H. Karsli

Application of complex-trace analysis to seismic data for random-noise suppression and temporal resolution improvement

Time-dependent amplitude and phase information of stacked seismic data are processed independently using complex trace analysis in order to facilitate interpretation by improving resolution and decreasing random noise. We represent seismic traces using their envelopes and instantaneous phases obtained by the Hilbert transform. The proposed method reduces the amplitudes of the low-frequency components of the envelope, while preserving the phase information. Several tests are performed in order to investigate the behavior of the present method for resolution improvement and noise suppression. Applications on both 1D and 2D synthetic data show that the method is capable of reducing the amplitudes and temporal widths of the side lobes of the input wavelets, and hence, the spectral bandwidth of the input seismic data is enhanced, resulting in an improvement in the signal-to-noise ratio. The bright-spot anomalies observed on the stacked sections become clearer because the output seismic traces have a simplified appearance allowing an easier data interpretation. We recommend applying this simple signal processing for signal enhancement prior to interpretation, especially for single channel and low-fold seismic data.

Ground-roll attenuation based on Wiener filtering and benefits of time-frequency imaging

Land-based reflection data sets always include many types of coherent noise. This article deals specifically with the ubiquitous problem of filtering noise known as ground roll. Ground roll is a particular type of Rayleigh wave and has high amplitude, low frequency, and low velocity. Ground roll is also dispersive and overwhelms the desired reflection signals unless special steps are taken in data acquisition and processing to get rid of it. Because of the dispersive character of this noise, shallow reflections at short offsets and deep reflections at long offsets are masked in the space-time domain and thus their waveforms are distorted. On the other hand, frequencies of ground roll and reflections overlap in the spectral domain (frequency or f-k). Figure 1 illustrates spectra of signal with ground-roll noise (black), signal (green), and ground-roll noise (red). Their frequencies clearly overlap in the low-frequency part of the spectrum.

Joint inversion of Rayleigh‐wave dispersion data and vertical electric sounding data: synthetic tests on characteristic sub‐surface models

In the traditional inversion of the Rayleigh dispersion curve, layer thickness, which is the second most sensitive parameter of modelling the Rayleigh dispersion curve, is usually assumed as correct and is used as fixed a priori information. Because the knowledge of the layer thickness is typically not precise, the use of such a priori information may result in the traditional Rayleigh dispersion curve inversions getting trapped in some local minima and may show results that are far from the real solution. In this study, we try to avoid this issue by using a joint inversion of the Rayleigh dispersion curve data with vertical electric sounding data, where we use the common-layer thickness to couple the two methods. The key idea of the proposed joint inversion scheme is to combine methods in one joint Jacobian matrix and to invert for layer S-wave velocity, resistivity, and layer thickness as an additional parameter, in contrast with a traditional Rayleigh dispersion curve inversion. The proposed joint inversion approach is tested with noise-free and Gaussian noise data on six characteristic, synthetic sub-surface models: a model with a typical dispersion; a low-velocity, half-space model; a model with particularly stiff and soft layers, respectively; and a model reproduced from the stiff and soft layers for different layer-resistivity propagation. In the joint inversion process, the non-linear damped least squares method is used together with the singular value decomposition approach to find a proper damping value for each iteration. The proposed joint inversion scheme tests many damping values, and it chooses the one that best approximates the observed data in the current iteration. The quality of the joint inversion is checked with the relative distance measure. In addition, a sensitivity analysis is performed for the typical dispersive sub-surface model to illustrate the benefits of the proposed joint scheme. The results of synthetic models revealed that the combination of the Rayleigh dispersion curve and vertical electric sounding methods in a joint scheme allows to provide reliable sub-surface models even in complex and challenging situations and without using any a priori information.

Spectral Domain Local Cancellation Procedure of Harmonic Noise in Seismic Data

We describe a simple and fast filtering procedure which is locally applied in spectral domain and uses iterative trimmed and truncated mean filter method (LITTM), to cancel harmonic noise with 50 or 60Hz and its multiples caused by power line during the seismic data acquisition in land and marine. The procedure doesn’t require any reference signal or an estimate accurately the fundamental frequency of the harmonic noise, but only it should be determined the approximate frequencies of the noise on the amplitude spectra. Real land and marine data examples show that the harmonic noise is filtered well without damaging the available frequencies around the fundamental frequency and provide clean outputs for later processes. We expect this procedure may be a useful tool to recover the signal masked by power line noise in other geophysical data.

High Resolution Deconvolution by Combining Fx Filtering and Cauchy Regularization

In this study, it is performed an inversion process that combines Cauchy regularization and FX filtering for a stable multi-channel high resolution deconvolution. Applications of the method are made on synthetic and post stack field data. From these applications, it is considered that resolution in the vertical direction and continuity in the lateral direction are more improved by successfully reduction random noise. Results show that the process provides more interpretable seismic sections.

Lineaments in the Shamakhy–Gobustan and Absheron hydrocarbon containing areas using gravity data

In this study, we purposed to investigate the edge of geostructures and position of existing faults of the Shamakhy–Gobustan and Absheron hydrocarbon containing regions in Azerbaijan. For this purpose, the horizontal gradient, analytic signal, tilt angle, and hyperbolic of tilt angle methods were applied to the first vertical derivative of gravity data instead of Bouguer gravity data. We obtained the maps that show the previous lineaments which were designated by considering the maximum contours of horizontal gradient, analytic signal maps, and zero values of tilt angle, hyperbolic of tilt angle maps. The geometry of basement interface was also modeled utilizing the Parker–Oldenburg algorithm to understand the sediment thickness and coherency or incoherency between the gravity values and basement topography. The lineaments were held a candle to most current tectonic structure map of the study area. It was seen that the techniques used in this study are very effective to determine the old and new lineaments in the Shamakhy–Gobustan and Absheron regions. The epicenter distribution of earthquakes within the study area supports the new lineaments which are extracted by our interpretation. We concluded that better comprehension of Azerbaijan geostructures and its effect on the large scale works will be provided by means of this study.

Investigation of soil structure in Uzungöl settlement area by Shallow Seismic Methods

This study was performed to relase the soil structure of Uzungol district of Trabzon city, a vocational area, where had been formed by a historical landslide and lake deposits and to evaluate its geotechnical characters by using seismic methods which are noninvasive, rapidly applicable and provide substantial information about the structure of investigated ground in a short time. For this purpose, seismic refraction, active-passive surface waves and seismic reflections in 16 profiles were gathered on four sub-areas and and evaluated by current favorable numerical methods. Although it considerably varies between profiles, the depth of basement, depositional base of deposits, was averagely obtained as 13.5-15m at upper elevation and 25-50m at lower elevation of the study area. Dynamic elastic parameters and average shear wave velocity of the upper 30m (VS30) of soil in the area were calculated. The soil classification of study area was interpreted as locally Z1 and Z2 class for TEC, B and C class for EC-8 code, C and D class for NERHP. According to VS30 (394-530m/s), ground amplification and predominant vibration period of the study area are respectively obtained as 1.5-2.1 and 0.23-0.30sec. On the other hand, all deposits are characterized by stiffness-solid soil, excluding arable soil from surface to a few meters depth. In addition, the first meters of bedrock shows weathered character, but deeper parts are very compact and hard. Therefore, a scientific infrastructure has been formed to carry out the engineering projects to be planned for Uzungol settletment safely and without damaging the environment.

Post-stack high-resolution deconvolution using Cauchy norm regularization with FX filter weighting

High-resolution deconvolution can mathematically be viewed as a regularized inverse problem. Besides, the result of the high-resolution deconvolution is generally accepted as reflectivity series of the layered media. On the other hand, lateral continuity is frequently poorer than vertical resolution on post-stack seismic section after application of any high-resolution deconvolution. However, because of the ill-posed inherent of the deconvolution problem, the Cauchy norm regularization term, a non-quadratic prior-information is widely used to provide the stability and uniqueness of the problem. But, it does not provide adequate quality of deconvolution if the noise in the data is strong. In this study, a stable and high-resolution deconvolution of post-stack seismic data was accomplished by an iterative inversion algorithm incorporating the Cauchy norm regularization with FX filter weighting. Cauchy norm regularization was utilized to force the solution to a spikiness structure, while the effective random noise reduction was performed by using the FX filter. Applications to synthetic and real post-stack data showed that the resolution in the vertical direction and continuity in the lateral direction are better improved. Thus, we think that this process makes seismic sections obtained especially from thin layered sedimentary basins more interpretable.

A Comparison Between Empirical Formulas And Impedance Ratio For The Calculation Of Soil Amplification: Synthetic And Real Cases

Summary Soil amplification is an important parameter to estimate the dynamic soil-structure interaction under earthquake loadings accurately. So, a good estimation of the soil amplification is required because the soil conditions of local sites have significant influences on the vulnerability of engineering structures. Although the soil amplification is directly related to impedance ratio between the rocks and soils, it is generally calculated trough empirical formulas based on Vs30 value, an average shear wave velocity (Vs) up to 30m depth. However, when the soil column includes rock units (Vs□700m/s) within the 30m depth, the empirical formulas lose their validity. In this study, we try to explain this issue and compare soil amplification values calculated by using Vs30 and impedance ratio for synthetic models and field cases which include rocks unit within the 30m depth. In synthetic models, the soil amplification for four scenarios for two-layered medium is calculated by most known empirical formulas and compared with that of impedance ratio. In field cases, we compare soil amplifications for shallow and deep bedrock cases. Synthetic and real results show that soil amplifications calculated by empirical formulas couldn’t characterize the real ground conditions, especially in the case of the hard-solid units in shallow depths.

The Sensitivity Analysis as a Non-uniqueness Indicator in the Inversion of Rayleigh-wave Dispersion Curve

In the Rayleigh-wave dispersion curve (RDC) inversion, layer thicknesses are typically fixed during the inversion process and may be estimated using available a priori knowledge. But, the RDC inversion process frequently suffers from non-uniqueness due to the use of erroneous or conjectural layer thicknesses. In this work, sensitivity analysis of S-wave and layer thickness is used to reveal the reliability and accuracy of the RDC inversion results in the non-uniqueness situation. For this purpose, a synthetic data is inverted with three different initial models through the same inversion parameters and their sensitivity patterns are compared. The sensitivity analyses demonstrate that the sensitivity pattern of layer S-wave velocity and thickness may present useful information about the quality of estimated parameters. In this way, the possibility of getting trapped in non-uniqueness may be decreased.