DInSAR investigation in the Pärvie endglacial fault region, Lapland, Sweden

Northern Fennoscandia bears witness to the Pleistocene glaciation in the form of a series of large faults that have been shown to have ruptured immediately after the retreat of the ice sheet, about 9500 years ago. The largest one, known as the Pärvie fault, consists of a 155 km long linear series of fault scarps forming north–northeast-trending, that stretch west of Kiruna, Lapland. End-glacial intra-plate faults of this extent are very rare in the continental crust and the Pärvie system represents one of the major fault zone structures of this type in the world. Seismological evidence shows that there is still noticeable seismic activity, roughly one event of magnitude 2 per year that can be attributed to the fault. Nevertheless assessing its state of activity is a difficult task due to the extent and remoteness of the area. This study is aimed at the determination of crustal motion around the Pärvie fault zone using the differential inter-ferometric synthetic aperture radar (DInSAR) technique, based on images acquired with the European Space Agency (ESA) satellites European Remote Sensing (ERS) 1, ERS-2, and the Environmental Satellite (ENVISAT). We present results achieved in terms of deformation of the crystalline bedrock along different sectors of the fault where high levels of coherence were obtained, even from image pairs several years apart. This finding does not exclude deformation in other segments, as observing conditions are not always as favourable in terms of data availability

Onsala Space Observatory – IVS Analysis Center

We briefly summarize the activities of the IVS Analysis Center at the Onsala Space Observatory during 2010 and give examples of results of ongoing work

Using a Superconducting Gravimeter in Support of Absolute Gravity Campaigning — A Feasibility Study

Preparing for joint analysis of absolute gravity (AG) campaigns, this report investigates whether astationary superconducting gravimeter (SCG) can provide a long-term stable measurement of sitedependentperturbations that help in reduction to the local value of little-g and its secular rate of change.The crucial element concerns the discrimination of instrumental drift components from trends of physicalorigin, where biasses in the inferred long-term drift rate may offset the rate that the reduced AG campaignsdeliver. Thus, the main objective is to include a set of gravity models and proxy series as completeas possible in the SCG analysis. Findings indicate consistency for dg/dt in the drift model at the 0.5 nm/s2/yrlevel using observations at Onsala Space Observatory from 2009 to 2017. In pursuit of the overridingobjective to improve the accuracy of secular rates of gravity owed to Glacial Isostatic Adjustment, ourapproach may even put numbers on a range of long-term changes due to atmosphere, hydrology, andnon-tidal ocean loading, namely the rate biasses reported here

Superconducting gravimeter and seismometer shedding light on FG5’s offsets, trends and noise: what observations at Onsala Space Observatory can tell us

Ten-year worth of absolute gravity (AG) campaigns at Onsala Space Observatory (OSO), Sweden, are simultaneously reducedusing synchronous data from a superconducting gravimeter (SG). In this multi-campaign adjustment, the a priori modelscommonly applied for each setup in AG-alone experiments are sidestepped in favour of SG records and a model to estimateits drift. We obtain a residual (hourly samples) at the 5 nm/s2 RMS level, reducing the SG data with a range of ancillary datafor the site’s exposure to ocean and atmospheric loading, and hydrology effects. The target quantity in AG projects in theBaltic Shield area is the secular change of gravity dominated by glacial isostatic adjustment with land uplift as its major part.Investigating into the details of the associated processes using AG requires a long-term stable reference, which is the aim ofinternational comparison campaigns of FG5 instruments. Two of these have been campaigning at OSO since 2009 when theSG had been installed. In the simultaneous inversion of all sixteen campaigns, we identify weaknesses of AG observations,like varying systematic offsets over time, excess microseismic sensitivity, trends in the AG data and side effects on the SG’sscale factor when campaigns are evaluated one by one. The simultaneous adjustment afforded us an SG scale factor verynear the result from a campaign with a prototype quantum gravimeter.Whence, we propose that single-campaign results maybe biased and conjectures into their variation, let alone its causes misleading. The OSO site appears to present manageableproblems as far as environmental influences are concerned. Our findings advocate the use of AG instruments and proceduresthat are more long-term stable (reference realization), more short-term stable too (setup drifts), less service craving and moreresilient to microseismic noise

Three months of local sea level derived from reflected GNSS signals

By receiving Global Navigation Satellite System (GNSS) signals that are reflected off the sea surface, together with directly received GNSS signals (using standard geodetic‐type receivers), it is possible to monitor the sea level using regular single difference geodetic processing. We show results from our analysis of three months of data from the GNSS‐based tide gauge at the Onsala Space Observatory (OSO) on the west coast of Sweden. The GNSS-derived time series of local sea level is compared with independent data from two stilling well gauges at Ringhals and Gothenburg about 18 km south and 33 km north of OSO, respectively. A high degree of agreement is found in the time domain, with correlation coefficients of up to 0.96. The root‐mean‐square differences between the GNSS‐derived sea level and the stilling well gauge observations are 5.9 cm and 5.5 cm, which is lower than for the stilling well gauges together (6.1 cm). A frequency domain comparison reveals high coherence of the data sets up to 6 cycles per day, which corresponds well to the propagation of gravity waves in the shallow waters at the Kattegat coast. Amplitudes and phases of some major tides were determined by a tidal harmonic analysis and compared to model predictions. From the GNSS‐based tide gauge results we find significant ocean tidal signals at fortnightly, diurnal, semi‐diurnal, and quarter‐diurnal periods. As an example, the amplitudes of the semi‐diurnal M2 and the diurnal O1 tide are determined with 1σ uncertainties of 11 mm and 12 mm, respectively. The comparison to model calculations shows that global ocean tide models have limited accuracy in the Kattegat area

Onsala Space Observatory: IVS Network Station

During 2012 we participated in 40 IVS sessions. As in the previous four years, we used the majority of the sessions that involved both Onsala and Tsukuba to do ultra-rapid dUT1 observations together with our colleagues in Tsukuba. We observed one four-station ultra-rapid EOP session together with Tsukuba, Hobart, and HartRAO. We also observed the RadioAstron satellite and several GLONASS satellites using the Onsala 25-m telescope. The highlight in 2012 was that our proposal to the Knut and Alice Wallenberg Foundation to establish a twin-telescope system at Onsala in accordance with the VLBI2010 recommendations was accepted

The relation between gravity rate of change and vertical displacement in previously glaciated areas

The rate of change of surface gravity, dg/dt, and vertical deformation rate of the solid surface, du/dt, are two observables of glacial isostatic adjustment (GIA). They contribute with different information on the same phenomenon. Their relation contains information of the underlying physics and a trustworthy relation allows to combine these observations to strengthen the overall observational accuracy of the phenomenon. In this paper we investigate the predicted relation between dg/dt and du/dt in previously glaciated areas. We use the normal mode approach for one dimensional earth models and solutions of the sea level equation with time-dependent coastline geometry. Numerical predictions of dg/dt and du/dt are computed for Laurentia, Fennoscandia and the British Isles respectively, using six different earth models. Within each region a linear trend is then fitted using the relation dg/dt = C du/dt + dg_0/dt. The estimated C and dg_0/dt differ more between the regions than between different earth models within each region. For Fennoscandia C ≈ −0.163 μGal/mm and for Laurentia C ≈ −0.152 μGal/mm. Maximum residuals between the linear trend and spatially varying model predictions of dg/dt are 0.04 μGal/yr in Fennoscandia and 0.17 μGal/yr in Laurentia. For the British Isles the results are harder to interpret, mainly since this region is located on the zero uplift isoline of Fennoscandia. In addition, we show temporal variation of the relation since the last glacial maximum till present-day. The temporal and spatial variation of the relation between dg/dt and du/dt can be explained by (i) the elastic respectively viscous proportion of the total signal and (ii) the spectral composition of the regional signal. Additional local effects, such as the Newtonian attraction and elastic deformation from local sea level changes, are examined in a case study for six stations in the Nordic absolute gravity network. The influence of these local effects on the relation between View the dg/dt and du/dt is negligible except for extreme locations close to the sea

Onsala Space Observatory - IVS Analysis Center

This report briefly summarizes the activities of the IVS Analysis Center at the Onsala Space Observatory during 2012 and gives examples of results of ongoing work

Fennoscandian strain rates from BIFROST GPS: A gravitating, thick-plate approach

The aim of this investigation is to develop a method for the analysis of crustal strain determined by station networks that continuously measurements of Global Navigation Satellite Systems (GNSS). The major new ingredient is that we require a simultaneous minimum of the observation error and the elastic and potential energy implied by the deformation. The observations that we analyse come from eight years worth of daily solutions from continuous BIFROST GPS measurements in the permanent networks of the Nordic countries and their neighbours. Reducing the observations with best fitting predictions for the effects of glacial isostatic adjustment (GIA) we find strain rates of maximum 5 nano/yr in the interior of the rebound area predominantly as areal strain. The largest strain rates are found in the Finnmarken area, where however the GNSS network density is much lower than in the central and southern parts. The thick-plate adjustment furnishes a simultaneous treatment of 3-D displacements and the ensuing elastic and potential energy due to the deformation. We find that the strain generated by flexure due to GIA is important. The extensional regime seen at the surface turns over into a compressive style already at moderated depth, some 50 km

Mobile quantum gravity sensor with unprecedented stability

Changes of surface gravity on Earth are of great interest in geodesy, earth sciences and natural resource exploration. They are indicative of Earth system's mass redistributions and vertical surface motion, and are usually measured with falling corner-cube- and superconducting gravimeters (FCCG and SCG). Here we report on absolute gravity measurements with a mobile quantum gravimeter based on atom interferometry. The measurements were conducted in Germany and Sweden over periods of several days with simultaneous SCG and FCCG comparisons. They show the best-reported performance of mobile atomic gravimeters to date with an accuracy of 39nm/s2, long-term stability of 0.5nm/s2 and short-term noise of 96nm/s2/√Hz. These measurements highlight the unique properties of atomic sensors. The achieved level of performance in a transportable instrument enables new applications in geodesy and related fields, such as continuous absolute gravity monitoring with a single instrument under rough environmental conditions.Peer Reviewe