Sea level reconstructions in the Black Sea basin and elsewhere rely on the identification of sea level markers and on the understanding of their post-genetic vertical movements. We present here evidence of a fast, bi-directional vertical displacement on the western Black Sea shore at Mangalia, Romania. We argue that an area situated near the shoreline was submerged 4 m, subsequently filled with marine silts and sands, then uplifted by 10 m, where it currently stands. Radiocarbon dating of several types of materials from the infill, as well as archaeological evidence, indicate that this displacement occurred during the eighteenth to nineteenth centuries. Mollusc shells found in anatomical connection close to the top of the sediment sequence have a 14C reservoir age offset of 900 years, probably due to the hard water effect. This is much larger than the 400 year offset that is generally considered for the Black Sea and highlights the problematic dating of Black Sea coastal sediments. The findings of this study offer strong evidence of short-term, local tectonic movements that should be considered when past sea levels are calculated, while at the same time serve a warning for urban and marine development planners.

A recent comprehensive study, considered as important for the geodynamic, crustal and lithospheric geological structures and active tectonics in Vrancea, presented geological updates based on geophysical and geological data interpretation: a) Wrench tectonics system, crossing NE-SW the Romanian territory; b) Romanian Trough, interpreted as the prolongation of the Polish Trough beneath the East Carpathians; c) Volcanism and intrusive processes in the Vrancea area; d) Geophysical and tectonic model for the Vrancea seismic zone. When interpreting causes of Vrancea zone crustal seismicity, they are here considered to be associated at crustal depths with active normal faults situated within a graben geological structure, in an extensional regime. At lithospheric level the causes of high magnitude seismicity are related to strike-slip movements of a regional transcurrent fault, in a transtensional regime. High magnitude seismic events are considered to be located at the junction of the WT Southern Fault with a NW-SE trending strike-slip regional fault system, namely the Peceneaga-Camena, Capidava-Ovidiu and Mangalia faults.

The Moesian Platform represents a major tectonic unit of the foreland of the Carpathians and Balkans, spanning across the southern part of Romania and the northern part of Bulgaria. Although the Moesian Platform is considered to be a stable tectonic unit, it has played a significant role in the geological history of the region, influencing the development of the surrounding Carpathian and Balkan mountain ranges, making it an area of interest for studying tectonic history, geological structures, and landscape evolution. In the southern part of the Moesian Platform in Romania, delineated to the north and to the east by the steep slopes of the Argeş River valley and to the south by the steep slopes of the Danube River valley, an elevated and W–E promontory-looking geomorphological feature identified by the local inhabitants as “hill” is distinct from the neighbouring flat relief of the Romanian plain. This study is the result of a comprehensive investigation into the geomorphological features and neotectonic structures within this region. An intriguing outcrop displaying a filled fault, cutting and displacing the Quaternary sedimentary formations of the recently named Argeş Promontory, shed light on recent tectonic activities that have influenced the landscape. By integrating field observations, geological, and tectonic data, as well as satellite geodetic data, our results contribute to a better understanding of the study area’s regional geodynamics, emphasizing the significant role of tectonic activity in shaping the present-day landscape.

A high magnitude earthquake (Mw = 6.4) occurred on November 26, 2019, at 2:54 AM, close to Durres city, Albania. Ten hours later, in Vrancea seismic zone occurred three seismic events (Mw = 1.7; 3.2; 2.6), with epicenters migrating eastward. During 26 and 27 November, a higher number of earthquakes occurred in Durres seismic zone, when comparing to its average seismicity. Almost simultaneously, significant seismic events have been recorded in Greece (N Peloponnesus ml = 3.8; W Crete ml = 6.0) and Bosnia-Herzegovina (ml = 5.9), on a regional NW–SE lineament. A recent study interpreted a wrench tectonics system across Romania, its southern NE–SW trending transcurrent fault being associated with the intermediate-depth, subcrustal seismicity in the Vrancea seismic zone. When extending south–westward the two transcurrent faults from Romania to Albania, resulted that most earthquake epicenters that occurred during 26 and 27 November 2019 in the Durres seismic area are located between them. A north–westward tectonic lineament, interpreted using seismic events occurred between W Crete and S Bosnia-Herzegovina during the same time interval, crosses the two transcurrent faults within the Durres–Shkoder seismic area, suggesting that the regional NE–SW and NW–SE fault systems have been activated during November 2019.

The name Intramoesian Fault was introduced in the scientific literature by Mircea Săndulescu in 1984. Săndulescu (1984) described the fault as being a sinistral transcrustal fault, after several dextral–sinistral displacement variations during geological time. The fault was located in the central part of the Moesian Platform, displaying NW–SE direction; it was continued south of the Danube river up to the Bulgarian Black Sea shelf, and northward underneath the Getic Nappe. Although this is the most accepted model of the Intramoesian Fault, used by many researchers as marker for the Moesian Platform compartments delineation, the Intramoesian Fault proved to be a complex and complicated tectonic target both at local and regional scale (in Space), being differently located on maps throughout history (in Time). The geological mapping of the Intramoesian Fault was not possible, as it does not outcrop and has no topographic expression, being concealed beneath a thick Neogene sedimentary cover, traces of regional faulting being hidden totally. This intriguing tectonic structure, still subject of debate, had a large variety of names and was identified so far as fault, fracture or tectonic contact. An extended documentation on the Intramoesian Fault and the Moesian Platform was carried out within the PhD Thesis “Intramoesian Fault: geophysical detection and regional active (neo)tectonics and geodynamics”, Doctoral School of Geology, Faculty of Geology and Geophysics, University of Bucharest. This PhD study offered the framework for a focused research on geophysical detection of the Intramoesian Fault and its regional tectonics and geodynamics, analysing and integrating a large number of geophysical and geodetic data, as well as geomorphological and geological observations. An updated regional tectonic and geodynamic model was developed within this study, showing that the Intramoesian Fault is composed of a number of segments, laterally displaced by several active regional NE– SW, N–S and W–E faults systems. Due to repeated junctions with the younger NE–SW strike-slip faults, and due to a NE–SW transcurrent fault in the Vrancea wrench tectonics system (Ioane, Stanciu, 2018), the Intramoesian Fault is displaced south–westward in the area close to the Carpathians. North of the Danube, a north–eastward displacement of the Intramoesian Fault was interpreted as due to an indentation of an Argeş – Danube Promontory along the Argeş (W–E) and Gabrovo – Veliko Tarnovo (NE–SW) faults.

Previous studies have shown that the Black Sea was subject to tsunami waves generation in the past (Altinok, 1999), with a total of twenty-two events generated. According to recent studies of Diaconescu et al. (2008), the Black Sea is divided in nine seismic sources. A more recent approach structures the area in ten different seismic sources, given by Moldovan et al. (2016, 2017). This study focuses mostly on the Istanbul seismic source, which triggered in the past high magnitude earthquakes followed by tsunami waves. The most recent event generated in the Black Sea was on 15 of October 2016, with a magnitude Mw = 5.1, at a depth of 10 km, with the following location: Latitude 42.19° N, Longitude 30.68° E. The focal mechanism determined through the moment tensor inversion (U.S. Geological Survey – USGS) indicates a reverse faulting type. For this event, few tsunami modeling scenarios were run. When using the exact parameters of the earthquake (Mw = 5.3), the simulations show no results. More simulations were computed, increasing the magnitude with steps of 0.2, from 7.0 up to 7.8. The modeling was accomplished using the Tsunami Analysis Tool (TAT), software provided by the Joint Research Center (JRC) from Ispra, Italy. The results of these tsunami simulations show low wave heights for a magnitude of 7.2, of maximum 0.42 m in Eregli (Turkey), 0.36 m in Zonguldak Eregli (Turkey), and 0.32 m in Kilimli (Turkey). For a magnitude of 7.6, the maximum wave heights are higher, considered to be moderate, of 1.59 m in Zonguldak Eregli (Turkey), 1.21 m in Eregli (Turkey). Moreover, there are three locations from the Romanian shoreline affected, as follows: 0.83 m in Mangalia, 0.5 m in Techirghiol and 0.39 m in Constanţa. In order to obtain a correlation of these simulations to real events of high magnitude, we will compare them with two past earthquakes from the Istanbul seismic area, generated on 12 of November 1999 (Mw = 7.2) and 17 of August 1999 (Mw = 7.6). Due to their location inland, the results for these two earthquakes display very low wave heights, of maximum 0.18 m. These events were also modeled using the same software, same methodology, considering as location an offshore position of the earthquakes, assumed as being generated on similar faults. The results were compared to the modeling output of the 2016 earthquake from October. For a better evaluation of the tsunami waves possibility of occurrence in the Istanbul seismic area, more information regarding the parameters of high magnitude earthquakes, their location and focal mechanism type, are necessary.

On 8th of September 2017, an earthquake of magnitude Mw 8.1 was generated offshore Mexico, Chiapas area, at 04:49 UTC, with a depth of 72 km and the following coordinates: Latitude 15.02 N, Longitude 93.81 W, 98 km away from Pijijiapan (Mexico). The fault plane solution of the event was normal plane. Maximum tsunami waves of 1.1 m were measured at Salina Cruz sea level station, following the earthquake. Tsunami modelling simulations were accomplished using the earthquake’s parameters (location, magnitude, depth) and moment tensor solutions given by 3 different agencies: United States Geological Survey (USGS), German Research Centre for Geosciences (GFZ) and Global Centroid Moment Tensor (GCMT). For every case studied, the affected locations, sea level estimates and maximum wave heights were computed. There are two software used for modelling, the Tsunami Analysis Tool (TAT), provided and developed by the Joint Research Centre, Ispra, Italy and TRIDEC Cloud, provided by the German Research Centre for Geosciences (GFZ), Potsdam, Germany. After analysing the modelling scenarios, a comparison between the results of the two software was accomplished, for the same earthquake parameters. The results show that the parameters of GCMT computed with TAT overestimate those computed with TRIDEC, of maximum 3.9 m wave height at Arista with TAT and 2.46 m with TRIDEC. For the GFZ parameters, the estimates give 3.5 m for Pasito de la Senora with TAT, compared to 1.64 m maximum waves at Puerto Madero with TRIDEC. For the USGS data set, the results are similar, maximum waves of 2.4 m at Pasito de la Senora with TAT, and 2.9 m at Puerto Madero with TRIDEC. The Salina Cruz station, where 1.1 m height waves were measured, gives results only for the simulations ran with TAT, with 1.0 m for the GFZ earthquake parameters, 0.6 m for USGS and 1.4 m for the GCMT parameters.

There are evidences of 22 past tsunamis generated in the Black Sea area. Shabla area is the most dangerous for the Romanian shoreline and triggered past high magnitude earthquakes and tsunamis. According to National Oceanic and Atmospheric Administration (NOAA) data base, 3 important events occurred in Shabla: the most recent, on 31st of March 1901, an earthquake of magnitude 7.2 triggered waves of 5 m, other sources estimating 2.5 - 3 m; the oldest documented event, in the1stCentury BC, in Bisone area, and the third one, year 543 AC, when a 7.5 magnitude earthquake generated tsunami waves of 2 - 4 m. Tsunami modeling was accomplished for Shabla area using two software, Tsunami Analysis Tool (TAT) and TRIDEC Cloud, and past earthquake parameters (location, depth, focal mechanism). A comparison between the results of the two software was accomplished, for the same input parameters: magnitudes of 7, 7.2, 7.5 and 8, depths of 5, 10 and 30 km and 5 fault plane solutions. The worst case scenario with TRIDEC software displays waves of maximum 2.62 m in Varna, for a magnitude 8 and a depth of 5 km, with 0.32 m in Constanta; the worst case using TAT software shows maximum waves of 4.3 m in Kamen Bryag, with 4Romanian locations affected (2 m waves in Costinesti). Moderate waves are given by scenarios using magnitude 7.5, with 0.6 - 0.8 m heights. For lower magnitudes (7 - 7.2), the modeling estimates very low waves, 0.2 - 0.4 m.

The Moesian Platform is considered to consist of two main compartments, with different geological age and petrographic features at the crystalline basement level, separated by the NW-SE trending Intramoesian Fault. Seismological data compiled from published local, regional and global earthquakes catalogues was used to illustrate and analyze the distribution of seismicity within the Moesian Platfom. A number of profiles across the Intramoesian Fault with the earthquake hypocenters are presented, aiming at detecting the tectonic contact between the Moesian Platform compartments.

The Harghita Mts are located in the central part of Romania and represent the youngest part of the East Carpathians Neogene-Quaternary magmatic belt. The Ciomadul magmatic structure, situated at the southern end of the Harghita Mts, includes the St. Ana Lake and several isolated domes, Puturosul and Balvanyos representing the easternmost outcropping volcanics.Traces of active post volcanic processes are widespread between Tusnad and Balvanyos localities, mostly represented by mineral groundwater springs (displaying a large variety of chemical characteristics) and moffeta (generated by gas emergences rich in CO2).The special interest in this post volcanic activities is given by the perspective of being used as a tool for economic development of the region, once famous for the curative properties of the mineralized groundwater resources and the abundant number of springs (naturally outcropping or tapped).The possibility to revive the great potential of this area is diminished by the small quantities of mineral groundwater offered by the springs nowadays still active and the unsuccessful wells drilled for mineral water exploitation during the last several decades.Benefiting of the specific low electric resistivity values of mineral groundwater in this post volcanic area (mostly ranging between 0.5 and 15 Omega m) it was recently considered that modern geophysical techniques, such as the Electric Resistivity Tomography (ERT), may contribute to locate underground aquifers bearing higher water resources.ERT survey lines were deployed in the Balvanyos, St. Ana Lake and Mohos Peat Bog areas trending N-S, E-W, NW-SE and NE-SW in an attempt to detect structural features involved in groundwater vertical displacement (faults, fractures, tectonic contacts) or its underground accumulations.The high variability of electric resistivity values illustrated in the ERT cross-sections may be interpreted in terms of groundwater quality, rarely here to be used for domestic consumption, but mostly for various medical treatments.

Shabla region is located in NE Bulgaria and belongs from tectonic point of view to the southeastern part of the Moesian Platform. The study area covers parts of the eastern slope of the North Bulgarian arch, from the Bulgarian – Romanian border to the north, to the Cape Kaliakra to the south and from Dobrich city to the west, to the Black Sea continental slope to the east. Block faulting, horsts and grabens of different rank are the typical structural features (Dabovski et al., 2002, Zagorchev et al., 2009). It is characterised by an active seismicity, with very strong earthquakes recordings (Oncescu et al., 1999, updated; http://www.emsccsem.org, 2016).

This study is based on an integrated interpretation of previous geological, geophysical data (gravity, magnetic, refraction and reflection seismic cross-sections), geochemical research (Hg spectrometry) and regional seismicity data, available from Romania and Bulgaria, in order to build local and regional-scale models of the Intramoesian Fault.Since the late '60, the Intramoesian Fault has been described as a trans-crustal fault, extending from underneath the Carpathians, across the Moesian Platform, to the Black Sea continental shelf, its path being ambiguously located on maps.As it does not outcrop, the geological mapping of the Intramoesian Fault was not possible, due to thick Quaternary sediments covering the Moesian Platform. Near surface weakly consolidated sediments hide traces of faulting, while the crystalline basement has never been intercepted by wells in the vicinity of the supposed path of the Intramoesian Fault.The integrated interpretation of airborne, ground and marine gravity and magnetic data, offer the possibility to interpret the position of the Intramoesian Fault at crustal depths, while seismic reflection and refraction data are considered to be a good constrain in advocating a "tectonic contact" of the two major compartments of the Moesian Platform along the Intramoesian Fault.Hg spectrometry measurements carried on in Gruiu area, crossing the supposed position of the Intramoesian Fault, had as main results a group of anomalies extended on a distance of 600 m, considered to be associated with this tectonic structure.Romplus earthquake catalogue reveals a NW-SE wide lineament of scattered epicenters in the Romanian central part of the Moesian Platform, between Mostistea and lalomita valleys, along the direction of the Intramoesian Fault. The seismic activity here is frequent, with low magnitude earthquakes (Mw 1 - 3) occurring between 5 and 60 km depth. Higher seismic activity, related to regional active tectonics, has been observed during 1955 - 1970 and also in other two important seismogenic areas: Fagaras - Campulung region (Romania) and Shabla region (Bulgaria).The geophysical detection of the Intramoesian Fault represents an important geotectonic goal when improving regional and crustal geophysical and geological models.

In the surroundings of Ciomadul Mountain, located in the southern extremity of the Harghita Mountains, Romania, intense discharge of dry (predominantly CO2, H2S) and wet emissions are known to occur, being an evidence of a deeply settled geothermal system.In this post-volcanic environment, an inventory of the water outflows was recently performed, aiming to update the old existing databases and to better document the permanent sources. The appearance of new (spontaneous) sources as well the dryness of other sources was observed during the monitored period extended over one year, being a phenomenon related to both internal (geological) and external (climate) factors.Despite the fact that Harghita Mountains also host the strongest heat-flow anomaly in Romania and hydrogeological records state the presence of a geothermal aquifer located at 800m depth (intercepted by a borehole in andesitic formations), only 2 sources (tapped water) monitored by the authors were identified to have a temperature overpassing 19 degrees C during the whole year. The highest value (28.5 degrees C) was recorded in the SNAM borehole, whose water upflows from similar to 300m depth.A total number of 37 sources, considered as permanent sources, were selected in order to analyse the time and space variability of post-volcanic activities in the area of Tusnad-Bicsad and Balvanyos. According to their spatial position they were divided into 5 groups: Tusnad area (formed by a group of 6 sources), Hammas-Vallato (grouping 11 sources), Balvanyos I (6 sources), Balvanyos II (5 sources) and Csiszar Cold Baths (9 sources).In terms of pH, the groundwater sources from the analysed area1 are classified as moderate to high acid waters, displaying values from 1.53 (u. pH) to 6.86 (u. pH), while the electrical conductivity parameter shows a wide range of values, between 139 and 50600 mu S/cm. The extreme value of 50600 mu S/cm was reported for a wet mofett, loaded with dissolved salts and with intense CO2 emissions.Physical parameters were further used to analyse the influence of the local tectonic on the area1 spreading of the sources (deployment on preferential alignments) and the possibility of interconnection between the sources upflow paths (based on physic-chemical parameters correlation).

In order to prevent land deterioration, when searching for buried objects with imprecise location, non-invasive and non-destructive geophysical methods can be applied. The success of these methods depends on the target dimensions, its properties in certain induced or natural physical fields and their contrast with the surrounding material, as well on the measurements profiles design.Such a test was executed for a buried water reservoir formed by two unequal wells with the maximum height of 3m. Each column was built up by concrete tubes having a diameter of 1.2m.Geophysical measurements, consisting in apparent electrical resistivity measurements, were executed using a multielectrode system. Several Electrical Resistivity (ERT) profiles, with different orientations, were delineated in order to intersect the area where the buried water reservoir was suspected to be located. ERT measurements were performed using Schlumberger, Wenner or Dipole-Dipole arrays, positioning the electrodes at an equidistance of 1m each.Two ERT profiles were previously executed in an undisturbed area in order to understand the local shallow geology illustrated by resistivity variations. ERT sections depicted an electrical layered structure formed by 3 distinct layers till the investigated depth of 7m.Despite the fact that the groundwater is often classified as electrically conductive, samples of water collected from the studied area showed low electrical conductivity properties. Due to the unexpected values obtained from the water collected during the geophysical measurements (32 mu S/cm, at a pH of 6.868) from a nearby spring, a new water probe was analyzed after 3 months of the completion of geophysical campaign. The results showed a small change, the electrical conductivity of the water taken from the reservoir being 30 mu S/cm, at a pH of 6.673, 0.0 salinity and TDS of 23ppm). The high electrical resistivity value of the phreatic aquifer from the studied location is a consequence of its refilling mainly by the raining water (electrical conductivity of mountain rain water collected from the study location was 20 mu S/cm at a pH of 6.759 and TDS of 10ppm).Despite the challenging environment and unexpected low conductance of the groundwater, by means of ERT data interpretation the buried water reservoir was successfully located.

Geophysical prospection for groundwater resources has several distinctive tasks, depending on the objectives: mapping a known water bearing structure, location of new spring or groundwater quality.The groundwater resources are extremely diversified: naturally enriched in salts or other minerals, naturally acidified (pH<5) or with excess of basicity, cold (<20 degrees C) or with increased temperature (hypothermal, thermal and hyperthermal).The use of the geophysical non-invasive techniques for groundwater investigation reduces the risk of drilling dry holes or to reach a certain type of water which is not of the particular interest (for example reaching cold water resource when the target is a hot water, or finding low mineralized water when the desired resource is a saline spring).Thus, it is very important to analyse the groundwater properties and to correlate them with the properties that can be investigated by non-invasive geophysical methods.In this paper the focus will be on groundwater parameters diversity, using as a main feature the electrical conductivity. The selection of this parameter is justified by the possibility of being tracked also by two indirect investigation methods: geoelectric and electromagnetic prospection. The approach is directed to observe the spatial but also the temporal water chemistry variation as reflected in several parameters that can be determined without expensive or time demanding laboratory analyses: electrical conductivity, hydrogen ion concentration (pH) and total dissolved solids (TDS that can be determined from electrical conductivity (sigma), using TDS-meters or by computing the total dissolved components concentrations).

This paper is a multidisciplinary presentation of the seismogenic area situated in the North-Dobrogea Orogen (Tulcea). This zone is characterized by significant crustal seismic activity, with crustal earthquakes of magnitude Ms >= 5.0 on the Richter scale. Geological and geophysical data for the area are presented. The seismicity of the region is presented by making use of the latest catalogues, exemplified with maps and a 3D figure. Focal mechanisms with their parameters for several earthquakes are analyzed together with the observation data (provided by different seismological stations). A brief presentation of the main geological features, which are characteristic of the tectonic units that build up the North-Dobrogean Orogene, outlines the diverse petrographic constitution of the various structural levels. In order to discuss the local seismic site effects two scenarios are considered, both of which take into account the characteristics of the seismogenic area. The first one considers the city exposed to an earthquake (superficial) from the E Vrancea zone and the second one considers the city exposed to a seismic event with magnitude M-w = 5.1 from Sf. Gheorghe fault. The earthquake epicentres are located in very active seismic areas. The important features taken into account are the nonlinear behavior of the upper soil strata, the effect of the bedrock elasticity, and different shear modulus and damping of the linear-equivalent-type system. Additionally, several local amplification functions are presented.