In recent years the global trend in seismological observations consists in increasing the number of measuring points and equipping them with broadband and highly sensitive sensors. However, this approach leads to a significant rise in the cost of measurements. One possible solution to this problem is the use of much cheaper geophones or short-period seismometers with an extended frequency range as additional sensors. The article discusses the process of synthesizing a correction filter circuit based on a biquadratic transfer function and provides schemes for broadening the frequency characteristics of sensors, including circuits for correcting the characteristics of the SM-3KV seismometer and the GS-20DX geophone in instrument design. The developed algorithm makes it possible to broaden the frequency response of the SM-3KV seismometer to the low-frequency region up to 0.02 Hz (natural frequency of 0.5 Hz) and the GS-20DX geophone to 1 Hz (natural frequency of 10 Hz).

In this work, we study the reaction of an aquifer lying in the roof of an iron ore deposit located near the town of Gubkin, Belgorod region, during massive explosions. The considered reservoir of pore-fractured type is composed mainly of shales and quartzites, which are characterized by different physical, mechanical, and filtration parameters. A comprehensive analysis of the hydrogeological responses of the aquifer and seismic data to the passage of seismic waves from massive explosions reveals differences in the response of water-saturated reservoirs, characterized by a difference in the structure of the pore-fractured space.

A new method for estimating the self-noise of the measuring channel of a seismometer is proposed, taking into account the linear relationship between the signal and noise. The method extracts noise using records of two identical measuring channels on the example of the SM-3KV short-period seismometer with an operating frequency range of 0.5–40 Hz. The method was tested on model signals for channel noise with a normal distribution, as well as microseismic noise records recorded on a pedestal by seismometers with locked and free inertial masses. Work with the model signals demonstrated that the accuracy of the numerical result when assessing the level of isolated noise depends on the value of the cross-correlation of the initial seismograms. Consideration of this dependence when calculating the self-noise of real measuring channels yields a noise level similar to the standard method based on separation of the incoherent component of the initial signals. The noise values in the 0.5–40 Hz range with a locked mass of the seismometer are 2.1 ± 0.3 nm/s according to the standard method and 2.2 ± 0.4 nm/s according to the new methods. The obtained values do not contradict the manufacturer’s data of the SM-3KV seismometer, which state that the self-noise level does not exceed 2 nm/s in the operating frequency range.

Abstract—Deformation regimes of water-saturated reservoirs under dynamic impact are studied using groundwater-level monitoring by precision measurements. As a quasi-stationary factor responsible for background poroelastic groundwater-level fluctuations in the reservoir–well system, the Earth’s tides are considered. Hydrogeological responses to the passage of seismic waves from remote earthquakes and mass blasts produced during iron ore mining are used for estimating relative deformation of water-saturated reservoirs. The study objects are located both outside the zone of active manmade impact on geological environment (in the territory of Geophysical observatory “Mikhnevo” of the Institute of Geosphere Dynamics of the Russian Academy of Sciences) and in the technogenically disturbed conditions—in the industrial region near Gubkin, Belgorod region. Integrated processing of seismic, barometric, and hydrogeological data synchronously recorded by the instrumental-measuring systems installed in the observation wells and at the near-head sites is aimed at revealing common regularities in the responses of water-saturated reservoirs to a dynamic impact. The comparative analysis of the amplitudes of groundwater level fluctuations and pressure variations in the reservoir–well system is carried out with the allowance for ground motion velocities and reduced distances from the remote earthquakes and mass explosions. The response of water-saturated porous- and fractured-porous type reservoirs is different. Alongside with the coseismic hydrogeological effects, the analysis revealed a postseismic groundwater-level rise and increase in pressure indicating a local change in the poroperm properties of a water-saturated reservoir. The maximum values of seismic-wave ground velocities and pressure in the reservoir–well system at which deformation regimes change from a poroelastic to quasi reversible response are established.

The article presents the results of precision hydrogeological monitoring, carried out within the operating iron ore deposit near the city of Gubkin, Belgorod region. The organization of an autonomous instrumentation-measuring complex at the wellhead areas of observation wells is described in detail. The methods of processing the series of synchronous recording of seismic, hydrogeological, and barometric data are considered. The proposed scientific and methodological approach to analyzing the obtained experimental data is oriented towards the background parameters of water-saturated reservoirs of pore and fractured-porous types (including the coefficients of barometric efficiency and tidal sensitivity) and studying the response of the well–aquifer system to mass explosions.

The application of special sensor correction methods may allow the use of short-period seismometers with an extended frequency range in the absence of broadband sensors to solve a wide range of problems associated with recording low-frequency signals. The paper considers an instrumental correction circuit that uses integrating elements to broaden the frequency range of the SM-3KV seismometer to the low-frequency region. In laboratory conditions, the modified seismometer was calibrated and the device was tested on microseismic noise, explosion, and earthquake records. Our analysis of microseismic noise shows the possibility of using this device for recording and analyzing microseismic noise at frequencies above 0.07 Hz. Analysis of explosion and earthquake records demonstrated that the circuit can be used for seismic monitoring, taking into account the features of the frequency and phase responses of the modified seismometers.

To solve various engineering problems, it is often necessary to record signals in the 0.1–2000 Hz range. The lower limit of this range is beyond the operating band of geophones. This article considers extending of geophone frequency responses in two ways: multiplication of the transfer functions and introduction of negative resistance. The applicability limits of these methods are estimated. The upper limit of the velocity recorded by the geophone is determined by the gap in which the coil is shifted relative to the sensor frame. The lower limit depends on the total instrument noise of the measurement channel, the main contribution to which is the Brownian noise of the mechanical oscillatory system and the noise of the measuring circuit. A prototype was constructed using multiplication of the transfer functions. Laboratory measurements on a shaking table and microseismic noise recordings demonstrated that the modified geophone operates as a velocity sensor with an eigenfrequency of 2 Hz. This value depends on the microseismic conditions of where of the measurement system is placed. Recording seismicity with the modified geophone made it possible to record massive blasts in mines and quarries in the frequency range up to 2 Hz. Thus, the research demonstrates that the modified geophone can be used to monitor local and regional seismicity as a counterpart to short-period seismometers.

The amplitude-frequency characteristics of a water-saturated reservoir under pressure head and non-pressure conditions were estimated for 2017–2018. The measuring wells are located at the territory of the geophysical observatory “Mikhnevo” of IDG RAS. A comparative analysis of the average monthly amplitudes of volumetric strain and groundwater level was performed. Volumetric strain and water level were calculated for period range of 0.5–28 hours in the sliding window of 0.5 hour without overlapping and for periods of semidiurnal and diurnal tidal waves.

In this paper we use the data of precision monitoring of confined aquifer at the territory of the Mikhnevo geophysical observatory in 2017–2018. New approach for identifying tidal waves in noisy initial data was applied. Comparative analysis of the main types of tidal waves in underground water level and theoretical volumetric strain of water-saturated reservoir was carried out. Such technique can be used for detection the main direction of water-bearing cracks, which can change in dependence on filtration mode of reservoir.In this paper we use the data of precision monitoring of confined aquifer at the territory of the Mikhnevo geophysical observatory in 2017–2018. New approach for identifying tidal waves in noisy initial data was applied. Comparative analysis of the main types of tidal waves in underground water level and theoretical volumetric strain of water-saturated reservoir was carried out. Such technique can be used for detection the main direction of water-bearing cracks, which can change in dependence on filtration mode of reservoir.

This paper reviews the methods of correcting the frequency response of short-period seismometers and geophones, i.e., the multiplication of the transfer sensor functions by the transfer function of the secondorder correction filter and the provision of a considerable attenuation in the oscillating system (h = 5–10) followed by correcting the frequency response with the first-order filter. The correction device circuit developed by the authors for expanding the frequency range of the GS-20DX geophone has been described. The proposed method has been proved to be effective according to the laboratory tests of the geophone with the frequency response correction according to this circuit.

We consider the main factors that affect underground water flow including aquifer supply, collector state, and distant earthquakes seismic waves’ passage. In geodynamically stable conditions underground inflow change can significantly distort hydrogeological response to Earth tides, which leads to the incorrect estimation of phase shift between tidal harmonics of ground displacement and water level variations in a wellbore. Besides an original approach to phase shift estimation that allows us to get one value per day for the semidiurnal M 2 wave, we offer the empirical method of excluding periods of time that are strongly affected by high inflow. In spite of rather strong ground motion during earthquake waves’ passage, we did not observe corresponding phase shift change against the background on significant recurrent variations due to fluctuating inflow influence. Though inflow variations do not look like the only important parameter that must be taken into consideration while performing phase shift analysis, permeability estimation is not adequate without correction based on background alternations of aquifer parameters due to natural and anthropogenic reasons.

Presented are the results of laboratory experiments on studying the variation of fault shear stiffness during a seismic cycle. It is shown that the slip mode correlates well with the specific value of fault stiffness k(s1) at the loading stage. As the fault goes over to a metastable state, its stiffness changes abruptly from ks1 to 0. This change can be detected in active monitoring, which consists in analyzing the frequency response of an oscillatory "block-fault" system. A periodic pulsed action on the "block-fault" system allowed us to reliably detect a relative decrease by 30% of the resonance frequency of its response when the system goes over to the metastable state.

The article proves the application of short-period sensors with extended frequency response as a reasonable alternative to broadband seismometers. We assessed uncertainties between magnitudes determined by short-period and broadband sensor data for earthquakes with M > 6 recorded at the Mikhnevo geophysical observatory in 2014. Data analysis consisted of body wave magnitude and surface wave magnitude estimates by standard seismological methods. Magnitude errors corresponded to the magnitude uncertainties in seismological catalogs.

В первой части данной работы исследован отклик разновозрастных структур на лунно-солнечные приливы, которые могут рассматриваться в качестве зондирующего сигнала для мониторинга состояния флюидонасыщенных коллекторов. Для выделения приливов из гидрогеологических, барометрических и сейсмических рядов применен комплексный подход к обработке данных, полученных на полигонах Института динамики геосфер РАН, Института геофизики НАН Украины и станции KIEV сейсмической сети IRIS. Выполнен сравнительный анализ экспериментальных и теоретических значений суточных и полусуточных приливных компонент в смещении грунта. Вариации приливов в уровне подземных вод сопоставлены с приливными компонентами, прослеженными в смещении грунта разновозрастных структур Московского и Украинского массивов, входящих в состав Восточно-Европейской артезианской области. Различие в откликах на приливы в уровне подземных вод и смещении грунта, вероятно, свидетельствует о влиянии дополнительных факторов на состояние массива, связанных, в частности, с прохождением сейсмических волн от землетрясений и изменением гидрогеодинамической обстановки.

The first part of this work is dedicated to the response of different-age structures to lunisolar tides, which can be considered as a sounding signal for monitoring the state of fluid-saturated reservoirs. The complex approach to processing the data obtained at the testing sites of the Institute of Geosphere Dynamics of the Russian Academy of Sciences, Institute of Geophysics of the National Academy of Sciences of Ukraine, and KIEV station of the IRIS seismic network is applied for recognizing the tides against the hydrogeological, barometric, and seismic series. The comparative analysis of the experimental and theoretical values of the diurnal and semidiurnal tidal components in the time series of ground displacements is carried out. The tidal variations in the groundwater level are compared with the tidal components revealed in the ground displacement of the different-age structure of the Moscow Basin and Ukrainian Shield, which are parts of the East European artesian region. The differences in the tidal responses of the groundwater level and ground displacement probably suggest that the state of the massif is affected by certain additional factors associated, e.g., with the passage of earthquake-induced seismic waves and the changes in the hydrogeodynamic environment.

The authors calculate possible errors in characterization of low-magnitude seismicity sources using the Brune model and methods of identification of seismic event energy class and local magnitude. The adequacy of the model has been proved by comparing its results with the recordings of seismic vibrations in the North Ural Bauxite Mine. The errors due to the drastic distortion of the emission spectrum become significant at the distance of 1000 m from the emission source and grow as the distance increases. Cases of great deviations from the similarity law are analyzed based on the actual seismic monitoring in the North Ural Bauxite Mine, in mines in Poland, Finland and Canada, as well as in water basins. It is shown that phenomena due to physical difference of various size fracturing dynamics do not radically change a seismic source capacity. Other causes, due to instrumentation shortcomings or incorrect data interpretation, may result in overestimated seismic energy and scaling-up of low-magnitude seismic events.

The paper presents the results of processing the data on variations of groundwater level in an aquifer opened by a well in a depth interval of 76–115 m. The obtained series are compared with the volume deformation of the aquifer, calculated theoretically using the ETERNA 3.0 tidal analysis program. Two components are detected in the long-period area: the one coherent to the luni-solar tides and the one incoherent to them. It is established that the phase shift between the variations of volume deformation of the aquifer and the corresponding variations of water level in the well depends not only on the stressed-deformed state of the surrounding rock massif, but on the position of the piezometric surface of the aquifer as well. Some peculiarities of the effects of luni-solar tides on variations of groundwater level are considered. The amplitudes of groundwater level and volume deformation of the aquifer, as well as the phase shift between these parameters are estimated for the detected tidal waves. The value of the amplitude factor lies in the range of 0.04–0.058 cm/nanostrain.