The paper presents the results of comparative analysis of the data regarding the multi-instrumental borehole monitoring data of changes in the geoenvironment stress-strain state and GPS data obtained in the time vicinity of the close strong Zhupanovsky earthquake. The purpose this study was to assess the feasibility of using GPS measurements on routine basis for effective monitoring of strong Kamchatka earthquakes in the area of Petropavlovsk-Kamchatsky. The Zhupanovsky earthquake active phase was chosen as a "test" time interval for comparing GPS and borehole monitoring data. This earthquake has been the strongest seismic event since 2000 in terms of the ratio of the earthquake focus length to the hypocentral distance. The time series borehole electromagnetic and geoacoustic data were compared with the dilatation series reflecting the relative changes in the area of a triangle composed of Kamchatka GPS observation network located in the Petropavlovsk geodynamic testing site. The analysis indicates a high degree of consistency in these time series. GPS data obtained during the active phase of the earthquake preparation is agree with the results of mathematical modeling expected values of volumetric strain on the daylight surface on the eve of the earthquake. A joint analysis of borehole and GPS data made it possible to specify the time limits for the stages of change in the stress-strain state of geoenvironment and to resolve ambiguity of interpretation of the electromagnetic and geoacoustic borehole measurement results at the final stage of preparing the Zhupanovsky earthquake.

Automated assessment of felt reports in accordance with the regionalized DYFI questionaries were implemented on mobile applications and messengers of the seismological service eqalert.ru. The new tool was tested on Sakhalin Island, which is considered as an active crustal region. We have developed a regression relationship between the peak ground acceleration and the community internet intensity for the studied area. The community internet intensity calculated from a large number of felt reports has a variance comparable to those given from a prediction equation of the physically based ground motion parameters. The given approach is considered as a state-of-art tool for the rapid collecting and assessment of macroseismic data. It may be used both with the weighted average method for generating high-quality shaking maps immediately following the felt earthquake. It is also a good way to involve the population in ground shaking measures.

The article presents data on the main stages of creating a network of multidisciplinary borehole measurements at the Petropavlovsk-Kamchatsky geodynamic testing area, its current configuration, the composition of the measurements, and technical support. Matters related to the choice of measuring boreholes are discussed, as well as organizational and technical solutions that ensured the creation and successful operation of the network for more than 20 years. Currently, the network includes five radiotelemetric points created on the basis of boreholes, where geoacoustic measurements, electromagnetic measurements with underground electric antennas, and other types of measurements are carried out. The network makes it possible to conduct promising fundamental scientific research in the study of endogenic processes associated with preparation of strong earthquakes. In the course of long-term measurements, it was found that the developed methods for monitoring changes in the stress-strain state of the geomedium, which are based on data from borehole geoacoustic measurements and measurements with underground electric antennas, can be successfully used in regional systems for medium- and short-term earthquake forecasting. Most of the technical tools used in the borehole measurement network are the authors’ own developments. In fact, the network is an experimental base for studying the processes of preparation of strong earthquakes in one of the most seismically active regions of the world, as well as the information base of a system for medium- and short-term forecasting of strong Kamchatka earthquakes, operating in the area of Petropavlovsk-Kamchatsky.

Созданная к настоящему времени на территории Петропавловск-Камчатского геодинамического полигона (ПГП) уникальная сеть непрерывных комплексных скважинных измерений (далее – «Сеть») дает возможность проведения перспективных фундаментальных научных исследований в области изучения эндогенных процессов, связанных с подготовкой сильных землетрясений. Кроме этого Сеть является информационной основой системы средне- и краткосрочного прогноза сильных камчатских землетрясений Института вулканологии и сейсмологии (ИВиС) ДВО РАН. Первый измерительный пункт Сети был создан в конце 1990-х годов на базе скважины Г-1, расположенной в черте г. Петропавловска-Камчатского. В этот период были организованы непрерывные скважинные геоакустические измерения на глубине 1035 м, дополненные в 2003 г. электромагнитными измерениями с подземной электрической антенной. Уже самые первые результаты показали, что геоакустические измерения, проводимые in situ в глубоких скважинах в сочетании с электромагнитными измерениями с подземными электрическими антеннами, позволяют получать научные результаты, недостижимые при измерениях на дневной поверхности. К таким результатам, в первую очередь, можно отнести открытие эффекта модулирующего воздействия слабых электромагнитных СНЧ полей на интенсивность геоакустической эмиссии горных пород [7, 20], а также установление и описание механизма указанного эффекта [3, 9, 21]. Указанные результаты легли в основу нового научного направления [6]. Следует также выделить разработку нового метода непрерывного мониторинга удельного сопротивления пород геосреды, базирующегося на использовании подземных электрических антенн [5]. В ходе многолетних измерений на ПГП было установлено, что разработанные методы мониторинга изменений напряженно-деформированного состояния (НДС) геосреды, основой которых являются данные скважинных геоакустических измерений и измерений с подземными электрическими антеннами, могут с успехом использоваться в региональных системах среднесрочного и краткосрочного прогноза землетрясений [6−9, 12, 18]. С января 2014 г. заключения о текущей сейсмической опасности для района г. Петропавловска-Камчатского, подготавливаемые лабораторией комплексного мониторинга сейсмоактивных сред ИВиС ДВО РАН на основе данных комплексных скважинных измерений, каждые две недели или чаще подаются в Камчатский филиал Российского экспертного совета по прогнозу землетрясений, оценке сейсмической опасности и риска, а также в Совет по прогнозу землетрясений и извержений вулканов ИВиС ДВО РАН.

Согласно данным последнего долгосрочного сейсмического прогноза [9] наиболее вероятным местом следующего сильнейшего (M ≥ 7.7) землетрясения для всей Курило-Камчатской дуги является протяженная сейсмическая брешь в районе Авачинского залива и южной части Камчатки. Неглубокое землетрясение с M ≥ 8.0 в районе Авачинского залива способно вызвать в г. Петропавловске-Камчатском и расположенных поблизости городов Елизово и Вилючинск сотрясения до девяти баллов и привести к гибели нескольких десятков тысяч человек. По этой причине достаточно надежный вероятностный краткосрочный прогноз такого землетрясения рассматривается авторами как наиболее актуальная и ответственная задача для настоящего момента.

We present the main results of the first stage of the study aimed at revealing the indicators of the changes in the stress-strain state (SSS) of the geoenvironment from the data of the long-term electromagnetic measurements with underground electric antenna in the Petropavlovsk-Kamchatskii geodynamic test site (PGS). Indicators are the most informative parameters. Their changes are associated with the preparation of nearby strong tectonic earthquakes. The physical basis of the method is the relationship between changes in the moisture content of a large volume of rock and tectonic stresses affecting the geoenvironment. We assume that such package of SSS indicators will be formed for the PGS on the basis of long-term complex borehole measurement data including measurements with underground electric antennas. We demonstrate the results of a comparison of the data on monitoring variations of the resistivity of rock to the results of other types of measurements carried out at the PGS.

The study focuses on improving the methodology and technology of detailed seismic zoning of the Sakhalin region and adjacent areas. A new regional GMPE (ground motion prediction equation) model derived from instrumental data of accelerometer and seismometer networks are considered, as well as imported new-generation advanced (NGA 2)models. The results of probabilistic seismic hazard analysis (PSHA) for Yuzhno-Sakhalinsk has made it possible to compare the hazard curves of physical parameters produced by different attenuation models. The advantages and disadvantages of the regional GMPE model are discussed based on this comparison. Practical recommendations are given.

In this work we have presented results of numerical simulation of streaming potential and electrokinetic current near the measuring well G-1 during the preparation of a strong earthquake. The problems of evolution of volumetric strain (on the first spatial scale), the change in the fluid filtration rate and evolution of the electrokinetic current (on the second spatial scale) near the measuring well related to the heterogeneity of the shear modulus are solved successively for the specific seismic event. It has been shown that change in the electrokinetic current near the G-1 correlates with the change in the geoacoustic emission parameters recorded in this well at the depth of 1 km.

The results of comparing the data of two methods of geophysical monitoring of the stress-strain state of a borehole of the geoenvironment in the zone of Petropavlovsk-Kamchatsky geodynamic testing site to the data on the focal mechanisms of earthquakes that occurred in this zone on the same time interval are presented.

We present the results of the long-term study which make it possible to assess the possibilities of two methods used at the Petropavlovsk-Kamchatskii geodynamic site (Russia) for continuous monitoring of the stress–strain state of geoenvironment. The methods are based on the borehole geoacoustic measurements and electromagnetic measurements with underground electric antennas. Combined with hydrogeochemical and hydrogeodynamic borehole measurements, these methods allow monitoring the changes in the parameters of geological environment and identifying the stages in the changes of its stress–strain state. As the examples, we present the results of the measurements in the time vicinities of the strongest seismic events that occurred during the period of joint borehole geoacoustic and electromagnetic measurements at the Petropavlovsk-Kamchatskii geodynamic site. We also analyze the data obtained in the time vicinities of the Tohoku mega-earthquake (March 11, 2011, Japan, Mw 9.1) and a close strong Zhupanovskoe earthquake (January 30, 2016, Mw 7.2) that occurred at the epicentral distances R = 107 km from Petropavlovsk-Kamchatskii. It is shown that the discussed methods are promising for medium- and short-term forecasting of the earthquakes.

Приводятся результаты сопоставления данных двух методов скважинного геофизического мониторинга напряжённо-деформированного состояния геосреды в зоне Петропавловск-Камчатского геодинамического полигона с данными по механизмам очагов землетрясений, произошедших в этой зоне на том же временном интервале.

The first regional attenuation relationship of peak ground accelerations is developed for Sakhalin Island based on data from a strong motion network and local network of seismometers. The applicability limits and standard error of the relationship are determined. The developed relationship is recommended for use in seismic hazard assessments for Sakhalin Island and the adjacent shelf, including updating of general seismic zoning maps. The ground motion prediction equation models calculated for other Earth regions suitable for Sakhalin are selected.

An earthquake with the moment magnitude M (w) = 5.8 occurred in the middle part of the Sakhalin Island, Russian Federation, on 14 August 2016, at 11:17 a.m. UTC. The earthquake source was located west of the Central Sakhalin Fault Zone, which is considered to mark the boundary between the Okhotsk and Eurasian (Amurian) plates. Moment tensor solution of the mainshock as well as the configuration of aftershock cloud suggests that the earthquake was caused by slip on a SW-dipping reverse fault. For the first time for Sakhalin, we have got the felt reports unified in accordance with DYFI. We also analyzed observed PGA values and, based on them, produced shaking maps.

A. Yu. OZEROV*, G. A. KARPOV*, V. A. DROZNIN*, V. N. DVIGALO*, Yu. V. DEMYANCHUK*, V. V. IVANOV*, A. B. BELOUSOV*’, P. P. FIRSTOV**, V. A. GAVRILOV*” , V. V. YASHCHUK” *’, and A. M. OKRUGINA* Institute of Volcanology, Far East Division, Russian Academy of Sciences, PetropavlovskKamchatskiy, 683006 Russia Institute of Volcanic Geology and Geochemistry, Far East Division, Russian Academy of Sciences, Petropavlovsk-Kamchatskiy, 683006 Russia Kamchatka Center for Monitoring Seismic and Volcanic Activity, Petropavlovsk-Kamchats­ kiy, 683006 Russia "** Experimental Seismological Team, Institute of Volcanology, Far East Division, Russian Academy of Sciences, Petropavlovsk-Kamchatskiy, 683006 Russia

The problems and procedures for obtaining high quality results of multidisciplinary geophysical monitoring at the stage of preliminary data processing are considered. The case study of solving different technical problems during the long-term multidisciplinary borehole geophysical observations at the Petropavlovsk- Kamchatsky geodynamic research area is described. The algorithms for preliminary data processing and flawed data discard combining automated approaches and expert screening developed by the authors are presented. Suppression of quasi-regular disturbances is especially important in the studies of interrelations between geoacoustic, electromagnetic, and meteorological processes and seismicity because of the clear diurnal periodicity in all these processes that significantly complicates the signal extraction from the noise. The key technical, organizational, and methodical measures aimed at improving the data should be provided at the project planning stage of the measurement system. The optimal selection and reasoned application of special procedures for data preprocessing can crucially affect the research results.

The mechanism is suggested to account for the modulating effect of weak audio-frequency (a few hundred Hz) electromagnetic fields on the geoacoustic emission intensity in the case when liquid phase (aqueous solution) in the pore-fracture space of the noise zone controlled by the geophone is the incompressible Newtonian fluid with constant viscosity and permittivity beyond the slipping plane of the electrical double layer.

Experience in introduction of an automatic system of earthquake source parameter calculation based on an existing seismic network is described. Open source software products for automatic seismic data processing are reviewed. Methods for real-time waveform stream processing are discussed in detail. Parameters of some subroutines of the system are described. Information flows and data life cycle in the developed automatic system are outlined. Earthquake location errors in the system are analyzed. The detection capability of seismic networks is evaluated.

The results of synchronous geoacoustic and electromagnetic measurements at three boreholes located in the Petropavlovsk-Kamchatsky geodynamic survey area with considerably different electromagnetic environments are studied. It is shown that reliable detection of geoacoustic emission responses to natural electromagnetic radiation in the range of 0.01–1.0 kHz is possible if geophones are placed in sufficiently deep boreholes. The results demonstrate the fundamental possibilty of using natural super-low-frequency electromagnetic radiation to monitoring of stress–strain states of the geological environment.

We propose a physical mechanism explaining the mechanism of modulation of the geoacoustic emission intensity by an external electromagnetic field in the audio-frequency range, which was previously revealed as a result of borehole measurements at the Petropavlovsk-Kamchatskii geodynamic testing area. It was established that electric double layers (EDL) at the interface between solid and liquid phases in a fluidsaturated geological medium play a key role in the mechanism proposed.