Active Seismic Surveys Research Articles

Joint multizonal transdimensional Bayesian inversion of surface wave dispersion and ellipticity curves for local near-surface imaging

SummaryPhysical properties of near-surface soil and rock layers play a fundamental role in the seismic site effects analysis, being an essential element of seismic hazard assessment. Site-specific mechanical properties (i.e. shear- and compressional-wave velocities and mass density) can be inferred from surface wave dispersion and horizontal-to-vertical or ellipticity data by non-linear inversion techniques. Nevertheless, results typically exhibit significant inherent non-uniqueness as different models may fit the data equally well. Standard optimization inversion techniques minimize data misfit, resulting in a single representative model, rejecting other models providing similar misfit values. An alternative inversion technique can be formulated in the Bayesian framework, where the posterior probability density on the model space is inferred. This paper introduces an inversion approach of surface wave dispersion and ellipticity data based on a novel multizonal transdimensional Bayesian formulation. In particular, we parametrize 1-D layered velocity models by the varying number of Voronoi nuclei, allowing us to treat the number of layers as an unknown parameter of the inverse problem. The chosen parametrization leads to the transdimensional formulation of the model space, sampled by a reversible jump Markov chain Monte Carlo algorithm to provide an ensemble of random samples following the posterior probability density of model parameters. The used type of the sampling algorithm controls a model complexity (i.e. the number of layers) self-adaptively based on the measured data's information content. The method novelty lies in the parsimonious selection of sampling models and in the multizonal formulation of prior assumptions on model parameters, the latter allows including additional site-specific constraints in the inversion. These assumptions may be based on, e.g. stratigraphic logs, standard penetration tests, known water table, and bedrock depth. The multizonal formulation fully preserves the validity of the transdimensional one, as demonstrated analytically. The resultant ensemble of model samples is a discrete approximation of the posterior probability density function of model parameters and associated properties (e.g. VS30, quarter-wavelength average velocity profile and theoretical SH-wave amplification function). Although the ultimate result is the posterior probability density function, some representative models are selected according to data fit and maximum of the posterior probability density function. We first validate our inversion approach based on synthetic tests and then apply it to field data acquired from the active seismic survey and single-station measurements of ambient vibrations at the SENGL seismic station site in central Switzerland.

Evidence for a grounding line fan at the onset of a basal channel under the ice shelf of Support Force Glacier, Antarctica, revealed by reflection seismics

Abstract. Curvilinear channels on the surface of an ice shelf indicate the presence of large channels at the base. Modelling studies have shown that where these surface expressions intersect the grounding line, they coincide with the likely outflow of subglacial water. An understanding of the initiation and the ice–ocean evolution of the basal channels is required to understand the present behaviour and future dynamics of ice sheets and ice shelves. Here, we present focused active seismic and radar surveys of a basal channel, ∼950 m wide and ∼200 m high, and its upstream continuation beneath Support Force Glacier, which feeds into the Filchner Ice Shelf, West Antarctica. Immediately seaward from the grounding line, below the basal channel, the seismic profiles show an ∼6.75 km long, 3.2 km wide and 200 m thick sedimentary sequence with chaotic to weakly stratified reflections we interpret as a grounding line fan deposited by a subglacial drainage channel directly upstream of the basal channel. Further downstream the seabed has a different character; it consists of harder, stratified consolidated sediments, deposited under different glaciological circumstances, or possibly bedrock. In contrast to the standard perception of a rapid change in ice shelf thickness just downstream of the grounding line, we find a flat topography of the ice shelf base with an almost constant ice thickness gradient along-flow, indicating only little basal melting, but an initial widening of the basal channel, which we ascribe to melting along its flanks. Our findings provide a detailed view of a more complex interaction between the ocean and subglacial hydrology to form basal channels in ice shelves.

High resolution tomography of the Tanlu fault zone near Hefei with passive seismic and magnetotelluric linear array data

As the largest fault trending NNE-SSW to NE-SW in the eastern Eurasia Continent, the Tanlu fault zone (TLFZ) extends over 2,400 km within China, roughly from Wuxue, Hubei Province, to Russia. Since the Quaternary period, the TLFZ has been an earthquake-prone area in eastern China where several major earthquakes resulted by tectonic compression occurred, causing tremendous casualties and significant economic losses. Many studies on different segments of the TLFZ have been carried out in the past few decades. However, numerous key questions regarding the fault zone remain unanswered due to a lack of clear subsurface characterization and fault delineation. In this study, we present high-resolution tomographic results across the TLFZ to the east of Hefei, where one 22-km-long passive seismic array with densely spaced short-period nodes, and a 24-km-long magnetotelluric array were deployed adjacent to each other. We find the velocity and resistivity variations are highly consistent with known surface geology. Sharp property contrasts in both the seismic shear wave velocity and electrical resistivity profiles clearly delineate the Tanlu F1 fault (TLF-1) near Hefei. More interestingly, an upwelling with distinct high velocity is imaged within the Hefei Basin to the west of the TLF-1, whereas a slanted block with low-velocity and low-resistivity seems to cut into or thrust upon the high-grade to low-grade middle-pressure rocks in the Zhangbaling uplift right below the Tanlu F2 ductile shear fault (TLF-2). The presented results show a new approach to characterize deep subsurface structure of the TLFZ beyond 2-km depths using passive data, which it is often difficult for active seismic surveys with refracted and reflected waves to image.

Peran Humas Sebagai Fungsi Publikasi Dalam Mensosialisasikan Kegiatan Survei Seismik Pt Elnusa Tbk

Public relations is the art of helping manage the objectives of an organization, the form of change that is facilitated in the organization, and a picture of philosophy. Public relations as a function of publication which has the ability to inspire everyone in achieving company goals. The activities of PT Elnusa Tbk's seismic survey made the public know and understand these activities. The purpose of this research is to determine the role of Public Relations as a publication function in socializing the seismic survey activities of PT Elnusa Tbk in 2D Selingsing, South Sumatra, to determine the persuasive communication of Public Relations as a function of publications in socializing the seismic survey activities of PT Elnusa Tbk in 2D Selingsing, South Sumatra, and for know the obstacles of PR as a publication function in socializing the seismic survey activities of PT Elnusa Tbk in 2D Selingsing, South Sumatra. This study uses a qualitative descriptive method. Data collected through interviews and field observations. In this research, it is concluded that from research to implementation of socialization activities carried out by the Public Relations of PT Elnusa Tbk have been well planned and carried out, where what is desired from the implementation in publishing PT Elnusa Tbk's seismic survey activities has been achieved. Conduct persuasive communication to communities affected by the seismic survey area in an open manner and door to door for those who are absent. Obstacles faced by PR when disseminating publications are residents who are absent and refuse, causing a long process of publishing the socialization of PT Elnusa's seismic survey in 2D Selingsing, South Sumatra.

Evaluating rock mass disturbance within open-pit excavations using seismic methods: A case study from the Hinkley Point C nuclear power station

Understanding rock strength is essential when undertaking major excavation projects, as accurate assessments ensure both safe and cost-effective engineered slopes. Balancing the cost-safety trade-off becomes more imperative during the construction of critical infrastructure such as nuclear power stations, where key components are built within relatively deep excavations. Designing these engineered slopes is reliant on rock strength models, which are generally parameterised using estimates of rock properties (e.g. unconfined compressive strength, rock disturbance) measured prior to the commencement of works. However, the physical process of excavation weakens the remaining rock mass. Therefore, the model also requires an adjustment for the anticipated rock disturbance. In practice, this parameter is difficult to quantify and as a result it is often poorly constrained. This can have a significant impact on the final design and cost of excavation. We present results from passive and active seismic surveys, which image the extent and degree of disturbance within recently excavated slopes at the construction site of Hinkley Point C nuclear power station. Results from active seismic surveys indicate that the disturbance is primarily confined to 0.5 m from the excavated face. In conjunction, passive monitoring is used to detected seismic events corresponding to fracturing on the cm-scale and event locations are in agreement with 0.5 m of disturbance into the rock face. This suggests rock disturbance at this site is relatively low and occurred during and immediately after the excavation. A ratio of seismic velocities recorded before and after excavations are used to determine the disturbance parameter required for the Hoek–Brown rock failure criterion, and we assess that rock disturbance is low with the magnitude of the disturbance diminishing more quickly than expected into the excavated slope. Seismic methods provide a low-cost and quick method to assess excavation related rock mass disturbance, which can lead to cost reductions in large excavation projects.

PT Elnusa Tbk Community Relations’ Communication Strategy in Providing Socialization of Seismic Survey Activities to the Community: A Case Study in Musi-Banyuasin Regency, South Sumatera

PT Elnusa Tbk Community Relations’ Communication Strategy in Providing Socialization of Seismic Survey Activities to the Community: A Case Study in Musi-Banyuasin Regency, South Sumatera

The application of ambient noise and reflection seismic exploration in an urban active fault survey

As the detection of urban active faults becomes increasingly important, high-resolution detection of urban blind active faults is very important for urban planning, land use, and disaster risk reduction. However, it is difficult to determine the corresponding surface positions in the city environment for noise and building restrictions. The active source reflection seismic technique is considered the best technique to image faults with a high resolution and deep penetration. However, urban geophysical exploration must often consider the complex urban environment, which includes moving vehicles, dense power grids, and irregular buildings. These features make active source reflection seismic exploration difficult for wide application due to its drawbacks of high cost and the necessary use of explosives. In contrast, ambient noise seismic surveys have the advantages of continuous ambient noise sources, low cost, and fast deployment. These advantages are good for urban exploration. Although ambient noise seismic surveys have a lower resolution than active seismic surveys, their ultrahigh-density layout can improve the resolution. We have conducted two active source seismic lines and two ambient noise seismic lines near the Huangzhuang-Gaoliying fault (HGF) in a northern suburb of Beijing. The autocorrelation and crosscorrelation results are consistent with the active source reflection seismic results. They revealed the location of the HGF, which is composed of a set of steep dip faults. The study of the combination of the two techniques demonstrates that ambient noise seismic surveys are effective for urban active fault detection, especially for larger scale area surveys, and active source reflection seismic surveys can be used for detailed surveys. The combination of the two techniques has a higher efficiency and lower costs and can be widely used in blind urban active fault surveys.

Compaction of the Groningen gas reservoir investigated with train noise

SummaryInduced seismicity in the Groningen gas field in the Netherlands has been related to reservoir compaction caused by gas pressure depletion. In situ measurement of compaction is therefore relevant for seismic hazard assessment. In this study, we investigated the potential of passively recorded deep borehole noise data to detect temporal variations in the Groningen reservoir. Train signals recorded by an array of 10 geophones at reservoir depth were selected from the continuous noise data for two 5-month deployments in 2015. Interferometry by deconvolution was applied to the high-frequency train signals that acted as stable, repetitive noise sources. Direct intergeophone P and S wave traveltimes were then used to construct the P- and S-wave velocity structure along the geophone array. The resulting models agree with independently obtained velocity profiles and have very small errors. Most intergeophone P wave traveltimes showed decreasing traveltimes per deployment period, suggestive of compaction. However, the retrieved traveltime changes are very small, up to tens of microseconds per deployment period, with uncertainties that are of similar size, about 10 microseconds. An unambiguous interpretation in terms of compaction is therefore not warranted, although the 10 μs error per 5-month period is probably smaller than can be achieved from active time-lapse seismic surveys that are commonly used to measure reservoir compaction. The direct P-wave amplitudes of the train-signal deconvolutions were investigated for additional imprints of compaction. Whereas the P-wave amplitudes consistently increased during the second deployment, suggestive of compaction, no such trend was observed for the first deployment, rendering the interpretation of compaction inconclusive. Our results therefore present hints, but no obvious effects of compaction in the Groningen reservoir. Yet, this study demonstrates that the approach of deconvolution interferometry applied to deep borehole data allows monitoring of small temporal changes in the subsurface for stable repetitive noise sources such as trains.

Erratum

Erratum

Imaging the active faults with ambient noise passive seismics and its application to characterize the Huangzhuang-Gaoliying fault in Beijing Area, northern China

Most serious geotechnical problems related to rock engineering are generated by the existence of faults. Detection of fault (especially active faults) is the first step to conduct any further in-depth studies in faulted rock mass or rock blocks. In this paper, we investigated the plausibility to image fault zones by passive seismic surveys using recorded ambient noise. The test site is in the north suburb of Beijing, northern China along the south bank of the northwest-southeast running Wenyuhe River, where the NNE-striking Huangzhuang-Gaoliying fault (HGF, active in the Holocene) is crossing. In general, the results are in good agreement with previous studies using active source seismics conducted in this area along the HGF and existing borehole drillings in the vicinity. Undoubtedly, Active source seismic reflection technique is the best technique to image fault in depth with high resolution. The drawback is its high cost and the necessity of using explosives, a practice usually prohibited in urban settings. In contrast, passive seismic surveys take the advantage of the ever-existing ambient noise source, and provide a low-cost technique, and fast deployment that can locate the fault effectively. Though the imaging resolution is lower compared to those obtained by active source seismic surveys, our passive seismic experiment at the Wenyuhe River site demonstrated that this approach is effective, especially for those faults with significant normal faulting component and the stratigraphy is significantly different on the two sides crossing the fault line.

Source‐Independent Passive Seismic Reverse‐Time Structure Imaging With Grouping Imaging Condition: Method and Application to Microseismic Events Induced by Hydraulic Fracturing

AbstractSeismic imaging with active seismic sources can be used to image subsurface structures such as faults, fractures, and layer interfaces with higher resolutions than tomographic methods. However, for characterizing large‐scale three‐dimensional structures, oftentimes it is too expensive and thus impractical to conduct active seismic survey. Seismic imaging using passive sources has been used to image structures through the “pseudoactive” source imaging by assuming source information is known. However, in practice there exist some uncertainties on source information including location, origin time, source time function, and radiation pattern, which can inevitably affect the final imaging result. In this study, we propose a new source‐independent passive seismic imaging method based on reverse‐time imaging with converted waves and a new imaging condition. This method uses the interference between P and S waves at conversion points for structure imaging by back‐propagating seismograms recorded by all receivers. Since no forward modeling is needed in this method, source information is not needed. A new grouping imaging condition is proposed to improve the image resolution, in which seismic receivers are divided into several groups and the separated P and S wavefields of different groups are multiplied and then stacked over time to get an image. We test the new method on both synthetic and real data sets based on a downhole microseismic system that is used for monitoring a shale gas hydraulic fracturing treatment. The results show that the proposed passive seismic imaging method does not depend on knowing source information and can achieve higher imaging resolution.

Wireless Geophone Sensing System for Real-Time Seismic Data Acquisition

Active seismic surveys, for the exploration of oil and gas reservoirs, are conducted using a huge network of geophone sensors (>10,000) covering a very large area and interconnected using seismic cables. Such cables enable reliable operation and fast data transfer, but account for a major percentage of the survey cost and limit its flexibility. In this paper, a wireless seismic data acquisition system that provides real-time data transmission for active seismic surveys is designed and implemented. A system that comprises a smart wireless sensor node and a gateway unit is demonstrated as a proof-of-concept. The smart wireless node comprises a geophone sensor, a high-resolution data acquisition system and a smart reconfigurable wireless communication module. The data acquisition system includes an electronic circuit for amplification and filtering, a single-board computer and a 24-bit analog-to-digital converter (ADC). The wireless communication module comprises a 2.4 GHz radio frequency (RF) transceiver connected to a pattern reconfigurable antenna. A microcontroller is employed to reconfigure the Yagi-Uda antenna to scan its radiation pattern in different directions and focus the radiated power in the direction of the nearest gateway. This high-gain directional antenna would allow communication between the sensor node and the gateway over a longer distance as compared with the monopole antenna conventionally employed in commercial wireless seismic systems. The proposed system, employing a reconfigurable antenna in the sensor node, has been implemented and tested and was able to successfully capture seismic data from the geophone sensor and transmit it wirelessly in real-time to the gateway unit, achieving a notable 25% enhancement in the communication range between the sensor node and the gateway. This communication range enhancement results in a significant 56% enhancement in the gateway's communication area coverage, when compared to similar systems that use conventional monopole antennas in their sensor nodes.

Seismic surveys reduce cetacean sightings across a large marine ecosystem

Noise pollution is increasing globally, and as oceans are excellent conductors of sound, this is a major concern for marine species reliant on sound for key life functions. Loud, impulsive sounds from seismic surveys have been associated with impacts on many marine taxa including mammals, crustaceans, cephalopods, and fish. However, impacts across large spatial scales or multiple species are rarely considered. We modelled over 8,000 hours of cetacean survey data across a large marine ecosystem covering > 880,000 km2 to investigate the effect of seismic surveys on baleen and toothed whales. We found a significant effect of seismic activity across multiple species and habitats, with an 88% (82–92%) decrease in sightings of baleen whales, and a 53% (41–63%) decrease in sightings of toothed whales during active seismic surveys when compared to control surveys. Significantly fewer sightings of toothed whales also occurred during active versus inactive airgun periods of seismic surveys, although some species-specific response to noise was observed. This study provides strong evidence of multi-species impacts from seismic survey noise on cetaceans. Given the global proliferation of seismic surveys and large propagation distances of airgun noise, our results highlight the large-scale impacts that marine species are currently facing.

Passive seismic horizontal to vertical spectral ratio (HVSR) surveying to help define bedrock depth, structure and layering in shallow coal basins

SummaryTrial passive seismic HVSR survey lines were carried out in the north-western part of the Wilga sedimentary basin in Western Australia, which is a small and shallow isolated sub-basin to the Perth Basin, sitting above rifted Archaean granite-gneiss basement rocks. The HVSR survey method was trialled to determine if it could resolve subsurface basin features quickly and cheaply. This trial HVSR survey was carried out as a series of transects along open walking tracks. It was very successful for mapping the general basin architecture by resolving bedrock depth to a maximum depth of close to 200 m along the survey transects, and defining a half-graben structure that forms the faulted eastern boundary of the basin, with the basin depth gently deepening toward the west. The HVSR data are also interpreted to have detected subtle layering within the basin sedimentary sequence to possibly map Permian black shale beds, coal measures and splits sitting below an unconformity of Cretaceous sedimentary cover. The passive seismic HVSR method has potential to be a robust survey method for defining basin architecture in shallow coal basins with poorly indurated basin fill deposits, especially in remote parts of the world with difficult access and limited exploration funds to carry out active seismic surveys.

Influence of Seismic Survey Activities on the Environment in Soy North Ward, Elgeyo Marakwet County, Kenya

Influence of Seismic Survey Activities on the Environment in Soy North Ward, Elgeyo Marakwet County, Kenya

Seismic Velocity Estimation Using Passive Downhole Distributed Acoustic Sensing Records: Examples From the San Andreas Fault Observatory at Depth

AbstractStructural imaging and event location require an accurate estimation of the seismic velocity. However, active seismic surveys used to estimate it are expensive and time‐consuming. During the last decade, fiber‐optic‐based distributed acoustic sensing has emerged as a reliable, enduring, and high‐resolution seismic sensing technology. We show how downhole distributed acoustic sensing passive records from the San Andreas Fault Observatory at Depth can be used for seismic velocity estimation. Using data recorded from earthquakes propagating near‐vertically, we compute seismic velocities using first‐break picking as well as slant stack decomposition. This methodology allows for the estimation of both P and S wave velocity models. We also use records of the ambient seismic field for interferometry and P wave velocity model extraction. Results are compared to a regional model obtained from surface seismic as well as a conventional downhole geophone survey. We find that using recorded earthquakes, we obtain the highest P wave model resolution. In addition, it is the only method that allows for S wave velocity estimation. Computed P and S models unravel three distinct areas at the depth range of 50‐750 m, which were not present in the regional model. In addition, we find high VP/VS values near the surface and a possible VP/VS anomaly about 500 m deep. We confirm its existence by observing a strong S‐P mode conversion at that depth.

Imaging vertical interfaces using acoustic time reversal

We have developed a novel approach to image vertical structures using multiply scattered waves. This method requires only a smooth seismic velocity model and data recorded at the surface. Previous methods to image near-vertical interfaces or faults using migration methods all require prior information about small-scale details in the seismic velocity model to infer the locations of multiple-scattering wave interactions. We used waves that had their last scattering interaction with near-vertical interfaces, while their other scattering points might be anywhere in the earth, including at the free surface. Our algorithm then images the final scattering point using a time-reversed mirror-style imaging condition, so we refer to the method as time-reversed mirror imaging. Artifacts in the images produced have clear causes and can be filtered out by stacking over shots and including contributions from multiples. Our numerical examples demonstrate the successful application of the method for staircase structures and a section of the Marmousi model. They also reveal a new way to diagnose errors in the smooth or reference velocity model used. In addition, our method can be used to image point scatterers in active seismic surveys or for event location in passive surveys.

Cost-Effective Seismic Exploration: 2D Reflection Imaging at the Kylylahti Massive Sulfide Deposit, Finland

We show that by using an advanced pre-stack depth imaging algorithm it is possible to retrieve meaningful and robust seismic images with sparse shot points, using only 3–4 source points per kilometer along a seismic profile. Our results encourage the use of 2D seismic reflection profiling as a reconnaissance tool for mineral exploration in areas with limited access for active seismic surveys. We used the seismic data acquired within the COGITO-MIN project comprising two approximately 6 km long seismic reflection profiles at the polymetallic Kylylahti massive sulfide mine site in eastern Finland. The 2D seismic data acquisition utilized both Vibroseis and dynamite sources with 20 m spacing and wireless receivers spaced every 10 m. For both source types, the recorded data show clear first breaks over all offsets and reflectors in the raw shot gathers. The Kylylahti area is characterized by folded and faulted, steeply dipping geological contacts and structures. We discuss post-stack and pre-stack data processing and compare time and depth imaging techniques in this geologically complex Precambrian hardrock area. The seismic reflection profiles show prominent reflectors at 4.5–8 km depth utilizing different migration routines. In the shallow subsurface, steep reflectors are imaged, and within and underneath the known Kylylahti ultramafic body reflectivity is prominent but discontinuous.

Low Frequency Broad Band Acoustic Propagation in Andaman Sea

During November 2017, an active source seismic survey was performed in Andaman sea to study the acoustic propagation characteristics. High power low frequency acoustic signals generated by 20-air gun array onboard ORV Samudra Ratnagar were recorded from INS Sagardhwani at four different depths within 8 km ranges in shallow and deep waters. Low frequency sound levels were estimated using root mean square and power spectral values. Amplitude levels were analysed with respect to arrival time variation with frequency and is presented.

Integrated Active and Passive Seismic Monitoring at the Decatur CCS Project

For holistic seismic monitoring of the progressing CO2 plume within the Mt. Simon sandstone reservoir at the Illinois Basin - Decatur CCS project, we aim to integrate passive microseismic data with complementary surface- and VSP data from active seismic surveys. A detailed microseismic analysis allows for spatial mapping of attenuation Q around the injection area. We identify time periods of possible reservoir changes in between active seismic time-lapse monitors and we can increase the temporal resolution of the 4D signal. In addition, finite-difference FD modeling of microseismic events can help explain the details of the observed waveforms including different phase arrivals for up- and downgoing waves. This, in turn, is essential to improve the depth resolution of microseismic event location and determine whether seismic activity is confined to the injection zone or growing outward. The discrimination of ray paths from FD modelling also allows to select the most relevant waveform phases for 4D time-lapse studies and is an important pre-processing step. In combination with simultaneous tomographic inversion of the velocity- and attenuation structure, it has the potential to maximize the resolution of 4D changes in the medium.