DOI: 10.3897/geostudies.3.e194004

Authors: Michael Arvanitis

Abstract: Active geothermal systems in the Mediterranean occur in a tectonically diverse belt shaped by subduction, slab rollback, back-arc extension, active faulting and Quaternary volcanism. These settings offer an excellent natural laboratory for integrated geophysical monitoring because the same systems combine deep heat sources, structurally controlled permeability, clay alteration, complex fluid phase changes and strong near-surface heterogeneity. This review evaluates the complementary roles of seismic methods, magnetotelluric and controlled-source audiomagnetotelluric imaging, self-potential, transient electromagnetic methods and ground-penetrating radar for the exploration and monitoring of Mediterranean geothermal fields. A new practical synthesis case study for Campi Flegrei is included to move beyond a purely narrative review: it compares method sensitivity, depth of investigation, uncertainty sources and decision value using original review-level plots and a transparent scoring matrix. Representative examples from Milos, Nisyros, Santorini, Etna, Ischia and western Anatolia are used to test transferability across different geothermal play types. The review concludes that future progress in Mediterranean geothermal characterization will depend less on any single technique than on uncertainty-aware integration of geophysical, geological, geochemical and geodetic information, supported by explicit reporting of resolution and alternative interpretations.

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DOI: 10.3897/geostudies.3.e176708

Authors: Plamena Raykova, Dimcho Solakov, Stela Simeonova

Abstract: Strong earthquake with moment magnitude MW7.5 hit the city of İzmit, Turkey with devastating effect in August 1999. The earthquake occurred in the North Anatolian Fault (NAF),and was followed by an intensive aftershock activity. It is assumed that the studied earthquake is a part of a seismic sequence that started in 1939 along the North Anatolian Fault. Over a period of 60 years or more, a series of large earthquakes moved progressively from east to west by the fault. The analysis of the space-temporal pattern of seismic clusters (foreshocks and aftershocks) distribution of the 1999 Turkey earthquake, is presented in the research. The properties of aftershock sequence (distinct cluster in space and time) allow for a time-dependent prediction of aftershock probabilities. Aftershock activity can sometimes cause more destruction than the main earthquake, due to factors such as radiation pattern, location and the cumulative nature of building damage. If the distribution of aftershocks over time is considered as a non-stationary Poisson process, the maximum likelihood method is used to estimate the parameters of the modified formula of Omori - power-low decay. A transformation from the time scale t to a frequency-linearized time scale τ is applied to test the correspondence between different statistical models and the occurrence of an aftershock sequence. As a final step of the study, a criterion - Akaike’s information criterion is used to determine the best model for the temporal distribution of aftershocks.The results of the study show that the precursor aseismic gap before the August 1999 MW7.5, Turkey earthquake is not observed. The aftershock sequence shows a complex temporal pattern - one secondary aftershock sequence with a different value of p – parameter.

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DOI: 10.3897/geostudies.2.e180731

Authors: Nadezhda Ilieva, Kamelia Petkova

Abstract: This study examines the transformations in fertility among Roma living in urban settings in Bulgaria by combining demographic data, a large-scale quantitative survey, and in-depth interviews. The findings reveal that despite the traditionally high fertility rates and favourable age structure characteristic of the Roma population during the 1990s and the early 21st century, the last two decades have been marked by a distinct decline in both overall fertility and adolescent childbearing. Changes in reproductive behaviour are shown to result from a complex interplay of socio-economic conditions, migration processes, educational trajectories, shifting family roles, and religious influences. The data demonstrate a strong association between the number of children, educational attainment, employment status and income levels, with higher levels of education and economic stability correlating with planned parenthood and smaller family size. At the same time, the large-scale migration of young Roma abroad exerts a dual effect: on the one hand, it generates a demographic vacuum at the local level, and on the other, it transfers norms of postponed parenthood and limited fertility. The interviews highlight increasing female emancipation and the growing role of education as an internal regulator of reproductive decision-making. The article argues that fertility should not be conceptualised as an isolated demographic characteristic, but rather as a reflection of social inequalities and the dynamic processes of adaptation within Roma communities.

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DOI: 10.3897/geostudies.1.e133185

Authors: Emil Oynakov, Mariya Popova

Abstract: The present study comprehensively analyzes seismic events recorded by the National Operative Telemetric System for Seismological Information (NOTSSI) in 2023. Seismic data are collected in real-time by 26 Bulgarian stations, supplemented by numerous stations from neighboring countries, enhancing the precision of hypocentral location determinations. The main kinematic parameters and the magnitude of the earthquakes are estimated utilizing an adaptation of the product HYPO’71. In the practice of NOTSSI, two types of magnitude estimates are used. Magnitude MP is determined by measuring the maximum amplitude of the P wave. The seismic moment magnitude MW is estimated from the seismic moment M0 - a quantity that combines the rupture area and the residual displacement along the fault with the strength properties of the medium (shear modulus µ). The present study transforms MP, into the more reliable and widely used magnitude scale MW.MW allows for homogenizing the magnitude estimates in the available seismological information and creating a homogenized catalog. The energetically homogenized catalog ensures compatibility of the input seismological information and a reliable assessment of the energetic distribution of earthquakes. The year 2023 was remarkable for the two devastating earthquakes, magnitudes M7.8 and M7.5, that occurred in Eastern Turkey on February 6th, followed by more than 40 000 aftershocks. They caused human losses and enormous material damage. Although they were more than 1500 km from the territory of Bulgaria, the main shocks were partially felt on the high floors of some buildings.The earthquakes analyzed in Bulgaria and its surroundings in 2023 were primarily low-magnitude events with uneven spatiotemporal distribution. The hypocenters’ depth distribution was in the upper levels of the earth’s crust. The largest number of events were registered in the Rilo-Rhodope seismic area, which covers the Struma and Rhodope seismic zones. The highest concentration of seismic events is observed again in the Struma seismic zone. In the Srednogorie region, along the Maritsa River valley, on June 7, 2023, occurred the strongest earthquake for 2023. It had a magnitude of 4.8 and an intensity of 6.5 in the epicentral area.Looking at the overall picture of earthquakes in Bulgaria in 2023, we should also note the weak seismic events in the Burgas and Strandzha regions in Southeastern Bulgaria and the region of Northwestern Bulgaria.For the last five years, 2023 has been characterized by the highest seismicity, as measured by the number of registered events (68 with MW>3) and the highest magnitude (MW4.8).

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DOI: 10.3897/geostudies.1.e120103

Authors: Yulia Kroumova, Tanya Trenkova, Stoyan Nedkov, Aleksandra Ravnachka

Abstract: In the contemporary digital world, data is a pivotal capital considered an economic factor for generating digital products and services. The rapid growth in data volume and their heterogeneity requires optimization of the data management in order to extract higher added value from them. In the context of this issue, one of the goals of the National Scientific Program “Environmental Protection and Risk Reduction from Adverse Events and Natural Disasters” is the creation of a unified geo-informational environment integrating the data from the work packages. To realize this goal, the present study examines certain aspects of data quality related to their usability. By reviewing basic standards for geospatial data, the metadata paradigm, and previous experience in data quality assessment, a theoretical framework with the main stages of a methodological approach evaluating the suitability of primary data sources for building a unified geoinformation database has been developed. The research results reflect the application of developed criteria systems (detailed and generalized) in analyzing the quality and the study of the suitability degree of selected information resources for one of the Program’s working packages. The results of extensive surveys from work program packages have been generalized. Selected primary data sources have been catalogued, and a multicriteria methodological approach has been developed to assess their quality in terms of their suitability for the unity of the database.

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DOI: 10.3897/geostudies.1.e115530

Authors: Neli Jordanova, Diana Jordanova

Abstract: Identification of magnetic minerals, which determine the magnetic properties of natural rocks, sediments and soils, is of crucial importance for any further interpretation of their magnetic signature in environmental or paleogeographical context. One of the major and widely used methods for determination of kind of magnetic phases in natural materials is by obtaining the Curie/Neel temperature of the respective magnetic mineral. In this contribution, we report a set of thermomagnetic measurements of high-temperature behavior of magnetic susceptibility for topsoils from the territory of Bulgaria, aiming to reveal the pedogenic and lithogenic signature. The data are considered and reported in respect to the parent rock type. Our results suggest that pedogenic magnetic minerals are represented mainly by fine-grained maghemite and/or hematite with possible Al-substitutions in the crystal lattice. This phase is expressed on the heating run of the thermomagnetic curve as a “hump” with a maximum at 250–300 °C. Coarse-grained magnetite is identified as a dominant lithogenic magnetic mineral. Hematite’s presence in a sub-set of red-colored soils is confirmed by additional analyses of isothermal remanence acquisition curves. Two hematite coercivity components were identified, related to pedogenic and lithogenic origin, respectively.

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DOI: 10.3897/geostudies.1.e113477

Authors: Vladimir Ivanov, Reneta Dimitrova, Ivelina Georgieva, Georgi Gadzhev, Kostadin Ganev, Nikolay Miloshev

Abstract: According to future climate projections, the expected thermal stress environmental conditions will get worse if the authorities do not apply appropriate measures for mitigation and adaptation to these changes. The health issues concerning air pollution and extreme temperatures have assumed great importance in recent years. The objective of this study is to estimate the thermal comfort in two of the biggest cities in Bulgaria - Sofia and Varna and their surroundings for the year 2017 by biometeorological indexes. We use computer simulations of the atmospheric parameters that define the thermal comfort indexes, by Advanced Research Weather Forecast Model WRF ARW version 3.9. We performed the simulations on four domains for 2017 with an output frequency of 1 hour. The outermost domain has a horizontal resolution of 9 km and encompasses the Balkan Peninsula. It uses initial and boundary conditions from the 0.25-degree NCEP Final Operational Model Global Tropospheric Analyses datasets with a time-frequency of 6 hours. The estimation of the thermal comfort conditions is performed with characteristics called indexes. The differences in the number of cases between the indexes are due to the specific definitions and the meteorological factors that each of them takes into account. Some of these characteristics have applications depending on the specific thermal conditions.

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DOI: 10.3897/geostudies.1.e115877

Authors: Marina Raykova, Alexander Naydenov

Abstract: Tourism is a very important sector for the Bulgarian economy with its GDP share varying between 10 and 13% before the COVID-19 health crisis. In 2021 domestic tourism accounted for 89% of the personal travel expenditures of Bulgarians. The purpose of the present paper is to analyse public attitudes towards the domestic leisure tourism in Bulgaria and its spatial distribution at the NUTS-2 regions and the residence place type level. The data used in the research are from a national representative survey based on a two-staged random sample stratified by the Bulgarian districts and the residence place type (capital, district administrative centre, town and village). The methodology includes: literature review, descriptive analysis, spatial analysis, average values, building one- and two- dimensional frequency distributions, statistical hypothesis testing, etc. The indicators used in the paper are: practices for domestic leisure tourism, stay duration in domestic resorts, frequency of domestic leisure tourism, people not practicing domestic leisure tourism, domestic leisure tourism average satisfaction level. The obtained results show the differences between those indicators in NUTS-2 and residence place type level, as well as between summer and winter leisure tourism. The presented results are of particular importance, since some of these differences are significantly large.

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