SEISMICITY of ARMENIA and ADJACENT TERRITORIES in 2015

We have analyzed the seismicity of Armenia and adjacent territories in 2015. The highest level of seismic activity was recorded in the northern part of the Republic, in the focal zone of the Spitak earthquake 1988. The tangible earthquakes of the territory of Armenia are described.

Physical and geological model of the Shalkar earthquake focal zone

The Shalkar earthquake focal zone is characterized by the strongest earthquakes of all that occurred in the southeast of the East – European Platform. A physical and geological model has been developed, on the basis of which the parameters of the Shalkar earthquake focal zone have been determined, which can be used to assess the intensity of shaking from possible earthquakes. The relationship between earthquakes in the southeast of the East European platform and deformations in the mantle is shown.

Creepex as a parameter of seismo-geodynamic studies based on geo-information systems

The GIS-EEDB (the Expert Earthquake Database) and GIS-ENDDB (the Earth’s Natural Disasters DataBase) geoinformation systems implement methods for spatial-temporal analysis of both classical and new characteristics of the seismogeodynamic process. One of the new characteristics is a normalized creepex parameter that can be used in the statistical approach to studying of seismicity to assess a relative contribution of “soft” (creep) and “hard” (explosion) movements to the overall process of focal radiation. In this paper, the following modifications of the creepex parameter are proposed and compared: 1) Cr0 Cr0_world and CrN CrN world as the result of reducing the parameters Cr0 and CrN of each event to the world average values of the creepex, obtained from the polynomial dependence of Cri_world (i = 0, N) on MS_world where Cri_world are calculated based on the world average estimates of Ms_world and mb_world at uniform intervals of the seismic moment (NEIC catalog), 2) Cr_bji as the result of reducing CrN of each event to CrN_bji i.e. to the average for the studied in this work BJI catalog creepex values obtained from the polygonal trend CrN (MS) of all the catalog events. The advantage of using the creepex parameter, reduced to the trend of averaging the magnitudes of the catalog in question, is revealed, since the smallest linear dependence of the creepex on the magnitude is achieved (in comparison with the classical and normalized creepex) and the symmetry in the maximum amplitude of the deviation of the parameter relative to zero is preserved. Examples of the application of the compared parameters in specific seismic-geodynamic studies of aftershock processes of the Molucca and Simushir earthquakes also demonstrate the advantage of the parameter Cr_bji n the observed correspondence of the variations of the latter to the known physical processes in the focal zone of the Kashmir event, studied by the seismic-geodynamic methods of the GIS-EEDB geographical information system.

Recovery of the parameters of a focal zone by the data of earthquakes

We present an approach for solving the inverse kinematic problem of seismic with internal sources, based on the method of multidimensional data approximation on irregular grids. The times of arrival of elastic waves to the seismic stations are considered as known. The hodographs from earthquake to the stations are approximated for further determining the velocities of longitudinal and transverse waves using the eikonal equation. The ratio of these velocities determines the Poisson’s ratio, and the other elastic parameters of the medium can be found in units of the density. The results of implementation of the approach, based on the real data, are presented.

Experimental Demonstration of a Stacked Hybrid Optoacoustic-Piezoelectric Transducer for Localized Heating and Enhanced Cavitation

Laser-generated focused ultrasound (LGFU) is an emerging modality for cavitation-based therapy. However, focal pressure amplitudes by LGFU alone to achieve pulsed cavitation are often lacking as a treatment depth increases. This requires a higher pressure from a transmitter surface and more laser energies that even approach to a damage threshold of transmitter. To mitigate the requirement for LGFU-induced cavitation, we propose LGFU configurations with a locally heated focal zone using an additional high-intensity focused ultrasound (HIFU) transmitter. After confirming heat-induced cavitation enhancement using two separate transmitters, we then developed a stacked hybrid optoacoustic-piezoelectric transmitter, which is a unique configuration made by coating an optoacoustic layer directly onto a piezoelectric substrate. This shared curvature design has great practical advantage without requiring the complex alignment of two focal zones. Moreover, this enabled the amplification of cavitation bubble density by 18.5-fold compared to the LGFU operation alone. Finally, the feasibility of tissue fragmentation was confirmed through a tissue-mimicking gel, using the combination of LGFU and HIFU (not via a stacked structure). We expect that the stacked transmitter can be effectively used for stronger and faster tissue fragmentation than the LGFU transmitter alone.

Development of microfluidic acoustic flow cytometry based on simultaneous ultrasound backscatter and photoacoustics for micron and sub-micron size objects

I developed a flow cytometer based on simultaneous detection of ultra-high frequency ultrasound backscatter and photoacoustic waves from individual micron scale objects, such as, cells, microparticles, and microbubbles owing in a microuidic channel. Individual micron scale objects are ow focused through a focal zone, where both ultrasound and laser pulses focus, in a microchannel of a polydimethylsiloxane (PDMS) based microuidic device. At the focal zone, the objects are simultaneously insonified by ultrasound (center frequency 375 MHz) and irradiated by nanosecond laser (532 nm wavelength) pulses. The interactions generate ultrasound backscatter and photoacoustic signals from the individual objects, which are strongly dependent on their size, morphology, and biomechanical properties, such as the Young's modulus, and optical absorption properties. These parameters can be extracted by analyzing the unique spectral features of the detected signals. At frequencies less than 100 MHz, the signals from the micron scale objects do not contain these unique spectral signatures, thus higher frequencies are required. Cell analysis is the main application of interest using the acoustic flow cytometer. Combining ultrasound backscatter and photoacoustics results in sufficient information about a single cell that can be used for single cell analysis and for diagnostics applications. However, the usage of this system is not limited to biological cells. This system can also be used for analyzing individual microbubbles, which are used as ultrasound contrast agents. During my research, a novel microuidic technique is developed to generate microbubbles of desired sizes by shrinking microbubbles from O(100) _m by applying a suitable vacuum pressure. These shrunken bubbles of different sizes can be used as samples to validate the acoustic ow system for microbubble analysis.

Development of microfluidic acoustic flow cytometry based on simultaneous ultrasound backscatter and photoacoustics for micron and sub-micron size objects

I developed a flow cytometer based on simultaneous detection of ultra-high frequency ultrasound backscatter and photoacoustic waves from individual micron scale objects, such as, cells, microparticles, and microbubbles owing in a microuidic channel. Individual micron scale objects are ow focused through a focal zone, where both ultrasound and laser pulses focus, in a microchannel of a polydimethylsiloxane (PDMS) based microuidic device. At the focal zone, the objects are simultaneously insonified by ultrasound (center frequency 375 MHz) and irradiated by nanosecond laser (532 nm wavelength) pulses. The interactions generate ultrasound backscatter and photoacoustic signals from the individual objects, which are strongly dependent on their size, morphology, and biomechanical properties, such as the Young's modulus, and optical absorption properties. These parameters can be extracted by analyzing the unique spectral features of the detected signals. At frequencies less than 100 MHz, the signals from the micron scale objects do not contain these unique spectral signatures, thus higher frequencies are required. Cell analysis is the main application of interest using the acoustic flow cytometer. Combining ultrasound backscatter and photoacoustics results in sufficient information about a single cell that can be used for single cell analysis and for diagnostics applications. However, the usage of this system is not limited to biological cells. This system can also be used for analyzing individual microbubbles, which are used as ultrasound contrast agents. During my research, a novel microuidic technique is developed to generate microbubbles of desired sizes by shrinking microbubbles from O(100) _m by applying a suitable vacuum pressure. These shrunken bubbles of different sizes can be used as samples to validate the acoustic ow system for microbubble analysis.

Laboratory investigation of coupled electrical interaction of fracturing rock with gases

In the coupled electric interaction of rock fractures and gas invasion, that is, when gases interact with newly created crack surfaces, the unpaired electrons within the rock crystal defects are thermally stimulated, released into the crack due to the temperature rise at the crack tip via plastic work, and attached to ambient gas molecules to electrify them in a negative state. Using a working hypothesis that this mechanism is the source mechanism of seismo-electromagnetic phenomena, we conducted laboratory experiments in which rocks were fractured with pressurized N2, CO2, CH4, and hot water vapour. Fractures were induced by a flat-ended indenter equipped with a flow channel, which was loaded against blocks of quartz diorite, gabbro, basalt, and granite. Fracture-induced negatively electrified gas currents at ~ 25 °C and ~ 160 °C were successfully measured for ~ ≥ 100 μs after full development of the crack. The peak electric currents were as high as 0.05–3 μA, depending on the rock species and interaction area of fractured rock and gas and to a lesser extent on the gas species and temperature. The peak current from fracturing granite, which showed higher γ-ray activity, was at least 10 times higher than that from fracturing gabbro, quartz diorite, and basalt. The results supported the validity of the present working hypothesis, that coupled interaction of fracturing rock with deep Earth gases during quasi-static rupture of rocks in the focal zone of a fault might play an important role in the generation of pre- and co-seismic electromagnetic phenomena.