Source model for the 1997 Zirkuh earthquake (MW: 7.2) in Iran derived from JERS and ERS InSAR observations

We present the first detailed source model of the 1997 M7.2 Zirkuh earthquake that ruptured the entire Abiz fault in East Iran producing a 125 km long, bended and segmented fault trace. Using SAR data from the ERS and JERS-1 satellites we first determined a multisegment fault model for this predominately strike-slip earthquake by estimating fault-segment dip, slip, and rake values using an evolutionary optimization algorithm. We then inverted the InSAR data for variable slip and rake in more detail along the multisegment fault plane. We complement our optimization with importance sampling of the model parameter space to ensure that the derived optimum model has a high likelihood, to detect correlations or trade-offs between model parameters, and to image the model resolution. Our results are in an agreement with field observations showing that this predominantly strike-slip earthquake had a clear change in style of faulting along its rupture. In the north we find that thrust faulting on a westerly dipping fault is accompanied with the strike-slip that changes to thrust faulting on an eastward dipping fault plane in the south. The centre part of the fault is vertical and has almost pure dextral strike-slip. The heterogeneous fault slip distribution shows two regions of low slip near significant fault step-overs of the Abiz fault and therefore these fault complexities appear to reduce the fault slip. Furthermore, shallow fault slip is generally reduced with respect to slip at depth. This shallow slip deficit varies along the Zirkuh fault from a small deficit in the North to a much larger deficit along the central part of the fault, a variation that is possibly related to different interseismic repose time

Improved source modelling through combined use of InSAR and GPS under consideration of correlated data errors: application to the June 2000 Kleifarvatn earthquake, Iceland

Simultaneous use of multiple independent data sets can improve constraints on earthquake source-model parameters. However, the ways in which data sets have been combined in the past are manifold and usually qualitative. In this paper we present a method to combine geodetic data in source model estimations, which includes characterizing the data errors and estimating realistic model-parameter uncertainties caused by these errors. We demonstrate this method in a case study of the June 2000 Kleifarvatn earthquake, which occurred on Reykjanes Peninsula in Iceland. We begin by showing to what extent additional data can positively influence the source modelling results, by combining both GPS and descending-orbit InSAR data, which were used in two earlier studies of that event, with InSAR data from an ascending orbit. We estimate the data error covariances of the InSAR observations and base the data weights in our model-parameter optimization on the corresponding data variance-covariance matrix. We also derive multiple sets of synthetic data errors from the estimated data covariances that we use to modify the original data to generate numerous data realizations. From these data realizations we estimate the model-parameter uncertainties. We first model the Kleifarvatn earthquake as a simple uniform-slip fault and subsequently as a fault with variable slip and rake. Our fault model matches well with the field observations of coseismic surface ruptures and its near-vertical dip (83°) agrees with the regional faulting style as well as with aftershock locations. The two published source models of the event, on the other hand, both differ from our model as well as differing for one another. These studies, which were based on the descending InSAR data alone (the first study) and on that same data and GPS data (the second study), both neglect correlations in the InSAR data and do not report model-parameter uncertainties. Therefore, to compare these results with our model, we simulate the earlier model estimation set-ups and provide realistic estimates of the model-parameters uncertainties for these cases. We then discuss the significance of the difference between the existing fault models and demonstrate that both the inclusion of additional independent data as well as the covariance-based data weights improve the model-parameter estimatio

The use of commercial cad software in snow avalanche run-out estimation

Linear infrastructures like highways and transmission lines often pass avalanche terrain both in remote and urban areas. In some cases these areas are quite wide, measured along the lines, and the number of avalanche paths can be counted in dozens or even hundreds. Avalanche hazard assessment can be quite tedious in such areas when conventional methods like α/β are used. In 2009 the state owned Icelandic Landsnet (Icegrid) was working on a 107 km long transmission line running from the power station in Blanda river northwest Iceland to the capital of North Iceland, Akureyri. Most of the line runs along valleys with high and steep mountains. Our work was a preliminary estimation of the avalanche hazard along the route. Due to a limited timeframe set for the work it was important to find a method to deal with all these avalanche paths in an efficient way. No previous work had been carried out for this transmission line but avalanche records were known in some areas, as the transmission line partly follows the state highway. A solution based on long experience in designing roads and highways using Bentley Microstation and GEOPAK software in Iceland was chosen. The GEOPAK design software has a very flexible cross section module that allows the user to write macro programs to solve specific problems. In snow avalanche context this would be to estimate avalanche run-out at given locations. This article describes how the commercial cad software can be used in estimating multiple avalanche runouts along transmission lines, using the α/β-method. This method can speed up the tedious work at the initial stage of avalanche hazard assessment along linear structures

Locking depth and slip-rate of the Húsavík Flatey fault, North Iceland, derived from continuous GPS data 2006-2010

Located at the northern shore of Iceland, the Tjörnes Fracture Zone (TFZ) is a 120 km offset in the mid-Atlantic Ridge that connects the offshore Kolbeinsey Ridge to the on-land Northern Volcanic Zone. This transform zone is seismically one of the most active areas in Iceland, exposing the population to a significant risk. However, the kinematics of the mostly offshore area with its complex tectonics have not been adequately resolved and the seismic potential of the two main transform structures within the TFZ, the Grímsey Oblique Rift (GOR) and the Húsavík Flatey Fault (HFF) in particular, is not well known. In summer 2006, we expanded the number of continuous GPS (CGPS) stations in the area from 4 to 14. The resulting GPS velocities after four years of data collection show that the TFZ accommodates the full plate motion as it is predicted by the MORVEL plate motion model. In addition, ENVISAT interferograms reveal a transient uplift signal at the nearby Theistareykir central volcano with a maximum line-of-sight uplift of 3 cm between summers of 2007 and 2008. We use a combination of an interseismic backslip and a Mogi model in a homogeneous, elastic half-space to describe the kinematics within the TFZ. With a non-linear optimization approach we fit the GPS observations and estimate the key model parameters and their uncertainties, which are (among others) the locking depth, the partition of the transform motion between the two transform structures within the TFZ and the slip rate on the HFF. We find a shallow locking depth of 6.3+1.7- 1.2 km and transform motion that is accommodated 34 ± 3 per cent by the HFF and 66 ± 3 per cent by the GOR, resulting in a slip velocity of 6.6 ± 0.6 mm yr-1 for the HFF. Assuming steady accumulation since the last two large M6.5 earthquakes in 1872 the seismic potential of the fault is equivalent to a Mw6.8 ± 0.1 even

Avalanche risk along a 420 kv transmission line in Iceland.

Two transmission lines between Fljótsdalur and Reyðarfjörður in northeast Iceland have been investigated concerning snow avalanche hazard. Given a specific level of probability of failure for both the lines less than approximately 6.5x10-4 per year, a total sum of 82 masts might be hit by avalanches. In addition some other masts might be influenced by avalanches passing under the lines between masts. For the 82 exposed masts, the avalanche impact forces are calculated due to the accepted risk level for the transmission lines and the forces are also calculated for the cables exposed to avalanches. For each mast, the risk level must be considerable lower than for the transmission lines, and this question has been treated statistically in this paper. In order to achieve the best possible basis for the calculations of the return periods of the avalanches, weather and snow analyses are performed for the surrounding weather observational stations. A model analysis is performed for some weather situations with a high avalanche risk in order to calculate the snow drift in the mountainous areas around the transmission lines

Present kinematics of the Tjörnes Fracture Zone, North Iceland, from campaign and continuous GPS measurements

The Tjörnes Fracture Zone (TFZ), North Iceland, is a 120 km transform offset of the Mid-Atlantic-Ridge that accommodates 18mmyr−1 plate motion on two parallel transform structures and connects the offshore Kolbeinsey Ridge in the north to the on-shore Northern Volcanic Zone (NVZ) in the south. This transform zone is offshore except for a part of the right-lateral strike-slip Húsavík-Flatey fault (HFF) system that lies close to the coastal town of Húsavík, inducing a significant seismic risk to its inhabitants. In our previous work we constrained the locking depth and slip-rate of the HFF using 4 yr of continuous GPS measurements and found that the accumulated slip-deficit on the fault is equivalent to a Mw6.8± 0.1 earthquake, assuming a complete stress release in the last major earthquakes in 1872 and a steady accumulation since then. In this paper we improve our previous analysis by adding 44 campaign GPS (EGPS) data points, which have been regularly observed since 1997. We extract the steady-state interseismic velocities within the TFZ by correcting the GPS data for volcanic inflation of Theistareykir—the westernmost volcano of the NVZ—using a model with a magma volume increase of 25× 106m3, constrained by InSAR time-series analysis results. The improved velocity field based on 58 GPS stations confirms the robustness of our previous model and allows to better constrain the free model parameters. For the HFF we find a slightly shallower locking depth of ∼6.2km and a slightly higher slip-rate of ∼6.8mmyr−1 that again result in the same seismic potential equivalent to a Mw6.8 earthquake. The much larger number of GPS velocities improves the statistically estimated model parameter uncertainties by a factor of two, when compared to our previous study, a result that we validate using Bayesian estimatio

Ocean Bottom Seismometer Clock Correction using Ambient Seismic Noise

Ocean-bottom seismometers (OBSs) are equipped with seismic sensors that record acoustic and seismic events at the seafloor, which makes them suitable for investigating tectonic structures capable of generating earthquakes offshore. One critical parameter to obtain accurate earthquake locations is the absolute time of the incoming seismic signals recorded by the OBSs. It is, however, not possible to synchronize the internal clocks of the OBSs with a known reference time, given that GNSS signals are unable to reach the instrument at the sea bottom. To address this issue, here we introduce a new method to synchronize the clocks of large-scale OBS deployments. Our approach relies on the theoretical time-symmetry of time-lapse (averaged) crosscorrelations of ambient seismic noise. Deviations from symmetry are attributed to clock errors. This implies that the recovered clock errors will be obscured by lapse crosscorrelations' deviations from symmetry that are not due to clock errors. Non-uniform surface wave illumination patterns are arguably the most notable source which breaks the time symmetry. Using field data, we demonstrate that the adverse effects of non-uniform illumination patterns on the recovered clock errors can be mitigated by means of a weighted least-squares inversion that is based on station-station distances. In addition, our methodology permits the recovery of timing errors at the time of deployment of the OBSs. This error can be attributed to either: i) a wrong initial time synchronization of the OBS or ii) a timing error induced by changing temperature and pressure conditions while the OBS is sunk to the ocean floor. The methodology is implemented in an open-source Python package named OCloC, and we applied it to the OBS recordings acquired in the context of the IMAGE project in and around Reykjanes, Iceland. As expected, most OBSs suffered from clock drift. Surprisingly, we found incurred timing errors at the time of deployment for most of the OBSs

Whole genome characterization of sequence diversity of 15,220 Icelanders

Understanding of sequence diversity is the cornerstone of analysis of genetic disorders, population genetics, and evolutionary biology. Here, we present an update of our sequencing set to 15,220 Icelanders who we sequenced to an average genome-wide coverage of 34X. We identified 39,020,168 autosomal variants passing GATK filters: 31,079,378 SNPs and 7,940,790 indels. Calling de novo mutations (DNMs) is a formidable challenge given the high false positive rate in sequencing datasets relative to the mutation rate. Here we addressed this issue by using segregation of alleles in three-generation families. Using this transmission assay, we controlled the false positive rate and identified 108,778 high quality DNMs. Furthermore, we used our extended family structure and read pair tracing of DNMs to a panel of phased SNPs, to determine the parent of origin of 42,961 DNMs.Peer Reviewe

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IAS 41 og skattaumhverfi landbúnaðarins

Á Íslandi tíðkast almennt ekki að kúa-, sauðfjárbú og önnur landbúnaðarstarfsemi geri ítarleg reikningsskil. Alla vega ekki af þeirri gráðu að huga þurfi að reikningsskilastöðlum og uppsetningu á ársreikningum. En til er reikningsskilastaðall, IAS41, sem fjallar um landbúnað. Þar er tekið á helstu málum landbúnaðarins sem myndu teljast til sérstöðu hans og hlutum sem er kannski óvenjulegt að túlka í reikningsskilum. Í þessu riti er farið yfir þann staðal og það gagn sem af honum er að hafa. En þó reikningsskilin séu takmörkuð þá er landbúnaður samt atvinnugrein eins og hver önnur og hefur sínum skyldum að gegna gagnvart sköttum. Í ritgerðinni verður fjallað um þessi atriði og verða þau líka borin saman við umhverfi og aðstæður landbúnaðar í Svíþjóð og á Nýja Sjálandi. En á milli þessara þriggja landa er töluverðan mun að finna vegna náttúruaðstæðna og ýmissa pólitískra áhrifa.Hólmgeir Flosason, Berghylsbúi