- Home
- Conferences
- Conference Proceedings
- Conferences
NSG2021 27th European Meeting of Environmental and Engineering Geophysics
- Conference date: August 29, 2021 - September 2, 2021
- Location: Hybrid
- Published: 29 August 2021
61 - 80 of 134 results
-
-
Active and Passive 3d Seismic Survey Around the Scrovegni Chapel Using Autonomous Nodes
Authors I. Barone, R. Deiana, A. Ourabah, J. Boaga and G. CassianiSummaryA dense 3D seismic survey, including both active and passive surface wave measures, has been performed around the Scrovegni Chapel in Padua (Italy), in order to provide a deeper understanding of the archaeological setting of the area. In particular, ambient noise has been characterized both in terms of amplitude and direction of propagation. A cross-correlation analysis of 22 hours of continuous recording allowed to reconstruct the virtual source gathers, which are symmetric and comparable to active gathers despite the directional character of noise, typical of an urban environment. These preliminary results demonstrate the potential of this dataset to bring new insights about the area.
-
-
-
Seismic Monitoring With Low-Cost MEMS Sensor Arrays in Italy
Authors V. Cascone, J. Boaga and G. CassianiSummaryMicro-Electro-Mechanical System (MEMS) sensors could efficiently integrate the use of common accelerometers to moderate/strong seismic events. In this study we present a new prototype of low-cost MEMS accelerometer, showing the results of a calibration experiment on the shake table apparatus. We install 16 new prototype of MEMS based accelerometers in two seismogenic sectors in Italy (Northern and Central Italy) in order to build distributed arrays. We find that these sensors are capable of recording seismic events (ML > 1.7) at distances in the order of tens of km. Moreover, MEMS seismic records are compared against the national accelerometric network data. In particular we compare the Peak Ground Accelerations (PGAs) and Spectral Accelerations. We find a good match of these two fundamental ground-motion parameters, demonstrating that these low-cost sensors could be an interesting choice for increasing the spatial density of stations and provide more accurate wavefield recordings.
-
-
-
Calibration of multi-frequency EMI data: example at a test site in Rouen (France)
Authors C. Finco, F. Rejiba, C. Schamper and L.H. Cavalcante FragaSummaryElectromagnetic induction (EMI) is an efficient method, widely used to characterize the ground a large range of applications from hydrogeology, archeology to pedology. It is particularly interesting as it is not only sensitive to electrical properties of the ground but also magnetic and in certain condition dielectric as well. However, to quantitatively interpret EMI measurements, the data needs to be calibrated. The calibration process usually requires additional measurements, often a DC resistivity sounding or profile. Multi-frequency EMI devices, like the GEM-2 (Geophex Ltd) do not allow depth soundings like multiple offsets devices but multi-parameters interpretation is possible more often as the contribution of the different parameters to the measurement varies with frequency. Using the consistency of the measurements at different frequencies, should allow the calibration of the out-of-phase part of the data without additional measurements. In particular the interpretation of the out-of-part of the lowest frequency data should theoretically give a very similar apparent conductivity.
An example from a well characterized test-site in Rouen is presented here, showing the apparent resistivity calculated from the data before and after this self-calibration process. The confrontation with an inverted DC resistivity profile, show a good agreement between the methods after the calibration.
-
-
-
Using 1C nodes in a 3C combination - benefits, and inconveniences
Authors A. Ourabah, L. Petronio, A. Affatato, L. Baradello, N. Goujon and Z. SongSummaryHigh-density multicomponent acquisition is perceived as the holy grail of land seismic, however, 3C is rarely considered when surveys are planned mainly because of the cost and bulkiness of 3C nodes and also the lack of land processing examples that could justify such spent, especially when it can be directed towards more proven benefits like increased trace density. Ironically, the availability and affordability of 3C data play a crucial role in developing the processing technology that could promote the acquisition of more 3C land surveys. The recent evolution in onshore nodal technology has brought to the market a variety of nodes of different sizes, shapes, and sensor types, some are small and light enough that even if combined in a 3C configuration remain smaller and lighter than a purpose-built 3C node. Acquiring a 1C, 2C or 3C survey with the same node’s inventory could be very attractive and could incite more users to attempt a 3C acquisition. In this paper, we demonstrate how piezoelectric nodes can be used in a 3C combination by comparing them to established geophone 3C sensors in a 2d S-wave survey. We also discuss the benefits and inconveniences of a such approach in land acquisition.
-
-
-
Airborne and ground-based TEM mapping in polar regions — Antarctica cases
Authors N. Foged, L. Meldgaard Madsen, S. Tulaczyk and D. GrombacherSummaryWe present transient electromagnetics (TEM) mapping results from different geological targets in polar environments, primary from two airborne TEM surveys and one ground -based TEM mapping campaign conducted in the McMurdo Dry Valleys and on the Ross Ice Shelf in Antarctica. With the different cases, we demonstrate that the TEM methods are well suited to image different subsurface structures in polar regions as they can provide valuable information on ice thicknesses and discriminate between e.g. glacier ice/sea ice, frozen/unfrozen sea water, frozen/unfrozen water systems (permafrost), and bedrock/glacier ice. We further demonstrate that a high data and instrumentation quality, as the ground-based and airborne TEM data produces consistent results.
-
-
-
The Application of Distributed Acoustic Sensing for Shallow Marine Investigations an Intertidal Case Study
Authors A. Trafford, S. Donohue, R. Ellwood, A. Godfrey and L. WacquierSummaryTypically, there is a paucity of geotechnical information available to designers of offshore foundations for marine renewable structures, which often results in highly conservative designs.
With an increased recognition of the value of shear wave velocity measurements as a critical design parameter in the marine geotechnical industry, there is a real requirement to develop a cost effective shear wave seismic data acquisition methodology.
This case study documents field trials at Dollymount Strand, Dublin using fibre optic cables as continuous seismic sensors for the collection of surface wave data. Data were collected using an OptaSense ODH4 interrogator connected to a 1000m long CST armoured single mode fibre optic cable. A Sercel Mini G airgun, operated from a survey vessel, was used as the seismic source.
The collection of data from an intertidal site allowed for direct comparison of different acquisition methodologies in both dry and flooded conditions.
The findings of the study showed that Distributed Acoustic Sensing (DAS) was effective at collecting shallow marine seismic data for analysis using the Multichannel Analysis of Surface Waves (MASW) method. Using DAS in this environment has great potential due to the rapid data acquisition compared to other currently available technologies.
-
-
-
Anomalous geomagnetic variations associated with the Etna volcanic activity during February 2021
By S. RiabovaSummaryA series of paroxysmal events separated by relative calm periods at Etna volcano (37.75 N; 14.99 E) began on February 16, 2021 and continued to February 28, 2021. The magnetic effect caused by the eruption of the Etna volcano were analyzed. The data of registration of three components of the magnetic field of Mikhnevo observatory and a number of INTERMAGNET observatories, located at different distances from the volcano, were used. The result of data analysis reveals significant anomalous changes in the Earth’s magnetic field during paroxysmal Etna volcanic activity. The morphology of anomalies is similar at different distances from the volcano. In general, amplitudes of geomagnetic anomalies do not exceed tens of nT. Anomalies are most pronounced in the horizontal component of the Earth’s magnetic field.
-
-
-
Modeling Hydrocarbon Bearing Reservoirs Using Fuzzy SVR and Electrofacies Analysis
Authors N. Moosavi and M. BagheriSummaryPermeability is one of the key petrophysical parameters of hydrocarbon bearing formations. One of the crucial roles of this parameter is to estimate production rate in oil bearing reservoirs. Permeability is usually measured by core plugs in laboratory. Although the measured value by this method is very precise, it is very expensive and time consuming. Furthermore, core data is not always available for all the wells. Over the last years, regression methods have been widely used to predict permeability in areas with core missing data. Among various regression approaches we selected SVM which works due to SRM and its produced model is less prone to over-fitting problems. Petro-physical properties in heterogeneous reservoirs vary in vertical displacements. So predicting them is difficult due to their abrupt changes. We exploited Electrofacies Analysis using Multi Resolution Graph-Based Clustering to partition formations due to their similarity. We also modified Support Vector Regression to FSVR by giving each data point a membership function to reduce effect of noise and outliers on data.The predicted outputs correlated with core data in the test well. The results show that predicted permeability from FSVR has a notably better correlation with real data compared to correlation outputs from SVR.
-
-
-
Imaging a near-vertical structure with seismic refraction tomography: an offshore study
Authors B. Benjumea, F. Bohoyo, C. Morales, M. Druet, A. Maestro, C. Rey-Moral and C. EscutiaSummarySeismic refraction tomography (SRT) can be a useful tool for detecting lateral velocity changes in the subsurface. In this work, we leverage a traditional seismic reflection offshore dataset to image a high velocity structure imbedded in sediments. The studied profile is located in the western edge of the South Orkney Microcontinent (SOM). Seafloor depth in this sector ranges between 268 and 304 m. The multichannel streamer of 120 channels and 1.4 km length allowed to detect refraction arrivals from the subsurface and used them as input for SRT to reconstruct a P-wave velocity model of the near–structure. A layered initial model provided the best result retrieving a sharp image of the velocity anomaly. Interpretation of this anomaly was supported by the comparison between the SRT velocity model and the multichannel seismic reflection image. Shallow subparallel layers of sediments characterized by velocities between 1500 and 2000 m/s overly a zone with older deformed sedimentary layers related to velocities ranging between 2500 and 3000 m/s. Within this second layer, a high-velocity anomaly (more than 4000 m/s) is delineated. Geological context supports interpreting this anomalous structure as metamorphic rocks or gabbroic bodies from PMA (Pacific Margin Anomaly) as part of the basement.
-
-
-
Typical Effects of the Registration Technology Implemented in the Gpr Receiver
Authors O. Gulevich, L. Volkomirskaya, A. Reznikov and V. VarenkovSummaryThe method of signal registration implemented in GPRs using frequency or time gating or nonlinear amplification of amplitudes may significantly impact the GPR data, in fact, distorting the reactions of rocks to the applied electromagnetic field of the probing signal. This distortion of the field occurs under various experimental conditions and may affect the ability to draw reliable inferences about rock characteristics if it is not taken into account when interpreting the GPR data.
Numerically calculated waveforms obtained in the approximation of geometric optics or significant simplifications of the models of propagation of electromagnetic signals cannot serve as a standard in GPR and be directly applied to a wide range of experimental results obtained by different GPRs, which differ in design.
We describe some of the typical effects of the GPR design on waveforms and some interpretational errors, which occur when the effect of the registration technology implemented in the receiver is not taken into account.
-
-
-
Evolution of the Orange Basin; Cretaceous Deepwater Fold-and-Thrust Belts to Cenozoic Mass Transport Systems
More LessSummaryThe focus of this study is on the deepwater Orange Basin, offshore SW Africa, in which several DWFTB systems are found. Previous studies have mainly focused on the 2D seismic interpretation of the Orange Basin, which is naturally limited. In this study, the availability of high-resolution, 3D seismic reflection data will allow us to constrain the strato-structural architecture of the deep-water Orange Basin from a Cretaceous DWFTB system to the overlying Cenozoic deposits using Schlumberger’s Petrel E & P software package for seismic interpretation. Understanding the architectural elements of southern Africa’s passive margin, and the tectonic evolution of the DWFTB systems contained within, is important in building on the scientific knowledge known of what occurs in these settings worldwide and in further constraining prospective sites for petroleum exploration in similar settings.
-
-
-
Complex Resistivity Imaging Using Controlled Source Electromagnetic Data
Authors J. Porté, J. Girard and F. BretaudeauSummaryControlled Source Electromagnetic (CSEM) method is an imaging technique using a multi-frequency electromagnetic signal to obtain the electrical resistivity of the underground, up to 3 km depth. This medium property is usually considered as a real and constant value in the quasi-static limit. Nevertheless, in some Earth materials, induced polarization (IP) phenomena are occurring when an electric perturbation is applied. These mechanisms are described by a frequency dependent complex resistivity (CR). CR is usually studied using electrical method with a direct current (DC) hypothesis, neglecting by the way electromagnetic induction.
We implemented a frequency dependent CR in the 3D Finite-Difference CSEM modelling and inversion code, POLYEM3D. A multi-stage approach is defined to undertake the multi-parameters problem according to their sensitivity. Furthermore, to manage an increasing number of parameters, second order polynomials are used to describe frequency variations of CR.
We show through synthetic inversions that we are able to recover a 3D complex resistivity image and its frequency variations from CSEM data in the IP/EM coupling domain, where IP signal is sufficiently large compared to EM induction.
-
-
-
Experiments and Modelling of Seismoelectrics in the Ultrasonic Range: A Comparison With Electrokinetic Theory
Authors V. Martins Gomes, D. Brito, S. Garambois, C. Bordes and H. BarucqSummaryAcoustical wave propagation in a fluid-filled porous media creates electromagnetic (EM) disturbances through a physical process referred in the literature as seismoelectric (SE) conversion. Two EM fields result from this conversion, one accompanies the seismic wave in the form of a transient electric field and the other is generated at interfaces and propagates independently with an electromagnetic wave behaviour. The latter has an arguably high potential of application in near-surface exploration, possibly comparable to other indirect EM methods. In what follows, an experimental setup conceived to measure both SE fields mentioned above was employed in the study of a porous saturated homogeneous medium with (1) and without (2) a thin layer inside. It was seen that measuring absolute potentials is more efficient for detecting the EM-wave generated at interfaces than using electric fields estimated from measured potential differences. Using a numerical code and an experimental source, the measured data was compared with the modelling showing there is a fair agreement between experiments and electrokinetic theory. Our results are promissing and open the path for a more in depth investigation of the SE conversion phenomena and its relation with physical properties.
-
-
-
Tectonic Evolution of the Deepwater Orange Basin (South Africa) Using 3d Reflection Seismic Data
Authors V. Mahlalela, M. Manzi and Z. JinnahSummaryThe application of seismic attributes to high-resolution 3D reflection seismic data acquired for the deepwater exploration block in the Orange Basin, offshore South Africa, provided insight into the mechanisms controlling deformation in hydrocarbon systems. The seismic interpretation was carried out on high-resolution, prestack time-migrated 3D seismic data that image post-rift sequences from the Upper Cretaceous to the Quaternary. Three post-rift sequences were identified in the seismic sections; post-rift sequences II, IV and V. Two slumping events caused by gravity failure of the margin were also identified in the Coniacian to Santonian and Late Cenozoic sequences. The seismic data also image a thrust fault system, which is interpreted to have been formed by episodic gravity failure from the Coniacian to Santonian. The thrust fault system soles into two detachment levels which coincide with the Cenomanian-Turonian boundary source rocks and top of the Turonian marine shale unit. The Late Cenozoic slumping event creates S to WSW and N to ENE dipping normal faults. The thrust faults exploit the S to WSW dipping normal faults to transport hydrocarbons to the seafloor to form pockmarks. Large submarine canyons were interpreted to have formed by a combination of the two slumping events.
-
-
-
Impact of the Dem’s Resolution on 2d and 3d-Eri Common Pratice
Authors Y. Fargier, T. Dezert, R. Antoine, A. Tonnoir and C. FauchardSummaryERI is commonly applied to structures and sites whose complex geometry can affect the measurement considerably. Photogrammetry is a recognized method for obtaining dense and precise measurements of a surface. However, in the worst scenario, this topographic information is not or too little taken into account during the inversion process of ERI leading to artifacts. In the opposite scenario, topographic point clouds are too dense to be fully used by inversion software. In this paper, we present the effect of these various scenarios based on the inversion of synthetic data simulated on a complex geometry with an embedded anomaly. The results show the limitations associated with certain current practices as well as the quality of inversion obtainable with a limited amount of topographic information.
-
-
-
Time-Lapse Monitoring of Moisture Induced Landslide Using Surface Waves at Hollin Hill Landslide Obsevatory
Authors L. Wacquier, J. Whiteley, D. Gunn, B. Dashwood, J. Chambers, A. Watlet, A. Trafford and S. DonohueSummaryThe Hollin Hill site has been used as a landslide research site to test different geophysical characterization and monitoring methods, to assess temporal and spatial stability. This abstract presents the use of surface waves content and its dispersive properties, in the context of moisture induced landslide monitoring of seasonal variations, using 16 seismic datasets acquired between October 2016 and August 2019. For each dataset, a 2D pseudo section of the landslide is assembled, and the relative difference between each dataset is calculated. The statistical distribution of each difference indicates a seasonal variation control or a soil moisture control on surface waves velocity measurements with time. Specifically, this approach shows potential for monitoring seasonal variability in elastic properties linked to changes in soil moisture, which has a direct impact on periods of more active slope movement. These results are currently being investigated further and will be discussed in future work.
-
-
-
Porosity of Near-Surface Soil Layers From 3d Elastic Full-Waveform Inversion: Tests on Synthetic Data
Authors Y. Kawasaki, R. Ghose and S. MinatoSummaryThe porosity of the shallow soil layers is a crucial information in hydrogeology, soil science, agriculture, and construction engineering. To resolve the spatial distribution of porosity in soil, 3D elastic full waveform inversion (FWI) can be a promising tool. In this research, we have tested 3D FWI on a realistic subsoil model constructed from field-measured data. Different source types, dominant frequency of the seismic source, and the inversion frequency have been examined on the synthetic dataset. Our results suggest that (1) the use of SH and Love waves leads to a higher accuracy compared to P-SV or Rayleigh waves, and (2) the use of a broader frequency range in inversion and/or a source wavelet of higher dominant frequency leads to more accurate and better resolved Vs and bulk-density models. Finally, the porosity values for the different layers have been estimated from the inverted bulk density profile. Our results indicate that 3D FWI has the potential to estimate reasonably accurately the Vs and density profiles, which can in turn offer 3D porosity distribution.
-
-
-
Monitoring Settling and Consolidation of Fluid Mud in a Laboratory Using Ultrasonic Measurements
Authors I. Fadel, A. Kirchek, M. Buisman, K. Heller and D. DraganovSummaryUltrasound measurements are routinely used to evaluate the safe depth for ships navigation - nautical depth - at waterways and ports using single-beam dual-frequency echo-sounders. The nautical depth is routinely defined by suspension density in the range of 1100–1300 kg/m3 in the mud layer. While ultrasound measurements have a weak sensitivity to density variations, calibration is always needed to convert ultrasound measurements into reliable indicators for nautical depth levels in the mud layers using densely distributed density rheological in-situ measurements.
We present a laboratory ultrasonic transmission experiment to monitor the fluid mud’s settling and consolidation processes using a sample from the Port of Rotterdam. We use P- and S-wave ultrasonic transducers in the frequency range between 200 to 1000 kHz. Our results show that the P-wave velocities slightly increase during the consolidation and settling process while the P-wave amplitudes decrease. On the other hand, we observe a high S-wave velocity that increases together with amplitudes over time. The P- and S-wave amplitude and S-wave velocity variation over time correlate well with the mud average density variation. The presented results can be very useful for fluid-mud monitoring at a lab scale, besides possible utilization for large-scale monitoring field campaigns.
-
-
-
Diffraction Recognition Using Deep Learning
Authors M. Markovic Juhlin, R. Malehmir and A. MalehmirSummaryDiffractions are important features in seismic data that carry information on small-scale geological entities. Because of their low-energy signal compared to the reflected waves, in order to image them, diffraction signal needs to be separated from the rest of the wavefield including ambient noise. Several methods have been developed for diffraction signal separation, and the newest trends include deep learning algorithms. Using deep learning, as a tool for diffraction recognition and separation has been promising particularly in sedimentary settings. In this study we use deep learning algorithm for diffraction classification in hardrock settings dominated with much lower signal-to-noise ratio and much higher background velocity. Staring with simple synthetic seismic sections and in order to make more complex case, we add more features such as different noise levels and reflection features with different dip directions. Results show good potential, taking into account a limited amount of training data. We also employed the developed algorithm on a real GPR dataset with strong diffractions to showcase the workflow. Our longer-term plan is to build a workflow enabling deep learning algorithms for hardrock seismic datasets in order to automatize feature extractions including diffractions.
-
-
-
Seismic SH Full Waveform Inversion: A tool for high-resolution near-surface characterization
Authors D. Köhn, M. Zolchow, R. Mecking, D. Wilken, T. Wunderlich, D. De Nil and W. RabbelSummaryIn recent years, Seismic Full Waveform Inversion (FWI) has been established as a high-resolution prospection method. Since 2014, the Applied Geophysics working group at Christian-Albrechts-University Kiel applied FWI to seismic SH data with different degrees of complexity for near-surface characterization tasks related to archaeological prospection and engineering geophysics. In this talk, we will review three of our field data applications which demonstrate the potential of FWI to resolve near-surface structures. The close collaboration with archaeologists allowed the unique opportunity to compare FWI results with the true subsurface structures. In the first example, SH-FWI is applied to field data from a transect over a medieval canal structure in southern Germany. The FWI is able to resolve the definition of the canal shape and small-scale structures within the canal. Significant surface topography poses another challenge for FWI. An example with significant surface topography is the Danewerk fortification wall in northern Germany. In this case, the FWI is able to resolve structures related to the construction history of the Danewerk. Finally, we applied a 2D SH-FWI workflow to resolve a partially collapsed excavation tunnel embedded deep inside a burial mound in Pergamon (Turkey).
-