Ring-Shaped Seismicity Structures in Southern California: Possible Preparation for Large Earthquake in the Los Angeles Basin

Some characteristics of seismicity in Southern California are studied. It is found that ring-shaped seismicity structures with threshold magnitudes M_th of 4.1, 4.1, and 3.8 formed prior to three large (M _w > 7.0) earthquakes in 1992, 1999, and 2010, respectively. The sizes of these structures are several times smaller than for intracontinental strike-slip events with similar magnitudes. Two ring-shaped structures are identified in areas east of the city of Los Angeles, where relatively large earthquakes have not occurred for at least 150 years. The magnitudes of large events which can occur in the areas of these structures are estimated on the basis of the previously obtained correlation dependence of ring sizes on magnitudes of the strike-slip earthquakes. Large events with magnitudes of M _w = 6.9 ± 0.2 and M _w = 8.6 ± 0.2 can occur in the area to the east of the city of Los Angeles and in the rupture zone of the 1857 great Fort Tejon earthquake, respectively. We believe that ring-structure formation, similarly to the other regions, is connected with deep-seated fluid migration.     

Vegetation as a factor in the system of natural environment preservation of Prebaikalia

A central role in the formation of the natural environment of Prebaikalia is played by vegetation having the environment-forming and environment-protective functions. Nowadays, it is experiencing ever increasing anthropogenic impacts which lead to disturbances in its structure and decrease its ecological potential. This creates certain challenges of a local and regional character, because the main territory of the region is within the zone of atmospheric influence and within the western portion of the central ecological zone of the Baikal natural territory focus on preserving the ecosystem of Lake Baikal as the UNESCO World Natural Heritage site. Therefore, the main direction of nature conservation activity aimed at improving the quality of the region’s natural environment remains focused on the preservation and recovery and of its primary vegetation. Some measures are suggested concerning ecologically oriented nature management in Prebaikalia. We have defined the goals for the scientific accompaniment of the measures for the preservation of vegetation as an important factor of the environmental quality. The paper demonstrates the effectiveness of integrated study into the entire florocenotic diversity of modern vegetation, its evolutionary-genetic basis and the ecological and dynamical potentials of plant communities for the purposes of forecasting the ecologically oriented development of the region’s natural environment. The recommendations are formulated in accordance with the State Ecological Program for the period until 2030. The map entitled “Protection of vegetation in Prebaikalia (recommendations for optimization of the ecological policy)” has been developed, which provides information on territories with a different environmental quality having regard to the ecological potential. The legend includes the following parts of the map: special preservation of primary vegetation (full and partial), recovery of disturbed vegetation (active and passive recovery of primary forests), and economic rational (ecologically oriented) use of vegetation.     

Flowage Lakes in the World: Analysis of Quantitative Characteristics and Their Effect on the Character of Flow Variations of Lake-Containing Rivers

Water Resources - A joint data repository on flowage lakes of the world and long-term flow variations in the rivers they regulate has been formed. The specific features of the flowage lake...     

Stellar-wind envelope around the massive supernova progenitor XRF/GRB 060218/SN 2006aj

The spectra of the supernova SN 2006aj identified with the X-ray flash (XRF) and gammaray burst XRF/GRB 060218/SN 2006aj taken with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences are found to exhibit features, which can be interpreted as hydrogen lines. Such features indicate the existence of a stellar-wind envelope around the massive star—the progenitor of the gamma-ray burst. The results of our modeling of two early spectra taken with the 6-m telescope 2.55 and 3.55 days after the explosion of the type-Ic supernova SN 2006aj (z=0.0331) are reported. The spectra are modeled in the Sobolev approximation using SYNOW code [1, 2]. The spectra of the optical afterglow of the X-ray flash XRF/GRB 060218 are found to exhibit spectral features, which can be interpreted as: (1) the P Cyg-profile of the Hα line for the velocity of 33000 km/s—a broad and small deformation of the continuum in the wavelength interval 5600–6600Å for the first epoch (2.55 days) and (2) a part of the P Cyg-profile of the Hα line in absorption blueshifted by 24000 km/s—a broad spectral feature with a minimum at 6100Å (rest wavelength) for the second epoch (3.55 days). Given earlier observations made with the 6-m telescope and the spectra taken with other telescopes (ESO Lick, ESO VLT and NOT) prior to February 23, 2006, it can be concluded that we are observing the evolution of optical spectra of the type Ic massive supernova SN2006aj during its transition from the short phase with the “shock breakout” into the external layers of the stellar-wind envelope to the spectra of the phase of rising supernova luminosity, which corresponds to radiative heating. We are the first to observe the signs of hydrogen in the spectra of a gamma-ray afterglow.     

Characteristic Features of the Colors of Shower Meteors and Sporadic Meteors from Observations with the Mini-MegaTORTORA System

Results of BV R observations of meteors in the Perseid, Taurid, Orionid, Geminid, and Lyrid showers, as well as sporadic meteors, carried out with the Mini-MegaTORTORA system are presented. Two-color diagrams for the brightness maxima are constructed. It is shown that meteors in the Perseid, Taurid, and Geminid showers form clusters in the two-color diagrams. Variations in color with a temporal resolution of 0.1 s are considered for some meteors.

     

A geothermal method for detecting gas hydrates in the bottom sediments of water basins

We formulate the fundamentals of the geothermal method for determining the hydrate saturation of bottom sediments. According to laboratory experiments (A.A. Trofimuk Institute of Petroleum Geology and Geophysics, A.V. Nikolaev Institute of Inorganic Chemistry), detecting gas hydrates in bottom sediments requires measurement of thermal conductivity at least twice at one bottom site, using a cylindrical probe with different heater power values. Changing the latter permits controlling gas hydrate stability and instability. A low-power probe does not destroy gas hydrates and permits measuring the true thermal conductivity of the sediments. Increasing heater power destroys gas hydrates near the probe and drastically increases effective thermal conductivity. Comparison between true and effective thermal conductivity clearly shows the presence of gas hydrates in the sample or their absence from it. A technique was proposed for the quantitative interpretation of changes in the temperature field of a cylindrical probe. It permits quite a precise determination of the mass of gas hydrate that decomposed in the layer surrounding the probe over a certain period. Also, it permits a rough estimation of the gas hydrate content of the sediments. Thermal conductivity can be measured in the field with submersible multichannel thermoprobes, which are commonly used for studying the heat flow through the bottom of water basins. Now it is important to perform field experiments, so that we gain the necessary experience with the geothermal method.     

Geobotanical forecasting in the nature management ecological optimization in Baikalian Siberia

An analysis is made of the geobotanical forecasting technique. Mapping is known to be recognized as the most powerful method of forecasting-geobotanical investigations. A close interrelation between geobotanical forecasting and vegetation mapping is demonstrated. To improve objectivity of the findings used cartographic models of modern and predicted vegetation which most fully represent the entire structuralcenotic diversity of plant communities in Prebaikalia, the central region of Baikalian Siberia. The predictive constructions are based on analyzing modern vegetation which always includes structural features of its future that manifest themselves in primary and stable derivative communities. We developed the legend and compiled the map (sc 1:200 000) of the region’s modern vegetation. The state of the natural environment of the Lena- Angara interfluve is assessed having regard to the various functions of plant communities in geosystems. The 1:200 000 map of probability-forecasted (within 200 years) vegetation is presented for Lena-Angara interfluve. It is shown that complete recovery of the primary structure will not occur within 200 years. It is found that it is necessary to carry out predictive-cartographic investigations for the whole of Baikalian Siberia as vegetation of this region is characterized by a decreased activity of recovery processes occurring under the influence of anthropogenic factors. The reason has to do with the harsh natural conditions where it is not worthwhile to pursue extensive nature management, such as is universally the case to date, leading to undesirable economic consequences, because the degree of disturbance to vegetation in a number of areas of Prebaikalia has now reached as critical level. It is concluded that a further policy of nature management on this territory must be built upon the new principles to be approved by government documents.