Satellite geodetic monitoring of the Vladikavkaz active fault zone: First results

A geodetic network of Global Satellite Navigation System (GNSS) observation sites was organized in 2014–2015 for studying the contemporary crustal motions in the zone of the Vladikavkaz deep fault (Milyukov et al., 2014; 2015). The measurements were conducted and the first velocity estimates obtained testifying to the consistency of crustal motions in the Vladikavkaz fault zone and the Ossetian region overall in the ITRG2008 system. The first results show that the velocities and directions of horizontal motions do not change upon the transition of the fault zone. In correspondence with the northeastern orientation of the site displacement vectors and sublatitudinal trend of the disjunctive zone, the presence of left-lateral strike-slip displacements along the branches of an active fault should be expected. However, the signs pointing to the activation of motion in the fault zone are absent. Besides, even the manifestation of weak seismicity has not been observed within the high-magnitude seismogenic Vladikavkaz zone associated with this fault for more than 25 years. This suggests the passive present state of this structure, one of the largest disjunctive structures of the Northern Caucasus. In order to verify this conclusion and revealing the kinematic pattern of the displacements associated with the fault structure it is reasonable to continue the measurements.     

Catastrophic detachment and high-velocity long-runout flow of Kolka Glacier, Caucasus Mountains, Russia in 2002

In September 2002, a catastrophic geomorphic event occurred in the Caucasus Mountains, southern Russia, in which almost the entire mass of Kolka Glacier detached from its bed, accelerated to a very high velocity (max. 65–80 m/s), and traveled a total distance of 19 km downstream as a glacier-debris flow. Based on the interpretation of satellite imagery obtained only 8.5 h before the event occurred, the analysis of seismograms from nearby seismic stations, and subsequent detailed field observations and measurements, we suggest that this remarkable event was not a response to impulse loading from a rock avalanche in the mountainside above the glacier, or to glacier surging, but due entirely to the static and delayed catastrophic response of the Kolka glacier to ice and debris loading over a period of months prior to the September 20 detachment. We reconstruct the glacier-debris flow using field observations in conjunction with the interpretation of seismographs from nearby seismic stations and successfully simulate the behaviour (runout, velocity, and deposition) of the post-detachment glacier-debris flow using a three-dimensional analytical model. Our demonstration of a standing-start hypothesis in the 2002 Kolka Glacier detachment has substantial implications for glacier hazard assessment and risk management strategies in valleys downstream from unstable debris-covered glaciers in the mountain regions of the world.     

Specific features of the technique of airborne gravity surveys at high latitudes

Specific features of the technique of airborne gravity surveys in the Arctic are considered. The main requirements for aerogravimetric complexes used for such surveys and for reference GPS stations located at high latitudes are formulated, as well as the conditions necessary for converting an aircraft into an aircraft-laboratory. Specific features of the planning of measurements of aerogravimetric profiles in the Arctic are described. The need in the operations necessary for the rapid estimation of the results is substantiated. The obtained regional gravimetric map on a 1:200000 scale is presented as an example.     

Allowance for seismic impact on high-frequency measurements by the Autograv CG-5 gravimeter

The joint study of the long-term stationary gravity observations using the Autograv CG-5 gravimeter in the conditions of a geophysical observatory and the data from the UGRA seismic station is carried out. The mathematical model of the sensing element of the gravimeter is constructed. The analysis of the gravimetric and seismic data is carried out. The corrections reducing the random component of the error in the gravimeter’s measurements are obtained.