Rockfall-Dammed Lakes in the Baikal Region: Evidence from the Past and Prospects for the Future

The mountain province of East Siberia, which includes the Baikal Rift system, is a zone of high tectonic and seismic hazard. Earthquakes and coseismic faulting are dangerous not only by themselves but also as far as they initiate rock collapse and downslope movement of unconsolidated deposits, which may block river valleys and produce rockfall-dammed lakes. Within some rifts of the rift system, evidence of past dammed lakes was discovered that arose instantly, in a geological sense, and flooded large areas of forest. In mountains around some rift basins, small living dammed lakes were encountered, as well as traces of catastrophic debris flows that may have accompanied breaching of earlier collapse-produced dams. Analysis of geomorphological setting in the region, especially in the Muya Rift Basin, revealed conditions favourable to hazardous origination of rockfall-dammed lakes. A large dammed lake may come into existence due to the collapse of bedrock over the narrow antecedent valley of Vitim in the Muya Rift. Preliminary estimates based upon data on the Vitim River discharge showed that the lake might form in as short as 27 days, though the rapidity of its formation, and hence the degree of the risk, can vary as a function of the highly variable amount of summer discharge of the river. Rockfall-dammed lakes may also originate in the floors of Chara and Tunka Rift Basins. Due to their rapid formation, lakes will bring about extensive flooding and cause danger to the taiga, railways and constructions in this populated developing area, and will cause degradation of the permafrost.     

Intersecting dilated convex polyhedra method for modeling complex particles in discrete element method

This paper describes a new method for representing concave polyhedral particles in a discrete element method as unions of convex dilated polyhedra. This method offers an efficient way to simulate systems with a large number of (generally concave) polyhedral particles. The method also allows spheres, capsules, and dilated triangles to be combined with polyhedra using the same approach. The computational efficiency of the method is tested in two different simulation setups using different efficiency metrics for seven particle types: spheres, clusters of three spheres, clusters of four spheres, tetrahedra, cubes, unions of two octahedra (concave), and a model of a computer tomography scan of a lunar simulant GRC‐3 particle. It is shown that the computational efficiency of the simulations degrades much slower than the increase in complexity of the particles in the system. The efficiency of the method is based on the time coherence of the system, and an efficient and robust distance computation method between polyhedra as particles never intersect for dilated particles. © 2014 The Authors. International Journal for Numerical and Analytical Methods in Geomechanics published by John Wiley & Sons Ltd.     

Focal Depths of Earthquakes in the Crimea–Black Sea Region

The problem of determining focal depths of earthquakes in the Crimea–Black Sea region is considered. Based on the results of interannual studies, it is found that the focal depths of Crimean earthquakes are mainly crustal, with maximum values of up to 60 km. Some recent publications, however, have described deep-focus earthquakes with depths of up to 300 km which were “revealed” in the Crimean region. In this respect, there arose the need to study such a large difference in estimated focal depths. Convincing examples show that the sensational “revelation” of deep earthquakes in Crimea was caused by incorrect processing of the experimental data, in particular, due to (1) a sharp distortion in the recorded arrival times of body waves, (2) exclusion of data from stations nearest to a source, (3) unreasonable arbitrary selection of data from seismic stations, and (4) dropping of data from the worldwide seismological network, including those on deep seismic phases. Thus, the conclusions about the presence of deep mantle earthquakes in Crimea are erroneous. We have redetermined the parameters of hypocenters and verified that the focal depths of earthquakes in the Crimea–Black Sea region are no more than 60 km. Based on these data, we analyze the features of the spatial distribution of focal depths to show that earthquake sources are grouped along conduits that dip southeastward, from the continental part of Crimea toward the Black Sea Basin, in the case of grouping of sources in the Alushta–Yalta and Sevastopol areas. The seismic focal layer of the Kerch–Anapa area dips northeastward, from the Black Sea beneath the North Caucasus.