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The Kumait oil field islocated in the Maysan Governorate southeastern Iraq, which was studied and interpreted by using 2D and 3D seismic data provided by the Oil Exploration Company using Petrel software. The study concerned the Mishrif Formation belongs to the Cretaceous Age. The reflector was detected based on synthetic seismograms and well logs for Kt-1 well. Structural maps (two-way time, velocity, and depth) were derived from seismic reflection interpretations to show several structural features, such as four isolated irregular enclosures representing the Kumait structure plunging NW-SE and demonstrating that the Kumait oil field is influenced by the Najd fault system trending NW-SE. The stratigraphic interpretation used the variance attribute to delineate the edge of the fault, which extended from the Mishrif Formation with a depth of 3090m and used the Direct Hydrocarbon Indicators (DHI) to identify the stratigraphic features in the research region and the extraction of seismic attributes. The applied seismic attributes, such as the instantaneous phase, show dim spots, flat spots, and mounds and is followed by down-lap; the instantaneous frequency, which offers low-frequency areas indicating a high probability of hydrocarbon accumulation; and the RMS amplitude, which shows high amplitude in the seismic data that conforms to the structure and confirms the presence of hydrocarbon. [ABSTRACT FROM AUTHOR]

Seismic waves generated by an earthquake can produce dynamic perturbations in the Earth’s gravity field before the direct arrival of P-waves. Observations of these so-called prompt elasto-gravity signals by ground-based gravimeters and broadband seismometers have been reported for some large events, such as the 2011 MW9.1 Tohoku earthquake. Recent studies have introduced prompt gravity strain signals (PGSSs) as a new type of observable seismic gravity perturbation that can be used to measure the spatial gradient of the perturbed gravity field. Theoretically, these types of signals can be recorded by in-development instruments termed gravity strainmeters, although no successful detection has been reported as yet. Herein, we propose an efficient approach for PGSSs based on a multilayered spherical Earth model. We compared the simulated waveforms with analytical solutions obtained from a homogeneous half-space model, which has been used in earlier studies. This comparison indicates that the effect of the Earth’s structural stratification is significant. With the help of the new simulation approach, we also demonstrated how the PGSSs depend on the magnitude of the seismic source. We further conducted synthetic tests estimating earthquake magnitude using gravity strain signals to demonstrate the potential application of this type of signal in earthquake early warning systems. These results provide essential information for future studies on the synthesis and application of earthquake-induced gravity strain signals.

In this paper, a simple numerical model is presented for analyzing arbitrarily shaped alluvial valleys subjected to propagating obliquely incident plane SH-waves. A time-domain half-plane boundary element method (BEM) was successfully used to prepare the model in which the interface needs only to be discretized. First, the problem was decomposed into two parts, a half-plane valley-shaped feature and a closed filled alluvium. Then, the method was applied to each part to obtain the considered matrices. Finally, by satisfying the continuity conditions at the interface, the coupled equation was transiently solved to determine the boundary values. All ground surface responses were also obtained in a secondary solution as internal points. After implementing the method in a general algorithm, several practical examples were analyzed to validate the responses. Moreover, an advanced numerical study was performed to sensitize the surface motion of semi-cylindrical alluvial valleys with variable shape ratios as synthetic seismograms and three-dimensional (3D) amplification patterns. The proposed method can easily be combined with other numerical methods to achieve nonlinear site responses. [ABSTRACT FROM AUTHOR]

In this paper, a homogeneous linear elastic half-plane model cluttered with multiple embedded arbitrarily-shaped inclusions is presented. The model was built based on the time-domain boundary element method established via the half-space Green's functions, subjected to propagating obliquely incident SH-waves. Using this method, the discretization was performed only on the interfaces. The full-contact posture was assumed between the inclusions and the surrounding domain. First, the problem was disintegrated into two parts including a multi-pitted half-plane and a system of randomly shaped closed filled solids. Then, by applying the method to each part, the influence coefficients of the matrices were obtained. Finally, to form a coupled equation for determining unknown boundary values in each time-step, the boundary/continuity conditions were satisfied on the interfaces. By implementing the method in an advanced developed algorithm, its efficiency was investigated by comparing the responses with those of the published works. To complete the obtained results, the synthetic seismograms and three-dimensional amplification patterns of the surface were presented. Also, some snapshots were illustrated to reveal the dispersion of the waves. The proposed method is a powerful tool for modeling various structures at the nano-scale and can be recommended to engineers for transient analysis of composite materials. [ABSTRACT FROM AUTHOR]

We estimate elastic and anelastic parameters and their evolution during laboratory rock deformation experiments, while developing a Monte Carlo waveform inversion. The transducer‐to‐transducer one‐source one‐station active seismic data of dry and water‐saturated samples are obtained from Zaima and Katayama (2018), https://doi.org/10.1029/2018JB016377. We first performed a trial‐and‐error estimate of the boundary conditions in order to suppress its influence on waveforms. The synthetic seismic data were generated using equivalent homogeneous models with different combinations of elastic and anelastic parameters with the aid of spectral element method. We compared them with the laboratory experimental data. Based on the comparisons, we obtained the time‐lapse variations of seismic velocities and attenuation of rock samples during deformation experiments, which we interpreted as crack developments. Our simultaneous estimation of elastic and anelastic parameters allowed us to detail the dynamics prior to the rock failure. Plain Language Summary: We developed a novel methodology to monitor the rock deformation in the laboratory using active seismic waveforms, comparing them against 3D synthetic seismograms. Our methodology can invert for the P‐ and S‐wave velocity changes as well as their attenuation quality factors. Changes in velocity and attenuation show the different trends especially just before rock failure, indicating the complexity of microcracks' evolution. Key Points: 3D numerical modeling with proper physical setting can simulate the waveforms in laboratory rock experimentsMonte Carlo waveform inversion for velocity and attenuation structure can image velocity and attenuation changes during rock deformationChanges in velocity and attenuation show the different trends especially before rock failure [ABSTRACT FROM AUTHOR]

The division and correlation of sequence stratigraphy are one of the essential steps in petroleum exploration. To comprehensively utilize the sequence stratigraphic information implied in multiple wireline well logs and improve the accuracy and reliability of sequence stratigraphic division, based on the edge detection, optimal partition, and natural evolution theories, and realizes the information fusion (formed one 'chromosome') of multiple wireline well logs (named as 'genes') which can reflect the feature information of sequence stratigraphy by using multipopulation genetic algorithm (MPGA) based on Fisher algorithm, in this study, geophysical data (wireline well logs and 3D seismic data) were used for spectral trend attribute analyses (wavelet transform, maximum entropy spectrum, time‐frequency analyses, and integrated prediction error filter). Since the seismic reflection characteristics of K1q were difficult to identify and considering subjective factors in conventional methods, a MPGA was also used to intelligently identify the sequence stratigraphy framework of the Lower Cretaceous Qingshuihe (K1q) Formation. Since the MPGA is an optimization algorithm, the code was run 10 times for accuracy with changes in the dividing layers. The optimal parameters in the process of data fusion (gene combination process) are selected. The sequence boundaries (SBs) searched by the MPGA matched those of the spectral trend attribute analyses, confirming that the MPGA was an effective, fast, and user‐friendly tool for defining the main SBs. MPGA can provide an optimal layering scheme ('elite population') through simultaneous searching at multiple depth ranges ('multipopulation'), recording the optimal SBs ('elite individuals') of each population and making the results more convinced. Although simulation solutions may not be unique, the MPGA still provides us a chance to gain some insights into the details of the stratigraphy. Based on this intelligent identification, the maximum flooding surface, two first flooding surfaces (FFS), and three SBs were defined in K1q. The cyclic patterns (prograding, aggrading, and retrograding) were identified. They showed the relationship between accommodation space (related to tectonic subsidence of the Chemo paleo‐uplift) and sediment supply. In addition, dynamic time warping (DWT) technique was used for sequence discrimination and correlation on the integrated prediction error filter analyses curve. A massive pebbly sandstone set, named 'bottom sandstone,' was identified in the lowstand system tract of SQ1 (K1q1), constrained by SB1 and FFS1, which was a favourable hydrocarbon exploration target. [ABSTRACT FROM AUTHOR]

We apply an updated computer algorithm for reflectivity synthetic seismograms to examine observational scenarios for seismic plane-wave propagation through horizontally stratified anisotropic media. Based on the commercial software package Matlab, the ANIMATIVITY software can compute synthetic seismograms using anisotropic models described either by a full elastic tensor or using common notations for an elastic tensor with a symmetry axis. This algorithm enables us to simulate wave propagation with high frequency components and to consider all transmission and reflection coefficients in one step. We validate the ANIMATIVITY code with synthetic P–S receiver functions in layered anisotropic media, compared against legacy reflectivity codes. Contrasting synthetic RFs for models with either sharp or gradual anisotropy transitions, we observe features in the gradual-transition models that could be misconstrued as caused by dipping interfaces. We find that S–P receiver functions have the potential to constrain anisotropy at depth via the back-azimuth variation of Sp-phase amplitude on the vertical component. We conclude that practical use of S receiver functions to investigate anisotropy will depend on accurate determination of the initial S-wave polarization. The ANIMATIVITY simulations of shear-wave splitting include S–P converted waves that precede the split SKS wave. [ABSTRACT FROM AUTHOR]

The main purposes of this research work are to estimate the coda–Q values using linear (log–log) and nonlinear (Gauss–Newton) regression techniques and to generate synthetic seismogram by white Gaussian noise modulated with an attenuation factor (e−kt) and a geomechanical spreading factor using a single backscattered model. A comparative study is carried out, for the estimation of coda–Q values from synthetic seismogram and from digital seismogram provided by three events recorded in three different seismic stations, namely Tezpur (TZR), Dokmok (DMK) and Seijusa (SJA) that occurred in Tezpur region, Assam, India. Here, both the models are compared in terms of outputs and accuracy as a function of lapse time and frequencies. Generally, linear model is used in most of seismological practices. But in this study, I am trying to use both linear and nonlinear models. Here, the main challenge is the estimation of coda–Q values using the nonlinear model. During the analysis, it was observed that, at the final part of the coda where the signal-to-noise ratio is greater than and equal to 5, the estimated coda–Q values have no significant difference for both linear and nonlinear models. But on the decreasing signal-to-noise ratio less than 5, the coda–Q values are overestimated in the linear model as compared to the nonlinear model. These observations are made for both the synthetic and digital seismograms. Through this study, I am trying to conclude that the coda–Q values are dependent on lapse time in both the linear and nonlinear models but are less pronounced in nonlinear techniques for both synthetic and digital seismograms. This effect is more evident when different coda durations are obtained by fixing the start time of coda analysis and increasing the end time of the same coda. This pattern is observed for all three events in Tezpur region and synthetic seismogram. Finally, the conclusion was drawn that the coda–Q values are dependent on lapse time and central frequencies for both the models. But, the significance levels are less in the case of nonlinear model for both synthetic and digital seismograms. [ABSTRACT FROM AUTHOR]

An advanced direct half-plane time-domain boundary element method (BEM) was applied to obtain the seismic response of a linear elastic irregular surface including periodically distributed semi-sine shaped valleys subjected to propagating obliquely incident plane SH waves. After developing the method for complex multiple surface topographies, some verification examples were solved and compared with those of the published works. Then, the transient response of a rough surface with 2–16 semi-sine shaped valleys was determined as synthetic seismograms. In this regard, the depth ratio of the valleys was sensitized. Finally, amplification patterns of the surface were presented in some cases. The results showed that the method was able to analyze the multipart models in the time-domain. Moreover, the response of the sinusoidal corrugated surfaces was very effective against seismic waves in forming different patterns. The method was recommended to researchers for transient analysis of complex engineering structures and composite materials in nanoscale. [ABSTRACT FROM AUTHOR]

The extensive application of pre-stack depth migration has produced huge volumes of seismic data, which allows for the possibility of developing seismic inversions of reservoir properties from seismic data in the depth domain. It is difficult to estimate seismic wavelets directly from seismic data due to the nonstationarity of the data in the depth domain. We conduct a velocity transformation of seismic data to make the seismic data stationary and then apply the ridge regression method to estimate a constant seismic wavelet. The estimated constant seismic wavelet is constructed as a set of space-variant seismic wavelets dominated by velocities at different spatial locations. Incorporating the weighted superposition principle, a synthetic seismogram is generated by directly employing the space-variant seismic wavelets in the depth domain. An inversion workflow based on the model-driven method is developed in the depth domain by incorporating the nonlinear conjugate gradient algorithm, which avoids additional data conversions between the time and depth domains. The impedance inversions of the synthetic and field seismic data in the depth domain show good results, which demonstrates that seismic inversion in the depth domain is feasible. The approach provides an alternative for forward numerical analyses and elastic property inversions of depth-domain seismic data. It is advantageous for further studies concerning the stability, accuracy, and efficiency of seismic inversions in the depth domain. [ABSTRACT FROM AUTHOR]

As a most important step in geological interpretation, stratigraphic correlation plays important roles in reservoir estimation and geologic modeling. A variety of datasets are used for stratigraphic correlation, such as well-logging data and seismic data, which are collected by different kinds of sensors. However, much uncertainty will be generated in the traditional course of stratigraphic correlation, because the complex underground geological structures cannot be comprehensively depicted by single dataset. Therefore, in this paper, we propose a visualization system to present and reduce the uncertainty in stratigraphic correlation based on the fusion analysis of multi-source datasets. First, a synthetic seismogram is modeled for each drilling well and a traditional time-depth conversion is conducted to match the seismic data and logging data. Then, an uncertainty model is proposed to quantify the depth difference between seismic horizons and stratigraphic structures extracted from different datasets. Furthermore, a set of visual designs are integrated into an uncertainty visualization system, enabling users to conduct intuitive uncertainty exploration and supervised optimization of stratigraphic correlation. Case studies based on real-world datasets and interviews with domain experts have demonstrated the effectiveness of our system in analyzing the uncertainty of stratigraphic correlation and refining the results of geological interpretation. [ABSTRACT FROM AUTHOR]

Traditional free vibration-based forward modeling approaches provide only the theoretical modal solution that lacks information regarding modal amplitudes. Moreover, they ignore the influence of source-receiver layout on the wavefield. Numerical wavefield modeling approaches can generate a dispersion spectrum mimicking the actual field test; however, numerical methods are not efficient in terms of computational time and produce numerical artifacts. Furthermore, they can be contaminated with leaky waves for soil strata with a high Poisson's ratio. This study presents a new wavefield modeling approach for developing full dispersion spectra of stratified media incorporating source-receiver configuration. The proposed method calculates the theoretical modal amplitude using the higher-order thin layer method and determines the vertical displacement responses at specified virtual receiver positions in the frequency-space domain. Afterward, it searches for spectral values at each frequency over a broad range of trial phase velocities to create a full dispersion spectrum. The accuracy and computational efficacy of the present method are demonstrated on different soil profiles adopted from literature, including normally dispersive media, irregularly dispersive media with high-velocity contrast, and a crustal level model. Results indicate the proposed approach can clearly distinguish the relative spectral amplitude of each mode and dominant dispersion trend. Calculated seismograms and dispersion images are compared with the existing 2D staggered grid finite difference method. Although both methods yield similar results, the current method is at least two orders (x102) faster than the staggered grid finite difference method. Unlike numerical approaches, the proposed method does not require additional computational resources to model materials with a high Poisson's ratio. Furthermore, it minimizes the contamination of leaky waves in the dispersion spectrum when modeling a high Poisson's ratio. The proposed method does not produce any numerical artifacts and can be used to generate accurate synthetic seismograms as well as dispersion spectra. In addition, the proposed wavefield modeling approach can be effectively used to develop an accurate and faster inversion scheme by including the entire dispersion spectrum. • Higher order thin layer method-based dispersion spectrum calculation of layered media. • The method incorporates source-receiver configuration. • Can eliminate the contamination of leaky waves in modeling high Poisson's ratio. • The computational time is insensitive to Poisson's ratio. • At least two orders faster than the existing staggered grid finite difference method. [ABSTRACT FROM AUTHOR]

The Foulden Maar is a terrestrial monogenetic volcanic crater found within the latest Oligocene–Late Miocene Waipiata Volcanic Field on the South Island of New Zealand. A geophysical characterisation of the Foulden Maar has been calibrated by acquiring a continuous 184 m drill core through the feature, which includes well preserved crater-lake sediments. Interpretations of gravity profiles, airborne and land-based magnetic data, and seismic reflection surveys reveal the geometry, density distribution and stratigraphy of the volcanic feature that formed on and in the schist basement of Central Otago. Six significant horizons are identified within a synthetic seismogram that ties core logs to the geophysical data. The investigation confirms a classic maar and diatreme structure consisting of a 1–1.5 km wide, c. 300 m deep crater overlying a thin vertical diatreme structure. [ABSTRACT FROM PUBLISHER]