analyzed.The results show that there is a distinct corresponding relation between gaseous radon and gaseous mercury densities and faulting activity,when the measurement conditions are basically the same,and it proves that the fault gasmetry method is an effective technique for study the activity and segmentation of active faults.     

Formation Conditions of Runoff and Hydrological–Morphological Processes in Deltas in Permafrost Zone: The Deltas of the Lena and Mackenzie Rivers

Water Resources - The article presents a study of the hydrological regime of the Lena and Mackenzie rivers, flowing in the zone of permafrost rocks of different types. Features typical of river...