The article is to complete the description of the special mapping method which theoretical basis and principles were published in [Seminsky, 2014]. With reference to data on the Ulirba site located in Priolkhonie (Western Pribaikalie), the content of special mapping is reviewed in detail. The method is based on paragenetical analysis of abundant jointing which specific feature is the lack of any visible displacement indicators. There are three stages in the special mapping method (Fig. 3) as follows:

Stage I: Preparation and analysis of previously published data on the regional fault structure (Fig. 1, А–Г), establishment of a networks of stations to conduct structural geological monitoring and mass measurements of joints, re­cord of rock data (Fig. 2, А), general state of the fault network (Fig. 1, Д–З), fracture density (Fig. 2, Б) and, if any, structures of the above-jointing level (Fig. 1, Е, З; Fig. 2, А).

Stage II is aimed at processing of field data and includes activities in four groups (II.1–II.4) as follows: Group II.1: construction of circle diagrams, specification of characteristics of joint systems and their typical scatters (Fig. 4, А), identification of simple (generally tipple) paragenesises, and determination of dynamic settings of their formation (translocal rank) (Table 1), evaluation of densities and complexity of the joint networks, analysis of their spacial patterns within the site under mapping, and identification of the most intensively destructed zones in the rock massif (Fig. 2, Б–В). Group II.2: comparison of jointing diagrams with reference ones showing joint poles (Fig. 4, Б–В; Е–З; Л–Н), and, in case of their satisfactory correlation, making a conclusion of potential formation of a specific joint pattern in the local zone of strike-slip, normal faulting or reverse faulting (Fig. 4,  Г–Д, И–К, О–П; Fig. 5; Fig. 7, Б), and determination of relative age relationships between such zones on the basis analysis of the scatter of joint systems, shearing angles and other relevant information. Group II.3: construction of a circle diagram for the specified mapping site with local fault poles (Fig. 8, Б), identification of conjugated systems and dynamic settings of their formation (Fig. 2), plotting the information onto the schematic map of the location under study, and marking the transregional fault zones (Fig. 7, В–К) with observation sites showing similar settings and paragenesises of local faults. Group II.4: comparison between diagrams of fault poles of local ranks with reference patterns selected according to the availability of conjugated pairs of fractures (Fig. 9, Б–Г); based on the above comparison, decision making on potential formation of a paragenesis of local faults in the strike-slip, normal and reserve/thrust fault zones (Fig. 9, Д–Ж), and delineation of boundaries of such zones in the schematic map by connecting the observation sites with similar solutions (Fig. 7, Л–Н).

Stage III is aimed at interpreting and includes comprehensive analyses of mapping results and priori information, construction of a final scheme of the fault zones showing their subordination by ranks (Fig. 7, О) and schemes of fault zones for various structure formation stages, showing types of faults and specific features of their internal patterns, i.e. definition of the peripheral sub-zone, sub-zones of fractures of the 2nd order and, if established, the sub-zone of the major fault (Fig. 7, Л–Н).

Prospects of the special mapping method can be highlighted upon its comparison with the conventional structural methods applied in studies of faults. On the one side, the method requires time-consuming mass mea­surements and special processing of 'dumb' joints; on the other side, it provides for analyses of abundant jointing data, ensures a high level of detail in mapping of patterns of fault zones, reveals rank subordination of faults and helps to determine other specific features of fractures and faults. Hence, a conventional study of sites with evident tectonics can be based on traditional structural methods, while the special mapping method is recommendable as an additional means of analyses providing information on specific elements of the fault patterns, including establishment of the internal zoning of faults, hierarchy of dynamic settings of faulting etc. In cases when direct observation of faults is limited as the study area is poorly outcropped, or in case of specialized studies such as drilling of wells, the special mapping method can be most useful when applied in its full scope.

With account of its specific features, this method is a promising tool for solution of theoretical problems related to studies of divisibility of the Earth's crust into zones and blocks and researches of regularities in development of fault zones in space and time. It can be useful for application-oriented surveys in geology, ore geology, engineering geology and hydrogeology that require detailed mapping of fault zones controlling many associated processes of key importance.

In previous studies, the northern hemisphere of the Earth is considered to be in compression while the southern one is in expansion. In this study, based on three different methods, we calculate average vertical variations of the two hemispheres from velocity field data under the ITRF2008 (International Terrestrial Reference Frame 2008) solution. Results show that the northern hemisphere is in expansion at the rate about 1 mm/yr, while the compression rate of the southern hemisphere is one order smaller than the expansion rate of the northern one. After the post glacial rebound effect is subtracted, results show that the expansion and compression rates of the northern and southern hemispheres are 0.46 mm/yr and –0.19 mm/yr, respectively. Transformation between the velocity fields under ITRF2008 and ITRF2000 can explain why different authors have different conclusions about the expan­sion/compression pattern of one hemisphere or the other. Anyway, the entire Earth is expanding at a rate about 0.2 mm/yr, and this estimation coincides with results of our previous studies. The mean variation rates of the radii at different latitudes have been calculated.

 

Results of the experimental long-term monitoring programme are presented. It is aimed at studying natural geophysical fields located above the gas deposit in the zone impacted by the active regional fault, and its objectives are to reveal how such fields are changing with time and to establish a relationship between the temporal changes and seismicity. According to the database it determines several typical indicators of variations in the geophysical fields, which take place only above the gas deposit. It is concluded that periods, when natural geophysical fields located above the gas deposit are unstable, are preceding the final phase of preparation of seismic events.

The inversion seismic tomography algorithm (ITS) was used to calculate 3D seismic anomalies models for velocities of P- and S-waves in the zone of the Sunda arc, Indonesia. In the area under study, strong earthquakes (M>4.8) are clustered in the zone of high P-wave velocities. Earthquake hypocenters are located in zones of both high and low velocity anomalies of S-waves. The giant Sumatra earthquake (December 26, 2004, Mw=9.0) ruptured the greatest fault length of any recorded earthquake, and the rupture started in the area wherein the sign of P-wave velo­city anomalies is abruptly changed. We calculated seismotectonic deformations (STD) from data on mechanisms of 2227 earthquakes recorded from 1977 to 2013, and our calculations show that the STD component, that controls vertical extension of rocks, is most stable through all the depth levels. In the marginal regions at the western and eastern sides of the Sunda arc, the crustal areas (depths from 0 to 35 km) are subject to deformations which sign is opposite to that of deformations in the central part. Besides, at depths from 70 to 150 km beneath the Sumatra earthquake epicentre area, the zone is subject to deformations which sign is opposite to that of deformations in the studied part of the Sunda arc. For earthquakes that may occur in the crust in the Sunda arc in the contact zone of the plates, maximum magnitudes depend on the direction of pressure imposed by the actively subducting plate, which is an additional criteria for determining the limit magnitude for the region under study.

 

A comparative study of major elements, trace elements, and isotopes in high- and moderate-Mg volcanic sequences of 16–14 and 14–13 Ma, respectively, has been performed in the Bereya volcanic center. In the former (small volume) sequence, contaminated by crustal material basalts and trachybasalts of K–Na series were followed by uncontaminated basanites and basalts of transitional (K–Na–K) compositions and afterwards by picrobasalts and ba­salts of K series. From pressure estimates using equation [Scarrow, Cox, 1995], high-Mg magma originated at the deep range of 115–150 km. In the latter (high-volume) sequence, basalts and basaltic andesites of transitional (Na–K–Na) compositions and basalts of Na series were overlain by basalts and trachybasalts of K–Na series. First, there was a strong melting of its shallow garnet-free part with coeval weak melting of more deep garnet-bearing portion, then only a deep garnet-bearing portion of the lithospheric mantle melted. It is suggested that the sequential formation of high- and moderate-Mg melts reflected the mid-Miocene thermal impact of the lithosphere by hot material from the Transbaikalian low-velocity domain, which had the potential temperature Tp as high as 1510 °С. This thermal impact triggered the rifting in the lithosphere of the Baikal Rift System.