Browsing by discipline "Geofysiikka"
Now showing items 21-37 of 37
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(2015)Kasviplanktonin määrä ja tuotanto on tärkeä tekijä Itämeren rehevöitymisen arvioinnissa. Kasviplankton reagoi nopeasti, jos veden ravinteiden (erityisesti typen ja fosforin) määrät tai suhteet muuttuvat. Kasviplanktonin kevätkukinta on merkittävä vuosittainen tapahtuma Itämerellä. Kevätkukinnan aikana saavutetaan kasviplanktonin kasvukauden huippu, ja suuri osa vuotuisesta tuotannosta tapahtuu kevätkukinnan aikana. Kevätkukinnan aikana kasviplanktonin määrä vedessä vaihtelee suuresti ajallisesti ja paikallisesti. Kevätkukinnan seurannassa saavutetaan paras ajallinen ja paikallinen kattavuus käyttämällä kaukokartoitusinstrumentteja ja Alg@line-mittauksia. Tässä tutkimuksessa kehitettiin ja testattiin kevätkukinnan indikaattoreita Suomenlahdella ja Saaristomerellä. Kevätkukinnan indikaattoreita ovat kukinnan alku, kesto, huippu eli suurin pitoisuus, huipun ajankohta ja kukinnan intensiteetti. Indikaattorit määriteltiin aluekohtaisesti a-klorofyllipitoisuuden aikasarjoista vuosina 2003–2011. Aikasarjat laskettiin Envisat-MERIS -instrumentin ja Alg@line-laivojen havainnoista. Tulokset osoittivat, että MERIS- ja Alg@line-aineistot soveltuvat kasviplanktonin kevätkukinnan indikaattorien määrittämiseen. Pilvisyys tai jääolot voivat ajoittain estää a-klorofyllin havaitsemisen MERIS-instrumentillla, jolloin Alg@line-mittauksia voidaan käyttää täydentämään havaintoja niillä alueilla, joiden läpi Alg@line-laivat kulkevat. Tuloksien mukaan kasviplanktonin indikaattorit, erityisesti intensiteetti, vaihtelevat eri alueilla paljon. Myös vuosien väliset erot ovat huomattavia. Kahdella tutkimusalueella MERIS- ja Alg@line-aineistoista laskettuja intensiteetti-indeksejä verrattiin toisiinsa ja pyrittiin määrittämään indeksin trendi kullakin alueella. Nousevia trendejä ei havaittu, mikä on Itämeren rehevöitymisen ja ekologisen tilan kannalta hyvä. Kasviplanktonin kevätkukinnan indikaattoreita voidaan tulevaisuudessa käyttää operatiivisesti. MERIS-instrumentin tilalla on mahdollista käyttää muita kaukokartoitusinstrumentteja, jotka soveltuvat a-klorofyllin seurantaan. Tulevan Sentinel 3A -satelliitin mukan oleva OLCI-instrumentti soveltuu parhaiten kevätkukinnan seurantaan Itämerellä. Ennen Sentinel 3A -satelliitin laukaisua käytössä ovat esimerkiksi Aqua MODIS -ja Suomi NPP VIIRS -instrumentit. Alg@line-aineistoa voidaan yhdistää kaukokartoitusaineistoihin, jolloin saadaan mahdollisimman suuri ajallinen ja paikallinen kattavuus.
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(2016)Pro Gradu-tutkielmassa tutkittiin Königsbergerin suhteen käyttökelpoisuutta magneettisen mineralogian tunnistuksessa kolmesta eri kohteesta olevien magneettikiisu- ja magnetiittipitoisten näytteiden tapauksessa. Königsbergerin suhdetta tutkitaan sekä kirjallisuuden avulla että tekemällä petrofysiikan mittauksia näytteistä ja määrittelemällä suhde näistä laskennallisesti. Lisäksi työssä syvennytään myös kiisu- ja grafiittipitoisten näytteiden magneettiseen mineralogiaan työn aikana tehtyjen termomagneettisten mittausten pohjalta. Tutkimusalueet sijaitsevat Itä-Suomessa Kainuun liuskejaksolla (Paltamo, Hakonen ja Rautavaara) ja tutkitut kivet ovat metamorfoituneita kiisu- ja grafiittipitoisia liuskeita sekä näiden yhteydessä kairattuja magnetiittipitoisia muuttuneisiin kivilajeihin kuuluvia näytteitä. Aeromagneettisten karttojen perusteella kaikissa kolmessa kohteessa havaitaan voimakkaat teräväreunaiset magneettiset anomaliat ja sähkönjohtavuuskarttojen perusteella ne ovat hyviä johteita. Peruspetrofysiikan (tiheys, magneettinen suskeptibiliteetti ja remanentti magnetoituma) mittaukset tehtiin 227 näytteelle ja Q-suhde määritettiin niille laskennallisesti. Tulosten perusteella Hakosen tutkimusalueelta määritetyt Q-suhteet vaihtelevat välillä 7-225, Paltamon välillä 3-155, Rautavaaran 3-205 ja magnetiittipitoisten verrokkinäytteiden välillä 0,2-124. Tiheysmittauksien perusteella Hakosen tutkimusalueelle määritetty tiheyden keskiarvo on 3019 kg/m3, Paltamon 2915 kg/m3, Rautavaaran 2994 kg/m3ja magnetiittipitoisten verrokkinäytteiden 2944 kg/m3. 15:sta näytteen magneettinen mineralogia määritettiin termomagneettisten mittausten avulla. Tulosten perusteella 12 kantaa magneettisena mineraalina ainoastaan magneettikiisua, kahdessa näytteessä havaittiin magneettikiisun lisäksi mahdollisesti hematiittia (primääri tai lämmityksen aikana sekundäärisesti magnetiitista syntynyt), yhdessä näytteessä havaittiin sekä magneettikiisua että magnetiittia ja kolmessa näytteessä magneettikiisun kaksifaasista muotoa (monokliininen ja heksagoninen magneettikiisu). Näytteet, joilla on korkeimmat Q-suhteet (Q>80) ei havaita kahden faasin koostumusta. Tulosten perusteella havaitut Q-suhteet ovat korkeita verrattuna kirjallisuudesta löydettyihin arvoihin ja viittaavat suureen sulfidipitoisuuteen ja monokliinisen magneettikiisun määrään grafiitti- ja kiisupitoissa näytteissä. Ne grafiitti- ja kiisupitoiset näytteet, jotka saavat kaikkein korkeimpia Q-arvoja arvoja kantavat oletettavasti aluemetamorfoosin sekundäärisesti synnyttämää magneettisesti hienorakeista magneettikiisua. Myös magnetiittipitoisten verrokkinäytteiden korkeammat Q-suhteet liittyvät alentuneeseen raekokoon ja sitä kautta kasvaneeseen remanenssiin. Q-suhteen avulla voidaan arvioida magneettista mineralogiaa, mutta työssä tutkittujen magneettisesti hienorakeisten magneettisten mineraalien tapauksessa menetelmä ei yksinään riitä niiden erottamiseksi toisistaan.
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(2013)Suomessa jääpeite kattaa vesistöjä 3 - 7 kuukautta vuodessa. Jokien jääolosuhteilla on suuri merkitys jokivarsien asukkaille ja teollisuuslaitoksille. Jokien jäätymiseen liittyvät ongelmat aiheuttavat suuria taloudellisia menetyksiä ja ympäristövahinkoja, vaikka niitä pyritäänkin ehkäisemään erilaisilla jääntorjuntamenetelmillä ja vesistönkäyttö- ja tulvantorjuntatoimenpiteillä. Kymijoella suurin ongelma on suppojää, joka aiheuttaa vahinkoja lähes joka vuosi. Kymijoki sijaitsee Kaakkois-Suomessa ja laskee Itämerelle Suomenlahteen. Kymijoen valuma-alueen pinta-ala on 37 107 km2, joka kattaa lähes 11 % koko Suomen pinta-alasta. Keskimääräinen virtaama joen pääuomassa on 283 m3/s. Kymijoki on valuma-alueeltaan ja virtaamaltaan maamme neljänneksi suurin joki. Tämän tutkimuksen ensimmäisenä tavoitteena oli valita sopivat mittauspisteet Kymijoen pääuomasta, sen kaikista haaroista ja lähtöjärvistä sekä tutkia niiden sopivuutta kuvaamaan Kymijoen olosuhteita. Kymijoen veden laatua ja jääoloja tutkittiin kenttämittauksina talvella 2011–2012. Toisena tavoitteena oli koostaa tehdyistä mittauksista kattava kuva Kymijoen jääolosuhteista ja veden laadusta talviaikana. Näitä tietoja verrattiin Kymijoen vesi- ja ympäristö ry:n vedenlaatututkimuksiin, Suomen ympäristökeskuksen virtaamahavaintoihin ja Ilmatieteen laitoksen säähavaintoihin. Kymijoen eri mittauspisteiden välillä oli hyvin paljon eroja jääkannen peittävyydessä ja rakenteessa, johtuen erilaisista olosuhteista ja Kymijoella käytetyistä jääntorjuntakeinoista. Osalla mittauspisteistä oli reunajäätä vain vähän tai ei jäätä ollenkaan ja osalla mittauspisteistä oli koko joen kattava kiinteä jääkansi. Jään paksuus eri mittauspisteillä vaihteli 0-55 cm välillä. Veden laatu oli koko Kymijoella kohtuullisen hyvä, vaikkakin eri osissa jokea oli selvästi havaittavissa vaihtelua. Happitilanne oli koko joella kohtuullisen hyvä ja suurimmat hapen kyllästysasteet olivat odotetusti hyvin vettä hapettavan koskijakson jälkeen. Sameudessa ja kiintoainespitoisuudessa oli huomattavan suurta vuodenaikaisvaihtelua. Lumen sulaminen keväällä ja runsaat sateet loppuvuodesta 2011 nostivat sameusarvoja selvästi. Perustuotannon vaikutus oli selvästi havaittavissa kesäkuun korkeissa kiintoainespitoisuuksissa. Kymijoen pH oli koko tarkastelujaksolla lähes neutraalilla tasolla. Kevään sulamisvesien happamoittava vaikutus ja perustuotannon pH:ta kohottava vaikutus olivat kuitenkin havaittavissa. Jätevesien sähkönjohtavuutta nostava vaikutus oli selvästi havaittavissa Kymijoella. Valon sironta ja näin ollen partikkelien määrä Kymijoella lisääntyi joen alajuoksulle päin. Kymijoen yläosien järvissä vesi oli huomattavasti puhtaampaa kuin varsinaisessa joessa ja myös partikkelien sirontavaikutukset olivat häviävän pieniä. Jään rakenteessa tai peittävyydessä ei havaittu merkittäviä eroja, jotka johtuisivat siirtymisestä yläjuoksulta alajuoksulle, vaan erot johtuivat lähinnä hyvin erilaisista virtausolosuhteista ja Kymijoella käytetyistä jääntorjuntakeinoista. Jääpuomien vaikutusta jääkanteen ei havaittu kaikilla mittauspisteillä, mutta muutamilla mittauspisteillä vaikutus oli merkittävä jääkannen rakenteeseen ja peittävyyteen. Veden laatu oli koko Kymijoella kohtuullisen hyvä, mutta se muuttui selvästi huonommaksi siirryttäessä alajuoksulle päin. Veden laadun muutokset aiheutuivat joen alajuoksulla sijaitsevista teollisuuslaitoksista ja vedenpuhdistamoista. Kymijoen kahden päähaaran välillä ei havaittu merkittäviä eroja. Veden laadussa ei havaittu kerroksellisuutta johtuen virtauksen turbulenttisesta luonteesta.
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(2013)In this Master's thesis the long-term changes in Baltic Sea ice characteristics were studied. In the Baltic Sea the length of ice season is 5-7 months. The amount of seasonal ice varies significantly from year to year. However, in the last 100 years there has been a decreasing trend in the ice occurrence, which has resulted mainly from climate warming. Both observations and model results were analyzed in order to find out the long-term ice statistics, changes in ice conditions and reasons behind these changes. Three stations along the Finnish coast were chosen, Kemi in the Bay of Bothnia, Utö in the Archipelago Sea and Loviisa in the Gulf of Finland. The time series were 120 years long including the dates of freezing and break-up, the length of ice season and the maximum annual ice thickness. The model used was NEMO/LIM-3 and the modeled time 1961-2007. The key questions for the thesis were the positive trend in ice thickness in Kemi station, the reasons for the 100 year long decreasing trends although the climate warming has not affected so long and the changes in drift ice thickness. The study results show that the probability of ice occurrence has been decreasing in Utö and is now 81 %. In Kemi and Loviisa the probability is still 100 %. The freezing date has become 7-24 days later, while the break-up date has taken place 11-20 days earlier in 100 years. Consequently, the observed length of ice season has become 18-46 days shorter in 100 years. The trend of the maximum annual ice thickness is not so uniform. In Kemi station, there is an increasing trend, whereas in Loviisa the trend is decreasing. According to the model, the maximum annual ice thickness has a decreasing trend also in Kemi. The maximum annual ice volume has a decreasing trend in the entire Baltic Sea and also in different basins (Bay of Bothnia, Bothnian Sea and Gulf of Finland). The modeled ice volume correlates well with the observed maximum annual ice extent even though the ice volume has higher inter-annual variations. The possible other reasons besides rise in air temperature were detected. Sea ice thickness depends in addition to air temperature also greatly on snow accumulation and ice dynamics. The observation sites are not documented, so the places may have changed. The observation sites are usually near harbors and the increasing shipping might have affected ice conditions. The land uplift has been over 1 meter in Kemi during the 120 years, so that might also have an influence on results. In Loviisa the nuclear power plant might have affected the past few decades.
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(Helsingin yliopistoHelsingfors universitetUniversity of Helsinki, 2010)The magnetic field of the Earth is 99 % of the internal origin and generated in the outer liquid core by the dynamo principle. In the 19th century, Carl Friedrich Gauss proved that the field can be described by a sum of spherical harmonic terms. Presently, this theory is the basis of e.g. IGRF models (International Geomagnetic Reference Field), which are the most accurate description available for the geomagnetic field. In average, dipole forms 3/4 and non-dipolar terms 1/4 of the instantaneous field, but the temporal mean of the field is assumed to be a pure geocentric axial dipolar field. The validity of this GAD (Geocentric Axial Dipole) hypothesis has been estimated by using several methods. In this work, the testing rests on the frequency dependence of inclination with respect to latitude. Each combination of dipole (GAD), quadrupole (G2) and octupole (G3) produces a distinct inclination distribution. These theoretical distributions have been compared with those calculated from empirical observations from different continents, and last, from the entire globe. Only data from Precambrian rocks (over 542 million years old) has been used in this work. The basic assumption is that during the long-term course of drifting continents, the globe is sampled adequately. There were 2823 observations altogether in the paleomagnetic database of the University of Helsinki. The effect of the quality of observations, as well as the age and rocktype, has been tested. For comparison between theoretical and empirical distributions, chi-square testing has been applied. In addition, spatiotemporal binning has effectively been used to remove the errors caused by multiple observations. The modelling from igneous rock data tells that the average magnetic field of the Earth is best described by a combination of a geocentric dipole and a very weak octupole (less than 10 % of GAD). Filtering and binning gave distributions a more GAD-like appearance, but deviation from GAD increased as a function of the age of rocks. The distribution calculated from so called keypoles, the most reliable determinations, behaves almost like GAD, having a zero quadrupole and an octupole 1 % of GAD. In no earlier study, past-400-Ma rocks have given a result so close to GAD, but low inclinations have been prominent especially in the sedimentary data. Despite these results, a greater deal of high-quality data and a proof of the long-term randomness of the Earth's continental motions are needed to make sure the dipole model holds true.
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(2020)The ST1 Deep Heat company has been developing an enhanced geothermal system for district heating in Espoo, Southern Finland by St1 Deep Heat Company. Complete project will consist of geothermal doublet which involves two wells expanding up to 6,1 km depth. The stimulation of the first well was conducted in summer of 2018 as a 7-week period during which the fluid permeability of the crystalline rock at the base of the well was increased by pumping water with high pressures into the well. The stimulation process interacts with the ambient stress field of the subsurface and similar processes have been associated with induced seismicity when the stress changes lead into earthquakes as pre-existing faults and cracks are activated and new ones are created. For the monitoring of the seismic activity associated with the project a seismic network was installed in the Espoo/Helsinki area. The network consisted of 12 borehole installed 3-component seismometers provided by ST1 Deep Heat Company and from 5 semi-permanent surface 3-component broadband seismometers and in total 100 geophones installed by the Institute of Seismology, University of Helsinki (later ISUH). The geophones were installed in 3 large 25 instrument arrays, 3 smaller 4- instrument arrays and as single stations. Data from suitable seismic stations from the Finnish Seismological network was also used in the study. The aim of the study was to map possible differences and trends in the determined event magnitudes between different types of seismic stations used in the seismic network during the stimulation. The effect of different filter choices on amplitude measurement is also studied and discussed for some of the seismic events involved in the study. The results are also compared to the traffic light system warning thresholds of the EGS project and automatically calculated magnitudes of the monitoring system. The Finnish local magnitude formula is also discussed considering near-source events. Reliability and behaviour of the seismic arrays used during the stimulation is studied and discussed. Azimuthal effects noted during the data processing are illustrated. According to the results there appears to be clear differences in estimated magnitudes between the different station types used in the network and differences and trends between the seismic arrays and between individual instruments of single arrays. In total 21 induced events were chosen based on their automatically determined magnitudes, favouring events with large as possible magnitudes. Magnitude range for the events was from ML 1.8 to ML 1,0. The events were picked for P- and S-wave arrivals and for amplitudes estimated from vertical component S wave arrivals. The locations and magnitudes of the events were determined using the currently used practices of the ISUH. Main tools used in the study are the Geotool software for waveform analysis, an ISUH program used for earthquake locating and GNU Octave programs written by the author used in the data procession.
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(2016)The ground motion induced by an earthquake and its attenuation as a function of magnitude and distance can be estimated by using various ground motion prediction equations (GMPE). From a historical perspective, the Fennoscandian shield has been a seismically quiet area with a scarcity of strong earthquakes. This has made the area nominally an area with a low seismic hazard. The lack of quantative strong motion data in an area with low seismic hazard and the subsequent lack of advanced theoretical models of seismic response have hindered the developement of GMPEs for the region. Using more direct empirical methods, which do not depend on pre-existing models and simulations of Fennoscandian seismicity, and by taking advantage of the comparatively large Fennoscandian shield ground motion database two GMPEs targeted for the Fennoscandian shield area were created. The created GMPEs are based on an existing attenuation relationship that targets Eastern North America, which is a stable continental area similar to the Fennoscandian shield. The current and historical stage of relative seismic quietness was preceded by a considerably more active phase during and after the deglaciation of the Weichselian continental ice shelf ca. 9000 - 15000 years ago. There is ample geological evidence that this postglacial faulting caused some of the largest known earthquakes that have ever occurred in a stable continental area. The moment magnitudes of the largest postglacial earthquakes have been estimated to have been in excess of 8.0. The magnitude contrast between the geologically recent postglacial seismicity and the available Fennoscandian ground motion database, which consists mostly of low magnitude events, implies that an empirical method can not provide a GMPE capable of reliably estimating the ground motion induced by a potential large postglacial faulting event. It is unlikely that such an event could occur today, but not completely impossible. The two GMPEs presented here are based on a ground motion database consisting of 6465 recordings from 1701 events with magnitudes between -1.0 – 5.2. The events were observed at 84 seismic stations around the Fennoscandian shield between 2003 and 2014. The first GMPE is an empirical model which takes an existing GMPE and uses a non-linear least squares regression method to refit the constant coefficients of the model to our regional ground motion database. The second GMPE is a referenced empirical model which works by multiplying the ground motion prediction of an existing GMPE with a function of certain seismological parameters. The multiplying function's coefficients are then fitted to the ground motion database. The resulting equations provide a reasonably good model of the peak ground acceleration (PGA) and spectral accelerations (SA) at 9 different frequencies: 0.5 Hz, 1.0 Hz, 2.5 Hz, 5 Hz, 10 Hz, 20 Hz, 25 Hz, 33.3 Hz, and 40 Hz. The GMPEs were further assessed by applying them to an independent regional earthquake and various higher magnitude external events that have originated in a presumably similar stable continental area. Based on these comparisons, the upper magnitude limits of applicability were independently estimated for PGA and each SA frequency. A tendency of the ground motion estimate to improve with increasing frequency at higher magnitudes can be seen. The distance ranges of the GMPEs were determined to be identical with the original base model.
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(2015)The purpose of this study is to develop a method for optimizing the data assimilation system of the HIROMB-BOOS -model at the Finnish Meteorological Institute by finding an optimal time interval and an optimal grid for the data assimilation. This is needed to balance the extra time the data assimilation adds to the runtime of the model and the improved accuracy it provides. Data assimilation is the process of combining observations with a numerical model to improve the accuracy of the model. There are different ways of doing this, some of which are covered in this work. The HIROMB-BOOS -circulation model is a 3D-forecast model for the Baltic Sea. The variables forecast are temperature, salinity, sea surface height, currents, ice thickness and ice coverage. Some of the most important model equations are explained here. The HIROMB-BOOS -model at the Finnish Meteorological Institute has a preoperational data assimilation system that is based on the optimal interpolation method. In this study the model was run for a 2-month test period with different time intervals of data assimilation and different assimilation grids. The results were compared to data from five buoys in the Baltic Sea. The model gives more accurate results when the time interval of the data assimilation is small. The thicker the data assimilation grid is, the better the results. An optimal time interval was determined taking into account the time the assimilation takes. An optimal grid was visually determined based on an optimal grid thickness, for which the added time had to be considered as well. The optimized data assimilation scheme was tested by performing a 12-month test run and comparing the results to buoy data. The optimized data assimilation has a positive effect on the model results.
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(2013)Finland is situated in an intraplate area of low seismicity. Seismic hazard analyses require an assessment of regional maximum earthquake magnitude. One of the methods for estimating maximum magnitude is relating it to the dimensions of active faults. Intraplate earthquakes usually occur when pre-existing zones of weakness are reactivated in response to the ambient stress field. Because minor earthquakes rarely cause surface ruptures, the reactivated faults have to be studied by indirect means. In this study structural lineaments are used as proxies for old shear zones, faults and fractures. Their orientation with respect to the crustal stress field is determined in order to find potentially unstable faults. Firstly the orientation of the stress field is determined by reviewing literature and available data on crustal stress in Finland. The main force causing the compressive stress field in Fennoscandia is the spreading of the mid-Atlantic ridge, which is why the plate motion of Finland relative to North America is also taken into account. An estimate of 115° to 135° is reached for the azimuth of the maximum horizontal stress in Finland. The stress regime is mostly reverse (minimum principal stress is vertical) according to stress indicators and focal mechanisms. The lineaments are split into straight segments for azimuth calculation. The segments are then divided into optimal orientation categories based on the horizontal angle between the segment and the maximum horizontal stress. Reverse faulting takes place perpendicular to and normal as well as transfer faulting takes place parallel to the maximum horizontal stress. The direction of strike-slip faulting depends on the coefficient of internal friction, which is around 0.6 for solid rock and as low as 0.2-0.4 for pre-existing fractures. With these values the Coulomb failure criterion gives an optimal angle of 30° to 40° to the maximum horizontal stress for strike-slip faulting. The lineament segments with the different faulting categories are shown with different colours in order to better visualise the regions hosting similar faulting directions. Some coefficients of internal friction were also calculated based on available stress magnitudes by assuming frictional equilibrium of pre-existing, optimally oriented zones of weakness. The data were scarce and only available for shallow depths. The calculated coefficients are quite high (0.7-0.8) near the surface and decrease with depth down to 0.4. A maximum earthquake magnitude of approximately 7 is suggested based on lengths of the lineament segments. An earthquake of such magnitude has a very low probability of occurring in Finland. This leads to the conclusion that the datasets used are too coarse for reliable estimates of fault length. Finally, the lineament orientations are compared with seismicity data. In western Lapland earthquakes are clearly linked to a reverse and transfer faulting system. In order to find differences in earthquake source mechanisms the earthquakes are divided into three depth categories. It seems that shallow earthquakes of depths less than 5 km most often occur near lineaments likely to reactivate as reverse and transfer faults, whereas earthquakes deeper than 15 km occur closer to lineaments optimal for strike-slip faulting. Earthquakes between the depths of 5 km and 15 km occur near lineaments of all orientations. The lineament orientation and seismicity maps will hopefully prove useful in further studies concerning the present structural framework of the Finnish crust. For reliable estimates of maximum earthquake magnitude based on fault length in Finland, faults should be studied in greater detail.
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(2019)This work presents a new set of petrophysical laboratory measurements from Kylylahti, a Cu-Au-Zn mine in the Outokumpu mining district, in the eastern Finland. Results are discussed and compared to earlier petrophysical data from the area. The study was aimed to provide a solid base for accurate interpretation of already existing geophysical exploration data and to new seismic data collected during the COGITO-MIN (COst-effective Geophysical Imaging Techniques for supporting Ongoing MINeral exploration in Europe) project. The sample set covered the most common rock types found in Kylylahti. A small set of samples represented sulphide mineralizations from several mining sites in the Outokumpu district. In the area, ophiolitic ultra-mafic massifs consisting of Outokumpu assemblage rocks, are embedded in Kalevian sediments, black schists and mica schists. Several massifs, Kylylahti being one of them, contain polymetallic (Cu-Co-Zn-Ni-Ag-Au-Cd-Sn-As-Se-Mo) massive, semi-massive or disseminated sulphide mineralizations. The petrophysical parameters measured were density, seismic P-wave velocity, porosity, magnetic susceptibility, intensity of remanent magnetization, inductive resistivity, galvanic resistivity and chargeability. Additional parameters calculated from the measurements were seismic impedance, Königsberger (Q) ratio and induced polarization (IP) estimates. Density data divides the Kylylahti rocks in three categories: 1) Massive and semi-massive sulphide mineralizations with an average density of 3750 kg/m 3 , 2) Outokumpu assemblage rocks with densities close to 3000 kg/m 3 and 3) Kalevian rocks with densities a bit under 2800 kg/m 3 . Sulphide disseminations are common in Outokumpu assemblage carbonate-skarn-quartz rocks and black schists elevating the densities when abundant. The average P-wave velocities for almost all Outokumpu assemblage rock types are a bit over 6 km/s. Soap stones, mica schists and black schists have lower P-wave velocities, around 5.5 km/s. Porosity of the samples was very low overall. Most of the Kylylahti rocks belong to paramagnetic group (susceptibilities under 2000 μSI). Serpentinites and tremolitic calc-silicate rocks (TRECS) belong to strongly magnetic group as well as samples rich in disseminated sulphides. Low Q ratios reveal that magnetic mineral in serpentinites and TRECS is coarse-grained magnetite. Samples with disseminated sulphides have high Q ratios, thus the disseminations are mainly monoclinic pyrrhotites. Both Kylylahti sulphide mineralizations and black schists are conductive as well as rocks rich in dissiminated sulphides. The rocks containing disseminated sulphides have high IP estimates. Conductivity of black schists is due to graphite and to some extent due to disseminated sulphides. Physical properties of the ore samples from different mining sites reveal the differences in their mineralogy, mainly their changing proportions of pyrite, pyrrhotite and magnetite. The differences are due to metamorphic zoning in the Outokumpu district; the degree of metamorphism becomes higher when going from east to west or from surface to depth. Recommended parameters, densities and P-wave velocities for seismic modelling in Kylylahti are given. Based on the results, the sulphide mineralizations should produce a detectable reflection against any background due to their high density. Also the other Outokumpu assemblage rocks have a clear contrast against the mica schists and black schists. Soap stones are an exception. The contact between Kalevian rocks and soap stones is hardly reflective at all, whereas soap stones in contact with other Outokumpu assemblage rocks form a reflecting contact.
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(2014)In groundwater sites located in Sodankylä, Lumiaho, Taikkomäki and Tullinkangas data has been collected from natural state springs for quality and from groundwater pipes for groundwater level studies. Quality measurements and groundwater level changes has been studied graphically and statistically to understand the variation and the cause and effect phenomena of hydrological processes. Quality parameters and groundwater level results has been compared to a time series study: ‘Groundwater level and quality changes in Finland 1975-1999’ by Finnish Environmental Institute and to the regulation 401/2001 about quality requirements for water in household consumption by Ministry of Social Affairs and Health. Groundwater level fluctuation has been compared with changes in precipitation and evaporation rates close to research sites, and with the typical behaviour of groundwater level in related regimes. Precipitation and evaporation data has been measured for each groundwater site from the closest meteorological stations. Evaporation has also been calculated using the Hamon equation. The quality measurements include the following parameters: pH, electrical conductivity, nitrite-nitrate as nitrogen, ammonium as nitrogen, oxygen, phosphate as phosphorus, iron and manganese. Despite the fact that chosen research sites represent natural state areas, human behaviour has had a noticeable effect on groundwater level and quality. In all measurement sites the pH results are in most cases more acidic and conductivity results smaller than they should be in water with good quality. However, these results have improved within last ten years in most cases. The values of nitrite-nitrate and ammonium were mostly good and median values were mostly outstandingly lower than the results measured before. The values of oxygen and phosphate were good. Also, with the exception of Sodankylä, the values of iron and manganese were good. Groundwater levels in research sites followed more or less the water levels related to each regime. In the very Northern site, Sodankylä, the melting of snow and ice every Spring happened earlier in the year within the last ten years compared to period 1975-1999. There were no such significantly noticeable trends at the other station with relation to the other points of comparison. The first evaluation of graphs showed the clearest connection between groundwater level, precipitation and evaporation in the researched moraine soil; Taikkomäki and Lumiaho. The connection was discovered in other sites too, but not as clearly.
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(2014)In this thesis I study the radiation balance and heat budget of a multiyear sea ice floe drifting in the central Arctic ocean. The objectives of the study were to quantify the vertical partitioning of shortwave- and longwave radiation and to quantify the different components of the heat budget of the floe in question, both inside and at its interfaces. The measurements were set up at 88 26.6N, 176 59.88W on 8th of August and carried out for ten days. The measurements were made as a part of the fourth Chinese National Arctic Expedition CHINARE2010. The measurement setup consisted of a net radiometer, four PAR-sensors, a pyrano-albedometer, three spectral radiometers, daily snow pit measurements, weather observations and six ice corings. With the data from these studies I was able to quantify the rate of melting and fluxes of heat both at the surface and at the bottom of the ice. The data allowed for examining the fraction of transmitted and conducted heat but were insufficient for properly quantifying the internal changes and spectral composition of the shortwave radiation at different depths. The surface was observed to be losing heat mainly in the longwave part of the spectrum. The average net radiation on top of the ice on wavelengths between 200 nanometers and 100 micrometers over the period was -25.0 Watts per square meter. The heat fluxes of the shortwave and longwave radiations were of opposite directions and the negative heat flux of the longwave radiation dominated until a distinct change in the radiative conditions on 17th of August. For the remainder of the period these heat fluxes nearly balanced each other and the average net radiation was -2.1 Watts per square meter. The latent and sensible heat fluxes were observed to have a minor role in the surface heat budget with averages of -1.5 Watts per square meter and -0.03 Watts per square meter respectively. The ice was observed to melt primarily at the bottom at a rate of 0.5 cm per day driven by the input of heat from the underlying ocean. Melting at the surface was not apparent until before the last two days of studies, when the upper layer of the snow cover melted. The changes in sea ice and snow cover were visually observed to exhibit significant spatial variability even on a single floe.
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(2017)Vuonna 2016 4. -- 9. lokakuuta toteutettiin mittausjakso kenttätyönä Intian Himalajalla sijaitsevalla Sunderdhunga-jäätiköllä. Tämä työ käsittelee jäätikön päällä tehtyjä lumikuoppa-, säteily- ja lumiasemamittauksia. Lumikuoppia kaivettiin kaksi Sunderdhunga-jäätikölle ja viereiselle Panuti-jäätikölle neljä. Lumikuopille toteutettiin tyypillisimmät lumikuoppamittaukset, joita ovat lämpötila-, tiheys-, kovuus- ja raekoon ja -muodon mittaukset. Lisäksi kosteus- ja tiheysmittauksia tehtiin neljässä lumikuopassa lumihaarukka-mittalaitteella. Säteilymittauksia toteutettiin Sunderdhungalla pyranometrillä, nettosäteilymittarilla ja PAR-sensoreilla, joilla mitattiin myös Panuti-jäätiköllä. Tässä työssä käsitellään mittausten perusteella jäätikön pinnan kerrostuneisuutta ja tarkastellaan pinnan ja ilman välistä lämmönvaihtoa, jossa suurimmaksi tekijäksi osoittautui pitkäaaltosäteily. Kenttämittauksissa havaittiin likainen kerros lumen ja ylivuotisen lumen välissä. Likaisessa kerroksessa oli paljon mustia partikkeleita ja tämän kerroksen vaikutuksia mm. lämmönjohtavuuteen ja tiheyteen tutkitaan. Tämä työ on osa Akatemian rahoittamaa Himalaja-projektia (toiminnassa 2013 -- 2017), jossa Helsingin yliopiston, Ilmatieteen laitoksen ja TERIn (The Energy and Resource Institute, Intiasta) oli tarkoitus yhdessä selvittää aerosolien kuten mustan hiilen määrä, kulkeutuminen ja vaikutukset jäätikön pintakerrokseen.
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(2019)Itämeren ja sen tilan tutkimus on perustunut rannikon läheisyydessä oleviin mittausasemiin sekä seurantamatkoihin, joita esim. Pohjanlahdella tehdään noin 4 kertaa vuodessa. Viimeisen parinkymmenen vuoden aikana Itämerellä ollaan kuitenkin alettu käyttämään kauppalaivoihin asennettuja läpivirtauslaitteistoja eli niin sanottuja FerryBoxeja, eli niin sanottuja SOOP:eja (ship of opportunity). Automaattiset mittausmenetelmät ovat lisääntyneet viime vuosina ja FerryBox on yksi niistä. Tässä tutkielmassa keskitytään Pohjanlahdella kulkevan M/V Transpaper -aluksen FerryBoxin suolaisuus- ja lämpötilamittauksiin. Keskeisiä kysymyksiä ovat: onko data luotettavaa, mitä data kertoo suolaisuuden ja lämpötilan alueellisista ja ajallisista muutoksista, sekä miten sitä voi hyödyntää Itämeren tilan seurannassa. Tässä työssä käytetty data on haettu CMEMS -palvelusta. Data sisälsi jonkin verran epäluotettavia havaintoja, joten sille tehtiin ylimääräinen laadunvarmennus. Laatutarkastettu data vastasi hyvin lähettyvillä tehtyjä CTD -mittauksia sekä reitin varrella olevia pysyviä mittausasemia. CTD- ja FerryBox -mittausten välillä on vahva korrelaatio. Data sopii hyvin suolaisuuden ja lämpötilan tutkimiseen Itämerellä, kunhan datan laatu on varmistettu. Suolaisuusdatasta nähdään hyvin vuosikierto, pintaveden ollen kesällä vähäsuolaisempaa kuin talvella. Pintasuolaisuus vaihtelee eniten rannikon lähellä Perämerellä ja Merenkurkun eteläosassa, jossa keskihajonta on jopa 0,7 ja vähiten Perämeren keskiosissa ja Selkämeren keski- ja eteläosissa, jossa se on alle 0,2. Vaikka vuosikierto on selvästi nähtävissä, nähdään myös selviä eroja vuosien välissä. Mittausajanjaksosta 2009--2017 vuodet 2016 ja 2017 olivat keskimääräistä vähäsuolaisempia ja 2011--2012 tavanomaista suolaisempaa. Myös lämpötilassa näkyy selvä vuosikierto, sekä vuosien välistä vaihtelua. Ajanjakson lämpimin vuosi oli 2014 ja kylmin 2017. Lämpötilan kuukausikeskiarvoista näkee, että ne ovat selvästi lämpimämmät kuin aiemmin kirjallisuudessa esitetyt lämpötilanarvot. Pintaveden lämpötila oli varsinkin pohjoisessa syksyllä kirjallisuudessa olevia arvoja lämpimpää. Varsinkin Perämerellä lokakuussa keskiarvolämpötila oli 6,7⁰C--10⁰C, joka on ylärajaltaan 4⁰C korkeampi kuin kirjallisuuden 4--6⁰C. Tämä oli oletettua, koska kirjallisuudessa käytetyt arvot ovat 70-luvun alussa julkaistuja ja muutkin tutkimukset ovat todenneet pintavesien lämpenemisen.
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(2016)Yksi tapa tarkastella maankamarassa etenevien seismisten aaltojen vaimenemista on määrittää tutkittavalle alueelle seisminen Q-arvo, joka kuvaa maa- tai kallioperän keskimääräisiä vaimenemisominaisuuksia. Seismisellä Q-arvolla on myös taajuusriippuvuus, eli sillä on eri arvo eri taajuuksilla. Tässä työssä määritettiin taajuusriippuvat Q-arvot P- ja S-aallolle tutkimalla näiden ensisaapujien alusta alkavan kolmen sekunnin aikaikkunan maksimiamplitudeja. Kohdealue tutkimuksessa oli Pohjois-Suomi. Havaintoaineisto koostui Suomen seismiseen asemaverkkoon kuuluvien, viiden seismografiaseman maanjäristysrekisteröinneistä. Asemat sijaitsivat Hetan, Sodankylän, Oulun, Kuusamon ja Tornion alueilla ja maanjäristykset olivat tapahtuneet enintään 200 km:n episentrietäisyydellä. Eri asemien rekisteröintejä tutkittiin yhteensä 181 kpl. Tutkimuksessa käytetty menetelmä on nimeltään coda-normalisointimenetelmä, jossa P- ja S-aaltojen amplitudiarvot normalisoidaan coda-aaltojen amplitudiarvoilla. Eri hyposentrietäisyyksillä saaduista arvoista saadaan regression avulla määritettyä Q-arvo eri taajuuksille, joista linearisoinnin avulla saadaan määritettyä taajuusriippuva Q-arvo. Tässä työssä P-aallolle saatiin taajuusriippuva Q-arvo Qp(f ) = 183(±12)f^0.64(±0.15) sekä S-aallolle Qs(f )=288(±30)f^0.67 (±0.23 ) . Saatuja tuloksia verrattiin samalla menetelmällä eri puolilta maapalloa saatuihin tuloksiin. Pohjois-Suomen alueella S-aaltojen vaimeneminen oli kaikkein vähäisintä verrattuna tektonisesti aktiivisempiin tai geologisesti nuorempiin alueisiin. Tuloksia verrattiin myös sekä Fennoskandian alueelle että geologisesti samankaltaisille alueille määritettyihin Q-arvoihin. Tässä työssä määritetty Qp-arvo ja sen taajuusriippuvuus ovat hyvin samankaltaisia Norjan alueelle määritettyjen Qp-arvojen kanssa. Qs-arvo puolestaan osuu keskivaiheille muihin arvoihin vertailtaessa, ollen hyvin samankaltainen kuin Pohjois-Amerikkaan ja Australiaan määritetyt Qs-arvot. Coda-normalisointimenetelmä osoittautui riittämättömäksi alueelle, jolta on vähän ja epätasaisesti jakautunutta havaintoaineistoa maanjäristyksistä. Seismisten aaltojen vaimenemiseen liittyviä tutkimuksia suositellaan jatkettavan, mutta jollain toisella menetelmällä. Eräs mahdollinen tutkimuskohde tulevaisuudessa voisi olla geometrisen leviämistekijän ja sen etäisyysriippuvuden määrittäminen Suomen kallioperälle.
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(2018)Lakes in the boreal region hold a significant importance in the global carbon cycle. They transport and store carbon and exchange it with the atmosphere. As turbulent transport is the most important process in transporting substances in water and air, special weight has been laid on studying turbulent processes in lakes. This work concentrates on turbulence in the surface boundary layer of Lake Kuivajärvi in Western Finland. A 16-day measurement campaign was carried out in Kuivajärvi in September 2014. An acoustic Doppler velocimeter (ADV) was used for high-frequency velocity measurements. The meteorological forcing had two distinct regimes during the campaign: a relatively calm and warm period during the first 13 days and a cold and windy period during the last three days. The two regimes were visible in the measured velocity as well as in the calculated turbulence parameters. The friction velocity in water was estimated to be 3*10^-4...2*10^-2 m/s during low winds and 2*10^-3...5*10^-2 m/s during high winds. In the low-wind regime, the friction velocity in water was generally smaller than the scaled friction velocity in air. In the high-wind regime, the situation was opposite. The common practice of estimating the water-side friction velocity from above-surface measurements isn't justified in all conditions. The viscous dissipation rate was calculated using the inertial subrange method and the neutral scaling. Dissipation rate estimates were from ~10^-10 to 10^-4 W/kg during the low-wind regime. During the high-wind regime, the estimates ranged from ~10^-7 to 10^-3 W/kg. It is likely that the highest dissipation rate estimates were erroneous as such high values have not been reported elsewhere in lakes. A simplified turbulent kinetic energy equation with dissipation rate, shear production and buoyancy production was tested. There was an imbalance of turbulence production and dissipation that was also related to the two meteorological regimes. Whether the equation should also include turbulent transport terms is an open question. The most important sources for errors were noise in the velocity time series and the effect of waves. It was shown that noise removal is an essential part of the ADV data analysis, however, noise-removal methods and methods for calculating the dissipation rate should be developed further. The installment of the ADV instrument should also be improved.
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(2008)The Weddell Sea on the Antarctic coast is one of the most important areas of deep-water formation in the oceans. The processes that result in deep-water formation depend on the sea area's oceanic transport mechanisms and on the climatological conditions. The primary purpose of this master’s thesis is to calculate the prevailing current conditions and to estimate changes in the water-mass properties in the Weddell Sea. This was performed by using hydrographic data collected during the SWEDARP 88/89 expedition. The first part of the thesis includes a literature study on the oceanographic conditions in the Weddell Sea. The study describes the conditions that regulate the Weddell Sea's circulation field and characteristic oceanographic processes. Transport calculations were performed by applying geostrophic methodology to data from the station network in the southwestern Weddell Sea. First, the baroclinic flow field was determined with the assumption that the cyclonic circulation of the Weddell Sea flows in a clockwise direction through each transect of the gyre. The barotropic component of the current field was then calculated using an inverse method which balances the transports through the measurement transects by meeting given criteria. These were that the transport of salt and mass is equal through each measurement transect. The total volume transport in the Weddell gyre was calculated to be about 19 Sverdrup (1 Sv = 10^6 m^3/s), which is about 60% of the transport estimated in the literature. The formation of Weddell Sea Bottom Water (WSBW) was estimated to 1.4 Sv. The primary result of the study was the amount of heat released from the water column to the atmosphere within the measurement area. The heat loss was calculated to 12 TW (terawatt). The unique SWEDARP 88/89 stations measured in the Filchner depression on the continental shelf would deserve further analysis and would enrich the studies of the global deep-water circulation.
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