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Kuchler, M., Craig-Thompson, A., Alofe, E. & Tryggvason, A. (2024). SubCity: Planning for a sustainable subsurface in Stockholm. Tunnelling and Underground Space Technology, 144, 105545, Article ID 105545.
Open this publication in new window or tab >>SubCity: Planning for a sustainable subsurface in Stockholm
2024 (English)In: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 144, p. 105545-, article id 105545Article in journal (Refereed) Published
Abstract [en]

With an expected increase in urbanisation and low-carbon transition efforts, the planning of cities is becoming more challenging, and societies need to rethink how urban infrastructures will be constructed in the future. There is a growing recognition that the use of space below the city will need to be significantly enhanced. However, once transformed, underground space becomes a permanent feature, and major metropolitan areas worldwide are gradually acknowledging the subsurface as a valuable, non-renewable resource, emphasising the necessity for long-term, comprehensive, and sustainable planning of its utilisation. Sweden, including the Stockholm region, has favourable geological conditions for building underground facilities and a long tradition of subsurface engineering. Despite these advantages, Stockholm lacks a comprehensive, long-term underground plan or strategy. For years, major subsurface projects have been driven by short-term needs, potentially hindering the optimal use of space below the cityscape. The overall purpose of this paper is twofold. First, we explore the nascent area of scholarly work concerned with the case of Stockholm’s subsurface. We do so by evaluating the current status and potential of urban underground planning in Stockholm municipality. Second, we seek to advance existing planning knowledge and practices concerning Stockholm’s subsurface by identifying several distinct but interrelated gaps and challenges that impede the immediate integration of urban underground space into strategic decision-making for the future of underground planning in Stockholm. We suggest that further research is necessary in several key areas to facilitate the effectiveness and sustainability of long-term urban underground use and planning in Stockholm City and its metropolitan area.

Place, publisher, year, edition, pages
Elsevier, 2024
Keywords
Subsurface, Underground, Underground urban space, Underground urban planning, Sustainable, Stockholm
National Category
Geophysics Infrastructure Engineering
Identifiers
urn:nbn:se:uu:diva-521583 (URN)10.1016/j.tust.2023.105545 (DOI)001145831500001 ()
Funder
Swedish Research Council Formas, 2021-00106
Available from: 2024-01-25 Created: 2024-01-25 Last updated: 2024-02-02Bibliographically approved
Gudmundsson, A., Bazargan, M., Hobé, A., Selek, B. & Tryggvason, A. (2021). Dike-Segment Propagation, Arrest, and Eruption at Fagradalsfjall, Iceland. In: : . Paper presented at AGU Fall Meeting 2021, New Orleans, LA and Online, 13-17 December, 2021.
Open this publication in new window or tab >>Dike-Segment Propagation, Arrest, and Eruption at Fagradalsfjall, Iceland
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2021 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

The volcanic eruption that began on 19 March 2021 at Fagradalsfjall is the first one to occur on the Reykjanes Peninsular for nearly 800 years and in Fagradalsfjall for about 6000 years. The feeder-dike was injected from a magma reservoir whose top is at about 10 km depth below the surface (but the reservoir itself reaches much greater depths). The dike formation involved at least two roof ruptures and resulting dike segments. The first occurred on 24 February and the second on 14 March 2021. The first rupture, marked by earthquakes of M23 close to the contact between the roof and the magma, occurred in the eastern half of the toppart of the reservoir. An injected dike segment propagated towards the surface but became arrested at the depths of 0.5-2 km. As its vertical propagation became arrested, while continuing to receive magma, the segment spread laterally, reaching an overall maximum dike strike-dimension (length) of about 10 km. The second rupture, also marked by earthquakes of M2-3, occurred about 1 km to the west of the first rupture. The injected dike segment following the second rupture eventually resulted in the dike propagating to the surface to feed the eruption which started on 19 March. We estimate the average vertical rate of the feeder-dike propagation at about 0.02 m s-1. This is an order of magnitude lower than common rates of lateral dike propagation in rift zones, yet similar to the average rate during the Bardarbunga (Iceland) 2014 dike propagation (around 0.04 m s-1). The initial volcanic fissure fed by the second dike segment had a length of less than 200 m and an opening of a fraction of a metre. Subsequently, several more ‘dike-fingers’ reached the surface and generated volcanic fissure segments. The total length of the discontinuous, segmented fissure is many hundred metres – but only one crater is presently active. Using the aspect ratio of the fissure and basic fracture mechanics, we estimate the magmatic overpressure (driving pressure) at the beginning of the eruption as about 3 MPa. The low driving pressure and small fissure opening displacement and length are in harmony with the very low volumetric flow (effusion) rate of about 10 m3 s-1.

National Category
Geosciences, Multidisciplinary Geology
Identifiers
urn:nbn:se:uu:diva-459799 (URN)10.1002/essoar.10508827.3 (DOI)
Conference
AGU Fall Meeting 2021, New Orleans, LA and Online, 13-17 December, 2021
Available from: 2021-11-29 Created: 2021-11-29 Last updated: 2022-02-10Bibliographically approved
Hobe, A., Gudmundsson, Ó., Tryggvason, A. & The SIL Seismological Group, -. (2021). Imaging the 2010-2011 Inflationary Source at Krysuvik, SW Iceland, Using Time-Dependent Vp/Vs Tomography. In: World Geothermal Congress 2020+1: . Paper presented at World Geothermal Congress 2020+1.
Open this publication in new window or tab >>Imaging the 2010-2011 Inflationary Source at Krysuvik, SW Iceland, Using Time-Dependent Vp/Vs Tomography
2021 (English)In: World Geothermal Congress 2020+1, 2021Conference paper, Published paper (Refereed)
Abstract [en]

Near Reykjavik, the capital of Iceland, lies the Krysuvik high-temperature geothermal area, which could potentially provide vast amounts of energy to this and surrounding towns and villages. Possible changes to the heat-source and/or hydrothermal system in this area are indicated by a period of surface deformation between 2007 and 2016 (Gudjonsdottir et al., 2018). This study provides subsurface images below Krysuvik and the neighboring areas with high resolution down to 10 km depth using 15 years of earthquake data. These images indicate regions of partial-melt and a large super-critical reservoir below ~5 km depth, which would serve well as a fluid source for a new power-plant. The robustness of this model is assessed using time-dependent seismic tomography. Through systematic study of known issues with time-dependent seismic tomography, it is shown that significant changes do occur in the results on time-scales comparable to the surface deformation. Changes that we assess and suggest are significant beyond e.g. the influence of differences in ray-path geometries and travel-time errors. Several hypotheses are developed based on these results and available information from multiple disciplines. Based on this integration of information with our results, the most likely explanations of the surface deformation signal are: 1) strong degassing of a magmatic source due to increased heat from deeper magmatic infiltration,and 2) bending and subsequent fracturing of an impermeable barrier by expanding fluids.

Keywords
Vp/Vs tomography, time-dependent seismic tomography, Krysuvik, geothermal energy, surface deformation
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-482651 (URN)
Conference
World Geothermal Congress 2020+1
Available from: 2022-08-24 Created: 2022-08-24 Last updated: 2022-10-06Bibliographically approved
Abril, C., Tryggvason, A., Gudmundsson, Ó. & Steffen, R. (2021). Local Earthquake Tomography in the Tjörnes Fracture Zone (North Iceland). Journal of Geophysical Research - Solid Earth, 126(6), Article ID e2020JB020212.
Open this publication in new window or tab >>Local Earthquake Tomography in the Tjörnes Fracture Zone (North Iceland)
2021 (English)In: Journal of Geophysical Research - Solid Earth, ISSN 2169-9313, E-ISSN 2169-9356, Vol. 126, no 6, article id e2020JB020212Article in journal (Refereed) Published
Abstract [en]

Local earthquake tomography has been carried out in the Tjornes Fracture Zone. This transform region connects the Mid-Atlantic Ridge to the Northern Volcanic Zone in Iceland in a mostly offshore area. The challenge to record seismic information in this area was the motivation for the North ICeland Experiment (NICE). Fourteen ocean-bottom seismometers and eleven on-land stations were installed in the project and operated simultaneously with the permanent Icelandic seismic network (SIL) during summer 2004. Data from the experiment were used to estimate P- and S-wave crustal velocities. Also, the gravity anomaly was derived for comparison with the tomographic results. Upper-crustal velocities are found to be relatively low in the offshore region. In particular, low velocities are mapped along the Husavik-Flatey Fault, where a more confined negative gravity anomaly and a sedimentary basin are found. Low velocities are also mapped along the Grimsey Oblique Rift and in a zone connecting these two main lineaments. The northern half of the aseismic Grimsey Shoal appears as a fast anomaly. Furthermore, localized high-velocity anomalies are found beneath northern Trollaskagi and Flateyjarskagi Peninsulas, where bedrock dates from Upper and Middle Miocene (10-15 Ma). Regions of low Vp/Vs ratios are mapped at depth along the main lineaments. Low velocities along the lineaments are interpreted as due to fracturing extending into the middle crust, while high velocities in the upper crust beneath Tertiary formations are associated with relic volcanoes. Low Vp/Vs variations along the lineaments are interpreted as due to the presence of supercritical fluids.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2021
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-363252 (URN)10.1029/2020JB020212 (DOI)000665206200017 ()
Funder
Swedish Research Council, 2003-3600German Research Foundation (DFG), Da478/13-1German Research Foundation (DFG), RI1220/2-1
Note

Title in dissertation list of papers: Local earthquake tomography and earthquake relocation in the Tjörnes Fracture Zone (North Iceland)

Available from: 2018-10-15 Created: 2018-10-15 Last updated: 2024-01-15Bibliographically approved
Hobe, A., Geirsson, H., Tryggvason, A., Gudmundsson, Ó. & The Sil Seismological Group, -. (2021). Seismicity Patterns Due to Magma Intrusions Underneath Geothermal Power Plants. In: World Geothermal Congress 2020+1: . Paper presented at World Geothermal Congress 2020+1.
Open this publication in new window or tab >>Seismicity Patterns Due to Magma Intrusions Underneath Geothermal Power Plants
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2021 (English)In: World Geothermal Congress 2020+1, 2021Conference paper, Published paper (Refereed)
Abstract [en]

The Reykjanes Peninsula, Iceland, could soon see a once-in-a-millennium eruption, based on its current unrest and its historical record. This period of volcano-tectonic events threatens nearby airfields, geothermal power plants, and the capital, Reykjavik, where two thirds of Iceland’s population reside. The main sources of risk are lava, volcanic ash, and M > 6 earthquakes on large strike-slip faults. Six such known faults lie between 15-35 km from the capital. Here, we investigate whether such large earthquakes and/or an eruption are likely, based on the seismicity seen so far. To do so, we look for specific seismicity patterns indicative of magmatically-induced deformation, and compare seismicity overviews of the current unrest, previous decades, and swarm activity in the 1970s. We identify several cascades of boundary movements in both the current unrest and the 1970s activity, that have neighboring segments activate from east to west along the peninsula. This direction is reversed during the current unrest in a slower cascade, which ended with a ~30 km long boundary segment moving. Based on this and other observations, we suggest that magma intrusion has accelerated boundary deformation significantly. We identify another pattern, where seismicity and surface deformation in Svartsengi, the most seismically active region during this period, is greatly reduced when this activity swaps to the neighboring Reykjanes system. We suggest magma intrusion is halted in one volcanic system, in favor of intrusion in another, and describe several possible mechanisms.We further describe possible scenarios, and their likelihood, for the evolution of the current unrest, which range from a rapid return to quiescence, to full-scale eruption. Whichever scenario occurs, M > 6 earthquakes on known faults near Reykjavik are likely.

Keywords
Seismicity patterns, geothermal power plant, magma intrusion, risk, oblique rift, reservoir stimulation
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-482654 (URN)
Conference
World Geothermal Congress 2020+1
Available from: 2022-08-25 Created: 2022-08-25 Last updated: 2022-10-06Bibliographically approved
Sadeghisorkhani, H., Gudmundsson, Ó., Li, K. L., Tryggvason, A., Lund, B. & Högdahl, K. (2021). Shear wave structure of southern Sweden from precise phase-velocity measurements of ambient-noise data. Geophysical Journal International, 225(1), 494-511
Open this publication in new window or tab >>Shear wave structure of southern Sweden from precise phase-velocity measurements of ambient-noise data
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2021 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 225, no 1, p. 494-511Article in journal (Refereed) Published
Abstract [en]

Rayleigh-wave phase-velocity tomography of southern Sweden is presented using ambient seismic noise at 36 stations (630 station pairs) of the Swedish National Seismic Network. We analyse 1 yr (2012) of continuous recordings to get the first crustal image based on the ambient-noise method in the area. Time-domain cross-correlations of the vertical component between the stations arc computed. Phase-velocity dispersion curves arc measured in the frequency domain by matching zero crossings of the real spectra of cross-correlations to the zero crossings of the zeroth-order Bessel function of the first kind. We analyse the effect of uneven source distributions on the phase-velocity dispersion curves and correct for the estimated velocity bias before tomography. To estimate the azimuthal source distribution to determine the bias, we perform inversions of amplitudes of cross-correlation envelopes in a number of period ranges. Then, we invert the measured and bias-corrected dispersion curves for phase-velocity maps at periods between 3 and 30 s. In addition, we investigate the effects of phase-velocity bias corrections on the inverted tomographic maps. The difference between bias-corrected and -uncorrected phase-velocity maps is small (<1.2 per cent), but the correction significantly reduces the residual data variance at long periods where the bias is biggest. To obtain a shear velocity model, we invert for a 1-D velocity profile at each geographical node. The results show some correlation with surface geology, regional seismicity and gravity anomalies in the upper crust. Below the upper crust, the results agree well with results from other seismological methods.

Place, publisher, year, edition, pages
Oxford University PressOXFORD UNIV PRESS, 2021
Keywords
Europe, Seismic interferometry, Seismic noise, Seismic tomography, Surface waves and free oscillations
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-443049 (URN)10.1093/gji/ggaa598 (DOI)000646864000028 ()
Available from: 2021-05-28 Created: 2021-05-28 Last updated: 2024-01-15Bibliographically approved
Hobe, A., Selek, B., Bazargan, M., Gudmundsson, A. & Tryggvason, A. (2021). Using Seismicity and Tomographic Imaging to Infer the Location and Rupture of the Reservoir that Supplies magma to the 2021 Eruption at Fagradalsfjall, Iceland. In: : . Paper presented at AGU 2021, New Orleans and Online, 13-17 December, 2021.
Open this publication in new window or tab >>Using Seismicity and Tomographic Imaging to Infer the Location and Rupture of the Reservoir that Supplies magma to the 2021 Eruption at Fagradalsfjall, Iceland
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2021 (English)Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

Although many deep-seated magma reservoirs have been detected beneath active volcanic systems in Iceland in recent decades, none were detected beneath the 5 volcanic systems on the Reykjanes Peninsula (RP) before the year 2020. This area, close to Iceland’s capital Reykjavik, was subject to an unrest period with numerous earthquakes, beginning in December 2019. Using this abundant seismicity to produce tomographic images of the RP, we discovered a high Vp/Vs anomaly below the volcanic system of Fagradalsfjall – the smallest of the 5 systems on the RP. This anomaly is clear on images as early as May 2020 and we interpret it as the top part of the source reservoir of the Fagradalsfjall Volcanic System, which now supplies magma to the eruption that started there on 19 March 2021. From the tomographic images, we infer that the roof of the reservoir is at ~10 km below the surface of the volcanic system, but the reservoir itself extends much deeper. We interpret the results as magma accumulation in the upper part of the reservoir at least by May 2020, and probably earlier, resulting in a slight magma-pressure increase and doming of the reservoir roof. The associated stress changes in the roof triggered several earthquake swarms throughout 2020 and into early 2021. Within the part of the roof closest to the reservoir (between 9-12 km depth) 40 earthquakes occurred during 2020. This number doubled again between 1 January and 19 March 2021, when the eruption began. We interpret the preceding earthquake swarm, which began on 24 February 2021 with an earthquake of M5.6, as being associated with the rupture of the roof of the reservoir and dike-segment injection. We interpret the increased activity on the 14th of March, and its location, as a second rupture and a new dike-segment injection which ultimately lead to the eruption, which is still on-going at the time of writing. The reservoir is the first one detected below any of the volcanic systems on the RP. Furthermore, the reservoir supplies magma to the first eruption on the RP for nearly 800 years and the first eruption in Fagradalsfjall for some 6000 years.

National Category
Geology
Identifiers
urn:nbn:se:uu:diva-459800 (URN)10.1002/essoar.10508916.1 (DOI)
Conference
AGU 2021, New Orleans and Online, 13-17 December, 2021
Available from: 2021-11-29 Created: 2021-11-29 Last updated: 2022-01-20Bibliographically approved
García Juanatey, M. d., Hübert, J., Tryggvason, A., Juhlin, C., Pedersen, L. B., Bauer, T. E. & Dehghannejad, M. (2019). 2D and 3D MT in the central Skellefte Ore District, northern Sweden. Tectonophysics, 764, 124-138
Open this publication in new window or tab >>2D and 3D MT in the central Skellefte Ore District, northern Sweden
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2019 (English)In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 764, p. 124-138Article in journal (Refereed) Published
Abstract [en]

New broadband magnetotelluric (MT) data have been acquired along two parallel profiles in the central part of the metallogenic Skellefte district in northern Sweden. The data were recorded as part of the Swedish 4D modelling of mineral belts project and cover an area with several economical and sub-economical deposits. The dimensionality and quality of the data were carefully analyzed and new error floors were systematically determined prior to inverse modelling in 2D and 3D. The algorithms used were EMILIA and WSINV3DMT. For the 2D inversion, only the determinant of the impedance tensor was used, while for the 3D inversion all elements were considered. The obtained models fit the inverted data, and image the main regional features. A detailed comparison reveals the superiority of the 3D model, both in model structures and data fit. After assessing the main features in the model, an interpretation is proposed and refined with the support of previous geophysical studies. The most interesting features are large and medium-sized conductors associated with crustal-scale shear zones and faults within the Skellefte Group rocks. These may be depicting a network of fossil pathways for hydrothermal fluid transport and as such, provide new insight into past processes in the area.

Keywords
Magnetotellurics, 3D inversion, Deep exploration, Brownfield, Shear zones, Mineral systems
National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
urn:nbn:se:uu:diva-178057 (URN)10.1016/j.tecto.2019.04.003 (DOI)000472697900008 ()
Projects
VINNOVA 4D modeling of mineral belts
Funder
Vinnova
Available from: 2012-07-26 Created: 2012-07-26 Last updated: 2021-06-14Bibliographically approved
Huang, G., Luo, S., Tryggvason, A., Li, H. & Nobes, D. C. (2019). First-arrival tomography with fast sweeping method solving the factored eikonal equation. Exploration Geophysics, 50(2), 144-158
Open this publication in new window or tab >>First-arrival tomography with fast sweeping method solving the factored eikonal equation
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2019 (English)In: Exploration Geophysics, ISSN 0812-3985, E-ISSN 1834-7533, Vol. 50, no 2, p. 144-158Article in journal (Refereed) Published
Abstract [en]

This paper presents a first-arrival tomography incorporating a fast sweeping method (FSM) solving the factored eikonal equation (factored FSM). The traveltime calculation method plays a significant role in velocity inversion. However, for a point source condition, all finite-difference based eikonal solvers suffer from the source singularity problem. Numerical error caused by source singularity will propagate from the source to all computational domains, and makes traveltimes inaccurate. A FSM solving the factored eikonal equation can deal with the source singularity problem very well. Therefore, a first-arrival tomography is developed by incorporating 2D and 3D factored FSMs to provide more accurate traveltimes in velocity inversion. For comparison, an open source package PStomo_eq is used to invert the same data set. It incorporates the traveltime calculation algorithms fdtime2d.c and fdtime3d.c. Traveltime accuracy tests show that factored FSM can generate more accurate traveltimes than FSM, fdtime2d.c and fdtime3d.c. Numerical and field data tests show that inversion with factored FSM can acquire much better tomograms than inversion with fdtime2d.c and fdtime3d.c. Therefore, it is worthwhile using a more accurate traveltime computation method in velocity inversion.

Place, publisher, year, edition, pages
TAYLOR & FRANCIS LTD, 2019
Keywords
seismic tomography, fast sweeping method, factored eikonal equation
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-392846 (URN)10.1080/08123985.2019.1577110 (DOI)000478064000004 ()
Available from: 2019-09-10 Created: 2019-09-10 Last updated: 2019-09-10Bibliographically approved
Wagner, F., Tryggvason, A., Roberts, R. & Gudmundsson, Ó. (2019). Processing automatic seismic event detections: an iterative sorting algorithm improving earthquake hypocentres using interevent cross-correlation. Geophysical Journal International, 219(2), 1268-1280
Open this publication in new window or tab >>Processing automatic seismic event detections: an iterative sorting algorithm improving earthquake hypocentres using interevent cross-correlation
2019 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 219, no 2, p. 1268-1280Article in journal (Refereed) Published
Abstract [en]

We present an iterative classification scheme using interevent cross-correlation to update an existing earthquake catalogue with similar events from a list of automatic seismic event detections. The algorithm automatically produces catalogue quality events, with improved hypocentres and reliable P- and S-arrival time information. Detected events are classified into four event categories with the purpose of using the top category, with the highest assessed event quality and highest true-to-false ratio, directly for local earthquake tomography without additional manual analysis. The remaining categories have varying proportions of lower quality events, quality being defined primarily by the number of observed phase onsets, and can be viewed as different priority groups for manual inspection to reduce the time spent by a seismic analyst. A list of 3348 event detections from the geothermally active volcanic region around Hengill, southwest Iceland, produced by our migration and stack detector (Wagner et al. 2017), was processed using a reference catalogue of 1108 manually picked events from the same area. P- and S-phase onset times were automatically determined for the detected events using correlation time lags with respect to manually picked phase arrivals from different multiple reference events at the same station. A significant improvement of the initial hypocentre estimates was achieved after relocating the detected events using the computed phase onset times. The differential time data set resulting from the correlation was successfully used for a double-difference relocation of the final updated catalogue. The routine can potentially be implemented in real-time seismic monitoring environments in combination with a variety of seismic event/phase detectors.

National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-376655 (URN)10.1093/gji/ggz362 (DOI)000491050200039 ()
Funder
Swedish Research Council, 2008:3754
Available from: 2019-02-07 Created: 2019-02-07 Last updated: 2020-01-03Bibliographically approved
Projects
Time-laps tomography in volcanic regions – means of better understanding volcanic and earthquake processes [2008-03754_VR]; Uppsala UniversityTime-laps tomography in volcanic regions – means of better understanding volcanic and earthquake processes [2008-07945_VR]; Uppsala UniversityWaveform and travel time tomographic methods for imaging lithospheric structures beneath the Baltic Shield [2009-00365_VR]; Uppsala UniversitySurface waves and thermal-compositional modelling of the Fennoscandian lithosphere [2011-04711_VR]; Uppsala UniversitySubCity: Future imaginaries of the city subsurface [2020-00048_Formas]; Uppsala University; Publications
Kuchler, M., Craig-Thompson, A., Alofe, E. & Tryggvason, A. (2024). SubCity: Planning for a sustainable subsurface in Stockholm. Tunnelling and Underground Space Technology, 144, 105545, Article ID 105545.
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-2511-187X

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