The Fennoscandian earthquake catalogue (FENCAT) assembles data on the natural seismicity in Fennoscandia, Northern Europe. We present an updated and standardized version of the catalogue originally published in the early 1990s. New instrumental data are recorded by the seismic networks of Denmark, Estonia, Finland, Norway and Sweden, and analysed by the Geological Survey of Denmark and Greenland, the Geological Survey of Estonia, the University of Helsinki in Finland, the University of Bergen and the NORSAR research foundation in Norway and Uppsala University in Sweden. The updated catalogue provides the available earthquake parameters in a brief, user-friendly version: origin time, source coordinates, focal depth, macroseismic data (maximum intensity and radius of the area of perceptibility), up to three observed magnitudes, seismic moment estimate and a standardized moment-related magnitude, mW(HEL), for each event. The standardized magnitude is defined in this paper and its relation to other magnitude scales is provided. Suspected non-earthquakes (e.g. frost events, explosions, human-induced events) have been removed. The standardized event magnitudes range from mW(HEL) -1.0 to 6.2. To enable the usage of earthquake data in a large variety of seismological, geological and earthquake engineering investigations, the data are not truncated at the low-magnitude end.The updated catalogue, FENCAT (2021), contains about 23 000 earthquakes for the period 1467-2021 in an area bounded by 54-75 degrees N latitudes and 0-45 degrees E longitudes. The completeness and quality of the earthquake solutions is best within the areal coverage of the above-mentioned networks.

Finland, which is characterized by very low seismicity, does not have a national seismic hazard map. However, site specific Probabilistic Seismic Hazard Assessments (PSHAs) for critical infrastructure, including nuclear power plants (NPPs), have been conducted. The sophisticated 2020 European Seismic Hazard Model (ESHM20) offers several advancements that could influence seismic hazard work in stable continental regions like Finland. As part of the SEISMIC RISK collaborative project involving the University of Helsinki, VTT Technical Research Centre of Finland, and the Geological Survey of Finland, a national PSHA model has been developed. The model is based on a Fennoscandian earthquake catalogue – FENCAT, compiled from Nordic national catalogues based on the observations from the national seismic networks. This allows for calculation of the recurrence parameters with lower magnitudes than the ESHM20. Although a preliminary comparison reveals only minor local differences at hazard levels, a more detailed examination at critical infrastructure sites is necessary. We have compared the regional hazard results obtained within the SEISMIC RISK project and hazard values of the ESHM20 at two NPP sites in Finland. Four criteria from the literature, compiled by Douglas et al. (2023), were employed for assessing the differences between the seismic hazard models. To this end, the mean, median, and 16th and 84th fractiles for the ESHM20 were obtained from the European Facilities for Earthquake Hazard and Risk (EFEHR) database hosted by EPOS–Seismology. A visual inspection of the hazard curves initially indicated consistently higher mean hazards from the Finnish model at the NPP sites compared to ESHM20. The lognormal distributions of the hazard models were estimated, and the differences were assessed for the return periods of 106, 104, 5000, 2475, and 475 years using the four criteria. The distributions revealed a significantly smaller standard deviation for the Finnish model than for the ESHM20. When comparing the two models, the mean Annual Frequency of Exceedance (AFE) changed by over 25% for the ground-motions corresponding to AEFs ≤ 10-4 and by more than 35% for ground-motions corresponding to 10-6 AFE. These findings underline the significant differences between the models. In summary, a minimum of two out of the four criteria are met at one of the NPP sites, and at the other NPP site, three out of four criteria are satisfied. This further highlights the significance of the differences between the ESHM20 and the Finnish hazard model. Nevertheless, while the observed change in hazard between the Finnish hazard model and the ESHM20 can be deemed substantial, it does not justify the use of the Finnish hazard model for the longer return periods. Further investigations, such as site-specific hazard assessments, are necessary for the return periods relevant to NPPs. Douglas, J., Crowley, H., Silva, V., Marzocchi, W., Danciu, L., & Pinho, R. (2023). Methods for evaluating the significance and importance of differences amongst probabilistic seismic hazard results for engineering and risk analyses: A review and insights. EGUsphere [preprint], https://doi.org/10.5194/egusphere-2023-991

We present a new seismic zoning model for the territory of Finland and adjacent areas in northern Europe for the purpose of seismic hazard mapping. The target region, mostly situated in the stable continental region of the Fennoscandian Shield, exhibits predominantly earthquakes below moment magnitude 3.0. We have delineated area seismic source zones by fusing seismological, geological, and geophysical data, and tectonic boundaries. The approach is warranted to find sufficient argumentation on the zoning due to the poor to non-existent seismicity data in the eastern and southeastern part of our target region. We have addressed the subjectivity included in delineation of zone boundaries by combining the preliminary delineations of four expert groups into a model with three levels of details: macro-, meso- and microlevel. We compare the new microlevel zoning with the regional zoning models of 2015 and 2016 and all the three zonings with the respective zonings of the 2020 European Seismic Hazard Model. We argue that the new zoning model SZ2025FI provides a sufficient basis for seismic hazard mapping on national and regional scales, as well as European and global mapping initiatives.

Properties of small earthquakes induced by fluid injection reflect the spatiotemporal evolution of important reservoir parameters, including the local stress field, pore space, rock permeability, fluid overpressure, and distributions of pre-existing fractures. Resolving detailed earthquake mechanisms and their uncertainties is key to the physical interpretation of source processes. Here, we report moment tensor (MT) patterns in response to two enhanced geothermal system stimulations through similar to 6-km-deep boreholes in the crystalline basement of the Fennoscandian Shield. A local monitoring network of 32 surface and borehole stations provided high-signal-to-noise ratio seismograms of the body-wave arrivals in the 5-10 Hz target range. Using a probabilistic waveform-fitting method with carefully selected data and manually revised inversion parameters, we obtain robust centroid MT solutions for 301 induced earthquakes with moment magnitudes Mw between 0.3 and 2.0. Most events exhibit reverse-faulting double-couple (DC) mechanisms that are not compatible with extrapolations from regional stress modeling. Our analysis resolves spatially variable distributions of the compensated linear vector dipole (CLVD) component around the injection well, which reflects the governing effect of the injection pressure. The spatial variation of the volumetric or ISO component suggests an ambient pore pressure or a geological control. Together, the CLVD and ISO components resolve a change in earthquake properties between the 2018 and 2020 injection experiments. We propose a source process that involves the interaction between a pressurized hydraulic fracture and surrounding shear fractures to explain coseismic compression and dilatation that are associated with the DC and CLVD components. Resolving the behavior of fluid-induced earthquakes in crystalline rock at this level of detail demonstrates the effectiveness of the employed processing methods and helps improve our understanding of hydromechanical feedback mechanisms in geothermal systems.

Understanding fluid injection induced seismicity is key to safe and successful operations of deep geothermal systems. Efficient geothermal energy extraction by an enhanced geothermal system (EGS) requires increased fluid flow between geothermal wells. The experimental 6-km-deep EGS in the Helsinki capital region, southern Finland is an intriguing natural laboratory in a cool Precambrian shield setting that yields excellent seismic data quality. We investigate the source processes of the earthquakes induced by weeks-long EGS stimulations in 2018 and 2020 via a probabilistic waveform fitting method. Detailed resolution of full moment tensor solutions and their opening components can reveal crucial information on earthquake nucleation and fluid flow patterns.We present results of a centroid full moment tensor analysis for ~250 events from 2018 and 16 events from 2020 in the moment magnitude range 0.5–1.9. We use three-component data of ~30 stations within a 9-km radius of the well-head site. We fit P- and S-phases by modeling synthetic waveforms using Green’s functions with a 20 m grid spacing based on a homogeneous velocity model. We employ automatic high signal-to-noise ratio waveform selection and automatically determined channel-wise correction coefficients for time shifts and amplitude scaling to represent small scale crustal variations not reflected in the velocity model. With the application of both waveform selection and channel corrections, the uncertainty of the moment tensor decreases on average by ~60 % and the location uncertainty by ~85 %. This results in a catalog of well-resolved moment tensors and centroid locations.The obtained high-quality solutions are dominated by reverse faulting mechanisms with variable compensated linear vector dipole (CLVD) contribution and non-significant isotropic component. The 3D event distribution reveals largest positive CLVD contribution in seismic sources close to the injection well, which indicates localized fracture opening under constant volume with a simultanous adjacent shear event. Farther from the well, seismic sources have pure double-couple mechanisms or even negative CLVD contribution which may be indicative of fracture lengthening or closing under constant volume at later stages of the stimulation.Identifying clusters with respect to source type and location within the 3D event distribution supports the interpretation of physical source processes and reveals fluid flow channels, and zones of weakness. Events with positive CLVD component occurring close to fluid-filled fractures are potentially nucleated by direct contact with the injected fluid and the associated pore pressure change. Events with zero or negative CLVD component on the outer parts of the seismicity distribution may have been nucleated by poroelastic stress transfers without a direct hydraulic contact to the injected fluid. Our findings suggest that the full extent of injection induced seismicity may not be indicative of fluid flow and thus it should not be used to estimate the extent of an artificially created connected fracture network of a geothermal reservoir.

Ilmastonmuutoksen hillitsemiseksi energiajärjestelmän on muututtava vähähiilisemmäksi. Geoterminen energia on Suomessa ja muualla maailmassa noussut yhdeksi päästöttömäksi uusiutuvan energian muodoksi, mutta sen rakentamiseen ja käyttöön sisältyy riskejä. Tässä artikkelissa tarkastelemme geotermisen energian seismisen riskin hallintaa monitoimijaisessa verkostossa. Keskitymme siihen, millaisena eri toimijat näkevät Seismologian instituutin aseman geotermisen energian hallinnan verkostossa. Pohdimme, miten geotermisen energian seismisen riskin hallinnan kaltainen kompleksinen politiikkaongelma jäsentyy institutionaalisesti epäselvässä tilanteessa ja millaisia tietoon ja tietämiseen liittyviä kysymyksiä nousee esiin. Analyysimme näyttää, miten politiikkaongelman ratkaisusta neuvotellaan samalla kun geotermisen energian hallintakäytännöt ja toimijoiden työnjako ovat vasta muotoutumassa. Tutkimuksemme myös osoittaa, että siirtymä hallinnosta hallintaan ei tee perinteistä hierakkista hallintoa ja normiohjausta tarpeettomaksi vaan päinvastoin: selkeä ja vakaa toimintaympäristö myös tukee uusien teknologioiden käyttöönottoa.

Alternative, carbon-free energy sources are essential to regulate the global climate crisis. Geothermal energy – i.e., heat harvested by geothermal systems by drilling geothermal wells to circulate water in a fractured hot rock mass at the depth of 1-7 km – has a huge potential as an environmentally friendly carbon-free energy source. One of the drawbacks is that geothermal systems can induce small-magnitude earthquakes that pose seismic risk to critical sensitive infrastructure. SEISMIC RISK - Mitigation of induced seismic risk in urban environments -project focuses on how to evaluate, mitigate and communicate seismic hazard and risk in an urban environment. Some of the associated challenges are the unclear regulatory, administrative and policy processes and unclear roles of the different actors. Another problem concerns defining what constitutes relevant information and how it should be disseminated to the public. One part of the project is to carry out interviews of stakeholders (energy companies, municipalities and state authorities) on, how they perceive the current situation. These will give information on 1) the extent to which different actors have a common understanding of the situation and potential risks, 2) who should be responsible for coordinating risk management, and 3) how citizens should be informed of potential risks and should they be able to participate in location decisions of such geothermal power plants. Another part of the project is focusing on, how social media can better be used for rapid communication of induced seismic events and for the gathering of observations. Currently social media (Twitter) is already used for rapid notification of seismic events to the public. Gathering of macroseismic observations is handled online.

The near-Earth environment is continuously changing by disturbances from external and internal sources. A combined research ecosystem is needed to be able to monitor short- and long-term changes and mitigate their societal effects. Observatories and large-scale infrastructures are the best way to guarantee continuous 24/7 observations and full-scale monitoring capability. Sodankylä Geophysical Observatory takes care of continuous geoenvironmental monitoring in Finland and together with national infrastructures such as FIN-EPOS and E2S enable extending and expanding the monitoring capability. European Plate Observing System of Finland (FIN-EPOS) and flexible instrument network of FIN-EPOS (FLEX-EPOS) will create a national pool of instruments including geophysical instruments targeted for solving topical questions of solid Earth physics. Scientific and new hardware building by FLEX-EPOS is essential in order to identify and reduce the impact of seismic, magnetic and geodetic hazards and understand the underlying processes. New national infrastructure Earth-Space Research Ecosystem (E2S) will combine measurements from atmosphere to near-Earth and distant space. This combined infrastructure will enable resolving how the Arctic environment change over the seasons, years, decades and centuries. We target our joint efforts to improve the situational awareness in the near-Earth and space environments, and in the Arctic for enhancing safety on ground and in space. This presentation will give details on the large-scale Earth-space infrastructures and research ecosystems and will give examples on how they can improve the safety of society.

Nordic EPOS - A FAIR Nordic EPOS Data Hub – is a consortium of the Nordic geophysical observatories financed by NordForsk. It is delivering on-line data to European Plate Observing System’s Thematic Core Services (EPOS’s TCSs). Nordic EPOS consortium comprises of the Universities of Helsinki, Bergen, Uppsala, Oulu and GEUS and Icelandic Meteorological Office. Nordic EPOS enhances and stimulates the ongoing active Nordic interactions related to Solid Earth Research Infrastructures (RIs) in general and EPOS in particular. Nordic EPOS develops expertise and tools designed to integrate Nordic RI data and to enhance their accessibility and usefulness to the Nordic research community. Together we can address global challenges in Norden and with Nordic data. The Nordic EPOS’s main tasks are to advance the usage of multi-disciplinary Solid Earth data sets on scientific and societal problem solving, increase the amount of open, shared homogenized data sets, and increase the scientific expertise in creating sustainable societies in Nordic countries and especially in the Arctic region. In addition to developing services better suited for Nordic interest for EPOS, Nordic EPOS will also try to bring forward Nordic research interest, such as research of Arctic areas in TCSs and EPOS-ERIC governance and scientific boards. The Nordic EPOS is organized into Tasks and Activities. The project has six main infrastructure TASKs: I - Training in usage of EPOS-RI data and services; II - Nordic data integration and FAIRness; III - Nordic station management of seismological networks, IV - Induced seismicity, safe society; V - Ash and gas monitoring; and VI- Geomagnetic hazards. In addition, the project has one transversal TASK VII on Communication and dissemination. The activities within the TASKs are workshops, tutorials, demos and training sessions (virtual and on-site), and communication and dissemination of EPOS data and metadata information at local, national and international workshops, meetings, and conferences.

This chapter investigates the Fennoscandian uplift area since the latest Ice Age and addresses the question if glacial isostatic adjustment may influence current seismicity. The region is in an intraplate area, with stresses caused by the lithospheric relative plate motions. Discussions on whether uplift and plate tectonics are the only causes of stress have been going on for many years in the scientific community.

Tectonic evolution of the Paleoproterozoic Vaasa migmatitic complex (VMC) in the central part of the Svecofennian accretionary orogen is deciphered using aeromagnetic and gravity maps, deep seismic and magnetotelluric profiles, and structural and metamorphic data. The VMC is a semicircular structure with migmatitic rim and granitic core composed of several subdomes. It evolved in three main tectonic events (D1-D3). The D1 event (ca. 1.89-1.88 Ga) corresponds to the stacking of supracrustal rocks and the formation of an inverted metamorphic gradient. Anatexis at LP-HT metamorphic conditions enabled the material to flow. The D2 event (ca. 1.88-1.87 Ga) corresponds to large-scale folding of the partially molten crust within an orocline. It is marked by folds with an E-W vertical axial planar foliation. The late D3 event resulted from mass redistribution owing to mechanical instabilities within the hinge of the orocline. It is marked by vertical shearing (ca. 1.87-1.85 Ga) in the marginal parts of the complex and along the granitoid subdomes. The seismic reflection profile (FIRE 3a) and magnetotelluric profiles (MT-PE and MT-B2) image large-scale D1 stacking structures within an accretionary prism. Near vertical breaks in crustal-scale reflectivity and conductivity models are interpreted as D3 shear zones. The VMC is an example of early mass and heat transfer within a collage of hot supracrustal rocks in an accretionary belt. Partial melting enhanced the flow of material, the production, and rise of magma as well as exhumation, marked by magmatic domes in the hinge of the orocline.

The Kokkola–Kymi Deep Seismic Sounding profile crosses the Fennoscandian Shield in northwest-southeast (NW–SE) direction from Bothnian belt to Wiborg rapakivi batholith through Central Finland granitoid complex (CFGC). The 490-km refraction seismic line is perpendicular to the orogenic strike in Central Finland and entirely based on data from quarry blasts and road construction sites in years 2012 and 2013. The campaign resulted in 63 usable seismic record sections. The average perpendicular distance between these and the profile was 14 km. Tomographic velocity models were computed with JIVE3D program. The velocity fields of the tomographic models were used as starting points in the ray tracing modelling. Based on collected seismic sections a layer-cake model was prepared with the ray tracing package SEIS83. Along the profile, upper crust has an average thickness of 22 km average, and P-wave velocities (Vp) of 5.9–6.2 km/s near the surface, increasing downward to 6.25–6.40 km/s. The thickness of middle crust is 14 km below CFGC, 20 km in SE and 25 km in NW, but Vp ranges from 6.6 to 6.9 km/s in all parts. Lower crust has Vp values of 7.35–7.4 km/s and lithospheric mantle 8.2–8.25 km/s. Moho depth is 54 km in NW part, 63 km in the middle and 43 km in SW, yet a 55-km long section in the middle does not reveal an obvious Moho reflection. S-wave velocities vary from 3.4 km/s near the surface to 4.85 km/s in upper mantle, consistently with P-wave velocity variations. Results confirm the previously assumed high-velocity lower crust and depression of Moho in central Finland.

Saucer-shaped intrusions of tens of meters to tens of kilometres across have been observed both from surface geological mapping and geophysical observations. However, there is only one location where they have been reported to extend c. 100 km laterally, and emplaced both in a sedimentary basin and the crystalline basement down to 12 km depth. The legacy BABEL offshore seismic data, acquired over the central Fennoscandian Shield in 1989, have been recovered and reprocessed with the main goal of focusing on this series of globally unique crustal-scale saucer-shaped intrusions present onshore and offshore below the Bothnian Sea. The intrusions (c. 1.25 Ga), emplaced in an extensional setting, are observed within both sedimentary rocks (<1.5 Ga) and in the crystalline basement (>1.5 Ga). They have oval shapes with diameters ranging 30–100 km. The reprocessed seismic data provide evidence of up-doming of the lower crust (representing the melt reservoir) below the intrusions that, in turn, are observed at different depths in addition to a steep seismically transparent zone interpreted to be a discordant feeder dyke system. Relative age constraints and correlation with onshore saucer-shaped intrusions of different size suggest that they are internally connected and fed by each other from deeper to shallower levels. We argue for a nested emplacement mechanism and against a controlling role by the overlying sedimentary basin as the saucer-shaped intrusions are emplaced in both the sedimentary rocks as well as in the underlying crystalline basement. The interplay between magma pressure and overburden pressure, as well as the, at the time, ambient stress regime, are responsible for their extensive extent and rather constant thicknesses (c. 100–300 m). Saucer-shaped intrusions may therefore be present elsewhere in the crystalline basement to the same extent as observed in this study some of which are a significant source of raw materials.