Initiation of acoustic emission in fluid-saturated sandstone samples

A rock behavior experiment with uniaxial compression revealed the effect of acoustic activity in loaded fluid-saturated Berea sandstone samples in response to an electric current. It is established that it is substantially intensified in periods of the current impact and decreases after its cut-off. The current impact also results in a growth of radial deformation indicating an increase in the sample volume. The effect of acoustic activation increases in response to increased heat emitted by the electric current during its flow through the sample, which allows the discovered effect to be explained by initiation of its destruction due to thermal expansion of the fluid in rock interstices and fissures.     

Geochemistry of isotopes (δ<Superscript>13</Superscript>C, δ<Superscript>18</Superscript>O) and formation conditions of lower-middle permian rocks in the Soyana River region (Arkhangel’sk district)

The results of study of the isotopic-lithological compositions of carbonate and terrigenous-carbonate rocks in the Soyana River section (northern East European Platform, Arkhangel’sk district) are presented. The results make it possible to identify 10 main lithotypes and show a wide variation range of δ¹³C (from −2.2 to +3.6‰, PDB) and δ¹⁸O (from 22.5 to 30.5‰, SMOW). These lithological features and isotopic compositions suggest that the rocks were formed in a shallow-marine setting characterized by rapidly changing sedimentation conditions in various facies (and/or paleoecological) zones: inlets, lagoons, supralittoral, littoral, and shoals. Periods of aridization and humidization are recorded. The results also indicate numerous synsedimentary short-term hiatuses and stages of increased continental runoff—episodic pulsatory input of clastic material with the continental paleoflows.     

The behavior of seasonal variations in induced seismicity in the Koyna–Warna region,western India

Based on the earthquake catalog data for the Koyna–Warna region of induced seismicity in western India, the seasonal variations in seismic activity associated with annual fluctuations in the reservoir water level are analyzed over the time span of the entire history of seismological observations in this region. The regularities in the time changes in the structure of seasonal variations are revealed. The seasonal seismic activity is minimal in May–June when the reservoir level is lowest. During the remaining part of the year, the activity has three peaks: the fall peak in September, winter peak in November–December, and spring peak in February–March. The first mentioned peak, which falls in the phase of the water level reaching its maximal seasonal value is considered as the immediate response of the fluid saturated medium to the additional loading under the weight of reservoir water. The two subsequent maxima concur with the decline phase in the reservoir level and are interpreted as the delayed response associated with the changes in the properties of the medium due to water diffusion. It is shown that the intensities of the immediate and delayed responses to the seasonal water level variations both vary with time as does their ratio. The probable factors affecting the variations in the intensity of the seasonal components of the reservoir-induced seismicity are discussed.     

Initiation of Rock Fracture by Fluids of Different Viscosities

Izvestiya, Physics of the Solid Earth - Abstract—The acoustic emission (AE) patterns observed in laboratory conditions at the initiation of fracture in rock samples by fluids of different...     

Laboratory Modeling of Aftershock Sequences: Stress Dependences of the Omori and Gutenberg–Richter Parameters

Izvestiya, Physics of the Solid Earth - Laboratory experiments on studying the aftershock regime are carried out on sandstone specimens at different levels of axial loading and uniform compression...     

Cyclic analysis and carbon and oxygen isotopes in low-middle permian deposits of the Iva-Gora section (Soyana River,Arkhangelsk Oblast)

On the basis of a cyclic analysis of the Iva-gora section (Soyana River, Arkhangelsk Oblast) three groups of different scale cyclites (sedimentation, sedimentation-eluvial, and eluvial) were distinguished. Each group is described in detail and characterized from the isotopic and geochemical point. As a result of data summary, conclusions on the conditions of the formation of the studied deposits and reasons for the cyclic character of the section are given.