An inversion of rayleigh waves dispersion curves as a tool to recognize the bedrock depth in Chorzów Stary, Poland

Identification of a bedrock beneath soft cover is one of the most important task in engineering geology. The location of boundary-overburden information may be used by investors, builders and municipal authorities to design an infrastructure or land-use plans. In such issues the application of appropriate geophysical methods is useful. However, in urban zones and areas characterized by subsurface soft layer the usage of certain methods (eg.: seismic refraction) is not advisable. The passive method of Refraction Microtremor (ReMi) can fulfill its tasks in the relatively difficult urban environment. The vertical S-wave velocity profiles were carried out as a result of inversion of Rayleigh wave dispersion curves obtained from ReMi method. The change of S-wave velocities allowed to distinguish shallow geological layers in the area of Chorzów Stary. Preliminary measurements allowed to identify the Carboniferous bedrock at a depth of 14 -18 m what has been confirmed by resistivity imaging. Furthermore, unconsolidated deposits are also recognized and the seismic results show a good correlation with the available geological information and resistivity imaging data

Target detection and classification using seismic signal processing in unattended ground sensor systems

This thesis studies the problem of target detection and classification in Unat-tended Ground Sensor (UGS) systems. One of the most challenging problems faced by target identification process is the design of a robust feature vector which is sta-ble and specific to a certain type of vehicle. UGS systems have been used to detect and classify a variety of vehicles. In these systems, acoustic and seismic signals are the most popularly used resources. This thesis studies recent development of target detection and classification techniques using seismic signals. Based on these studies, a new feature extraction algorithm. Spectral Statistics and Wavelet Coef-ficients Characterization (SSWCC), is proposed. This algorithm obtains a robust feature vector extracted from the spectrum, the power spectral density (BSD) and the wavelet coefficients of the signals. Shape statistics is used in both spectral and PSD analysis. These features not only describe the frequency distribution in the spectrum and PSD, but also shows the closeness of the magnitude of spectrum to the normal distribution. Furthermore, the wavelet coefficients are calculated to present the signal in the time-frequency domain. The energy and the distribution of the wavelet coefficients are used in feature extraction as well. After the features are obtained, principal component analysis (PGA) is used to reduce the dimension of the features and optimize the feature vector. Minimum-distance classifier and k-nearest neighbor (kNN) classifier are used to carry out the classification. Experimental results show that SSWCC provides a robust feature set for target identification. The overall performance level can reach as high as 90%

APPLICATION OF SEISMIC RADIAL ANISOTROPY FOR NEAR-SURFACE FRACTURES IDENTIFICATION

Fractures significantly control the groundwater flow and solute transport in geological settings of low-permeable rocks. Fractures also affect seismic wave propagation. For instance, they can create a directional dependence of seismic velocity with respect to their orientations, known as seismic anisotropy. Seismic radial anisotropy as used here is the difference between the velocity of a vertically polarized S-wave (SV) and one polarized horizontally (SH). In this thesis, seismic radial anisotropy was used to evaluate its usefulness for correlating with near-surface fractures. The seismic radial anisotropy models were obtained at two sites from dispersion analyses of the Rayleigh waves, with vertical polarization, and Love waves, with horizontal polarization, using the Multichannel Analysis of Surface Waves (MASW) method. The seismic radial anisotropies at these two sites in different geological settings (one metamorphic-igneous bedrock and the other sedimentary), shows a strong correlation of seismic radial anisotropy with near surface fractures, and hence, can be used to characterize near-surface fractures

Microseismic positioning of an isolated working face under complex geological conditions and its engineering application

In view of the inability to accurately locate vibrations in isolated workings under complex geological conditions, an adaptive rotational categorization method, a downhill comparison method based on time-frequency analysis (TFA-DC method), a variable-step acceleration search method, and a dual-phase seismic source location method (TD-DL method) are proposed. A set of integrated software with features of “visualization”, “interactive” and “one-click” was developed for microseismic data processing. Results show that compared with the improved STA/LTA method, the recognition accuracy of the island working face microseismic signal by the adaptive wheel classification method is increased by 4.8%. Compared with the improved STA/LTA method, the TFA-DC method has the advantage that it can simultaneously pick up the exact p wave and the peak S wave, and the failure ratio is 0. Compared with simulated annealing algorithm and genetic algorithm, stepwise accelerated search method has better results. The standard deviation of objective function value, location error and wave velocity error are all 0. Method improves the positioning of the TD - DL detector coordinates, dual phase and coherence of known information, such as the positioning result positioning error is only the p wave and S wave ChanZhen phase positioning method of 9.5% and 14.5%, to a certain extent offset the p wave and S wave ChanZhen phase calculation of the positioning error, so as to improve the effect of source localization precision of the inversion

GFZ Wireless Seismic Array (GFZ-WISE), a Wireless Mesh Network of Seismic Sensors: New Perspectives for Seismic Noise Array Investigations and Site Monitoring

Over the last few years, the analysis of seismic noise recorded by two dimensional arrays has been confirmed to be capable of deriving the subsoil shear-wave velocity structure down to several hundred meters depth. In fact, using just a few minutes of seismic noise recordings and combining this with the well known horizontal-to-vertical method, it has also been shown that it is possible to investigate the average one dimensional velocity structure below an array of stations in urban areas with a sufficient resolution to depths that would be prohibitive with active source array surveys, while in addition reducing the number of boreholes required to be drilled for site-effect analysis. However, the high cost of standard seismological instrumentation limits the number of sensors generally available for two-dimensional array measurements (i.e., of the order of 10), limiting the resolution in the estimated shear-wave velocity profiles. Therefore, new themes in site-effect estimation research by two-dimensional arrays involve the development and application of low-cost instrumentation, which potentially allows the performance of dense-array measurements, and the development of dedicated signal-analysis procedures for rapid and robust estimation of shear-wave velocity profiles. In this work, we present novel low-cost wireless instrumentation for dense two-dimensional ambient seismic noise array measurements that allows the real–time analysis of the surface-wavefield and the rapid estimation of the local shear-wave velocity structure for site response studies. We first introduce the general philosophy of the new system, as well as the hardware and software that forms the novel instrument, which we have tested in laboratory and field studies

Evaluation of geophone ground coupling using geophone/hydrophone comparison

Ground coupling defines the transfer function from ground motion to geophone motion. Ground coupling can be described using a variety of models, which must all be adequately parametrized before being used on data. The ocean bottom seismometers and ocean bottom cables are the devices confronted to ground coupling problems. Besides the velocity measurements made via geophones, the mentioned two types of devices allow pressure measurements due to presence of hydrophones. In this paper, we introduce a method that searches iteratively for the velocity boundary conditions which, when applied to a finite element model, allow the simulation results to fit with pressure data measured by the hydrophones. The iterative process is supported by a genetic algorithm. The obtained velocity values provide the evaluation of ground coupling of the geophones.В этой статье предложен метод итерационного поиска граничных условий для скоростей, которые, будучи примененными в конечно-элементной модели, позволяют согласовать результаты моделирования с данными о давлении, измеренном с помощью гидрофонов. Итерационный процесс реализован в виде генетического алгоритма. Полученные значения скорости обеспечивают оценку сцепления сейсмоприемников с грунтом.У цій статті запропоновано метод ітераційного пошуку граничних умов для швидкостей, які, будучи застосованими в скінченно-елементної моделі, дозволяють узгодити результати моделювання з даними про тиск, виміряний за допомогою гідрофонів. Ітераційний процес реалізовано у вигляді генетичного алгоритму. Отримані значення швидкості забезпечують оцінку зчеплення сейсмоприймачів із грунтом