A high-resolution ground and marine magnetic survey was executed to determine the structure of the subsurface and the thickness of the sedimentary cover in the Mygdonian Basin. A spacing of approximately 250 m or 500 m between measurement stations was selected to cover an area of 15 km × 22 km. Edge detectors such as total horizontal derivative (THDR), analytic signal (AS), tilt derivative (TDR), enhanced total horizontal gradient of tilt derivative (ETHDR) were applied to map the subsurface structure. Depth was estimated by power spectrum analysis, tilt derivative, source parameter imaging (SPI), and 2D-forward modeling techniques. Spectral analysis and SPI suggest a depth to the basement ranging from near surface to 600 m. For some selected locations, depth was also calculated using the TDR technique suggesting depths from 160 to 400 m. 2D forward magnetic modeling using existing boreholes as constraints was carried out along four selected profiles and confirmed the presence of alternative horsts and grabens formed by parallel normal faults. The dominant structural trends inferred from THDR, AS, TDR, and ETHDR are N–S, NW–SE, NE–SW and E–W. This corresponds with the known structural trends in the area. Finally, a detailed structural map showing the magnetic blocks and the structural architecture of the Mygdonian Basin was drawn up by collating all of the results.

The Mygdonian Basin is located about 45 km NE of the city center of Thessaloniki in northern Greece. We conducted an electromagnetic (EM) survey that covers parts of the epicenter area between Lake Volvi and Lake Langada of the local 1978 earthquake that caused structural damage in the city center of Thessaloniki. Ambient noise measurements in the basin strongly suggest a complex 3-D tectonic setting. Hence, near-surface electromagnetic measurements were carried out to map the local fault pattern in the research area. We conducted radiomagnetotelluric (RMT) and transient electromagnetic (TEM) measurements along eight profiles, giving a total number of 443 RMT and 107 TEM soundings to study the spatial electrical conductivity distribution. In this context, RMT data are used to study the shallow conductivity structure down to about 35 m, whereas the TEM data explore the conductivity distribution down to a depth of 200 m. The 1-D and 2-D interpretation of RMT and TEM data indicate a local fault pattern in the survey area that was also studied by 3-D modeling of the RMT data.

The mineralogical composition of intraseam layers from Lofoi lignite deposits (northwest Greece) is the subject of the present study. The samples were examined by means of X-ray diffraction (XRD), thermo-gravimetric (TG/DTG) and differential thermal analysis (DTA), and Fourier transform infrared (FTIR) spectrometry. The clay minerals prevail in most samples, with illitemuscovite being the dominant phase, and kaolinite and chlorite being the other major clay components. No smectite was found. Quartz and feldspars, dominate in two cases. The studied materials are characterized as clays to clayey sands, showing significant similarities with the intraseam layers of the adjacent Achlada lignite deposits.

New magnetotelluric (MT) data in north-west Fennoscandia were acquired within the framework of the project "Magnetotellurics in the Scandes" (MaSca). The project focuses on the investigation of the crustal and upper mantle lithospheric structure in the transition zone from stable Precambrian cratonic interior to passive continental margin beneath the Caledonian orogen and the Scandinavian Mountains in western Fennoscandia. An array of 59 synchronous long period and 220 broad-band MT sites was occupied in the summers of 2011 to 2013. We estimated MT transfer functions in the period range from 0.003 to 10(5) s.The Q-function multi-site multi-frequency analysis and the phase tensor were used to estimate strike and dimensionality of MT data. Dimensionality and strike analyses indicate generally 2-D behaviour of the data with 3-D effects at some sites and period bands. In this paper we present 2-D inversion of the data, 3-D inversion models are shown in the parallel paper. We choose to invert the determinant of the impedance tensor to mitigate 3-D effects in the data on our 2-D models. Seven crustal-scale and four lithospheric-scale 2-D models are presented. The resistive regions are images of the Archaean and Proterozoic basement in the east and thin Caledonian nappes in the west. The middle and lower crust of the Svecofennian province is conductive. The southern end of the Kittila Greenstone Belt is seen in the models as a strong upper to middle crustal conductor. In the Caledonides, the highly conductive alum shales are observed along the Caledonian Thrust Front. The thickest lithosphere is in the Palaeoproterozioc Svecofennian Domain, not in the Archaean. The thickness of the lithosphere is around 200 km in the north and 300 km in the south-west. (c) 2015 Elsevier B.V. All rights reserved.

ABSTRACT Mud volcanism is commonly observed in Azerbaijan and the surrounding South Caspian Basin. This natural phenomenon is very similar to magmatic volcanoes but differs in one considerable aspect: Magmatic volcanoes are generally the result of ascending molten rock within the Earth's crust, whereas mud volcanoes are characterised by expelling mixtures of water, mud, and gas. The majority of mud volcanoes have been observed on ocean floors or in deep sedimentary basins, such as those found in Azerbaijan. Furthermore, their occurrences in Azerbaijan are generally closely associated with hydrocarbon reservoirs and are therefore of immense economic and geological interest. The broadside long‐offset transient electromagnetic method and the central‐loop transient electromagnetic method were applied to study the inner structure of such mud volcanoes and to determine the depth of a resistive geological formation that is predicted to contain the majority of the hydrocarbon reservoirs in the survey area. One‐dimensional joint inversion of central‐loop and long‐offset transient electromagnetic data was performed using the inversion schemes of Occam and Marquardt. By using the joint inversion models, a subsurface resistivity structure ranging from the surface to a depth of approximately 7 km was determined. Along a profile running perpendicular to the assumed strike direction, lateral resistivity variations could only be determined in the shallow depth range using the transient electromagnetic data. An attempt to resolve further two‐dimensional/three‐dimensional resistivity structures, representing possible mud migration paths at large depths using the long‐offset transient electromagnetic data, failed. Moreover, the joint inversion models led to ambiguous results regarding the depth and resistivity of the hydrocarbon target formation due to poor resolution at great depths (>5 km). Thus, 1D/2D modelling studies were subsequently performed to investigate the influence of the resistive terminating half‐space on the measured long‐offset transient electromagnetic data. The 1D joint inversion models were utilised as starting models for both the 1D and 2D modelling studies. The results tend to show that a resistive terminating half‐space, implying the presence of the target formation, is the favourable geological setting. Furthermore, the 2D modelling study aimed to fit all measured long‐offset transient electromagnetic Ex transients along the profile simultaneously. Consequently, 3125 2D forward calculations were necessary to determine the best‐fit resistivity model. The results are consistent with the 1D inversion, indicating that the data are best described by a resistive terminating half‐space, although the resistivity and depth cannot be determined clearly.

The general aim of this study is, for the first time, to investigate the inner structure of mud volcanoes in Azerbaijan using several near-surface electromagnetic methods. The central-loop transient electromagnetic (TEM) method and the radiomagnetotelluric (RMT) method were applied on mud volcanoes near Perekishkul, Azerbaijan. These methods complement each other in terms of depth of investigation. In particular, the RMT method generally resolves the very shallow resistivity structures (<10 m) directly beneath the mud volcanoes, whereas the TEM method provides a resolution of up to 100- to 150-m depth. The obtained data sets were processed and interpreted individually. The TEM data were interpreted by conventional 1-D inversion algorithms, i.e., Occam's and Marquardt inversion, and by a quasi-2-D laterally constrained inversion. The RMT data were interpreted by 2-D inversion. Subsequently, a combined model regarding the sediments and corresponding resistivities for the area around the mud volcanoes was derived. Overall, a resistivity range of 1–20 Ω-m was observed. The resistivity models obtained from TEM support the assumption of a three-layer subsurface for the resolved depth range. Also, a lateral resistivity variation caused by the mud volcanoes was observed. Furthermore, the RMT results indicate the presence of shallow low resistivity structures, which can be interpreted as mud reservoirs.

The depositional palaeoenvironment of the Neogene Achlada lignite deposit (western Makedonia, Greece) was deciphered with respect to the evaluation of the macro-petrographic characteristics, and the data resulted from coal petrographic analyses.The total thickness of the studied lignite seam is similar to 26 m and consists of organic and inorganic alternations. The macro-petrographic observations suggest extremely high contributions of woody-originated tissue (xylite) from a single tree type, among the lignite layers, whereas, numerous in situ stems and trunks were observed. The results of the coal petrographic analysis indicate the dominance of huminite (883 vol.%), whereas liptinite and inertinite show much lower values (11.0 vol.% and 0.7 vol.% respectively). High contribution of mineral matter is also observed in many cases. Ulminite types A and B are the most abundant macerals, whereas the content of ulminite B is followed by the xylite content. Facies modeling using maceral composition and maceral indices suggested the alternation of forest swamp and reed-moor environments where peat accumulated under highly-saturated and intensely-anoxic conditions. A terrestrial origin with wet forest to piedmont plain depositional conditions was suggested by the Gelification Index (GI) and Tissue Preservation Index (TPI) plot. A cross-plot of the ground water index (GWI) vs. the vegetation index (VI) suggested swamps under mesotrophic and rheotrophic hydrogeological conditions, where the dominant source for the peat was woody vegetation and vegetation high in preservation potential.The overall macro and micro characteristics of the Achlada lignite suggest a depositional palaeoenvironment that includes three independent parts: a) the main channel of a meandering river system; b) the floodplain area; and c) the oxbow lake. The establishment of telmatic/limnotelmatic conditions in this palaeoenvironment resulted in the formation of the entire Achlada lignite deposit, whereas numerous flood episodes interrupted the peat accumulation and resulted in the deposition of clay-rich sediments. (C) 2015 Elsevier B.V. All rights reserved.

During 2009 and 2010 electromagnetic (EM) soundings and a high-resolution magnetic survey were conducted to study the deeper structure of the peat-lignite deposit in the Philippi sub-basin in Northern Greece. The primary intention of investigating the basement structure of the Philippi sub-basin is to propose the ideal location for a deep and continuous paleoclimate drill site.Data were collected along a 12 km transect (NNE-SSW) through the largest extension of the basin from Krinides at the North to Eleftheroupolis at the South. We used a combined set of Radiomagnetotelluric (RMT), Time Domain Electromagnetic (TEM) and Audiomagnetotelluric (AMT) soundings to derive a 2D model of the electrical resistivity distribution versus depth using a joint inversion approach. This model was then cross correlated with a 2D forward model of magnetic anomaly data. The magnetic survey detected strong anomalies in the North that appeared to have been generated by the Philippi granitoid pluton. All three individual data sets support each other and have jointly been analyzed. From this study we yield an asymmetric graben model of the basin structure that shows maximum thickness (ca. 500 m) in the northern part of the basin leading to a reduction of the thickness to the South. The interface between the basin fill and the bedrock ascend steeply in the North. The overall assessment of the deeper basin structure reveals a detachment system that is in good accordance with previous findings. (C) 2015 Elsevier B.V. All rights reserved.

The mineralogical composition and the resulting behavior upon firing of samples from the intercalated clay seams of the Achlada lignite-bearing sequence (west Macedonia, N. Greece) were examined. The resulting data sets were interpreted in order to evaluate the possible use of the studied clays in the production of structural ceramics. The mineralogical composition of the studied clays was accomplished by means of X-ray diffraction (XRD), thermo-gravimetric (TG), differential thermo-gravimetric (DTG) and differential thermal analysis (DTA) and Fourier Transform-Infrared (FT-IR) spectrometry. The clay minerals prevail in all samples, with illite being the dominant phase and kaolinite and chlorite comprising the rest of the clay components. No smectite was found that would negatively affect the produced ceramics. Other mineral phases identified were mainly quartz and feldspars and subordinated siderite. The classification of the clays using appropriate ternary diagrams suggests their possible use in the production of red-stoneware products in ceramic industry. Casting molds were fired at various high temperatures (up to 1300°C). The mineralogical composition was examined by comparative XRD and FT-IR studies. The results suggested that the formation of both vitrified mass and new crystalline phases, such as Al–Si-spinels and hematite (alpha/a-Fe2O3), starts at ~1000°C. The presence of vitrified mass becomes stronger with increasing firing temperature (~1100°C), enclosing as the neo-formed phases as the residues of quartz and feldspars. At ~1200°C mullite [3Al2O3∗2SiO2] began to form which contributes to the resistance of the ceramic product.

Common studies on the static electric field distribution over a conductivity anomaly use the self-potential method. However, this method is time consuming and requires nonpolarizable electrodes to be placed in the ground. Moreover, the information gained by this method is restricted to the horizontal variations of the electric field. To overcome the limitation in the self-potential technique, we conducted a field experiment using a non conventional technique to assess the static electric field over a conductivity anomaly. We use two metallic potential probes arranged on an insulated boom with a separation of 126 cm. When placed into the electric field of the free air, a surface charge will be induced on each probe trying to equalize with the potential of the surrounding atmosphere. The use of a plasma source at both probes facilitated continuous and quicker measurement of the electric field in the air. The present study shows first experimental measurements with a modified potential probe technique (MPP) along a 600-meter-long transect to demonstrate the general feasibility of this method for studying the static electric field distribution over shallow conductivity anomalies. Field measurements were carried out on a test site on top of the Bramsche Massif near Osnabruck (Northwest Germany) to benefit from a variety of available near surface data over an almost vertical conductivity anomaly. High resolution self-potential data served in a numerical analysis to estimate the expected individual components of the electric field vector.During the experiment we found more anomalies in the vertical and horizontal components of the electric field than self-potential anomalies. These contrasting findings are successfully cross-validated with conventional near surface geophysical methods. Among these methods, we used self-potential, radiomagnetotelluric, electric resistivity tomography and induced polarization data to derive 2D conductivity models of the subsurface in order to infer the geometrical properties and the origin of the conductivity anomaly in the survey area The presented study demonstrates the feasibility of electric field measurements in free air to detect and study near surface conductivity anomalies. Variations in Ez correlate well with the conductivity distribution obtained from resistivity methods. Compared to the self-potential technique, continuously free air measurements of the electric field are more rapid and of better lateral resolution combined with the unique ability to analyze vertical components of the electric field which are of particular importance to detect lateral conductivity contrasts. Mapping Ez in free air is a good tool to precisely map lateral changes of the electric field distribution in areas where SP generation fails. MPP offers interesting application in other geophysical techniques e.g. in time domain electromagnetics, DC and IP. With this method we were able to reveal a ca. 150 m broad zone of enhanced electric field strength. (C) 2013 Elsevier B.V. All rights reserved.

We present a preliminary assessment of the potential utility of various geophysical measurements carried out over a quick-clay landslide site in south-west Sweden. The multidisciplinary approach includes active P- and S-wave seismic investigations, including 2D and 3D reflection and refraction surveys, passive single and 3C seismic surveys, electrical resistivity tomography and electromagnetic surveys including controlled-source and radio-magnetotellurics, ground-penetrating radar and potential field studies. The P-wave and particularly S-wave reflection seismic data show a high-resolution image of bedrock topography and the stratigraphy of a 100 m thick sequence of sediments that lies on top, which include lightly consolidated quick-clays. Of particular interest is the identification of a layer of relatively coarse-grained material between 10-20 m below the ground surface. Geotechnical investigations indicate that most but not all quick-clays at the site are located above this layer. Further studies are required to determine the importance of their relationship and whether the coarse-grained layer may have had a role in triggering quick-clay landslides in the region. Geoelectrical and electromagnetic methods provide high-resolution images of the unconsolidated subsurface and particularly the normal and leached clays. Radio-magnetotelluric methods proved valuable near the river where traditional geoelectrical methods failed to provide sufficient depth coverage. The study shows that geophysical data are able to image major subsurface structures associated with quick-clay landslides.

During 2009 and 2010 geophysical soundings have been conducted to study the basement structure of the Neogene Philippi Basin in Northern Greece. Primary task was to give an estimate of the top of basement distribution along a 12 km transect through the basin and then to choose the most promising drilling location for a climate change study. Different electromagnetic methods, each sensitive for different exploration depth, were applied to obtain a dataset suitable for a later joint inversion. Those methods are supporting each other to overcome resolution problems laterally and horizontally. During the first campaign we stated that the Time Domain Electromagnetic Soundings (TEM) did not succeed in reaching the basement in the centre of the basin, consequently we used, in a second stage, a combined set of radiomagnetotelluric (RMT) and audiomagnetotelluric soundings (AMT) to estimate a first 2D conductivity model. Since the scalar RMT data are measured solely in TM-mode configuration, we confine ourselves to this mode in the modeling. The obtained TM-mode resistivity model was then in turn the starting model for a 2.5D forward modeling of high resolution magnetic field anomaly data. Both individual methods support each other and can have jointly been analyzed.

During the project “Euroseistest Volvi-Thessaloniki”, a strong-motion test site (EUROSEISTEST) for Engineering Seismology was installed in the Mygdonian Basin between the two lakes Volvi and Lagada ca. 45 km northeast of Thessaloniki (Northern Greece). The basin itself is a neotectonic graben structure (5 km wide) with increased seismic activity along distinct normal fault patterns. Fluvioterrestrial and lacustrien sediments (approximately 350-400 m thick) are overlying the basement consisting of gneiss with schist. To improve the seismic wave propagation model it is vital to know about site effects, e.g. the geotectonic properties of the area such as the topof-basement, vertical tectonic boundaries (faults and basement fracturation) and the geothermal regime. Therefore, we carried out near surface EM studies to understand the distribution of the active faulting and the top of basement structure of this particular area. The RMT (Radiomagnetotelluric) and TEM (Transient electromagnetic) measurements were carried out on three profiles and thirty sounding. The inverted RMT and TEM data show generally a four layer model. The layers are indicated as metamorphic and sediment rocks, which are in detail: marly silty sand with gravel (>> 100 Ωm), marly silty sand with clay (50 100 Ωm), sandy clay (30 – 50 Ωm) and silty sand (10 30 Ωm). Due to the high resistivity of the top layer, the skin depths of the RMT soundings are around 35 m. The TEM data gives detail information of the lower structure down to a depth of 200 m. According to our analysis, a normal fault next to the Euroseistest could be located having a strike direction of N 60 E. The joint interpretation of RMT and TEM data proves to be an effective tool to investigate complex geology structures.

To improve the seismic wave propagation model it is vital to know about site effects, e.g. the geotectonic properties of the area such as the top-of-basement, vertical tectonic boundaries (faults and basement fracturation) and the geothermal regime. Therefore, we carried out near surface EM (Electromagnetic) studies to understand the distribution of the active faulting and the top of basement structure of this particular area. The RMT (Radiomagnetotelluric) and TEM (Transient electromagnetic) measurements were carried out on eight profiles, 440 RMT and 104 TEM soundings were realized. The inverted RMT and TEM data show generally a four layer model. The layers are indicated as metamorphic and sediment rocks, which are in detail: marly silty sand with gravel (>> 100 Omega m), marly silty sand with clay (50 - 100 Omega m), sandy clay (30 50 Omega m) and silty sand (10 - 30 Omega m) with varying thickness. Due to the high resistivity of the top layer, the skin depths of the RMT soundings are around 35 m. The TEM data gives detail information of the lower structure down to a depth of 200 m. According to our analysis, a normal fault next to the Euroseistest could be located having a strike direction of N 60 E. The joint interpretation of RMT and TEM data proves to be an effective tool to investigate complex geology structures.

SUMMARY During 2006 and 2007 a total number of 92 MT/GDS sites were deployed in the Mygdonian basin (Northern Greece) to gain knowledge about the basement structure by means of 2D and 3D MT data inversion and to give information about the top-of-basement depth for seismic wave propagation models. The structure of the basement is fairly well revealed by the data.