Active Seismic Exploration Research Articles

Hydroacoustic Monitoring of Mayotte Submarine Volcano during Its Eruptive Phase

Submarine volcanoes are more challenging to monitor than subaerial volcanoes. Yet, the large eruption of the Hunga Tonga-Hunga Ha’apai volcano in the Tonga archipelago in 2022 was a reminder of their hazardous nature and hence demonstrated the need to study them. In October 2020, four autonomous hydrophones were moored in the sound fixing and ranging channel 50 km offshore Mayotte Island, in the North Mozambique Channel, to monitor the Fani Maoré 2018–2020 submarine eruption. Between their deployment and July 2022, this network of hydrophones, named MAHY, recorded sounds generated by the recent volcanic activity, along with earthquakes, submarine landslides, marine mammals calls, and marine traffic. Among the sounds generated by the volcanic activity, impulsive signals have been evidenced and interpreted as proxy for lava flow emplacements. The characteristics and the spatio-temporal evolution of these hydroacoustic signals allowed the estimation of effusion and flow rates, key parameters for volcano monitoring. These sounds are related to the non-explosive quenching of pillow lavas due to the rapid heat transfer between hot lava and cold seawater, with this process releasing an energy equivalent to an airgun source as used for active seismic exploration. Volcano observatories could hence use autonomous hydrophones in the water column to detect and monitor active submarine eruptions in the absence of regular on-site seafloor survey.

Shear-Wave Velocity Model from Site Amplification Using Microtremors on Jeju Island

This study examines shear-wave velocity structures in the Jeju region utilizing horizontal-to-vertical spectral ratios (HVSRs) of environmental noise, focusing on identifying significant low-velocity layers (LVLs). Although conventional methodologies predominantly involve borehole and active seismic exploration, recent advancements in the diffuse-field theory of seismic waves have offered a theoretical foundation for this approach. In the volcanic region of Jeju Island characterized by unique geological features, a pervasive LVL composed of quaternary marine sediments and the Seoguipo sedimentary layer has been observed. These components are crucial for site amplification and attenuation in seismic microzonation. The present study introduces a novel discovery of a distinct LVL, specifically at the UDO site, suggesting that its origin may be attributable to a local magmatic intrusion event. Advanced algorithms and HVSR curve analysis have enabled reliable inversion processes, enhancing the comprehension of the subsurface geology of Jeju. These insights are essential for seismic microzonation practices and contribute significantly to the development of seismic design standards in the Jeju region.

3-D body-wave tomography from the seismic ambient noise recorded by a dense array in the Dehdasht area, Iran

SUMMARY The strong attenuation of the thick sedimentary layers in the Dehdasht region, Iran, renders active seismic exploration surveys difficult. The imaging of the existent limestone reservoirs is limited to the shallow subsurface due to the strong attenuation of seismic waves. Here, we discuss a different approach to imaging the subsurface using body waves extracted from the cross-correlation of the seismic ambient wavefield. We discuss the technical challenges to extracting clear P-wave arrivals from the seismic ambient wavefield of a dense 3-component seismic array deployed in the Dehdasht basin. We invert the data for the 3-D P-wave velocity structure and compare the velocity model with results from the 2-D active seismic surveys in the area. The results show the potential of using body waves extracted from the seismic ambient wavefield for imaging purposes in highly attenuating areas.

Active seismic exploration along a human lunar mission traverse analogue in the San Francisco volcanic field

Lunar surface activities during Apollo and terrestrial analogue lunar mission simulations have commonly focused on traverses that prioritize surface observations and sample collection activities. Along the way, geophysical measurements are often made. However, they are not necessarily made in a way that optimizes information about the physical subsurface properties, which is something that geophysics can provide. In 2010, NASA simulated a high-quality multiweek human lunar rover traverse analogue mission in the San Francisco volcanic field in Arizona. The traverse route and associated science station locations were selected based on addressing surface observation and sampling tasks. Geophysical studies were not included in the simulation. We returned to the same field area and obtained data on 19 active seismic refraction geophone lines from the science station locations accessed during the simulation. We analyzed the data to calculate 1D seismic velocity profiles for each of the lines. Results revealed up to seven distinct seismically defined material types, including a nearly ubiquitous veneer of regolith of variable thickness at the surface. Results also provided depth and thickness of the seven material types in the first 60 m of the subsurface at each of the science station locations. These cannot be obtained by geologic observations of the outcrops. Systematic interpretation of the area's overall subsurface stratigraphy was not feasible due to the geophysically nonsystematic nature of the original traverse's prioritization of the science station locations. The added geophysical understanding of a region could drive additional geologic investigations to locate samples of otherwise unknown material through the location of surface exposures or coring. This emphasizes the importance of synchronizing geologic and geophysical research requirements during lunar traverse planning and execution to optimize addressing scientific and utilization questions.

Correlation-Based Interferometry Method to Enhance Near-Surface Reflection Signals in Surface Active Seismic Exploration

In surface active seismic exploration, the near-surface imaging based on reflection signals provides valuable information for mineral exploration and deeper resources. However, the strong noises at near surface and stretching effects at nonzero offsets with conventional seismic data processing method severely damage the seismic reflection signals with low fold at near surface. The innovative method for the enhancement of seismic signals is the seismic interferometry method. However, due to the one-sided illumination, the seismic interferometry is still not suitable for the retrieval of reflection signals in most practical situations. In this article, we present the correlation-based interferometry (CI) method to enhance the reflection signals for near-surface imaging using the first cross correlation to construct virtual reflection signals and the second cross correlation to achieve the interferometric normal move-out (INMO) correction of the seismic reflection events with no stretching, which keeps the high resolution of near-surface reflection signals. Meanwhile, because of constructive interference stack, the CI method can significantly improve the signal-to-noise ratio (SNR) of reflection signals. The synthetic and field seismic data examples illustrate that the data-driven CI method performs better than the conventional stack (CS) method based on the velocity model for the near-surface reflection imaging.

Snow crab (Chionoecetes opilio) hepatopancreas transcriptome: Identification and testing of candidate molecular biomarkers of seismic survey impact

The eastern slope of the Grand Banks, Newfoundland and Labrador, Canada, represents an area where active seismic exploration overlaps extensively with an important snow crab (Chionoecetes opilio) fishery. Field studies were conducted in 2016 and 2017 to investigate the potential impact of seismic oil and gas surveying exposure on the transcriptome of the snow crab hepatopancreas, which is involved in metabolism and response to environmental stress. In 2016, snow crabs were subjected to 2D seismic noise for 2 h and sampled before (i.e. pre-seismic), and 18 h and 3 weeks after exposure in Carson Canyon (CC). In 2017, the 2D seismic exposure was repeated and samples were collected before and 1 day, 2 days, and 6 weeks after exposure in CC. Additionally, in 2017, snow crabs were subjected to 3D seismic noise for 2 months and sampled during and 6 weeks after exposure at a site north of CC. In both years, snow crabs were also collected from a separate non-seismic exposed site [Lilly Canyon (LC)]. RNA-seq was used to identify candidate seismic-responsive molecular biomarkers in 2016. The quantified transcripts of individuals (i.e. n = 10 from each of the four 2016 groups) were compared using two differential expression analysis methods (DESeq2 and edgeR), identifying a total of 1088 and 389 differentially expressed transcripts, respectively. Real-time quantitative polymerase chain reaction (qPCR) assays were designed and run for 83 of these transcripts to confirm RNA-seq results, identifying 9 transcripts with significantly higher expression after seismic exposure at the CC site, and 14 transcripts with significant differential expression between the CC site and the non-seismic LC site. Functional annotations associated with candidate seismic-responsive genes included oxidoreductase activity, apoptotic process, and inflammatory response. To further investigate the performance and utility of candidate biomarkers identified using the 2016 samples, expression levels of 20 selected transcripts were then examined in 2017 samples using both qPCR and multivariate statistical analyses. Principal component analysis of qPCR data separated exposure groups in 2016 but did not result in clear separation of groups in 2017, although some transcripts showed similar trends in both years. This work has built a strong foundation for future research involving the snow crab hepatopancreas transcriptome and its potential responses to environmental stressors including seismic surveying noise.

Study on the characteristics of microseismic wave field of complex medium model in coal mine

In order to provide an effective theoretical basis for the location of microseismic source, active seismic exploration technology, and internal medium structure inversion of coal mine in different areas, we analyze the propagation law of microseismic wave in different medium accurately and intuitively. In this paper, we first studied the finite difference method suitable for the analysis of wave field characteristics of coal and rock medium in a coal mine. Then, we established the typical models of coal-rock combination multi-layer medium, fault-bearing coal-rock medium, coal-rock dual-phase medium of water-bearing and gas-bearing and stochastic medium model, and random medium model. Finally, we obtained the wave field snapshot and single shot recording of different medium model. The research shows that the high-order finite difference method can accurately obtain P and S waves field characteristics under different media conditions. The wave field characteristics of different medium models are different. In the coal-rock combination multi-layer model, the transmitted wave, transmitted converted wave, reflected wave, and reflected converted wave are generated on the different medium interfaces. In the fault model, not only the transmitted wave, transmitted converted wave, reflected wave, and reflected converted wave but also the refracted and diffracted waves are produced at fault area. In the coal-rock dual-phase medium of water-bearing and gas-bearing model, three types of waves are excited by the source, which are fast longitudinal (P) waves, transverse (S) waves, and slow longitudinal (P) waves. However, the propagation of slow longitudinal wave is different in these models. Under the stochastic media model, there are very complex scattering waves. The snapshots at different time further describe the wave field’s dynamic characteristics vividly, which establish the theoretical basis of the analysis of microseismic waves. Based on the analysis of the wave field characteristics of coal and rock in the mine, it can provide theoretical support and basis for the active seismic exploration and internal medium structure inversion of coal mine in different areas. What’s more, a more practical wave velocity model can be established to provide an effective theoretical basis for the location of microseismic source. When there is a disaster in the coal mine, we can determine the exact location of the source as soon as possible and take corresponding measures.

An Iterative Focal Denoising Strategy for Passive Seismic Data

Passive seismic source imaging can extract geophysical information from underground noise and has been widely utilized in geophysical research. Compared with conventional active seismic exploration, it is low-cost and eco-friendly; however, the application of passive seismic data is limited by coherent noise in the virtual-shot gathers. An approach involving direct denoising in the virtual-shot gathers has not previously been discussed; therefore, we present an iterative denoising strategy for passive seismic data. The reflection-preserving characteristic of focal transformation is adopted in the virtual-shot gathers to eliminate the coherent noise, and L1-norm sparse inversion is utilized to obtain a more accurate solution during focal transformation. A key aspect of this strategy is clean focal operator building at high noise levels. We apply local similarity as the criterion for extracting the majority of reflection energy for the focal operator. Because of strong coherent noise, a clean focal operator cannot be obtained in one iteration. We therefore obtain both denoised passive seismic data and a clean focal operator by denoising using a cleaner focal operator and operator building using updated denoising results. The presented approach can overcome the limits of coherent noise in virtual-shot gathers, which is significant for subsequent data processing and wider application. Synthetic examples achieve excellent performance in coherent noise attenuation and reflection energy reconstruction, especially in far-offset sections.

Three-dimensional supervirtual seismic refraction interferometry

Improved supervirtual interferometry (SVI) method that enhance the signal-to-noise ratio (SNR) of noisy seismic refraction data is presented. This 3D supervirtual algorithm is helpful in removal of side lobes caused by convolution in the conventional 3D SVI method. In this study, we extend the supervirtual seismic refraction interferometry method to 3D geometries commonly used in active seismic exploration. To achieve this objective, synthetic 3D seismic refraction data were created using single patch orthogonal geometry. Simple two-layers velocity model was used. A zero phase wavelet was convolved with the refraction travel time to create the seismic wiggle trace. The refraction arrival is computed using the equation for horizontal refractor case and is not adapted for dipping refractor. Noise of Gaussian distribution with zero mean and 0.25 standard deviation was added to simulate a case of moderate ambient noise. The supervirtual algorithm, consisting of crosscorrelation, alignment, summation, and first arrival calculation is performed. By aligning and summation of all the correlogram, the stationary position of source-receiver pairs as required in the 2D supervirtual method are eliminated in this case. Synthetic data presented in this study shows accurate first arrivals after the application of the 3D SVI and traces with much better SNR than the actual traces.

Reflection images from ambient seismic noise

One application of seismic interferometry is to retrieve the impulse response (Green’s function) from crosscorrelation of ambient seismic noise. Various researchers show results for retrieving the surface-wave part of the Green’s function. However, reflection retrieval has proven more challenging. We crosscorrelate ambient seismic noise, recorded along eight parallel lines in the Sirte basin east of Ajdabeya, Libya, to obtain shot gathers that contain reflections. We take advantage of geophone groups to suppress part of the undesired surface-wave noise and apply frequency-wavenumber filtering before crosscorrelation to suppress surface waves further. After comparing the retrieved results with data from an active seismic exploration survey along the same lines, we use the retrieved reflection data to obtain a migrated reflection image of the subsurface.

Brief note for consideration of active seismic exploration on Mars

Considerable controversy has arisen regarding the existence of water and water ice below the surface of Mars. Results of laboratory internal friction measurements on strongly outgassed rocks, recently made as part of an effort to interpret the high seismic Q values observed in the lunar crust, show that moisture absorbed in pores and cracks causes the low Q values. Unfortunately, the Viking seismology investigation found a surprisingly inactive planet. This note makes the case for active seismic exploration in order to ascertain the existence of liquid water in the crust from Q determinations.

Directional Acoustic-Velocity Distribution in a Petroleum Reservoir

Abstract Experimental conditions, theoretical considerations, and results of adirectional acoustic-velocity survey in the plane of formation of an oilreservoir in Pennsylvania are given. More than 60 blasting-cap acoustic sourceswere discharged opposite the Bradford Third sand in 10 different wells locatedwithin a 1,200- by 1,350-ft rectangular array of 41 wells. Each source wasmonitored simultaneously by 11 different hydrophones strategically locatedwithin the 41-well array. Both acoustic sources and sensors were located at theformation elevation, about 2,000 ft below the surface, so that the in-situvelocities determined were in the plane of the sandstone formation. Well-to-well acoustic velocities were calculated and are presented in tabularand graphical form. The velocity data were further analyzed statistically toyield over-all reservoir velocity trends. Results of the study show that thereservoir is acoustically heterogeneous, with local variations in P-wavevelocity of as much as 20 percent. The over-all P-wave velocity trend for thereservoir was greater in the east-west direction than in the north-southdirection by about 700 ft/sec. The mean acoustic velocity for all wells in alldirections was 15,621 ft/ sec. The acoustic-velocity distribution is also correlated to directionalpermeability data obtained by oriented core analyses. Introduction The directional variation of geophysical properties affecting wave propagationhas long been known. A brief examination of the history and evolutionaryprocesses of sedimentary rock should leave no doubt about the nature of theformations. However, little attention has been given to directional propertiesin the evaluation and recovery of natural resources. Evaluation of thedirectional acoustic (seismic) velocity distribution in reservoirs is perhapsthe most promising means of evaluating directional reservoir properties. Themagnitude of directional variation can be predicted to a degree by consideringthe lithology and the geological features of an area. However, there are alwaysuncertainties in the study of wave propagation through the earth; numerousvariables influencing wave-propagation velocities have been determined. This research was initiated originally to aid in acoustically mapping thegrowth of hydraulically induced fractures in time and space, and to assist indelineating existing fracture systems. The reservoir investigated had been thesubject of other research programs, and considerable information was available.Using the available information, however, large directional variations inacoustic velocities over small areas would not necessarily have beenanticipated. As will be shown, the velocity variations were substantial andwere correlatable, to a degree, with other geophysical and reservoirproperties. Since the late 1940's and early 1950's, a tremendous amount of work has beendone in active and passive seismic monitoring and in the general area of wavepropagation through geological materials. Most of the work falls into one offour general categories:active seismic exploration,passive earthquakeor nuclear undergroundexplosion monitoring,active oil and gas welllogging, androck noise and slope-stability studies. Obviously, eachcategory directly or indirectly involves the directional nature of propagationvelocities. The first two categories, and usually the fourth, are associatedwith very low frequency monitoring systems, such as geophones usually operatingin the 0- to 50-hz range. Frequencies used in Category 3 are usually in the20-khz range since the waves typically are transmitted only 3 ft verticallyfrom a transmitter to a receiver.

Seismic Space-Time Processing

Frequency filtering and spatial filtering have been usefully applied for many years to the problem of extraction of signals from noise in active seismic exploration and in passive earthquake surveillance. Because broadband (octave or more) transients are of interest in both areas, frequency dependent spatial filtering has been frequently used. In some cases, interfering noise is spatially nonrandom, and “optimum” space-time filters are used to advantage. Essentially similar spatial response is usually obtained independent of the “optimization” criteria (e.g., least squares, maximum likelihood). Similar techniques may be used to employ arrays with complex inter-element signal relationships (such as combinations of horizontal and vertical motion seismometers). Although useful coherent properties of signal and noise can be exploited with an assumption of space stationarity, time stationarity, or space-time stationarity, in many cases use of space-time varying optimization is worthwhile and is being increasingly employed. Some of the current approaches to tracking down useful statistical space-time properties of signal and noise and their exploitation in seismic information extraction will be discussed.