GEOFYSIKK

Deep structures of the Norwegian margin: 2D/3D modelling and crustal evolution of the Rån ridge area

NGU-RAPPORT
2015.072
Publikasjonstype
Utgivelsesår
2016
ISSN
0800-3416
Prosjektnr
363700
Summary
2D/3D crustal models of the southwestern Vøring Basin have been established from gravity,
magnetic and recent seismic data. The Rån ridge area, in particular, has been investigated and discussed.
Two regional 2D seismic lines (MNR07-7319 and MNR8-7292) provided by Repsol have been modelled
across the soutwestern Vøring Basin. They helped to better constrain some of the controversial crustal
units as well as the top basement and Moho depths. The modelling shows that the continental crust has
been highly stretched and thinned in large parts of the southwestern Vøring Basin. Depth to basement
estimation suggests also that Triassic-Jurassic sediments are probably preserved on the Rån ridge, less
affected by the thinning process compared to the adjacent sub-basins. The modelling shows that the
Hevring sub-basin (as newly defined in this report) represents one of the thinnest crustal segments of the
Vigrid Syncline. To explain the apparent lack of classic rotated fault blocks in the Vigrid Syncline and
Hevring sub-basin, a decoupled model suggesting crustal boudinage is proposed to explain the evolution
of the Rån ridge. The LCB often coincides with the crustal raft and/or 'boudin' as modelled at the present
day. 3D seismics on the Rån ridge also show that deep lower-crustal bodies (LCB) already controlled the
structural style in the early rifting stage of the rifted margin and before the onset of more drastic crustal
thinning expected in the Late Jurassic - Early Cretaceous. A distinct phase of mid. Cretaceous extension is
also recognised in the Rån basin. It preceded the Late Cretaceous-Paleocene event leading to breakup in
the outer part of the outer Vøring Basin. The Rån ridge seems to have not been affected by this last rifting
event. The high-density lower-crustal block underneath the Rån ridge most likely represents old remnants
of the original Caledonian crust.
Forfattere
Gernigon, Laurent
Haase, Claudia
Tilgjengelig
NGU-biblioteket
Prosjekt
Deep structures of the Norwegian margin

Helicopter-borne magnetic, electro-magnetic and radiometric geophysical survey in Meråker, Trøndelag County

NGU-RAPPORT
2021.039
Publikasjonstype
Utgivelsesår
2022
ISSN
0800-3416
Prosjektnr
388900
Summary
As an addition to NGU’s general geophysical mapping in Trøndelag, NGU conducted a high-resolution airborne geophysical survey in Meråker area in Trøndelag County on request of Norra Metals. This report describes and documents the acquisition, processing and visualization of the acquired datasets and presents them in maps. The geophysical surveys consist of 1054 line-km data, covering an area of 219 km2 flown on July 21st, 2021.
The NGU modified Geotech Ltd. Hummingbird frequency domain electromagnetic system supplemented by an optically pumped Cesium magnetometer and the Radiation Solutions 1024 channels RSX-5 spectrometer mounted on a AS350-B3 helicopter was used for data acquisition.
Forfattere
Mrope, Frida Mathayo
Dumais, Marie-Andrée
Ofstad, Frode
Stampolidis, Alexandros
Nasuti, Aziz
Kristiansen, Tom
Tassis, Georgios
Kommune
MERÅKER
Fylke
TRØNDELAG
Tilgjengelig
NGU-biblioteket
Prosjekt
Flygeofysisk kartlegging av Norge

Helicopter-borne magnetic, electro-magnetic and radiometric geophysical survey in Bleikvasslia, Nordland County

NGU-RAPPORT
2021.036
Publikasjonstype
Utgivelsesår
2022
ISSN
0800-3416
Prosjektnr
388900
Summary
As an addition to NGU’s general geophysical mapping in Nordland, NGU conducted a high-resolution airborne geophysical survey in Bleikvasslia area in Nordland County on request of Norra Metals. This report describes and documents the acquisition, processing and visualization of the acquired datasets and presents them in maps. The geophysical surveys consist of 326.7 line-km data, covering an area of 59.3 km2 flown on August 21st, 2021.
The NGU modified Geotech Ltd. Hummingbird frequency domain electromagnetic system supplemented by an optically pumped Cesium magnetometer and the Radiation Solutions 1024 channels RSX-5 spectrometer mounted on a AS350-B3 helicopter was used for data acquisition.
Forfattere
Stampolidis, Alexandros
Dumais, Marie-Andrée
Ofstad, Frode
Mrope, Frida Mathayo
Nasuti, Aziz
Kommune
HEMNES
Fylke
NORDLAND
Tilgjengelig
NGU-biblioteket
Prosjekt
Flygeofysisk kartlegging av Norge

Helicopter-borne magnetic, electro-magnetic and radiometric geophysical survey in Evje and Hornnes and Iveland, Agder County

NGU-RAPPORT
2021.030
Publikasjonstype
Utgivelsesår
2021
ISSN
0800-3416
Prosjektnr
388900
Summary
As an addition to NGU’s general geophysical mapping in Agder, NGU conducted a high-resolution airborne geophysical survey in Evje & Hornnes and Iveland area in Agder county on request of Norse Minerals AS.
This report describes and documents the acquisition, processing and visualization of the acquired datasets and presents them in maps. The geophysical surveys consist of 301 line-km data, covering an area of 31.5 km2 flown on June 12th, 2021.
The NGU modified Geotech Ltd. Hummingbird frequency domain electromagnetic system supplemented by an optically pumped Cesium magnetometer and the Radiation Solutions 1024 channels RSX-5 spectrometer mounted on a AS350-B3 helicopter was used for data acquisition.
Forfattere
Mrope, Frida Mathayo
Dumais, Marie-Andrée
Ofstad, Frode
Baranwal, Vikas Chand
Tassis, Georgios
Kommune
EVJE OG HORNNES
IVELAND
Fylke
AGDER
Tilgjengelig
NGU-biblioteket
Prosjekt
Flygeofysisk kartlegging av Norge

Geofysikk. Elektriske metoder. Bruk, teori, utførelse og eksempler på tolkinger

NGU-RAPPORT
2023.016
Publikasjonstype
Utgivelsesår
2024
ISSN
0800-3416
Prosjektnr
329500
Summary
Rapporten er ment som et kompendium for undervisning ved NTNU, men også ved andre universiteter i
Norge. Andre interesserte inviteres også til å studere muligheter og begrensninger ved elektriske
målinger. Det gis en detaljert oversikt over:
• Ord og uttrykk
• Grunnleggende teori inklusive materialegenskaper
• Faktorer som påvirker elektriske målinger
• Vertikale elektriske sonderinger (VES), datainnsamling, inversjon og tolking
• 2D resistivitet (ERT), datainnsamling, inversjon og tolking
• Muligheter og begrensninger ved 2D resistivitet (Modellering)
• Selv Potensial (SP), datainnsamling, inversjon og tolking
• Indusert Polarisasjon (IP), datainnsamling, inversjon og tolking
• Oppladet potensial (CP), datainnsamling, inversjon og tolking
• Elektriske borehullsmålinger, ERT, SP, IP og CP
Eksempler på gode resultater innenfor:
• Forundersøkelser for tunneler
• Kartlegging og karakterisering av leire
• Kartlegging av grunnvann og grunnvannsforurensing
• Kartlegging av sand- og grusforekomster
• Kartlegging av ustabile fjellparti
• Kartlegging av permafrost
• Resistivitet i kombinasjon med andre metode
Forfattere
Rønning, Jan S.
Tilgjengelig
NGU-biblioteket

Trenching and 14C dating of the postglacial Stuoragurra Fault Complex in Finnmark, Northern Norway, and geohazard implications

NGU-RAPPORT
2023.026
Publikasjonstype
Utgivelsesår
2023
ISSN
0800-3416
Prosjektnr
404400
Summary
The Stuoragurra Fault Complex (SFC) constitutes the Norwegian part of the larger Lapland Province of postglacial faults in northern Fennoscandia. The 90 km long SFC consists of two separate fault systems: the Máze Fault (revised) System in the southwestern area and the Iešjávri Fault System to the northeast. The distance between the fault systems is 12 km. The faults dip at an angle of 30–75° to the SE. Here we present data from trenching of different fault sections. The trenching reveals deformed overburden in all 11 sites and inclusions of peat and organic bearing soil in the deformed and partly overrun loose deposits on the footwall in most of the sites. Radiocarbon dating of macro remains of plants located in buried and severely deformed sediment horizons indicates late Holocene ages for the (final) formation of the different fault segments, more specifically that the faulting at Fitnajohka and Máze in the Máze Fault System formed during earthquakes younger than c. 470-500 years ago.
Forfattere
Olsen, L.
Olesen, O.
Kommune
KAUTOKEINO
KARASJOK
ALTA
PORSANGER
Fylke
TROMS OG FINNMARK
Tilgjengelig
NGU-biblioteket
Prosjekt
GoN - Geophysics of Norway GIS & Atlas

Resistivitetsundersøkelser Kristiansand kommune, Agder

NGU-RAPPORT
2023.018
Publikasjonstype
Utgivelsesår
2023
ISSN
0800-3416
Prosjektnr
388500
Summary
NGU har utført undersøkelser med bakkegeofysikk i Kristiansand kommune for å følge opp enkelte områder som kan inneholde jarositt. Valgt metodikk er ERT, en metode som NGU har god erfaring med for å påvise forvitret fjell. Basert på områder hvor det påvist jarositt ble det valgt ut fire områder for videre oppfølging. Disse ble valgt basert på resultatet fra prøvetaking gjort i tidligere undersøkelser. Områdene ble i tillegg sammenliknet med NGU sitt AMAGER-kart for området. Dette er et produkt av topografi og magnetiske data hvor resultatet er et aktsomhetskart som viser potensielle områder med oppsprukket fjell eller forvitring.
Forfattere
Larsen, Bjørn Eskil
Gellein, Jomar
Kommune
KRISTIANSAND
Fylke
AGDER
Tilgjengelig
NGU-biblioteket
Prosjekt
Berggrunnsressurser og -utfordringer i Kristiansand

Helicopter-borne magnetic, electromagnetic and radiometric geophysical survey in Forollhogna area, Innlandet and Trøndelag Counties

NGU-RAPPORT
2022.018
Publikasjonstype
Utgivelsesår
2023
ISSN
0800-3416
Prosjektnr
388900
Summary
NGU conducted an airborne geophysical survey in Forollhogna area, in Rennebu, Midtre
Gauldal and Holtålen municipalities in Trøndelag County, and Tynset, Tolga and Os
municipalities in Innlandet County, as part of NGU’s general airborne mapping program. The
data acquisition in Forollhogna area was carried out from June 23rd to July 20th, 2021.
This report describes and documents the acquisition, processing and visualization of the
acquired datasets and presents them in maps. The geophysical survey consists of 8214 linekm data, covering an area of 1609 km2, flown from the base near Orvos (Flight 1-38) and from
the base near Frigården (Flight 39).
The NGU modified Geotech Ltd. Hummingbird frequency domain EM system supplemented
by an optically pumped Cesium magnetometer and the Radiation Solutions 1024 channels
RSX-5 spectrometer mounted on a AS350-B3 helicopter were used for data acquisition.
The data collected were processed at NGU using Geosoft Oasis Montaj software. Raw total
magnetic field data were corrected for diurnal variation and leveled using Geosoft microlevelling algorithm. Radiometric data were processed using standard procedures as
recommended by International Atomic Energy Association (IAEA).
EM data were filtered and leveled using both automated and manual levelling procedures.
Apparent resistivity was calculated from in-phase and quadrature data for three coplanar
frequencies (880Hz, 6.6kHz and 34kHz), and for two coaxial frequencies (980Hz and 7kHz)
separately using a homogeneous half space model.
All data were gridded using cell size of 50x50 meters and presented as 40% transparent
grids with shaded relief on top of topographic maps.
Forfattere
Ofstad, Frode
Dumais, Marie-Andrée
Barnes, Pierre-Carl
Kristiansen, Tom
Mrope, Frida Mthayo
Kommune
OS
MIDTRE GAULDAL
HOLTÅLEN
TOLGA
RENNEBU
Fylke
INNLANDET
TRØNDELAG
Tilgjengelig
NGU-biblioteket
Prosjekt
MINN - Helikoptermålinger

The SYM model to optimize geophysical deep-sea research with special application to Seafloor Massive Sulfides (SMS)

NGU-RAPPORT
2021.010
Publikasjonstype
Utgivelsesår
2021
ISSN
0800-3416
Prosjektnr
389600
Summary
This report describes the work done for the 1-year collaboration project between NGU and Equinor:
Seafloor massive sulfide (SMS) geophysical model. The project aims to establish a synthetic model for
the purpose of optimizing subsea acquisition and detection limits for SMS bodies at the seafloor via
AUV (autonomous underwater vehicle) geophysical surveys.
At the first stage of the project, a 3D layered geo-model is built for the study purpose. We call this model
the SYM model. An ultra-slow spreading mid-ocean ridge from the North Atlantic has been referenced
to establish the geological setting for this synthetic model. The SYM model size is ~100 km x 150 km
laterally with 100 m resolution, and 10 km vertically with 500 m resolution. Real bathymetry is used from
a region between Mohns Ridge and Knipovich Ridge as the starting point of the model design, based on
which a sediment layer, the pillow basalt and gabbro layer, the Moho, together with an intra mantle layer
to simulate mantle variations and/or Curie depth, have been built into the model with varying thickness –
thinner at the ridge, thicker further away from the ridge. Last but not least, 17 basalt-hosted SMS bodies
and 1 ultramafic-hosted SMS body have been imbedded into the model at or near the seafloor.
For the second part of the project, the model was transferred into an indexed voxel model to facilitate an
easy change between different petrophysical model parameters. Subsequently, forward modelling of
gravity and magnetic potential fields (and their gradients) has been conducted schematically on the
synthetic model to determine the optimal survey design for AUV acquisition of geophysical data.
Conclusions drawn from our synthetic tests describe what should be expected in an ideal environment
using AUV surveys for SMS detection. In this project, we also discuss challenges in practice regarding
instrumentation limitation, positioning precision, survey efficiency considerations, processing errors, etc.
Possible extensions of the project are discussed. For example, including more types of geophysical
data – namely, SP (self-potential) and EM (electromagnetic) – in addition to the potential fields. The 3D
synthetic voxel model could be used for benchmarking a variety of theoretical algorithms for deep sea
geological understanding, such as Curie-depth determination, hydrothermal studies, seismic imaging,
multi-geophysical data modelling and integration
Forfattere
Wang, Ying
Szitkar, Florent
Brönner, Marco
Tilgjengelig
NGU-biblioteket

Borehole logging in Smøla and Bømlo

NGU-RAPPORT
2021.005
Publikasjonstype
Utgivelsesår
2021
ISSN
0800-3416
Prosjektnr
380200
Summary
AS a part of the Base 2 project NGU has performed geophysical borehole logging in four boreholes at Smøla, Møre and Romsdal county and three at Bømlo, Vestland county. The purpose of the drilling and logging was to study onshore deep weathered basement rocks. Such rocks can be a potential oil reservoir offshore, on the continental shelf.
The logged parameters were resistivity, porosity, seismic velocity, water conductivity, total gamma radiation, spectral gamma, magnetic susceptibility, Induced Polarisation, and Self Potential. All boreholes were logged using acoustic and optical televiewer. Flow measurements and pumping were performed. Lugeon test were done by the drilling company.
The results show heavily fractured rock in all boreholes. Especially in Bh4 at Smøla the resistivity was very low. Combined with low p-wave velocity and fracturing it can be interpreted as weathered and altered rock. IP anomalies may indicate clay.
The Lugeon tests showed quite low values and correlates well with the fracture frequency. From the Lugeon numbers the hydraulic conductivity and permeability are calculated. Calculated apparent porosity from the resistivity log, using Archi's law, is in the same range as laboratory porosity measurements on cores performed by NTNU. Most of the porosity values are in the range of 1 – 4 %.
Flow measurements showed no vertical flow in the boreholes and no in/out flow from fractures. Pumping indicated very low water capacity in all wells except Bh3, Bømlo. Near surface water just below the casing flowed into the borehole.
Bh2 at Bømlo was stuck at 27 m depth. Reopening of the borehole failed, and masses (sand, clay) flowed into the borehole and blocked it.
Forfattere
Elvebakk, Harald
Gellein, Jomar
Larsen, Bjørn Eskil
Kommune
SMØLA
BØMLO
Fylke
MØRE OG ROMSDAL
VESTLAND
Tilgjengelig
NGU-biblioteket