Travel-time Curves Research Articles

Integrating seismic refraction and electrical approaches in determining geophysical properties of near-surface cavities in Calabar-Ikom highway, Odukpani, Cross River State, Nigeria

Integrated seismic refraction tomography (SRT) and electrical resistivity tomography (ERT) were used to study near-surface cavities with the aim of determining their geophysical properties. Five seismic refraction profiles around the study area were carried out using a 24-channel seismograph (ES-3000) while four ERT and ERT profiles were also conducted with IGIS resistivity meter and PLOTREFA software respectively. The data was processed using the RES2DINV software. Travel-time curves and velocity models were generated from the processed SRT data for each survey line, and 2-D inverted apparent resistivity models along the same lines were also generated for the purpose of comparison respectively. The results as obtained from the profiles showed SRT 1 (with a modelled velocity of 1,216 m/s in layer two at a depth of approximately 11 m - 20 m beneath the subsurface and an estimated cavity diameter of 11 m) and ERT 1 (with an apparent resistivity of approximately 826 Ωm and a depth of approximately 12.5 m – 16 m) indicates that the near-surface cavity outcrop links with a close-by mountainous structure in the EW direction. Profiles SRT 2 (with an approximately modeled velocity layer of 980 m/s in layer two at an approximate depth of 3.5 m – 7.0 m) and SRT 3 (with a modeled velocity layer of approx. 1,000 m/s in layer two at an approximate depth of 4.0 m – 7.0 m and 3.0 m – 9.0 m); ERT 2 (with an apparent resistivity of approximately 80 Ωm); and ERT 3 (with apparent resistivities of 116 Ωm and 182 Ωm at depths of approximately 3.5 m to 6.4 m and 4.0 m to 15.8 m) indicates that the surface cavity outcrop extends underneath the road network (Odukpani Central Section of Calabar-Ikom Highway) with a width of approximately 12 m. Profiles SRT 4 and SRT 5 (with an average velocity layer of 1,000 m/s in layer two at an approximate depth of 6.0 m – 13.2 m), and ERT 4 (with apparent resistivity ranging between 121 Ωm and 172 Ωm) at a depth of approximately 9.5 m to 20.0 m reveal that the near-surface cavity extends up to about 11 m across the highway and about 120 m away from the edge of the road. The above result will serve as reliable technical information to Transport and Building Construction Engineers on the presence of cavities along road networks and settlement areas in Odukpani Local Government Area. The recommendation is also made for the use of other geophysical techniques like Ground Penetration Radar (GPR) in conjunction with SRT and ERT to get higher-resolution imagery of the study area.

Monitoring seismicity triggered by geothermal site shutdown with a surface DAS array at Brady Hot Springs

SUMMARY Seismicity induced by fluid injection including wastewater injection, hydrofracking and enhanced geothermal system (EGS) site production draws public attention. Dense arrays have been deployed to improve monitoring capability. In 2016 March, the PoroTomo experiment deployed an 8.6-km-long fibre-optic cable for distributed acoustic sensing (DAS) in the geothermal field at Brady Hot Springs, Nevada, covering an area of 1.5 by 0.5 km. The goal was to assess an integrated technology for characterizing and monitoring temporal changes in the rock mechanical properties of an EGS reservoir in three dimensions. We applied a neural network designed for earthquake detection called ADE-Net2 to the DAS data set to detect seismic events in continuous records. We were able to detect a total of 90 earthquakes, which included 21 events that had not been reported by a previous template-matching study. Additionally, we were able to successfully detect almost all of the active source signals, with only seven events being missed. We used the STA/LTA (short-/long-term average) method to pick arrivals and a clustering method to remove outliers. We initially tried a standard event location algorithm, but the low signal-to-noise ratio resulted in significant picking uncertainty that is up to ∼0.5 s, leading to large location uncertainty. Therefore, we developed a new location method based on the similarity between the theoretical traveltime curve and picked moveout. A grid search scheme was adopted to find the optimal point at which the traveltime curve is most similar to the picked one. Most newly detected earthquakes locate southwest of the DAS array, where five earthquakes were reported by a local seismic network. The plant began shutting down at 19:15 UTC on the March 13, and most earthquakes occurred on the March 14, indicating a relationship between the seismicity and the pressure changes caused by the shutdown of the plant. The pressure changes at epicentres obtained from a simplified model range from 71 to 157 kPa, exceeding a typical earthquake trigger threshold of 10 kPa.

Determination of effective seismic wave velocities using time gradients obtained from response and CDP reflection hodographs

Seismic wave velocities, including effective velocities, play a critical role in the kinematic processing and interpretation of 2D and 3D seismic data. Along with other parameters of elastic waves, the geological efficiency of seismic exploration also depends on the level of knowledge of the velocity model of the medium, on the accuracy of information about velocities. The article briefly lists the main methods for determining the effective velocities according to the seismic wave field, developed and applied in the practice of seismic research. The methods used to determine the effective velocities of reflected waves can be divided into two groups: methods for determining the effective velocities based on automatic or visual tracking of the in-phase axes (i.e. hodographs) of reflected waves on seismic records, then their approximation by hyperbolas constitute the first group, and the second the group consists of methods based on the application of the analysis of the seismic wave field in controlled directions on the seismograms of a common depth point (CDP). Each proposed method for determining effective speeds has advantages and disadvantages. The article focuses on the industrial method, widely used at present, based on the analysis of the wave field in controlled directions, which do not provide sufficient information to solve the main problems of kinematic interpretation. The main disadvantages of the existing methods are indicated. The article describes a new method for determining the effective velocity, which is fundamentally different from the methods that are still used in the practice of seismic exploration. The fact is that in this method, seismic survey data of single and multiple profiling are not used separately, as it was in the methods used in seismic survey practice so far, but together. Formulas have been derived for determining the effective velocity based on the time gradients of the travel time curves of the CSP and CDP of reflected waves, which makes it possible to determine the speeds even from incomplete travel time curves. A technique for determining the effective speed has been developed and a sequence of procedures has been determined for solving the problem. The results of research are given on a specific example by solving the direct and inverse problems for the Sazhdag area between the Kura and Gabyrra rivers. The influence of errors in the values of the parameters included in the formula for calculating the effective speed on the final results is studied. At the end of the article, the main advantages of the proposed method are indicated.

TIMCPOT: Tcl/Tk Interface for Measuring Crustal Phase-Onset Time

Abstract In recent years, the seismological community has seen an amazing increase in the amount of seismic arrival time picks with the help of artificial intelligence. But, the accuracy of this data remains a challenge to seismologists. In comparison with automatic picks, manual picks have sufficient reliability and accuracy because manual picks are often used not only as a benchmark to evaluate automatic picking algorithms, but also as training samples to train artificial intelligence models. However, measurement through manual labor is a laborious and time-consuming task. To alleviate the manual labor involved in measuring phase arrival time, we developed a graphical interface named Tcl/Tk Interface for Measuring Crustal Phase-Onset Time (TIMCPOT). The TIMCPOT is mainly equipped with two modules: one is designed for measuring seismic arrival time, and the other is for relocating hypocenter. TIMCPOT simplifies user interaction with seismic data, thus reducing most manual labor. TIMCPOT provides several graphical workflows to carry out detection, identification, revision, and comparison operations on measurement work. The measurement procedure can be operated either manually or by autopicker. For the sake of allowing the user to interact easily with seismic data, TIMCPOT is designed to be executed in a semiautomatic model during several necessary procedures such as visually inspecting results and manually modifying picks. By applying a near real-time displaying technique, TIMCPOT can create a travel time curve figure and comparison chart for manual picks in a timely fashion, which provides a rapid way to estimate data quality. The measurement efficiency and travel time data quality have been significantly improved using this graphical interface. An explicit demonstration was shown to validate the powerful performance mentioned earlier. The primary advantage of TIMCPOT is that it reduces manual labor while retaining valuable manual experience on measuring phase picks. Of course, TIMCPOT has several limitations. However, most limitations will be improved in future development.

Prediction of the probabilistic water leak location in underground pipelines using Monte Carlo simulation

Abstract The water loss rates in Brazil are still very concerning and cause huge financial, social, and environmental damages. Although great advances have been made in acoustic leak detection methods, some of them are intrusive or at least demand convenient access points to the pipe's surface. Furthermore, some methods are expensive and require a highly experienced and qualified operator. Thus, the goal of this paper is to establish a benchmark using a simplistic analytical model for the ground surface analysis for leaks location, simplifying the search process carried out in water networks, and requiring minimal system interference. For leak location prediction, the proposed method considered two seismic wave paths – the compressional body waves and the Rayleigh superficial waves. The traveltime curves of the compressional waves are calculated as a function of the surface wave's experimental information. Monte Carlo Simulations were carried out to test each model's precision considering uncertainties related to the input parameters of the problem. At last, through a parametric study, the two seismic events were combined to obtain better accuracy in predicting the leakage epicenter location. In the results, the maximum absolute error found was 15 cm, and the minimum improvement obtained with the parametric study was 27.4%.

АНАЛИТИЧЕСКИЕ РЕШЕНИЯ ЗАДАЧ КОМПЕНСАЦИИ НЕОДНОРОДНОСТИ ВЕРХНЕЙ ЧАСТИ РАЗРЕЗА В СЕЙСМОРАЗВЕДКЕ МОВ

The solution of the problem of compensation of the near-surface heterogeneity (NSH) is an obligatory component of the digital processing technology of CDP data. The main result in the theory of solving this problem was determined by the equation of the normal traveltime curve of the common mid point with an additive component describing static corrections at the points of shotpoint and geophone. The substantiation of methods for compensation of heterogeneity based on the structure of high-speed model of the NSH is carried out in the present paper. Three variants of the NSH model corresponding to the zone of low velocities, heterogeneity of underlying bedrock deposits and variable relief of daytime surface are considered. The research subject is analytical methods for solving the problem of field continuation aimed at eliminating the influence of NSH on the kinematic parameters of wave field: method of static corrections and parametric method. Applications of methods are determined by the ratio of near-surface section velocities and underlying deposits. The requirements to the methodology of field observations and digital data processing ensuring the uniqueness of problem solution are considered for the compensation problem of heterogeneity of low-velocity zone.

TRAVEL TIME CURVES FOR YUCCA TEST SITE (NEVADA TEST SITE) – SEISMIC ARRAYS «OZHEREL’E» (GEOPHYSICAL OBSERVATORY «BOROVOYE»)

This paper presents the travel times of P waves for 8 Yucca Flat (Nevada Test Site NTS) explosions from 1979 to 1984, with magnitudes mb = 4.9–5.9. Travel times were obtained by revising seismograms from the archives Sadovsky Institute of Geosphere Dynamics for the subsystem “Ozherel’e” (Necklace) of peripheral points Zerenda, Vostochniy, Chkalovo of the large-base seismic array system (SAS) of the geophysical observatory Borovoye. This system has been operating since 1979 on the territory of Kazakhstan. By the example of registration of underground nuclear explosions at the Yucca site of the Nevada Test Site (NTS), local travel time curves and linear trends in the P wave travel time in the range of epicentral distances 89.3110°–90.3701° are investigated. We estimate of the velocities of effective P waves for the Yucca-“Ozherel’e” and peripheral points.

Automatic Time Picking for Weak Seismic Phase in the Strong Noise and Interference Environment: An Hybrid Method Based on Array Similarity.

The extraction of travel-time curve of seismic phase is very important for the subsequent inference of the structural properties of underground media in seismology. In recent years, with the increase in the amount of data, manual processing is facing significant challenges, and automatic signal processing has gradually become the mainstream. According to the similarity of array signals and considering the elimination of outliers, we propose an improved multi-channel cross-correlation method using the L1 norm measure to obtain preliminary results, which builds on a new controllable measurement mode. Then, the post-correction step is carried out in combination with the signal gain property of beamforming technique. Based on these two methods, this paper proposes a new scheme of automatic arrival time picking. We apply the scheme to actual data to verify the effects of the two methods step by step. The entire scheme achieves fine results: direct water waves, seismic waves refracted by the crust and seismic waves reflected by the upper mantle are automatically detected. In addition, compared with the two traditional methods, the scheme proposed in this paper has a better overall effect and a reasonable computation cost.

Geotechnical Characterization of the Subsurface Using Seismic and Electrical Resistivity Techniques in Mikinduri Meru County, Kenya

Abstract Geotechnical study of the Mikinduri area was conducted with the aim to establish the causes of landslides and ground subsidence during the heavy rainfall. Sounding curves, travel time curves, 2D geoelectric sections, and 2D seismic models revealed 3-5 lithologic units to a depth of 30-250m. The study established thick loose alluvium deposits mixed with clay to a depth of 0.3-15m on an impermeable sub-basement as the possible major trigger of the landslides witnessed during rainy seasons. The thick alluvium deposits are due to erosion. They have been transferred by the location of the Mikinduri area, which lies in the lower regions of the Nyambene domes. Geologically, the domes were formed during Mount Kenya volcanic series and parasitic activities between the early Miocene and late Pleistocene eras. Resistivity modeling revealed deep geologic structures, including possible intrusions extending from 50m deep and faulted regions to a depth of 60-150m in the central and northeast area of study. The faulted area is highly saturated, as revealed by the low resistivity values. The delineated top black cotton soils and alluvium deposit are 40-50% clay and have poor foundation bearing capabilities. In contrast, compacted gravel, silt, and compact basaltic rock basement have good foundation capabilities. Keywords: Geotechnical, characterization, subsurface, seismic, electrical resistivity, foundation, geoelectric layer, Mikinduri Meru, Kenya.

Sensitivity analysis to near-surface velocity errors of the Kirchhoff single-stack redatuming of multi-coverage seismic data

We present a study of a Kirchhoff-type redatuming approach for irregular multi-coverage land seismic data to remove the disturbing influence of rugged topography and a considerable near-surface velocity inhomogeneity, like a thick weathering layer, on the subsurface reflections. The redatuming method is physically more justified than the commonly used field-static correction methods that provide - in the indicated situation - non-physical temporal adjustments (field statics) by shifting traces in time, which lead to sub-optimal imaging and inversion of the reflections. The redatuming procedure studied here is different: It transforms the multi-coverage seismic reflection data on the irregular measurement surface to a regular measurement configuration on a pre-specified datum, below the inhomogeneous velocity overburden. This is done by stacking/summing the input traces with certain operators or traveltime curves which are calculated by ray tracing. In this way, incoherent subsurface reflections in the input data become coherent and thus recognizable in the output data. To have this happen, the redatuming operation requires a good approximation of the overburden velocity model and a reasonable one of the sub-burden homogeneous velocity model (below the datum). Then the multi-coverage output data on the new flat datum can be imaged and inverted much better than with standard data processing, i.e., with field-static correction. This work is dedicated to explaining the single-stack Kirchhoff-type redatuming approach kinematically using a synthetic model and data based on a real geological situation. However, our main aim is to study the sensitivity of this redatuming method to errors of the overburden velocity model, which is determined from multi-coverage seismic data using first arrivals traveltime tomography commonly used in the oil industry. We apply the redatuming process to a multi-coverage synthetic seismic dataset generated from the models that represent the real geological situation with irregular measurement surfaces and inhomogeneous overburden or near-surface velocity. To assess accuracy, the redatumed data was migrated in depth-domain and the results showed the correct positioning of the reflectors. The results revealed that this redatuming method produces reliable and accurate redatumed data even using approximate velocity models, which can be useful for prestack time and depth imaging.

Evaluation of Geotechnical Parameters and Attributes of Amassoma Soil in Bayelsa State, South-south, Nigeria, Using Seismic Refraction Analysis as an Indicator for Its Engineering Strength Determination

In this paper, we have carried out analysis of seismic refraction data obtained from two locations around Amassoma and its environs in Bayelsa State, South-South, Central Niger Delta, Nigeria. The core objective of the study was to evaluate the elastic parameters and attributes of the soil and its geotechnical conditions in order to determine its soil strength to carry load . These geophysical parameters and attributes include the p-wave and s-wave velocities, Vp /Vs ratio, dynamic Poisson ratio σ, rigidity modulus μ, bulk incompressibility K, Young’s modulus E, lamda-rho (lame’s) attribute λρ, K/μ ratio, and E/μ ratio. The layer velocities were obtained as the inverse of the slope of the travel time versus geophone distance curves plotted with the available refraction data, while the layer thicknesses were obtained from the intercepts of the plots. The p-wave and s-wave velocities were used as inputs in various mathematical relations to obtain the elastic moduli and their ratios. The results obtained depict a two-layer model, with the mean p-wave velocities of the layers generally found to lie in the 218m/s - 392m/s range and mean s-wave velocities in the 128m/s -231m/s range. The Vp/Vs ratio (the lithology discriminator) has values lying between 1.699 and 1.7 and the dynamic Poisson ratio has values between 0.235 and 0.240 . The moduli have most of their values above 3.0 x 107 N/m2 and their ratios are clearly more than unity. Overall, these results show that the topsoil and underlying sediments in the study area which are composed mainly of clay and sandy clay can be described as well consolidated and competent geomaterials that can support foundation structures and loads placed on them. In the final analysis, all the results obtained were found to be in agreement with the values reported in the literature for the Niger Delta and across the globe. The seismic refraction method has therefore been shown in this study as an effective technique for assessing the geotechnical strength of the soil.

PAHUTE MESA TRAVEL TIMES AT KURIL–KAMCHATKA SEISMIC STATIONS

This research fulfills additional information about the lithosphere below Southeastern Asia and the northern Pacific. The area is interesting for researchers because of the Kuril–Kamchatka subducted lithosphere. The availability to study an underground structure is complicated, because of Pacific Ocean. The significance of this research concerns epicentral distances ~54°–70° or ~6000–7000 km. During the Cold War of the 20th century and the classification of information between the largest nuclear states the Soviet Union (USSR) and the United States of America (USA), data on the registration of nuclear explosions were not published, however, underground nuclear explosions (UNE) were recorded. Thanks to an employee of the laboratory 5-s of the Institute of Physics of the Earth named after O.Yu. Schmidt of the USSR Academy of Sciences Kh.D. Rubinstein is kept at the Institute for the Dynamics of Geospheres of the Russian Academy of Sciences named after Academician M.A. Sadovsky (IDG RAS). Only after 1985 reports from some seismic stations of the former USSR began to be published in the operational reports of the United Geophysical Survey of the Russian Academy of Sciences (GS RAS). As it has not been yet published anywhere, we collect them and obtain the travel times were by revising seismograms from the archives IDG RAS and GS RAS for five Kuril–Kamchatka seismic stations (Bering, Esso, Severo-Kurilsk, Kurilsk). The 48 Unites States UNE at Pahute Mesa (at Nevada Test Site) from 1968 to 1990 are used for travel time curve building. We measure P waves travel times (tp) on historical seismograms for the ray travel path between Pahute Mesa tests and Kuril–Kamchatka stations. The body-waves magnitudes (mb) vary from 5.3 to 6.5. We obtain arrivals for: 1 UNE at Bering station, 7 UNE at Esso station, 45 UNE at Petropavlovsk, 18 UNE at Severo-Kurilsk and 12 at Kurilsk. We build a travel time function using linear regression algorithm as tp=k·Δ°+b, where Δ° is the epicentral distance, k and b are arbitrary constants. We show that travel time deviations, associated with nonlinearity of the Earth. We estimate the effective velocities of P waves for the Pahute Mesa – Kuril–Kamchatka travel path as coefficient k in the linear equation. Effective velocity is equal to 7.5 km/s.

Instantaneous speed as a tool for defining accessibility in the road network of Ocaña, Colombia

The application of the concept of instantaneous speed to the movement of vehicles on a city’s road network made it possible to establish average operating speeds. With the help of software based on geographic information systems, it was possible to determine the minimum travel times required by vehicles to move between two points on the network. Through the above analysis of speeds and travel times, applied to the road network of the municipality Ocaña, Colombia, it was possible to establish the time required by various types of vehicles to travel between the different points of the road network, allowing to define the level of accessibility to move between different areas of the city. The analysis required the updating, characterization, georeferencing and determination of the instantaneous speeds for each trip in the different arcs of the network and the subsequent determination of the average travel time curves in the network. The urban area of the city is covered with an average travel time of 15 minutes and the operating speeds are between 5 km/h and 31 km/h, with variations depending on the type of vehicle (bus, taxi, motorcycle).

Travel Time Curves of Seismic Waves from Underground Explosions on Amchitka Island

Travel Time Curves of Seismic Waves from Underground Explosions on Amchitka Island

Comparing the performance of stacking-based methods for microearthquake location: a case study from the Burträsk fault, northern Sweden

SUMMARY Traditional earthquake location relying on first arrival picking is challenging for microseismic events with low signal-to-noise ratio. Over the past years, alternative procedures have been explored based on the idea of migrating the energy of an earthquake back into its source position by stacking along theoretical traveltime curves. To avoid destructive interference of signals with opposite polarity, it is common to transform the input signals into positive time-series. Stacking-based source location has been successfully applied at various scales, but existing studies differ considerably in the choice of characteristic function, the amount of pre-processing and the phases used in the analysis. We use a data set of 62 natural microearthquakes recorded on a 2-D seismic array of 145 vertical geophones across the glacially triggered Burträsk fault to compare the performance of five commonly used characteristic functions: the noise filtered seismograms and the semblance, the envelope, the short-term average/long-term average ratio and the kurtosis gradient of the seismograms. We obtain the best results for a combined P- and S-wave location using a polarity-sensitive characteristic function, that is the filtered seismograms or the semblance. In contrast, the absolute functions often fail to align the signals properly, yielding biased location estimates. Moreover, we observe that the success of the procedure is very sensitive to noise suppression and signal shaping prior to stacking. Our study demonstrates the usefulness of including lower quality S-wave data to improve the location estimates. Furthermore, our results illustrate the benefits of retaining the phase information for location accuracy and noise suppression. To ensure optimal location results, we recommend carefully pre-processing the data and test different characteristic functions for each new data set. Despite the suboptimal array geometry, we obtain good locations for most events within ∼30–40 km of the survey and the locations are consistent with an image of the fault trace from an earlier reflection seismic survey.

STUDY OF THE NEOTECTONIC STRUCTURE OF THE BRATSK WATER RESERVOIR BED

Production of natural gas and crude oil in the eastern regions of Russia was accelerated in the past decade, and both the upstream and midstream segments of the oil and gas industry continue to grow at a fast pace. Innovative solutions are needed for engineering and construction surveys aimed to justify options for choosing routes and methods for laying underwater pipeline sections across large rivers and water reservoirs. In our region, positive experience has been gained by employing modern technologies to optimize routing and reduce the costs of detailed surveys. In the project of the Kovykta – Sayansk – Angarsk – Irkutsk gas pipeline construction, an optimal route across the Bratsk water reservoir was chosen based on the results of several stages of investigation, including continuous seismic profiling and side-scan sonar scanning of the reservoir bed. At the first stage, the mosaic maps of side-scan sonograms and a 3D digital model of the reservoir bed bathymetry were constructed and used to develop and propose three options for the gas pipeline design and its route across the reservoir area. At the second stage, detailed underwater and onshore geophysical and drilling operations were carried out along the proposed routes. Based on the transverse profiles, a decision was taken to lay the pipeline section across the reservoir area in a trench along the northern route, which was justified as an economically and technologically optimal solution. In the winter period when the water reservoir surface was covered with thick ice, the northern route was investigated in detail by drilling and seismic survey operations using vertical seismometer cable assemblies and the inverse travel time curve technique. With reference to the velocity law, the travel time sections were processed and converted into depth profiles. A petrophysical model of bottom sediments was constructed, and a scheme was developed to ensure proper processing and interpreting of seismic and acoustic data. Four structural-material complexes were identified: modern silts; underwater eluvial and alluvial deposits; disintegrated and low-strength bedrocks of the Upper Lena Formation; and unaltered bedrock sandstones and siltstones. The continuous seismic profiles and the data from the vertical seismometer cable assemblies were interpreted, and a neotectonic map of bottom sediments was constructed. By analyzing the fault kinematics, it was revealed that normal faults and reverse faults with low-amplitude horizontal shear dominated in the study area; the mapped faults were mainly rootless structures; and displacements along the faults occurred due to a laminar flow of the Cambrian salt layers. An increase in tectonic activity from north to south was explained by the correspondingly degraded strength properties of the bedrocks. Modern neotectonic structures detected from the survey results gave evidence that that the hydrostatic pressure increased after the reservoir had been filled with water, and the phenomenon of reservoir-related seismicity was observed in the study area. Based on the comprehensive geological and geophysical survey data, the geological and engineering conditions of the proposed construction sites were clarified, and the most appropriate route and design of the gas pipeline section across the reservoir area was approved. This study provided the pipeline designers with the qualitative and quantitative information on the phenomena and factors complicating the conditions for laying the gas pipeline in the study area.

Determination of underground voids in the surface of the earth section

One of the negative factors that affects the performance of various works on the Earth’s surface are voids in the surface part of the earth’s section. They are formed for various reasons. In most cases, these reasons are associated with irresponsible human activities. This can be excavation through adits, groundwater abstraction, or a breakthrough of underground utilities. In some cases, a disturbance in the ecological balance leads to the fact that the rivers go underground. Large areas of earth and sandstone are washed away. There is a danger of a collapse of the territory. Heavy rains are exacerbating this situation. These formed voids must be identified in a timely manner. Therefore, in places of their possible formation, it is necessary to constantly monitor the territory. The paper proposes an easy-to-use method for detecting these voids by imaging using refracted waves. For this, the collected data was processed using two different techniques. In the first case, the correlation of the first peaks on all seismograms is performed. This made it possible to obtain a depth-velocity section. The second method consists in reducing the travel time curves of the first refracted wave and obtaining a summarized seismic section. In this case, voids are distinguished by the loss of correlation of the axes of in-phase of the reduced time. This allows you to identify even small voids that form under the soil. With the deterioration of the ecological state, more and more voids are formed. To eliminate them, it is necessary to take prompt measures.

NUMERICAL ALGORITHM FOR ESTIMATING THE VELOCITY CHARACTERISTICS OF THE MEDIUM IN THE VOLCANIC ZONE

This paper proposes an approach to the calculation and assessment of local velocities of seismic P-waves in a volcanic zone based on the use of the grid method. The numerical algorithm is tested on the experimentally obtained arrival times of P-waves from a vibration source of the SV-10/100 type for the mount Karabetova mud volcano. Registration was carried out by 35 receivers during sounding from 5 points of the vibrator in the frequency range of 10-60 Hz. It follows from the results of numerical modeling that the selection of nonlinearity in the travel time curve of seismic P-waves in the area of a volcanic edifice is possible with the number of grid nodes from 60x60 or more, which corresponds to 31.2 m along the X-axis and 48.1 m along the Y-axis. The obtained results of the distribution of local velocities are consistent with the previously obtained geological structure of the study area and indicate the presence of higher velocities in the area of the anticlinal fold passing through the volcano zone.

Solving the Brokett problem based on robust stabilization

The paper proposes a method for solving the Brockett problem based on the synthesis of robust modal control for systems with non-stationary parameters, which does not require complex adaptation algorithms that involve the introduction of a variable regulator matrix. A transition to the task of synthesizing the regulator is shown, using a certain optimality criterion with limitations, which provides similar values to those of the regulator coefficients. A practical numerical example of setting and solving this problem is presented, which confirms the effectiveness of the proposed method. To illustrate the results obtained, a root travel time curve was constructed for two systems: robust and non-robust.

Travel time curves and isochron maps from the Borovoye digital archive for the Nevada and Semipalatinsk Nuclear Test Sites

The paper presents generalized parameters of digital seismograms of the Borovoye Geophysical Observatory (BRVK). The seismograms were obtained after reformatting the archive of the Institute of Geosphere Dynamics (IDG RAS). For this research, we consider looking at the most representative entries – underground nuclear explosions (UNE). The particular interest is the analysis of the P-wave travel times at the regional distances Δ≈5–7° and Δ≈89–91°. These deep paths cross the boundaries of the Earth crust, mantle and outer core. There are UNE digital records at the Semipalatinsk Test Site (ΔSTS ≈5.56–6.27°) and at the Nevada Test Site (ΔNTS≈89.77–90.15°). For this reason, we use UNEs from STS and NTS from 1967 to 1992. UNEs locations and magnitudes are taken from published open sources. The results for P-wave travel time curves on the BRVK – NTS and BRVK – STS paths and the isochron maps are obtained. The linear functions for travel time curves are defined by the linear regression. The resulting seismic travel time curves for P waves are compared to AK135. Because global one-dimensional seismic reference models are non-unique solution to regional seismic data, in terms of physical structure. The results help identify seismic wave velocities at the source-receiver travel paths and character of geologic media. Such physical models could significantly facilitate physical interpretation of seismic structures in the area of Central Asia (e.g. Tien Shan) and global.