Authors:O. Baykara, M. İnceöz, M. Doğru, E. Aksoy, and F. Külahcı
On-line monitoring of soil radon (222Rn) concentration system was constructed on one of the main active fault zone of East Anatolian Fault System (EAFS) in Turkey.
The preliminary results, observed during the second part of 2004 and first part of 2005 is presented. During the monitoring
of soil radon concentration, numerous anomalies that equal or twice standard deviation were observed. In addition, the variation
of the radon concentration was examined between the mean values and plus/minus two standard deviations and any increase in
radon concentration above this limit was assumed to be 222Rn anomalies. These anomalies usually appeared between a few days or weeks before the earthquakes occurrence. The obtained
data were also compared as considered respect to the earthquakes occurred in a 100 km radius of the fault system.
The natural radioactivity concentration and some heavy metals in various water and soil samples collected from seismically
active area have been determined. Gross-alpha and beta concentrations of different 33 water samples and some heavy metal (Fe,
Pb, Cu, K, Mn, Cr and Zn) concentration in 72 soil samples collected from two major fault systems (North and East Anatolian
Active Fault Systems) in Turkey have been studied. This survey regarding gross-alpha and beta radioactivity and some heavy
metals concentrations was carried out by means of Krieger method using a gross-alpha and beta-counting system and atomic absorption
spectrometry (AAS), respectively. Also, gross annual effective dose from the average gross-alpha activity in waters were calculated.
Authors:O. Baykara, M. İnceöz, F. Külahcı, M. Doğru, and E. Aksoy
222Rn concentrations along the seismic active area (some distinct in East Anatolian Active Fault System (EAFS), Turkey) were
determined by using passive and active (prompt) methods including CR-39 and Markus-10, respectively. It was observed that
the changing of 222Rn concentration along the fault lines, crossing the main East Anatolian Fault Line, has shown similar characteristics for
both methods. The mean 222Rn concentrations were found to be between 1.2 and 3.6 kBq·m−3 and, 2 and 70 kBq·m−3 by using passive and prompt methods, respectively. Nevertheless, some measured terrestrial gamma-radiation dose rate in the
same area has weak positive correlation to 222Rn concentration. Terrestrial gamma-dose rate at 1 m above the ground in the same sampling point, as for 222Rn concentration measurement were made, varied from 8.5 to 10.6 μR·h−1.
Authors:Nawal Bouya, Hmidou El Ouardi, Hassania El Habibou, Véronique Ansan, and Eric Mercier
The aim of this work is to interpret the geologic structures of the Agourai area (Paleozoic and Mesozoic structures) from processed magnetic maps. The detected magnetic anomalies from different standard methods used in aeromagnetism (Residual map, RTP map, horizontal gradient map) were compared to geologic structures and permit enhancing the mapping quality of some areas, and thus defining many geologic features. Existing geologic maps and geologic field studies allow interpreting some detected anomalies. It was thus possible to define the limits between the Paleozoic basement and the Mesozoic cover, to determine magnetic anomalies according to NE-SW trends compatible with the regional geologic structures and finally to detect a NE to SW-oriented fault system in the Mesozoic cover of the Agourai Plateau. Despite the reliability of this approach, some folded basaltic sills occurring in this region were not well detected, probably because of their reduced thickness.
In the area where the Darnó Fault belt breaks up as a horsetail fault system in southern Slovakia and northwestern Hungary, beside the dominant lithologies such as calcareous siltstone and claystone several peculiar lithofacies generated in different paleoenvironments of the Buda (Hungarian) Paleogene and Fiľakovo/Pétervásara Eggenburgian Basins occur. Laminated limestone and shale classified as oil shale from the village of Drienovec, the Szendrö and the Bátka vicinities (Eocene-Oligocene and Early Miocene in age) came to existence in coastal lagoons and/or subtidal lagoons under anaerobic conditions at the bottom and affected by seasonal weather changes. The Bátka, Novaj, Budikovany, Bretka bioclastic and organogenic limestone units (Kiscellian and Egerian in age respectively) were deposited under shallow marine littoral conditions. The Drienovec and Szuhogy Conglomerate units originated under fluviatile conditions. Almost all mentioned lithologies were generated in genetic (conglomerate) or spatial (oil shale) relationship to the Darnó Fault Belt. The Bátka Limestone as well as the Hostišovce Member are related to the Šafárikovo Rise, a faulted structure perpendicular to the course of the Darnó Fault Belt.
We present the results of a fault reactivation study that used the analog modeling technique. The modeled tectonic processes represent the formation and subsequent deformation of the Derecske Trough and have implications for the evolution of the entire Pannonian basin system. Structural inversion of former thrusts led to normal faulting during the Miocene and corresponds to the formation, whereas subsequent reactivation of these faults in a strike-slip manner during the late Miocene to Quaternary represents neotectonic deformation of the basin. Modeling results show that reactivation of thrust faults in a transtensional manner can occur in a broad range of dip angles, and of angular differences between the maximum principal stress axis and the strike of the fault. The reactivation pattern of strike-slip zones in sandbox models critically depends on the orientation of the fault system with respect to the confining stress field, on the material property of the sand, and on the presence of a lubricant layer, representing a potential detachment horizon at the base of the models. The shear zones at the border zones of the Derecske pull-apart basin are prone to further reactivation, regarding the present-day stress field in the area. These inferences are confirmed by the recent seismic activity of the area, and point to the key importance of fault reactivation studies during seismic hazard assessment.
The aim of our study is to determine the design ground acceleration values at the whole territory of Debrecen and to accomplish the seismic risk map of Debrecen using synthetic seismograms. Synthetic seismograms are computed by the so called ``hybrid technique" along 11 different profiles crossing the city. The hybrid technique consists of the modal summation method, followed by finite difference modelling. 11 independent computations have been performed using the same seismic source but different profiles. The seismic source has been located in the so called “Mobile Zone”, which is a seismically active fault system in Érmellék region. The focal mechanism and the homogeneous and heterogeneous parts of the profiles are known from geophysical and geological data of the investigated area. As the results of the computations PGA grid maps of Debrecen for the 3 different components and the spectral acceleration (response spectra, SA) charts of the synthetic seismograms for the transversal components came into existence. The seismic risk map of the city has been completed from the SA charts created from the synthetic seismograms and from the grid map of the buildings in Debrecen with different number of floors by applying GIS tools.
Magnetotelluric method (MT) offers opportunity to detect crustal fluids along faults due to their high conductivity anomaly. Supposing that fluids deposited minerals in the conductive fractures (faults, dykes) decreasing the resistivity, the high seismicity in the area can be explained by the presence of these fluids. MT measurements were carried out in the period range 0.001–420 s crossing the Kalabsha fault (Aswan, Egypt) and Remiremont fault (Southern Vosges, France). In these work we detect geoelectrical resistivity anomalies of the Earth’s crust and link them to local seismic activity. Seismic events having magnitude (M<5) are found along fault zones in Kalabsha and Remiremont. The goals of our measurements are various. We would like to determine the precise location of the active faults, to study the connection of the Remiremont and Kalabsha seismicity to the MT resistivity structures, and to support the idea of the influence of the fluid-bearing conducting faults in the Remiremont and Kalabsha areas to the earthquake. These applications afford the unusual opportunity to study the percolation of water into the faults system and its effect on the seismicity, to reveal geological structures and the stress field covered by thin Quaternary formations. Data are analysed by 2D simultaneous inversion of both polarizations. The resulting models are compared with the local seismicity map. Our MT model reveals the conductive signature of the fault, as well as geological and tectonic stresses prevailing in active regions.