Abstract: Abstract Investigations of hydraulically induced micro-seismicity are typically connected with magma injections, exploitation of geothermal fields and salt mines. Our study examines the seismicity and seismic sources in a peri-platform region with long salt production history. In addition, a very large site for extraction of aggregates and limestone is presented in the area. Increased seismicity in the region has been observed for several decades as during the study period of the last 12 years, more than 1000 events with magnitude \(M < 4.3\) have been registered. To study the complex seismic sources concentrated in such small area spatial distribution of seismicity and fault plane solutions are analyzed together with available geological and geophysical data, in order to connect registered earthquakes swarms with geological structures. Results show that several faults are outlined from geological information and confirmed by interpretation of geophysical data. Very different focal mechanisms calculated for the 13 earthquakes in the near region of the salt production site cannot propose a dominant fault mechanism and confirm the complexity of the seismic sources in the area. Our results suppose that activation of some of these structures is more likely due to water injected in the salt dome as part of the production process, which changes the stress equilibrium in the Earth crust. PubDate: 2020-02-14

Abstract: Abstract As a kind of geomagnetic data processing, downward continuation of potential field plays an important role in geologic interpretation and geomagnetic localization. The inherent instability of larger distance downward continuation restricts its practical applications. In this paper, we report a kind of one-step compensation downward continuation method free of iteration using the equivalent wave number domain continuation operator, which will speed downward continuation compared to iterative compensation, and prove theoretically the convergence of the downward continuation filtering factor about one-step immune-iterative compensation. The frequency responses of the low-pass filter factor are also discussed by different damping factors, iterative numbers and continuation depths. The regularity analysis of one-step compensation method is also discussed. We use the theoretical model of magnetic bodies and real data to test experimentally the immune-iterative compensation algorithm based on the equivalent wave number domain continuation factor, respectively. The results all show high accuracy and good stability of the one-step compensation downward continuation algorithm. The performances of downward continuation including three kinds of algorithms are demonstrated by three parameters, and comparisons prove the reported algorithm has less calculated error than the generalized inverse method, and less elapsed time than the iterative compensation method. PubDate: 2020-02-11

Abstract: Abstract The self potential data interpretation is very important to delineate and trace the mineralized zones in several regions. We study how to interpret self potential anomalies due to a finite two-dimensional inclined dike using the particle swarm algorithm. However, the precise estimation of the model parameters during the inverse solution are unknown. Here, we show that the particle swarm algorithm is capable of estimating the unknown parameters with acceptable accuracy. The evaluated parameters are the polarization parameter, the depth, the inclination angle, the width, and the location of the source of the target. We found in controlled in free-noise synthetic case that the particle swarm algorithm has a remarkable capability of assessing the parameters. For a noisy case, the results also are very competitive. Furthermore, it is utilized for real mineralized zones examples from Germany and India. Our results demonstrate how the particle swarm algorithm overcomes in trapping in local minimum solutions (undesired) and go faster to the global solutions (desired). Finally, the target parameters estimated are matched with accessible geologic and geophysical information. PubDate: 2020-02-07

Abstract: Abstract As one of the major regions of carbonate rock oil–gas exploration in western China, Tazhong area of the Tarim Basin has severe environment and complex ground surface conditions, hence the signal to noise ratio (SNR) of the field seismic data is extremely low. To improve the SNR of desert seismic data is a crucial step in the following work. However, the random noise in desert seismic characterizes by non-stationary, non-gaussian, non-linear and low frequency, which are very different from the random Gaussian noise. In addition, the effective signals of desert seismic generally share the same frequency band with strong random noise. These all make some traditional denoising methods cannot suppress it well. Therefore, a new noise suppression framework based on improved PSO–SVM is proposed in this paper. First, we extract the correlation of noisy desert seismic data to form feature vector. Subsequently, the model of improved PSO–SVM was built to classify the extracted feature, thereby identifying the position of the seismic events. Finally, second-order TGV filter was applied for obtaining denoised results. We perform tests on synthetic and field desert seismic record and the denoising results show that the proposed method can effectively preserve effective signals and eliminate random noise. PubDate: 2020-01-31

Abstract: Abstract The propagation characteristics of crustal Lg waves have been investigated in and around geotectonically complex Indo-Burman Ranges (IBR) of North Eastern region (NER) of India. To cater towards seismic hazard assessment and civil engineering practices, Lg attenuation has been studied by determining the regional average quality factor (QLg) in the frequency range of 0.5–5 Hz. The Lg attenuation regional model for IBR and its vicinity areas devised is given as \(Q_{Lg} = (407 \pm 0.00082)f^{{\left( {1 \pm 0.1864} \right)}}\). The attenuation coefficient (Q0 = 407) in the model represents a moderately attenuating lithosphere in the study area. The power of frequency dependence (η = 1) is indicative of the fact that Lg attenuation in IBR and its adjoining areas is not only highly frequency dependent, but also the tectonic activity in IBR is currently high. Frequency dependence of Lg attenuation indicates that scattering mechanism plays a dominant role in attenuation of Lg waves. This is possible when the lithosphere beneath is highly heterogeneous in nature which is caused due to the subduction tectonics of IBR. A scrutiny of the corner frequencies (fc) in the Lg spectra has indicated the role of path and site effects in the scattering of Lg energy. Predominant frequency of Lg in IBR has been observed to be around 2 Hz, which falls within the natural frequency range of common structures (1–10 Hz) which may be a concern for civil engineering safety. This Lg attenuation model will be helpful in the prediction of ground motion, and will play a pivotal role in adopting a suitable seismic coefficient for civil engineering designs in order to mitigate seismic hazard in the IBR and its nearby areas in NER of India. PubDate: 2020-01-23

Abstract: Abstract Elimination of random noise is crucial in seismic data processing. Especially in desert area, field record generally has problems of weak effective reflection wave and strong noise due to its special surface factors. Besides, desert noise has characteristics of low-frequency, non-stationary and non-Gaussian. Thus, it is difficult to separate the effective signal from desert noise in low-frequency band. In order to solve these problems, this paper proposes an iterative low-rank denoising method based on synchrosqueezed wavelet transform (SWT). The algorithm first transforms seismic signal into time–frequency domain by SWT, then the signal is decomposed by iterative low-rank decomposition. Different from a traditional low-rank algorithm, this paper performs an adaptive iterative convergence on low-rank decomposition algorithm. When the error of decomposition reaches the predetermined range, the effective low-rank component is extracted. In the end, the low-rank matrix is converted back to time domain by inverse SWT to achieve the denoising. The results of the synthetic and field records verify the effectiveness of the proposed method so that it can be applied to the denoising of desert seismic data. In addition, the surface waves in real desert seismic record have obvious suppression effects and the advantages of the algorithm are shown in the comparison experiments. PubDate: 2020-01-22

Abstract: Abstract Reservoir evaluation of tight sandstone involves the determination of reservoir properties from samples and logs. In the calculation of water saturation, Archie formula is an important fundamental and connection between log evaluation and petrophysics. Highly accurate parameters of Archie formula are the key to the log evaluation of gas-bearing tight sandstone. At present, there are two methods of the rock-electric experiment to measure parameters of Archie formula: water increment (imbibition) and water decrement (centrifugation). In this paper the experimental measurement of a group of tight sandstone has been designed and the results of the two experimental ways are quite different. In the experiment, the distribution of brine is a main factor affecting the electrical properties of rocks. Fluid distribution model during imbibition and drainage is used to explain the results of rock electrical experiments, and the results are verified by nuclear magnetic resonance measurement. In the end, the Pickett chart method of actual data is used to compute the ranges of the saturation exponent n approximately, then to verify the correctness of the theoretical analysis. The results demonstrate that the centrifugal method is more applicable. In the log evaluation of tight sandstone, the appropriate choice of the method which can get accurate rock electrical parameters is important. Reliable evaluation will provide support for future development of gas-bearing tight sandstone. PubDate: 2020-01-13

Abstract: Abstract By utilizing data from the National Seismic-Monitoring Network of Turkey, operated by AFAD (Disaster and Emergency Management Presidency, Ministry of the Interior), power spectra of 198 stations distributed countrywide are computed and probability density functions as well as diurnal, weekly, monthly and annual spectrogram-graphics, hence, are obtained. Observed noise levels are the result of natural background noise, cultural noise as well as instrument installation practice and equipment defects. Countrywide noise distribution is displayed on a map and noise models for Turkey are developed in the study. Various suggestions are also given for some of the technical problems deducted from noise analyses in relation to the construction of the station, equipment faults, and defects. PubDate: 2020-01-04

Abstract: Abstract In precise point positioning (PPP), the zenith hydrostatic delay (ZHD) is traditionally treated as a priori value from the ZHD model but the zenith wet delay (ZWD) is treated as an unknown parameter to estimated. For some near real-time PPP tasks, priori ZHD from the blind ZHD models are often used because external meteorological measurement or information about atmospheric pressure or ZHD can not be obtained in such conditions. On the other hand, a priori ZHD errors can project into GNSS height estimates errors in the PPP analysis, because unmodeled part of the ZHD is usually absorbed into the estimated ZWD while there is the difference between the hydrostatic mapping function and the wet mapping function. In this study, we found the errors of the ZHD seasonal models are not always less than those of the ZWD seasonal models, which implies that the traditional strategy for treating ZTD (priori ZHD and estimated ZWD) is not always the best choice when using the blind zenith tropospheric delay (ZTD) models. A decision model for the ZTD blind model (DMZBM), which is a new strategy of dealing with ZTD in PPP when using blind ZTD models, was proposed. For most cases, the traditional strategy works while for some exception cases, it is recommended that priori ZWD from the blind ZWD model was set but ZHD is treated as an unknown parameter to estimated. The DMZBM can directly reduce ZHD–ZWD mutual absorption errors which potentially reduce GNSS height estimates errors due to the difference between the hydrostatic mapping function and the wet mapping function. The results show that there are significant reductions of ZHD–ZWD mutual absorption errors in polar regions when using the new ZTD-treating strategy. PubDate: 2020-01-03

Abstract: Abstract Ionospheric anomalies have been shown to occur a few days before several large earthquakes. The published works normally address examples limited in time (a single event or few of them) or space (a particular geographic area), so that a clear method based on these anomalies which consistently yields the place and magnitude of the forthcoming earthquake, anytime and anywhere on earth, has not been presented so far. The current research is aimed at prediction of large earthquakes, that is with magnitude Mw 7 or higher. It uses as data bank all significant earthquakes occurred worldwide in the period from January 1, 2011 to December 31, 2018. The first purpose of the research is to improve the use of ionospheric anomalies in the form of TEC grids for earthquake prediction. A space–time TEC variation estimator especially designed for earthquake prediction will show the advantages with respect to the use of simple TEC values. Further, taking advantage of the well-known predictive abilities of the Gutenberg–Richter law’s b-value, a combined estimator based on both TEC anomalies and b-values will be designed and shown to improve prediction performance even more. PubDate: 2020-01-02

Abstract: Abstract A collapse column is a geological structure formed by the dissolution of a soluble rock layer under certain hydrogeological conditions. This forms a cavity, which is filled by the overburden. Collapse columns have a great impact on coal mining safety. In this work, a model of a concealed collapse column is constructed according to its diameter, and the finite difference method is used to simulate it using an acoustic equation. The seismic record characteristics of the collapse column are analyzed. In the seismic section, the attributes of the reflected wave of the concealed collapse column in the coal seam are small and undetectable, and the reflected wave of the auxiliary horizon (the upper interface of Ordovician limestone) is in-phase axis. It is difficult to artificially identify concealed collapse columns with small diameters when twisting or dislocation occurs. However, the reflected wave properties clearly indicate an annular anomaly on the horizon property plane, which helps to identify the concealed collapse column. Finally, the seismic attributes of reflected waves at the interface between the 10# coal seam and Ordovician limestone roof in the BY mining area of TY mine are identified using high-density three-dimensional seismic data to verify the effectiveness of the proposed method in identifying concealed collapse columns. PubDate: 2019-12-12

Abstract: The Global Positioning System (GPS) permanent stations at the equatorial and southern sub-tropical hydrobelts of South America undergo the highest seasonality on the Earth due to hydrological loadings. Fortunately, there are products that account for such variations, although some of them have not been properly evaluated. For instance, global solutions of Gravity Recovery and Climate Experiment (GRACE) are band-limited to lower frequencies; therefore, comparisons with GPS data must account for such spectral inconsistencies. It is proposed to spatially average 39 GPS sites by applying Gaussian smoothing, which allows comparisons with long-wavelength part of GRACE solutions by Center for Space Research (CSR), GeoForschungszentrum, and Jet Propulsion Laboratory. Comparisons are also carried out with loadings from Noah-driven Global Land Data Assimilation System (GLDAS) and GRACE mass concentration (mascon) solution by Goddard Space Flight Center. Results show that CSR best reduces the variances of the radial displacements considering both spatially filtered (70%) and unfiltered (53%) GPS data covering the period from Jan 2010 to Dec 2015. However, GLDAS-Noah underestimates the amplitudes of vertical loadings, which might be due to unmodeled inland water and groundwater storages. While acknowledging that a denser distribution of GPS stations is needed, the findings still shed light on the quality of the global hydrological loading products based on GRACE and GLDAS datasets, which might be of interest to the respective science teams. Graphic abstract PubDate: 2019-12-07

Abstract: Abstract A combined empirical mode decomposition (EMD) and multichannel singular spectrum analysis (MSSA) model (EMD–MSSA model) was used for extraction of the gravity tide correction without a priori information (e.g., station coordinates) from static relative gravimetric data. Static observational data acquired using a CG-5 relative gravimeter over 16 days were used to investigate the feasibility and reliability of the proposed method. The singular spectrum analysis (SSA) method and empirical mode decomposition (EMD)–independent component analysis (ICA) method were also adopted for comparison. Experimental results show that the time series of the gravity tide correction estimated using EMD–MSSA, SSA and EMD–ICA methods are consistent with a theoretical reference (the Longman formula). The gravity tide correction estimated using the EMD–MSSA method is closer to the theoretical model than other methods, the root-mean-square difference of the residuals between estimated values and theoretical values are smallest, and the accuracy of the gravity tide correction time series derived using the EMD–MSSA method is thus highest. The correlation coefficient of extraction results and GT is highest for the results extracted using the EMD–MSSA method. The experimental results show that using the EMD–MSSA model, which combines the advantages of the MSSA and EMD signal processing methods, improves the extraction estimation accuracy and reliability of the gravity tide correction from relative gravimetric data. PubDate: 2019-12-01

Abstract: Abstract The signal-in-space (SIS) anomalies caused by satellites and control segments can greatly affect the reliability and safety of navigation and positioning users. The prior information associated with the failure of the Advanced Receiver Autonomous Integrity Monitoring (ARAIM) algorithm were obtained by the evaluation of SIS failure rates broadcasted with navigation ephemeris to investigate the integrity of navigation and positioning. For the existing ARAIM algorithm, the failure rate of satellites in the BeiDou Navigation Satellite System (BDS) is a conservative estimate, which is inconsistent with the actual SIS performance of BDS. Only the accurate detection of the SIS anomalies of BDS satellites can provide an effective reference to associate with failure. Therefore, to improve the accuracy of SIS anomaly detection for BDS satellites, and to provide higher integrity services for users, this study presents an improved method of SIS anomaly detection with precise ephemeris. The median method was used to detect a gross error in clock data before the calculation of clock datum, and the combination of an experience threshold and trimmed mean was used to determine the anomaly detection threshold. The feasibility and efficiency of the proposed method were also analyzed using data collected between 2015 and 2016. The detection results show that the constellation fault caused by erroneous clock data can be avoided, and the SIS anomalies can also be detected using the proposed method. Additionally, through the comprehensive tests performed in this study, it was found that from 2015 to 2016, the average accumulated duration of anomalies for BDS satellites was 10 h for geostationary orbit (GEO) and incline geosynchronous orbit (IGSO) and 55 h for medium earth orbit (MEO), respectively. These anomalies were primarily caused by the satellite clock. PubDate: 2019-12-01

Abstract: Abstract Burdur Fault (BF) is located in Fethiye Burdur Fault Zone and it has formed in three main sections as Gölbaşı–Gökçebağ, Burdur and Yassıgüme–Çendik. The Neogene Basin is a NE–SW oriented depression basin which forms Plio-Quaternary aged lacustrine and alluvial deposits. Paleo-seismic structures on lacustrine sediments were studied with three excavation surfaces at the BF segments in Burdur settlement area. The relationships between different paleo-seismic structures were explained in detail. Although we have obtained new data for the timing of past earthquakes, it is to determine the shear rate of BF segments. Lacustrine sediments and alluvium sequences showing clear evidence of the shearing movement effects were observed. Studies on slopes of foundation excavations on BF segments and near the segment were investigated. Stratified lacustrine sediments observed, each of consisting thin clay layers which is weakly developed in the marl unit excavation surfaces near the Gökçebağ segment. Thin layered lacustrine sediments developed that intersect with a parallel–parallel fractures that filled with collapsed sediments expose near the Burdur segment. In both excavation surfaces, the lower sedimentary unit is covered with a fine sand. The claystone and marl intercalations are discontinuous in the lateral direction and consist of alluvial and lacustrine deposits observed in excavation surfaces near the Yassıgüme–Çendik segment. This study emphasizes that the importance of geological structure has a significant impact on the formation of fault segments. PubDate: 2019-12-01

Abstract: Abstract Ultra-rapid clock products provide the main parameters for real-time or near real-time precise point positioning services. However, it has been found that BeiDou ultra-rapid clock offsets do not meet the requirements for high-accuracy applications because of their low accuracy, especially regarding the prediction parts. This study proposes an improved model for BDS satellite ultra-rapid clock offset prediction based on BDS-2 and BDS-3 combined estimation. First, the preprocessing of the clock offset based on frequency data and a denoising method that employed a Tikhonov regularization algorithm was introduced to refine the observed series for predictive modeling. Second, given the coexistence of BDS-2 and BDS-3 satellites and the advantages of the BDS-3 onboard atomic clock, inter-satellite correlations between different satellites were used to adjust the stochastic function in estimating the coefficients for the prediction model. Third, to further improve the accuracy of the prediction model, the residuals of the clock offsets were analyzed by partial least squares regression, in which the main components related to the clock offsets were modeled by a back-propagation neural network. Six experimental schemes were introduced to verify the improved model. Experiments were divided into two groups to compare the preprocessing strategy and prediction model. The experimental results indicated: (1) both the BDS-2 and BDS-3 predicted clock offsets were mutually beneficial in the improved model; (2) because of the lower quality of the observed clock offset from BDS-3, preprocessing was used to improve the prediction accuracy by 1.0–15.2% for BDS-2, and reaching 23.2–31.9% for BDS-3; (3) the accuracy of the clock offsets were improved by 30.7–47.3% for BDS-2, and by 49.9–59.3% for BDS-3 within an 18-h period. The proposed improved model was found to have a significant effect on optimizing the ultra-rapid clock products of the International GNSS Monitoring and Assessment Service and GNSS analysis centers. PubDate: 2019-12-01

Abstract: Abstract The study area comprises the NE–SW trending Burdur Basin situated at the tectonically active northeastern part of the Fethiye–Burdur Fault Zone (FBFZ), SW Turkey. The basin demonstrates a half graben geometry hosting lacustrine sedimentary deposits from the Late Miocene onward and is bounded by normal faults on its southern side namely the Burdur Fault Zone. In this study, gravity anomalies over the Burdur sedimentary basin were inverted for the first time in terms of mapping its basement relief. The algorithm used for inverting the gravity anomalies provides accuracy depth estimates by incorporating an exponential increase in density with depth at its inversion procedure. Thus the obtained depth configuration yields also a major improvement on the results of depth content of the sedimentary infill reported previously by other studies that used a constant density contrast in their interpretation. Along the east of Burdur Fault from south to north, the basement depth to the southern end of Burdur Basin is ca 1.8 km and gets shallower to ca 0.6 km towards the north around the Burdur city. The deepest section of the basin is ca 3.2 km to the western side of the Burdur Fault close the southern end of the Burdur Lake. Towards north, out of the depression area of the Burdur Basin, the sedimentary infill is about in range of 0.4–1.2 km. The lateral limits of the basin structure have also been outlined by a recent edge detection method based on the logistic function of the total horizontal gradient (LTHG). The LTHG map related to the Burdur Basin shows maximal amplitudes trending NE–SW as two major lines that clearly delineates the segments of the Burdur Fault Zone to the S-SE of Burdur Lake. The inverted basin depth model by a cross-section perpendicular to the regional strike of the basin represents two-step depositional area of the sedimentary fills confirming a geometry of a half graben structure. PubDate: 2019-12-01

Abstract: Abstract This paper proposes a heuristic singular spectrum analysis (SSA) approach to extract signals from suspended sediment concentration (SSC) time series contaminated by multiplicative noise, in which multiplicative noise is converted to approximate additive noise by multiplying with the signal estimate of the time series. Therefore both the signal and noise components need to be recursively estimated. Since the converted additive noise is heterogeneous, a weight factor is introduced according to the variance of additive noise. The proposed heuristic SSA approach is employed to process the SSC series in San Francisco Bay compared to the traditional SSA and homomorphic log-transformation SSA approach. By using our heuristic SSA approach, the first 10 principal components derived can capture 96.49% of the total variance with the fitting error of 6.17 mg/L, better than those derived by traditional SSA approach and homomorphic log-transformation SSA approach that catch 88.97% and 87.35% of the total variance with the fitting errors of 14.47 mg/L and 15.03 mg/L, respectively. Therefore, our heuristic SSA approach can extract more signals than traditional SSA and homomorphic log-transformation SSA approach. Furthermore, the results from the simulation cases show that all the mean root mean squared errors and mean absolute errors derived by our heuristic SSA are smaller than the traditional and homomorphic log-transformation SSA, which indicate that the extracted signals by heuristic SSA approach are much closer to the real signals than those by the other two approaches. Therefore it can be conclude that our heuristic SSA approach performs better in extracting signals from SSC time series contaminated with multiplicative noise. PubDate: 2019-12-01

Abstract: Abstract As a preliminary three-dimensional numerical analysis, this research aims to detect future zones of high-stress accumulation caused by the interaction of active faults within a 3D topographic geological block based on finite-element analysis. Stress analysis of the three-dimensional topographic model covers both static and dynamic loading caused by topographic loads and crustal movements, and can provide more realistic results. There are many applications to create topographic models from xyz data. Nevertheless, these models do not have the properties required in analytical software. Solid meshing of topographic blocks is abstruse and consumes much time and high CPU usage. Therefore, we first try to create a validated topographic shell model through the introduced methods including nodal projection and statistical analysis, and then upgrade it to a solid model. The stress equations are then assigned to each element of the solid model. The outputs include stress accumulation zones in both pre-failure and failure mode for the whole model. In addition, energy diagrams show the rate of main energies per time and accordingly, represent the perception of power for each energy output. Energy drop during the initial run time is consistent with the collision of the blocks of the model. PubDate: 2019-12-01

Abstract: Abstract The results of mathematical modeling of electrical soundings with the AMNB (Schlumberger, Wenner) arrays and the proposed combined AMN + NMA array above horizontally layered medium and including a ball medium are presented. It is shown that the combined array has two main advantages: the current penetration depth is greater at the same position of outer electrodes of the considered arrays; edge effects are smaller due to bilateral measurements with respect to the central receiving electrode; a geoelectric inhomogeneity is delineated at the pseudosections of the apparent resistivity. The quantitative interpretation of the sounding curves obtained with the AMN + NMA array can be carried out by an existing software for inversing of data of the symmetric Wenner (AMNB) array with electrode spacing equal to 1/3 of supplying dipole. The results of application of the new technique of electrical soundings by the combined array in the study of state of the dam on sedimentation tank of liquid chemicals are presented. On the geoelectric sections and the pseudosections of the apparent resistivity, areas of increased electrical conductivity in body and base of the dam are detected. Filtration of water from the reservoir occurs through these areas. Soundings with the AMN + NMA array are expedient for studying of a geological medium at small depths where the medium is horizontally-heterogeneous, and also for solving of engineering-geological problems. PubDate: 2019-11-25