Allocation of active morphostructures of the Northern Ladoga using a complex of geological and geomorphological data

Based on the analysis and generalization of geological and geomorphological information, including new data obtained by the authors, we developed a scheme of activated Precambrian morphostructures of the Northern Ladoga area. When we compiled it, the severity of the ancient structures in the relief, the confinement of the epicenters of earthquakes, paleoseismic dislocations, helium and radon anomalies to them, as well as the results of the analysis of the movement of GPS points, computer and physical modeling on equivalent materials were taken into account.

Eocene paleoseismic dislocations of the Ak-Kaya Mountain (Belogorskiy district, Crimea)

The article considers features of boundary Cretaceous–Eocene deposits in Belogorskiy district of Central Crimea. Structures interpreted as paleoseismic dislocations are described, their age, features of composition, history of formation are specified, magnitude and intensity of paleoearthquake are estimated. Steeply dipping fractures in Cretaceous rocks are regular and associated with dip and strike of the main regional structures. Their formation was caused by a transverse stretching during the main uplift of the structures at the beginning of the Eocene coinciding with the main phase of folding in Northern Turkey.

Evaluation of GPR capabilities in the study of seismogenic faulting and deformation in the bottom sediments of Lake Upoloksha (northeast of the Fennoscandian shield)

The article describes the experience of using the GPR method to study the bottom sediments of Lake Upoloksha located in the Kola Peninsula, Russia. Such sediments are viewed as good archives of various Holocene geodynamic processes, including tectonic and paleoseismic events. This small lake is located in the zone of the active NW-striking lineament, which length is more than 20 km. A series of åsars (eskers) stretches along the lineament. In the previous studies, the bottom sediments of the lake were investigated by geological methods, including core sampling, lithological and micro-palaeontological analysis of sediments. The studies have revealed a horizon which features are indicative of catastrophic changes in the sedimentation conditions due to a single impact. Our study aimed at evaluating the level of informativeness of the GPR method for detecting disturbances in the bottom sediments and new paleoseismic dislocations. The study referred to the hypothesis of the distribution of seismic foci in the Kola Peninsula in the Holocene. A ground-penetrating radar OKO-2 and an antenna unit (150 MHz) were used to survey of Lake Upoloksha in detail. The positions of the main stratigraphic horizons of the bottom sediments were clarified, and their thicknesses were measured more precisely. The GPR measurement error in comparison to the drilling data did not exceed ±0.2 m, which corresponds to the resolution of the antenna used in the survey. The GPR data confirmed the existence of seismic dislocations identified by the geological methods and discovered new zones of displacement and deformation in the organogenic and mineral bottom sediments. The survey detected vertical displacements, which amplitudes vary from 1.3 to 1.7 m, and landslides caused by seismogravitational rock collapse. Based on the GPR data, a bathymetric map was constructed. It shows the positions of the two basins of Lake Upoloksha. The survey provided the basis for a model showing the isosurface of the top of the mineragenous sequence. In the central part of the mineral-base model, there is a series of individual stepwise blocks of the sublatitudinal strike, which result from seismic movements. The GPR survey of Lake Upoloksha demonstrates that the GPR method can be successfully applied to estimate the mineral and organogenic parts of the bottom sediments, study their lithostratigraphic features, and detect changes in the structure of the bottom sediments. Based on the GPR data, it becomes possible to map even the small-scale disturbances.

Parageneses of fractures in large fault zones of West Transbaikalia

Our study was focused on the parageneses of heterogeneous fractures in the large fault zones of West Transbaikalia,Russia. We reconstructed the latest deformation in the fault zones of Transbaikalia, within which paleoseismic dislocations are known and M 4.7 earthquakes take place. To obtain statistically justified solutions on the kinematic types of the largest faults ofWest Transbaikalia, we collected the required data and conducted the structural and paragenetic analysis of the fractures in the study area. In the Chikoi-Ingoda, Khilok, North Tugnui andNorth Zaganfault zones, we created a network of 54 observation points and measured more than 5500 details of local fractures and faults. Recorded were the observed slickensides, the displacements of markers, and other details of rock fracturing. Based on the analysis results, we calculated a ratio of heterochronous dynamic settings for formation of the observed fault group. It shows that NW-SE-trending extension and compression are dominant in the study region. The parageneses of E-NE-striking faults, i.e. regional faults longitudinal to the depressions ofWest Transbaikalia, are abundant in the studied fault zones and generally observed in heterochronous formations, including the Cenozoic sediments. This fact, along with the focal mechanisms of the recently recorded earthquakes, suggests that these faults are young. Besides, in the Tugnui basin and the area southeast of the Chikoy depression, the right-lateral strike-slip setting was reconstructed for E-NE-trending faults. Our study pioneers in the quantitative analysis of the fault parageneses ofWest Transbaikalia. Considering the development of the network of large faults in the study area, we reconstructed the main stages and the kinematic types of the second-order fractures that constitute the internal structure of the studied fault zones at each stage of their tectonic development.