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The oscillatory bubble pulses generated by airguns in seawater are known to produce artefacts in seismic images. Although such artefacts are suppressible by employing larger airgun arrays in acquisition, small airgun arrays are used more often now to minimize the environmental impacts, thus raising the need for further suppressing bubble pulses at data processing stage. For a deep marine reflection dataset recently acquired by a small airgun array, we compare the effectiveness of three popular debubbling methods that estimate the far‐field source signature based on theoretical simulation and wavelets extracted from seafloor reflections and direct arrivals, respectively. In this case, due to the lack of near‐field measurements for calibration, the debubbling via simulation underperforms the two wavelet extraction methods. Overlapping events in the noisy response of seafloor sediments lead to the failure of the wavelet extraction from primary seafloor reflections. The estimated source signature based on direct arrivals achieves the best bubble suppression result, indicating the importance of signal‐to‐noise ratio and a low level of directionality of the small airgun array source. [ABSTRACT FROM AUTHOR]

The field of anion supramolecular chemistry has received more and more attention in recent years. Anions with diverse types and geometries have been widely used for the synthesis of ionic spin crossover (SCO) complexes. This review is devoted to anion effects on the molecular, supramolecular structures and magnetic properties of discrete SCO compounds. Firstly, typical anions used in the synthesis of these compounds are briefly summarized according to their various geometries. This is followed by a collection of representative examples of anion‐based SCO compounds, whose SCO properties are analyzed in terms of supramolecular interactions, geometry and charge of anions. In the third part, anion effects on SCO complexes of different kinds of metal centers and ligands are outlined and finally remarks on the synthesis new type of ionic SCO complexes in the future are described. [ABSTRACT FROM AUTHOR]

Seismic attenuation values based on inverse Q‐filtering are useful in enhancing seismic data resolution for quantitative interpretation. However, as field attenuation estimations are often contaminated by noise and overburden effects, an inverse Q‐filter may reduce the signal‐to‐noise ratio. To help reservoir mapping with seismic resolution enhancement, we use well logs and surface seismic data to estimate the attenuation of a depth interval composed of several carbonate oil reservoirs onshore the Arabian Peninsula. From applying a prestack Q inversion on τ–p gathers from a large 3D seismic survey, the estimated effective attenuation values show spatially coherent patterns, likely corresponding to changes in the petrophysical and fluid properties. The patterns of the estimated effective attenuation values correlate considerably with the anticline geometry, with higher values on its crest than its flanks. The small percentage of the negative effective attenuation values indicates that the apparent attenuation and overburden effects are insignificant. At well locations, the effective attenuation values show a good correlation with the average porosity of the main reservoir, verifying that they are related to changes in petrophysical properties in the analysis interval. We propose an extended inverse Q‐filter with two additional parameters to make it more robust and flexible and test it with synthetic and field datasets. We estimate a multiple‐scattering attenuation value from well logs and use it in the proposed filter for the field dataset. The compensation for the multiple‐scattering effects suppresses the overprints of the data components unrelated to the target interval, hence benefitting the quantitative data interpretation. [ABSTRACT FROM AUTHOR]

• A series of three new mononuclear manganese(III) Schiff-base complexes. • The change of substituents or anions affects the spin crossover (SCO) properties. • Magnetic measurements provided firm evidence for the cooperative SCO effects in complexes 2 and 3 , while complex 1 persists in the HS state. • Complex 3 exhibits a surprisingly gradual SCO process with a hysteresis width of 6 K at lower temperature. The flexible hexadentate Schiff-base ligands (R-sal-N-1,5,8,12)2− can be easily obtained by modifying the different substituents at the 5 or 3,5 positions on the phenyl rings of the salicylaldehyde. We report in this paper the syntheses, crystal structures and magnetic properties of three new mononuclear manganese(III) complexes [Mn(R-sal-N-1,5,8,12)]Y (R = 5-H, Y = BF 4 (1); R = 3,5-diCl, Y = SbF 6 (2); R = 5- t Bu, Y = ClO 4 (3)). All the complexes have an analogous monocationic MnN 4 O 2 surrounding offered by the flexible hexadentate ligand in a distorted octahedral geometry. Magnetic susceptibility measurements demonstrated that complex 1 maintains a high-spin (HS) state between 2 and 400 K due to the closing packing, while complex 2 shows a cooperative and complete one-step thermo-induced spin state switching with T 1/2 of 194 K. As for complex 3 , single-crystral X-ray structural studies show the existence of a large amount of HS manganese(III) ions at 100 K and it exhibits a surprisingly gradual SCO process with a hysteresis width of 6 K at lower temperature. [ABSTRACT FROM AUTHOR]

The crystal structures and magnetic properties of three Mn(III) Schiff-base complexes [Mn(3-OMe-sal-N-1,5,8,12)]AsF 6 ·H 2 O (1) , [Mn(4-OMe-sal-N-1,5,8,12)]AsF 6 ·H 2 O (2) and [Mn(5-OMe-sal-N-1,5,8,12)]AsF 6 (3) have been studied. Complexes 1 and 2 show gradual SCO behavior. The transition temperatures of 2 is 98 K higher than that of 1. Due to the absence of crystallizing solvent water molecule, complex 3 maintains a HS state in the test temperature range. [Display omitted] Spin crossover (SCO), as a molecular bistable phenomenon, has attracted extensive interest. In this paper, the syntheses, crystal structures and magnetic properties of three Mn(III) hexadentate Schiff-base complexes [Mn(3-OMe-sal-N-1,5,8,12)]AsF 6 ·H 2 O (1) , [Mn(4-OMe-sal-N-1,5,8,12)]AsF 6 ·H 2 O (2) and [Mn(5-OMe-sal-N-1,5,8,12)]AsF 6 (3) have been reported. The substituent positions of ligands and solvent molecules have a cooperative effect on SCO behavior. Complex 1 shows a complete SCO between the high-spin (HS, S = 2) and low-spin (LS, S = 1) states without thermal hysteresis, and complex 2 shows a gradual incomplete SCO behavior. The transition temperatures of 2 (T 1/2 = 241 K) is 98 K higher than that of 1 (T 1/2 = 143 K), which indicates that the ligand field strength of (4-OMe-sal-N-1,5,8,12)2– is stronger than that of (3-OMe-sal-N-1,5,8,12)2–. Due to the absence of crystallizing solvent water molecule, complex 3 maintains a HS state in the test temperature range. [ABSTRACT FROM AUTHOR]

Accurately estimated interval attenuation (1/Q) values have several applications, such as in quantitative interpretation and seismic resolution enhancement. Although Q values can be estimated by measuring the spectral ratio between seismic reflections from a target and a reference reflector, the results are influenced by factors such as overburden inhomogeneities. Here, we quantitatively analyze the overburden influence on interval Q estimations using the spectral ratio method, time—space domain prestack Q inversion (PSQI), and τ-p domain PSQI. We compare these three methods using a synthetic dataset and a field dataset acquired onshore the Arabian Peninsula. Synthetic seismic gathers are generated from a three-layer model with a low-Q inclusion in the first layer to mimic overburden inhomogeneity. The field data are preconditioned image gathers from a producing oil field. The synthetic data test shows that the small low-Q body produces a considerable error in estimated Q values. The smallest error (i.e., 13.3%) is in the τ-p domain PSQI result. Theoretically, τ-p domain PSQI could obtain more accurate Q values when there are overburden influences because of the simultaneous inversion scheme and the application in the τ-p domain. The field data application also illustrates that the τ-p domain PSQI produces reasonable interval Q values. Our measured Q values are also comparable with the Q values estimated from hydrocarbon saturated carbonate reservoirs. [ABSTRACT FROM AUTHOR]

Variations in the topography and thickness of the near-surface low-velocity weathering zone negatively impact the quality of onshore seismic data and images. Such impact can be mitigated using accurate near-surface velocity models. We propose to estimate near-surface velocities using a layer-cell tomography method which sequentially combines the model parameterizations of multiscale deformable-layer tomography (DLT) and cell tomography. We first estimate the long-wavelength velocity variations using multiscale DLT, which maps the undulating geometry of the weathering base where the angular coverage of first-arrival raypaths is limited. Then we convert the solution model of multiscale DLT into a cell model, and further determine the short-wavelength velocity variations using cell tomography. We test the proposed layer-cell tomography method using synthetic datasets and a field dataset. The results indicate that the new method improves the resolution of the velocity model from the multiscale DLT, and reduces the artifacts in the velocity solution compared to those observed in the cell tomography method. Reverse time migration of the synthetic data shows that using the velocity model from the layer-cell tomography method gives more accurate images of reflectors. For the field dataset test, the layer-cell tomography method yields a high-resolution near-surface velocity model that could be validated by the improvements in the tomostatic correction results. [ABSTRACT FROM AUTHOR]

Using directional waves is advantageous in subsurface seismic imaging because such waves are localized in space and time. Hence, the recorded data contain information mostly about the illuminated targets. However, most seismic field data are physically generated by point sources that excite wavefield propagating into all directions and interact with all parts of the medium. How to convert point-source wavefields into a wavefield due to a directional wave packet without physically exciting it, is the subject of investigation here. In particular, we investigate the Gaussian wave packet (GWP) which is a directional wave packet localized in space and time. GWP is an exact solution of the wave equation and it differs from the widely used asymptotic solutions such as Gaussian Beams or Gaussian Packets. The spatial localization and propagation direction of GWP are controlled by parameters chosen by users. We propose a method to synthesize GWP field data in complex media using recorded shot records of point sources based on the reverse-time concept. To assess the quality of the synthesized GWP data, we study the influences from point-source wavelets and the spatial interval between point sources. Finally, we present the constructed GWP fields in two numerical examples. We also show one application of the GWP data in seismic imaging using multiples. [ABSTRACT FROM AUTHOR]

• Four new MnIII hexadentate Schiff base complexes. • The change of substituent position affects the spin crossover property. • The nature and geometry of the counter anions play a dominant role in the supramolecular interactions. • Hirshfeld analysis. In this paper, the syntheses, crystal structures and magnetic properties of spin crossover (SCO) salts of formula [Mn(4-OMe-sal-N-1,5,8,12)]SbF 6 ‧0·45H 2 O (1), [Mn(3-OMe-sal-N-1,5,8,12)]SbF 6 ‧H 2 O (2), [Mn(4-OMe-sal-N-1,5,8,12)]ClO 4 ‧H 2 O (3) and [Mn(3-OMe-sal-N-1,5,8,12)]Br (4) have been reported. Magnetic susceptibility measurements demonstrate that complex 1 shows a gradual one-step SCO between the high-spin (HS, S = 2) and low-spin (LS, S = 1) states without thermal hysteresis. The transition temperatures T 1/2 of the 4-OMe-SbF 6 (1) salt estimated from the magnetic susceptibility measurement is 213 K. As for complex 2, π···π stacking interactions lead to more close stacking which hinder the flexibility of the whole ligand and it is stable in the HS state in the temperature range of 2–300 K. Both complexes 3 and 4 exhibit incomplete spin crossover behavior. These results are consistent with Hirshfeld analysis. Electrochemical analysis indicates that the change of methoxy‑substituent position from 4 to 3 decreases the electron density on the metal center. [ABSTRACT FROM AUTHOR]

The seawater column is typically taken as a homogeneous velocity layer in wide-angle crustal seismic surveys in marine environments. However, heterogeneities in salinity and temperature throughout the seawater layer result insignificant lateral variations in its seismic velocity, especially in deep marine environments. Failure to compensate for these velocity inhomogeneities will introduce significant artifacts in constructing crustal velocity models using seismic tomography. In this study, we conduct numerical experiments to investigate the impact of heterogeneous seismic velocities in seawater on tomographic inversion for crustal velocity models. Experiments that include lateral variation in seawater velocity demonstrated that the modeled crustal velocities were contaminated by artifacts from tomographic inversions when assuming a homogeneous water layer. To suppress such artifacts, we propose two strategies: 1) simultaneous inversion of water velocities and the crustal velocities; 2) layer-stripping inversion during which to first invert for seawater velocity and then correct the travel times before inverting for crustal velocities. The layer-stripping inversion significantly improves the modeling of variation in seawater velocity when preformed with seismic sensors deployed on the ocean bottom and in the water column. Such strategies improve crustal modeling via wide-angle seismic surveys in deep-marine environment. [ABSTRACT FROM AUTHOR]

Reverse time migration (RTM) is a seismic imaging method to map the subsurface reflectivity using recorded seismic waveforms. The practice in exploration seismology has long established a two-fold approach of seismic imaging: Using velocity modeling building to establish the long-wavelength reference velocity models, and using seismic migration to map the short-wavelength reflectivity structures. Among various seismic migration methods for different situations, RTM is the only method that is capable to use all seismic wave types that can be computed numerically. Being initiated in early 1980's, RTM seeks an image of the subsurface reflectivity as the best match in an image space between the extrapolation of time-reversed waveform data and the prediction based on estimated velocity model and source parameters. Judging the image quality in the same space of forming the images is more advantageous than the approaches of modeling and inversion which seek the solution in the model space but judge its fitness in data space. Considering that most seismic migration applications today still use primary reflection as the only signal, the capability of RTM to use all computable wave types is unique and helpful reducing the imaging artifacts due to mistaking non-primary waves as primary reflections. Hence, we refer to those RTM algorithms using only primary reflections as the first-generation RTM methods, and the RTM algorithms making a full use of primary reflections, multiple reflections and other non-primary waveform data as the second-generation RTM methods. This paper reviews the development history of the RTM along with its major challenges, current solutions, and future perspectives. [ABSTRACT FROM AUTHOR]

Least-squares migration (LSM) is a data-fitting imaging approach seeking the seismic reflectivity image of the most accurate amplitude and optimal resolution. However, the high computational cost of LSM has hindered its broad application. In this study, we combine a convolutional neural network (CNN) with LSM to significantly improve the computational efficiency while retaining the imaging quality. Taking CNN as a "projector," we treat LSM as the "projection" from the ordinarily migrated images to the least-squares updated images. We conduct this CNN-assisted LSM in the shot gather domain using a Gaussian beam migration and the corresponding LSM. The training data for CNN consist of 10–15% of all shot gathers, with the Gaussian beam migrated shot gathers as the input and the LSM shot gathers as the target. After the training, the processing time for the remaining shot gathers took several minutes for 2D cases. The results from testing with the Sigsbee 2B synthetic dataset and a field marine dataset indicate the CNN-assisted LSM saved 80–90% of the computation time of the full LSM and achieved significantly higher image fidelity than that of the ordinary migration. [ABSTRACT FROM AUTHOR]

The reaction of Mn(Ⅱ) salts prepared with (5-I-sal-N-1,5,8,12)2− ligand where the hexadentate ligand is the product of the reaction of 5-iodosalicylaldehyde and N,N'-bis(3-aminopropyl)ethylenediamine in situ in MeOH/EtOH provided five complexes, [Mn(5-I-sal-N-1,5,8,12)]Y (Y = PF 6 − (1), AsF 6 − (2), SbF 6 − (3), BF 4 − (4), ClO 4 − (5)). All complexes crystallize without crystallizing solvents, except 4 with a H 2 O solvent molecule. Different structural features and magnetic profiles have been observed in complexes 1 − 3. Owing to the cooperativity of the N H···F and N H···I hydrogen bonds and I···π, I···F interactions, complexes 1 and 3 persist in the HS state at 2 − 400 K while complex 2 shows a gradual SCO with T 1/2 is about 265 K. Hirshfeld face analysis reveals that the presence of different interactions in complexes 1 − 3. With decreasing the temperature, complex 4 undergoes an almost full SCO with T 1/2 = 272 K, while complex 5 shows an incomplete SCO and remains 50% HS state until 30 K. [ABSTRACT FROM AUTHOR]

Clustering earthquakes refer to the seismic events that occur closely with each other in time and space. Because their overlapping waveform records make it difficult to pick the first arrivals, the hypocenters of clustering earthquakes cannot be determined accurately by traveltime location methods. Here we apply a reverse-time imaging (RTI) method to map clustering earthquakes. Taking the advantage of directly using waveforms, the RTI method is capable to map either a single small earthquake or some densely distributed clustering earthquakes beneath a 2-D seismic array. In 3-D case the RTI method is successfully applied to locate the long-offset doublet earthquakes using the data from a set of sparsely distributed surface stations. However, for the same acquisition geometry, the RTI encounters challenges in mapping densely distributed clustering earthquakes. While it is obvious that improving the mapping of clustering earthquakes requires a denser receiver network with wider range of illumination angles, it is necessary to verify the actual resolution of the RTI method with synthetic data. In our study area in the Three Gorges region, our tests in 3-D case suggest that some events beneath the linear aligned sub-arrays have reasonable resolution. [ABSTRACT FROM AUTHOR]

With the development of computational power, there has been an increased focus on data-fitting related seismic inversion techniques for high fidelity seismic velocity model and image, such as full-waveform inversion and least squares migration. However, though more advanced than conventional methods, these data fitting methods can be very expensive in terms of computational cost. Recently, various techniques to optimize these data-fitting seismic inversion problems have been implemented to cater for the industrial need for much improved efficiency. In this study, we propose a general stochastic conjugate gradient method for these data-fitting related inverse problems. We first prescribe the basic theory of our method and then give synthetic examples. Our numerical experiments illustrate the potential of this method for large-size seismic inversion application. [ABSTRACT FROM AUTHOR]

When a doublet of closely spaced microearthquakes occur nearly simultaneously, their overlapping waveforms complicate the picking of first-arrival times and challenge traveltime-based location methods to estimate the location and origin time of each event in the doublet. The reverse-time imaging (RTI) method locates earthquakes by backpropagating the reconstructed wave fronts of P and S waves to the source locations thereby removing the need to pick first arrivals. Using an elastic RTI method, we successfully estimated the locations and origin times of a doublet of microearthquakes: an ML0.1 event reported by local earthquake monitoring system and second microearthquake that occurred 0.7 s earlier that was missed by the official monitoring network in the Three Gorges Reservoir region, China. We introduce a time–depth constrain to estimate the origin time and to evaluate how robust the imaged source location is with respect to possible errors in the velocity model. For our case, a model with slightly lower velocities will result in an earlier origin time but will have less effect on the estimated source depth. Results of this study suggest that, by applying the RTI method it is possible to locate doublets with overlapping first arrivals. [ABSTRACT FROM PUBLISHER]

The Tan-Lu Fault Zone (TLFZ) is the largest strike-slip system in East Asia. The central TLFZ has four main branch faults across a width of 20– 40 km, and both the great 1668 Tancheng Earthquake (M8.5) and the Anqiu Earthquake (M7.0) occurred on its two eastern branch faults. Due to the lack of recent earthquakes and stations around a seismic-quiescent segment of the TLFZ centered near the 70 BCE Anqiu Earthquake, previous tomographic images have resolutions coarser than 20 km in the middle and lower crust, unable to show how the crust is faulted along the TLFZ. To improve the resolution, we deployed a 70-km-long W- E -trending seismic array with 38 portable seismographs across the TLFZ at 36.1°N. Using one month of teleseismic records and a newly developed multiscale teleseismic tomography method, our P-wave velocity profile has achieved a resolution of 5 km × 5 km in shallow crust, and 10 km × 10 km in deep crust, as shown by the resolution tests. The profile's velocity variation correlates well with surface geology and crustal electrical resistivity profiles. The new profile provides clues for the depth distribution of major TLFZ branches, and indicates the two eastern TLFZ branch faults cut through the crust along a column-shaped low-velocity anomaly. This low-velocity column is associated with low-resistivity anomalies in the upper and lower crust, indicating a likely presence of fluids in the faulted rocks. This crustal faulting interpretation is consistent with the Moho geometry of previous receiver function studies, with an alignment between a receiver function Moho dome and a large low-velocity anomaly. Though seismicity is sparse near the profile, our interpreted crust-cutting location is in line with a linear cluster of recent TLFZ earthquakes about 20 km south of the profile, indicating that this quiescent segment could be a 150 km seismic gap along the central TLFZ. • The multiscale teleseismic tomography is revised and used to construct a high-resolution velocity model. • High resolution Vp model reveals the depth distribution of the TLFZ. • The eastern TLFZ branches cut through the crust along a vertical low-velocity zone. • A 150 km seismic-quiescent segment of the central TLFZ is recognized to be a seismic gap. [ABSTRACT FROM AUTHOR]

The interplay of host‐guest interactions and controlled modulation of spin‐crossover (SCO) behavior is one of the most exploited topics regarding data storage, molecular sensing, and optical technologies. This study examines the effect of solvents on the spin‐crossover (SCO) behavior of manganese(III) complexes [Mn(sal‐N‐1,5,8,12)]I•S (S=CH3OH, C2H5OH, CH3CN) (1) and [Mn(sal‐N‐1,5,8,12)]I3 (2), where (sal‐N‐1,5,8,12)2− is 2,2′‐((1E,13E)‐2,6,9,13‐tetraazatetradeca‐1,13‐diene‐1,14‐diyl)diphenol synthesized by salicylaldehyde and 1,2‐bis(3‐aminopropylamino)ethane. The complexes, crystallizing in orthorhombic or monoclinic systems, exhibit similar supramolecular arrangements with one‐dimensional cationic chains at low temperatures. Magnetic studies reveal that solvent inclusion sharpens the SCO transition and lowers the transition temperature. Specifically, 1⋅CH3OH shows a 13 K thermal hysteresis due to methanol's mobility through the channels in the cationic framework. Although the solvent‐free compound was not obtained, compound 2 with a linear I3− anion was synthesized, displaying extensive cation‐anion contacts and a distinct 13 K thermal hysteresis upon heating due to altered intermolecular cooperativity. This emphasizes the significant role of solvent introduction and variation in crystal packing and their impact on the SCO properties. [ABSTRACT FROM AUTHOR]

Abstract: While tilted transverse isotropy (TTI) is a good approximation of the velocity structure for many dipping and fractured strata, it is still challenging to estimate anisotropic depth models even when the tilted angle is known. With the assumption of weak anisotropy, we present a TTI traveltime inversion approach for models consisting of several thickness-varying layers where the anisotropic parameters are constant for each layer. For each model layer the inversion variables consist of the anisotropic parameters ε and δ, the tilted angle φ of its symmetry axis, layer velocity along the symmetry axis, and thickness variation of the layer. Using this method and synthetic data, we evaluate the effects of errors in some of the model parameters on the inverted values of the other parameters in crosswell and Vertical Seismic Profile (VSP) acquisition geometry. The analyses show that the errors in the layer symmetry axes sensitively affect the inverted values of other parameters, especially δ. However, the impact of errors in δ on the inversion of other parameters is much less than the impact on δ from the errors in other parameters. Hence, a practical strategy is first to invert for the most error-tolerant parameter layer velocity, then progressively invert for ε in crosswell geometry or δ in VSP geometry. [Copyright &y& Elsevier]

While seismic imaging for crustal and mantle structures has traditionally relied on surface wave and refraction data, the use of reflection data for crustal-scale targets has been largely limited to the common midpoint (CMP) stack techniques. The rapid increase in the number of seismograph array deployments in recent years in crustal and mantle seismology has reached a level such that a re-examination of the imaging techniques is becoming necessary. In this paper we show the advantage of prestack depth imaging for crustal reflection studies, based on data from two reflection surveys of the Los Angeles Regional Seismic Experiment (LARSE) to map faults and crustal-scale structures. Our analysis indicates that the quality of the previous images of these surveys is limited by the CMP stack technique. For comparison, we present here depth images of the same LARSE data using wave equation prestack depth imaging and a tomographic velocity model based on first arrivals of the LARSE surveys and local earthquakes. Our new images are considerably improved over previous images in terms of resolution and reflector continuity. The new images show reflectors throughout the crust and suggest truncations in the Moho associated with the San Andreas Fault. A series of bright reflector segments, which are associated with the San Gabriel and San Andreas faults have been identified and might represent reflections from the fault zones. Our results suggest that the presence of high noise level, strong lateral velocity heterogeneity and wide angle geometry argue for, rather than against, the use of prestack depth imaging over the simple CMP stack techniques. As demonstrated in this study, it is now viable to conduct prestack depth imaging of crustal reflection data using a velocity model based on earthquake first arrivals thanks to the dense acquisition deployment. [ABSTRACT FROM AUTHOR]

Abstract: We analyzed a global tomographic model for the Tibet–Himalayan collision zone, which indicates that the Indian lithospheric slab has been subducted subhorizontally beneath nearly the entire Tibetan plateau to depths of 165–260km. Tibetan velocity structure is low in its crust and high in its lithospheric mantle at depths between 75 and 120km. We interpret an asthenospheric layer positioned above the subducted Indian slab at depths between 120 and 165km beneath the Tibetan plateau. Beneath the central portion of the plateau a low-velocity anomaly exists from the crust down to 310km depth, indicating mantle upwelling through a weakened part of the subducted slab. We present a model, which explains that, the uplift history and low relief of the Tibetan plateau is a result of subhorizontal subduction and heating of Indian lithosphere that is separated from Tibetan lithosphere by a thin channel of asthenosphere. Two predictions made by our model are: (1) the amount of shortening in the Himalayas is equivalent to the amount of underthrusted Indian mantle lithosphere; and (2) a young mantle geochemical signature should be present along the entire southern portion of the Tibetan plateau. [Copyright &y& Elsevier]

Discusses variations in the maximum depth of earthquakes in southern California. How earthquake magnitude is proportional to fault area; Finding that the depth distribution of southern California earthquakes indicates that areas underlain by schist basement rocks have a shallower maximum depth of earthquakes than do areas with other types of basement rocks.

Distributed acoustic sensing provides seismic sensors distributed every few metres over each fibre optic cable of several kilometres in length, serving as an ultra‐dense array for both surface and downhole seismic acquisitions. It is well‐recognized now that distributed acoustic sensing acquisition configuration can have profound effect on data quality, notably the choice of the gauge length and lead‐in cable length on the resulting signal to noise ratio. In this paper, we present a detailed study on how these effects behave differently over various signalling frequency bands. We derive the signal to noise ratio as a function of the peak frequency, gauge length and lead‐in cable length, and demonstrate significantly different 80 SNR samples behaviours over low, middle and high frequency bandwidths, respectively. These results, not only reveal the underlying mechanism for signal and noise variation as function of acquisition parameters, but also help identifying the desired gauge and cable lengths that better serve particular applications, such as inversion and imaging which take information from different frequency bands. A field data has been used to demonstrate these frequency‐dependent behaviours. [ABSTRACT FROM AUTHOR]

In manganese(III) complexes with BPh4− as the counter anion, the ligand field strength and non-covalent interactions between cations and anions of the flexible Schiff-base ligands (R-sal-N-1,5,8,12)2− are tuned by modifying the different substituents at the 5-position or 3,5-positions on the phenyl rings of the salicylaldehyde, and the magneto-structural properties of complexes 5-I-BPh4 (1), 5-tBu-BPh4 (2), 5-OCH3-BPh4 (3), naphth-BPh4 (4) and 5-Br-3-OCH3-BPh4 (5) are investigated. Complex 1 undergoes an incomplete SCO with two different Mn(III) sites, while complexes 2 and 3 remain in the HS state throughout the entire temperature range, suggesting the absence of magnetic state conversion. Under the effect of solvent, complex 4 shows different magnetic properties. Upon solvent loss, 4 displays a more complete SCO with a T1/2 of 140 K. In contrast to the complexes described above, complex 5 possesses two substituents, namely 5-Br and 3-OCH3. As a result, it exhibits an abrupt SCO effect due to the significantly stronger intermolecular cooperativity. [ABSTRACT FROM AUTHOR]

The quality of seismic migration images strongly depends on accurate velocity models. However, migration velocity models often contain errors causing artifacts which degrade seismic resolution and fidelity. Here, we propose a method to enhance seismic migration images using processes in angle-domain common-image-gathers (ADCIGs), without requiring modification to the velocity model. The ADCIGs impacted from velocity errors show non-flat gathers and scattered noise. To enhance the imaging quality in ADCIGs, these problems need to be treated prior to stacking. Ideally, layers in ADCIGs should be flat without smearing amplitudes through all angles. Using this principle, we iteratively process one reflection at a time by isolating it into a local window and then flattening it. Also, we apply internal processing steps to enhance the signal. The algorithm for segregating a reflection, referred to as the connected-component labeling (CCL) method, is the primary method for extracting any feature that has a continuous form within the ADCIGs. Moreover, this method is insensitive to scattered noise so it is a suitable approach for classifying reflections or noise. To test the efficiency of this algorithm, we create ADCIGs containing relatively poor-quality images using an inaccurate migration velocity model. The primary objective of this test is to show how well the CCL method can select various forms of reflections in the presence of various levels of noise. The results show that the CCL method is capable of individually decomposing a reflection, which can facilitate processing in the internal workflow. Finally, we evaluate the quality of processed migration images by comparing our processed Poynting-vector reverse time migration (PVRTM) images with reverse time migration applied Laplacian filter and partial stacked PVRTM. These comparable migration images are benchmarked against a baseline synthetic reflector model. The essential improvements of our method are addressed by the migration sections, namely the removal of diffraction artifacts at both small and large scales and the improvement of phase coherency. The final stacked migration image produced with our methods shows clearer geological features that are capable of delivering a more reliable seismic interpretation. [ABSTRACT FROM AUTHOR]

Accurate delineation of the salt flank is important for oil and gas exploration in areas with salt intrusion. We describe the application of deformable-layer tomography (DLT) to invert for the geometry of salt flank using travel times of transmitted P- and S-waves from surface sources to downhole receivers. The DLT allows us to take advantage of a common situation that the salt velocity is known and generally invariant, but we need to determine the variable geometry of salt flank. We demonstrate our new method using a physical model experiment mimicking the setup of a walkaway vertical-seismic-profiling (VSP) survey. We first use picked P-wave arrivals to invert for the salt flank geometry; the sinusoid shape of the salt flank is estimated fairly by the DLT due to the uneven P-wave raypath coverage. As an improvement, we further incorporate the S-wave arrivals in the DLT. The picking of S-wave arrivals is assisted with modeled S-wave arrivals based on the P-wave DLT model. The DLT solution using both P- and S-wave arrivals delineates the salt flank geometry more accurately than that using P-wave arrivals alone. The salt flank delineation using DLT can complement with the conventional salt proximity and migration methods. It could also serve as constraints or the initial model for the full-waveform inversion of salt geometry. [ABSTRACT FROM AUTHOR]

In the exploration and production of fossil resources, the characterization of rock facies is critical for estimations of rock physical properties, such as porosity and permeability, and for reservoir detection and simulation. We propose a new machine learning (ML) algorithm for characterizing rock facies using a convolutional neural network (CNN) with feature engineering and data padding strategies. In the new ML algorithm, we extend rock feature data from 1-dimensional "profile" to 2-dimensional maps by padding the original dataset. The 2-dimensional padded rock facies map enables the CNN to capture the inherent geological features while keeping the local continuities. In this new ML algorithm, we only need a simple CNN design and structure to efficiently achieve accurate classification of rock facies. We test the feasibility of applying this new algorithm using a verifiable well logging dataset from the Panoma gas field in southwest Kansas. The results show that our new ML algorithm with a simple CNN structure has achieved higher accuracy in classifications of rock facies in comparison with the CNN results of the 2016 SEG ML contest. This new ML algorithm has application potential in automatic rock facies characterization with high accuracy and efficiency. [ABSTRACT FROM AUTHOR]

In this paper, we introduce the halogen substituents (F, Cl, Br, I) to explore their influence on the structures and SCO properties of the Mn(III) complexes. [Display omitted] Six mononuclear Mn(III) complexes with hexadentate Schiff-base ligand, the products of the reaction between a N,N ′-bis(3-aminopropyl)ethylenediamine or triethylenetetramine and 5-X-salicylaldehyde have been synthesized: the I− salts of complexes 1 – 3 exhibit a gradual SCO behavior, [Mn(5-Cl-sal-N-1,5,8,12)]I (1) shows a nearly complete SCO with T 1/2 = 125 K, whereas [Mn(5-Br-sal-N-1,5,8,12)]I (2) and [Mn(5-I-sal-N-1,5,8,12)]I (3) show a gradual and incomplete SCO above room temperature. [Mn(5-F-sal-N-1,4,7,10)]I (4) predominantly remains HS state at all temperatures. [Mn(5-I-sal-N-1,5,8,12)]NO 3 (5) and [Mn(5-F-sal-N-1,5,8,12)]NO 3 (6) show an almost full conversion to the HS state and a more gradual SCO having the T 1/2 value of 282 K for 5 and 159 K for 6, respectively. [ABSTRACT FROM AUTHOR]

Marine seismic reflection surveys are often masked by strong water-bottom multiples that limit the use of data beyond the first multiple waves. In this study, we have successfully suppressed much of the multiple artifacts in the depth images of two of the marine seismic reflection profiles from the Los Angeles regional seismic experiment (LARSE) by applying reverse time migration (RTM). In contrast to most seismic reflection methods that use only primary reflections and diffractions, the two-way RTM migrates both primaries and multiple reflections to their places of origination: seabed multiples to the sea bottom and primaries to the reflecting interfaces. Based on the RTM depth sections of LARSE lines 1 and 2, we recognize five stratigraphic units from the sea bottom to a depth of 6 km. These units are Pliocene and younger strata, probably Miocene syntectonic strata, two deeper sequences of unknown age and lithology as well as Miocene volcanic layers on Catalina ridge. Several inferred igneous intrusions in the upper crust comprise a sixth unit. The existence of a thick sedimentary section in the Catalina Basin, which might include Paleogene and Cretaceous fore-arc strata, has important geologic significance. If borne out by further studies, significant revisions of current structural and stratigraphic interpretations of the California borderland would be warranted. [ABSTRACT FROM AUTHOR]

Seismic illumination plays an important role in subsurface imaging. A better image can be expected either through optimizing acquisition geometry or introducing more advanced seismic migration and/or tomographic inversion methods involving illumination compensation. Vertical cable survey is a potential replacement of traditional marine seismic survey for its flexibility and data quality. Conventional vertical cable data processing requires separation of primaries and multiples before migration. We proposed to use multi-scale full waveform inversion (FWI) to improve illumination coverage of vertical cable survey. A deep water velocity model is built to test the capability of multi-scale FWI in detecting low velocity anomalies below seabed. Synthetic results show that multi-scale FWI is an effective model building tool in deep-water exploration. Geometry optimization through target oriented illumination analysis and multi-scale FWI may help to mitigate the risks of vertical cable survey. The combination of multi-scale FWI, low-frequency data and multi-vertical-cable acquisition system may provide both high resolution and high fidelity subsurface models. [ABSTRACT FROM AUTHOR]

Abstract: Rayleigh wave dispersion can be induced in an anisotropic medium or a layered isotropic medium. For a layered azimuthally anisotropic structure, traditional wave equation of layered structure can be modified to describe the dispersion behavior of Rayleigh waves. Numerical stimulation results show that for layered azimuthal anisotropy both the dispersion velocities and anisotropic parameters depend principally on anisotropic S-wave velocities. The splitting S-wave velocities may produce dispersion splitting of Rayleigh waves. Such dispersion splitting appears noticeable at azimuthal angle 45°. This feature was confirmed by the measured results of a field test. The fundamental mode splits into two branches at azimuthal angle 45° to the symmetry axis for some frequencies, and along the same direction the difference of splitting-phase velocities of the fundamental model reaches the maximum. Dispersion splitting of Rayleigh waves was firstly displayed for anisotropy study in dispersion image by means of multichannel analysis of surface waves, the image of which provides a new window for studying the anisotropic property of media. [Copyright &y& Elsevier]

Exploration of cost-efficient and high-performance photocatalyst for H 2 evolution by using a facile approach is of great importance. In this manuscript, a facile one-pot method was employed to fabricate MoS 2 /CdS heterostructures with MoS 2 intimately grown on the surface of CdS resulting in the formation of well-defined heterostructures. Screen experiment reveals the optimized photocatalytic H 2 evolution performance of MoS 2 /CdS is far exceeding that of pristine CdS by a factor of more than 162. The outstanding performance can be ascribed to the formation of heterostructures which accelerate charge transportation and separation, and the MoS 2 serving as a cocatalyst for the decrease of H 2 overpotential. Moreover, the photocatalytic mechanism of the MoS 2 /CdS was carefully investigated, which contributes to the deep understanding of the photocatalytic process and the designation of other low-cost and high-efficient photocatalyst. Image 1 • The MoS 2 /CdS nanoheterostructures were synthesized by using one-pot approach. • The H 2 evolution rate of MoS 2 /CdS is 162 times higher than that of pristine CdS. • The extraordinary performance is attributed to the well-defined heterostructures. • The photocatalytic mechanism was detailedly investigated. [ABSTRACT FROM AUTHOR]

For full-waveform inversion (FWI) with sparse survey layout, it is crucial to optimize the source and receiver geometry toward full-wave illumination. We propose a sparse geometry optimization method and workflow for target-oriented FWI using finite-frequency illumination analysis. The frequency-dependent impact of a source-receiver pair to the wavefield sensitivity kernel and diagonal terms of approximate Hessian matrix are derived under visco-acoustic model assumptions. Based on the reciprocity principle, we use virtual sources in target zone to efficiently calculate the Green's function and illumination from acquisition surface. Optimal locations of sparse receivers are determined by comparing band-limited illumination at reference stations and their surrounding region through an illumination attribute scan. FWI model residual errors are used to evaluate the performance of optimized geometry layout for a given target zone. The performances of different geometries are compared to determine a suitable frequency band for FWI geometry optimization. Synthetic deep water model and ocean bottom node acquisition geometry are used to verify the feasibility of the workflow. Numerical tests in target-oriented FWI show that optimized geometry with constraints of band-limited illumination below10 Hz has better performance than that above 10 Hz. An extension of our geometry optimization method to sparse source configuration is straightforward. • Target-oriented acquisition experiment design. • Finite-frequency illumination analysis. • High resolution multi-scale seismic imaging. • Environment friendly acquisition planing. • Deep-water velocity modeling. [ABSTRACT FROM AUTHOR]

Ground-based hyperspectral imaging is used for development of digital outcrop models which can facilitate detailed qualitative and quantitative sedimentological analysis and augment the study of depositional environment, diagenetic processes, and hydrocarbon reservoir characterization in areas which are physically inaccessible. For this investigation, ground-based hyperspectral imaging is combined with terrestrial laser scanning to produce mineralogical maps of Late Albian rudist buildups of the Edwards formation in the Lake Georgetown Spillway in Williamson County, Texas. The Edwards Formation consists of shallow water deposits of reef and associated interreef facies. It is an aquifer in western Texas and was investigated as a hydrocarbon play in south Texas. Hyperspectral data were registered to a geometrically accurate laser point cloud-generated mesh with sub-pixel accuracy and were used to map compositional variation by distinguishing spectral properties unique to each material. More calcitic flat-topped toucasid-rich bioherm facies were distinguished from overlying porous sucrosic dolostones, and peloid wackestones and packstones of back-reef facies. Ground truth was established by petrographic study of samples from this area. This research integrates high-resolution datasets to analyze geometrical and compositional properties of this carbonate formation at a finer scale than traditional methods have achieved and to model the geometry and composition of rudist buildups. [ABSTRACT FROM AUTHOR]

Mapping the crustal structure beneath the South Yellow Sea (SYS), which includes the collision zone between the North China Block and the South China Block, will help to reveal the geologic history and relationship between these geologic blocks. Previous interpretations of the crustal structure of the SYS did not use detailed seismic velocity structure as a constraint. We produced an upper crustal velocity model of the northern SYS using a new wide-angle seismic dataset. Velocity anomalies resolved by our models correlate well with known features such as sedimentary basins and the tectonic uplifts in the SYS as low- and high-velocity anomalies, respectively. As might be expected, not only major faults and/or lithologic boundaries were found to be associated with large velocity gradients, but also our models exhibited resolvable deeply penetrating vertical low-velocity anomalies associated with the locations of strike-slip faults that were poorly resolved in an older seismic reflection profile. Our interpretations of the locations of major faults were based on the stacked seismic reflection profile and velocity modelling of wide-angle seismic array data and were extended to neighbouring regions by following trends in gravity, magnetic and earthquake location data. Faults traversing the North Basin of the SYS converged with the onshore Jia-Xiang Fault (JXF), suggesting that the branching of the JXF fault system controlled the formation of the North Basin. The distribution of the strike-slip faults resolved by our modelling of the JXF leads us to propose a model for the North Basin as a strike-slip stress regime that is consistent with the known tectonic framework. These models will be useful for future analysis of the regional tectonic evolution of the SYS region. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Full-waveform inversion (FWI) is an advanced seismic imaging method for determining high resolution velocity models of different scales, such as in subseafloor geo-hazard monitoring and risk analysis. Among all two-way wave-equation based modeling methods, a mixed-grid finite-difference modeling (FDM) in frequency domain has the advantage of low numerical dispersion errors for mesh size up to 1/4 wave-length. However, irregular source and receiver positions situated away from the FDM nodes introduce position approximation error (PAE) as large as half mesh size. When a source or receiver is situated in strong heterogeneity or near a free surface, the PAE induces imaging artifacts in high frequencies. We propose an imaging artifact suppression method for multi-scale FDM and FWI in marine seismic survey. The delta function of the source or receiver position is approximated by a discrete Kaiser-windowed sinc function in unbounded medium. The free-surface effects to sources and receivers are compensated with the mirror source concept. The final coefficients for delta function approximation and wavefield interpolation are spatially confined tensor products. The results using ocean bottom cable and vertical cable survey layouts in synthetic models validate the accuracy and feasibility of this new FDM and FWI strategy. The FWI tests shows that this strategy has reduced small scale artifacts at high frequencies for survey layouts of good and poor illuminations. The extension of our method to 3-D visco-acoustic model or reverse time migration is straightforward. • High resolution subseafloor geo-hazard monitoring. • Multi-scale visco-acoustic seismic inversion. • Seismic imaging artifacts suppression. • Positioning errors in marine environment. • Velocity model building for shallow marine strata. [ABSTRACT FROM AUTHOR]

How to determine the wavelet of air gun source and how to improve the performance of air gun source have gradually become two important topics in the field of air gun. The existing performance evaluation system of air gun array can only evaluate the performance of air gun from a single point of view, and can not characterize the change of three-dimensional acoustic field produced by air gun array. We first use the Van der Waals air gun wavelet model to simulate the three-dimensional air gun spatial wave field under real conditions. The experimental and modeled data are in good agreement at different pressure amplitudes and frequencies. Then, based on the three-dimensional spatial acoustic field simulated by the model, we proposed a facial characteristics to evaluate the time domain and frequency domain characteristics of the three-dimensional acoustic field. In this air gun wavelet evaluation system, we extend the evaluation parameters such as zero peak, peak-to-peak amplitude, bubble period and main bubble ratio from single wavelet to acoustic field, from one dimension to three dimension. By introducing the instantaneous property of wavelet, we can observe the amplitude, phase and frequency of the far-field wavelet from different angles. The experimental results show that the proposed air gun wavelet evaluation system can evaluate the spatial wave field from any Angle with multiple parameters, and effectively guide the optimization of the structure of the air gun array. • The Van der Waals air gun source model predicts the broadband data reasonably well • The actual data of air gun acoustic field is in agreement with the predicted data • The acoustic field distribution is demonstrated with the 3-D facial patterns [ABSTRACT FROM AUTHOR]