Seismic Land Research Articles

Combination of Fourier and CRS-Based Reconstruction Algorithms in Land Seismic Data

ABSTRACT. The reconstruction based on the partial CRS stacking operator presents higher signal-to-noise ratio and better continuity of events. However, irregularly sampled land data often introduce errors in the CRS attributes, creating artifacts that contaminate the seismic data. Recently, the combination of Fourier and CRS-based reconstruction algorithms has significantly solved these problems. The approach consists of applying a Fourier-based interpolation method as a regularization operator to the original data and then the CRS attributes are searched in the reconstructed data. The CRS attributes determined in this way are more accurate and they can be applied in two different forms, either in the interpolation and regularization of the original data or in the denoising of the Fourier-based reconstructed data. We propose to compare the combination of the Fourier-based interpolation methods MWNI and MPFI with the CRSbased interpolation method in order to evaluate which is the best preconditioner of the prestack data to search the CRS attributes. We applied the proposed flowcharts combining the interpolation methods mentioned above to the land seismic data from the Tacutu basin, which is vintage data with very low fold and noisy. The reconstructed data obtained by the combinations show significant improvements compared to the data reconstructed using the algorithms separately, in other words, the weaknesses and limitations of each method are overcome when they are applied in combination. The MWNI+CRS combination flow produces the best results, with the stacked section of reconstructed data showing better noise removal, enhancement of coherent events, better definition and continuity of steeply dipping events.

The First Network of Ocean Bottom Seismometers in the Red Sea to Investigate the Zabargad Fracture Zone

In the last decades, the slow-spreading Red Sea rift has been the objective of several geophysical investigations to study the extension of the oceanic crust, the thickness of the sedimentary cover, and the formation of transform faults. However, local seismology datasets are still lacking despite their potential to contribute to the understanding of the tectonic evolution of the Red Sea. The Zabargad Fracture Zone is located in the Northern Red Sea and significantly offsets the rift axis to the East. Thus, it is considered a key tectonic element to understand better the formation of the Red Sea rift. To fill the gap in the dataset availability, we deployed the first passive seismic network in the Red Sea, within the Zabargad Fracture Zone. This network included 12 Lobster OBSs from the DEPAS pool, 2 OBS developed and deployed by Fugro, and 4 portable seismic land stations deployed on islands and onshore on the Saudi Arabian coast. Our data-quality analysis confirms that the head-buoy cable free to strum, as well as other additional elements of the DEPAS OBSs, generate seismic noise at frequencies $>$ 10 Hz. However, the Fugro OBSs show high-frequency disturbances even if they lack vibrating elements. Comparison between land and OBS stations reveals that noise between 1 and 10 Hz is due to ocean-generated seismic noise, and not due to resonance of the OBS elements. We also found that waveforms of teleseismic earthquakes recorded by the Fugro OBSs, islands, and onshore stations have comparable signal-to-noise ratios. Instead, differences in signal-to-noise ratio for local earthquakes are affected more by site and path effects than instrument settings.

The portable hand streamer — Rapid seismic imaging for shallow targets

In this paper, we introduce a portable hand streamer seismic system. The system is appropriate for characterizing the mechanical properties of geologic and engineered materials in the upper 5 to 10 m depth and for reflection imaging from tens to hundreds of meters depth. Unlike other seismic land streamer systems that are typically pulled behind a vehicle with a long string of geophones, our recording system and electric seismic source are contained within an electric utility cart to allow ease of mobility for a single operator. Our 48-channel contact-coupled streamer is tethered to the cart to enable low-effort data collection. Similar to a ground-penetrating radar system, this approach allows rapid data collection on roads, sidewalks, undeveloped paths, and native materials. Signal processing through standard surface- and body-wave approaches follows data collection. We present three case studies where we (1) map Quaternary and older strata to identify active faulting, (2) map shallow bedrock, and (3) identify the footprint of previous subsurface engineered structures. We suggest that this low-cost tool and approach can be used for decameter-scale subsurface site characterization in two or three dimensions. Future advances involve the integration of an autonomous vehicle with a fully programmable seismic source and wholly automated signal processing to enable real-time analysis of shallow seismic data.

Ambient Noise Monitoring and HSE Risk Mitigation by the Deployment of IoT Technology on Land Seismic Crews

Ambient Noise Monitoring and HSE Risk Mitigation by the Deployment of IoT Technology on Land Seismic Crews

Developing a distributed acoustic sensing seismic land streamer: Concept and validation

Motivated by existing cabled seismic land-streamer designs, we develop a distributed acoustic sensing (DAS) land-streamer system for high-resolution near-surface seismic data acquisition. The system consists of a DAS interrogator unit (IU), a fiber-optic cable attached beneath a fire-hose assembly for environmental isolation and improved fiber-ground coupling, and a vehicle-mounted accelerated weight-drop source. The DAS land streamer is easily deployed and towed along the ground surface, allowing for spatially dense data acquisition. We report two field tests with the developed hardware to evaluate the DAS land-streamer performance. The first test investigates the effects of hose weight on the surface-deployed fiber and indicates that this approach improves fiber-ground coupling and leads to an improved signal-to-noise ratio (S/N). The second test demonstrates that the DAS land streamer records waveforms with similar phase and moveouts as those recorded by horizontal geophones but offers a higher native spatial density advantage than standard geophone arrays, leading to spatially dense waveforms, improved S/N after postprocessing, and superior surface-wave acquisition array mobility. Our findings suggest that a DAS land streamer is a promising alternative to traditional geophone-based surveys and may offer several advantages, such as faster survey acquisition speed and lower field costs due to reduced acquisition hardware requirements. However, methodological limitations include recording a single horizontal ground-motion component, a dependence on favorable fiber-ground coupling conditions, and the upfront cost of IU procurement. A DAS land streamer may be useful in numerous subsurface applications, such as (pseudo) 1D multichannel analysis of surface waves or 2D surface-wave inversion for S-wave velocity model estimation for geophysical, geologic, geotechnical, and environmental investigations.

Assessment of Land Deformation and the Associated Causes along a Rapidly Developing Himalayan Foothill Region Using Multi-Temporal Sentinel-1 SAR Datasets

Land deformation has become a crucial threat in recent decades, caused by various natural and anthropogenic activities in the environment. The seismic land dynamics, landslides activities, heavy rainfall resulting in flood events, and subsurface aquifer shrinkage due to the excessive extraction of groundwater are among the major reasons for land deformation, which may cause serious damage to the overall land surface, civil infrastructure, underground tunnels, and pipelines, etc. This study focuses on preparing a framework for estimating land deformation and analyzing the causes associated with land deformation. A time-series SAR Interferometry-based technique called PsInSAR was used to measure land deformation, using Sentinel-1 datasets from 2015 to 2021 by estimating land deformation velocities for this region. The obtained PSInSAR deformation velocity results ranged between −4 mm to +2 mm per year. Further, land use land cover (LULC) changes in the area were analyzed as an essential indicator and probable cause of land deformation. LULC products were first generated using Landsat-8 images for two time periods (2015, 2021), which were then evaluated in accordance with the deformation analysis. The results indicated an increase in the built-up areas and agricultural cover in the region at the cost of shrinkage in the vegetated lands, which are highly correlated with the land subsidence in the region, probably due to the over-extraction of groundwater. Further, the outer region of the study area consisting of undulating terrain and steep slopes also coincides with the estimated high subsidence zones, which could be related to higher instances of landslides identified in those areas from various primary and secondary information collected. One of the causes of landslides and soil erosion in the region is identified to be high-level precipitation events that loosen the surface soil that flows through the steep slopes. Furthermore, the study region lying in a high seismic zone with characteristic unstable slopes are more susceptible to land deformation due to high seismic activities. The approach developed in the study could be an useful tool for constant monitoring and estimation of land deformation and analysis of the associated causes which can be easily applied to any other region.

Late Quaternary Activity: Kouma Fault

The Kouma Fault, located at the northern foot of the Mangshan Mountain in Luoyang City, Henan Province, China, is an active fault newly discovered in the field seismic geological survey. The Kouma Fault is a normal fault that is approximately 30 km in length, near the east-west strike, and the north dip. The study on the nature of the Quaternary activity of the Kouma Fault is of great significance to the potential seismic source zone division, urban and rural land planning, site selection for major projects, the assessment and prevention of earthquake disaster risk. Through a series of seismic geological surveys, 12 fault outcrops were discovered, which were all distributed on the slopes of the loess gullies. The Kouma Fault cuts loess, clay, sand, and gravel. The fault planes and scratch can be seen clearly. The filling in the fault zone is dominated by clay, loess, and pebbles, among others. When the width of the fault zone is smaller (10–30 cm), most clay in the zone is laminated in occurrence. The laminated surface is almost parallel to the fault plane and the long axis direction of pebbles in the fault zone is almost parallel to the fault plane. When the width of the fault zone is greater (for instance, 1.6 m), the clay and loess in the fault zone are massive. The composite drilling geological section and trench reveal two paleoseismic events of the Kouma Fault, the paleoseismic event I occurred at the fault in the Middle Pleistocene; the paleoseismic event II occurred at the fault in the later period of the Late Pleistocene, and the vertical offset of the upper Pleistocene bottom boundary is 13.57 m. Based on the OSL age data in the fault G1 outcrop of the fault and TC1 and TC2 trenches, the latest activity age of the Kouma Fault may be defined within the range of (38.84 ± 4.69) to (40.90 ± 4.45) kaB.P. The latest active age of the Kouma fault is the late of Late Pleistocene. The average vertical slip rate of the fault during the Late Pleistocene has been 0.11 mm/a.

The Importance of Accurate Timing on Land Seismic Data

Although the requirement for accurate timing of both the sources and receivers used for land seismic data acquisition has long been known, the numerical requirement for, and impact of, timing accuracy on data quality is poorly defined. In this paper we derive a method for determining the theoretical timing requirement for data acquisition. We then demonstrate the impact of poorly timed data on data quality and examine our ability to remove timing errors in data processing. Source timing variations can be corrected through the application of surface-consistent static correction but only if multiple shots have not been stacked during acquisition. Receiver timing variations are more problematic and the ability to correct for them relies on a sufficiently dense acquisition geometry.

Land Seismic Recording Systems in a Changing World — a 2021 Review

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Seismic solutions utilizing existing in-mine infrastructure for mineral exploration: A case study from Maseve platinum mine, South Africa

We demonstrate the application of seismic methods using in-mine infrastructure such as exploration tunnels to image platinum deposits and geologic structures using different acquisition configurations. In 2020, seismic experiments were conducted underground at the Maseve platinum mine in the Bushveld Complex of South Africa. These seismic experiments were part of the Advanced Orebody Knowledge project titled “Developing technologies that will be used to obtain information ahead of the mine face.” In these experiments, we recorded active and passive seismic data using surface nodal arrays and an in-mine seismic land streamer. We focus on analyzing only the in-mine active seismic portion of the survey. The tunnel seismic survey consisted of seven 2D profiles in exploration tunnels, located approximately 550 m below ground surface and a few meters above known platinum deposits. A careful data-processing approach was adopted to enhance high-quality reflections and suppress infrastructure-generated noise. Despite challenges presented by the in-mine noisy environment, we successfully imaged the platinum deposits with the aid of borehole data and geologic models. The results open opportunities to adapt surface-based geophysical instruments to address challenging in-mine environments for mineral exploration.

Application of common reflection surface (CRS) to velocity variation with azimuth (VVAz) inversion of the relatively narrow azimuth 3D seismic land data

Abstract The fracture direction and its intensity are critical properties related to hydrocarbon characterization and identification. Both these properties have an essential role in identifying the direction of hydrocarbon migration, determining the sweet spot area, and optimizing the drilling design. The velocity variation with azimuth (VVAz) is a well-known method to estimate the fracture direction and its intensity. This method is of widespread interest because it predicts the properties based on seismic data without any practical constraints. Despite this interest, the technique requires rich azimuth 3D seismic data in our case, which is rare. This study aims to apply regularization and interpolation by including the wave front attributes based on the Common Reflection Surface (CRS) method before the VVAz inversion. The motivation of using the CRS method is to enrich the current azimuth of the 3D seismic data and improve the S/N ratio. The synthetic and the real 3D seismic data are evaluated to examine the interpolation scheme of the proposed CRS method’s performance. Based on the evaluation of the 3D seismic data after regularization, the amplitude versus offset (AVO) phenomena, and the VVAz inversion results are relatively consistent (or matched) with the model. A similar result is found for the case of real 3D seismic data. A significant positive correlation between the fracture intensity of FMI and the real seismic data of about 0.9 is obtained. Therefore, CRS can be used as a regularization and interpolation method before the VVAz inversion of the relatively narrow azimuth 3D seismic data.

Digital innovation for the post-earthquake “second emergency phase” (SEP). Research experience in Central Italy

The housing emergency that follows natural disasters is generally dealt with “temporary” prefabricated housing, usually designed for short and medium-term life cycle and often arranged in dormitory suburbs, mostly devoid of any basic facility. When the rebuilding processes takes time, as usually happens, those settlements end up causing a “second emergency”, with dramatic repercussions on people's health and communities' cohesion.Facing this problem, some international experiences match digital technologies with lightweight building systems and local unskilled labor to produce innovative and temporary shelters. Among these studies, the works of Hiroto Kobayashi in the Far East and his “veneer building system” are particularly significant.Italy is a seismic land where “reconstruction” has always been a disputed process that forces people to live a long time in those kinds of settlements. A recent example is the 2016/17 Central-Italy earthquake. After four years, less than 5% of the 80 thousand uninhabitable houses have been rebuilt or recovered. People are worried about an uncertain future.This paper presents the outcome of a design experience carried out, in partnership, with the Italian University of Camerino and the Japanese Keio University. Two innovative “mobile” pavilions (for cultural activities) were built in Amandola, one of the Italian villages heavily damaged by the 2016/17 earthquake. The local student community was engaged; digital technologies were applied; the veneer system was experienced. This work represents an unusual application of digital technologies in the Central-Italy disaster area as well as an original implementation of the veneer system.

Inversion of explosive source land seismic data to determine source signature parameters

ABSTRACTIn seismic land exploration, where terrain conditions limit the use of vibrator sources, explosive sources are the preferred choice, and in situations where low‐frequency energy is essential, explosive is the preferred source, because it contains energy down to DC (0 Hz). I present a new method to estimate the source time functions of explosion source seismic data, using a modified acquisition method, data processing, modelling and inversion. Two shots of different sizes are fired into the same geophone spread with source–receiver geometry arranged such that the Green's functions are essentially the same. The spectral ratio of corresponding seismic traces is then the spectral ratio of the source time functions. A corresponding synthetic ratio filter is calculated from Blake's explosion source model for the sources within each pair. Each modelled source is defined by five parameters: the minimum radius a of the elastic zone, the internal pressure p0 at a, the density of the rock ρ and two elastic constants for an isotropic rock, the P‐wave velocity c and Poisson's ratio σ. A grid search finds the source parameters that minimise the difference between the measured and synthetic filters for each source pair, thus yielding the two source time functions, but not their absolute amplitudes. Deconvolution of the shot records within each pair for the minimum‐phase source time functions recovers the estimated earth impulse response gathers, convolved only with the response of the recording system. The improved knowledge of the source signature is then helpful in subsequent processing, especially for reverse time migration, full waveform inversion and amplitude‐versus‐offset analysis. I consider shots at different depths in the same shot hole and shots at the same depth in different shot holes. The former configuration minimises differences in geophone coupling, and, in operations, quality control procedures must be met. There is considerable variation in recovered source parameters from place to place, caused by variations in charge size, soil or rock properties and source coupling.

A Reappraisal of the Seismicity of Sardinia, Italy

Abstract In popular opinion, Sardinia is the only nonseismic region of Italy. Most researchers are likely to agree, up to a point. Geology-wise, the Sardinia–Corsica block is among the stablest areas of the Mediterranean. History-wise, up to 2011, only one Mw 5.1 event located offshore Sardinia was listed by Italian seismic catalogs (13 November 1948). Seismic networks record only a few, low energy (Mw<5) events, mostly located offshore and with little or no effects on land. Seismic hazard in Sardinia is very low. “Low,” yes, but not “totally lacking.” We present the results of a recent reappraisal of Sardinian seismicity. We gathered information on three major earthquakes (1616, 1771, and the 1948–1949 sequence). Another sequence (January–March 1901) was re-evaluated, identifying its previously unknown main event. It was confirmed that some earthquakes (1870, 1906, 1922, and 1924) had low magnitudes and scarce to nil macroseismic effects, whereas some other turned out either very doubtful or wholly fictitious (1835, 1838, 1855, and 1898). The seismic hazard of Sardinia can now be reassessed on a sounder basis than before. We hope that our work will help the people of Sardinia to improve their awareness of living in a seismic land, if with a low level of seismicity.

Velocity model estimation by means of Full Waveform Inversion of transmitted waves: An example from a seismic profile in the geothermal areas of Southern Tuscany, Italy

We propose an FWI strategy that makes use of transmitted waves as input data and utilizes both global and local optimization methods to estimate the P-wave velocity model of the subsurface. We envisage that our approach may be applicable to difficult seismic land data, like those from geothermal areas characterised by complex geological structures. As a test case, we considered the CROP/18A seismic reflection profile that crosses the geothermal field of Larderello (southern Tuscany, Italy). The aim is to estimate the P-wave velocity model down to a few kilometres depth below the surface that could be used as complementary information to the standard seismic reflection image which, in this case, does not show interpretable reflections in a range of depths accessible to industrial drillings.One innovative aspect of the inversion we propose with respect to conventional FWI approaches is its independence of a starting model that, ideally, should reproduce the true long wavelength velocity structure of the subsurface and that may be rather difficult to obtain in case of low quality data and complex geology. We lessen the dependence on knowledge of a suitable starting model by performing a sequence of two inversions. First, we employ a genetic-algorithm (GA) based inversion, a global optimisation method that does not require any specific starting model, resulting in a long wavelength, low-resolution velocity model. This model then becomes the starting model for a second FWI, driven by a local optimisation algorithm, aimed at bringing in the fine details of the subsurface velocity structure. The reliability of the final model is checked by comparing observed and predicted waves for many common shot gathers along the seismic line and through the matching between the velocities measured by check shots in two nearby wells and the FWI velocities in the same locations. Many details of the velocity field, likely related to metamorphic and igneous formations, become apparent and may complement the interpretation of the standard reflection image. From these results, it appears that the use of transmitted waves and of the FWI approach discussed here may effectively improve the information for geophysical interpretation of challenging seismic land data, such as those that characterise many areas of geothermal exploration.

Tertiary Waves Measured during 2017 Pohang Earthquake Using an Underwater Glider

An underwater glider equipped with a hydrophone observed the acoustic sounds of an earthquake that occurred on 15 November 2017 05:29:32 (UTC) in the Pohang area. The underwater glider observed the earthquake sounds after 19 s (05:29:51) at approximately 140 km from the Pohang epicenter. In order to distinguish the earthquake sound from the glider’s operation noise, the noise sources and Sound Pressure Level (SPL) of the underwater glider were analyzed and measured at laboratory tank and sea. The earthquake acoustic signal was distinguished from glider’s self-noises of fin, pumped Conductivity-Temperature-Depth profiler (CTD) and altimeter which exist over 100 Hz. The dominant frequencies of the earthquake acoustic signals due to the earthquake were 10 Hz. Frequencies at which the spectra had dropped 60 dB were 50 Hz. By analysis of time correlation with seismic waves detected by five seismic land stations and the earthquake acoustic signal, it is clearly shown that the seismic waves converted to Tertiary waves and then detected by the underwater glider. The results allow constraining the acoustic sound level of the earthquake and suggest that the glider provides an effective platform for enhancing the earth seismic observation systems and monitoring natural and anthropogenic ocean sounds.

Modeling Land Seismic Exploration Random Noise in a Weakly Heterogeneous Medium and the Application to the Training Set

In seismic exploration, random noise is an obstacle to the extraction of the effective signals, so the investigation aimed at random noise is the basis of signal processing. It is of great significance to analyze the noise properties and establish accurate noise models. Since the complex changes of the actual medium seriously affect propagation characteristics, it is necessary to establish a noise model in a more realistic medium. In this letter, we suppose a weakly heterogeneous medium whose properties vary with the position. And the link between the Lam constants of the medium and noise properties is established. Therefore, a wave equation is deduced in that medium to describe the propagation law of desert seismic exploration random noise. Based on the Greens function, the random noise field is obtained by superimposing all wave fields excited by each pointlike source. Afterward, quantitative comparisons between the actual random noise and the proposed random noise model are given. The results manifest that there are significant similarities in mathematical characteristics between them. Moreover, compared with the noise model in the homogeneous medium, the proposed noise model is more reliable. In order to prove the application value of the random noise model, it is first applied to construct a complete training set for denoising convolutional neural networks, which is valuable for attenuating the desert seismic exploration random noise. This is an effective way to extend noise data. Consequently, this feasible application will strongly promote the application of neural networks in seismic exploration.

Seismic Hazard Assessment and Land Use Analysis of Mangalore City, Karnataka, India

ABSTRACT This article presents a combined seismic risk assessment of Mangalore city, considering seismic hazard and Land Use (LU) patterns. Probabilistic seismic hazard analysis was carried out considering different source models and attenuation relations to predict Peak Ground Acceleration at every square kilometer. LU of the area was assessed using GIS tools with the built-in supervised Gaussian maximum likelihood algorithm on processed remote sensing data from temporal Landsat images. The risk map showed the concentration of built-up area South-West, toward the sea and the seismic hazard following an increasing trend from the coast to further inland.

Parallel GPU-based Implementation of One-Way Wave Equation Migration

We present an original algorithm for seismic imaging, based on the depth wavefield extrapolation by the one-way wave equation. Parallel implementation of the algorithm is based on the several levels of parallelism. The input data parallelism allows processing full coverage for some area (up to one square km); thus, data are divided into several subsets and each subset is processed by a single MPI process. The mathematical approach allows dealing with each frequency independently and treating solution layer-by-layer; thus, a set of 2D cross-sections instead of the initial 3D common-offset vector gathers are processed simultaneously. This part of the algorithm is implemented suing GPU. Next, each common-offset vector image can be stacked, processed and stored independently. As a result, we designed and implemented the parallel algorithm based on the use of CPU-GPU architecture which allows computing common-offset vector images using one-way wave equation-based amplitude preserving migration. The algorithm was used to compute seismic images from real seismic land data.

The Characteristics of Microseisms in South China Sea: Results From a Combined Data Set of OBSs, Broadband Land Seismic Stations, and a Global Wave Height Model

AbstractIt has long been recognized that ocean gravity waves can generate microseisms through their interactions and coupling with the solid earth. Their generation mechanisms, wave types, and propagation have been studied and debated intensively. In this study, we focus on the characteristics of microseisms in South China Sea (SCS) and compare them with globally observed microseisms. We use data from six ocean bottom seismometers, 10 publicly available broadband land seismometers near SCS, and a reanalyzed global wave height model from 1 May 2012 to 20 August 2012 (UTC), the time span of ocean bottom seismometers' data. We apply three techniques including power spectral density, correlation, and frequency dependent polarization analysis. Our results show that (1) microseisms observed in SCS are dominated by sources from adjacent oceans, instead of the common global sources from the Pacific, Atlantic, or Indian Ocean; (2) the split of double‐frequency microseisms (DFMs) is observed in SCS, especially on land stations: the sources are located near the central sea basin for long‐period DFMs (0.1–0.25 Hz) and are local near stations for short‐period DFMs (0.25–0.5 Hz); (3) typhoons both strengthen microseisms and affect the source locations of microseisms with the biggest influence on the short‐period DFMs; and (4) microseisms in or near SCS are a mixture of Love and Rayleigh waves and the relative dominance of Love and Rayleigh waves changes with locations.