| 1. |
|
|
| 2. |
- Brodic, Bojan, et al.
(författare)
-
Innovative seismic imaging of volcanogenic massive sulfide deposits, Neves-Corvo, Portugal - Part 1 : In-mine array
- 2021
-
Ingår i: Geophysics. - : Society of Exploration Geophysicists. - 0016-8033 .- 1942-2156. ; 86:3, s. B165-B179
-
Tidskriftsartikel (refereegranskat)abstract
- To evaluate and upscale the feasibility of using exploration tunnels in an operating mine for active-source seismic imaging, a seismic experiment was conducted at the Neves-Corvo mine, in southern Portugal. Four seismic profiles were deployed in exploration drifts approximately 650 m beneath the ground surface, above the world-class Lombador volcanogenic massive sulfide deposit. In addition to the tunnel profiles, two perpendicular surface seismic profiles were deployed above the exploration tunnels. The survey was possible due to a newly developed prototype global positioning system (GPS) time transmitter enabling accurate GPS synchronization of cabled and nodal seismic recorders, below and on the surface. Another innovative acquisition aspect was a 1.65 t broadband, linear synchronous motor (LSM) driven - electric seismic vibrator (e-vib) used as the seismic source along two of the exploration tunnels. We have evaluated the challenges and innovations necessary for active-source tunnel seismic acquisition, characterized by high levels of vibrational noise from the mining activities. In addition, we evaluated the LSM vibrator's signal and overall seismic-data quality in this hard rock mining environment. Our processing results from the tunnel data and 3D reflection imaging of the Lombador deposit below the exploration tunnels were checked for consistency through constant-velocity 3D ray-tracing traveltime forward modeling. For imaging purposes, 3D Kirchhoff prestack depth and poststack time-migration algorithms were used, with both successfully imaging the targeted deposit. The results obtained show that active-source-seismic imaging using subsurface mining infrastructure of operational mines is possible. However, it requires innovative exploration strategies, a broadband seismic source, an accurate GPS-time system capable of transmitting GPS-time hundreds of meters below the surface, and careful processing. The results obtained open up possibilities for similar studies in different mining or tunneling projects.
|
|
| 3. |
- Brodic, Bojan, et al.
(författare)
-
Multicomponent broadband digital-based seismic landstreamer for near-surface applications
- 2015
-
Ingår i: Journal of Applied Geophysics. - : Elsevier BV. - 0926-9851 .- 1879-1859. ; 123, s. 227-241
-
Tidskriftsartikel (refereegranskat)abstract
- During the last few decades there has been an increased demand for infrastructure, along with a greater awareness of environmental issues in the construction industry. These factors have contributed to an increased interest in using seismic methods for near surface characterization, particularly in urban environments. Seismic sensors not affected by anthropogenic electromagnetic noise are therefore important, as well as an acquisition system that is easy to deploy, move and non-invasive. To address some of these challenges, a multicomponent broadband MEMS (micro-electro mechanical system) based landstreamer system was developed. The landstreamer system is fully digital, therefore it is less sensitive to electrical or electromagnetic noise. Crosstalk, leakage and tilting tests show that the system is superior to its predecessors. The broadband nature of the sensors (theoretically 0–800 Hz), 3C (three-component) recording and the close spacing of the sensors enable high-resolution imaging. The current streamer configuration consists of 20 sensors 4 m apart and 80 sensors 2 m apart. The streamer can easily be combined with wireless recorders for simultaneous data acquisition. In this study, we present results from testing of the streamer with various sources, such as a shear wave vibrator and different types of impact sources. MEMS-sensors and their high sensitivity allowed recording clear reflections that were not observed with coil-based sensors. A complementary test was also carried out at a planned access ramp for an urban tunnel where potential poor quality rocks had been identified by drilling. First-break traveltime tomography showed that these poor quality rocks correlate with low velocity zones. The presented landstreamer system has great potential for characterizing the subsurface in noisy environments.
|
|
| 4. |
- Hudson, Lawrence N, et al.
(författare)
-
The database of the PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) project
- 2017
-
Ingår i: Ecology and Evolution. - : John Wiley & Sons. - 2045-7758. ; 7:1, s. 145-188
-
Tidskriftsartikel (refereegranskat)abstract
- The PREDICTS project-Projecting Responses of Ecological Diversity In Changing Terrestrial Systems (www.predicts.org.uk)-has collated from published studies a large, reasonably representative database of comparable samples of biodiversity from multiple sites that differ in the nature or intensity of human impacts relating to land use. We have used this evidence base to develop global and regional statistical models of how local biodiversity responds to these measures. We describe and make freely available this 2016 release of the database, containing more than 3.2 million records sampled at over 26,000 locations and representing over 47,000 species. We outline how the database can help in answering a range of questions in ecology and conservation biology. To our knowledge, this is the largest and most geographically and taxonomically representative database of spatial comparisons of biodiversity that has been collated to date; it will be useful to researchers and international efforts wishing to model and understand the global status of biodiversity.
|
|
| 5. |
- Hudson, Lawrence N., et al.
(författare)
-
The PREDICTS database : a global database of how local terrestrial biodiversity responds to human impacts
- 2014
-
Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 4:24, s. 4701-4735
-
Tidskriftsartikel (refereegranskat)abstract
- Biodiversity continues to decline in the face of increasing anthropogenic pressures such as habitat destruction, exploitation, pollution and introduction of alien species. Existing global databases of species' threat status or population time series are dominated by charismatic species. The collation of datasets with broad taxonomic and biogeographic extents, and that support computation of a range of biodiversity indicators, is necessary to enable better understanding of historical declines and to project - and avert - future declines. We describe and assess a new database of more than 1.6 million samples from 78 countries representing over 28,000 species, collated from existing spatial comparisons of local-scale biodiversity exposed to different intensities and types of anthropogenic pressures, from terrestrial sites around the world. The database contains measurements taken in 208 (of 814) ecoregions, 13 (of 14) biomes, 25 (of 35) biodiversity hotspots and 16 (of 17) megadiverse countries. The database contains more than 1% of the total number of all species described, and more than 1% of the described species within many taxonomic groups - including flowering plants, gymnosperms, birds, mammals, reptiles, amphibians, beetles, lepidopterans and hymenopterans. The dataset, which is still being added to, is therefore already considerably larger and more representative than those used by previous quantitative models of biodiversity trends and responses. The database is being assembled as part of the PREDICTS project (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems - ). We make site-level summary data available alongside this article. The full database will be publicly available in 2015.
|
|
| 6. |
- Malehmir, Alireza, et al.
(författare)
-
High-resolution Multicomponent Hardrock Seismic Imaging of Mineral Deposits and their Host Rock Structures
- 2014
-
Konferensbidrag (refereegranskat)abstract
- Although applied in the past, there are only a few cases demonstrating the advantages of multicomponentseismic data for mineral exploration. To illustrate this, a test survey using sixty 3C-digital sensors, spacedbetween 2 to 4 m and assembled in a 160 m long landstreamer, was carried out to provide information onshallow structures hosting mineralization and also a magnetic lineament with an unknown origin. Thesurvey, totally about 1.3 km long, was complemented by Radio MagnetoTelluric (RMT) measurements.Although an explosive source was used to generate the seismic signal, the seismic data show good qualityfor all the three components. Supported by the RMT results, clear reflections are observed in thehorizontal component data at about 25 m depth, one of them steeply dipping, likely associated with themagnetic lineament. Field static corrections were well estimated thanks to the close shot and receiverspacing and the broadband frequency content of the data. This study demonstrates that multicomponentseismic data can be useful for providing information on shallow structures and linking them to the surfacegeology. The vertical component data, however, show deeper penetration and better image the crystallinebasement and its undulated/faulted surface at about 50 m depth.
|
|
| 7. |
|
|
| 8. |
- Pedersen, Laust B., et al.
(författare)
-
Some characteristics of the electromagnetic field from radio transmitters in Europe
- 2006
-
Ingår i: Geophysics. - : Society of Exploration Geophysicists. - 0016-8033 .- 1942-2156. ; 71:6, s. G279-G284
-
Tidskriftsartikel (refereegranskat)abstract
- The radiomagnetotelluric (RMT) method utilizes man-made signals generated by distant transmitters or by dedicated local transmitters. Man-made electromagnetic (EM) signals in the 1-250-kHz frequency band come mainly from two sources: (1) distant radio transmitters operating in the 15-250-kHz band and (2) nearby or distant industrial sources emitting either transients or higher harmonics of 50 Hz. The natural or background EM signals form a kind of noise floor. In Europe for the 15-250-kHz band, there generally are sufficient transmitters available to estimate the EM transfer functions completely, i.e., the full impedance tensor and the tipper vector. We show examples of the variability of power spectra and azimuthal distributions of transmitters from sites in Sweden, Hungary, The Netherlands, and Spain. We also show that the estimated transfer functions are stable as a function of time; even under typical noisy conditions, simple stacking of spectra in narrow frequency bands provides good-quality estimates of transfer functions.
|
|
| 9. |
- Wang, Shunguo, et al.
(författare)
-
Controlled Source Boat-towed Radio-magnetotellurics for Site Investigation at Äspö Hard Rock Laboratory, Southeastern Sweden
- 2017
-
Konferensbidrag (refereegranskat)abstract
- The radio-magnetotelluric (RMT) method has traditionally been used for land investigations. However, with the development of the boat-towed RMT system, this method is used on shallow water. The lowest frequency of the RMT method is about 14 kHz and in addition water resistivity is quite low in some cases, therefore controlled source measurements is naturally considered for data acquisition. In order to resolve a fracture zone under a brackish water body, the controlled source boat-towed RMT (CSRMT) approach was tested. CSRMT and RMT one-dimensional inversions were carried out separately to analyze galvanic distortions and source effects in our dataset. Serious distortions observed in both inversions as well as the two-dimensional (2D) structure observed in our previous study made us consider 2D inversion for modeling the data. Due to the sufficiently large distance between transmitter and receivers, the CSRMT data were inverted using a 2D inversion code originally designed for plane-wave RMT data. Occam and damped Occam schemes were used in our 2D inversions for CSRMT and RMT data. The results show that CSRMT can better resolve the fracture zone than RMT. This study further illustrates the use of the boat-towed RMT system and particularly when combined with controlled source.
|
|
