Onshore Seismic Data Research Articles

Monitoring volcanic activity with distributed acoustic sensing using the Tongan seafloor telecommunications cable

AbstractThe devastation caused by the January 2022 eruption of Hunga Tonga-Hunga Ha’apai volcano (HTHH) in the Tongan archipelago reminded us of the importance of monitoring shallow-sea volcanic activity. Seismic observations are essential for such monitoring, but there were no operational seismic stations in Tonga at the time of the eruption. There are only a few islands near Tongan volcanoes, and installation and maintenance of seismic stations on remote islands are expensive. Seismic observations based on distributed acoustic sensing (DAS) using a seafloor cable may provide a more practical and economical solution. To investigate the potential of this approach, we made preliminary DAS observations for 1 week using the seafloor domestic broadband telecommunications cable in Tonga. DAS equipment was installed at the landing station of the seafloor cable at Nuku’alofa on Tongatapu, the main island of Tonga. To provide reference data, we installed several seismometers on Tongatapu. The DAS data we obtained showed high noise levels in areas of shallow coral reef, but noise levels decreased greatly in deeper water areas, indicating that DAS is suitable for seismic observations of the deep seafloor. We detected many local and regional earthquakes during our week of observation and determined 17 earthquake hypocenters by picking P- and S-wave arrival times from the DAS and onshore seismic data. Although most of these were tectonic events related to the subduction of the Pacific plate along the Tonga trench, several events were detected around the volcanic chain of the Tongan archipelago including one event beneath the HTHH crater, implying that activity at HTHH has continued since the 2022 eruption. The much lower cost of installation of DAS equipment compared to that for pop-up type ocean-bottom seismometers and the ability of DAS systems to monitor seismic activity in real-time make it an attractive option for monitoring the activity of HTHH and other volcanoes near seafloor cables in the Tongan archipelago. Graphical Abstract

APPLICATION OF SURFACE CONSISTENT AMPLITUDE CORRECTION (SCAC) IN THE "HRNR" FIELD

This research aims to enhance the quality of 3D onshore seismic data and understand subsurface structures in a study area. We implemented the Surface Consistent Amplitude Correction (SCAC) method in seismic data processing. This study's results demonstrate that using SCAC significantly improves the quality of seismic data amplitudes, especially in eliminating previously disruptive noise in the analysis. Following the application of SCAC, seismic data amplitudes become clearer and stronger. The interpretation of the enhanced seismic data with SCAC revealed the presence of a significant geological structure, namely a reverse fault, which has significant implications for subsurface understanding. The location of this reverse fault was identified at inline 190 within the CMP range of 60 to 120, with time domain depths ranging from 150 ms to 1250 ms in the southwestern part of the cross-section. This research highlights that SCAC plays a key role in enhancing seismic data resolution and enables the identification of reverse faults that were previously challenging to discern. These findings make a crucial contribution to understanding subsurface geology in the study area and hold significant potential in the context of natural resource exploration. This study firmly establishes that SCAC is an effective tool in improving seismic data quality and revealing important geological structures, especially reverse faults, which can be a primary focus in subsurface geological studies in this research area.

An Efficient Transfer Learning-Based OBS Seismic Phase Picker (OBSPD) Trained on Cascadia Subduction Zone Earthquake Dataset

Abstract Earthquake monitoring and many seismological studies depend on seismic phase arrivals. Thus, detecting seismic events and picking the phase arrival times are fundamentally important. In the recent years, seismic phase picking models based on deep learning approaches have been widely developed. These deep learning models can achieve better performances than traditional phase picking methods and improve the quality of phase picking for land-based earthquake monitoring. However, these models might not perform well on data from ocean-bottom seismometers (OBSs), because they are trained exclusively using onshore seismic data and have limited out-of-distribution generalization ability. Nevertheless, there are insufficient labeled OBS phase arrivals dataset to train a deep learning model from scratch. In this study, we developed an automatic phase detection model for OBS data (OBS phase detection [OBSPD]) using the transfer learning approach based on an existing U-GPD model with pretrained weights from a generalized phase detection model feature extraction system. We developed OBSPD with a limited amount of training data (2784 three-component event waveforms) from the Cascadia subduction zone (CSZ) OBS deployments. Our results show that transfer learning can achieve lower model loss with less overfitting compared to when training a model from scratch. Our new OBSPD model outperforms four existing deep learning pickers in terms of phase detection accuracy with smaller arrival time residuals on a test OBS dataset at CSZ, especially for P phases.

Automatic 3D fault detection and characterization — A comparison between seismic attribute methods and deep learning

Seismic interpretation is crucial for identifying faults, fluid concentrations, and flow migration pathways in the oil and gas industry. Algorithms have been developed to identify faults using seismic data and attributes such as changes in amplitude, phase, polarity, and frequency. Despite technological advancements, challenges remain in seismic interpretation due to noise, quality of data, and fault dimensions. Deep learning has recently been applied to image faults from seismic data, making the process faster and more reliable. This paper evaluates the performance of deep neural networks (DNN) in fault interpretation by comparing the results with traditional seismic attributes in onshore seismic data. Our results indicate that the DNN reveals more structural detail, which is essential in characterizing 3D fault geometry. In addition, DNN results show better continuity, fewer false positives, and are less affected by noise in the onshore seismic data used in this case. The 3D fault model from DNN identifies faults and their fault segments with greater variability of strikes and reveals more minor faults. Based on the DNN fault model, we characterized the 3D geometry of a new fault in the Rio do Peixe Basin without noise influence.

Seismic characterization of Cenomanian–Turonian carbonate platform based on sedimentological and geophysical investigation of onshore analogue outcrop (northern Lebanon)

AbstractOutcrop analogues play a key role in the characterization of subsurface carbonate platforms. The lack of well data and relevant outcrop analogues can result in the misinterpretation of seismic data. To address this issue, we apply an integrated workflow based on sedimentology, geophysics and petrophysics on outcrop analogues present onshore Lebanon, to constrain the carbonate platform's properties on onshore seismic data. A thorough sedimentary description is completed for a 400‐m‐thick Cenomanian–Turonian carbonate platform located in Kfarhelda, northern Lebanon. P‐wave velocity is acquired directly on the outcrop, and the petrophysical properties are measured on 44 samples. A 1D synthetic seismogram is computed with Ricker wavelet 25 Hz resembling seismic resolution. The resulting reflectors are mainly (1) high amplitude reflectors at the limit between two facies with contrasting physical properties enhanced by diagenesis, (2) moderate amplitude reflectors corresponding to stratigraphic limits at the transition between facies and (3) very low amplitude reflectors in karstified units. The integration of outcrop and seismic data is based on the generation of the synthetic seismogram to identify the geological origin of reflectors. The best fit between the synthetic seismic and seismic profile is used to interpret a seismic facies representing bedded limestones of Sannine and Maameltain formations (Cenomanian–Turonian). Two other distinctive reflectors are identified at the boundary of the Marly Limestone Zone, and the Channel facies unit characterized by bioclastic packstone to floatstone. This study highlights the importance of using outcrop analogues to identify the seismic signal of stratigraphic sequences and improve the interpretation of onshore seismic data.

Onshore model building using elastic full-waveform inversion on surface and body waves: A case study from Sultanate of Oman

We have determined the potential of the elastic full-waveform inversion (FWI) to overcome some difficult challenges in onshore seismic imaging. The approach allows for simultaneous inversion of surface and body waves and, theoretically, is free from the limitations of traditional dispersion curve analysis and traveltime inversion. Indeed, identification and separation of different wavefield types are not required, and all wave types can be treated within a unified inversion scheme. However, FWI requires a reasonably good initial model, and the sensitivity of the misfit function with respect to the different wave types should be appropriately accounted for. This is the most essential step with onshore seismic data because the ground roll is much more energetic in comparison with the body waves. Our approach is based on a time-offset weighting function to balance the contribution of the different wave types in combination with a conventional frequency continuation approach. We first illustrate the feasibility of our approach on a 2D synthetic example representing a complex geology from south Oman. Then, we develop a 3D real data example from south Oman, where the application of our workflow till 8 Hz plays a pivotal role in retrieving a reliable model and in explaining the entire observed wavefields. In this example, the inversion of the ground roll helps improving the recovery of the shallow part of the earth, and hence better constraining the inversion of the body waves.

Subsurface Fluid Flow Feature as Hydrocarbon Indicator in the Alamein Basin, Onshore Egypt; Seismic Attribute Perspective

The interpretation of subsurface fluid flow features in seismic reflection data is a key part of identifying the presence of hydrocarbon and active petroleum systems. Currently, this kind of study is mainly conducted utilizing offshore seismic reflection data with very limited cases utilizing onshore seismic reflection data. In addition, the Alamein basin is an area of prolific study in onshore Egypt, with most related studies concentrating on basin analysis and reservoir characterization. Therefore, in our study we aimed to make practical and effective use of onshore seismic reflection data with seismic attribute analysis to describe seismic facies, delineating and interpreting subsurface fluid flow features. The relatively vertical V-shaped and pipe or concave-up-shaped features with distorted reflections inside them are revealed through the analysis of variance, sweetness, chaos, instantaneous frequency and the RMS amplitude of seismic attributes. These subsurface fluid flow features are a product of mature source rock that migrates hydrocarbon vertically through faults (especially deep-seated faults) and fracture systems (fault and fracture-related subsurface fluid flow features). The classification scheme presented in our study could be implemented in the onshore case worldwide.

The value of very low frequencies and far offsets for seismic data in the Permian Basin: Case study on a new dense survey from the Central Basin Platform

The depth of penetration and multidimensional characteristics of seismic waves make them an essential tool for subsurface exploration. However, their band-limited nature can make it difficult to integrate them with other types of ground measurements. Consequently, far offsets and very low-frequency components are key factors in maximizing the information jointly inverted from all recorded data. This explains why extending seismic bandwidth and available offsets has become a major industry focus. Although this requirement generally increases the complexity of acquisition and has an impact on its cost, improvements have been clearly and widely demonstrated on marine data. Onshore seismic data have generally followed the same trend but face different challenges, making it more difficult to maximize the benefits, especially for full-waveform inversion (FWI). This paper describes a new dense survey acquired in 2020 in the Permian Basin and aims to objectively assess the quality and benefits brought by a richer low end of the spectrum and far offsets. For this purpose, we considered several aspects, from acquisition design and field data to FWI imaging and quantitative interpretation.

The growing role of onshore seismic data in Australia

The growing role of onshore seismic data in Australia

A Layer-cell Tomography Method for Near-surface Velocity Model Building Using First Arrivals

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.

A skeptic's view of VVAz and AVAz

We have applied a modern amplitude- and azimuth-preserving seismic data processing workflow to the SEG Advanced Modeling Program (SEAM) Phase II Barrett classic data set — an orthorhombic synthetic seismic model that has extremely dense sampling of all azimuths and offsets. We analyze the resulting prestack depth-migrated offset vector tiles with a variety of methods and software. Note that we only analyze the P-P wave mode, which is the focus of our study. We demonstrate that observed azimuthal changes cannot be correlated with the model's reservoir properties. We have made the migrated data available through SEAM. Compared to modeled data, real onshore seismic data have significantly lower amplitude fidelity, higher noise levels, and more uncertainty in the migration velocity field used for processing. Since we are unable to relate the anisotropy measured from the fully sampled clean SEAM Phase II Barrett synthetic seismic data to the model's known anisotropy, we conclude that it is highly unlikely that azimuthal variations observed on real onshore seismic data will be predictive of reservoir fracture properties.

Land FWI in the Delaware Basin, west Texas: A case study

As part of a wide-reaching full-waveform inversion (FWI) research program, FWI is applied to an onshore seismic data set collected in the Delaware Basin, west Texas. FWI is routinely applied on typical marine data sets with high signal-to-noise ratio (S/N), relatively good low-frequency content, and reasonably long offsets. Land seismic data sets, in comparison, present significant challenges for FWI due to low S/N, a dearth of low frequencies, and limited offsets. Recent advancements in FWI overcome limitations due to poor S/N and low frequencies making land FWI feasible to use to update the shallow velocities. The chosen area has contrasting and variable near-surface conditions providing an excellent test data set on which to demonstrate the workflow and its challenges. An acoustic FWI workflow is used to update the near-surface velocity model in order to improve the deeper image and simultaneously help highlight potential shallow drilling hazards.

A case study of azimuthal fracture characterization in Cambay Basin, India

Shale gas, shale oil, tight-sand, heavy oil, gas hydrates and CBM are most important unconventional hydrocarbon resources of the 21st century. Tight-sand and shale plays are of low permeability, to exploit hydrocarbon economically, their permeability are increased artificially by creating fractures, which is termed as fracking. Ever widening gap between import and domestic hydrocarbon production in India mandates efficient exploitation of unconventional hydrocarbons. Prevailing hydrocarbon market does not support acquisition of specialized seismic data and specialist software for unconventional hydrocarbon exploitation. It is imperative to devise cost effective way of exploiting tight sand, shale oil and gas. Natural fractures in tight sand and shale plays are helpful in production, its characterization is important. Since seismic amplitude varies along and across swarms of fractures, Multi-Azimuth seismic data can be analyzed for fracture characterization. Onshore seismic data, which are acquired and processed for conventional seismic exploration, can be used in unconventional exploration/exploitation after 5d interpolation of the seismic data in inline, crossline, offset, azimuth and frequency. We analyze seismic amplitude variation with offset and azimuth using conventional seismic data from Cambay Basin, in India for fracture characterization by making the data rich in azimuth by 5d interpolation.

Using Tsunami Waves Reflected at the Coast to Improve Offshore Earthquake Source Parameters: Application to the 2016 Mw 7.1 Te Araroa Earthquake, New Zealand

AbstractThe Te Araroa earthquake occurred on 2 September 2016 (local time) offshore of the northeastern coast of New Zealand's North Island (Mw 7.1). When this event occurred, ocean bottom pressure gauges (OBPs), installed ~170 km south of the source area, clearly recorded direct tsunami from the source to OBPs (~ −1.5 cm), and tsunami from coastal reflections (~2 cm). We estimate the centroid location that best reproduces the OBP waveforms. When using the direct wave alone, the centroid location is poorly constrained, with a horizontal uncertainty of ~100 km. By combining both direct and reflected tsunami waveforms, we obtain a centroid location near the Global Centroid Moment Tensor centroid (~80 km northeast from the coast) with smaller uncertainty (~40 km). We also estimate the earthquake source dimension (length and width) and found that the models using coastal reflections require a source dimension larger than ~30 km long. Based on the slip distribution obtained by the finite fault inversion, we obtain an energy‐based stress drop ΔσE of 1.0 MPa, consistent with typical earthquake stress drop values. This study shows that the information added by coastal reflected tsunami provides much tighter constraints on the centroid location, source dimension, and stress drop of offshore earthquakes, which is difficult to obtain from the onshore seismic data alone. Future studies should utilize the information provided by coastal reflected waves to improve earthquake source modeling using ocean bottom pressure data.

Application of 3-D FKK Filtering in 3-D High-density Onshore Seismic Field Data

For linear noise such as seismic ground roll, 3-D frequency-wavenumber-wavenumber (3-D FKK) domain filtering suppression is better than 2-D frequency-wavenumber (F-K) domain filtering. In recent years, with the continuous development of computer processing speed and memory capacity, high-density data acquisition in seismic exploration has been widely applied in the hydrocarbon industry, opening up the application of 3-D FKK filtering methods. We applied the 3-D FKK filtering software to a 3-D high-density onshore seismic field dataset from a coal mine in western China. The case study demonstrates that the linearity of the noise in the field data is better represented by constructing the single shot records as a minimum dataset. Both theoretical synthetic models and the 3-D high-density onshore seismic field data numerical filtering experiments demonstrate that the feasibility of 3-D FKK filtering.

3-D Butterworth Filtering for 3-D High-density Onshore Seismic Field Data

Three-dimensional seismic survey is widely applied, but 3-D filtering technology has yet to be fully utilized for the analysis of seismic field data. The common approach is to first filter inline and then crossline. However, an effective 3-D filtering method is expected to eliminate coherent noise, such as the ground roll. We propose a 3-D Butterworth filtering method in the time-space domain. Firstly, a Butterworth-type filter in the frequency-wavenumber-domain is designed to suppress the linear noise with a specific apparent velocity. Secondly, transforming this filter to the time and space domain yields 3-D partial differential equations (PDEs), which are applied to suppress the linear noise. Factorizing the finite-difference equations in a different direction other than decreasing the 3-D PDEs to 2-D PDEs produces a highly accurate and efficient algorithm. Designing the 3-D Butterworth filter, selecting the filtering parameters, and showing its application to synthetic data and a 3-D high-density onshore seismic field data from a region in western China are discussed in detail. Numerical experiments with 3-D high-density onshore seismic field data demonstrate that it is more effective than the 3-D frequency-wavenumber-wavenumber (FKK) filtering method.

Estimation of Seismic Centroid Moment Tensor Using Ocean Bottom Pressure Gauges as Seismometers

AbstractWe examined the dynamic pressure change at the seafloor to estimate the centroid moment tensor solutions of the largest and second largest foreshocks (Mw 7.2 and 6.5) of the 2011 Tohoku‐Oki earthquake. Combination of onshore broadband seismograms and high‐frequency (~20–200 s) seafloor pressure records provided the resolution of the horizontal locations of the centroids, consistent with the results of tsunami inversion using the long‐period (≳10 min) seafloor pressure records although the depth was not constrained well, whereas the source locations were poorly constrained by the onshore seismic data alone. Also, the waveforms synthesized from the estimated CMT solution demonstrated the validity of the theoretical relationship between pressure change and vertical acceleration at the seafloor. The results of this study suggest that offshore pressure records can be utilized as offshore seismograms, which would be greatly useful for revealing the source process of offshore earthquakes.

Design of an Optimal High Pass Filter in Frequency - Wave Number (F-K) Space for Suppressing Dispersive Ground Roll Noise from Onshore Seismic Data

The ultimate goal in seismic signal processing (pre- processing or main processing) is to enhance the signal to noise ratio (S-N-R). In this study, two high pass (low cut frequency) filters were designed in frequency - wave number (F-K) space and applied to onshore 3D seismic data acquired from a typical Niger Delta field to suppress dispersive ground roll in a bid to enhance S-N-R. The seismic shot records were initially displayed to show the seismic data ensembles in the conventional offset - time (X-T) domain. A frequency - wave number spectrum was then created using a VISTA software algorithm to analyze the spectral patterns of the signals and noise. Two high pass filters were then designed in the F-K space to mute the low frequency ground roll from the data. The filters were then applied to the entire seismic data ensemble for the filtering operation. The results obtained after the two filtering operations were compared to ascertain the optimal filter which was most effective for the suppression of the unwanted ground roll noise.

Offshore Rayleigh group velocity observations of the South Island, New Zealand, from ambient noise data

We thank Captain and Crew of the R/V Thomas G. Thompson (cruise TN229), the R/V Roger Revelle (cruise RR1002), and the SIO OBSIP facility for expert assistance at sea. The OBS instruments used in this field program were provided by the U.S. National Ocean Bottom Seismic Instrumentation Pool (http://www.obsip.org). MOANA seismic data are archived at the IRIS Data Management Center. The collection of ocean bottom seismic data was funded by the National Science Foundation under grants EAR-0409564, EAR-0409609, and EAR-0409835. New Zealand onshore seismic data made available by the GeoNet project, sponsored by EQC, GNS Science, and LINZ. J. Stachnik acknowledges support from the CIRES postdoctoral fellowship program.. F.-C. Lin was supported by NSF grant CyberSEES- 1442665 and the King Abdullah University of Science and Technology (KAUST) under award OCRF-2014-CRG3- 2300. We thank Martha Savage, Dan Zietlow, Justin Ball, Craig Jones, Bill Fry, and Peter Molnar for valuable comments and discussion, and John Collins for leading the MOANA OBS experiment. We thank two anonymous reviewers and Editor Mike Ritzwoller for their constructive comments.

Triassic to recent tectonic evolution of a crestal collapse graben above a salt-cored anticline in the Glückstadt Graben/North German Basin

In this study we investigate faulting above a salt wall in the Glückstadt Graben/North German Basin. Two supra-salt faults are mapped from coast to coast over a distance of 6–9km based on offshore and onshore seismic data. These faults form a ca. 2km wide crestal collapse graben and pierce the seafloor. Salt wall evolution started in the early Late Triassic to Early Jurassic due to regional extension and resulting sub-salt faulting. The salt wall was eroded following exposure to costal and sub-aerial erosion by the regional Mid-Late Jurassic to Early Cretaceous uplift. Late Cretaceous to Early Paleogene compressional tectonics reactivated the vertical salt movement and shortened the salt wall, creating a salt-cored anticline with the crestal collapse graben above. The supra-salt faults were reactivated between the Late Eocene and Middle Miocene when the principal horizontal stress orientation changed from a NE–SW to a NW–SE, the present-day orientation. Stratigraphic data indicate that these faults moved mainly in the Cenozoic. Several observations strongly suggest that the faults continued developing during the Pleistocene until today: (i) the Pleistocene Unconformity is concave upwards and cut by faults; (ii) growth strata within the marine Holocene deposits above the graben imply recent tectonic movements; (iii) onshore high-resolution P-wave vibroseis data of the south-eastern Eckernförde Bay suggest about 10m of faulted Holocene strata; and (iv) marine seismic data show the faults piercing the seafloor. We suggest that the recent salt tectonics and upward propagation of supra-salt faults resulted from differential ice-sheet loading. That effect on the salt wall stopped once ice grew over the whole structure, at which time the wall subsided because of ice loading. The salt wall and faults were reactivated again once the ice front retreated so that the ice loaded only one side of the structure.