seismicity of the reykjanes peninsula 1971 1976 abstract the reykjanes peninsula oblique rift a segment of the mid atlantic plate boundary connects the reykjanes ridge to the rift zones of iceland the axis of the deformation zone of the plate boundary can be traced as a rather narrow epicentral zone of earthquakes that is highly oblique to the spreading direction of the north america plate with respect to the eurasia plate the seismicity of the area is episodic active periods with a duration of about a decade are separated by more quiet periods of one to two decades our observation period spans a good part of an episode that began in 1967 and ended in 1975 nine earthquake swarms illuminate a 50 km long segment of the plate boundary the epicentral zone cuts obliquely across the fissure swarms of the volcanic systems of the peninsula geothermal areas are preferentially located at the intersection of the fissure swarms with the seismic zone outside the intersections with the seismic zone the fissure swarms show very low seismicity the tectonic characteristics gradually change along the plate boundary segment from being similar to those of a spreading segment in the western part to being more like a transform zone in the eastern part this is seen in the type of earthquake sequences maximum magnitude and type of faulting

the structure of seismogenic strike slip faults in the eastern part of the reykjanes peninsula oblique rift sw iceland abstract a considerable part of the seismic risk to the capital area of iceland is provided by a series of strike slip faults at the mid atlantic plate boundary within a distance range of 15 35 km about two thirds of the icelandic population lives within this distance range from the source areas of m 6 6 5 earthquakes the structure of the plate boundaries in sw iceland is relatively complex three branches meet in the hengill triple junction the oblique rift of the reykjanes peninsula the south iceland seismic zone a transform zone and the western volcanic zone a rift zone the reykjanes peninsula oblique rift has an over all trend of 70 highly oblique with respect to the spreading direction 101 in this region it contains both volcanic systems and seismogenic strike slip faults the fissure swarms of individual volcanic systems contain normal faults and fissures with a ne trend also quite oblique to the plate boundary the fissure swarms fade out towards the ne and sw as they extend into the plates on either side overprinting this pattern of volcano tectonic structures are sets of parallel northerly striking transcurrent faults that generate the largest earthquakes in this zone their surface expressions are en echelon fracture arrays and push up structures the sense of displacement is right lateral in the 15 km long section of the rift studied here we find evidence for at least six faults of this type the length of individual faults may exceed 12 km the distance between them varies from 1 to 5 km and together they form a bookshelf type fault system taking up the left lateral component of plate movements across the oblique rift zone

coseismic stress changes and crustal deformation on the reykjanes peninsula due to triggered earthquakes on 17 june 2000 1 a large mw 6 5 earthquake struck the south iceland seismic zone sisz on 17 june 2000 the 17 june main shock triggered increased seismicity over a large area and significant slip on at least three distinct faults on the reykjanes peninsula up to 87 km to the west of the event a second large mw 6 4 earthquake in the sisz occurred on 21 june 2000 about 17 km west of the 17 june main shock this event does not appear to have triggered as much activity on the reykjanes peninsula as the 17 june main shock although the epicenter was closer crustal deformation signals due to the june 2000 earthquakes on the reykjanes peninsula were observed with campaign and continuous gps and synthetic aperture radar interferometry with the largest coseismic deformation signal near lake kleifarvatn we model the faults using three uniform slip rectangular dislocations in an elastic half space best fit uniform slip models consistent with seismic and geodetic data indicate that all three faults trend n s and the motion on them was primarily right lateral strike slip our study suggests that the event near kleifarvatn had a significantly larger moment than seismic estimates indicating a component of aseismic slip on the fault lasting no more than several hours static coulomb failure stress change calculations indicate that the event at kleifarvatn increased the coulomb stress at the hypocenter of the nupshlidarhals event by 0 1 0 2 mpa as well as loading the hvalhnukur fault

geodynamics of iceland and the signatures of plate spreading abstract iceland rising to more than 2 km above sea level originates from the interaction of a mid oceanic ridge and excessive mantle upwelling the plate boundary between the north american and eurasian plates traverses iceland as a series of seismic and volcanic rift zones the building blocks of the volcanic zones are about 32 volcanic systems typically consisting of a central volcano often with a caldera and an associated fissure swarm one or more recent revision of geometry and nature of the volcanic systems include new constraints on the fissure swarms of western volcanic zone and the one active in 2014 2015 associated to the bar arbunga central volcano countrywide seismic network and historical earthquake activity shows that seismicity is most pronounced in transform zones in south and north iceland and at central volcanoes undergoing volcanic unrest in a two year period 2015 2016 the most seismically active volcanoes were katla and bar arbunga measurements of ground deformation using both gps geodesy and interferometric analysis of synthetic aperture radar images acquired by satellites insar reveal well the present day plate spreading process in iceland geodetically measured spreading rate across iceland is consistent with global plate motion models morvel2010 18 19 mm yr in direction n 100 105 e accommodated by a single rift zone in north iceland overlapping rifts in south iceland and a highly oblique rift on the reykjanes peninsula glacial isostatic adjustment gia in response to ice retreat since 1890 is an additional important processes on a regional scale in iceland responsible for rise of central part of iceland of 30 mm year

off rift and rift zone palaeostresses in northwest iceland abstract the vestfirdir peninsula of northwest iceland consists mainly of gently dipping basaltic lava flows 8 14 ma old detailed studies of its principal tectonic elements basaltic dykes normal faults and minor faults and observations of the trends of the major fjords and valleys make it possible to reconstruct the evolution of the associated stress field the results show that a kink shaped curved rift zone existed in this area until about 5 ma ago in the northern part of the peninsula the rift zone trended nne but ene in the southern part it is proposed that the tectonic elements of the vestfirdir peninsula were generated in two stress fields one operating inside the rift zone the other operating outside it the rift zone stress field was responsible for the formation of most normal faults dykes and the main extension direction inferred from the minor faults conversely the off rift stress field was responsible for the formation of several holocene normal faults in the southern part of the peninsula the direction of the secondary extension inferred from the minor faults as well as for most major fjords and valleys in the area boundary element studies suggest that the off rift stress field generated on the concave side of a curved rift zone is different from that generated on its convex side absolute tensile stresses that encourage the formation of valleys and fjords concentrate very near to or at the convex margin but at a considerable distance from the concave margin applying these model results to iceland as a whole it is concluded that the valley formation in northwest iceland occurred at a large distance form the associated rift zone whereas in east iceland the valleys formed near to the margin of the rift zone furthermore the model predicts that zones of relative tension may propagate radially from the convex side of the rift zone and act as magma channels for volcanoes the location and orientation of major fjords and valleys in east and northwest iceland as well as the existence of several major off rift holocene volcanoes support the model predictions

modelling circumpolar deep water intrusions on the amundsen sea continental shelf antarctica results are presented from an isopycnic coordinate model of ocean circulation in the amundsen sea focusing on the delivery of circumpolar deep water cdw to the inner continental shelf around pine island bay the warmest waters to reach this region are channeled through a submarine trough accessed via bathymetric irregularities along the shelf break temporal variability in the influx of cdw is related to regional wind forcing easterly winds over the shelf edge change to westerlies when the amundsen sea low migrates west and south in winter spring this drives seasonal on shelf flow while inter annual changes in the wind forcing lead to inflow variability on a decadal timescale a modelled period of warming following low cdw influx in the late 1980 s and early 1990 s coincides with a period of observed thinning and acceleration of pine island glacier

formation of oskjuvatn caldera at askja north iceland mechanism of caldera collapse and implications for the lateral flow hypothesis the oskjuvatn caldera at askja volcano north iceland was formed as a result of an explosive eruption at askja on 28th 29th march 1875 oskjuvatn is one of the youngest collapse calderas on earth and its initiation and growth were observed and documented by explorers and geologists working in the askja region between 1875 and 1932 it is an example of caldera formation where the volume of the caldera collapse far exceeds the volume of associated erupted products the discrepancy between the collapse volume and associated erupted products has been used by previous workers as a justification for the hypothesis that the injection of lateral dykes from askja fed the february to october 1875 n jahraun fissure eruptions at the sveinagja graben some 60 km north of askja however historical accounts documenting the caldera formation in sufficient detail show clearly that oskjuvatn formed by piecemeal collapse taking over 40 years to reach its current form we use these accounts to undertake a detailed examination of the stages of caldera collapse and to compare them with the known magmatic output of askja in the years following the 1875 eruption arcgis software was used to calculate the volume of oskjuvatn during the various stages of collapse and the volume of material erupted after 1875 while a dyke extending between askja and sveinagja may be implied to account for the missing volume our results demonstrate that the volume of oskjuvatn in july 1875 closely corresponds to the volume of rhyolitic material erupted on 28th 29th march 1875 in addition geochemical evidence indicates that the n jahraun magmas were sourced from a deeper reservoir rather than by lateral injection from askja s shallow crustal magma chamber we therefore suggest that the injection of sills and dykes in a coherent intrusion complex beneath askja central volcano combined with background deflation of the magma storage zone beneath oskjuvatn caldera over 30 to 40 years following 1875 satisfactorily accommodates the volume required to form oskjuvatn caldera

rift transform kinematics in south iceland deformation from global positioning system measurements 1986 to 1992 crustal deformation in the plate boundary regions in south iceland is estimated from repeated global positioning system gps geodetic measurements in the period 1986 1992 we compare coordinate solutions for the 1986 and 1989 surveys with the results from the most recent survey in 1992 horizontal position uncertainty is about 2 cm for the 1986 and 1989 coordinates and about 4 mm for the 1992 coordinates little internal deformation is observed in the area west of the western volcanic zone within the north american plate and at the southern tip of the eastern volcanic zone within the eurasian plate the observed relative velocity of these two areas is 2 1 0 4 cm yr in direction n117 11 e 1 uncertainties compatible with the 1 94 cm yr widening in direction n 104 e across south iceland predicted from the nuvel 1 global plate motion model left lateral shear strain is developing across the intervening transform zone the e w trending south iceland seismic zone sisz strain is concentrated within a 20 to 30 km wide zone that correlates with seismic activity in the sisz about 85 15 of the relative plate motion is accommodated by this zone in such a way that the area south of the sisz is moving toward the east with the eurasian plate and the area north of the sisz is moving toward the west with the north american plate accordingly north of the sisz the western rift zone can accommodate a maximum of 15 15 of the relative plate motion within the sisz the shear strain results in an anticlockwise rotation of lineaments oriented north south at a rate of 0 5 1 rad yr the shear strain accumulation can be accommodated by bookshelf faulting on mapped recent north south faults in the sisz if the deformation is accommodated by an array of n s faults spaced 1 5 km apart an average slip rate of about 0 5 5 mm yr is required on each fault the rate of geometric moment release due to earthquakes averaged over centuries m 0 expected from such an array is about the same as expected from a simple transform fault 2vad where 2v is the relative plate motion a is the total length of the seismic zone and d is the thickness of the brittle crust if 2v 0 85 0 15 1 94 cm yr d 10 15 km ana a 75 85 km then m 0 1 0 2 5 107 m3 yr comparable to the rate of geometric moment release in large historical earthquakes in the sisz for the last several centuries we conclude that historical seismicity in the sisz can be attributed to left lateral shear accumulation across the seismic zone at a similar rate throughout historical times as during the years 1986 1992

controls on the geometry of a holocene crater row a field study from southwest iceland the reykjanes peninsula rift zone in southwest iceland is a highly oblique segment of the mid atlantic ridge system which accommodates nw se extension during rifting episodes that consist of eruptions and normal faulting and e w left lateral shear strain along strike slip faults during longer amagmatic periods dominant tectonic features on the peninsula are a series of generally ne striking sub parallel eruptive fissures and normal faults and a cross cutting zone of n s striking right lateral strike slip faults the last series of rifting episodes ended in 1227 and a proposed 1 000 year cyclicity predicts the start of a new series of eruptions within the next 200 years in order to more accurately characterize the nature of eruptions on the reykjanes peninsula we present a new spatially accurate map of the 2 350 year old sundhnukur crater row in the western part of the peninsula which was examined in detail in order to determine the structural controls on crater row geometry and to understand the interactions that take place between eruptive fissures and pre existing geological structures volcanism is sometimes influenced by small perturbations in the surroundings such as gravitational loading topography changes in crustal properties or the presence of fault zones but there are few field examples showing how fissures are influenced by these pre existing structures we identify 27 fissure segments ranging in strike from 006 to 053 with varying spacing and overlap between them significant local variability in strike and stepping sense of segments occurs in proximity to topographic highs as well as within zones of faulting that pre date the crater row strike also varies at the northern end of the crater row as it approaches a region of older crust at the rift margin our data support numerical and laboratory modeling results which show that local topography pre existing fractures and crustal properties influence the path taken by magma on its way through the shallow crust

fracture populations on the reykjanes peninsula iceland comparison with experimental clay models of oblique rifting 1 we have used high resolution scanned air photos and field measurements to analyze fracture population systematics for the reykjanes fissure swarm in order to determine the effect of rift obliquity on the evolution of fracture populations on the reykjanes peninsula sw iceland the peninsula is oriented approximately 30 oblique to the direction of plate motion data show significant differences between the strike length and degree of development of fractures along the margin of the fissure swarm and those in the center of the zone of active volcanism along the margin fractures are long highly segmented extension fractures and normal faults with offset on the order of several meters and a predominant strike 20 oblique to the trend of the plate boundary rift axis in the center of the zone of active volcanism fractures are generally shorter straighter fewer in number and strike approximately perpendicular to the direction of maximum horizontal extension and parallel to the trend of eruptive fissures right lateral oblique slip faults striking approximately perpendicular to the spreading direction are present in the center of the rift zone scaled experimental models of oblique extension predict a significant change in fracture strike at the rift margins due to the presence of a secondary stress field on the reykjanes peninsula this corresponds to the boundary between thicker and thinner brittle crust the models confirm that right lateral oblique or strike slip faults accommodate significant left lateral shear where deformation is distributed in a rift zone

strain accumulation along an oblique plate boundary the reykjanes peninsula southwest iceland strain accumulation along an oblique plate boundary the reykjanes peninsula southwest iceland

circulation and melting beneath george vi ice shelf antarctica introduction george vi ice shelf sandwiched between the western coast of palmer land and the eastern coast of alexander island is the largest and most studied of the west antarctic peninsula ice shelves it covers an area of approximately 25 000 km2 and is underlain by circumpolar deep water cdw with temperatures in excess of 1oc giving rise to rapid basal melting bishop and walton 1981 lennon et al 1982 the maximum ice thickness of about 500 m occurs about 70 km from the southern ice front where a ridge of thick ice extends across george vi sound near 70ow see figure 1 effectively dividing the upper water column into northern and southern regions the northern ice front which faces marguerite bay appears to be near the geographical limit of ice shelf viability and has undergone a gradual retreat in recent decades lucchitta and rosanova 1998 a timeframe over which much of the nearby wordie ice shelf disintegrated doake and vaughan 1991 there is extensive surface melting over the northern parts of the ice shelf and much of the ice column near the northern ice front appears to be temperate paren and cooper 1986 conditions in the south where the ice front faces into ronne entrance are colder and the ice front position appears to be steady the vast majority of the flow into the ice shelf comes from palmer land but basal melting is sufficient to remove most of this so that the ice is derived almost exclusively from local accumulation by the time it reaches the ice fronts potter et al 1984 there is some evidence at the margins of the ice shelf to suggest that it may have disappeared completely during the early holocene before reforming sugden and clapperton 1981 bentley et al 2005

geodetic investigation of plate spreading along a propagating ridge the eastern volcanic zone iceland summary hotspot ridge interactions lead to the dynamic evolution of divergent plate boundaries including propagating and overlapping ridge segments in southern iceland the eastern volcanic zone evz formed approximately 2 3 ma ago during the last eastward ridge jump from the western volcanic zone wvz and is propagating to the southwest into the tertiary lithosphere of the eastern volcanic flank zone north america eurasia relative plate motion is partitionedbetweentheeasternandwvzs weutilizenewterrestrial dry tilt andspace gps and insar geodetic data to investigate the nature of plate spreading and magma tectonic interaction at the southern terminus of this propagating ridge system we present a new gps derived horizontal velocity field covering the period 1994 2006 new insar analyses for the periods 1993 2000 and 2003 2007 and models of plate spreading across this region the velocity field indicates horizontal surface deformation consistent with plate spreading across and the propagation of the evz the dry tilt and insar data show transient deformation signals associated with magmatic processes the velocity field is corrected for these transient deformation sources in order to investigate the nature of secular plate motion our model results indicate a decrease in spreading rate from northeast 15 mm yr 1 to southwest 9 mm

geometry formation and development of tectonic fractures on the reykjanes peninsula southwest iceland abstract a study was made of 903 fractures most of which are of postglacial age on the reykjanes peninsula some 120 fractures belonging to the vogar fissure swarm he completely within the same postglacial lava flow and were studied in great detail for the vogar fractures 75 are pure tension fractures and 25 are normal faults the average length of the vogar fractures is 611 m the average width is 0 6 m the average spacing measured perpendicular to the average strike n54e of fractures is 456 m the estimated average depth is of the order of several hundreds of meters and the average throw of the faults is 2 3 m all major fractures on the peninsula appear to have formed by coalescence of smaller fractures as a result of absolute tensile stress the fractures group into four fissure swarms each being a part of a volcanic system which it is proposed is fed by an elongated partially molten magma reservoir located at a depth of about 8 km beneath the peninsula it is suggested that a slight magmatic pressure increase in these reservoirs and resulting uplift and tensile stress at the surface is the main cause of postglacial fracture formation

crustal deformation from 1992 to 1995 at the mid atlantic ridge southwest iceland mapped by satellite radar interferometry satellite radar interferometry observations of the reykjanes peninsula oblique rift in southwest iceland show that the reykjanes central volcano subsided at an average rate of up to 13 millimeters per year from 1992 to 1995 in response to use of its geothermal field interferograms spanning up to 3 12 years also include signatures of plate spreading and indicate that the plate boundary is locked at a depth of about 5 kilometers below that depth the plate movements are accommodated by continuous ductile deformation which is not fully balanced by inflow of magma from depth causing subsidence of the plate boundary of about 6 5 millimeters per year

downslope convection north of elephant island antarctica influence on deep waters and dependence on enso 1 we present a long time series 1992 2001 of bottom temperature from 1040m on the continental slope north of elephant island antarctic peninsula a strong annual signal is apparent with minimum temperatures during or following the austral winter and a range similar to that found in much shallower waters on the adjacent shelf individual convective events are observable as large amplitude cold spikes that are confined to the period of seasonally coldest temperatures these plumes are dense enough to seasonally displace the circumpolar deep water and directly inject cold water into the deep open ocean the coldest water occurred when anomalous sea ice conditions were prevalent caused by the strong 1997 98 enso event we thus expect repeats of such strong convective events on enso timescales the observed long term warming and reduction in sea ice along the peninsula may however act to suppress this mode of ventilating the deep southern ocean

climate change in the western antarctic peninsula since 1945 observations and possible causes temperature records from stations on the west coast of the antarctic peninsula show a very high level of interannual variability and over the last 50 years larger warming trends than are seen elsewhere in antarctica in this paper we investigate the role of atmospheric circulation variability and sea ice extent variations in driving these changes owing to a lack of independent data the reliability of antarctic atmospheric analyses produced in the 1950s and 1960s cannot be readily established but examination of the available data suggests that there has been an increase in the northerly component of the circulation over the peninsula since the late 1950s few observations of sea ice extent are available prior to 1973 but the limited data available indicate that the ice edge to the west of the peninsula lay to the north of recently observed extremes during the very cold conditions prevailing in the late 1950s the ultimate cause of the atmospheric circulation changes remains to be determined and may lie outside the antarctic region

strain accumulation 1986 1992 across the reykjanes peninsula plate boundary iceland determined from gps measurements gps geodetic observations 1986 1992 spanning the oblique plate boundary on the reykjanes peninsula sw iceland show that left lateral shear strain is accumulating in the area the principal strain rates are 1 0 255 0 055 strain yr extension at n121 6 e and 2 0 190 0 053 strain yr contraction at n31 6 e the principal axis of extension is perpendicular to the strike of fractures within volcanic systems on the peninsula the direction of maximum left lateral shear strain is n76 6 e the same as the trend of the seismic zone on the peninsula tensor shear strain in this direction is 0 222 0 054 strain yr continuous aseismic slip of the north american eurasian plates below a 5 11 km locking depth on the peninsula can explain the observed depth of earthquakes the width of the deformation zone determined from recent fissuring and faulting and the gps measurements of strain

a behavioral template beach profile model for predicting seasonal to interannual shoreline evolution 1 this contribution presents a simple behavioral template model for beach profile evolution which is calibrated and tested against a 6 year time series of shoreline position derived from a coastal imaging system at the gold coast australia from a coastal management perspective the position of the shoreline is arguably one of the most important morphodynamic parameters to be monitored and predicted and therefore forms the focus of this paper the template model attempts to encapsulate some of the current understanding of coastal dynamics deduced from both scientific investigations and observations the model framework is based on a simple relaxation model whereby the profile approaches a template exponentially with time under conditions of constant forcing the template evolves dynamically in response to incident wave forcing such that when a threshold value of the dimensionless fall velocity hs wtp where hs offshore significant wave height tp peak wave period and w sediment fall velocity is exceeded the beach face erodes and flattens and the shoreline retreats landward forming an erosional scarp and a breakpoint bar conversely when the falls below threshold progradation and steepening of the shoreface ensues accompanied by the evolution of a swash bar and breakpoint step the gold coast data are used to calibrate the threshold value of 4 0 which is close to the time series mean 3 8 testing the calibrated model on unseen data shows that it is able to reproduce the dominant seasonal interannual shoreline succession observed at this site and up to 77 of the detrended shoreline variability

ground deformation due to steam cap processes at reykjanes sw iceland effects of geothermal exploitation inferred from interferometric analysis of sentinel 1 images 2015 2017

the 1994 1995 seismicity and deformation at the hengill triple junction iceland triggering of earthquakes by minor magma injection in a zone of horizontal shear stress since july 1994 an unusually persistent swarm of earthquakes m 4 0 has been in progress at the hengill triple junction sw iceland activity is clustered around the center of the hromundartindur volcanic system geodetic measurements indicate a few centimeters uplift and expansion of the area consistent with a pressure source at 6 5 3 km depth beneath the center of the volcanic system the system is within the stress field of the south iceland transform zone and the majority of the recorded earthquakes represent strike slip faulting on subvertical planes we show that the secondary effects of a pressure source modeled as a point source in an elastic half space include horizontal shear that perturbs the regional stress near the surface shear stress is enhanced in quadrants around the direction of maximum regional horizontal stress and diminished in quadrants around the direction of minimum regional stress the recorded earthquakes show spatial correlation with areas of enhanced shear the maximum amount of shear near the surface caused by the expanding pressure source exceeds 1 strain sufficient to trigger earthquakes if the crust in the area was previously close to failure

crustal deformation at the oblique spreading reykjanes peninsula sw iceland gps measurements from 1993 to 1998 in 1993 and 1998 a 38 point gps network was surveyed on the reykjanes peninsula sw iceland according to the nuvel 1a plate motion model the spreading rate of the north american and eurasian plates in sw iceland is 18 9 0 5 mm yr toward n102 7 1 1 e highly oblique to the plate boundary instead of oblique spreading the measurements indicate left lateral shear strain accumulation parallel to the reykjanes peninsula seismic zone n76 e at the rate of about eyx 0 2 strain yr tensor shear strain subsidence is generally observed toward the seismic zone a local maximum subsidence of 60 mm was measured in the svartsengi geothermal area subsidence in this area has previously been detected with geodetic measurements and is considered a result of geothermal usage expansion was observed in the area of the hengill triple junction this is probably a result of magma accumulation beneath mount hromundartindur as previous seismic and geodetic measurements have indicated using a simple screw dislocation model we fit the majority of the data assuming a left lateral shear zone at depth along the seismic zone we estimate locking depth of 6 5 km and deep slip rate of 16 5 mm yr the maximum left lateral displacement predicted by the screw dislocation model 11 85 0 06 mm yr is consistent with the observed value of 11 9 0 5 mm yr if the hengill area is excluded little extension is observed across the peninsula the discrepancy between the nuvel 1a oblique spreading and the observed transcurrent motion is thought to be caused by lack of magma intrusion into the crust during this time period

the continental margin in iceland a snapshot derived from combined gps networks abstract the tectonical setting in iceland is quite complex due to the interaction of the iceland hot spot and the mid atlantic ridge while in the north of the island one active spreading zone exists the divergent motion in the centre and the south is distributed over at least two volcanic rift zones the spreading rate increases linearly along the western volcanic zone from north to south up to 8 mm yr at the hengill triple junction on the contrary the spreading rate of the parallel eastern volcanic zone decreases from 16 mm yr down to 6 mm yr at the island s southern coast the hreppar microplate between the two predominant rift zones has an independent motion which is distinct from that of the eurasian and north american plates a new detected feature is the spreading activity around the hofsjokull volcanic zone located in the centre of iceland with a significant rate of 6 mm yr during this investigation the coordinate sets of nearly 20 years of gps data acquisition on iceland were combined to get a velocity field for the surface of iceland this velocity field is based on a linear kinematic model with the consideration of local non linear effects like volcano up doming and displacements due to major earthquakes

spatial variation in seabed temperatures in the southern ocean implications for benthic ecology and biogeography the antarctic seabed has traditionally been regarded as cold and thermally stable with little spatial or seasonal variation in temperature here we demonstrate marked spatial variations in continental shelf seabed temperature around antarctica with the western antarctic peninsula shelf significantly warmer than shelves around continental antarctica as a result of flooding of the shelf by circumpolar deep water from the antarctic circumpolar current the coldest shelf seabed temperatures are in the weddell sea ross sea and prydz bay as a consequence of seasonal convection associated with strong air sea heat fluxes and sea ice formation these waters constitute the dense precursors of antarctic bottom water and can descend down the adjacent slope to inject cold water into the southern ocean deep sea deep sea seabed temperatures are coldest in the weddell sea and are progressively warmer to the east there is a distinct latitudinal gradient in the difference between seabed temperatures on the shelf and in the deep sea with the deep sea warmer by up to similar to 2 k at high latitudes and colder by similar to 2 k around sub antarctic islands these differences have important consequences for benthic ecology and biogeography understanding the evolutionary history of the antarctic marine biota and the impact of regional climate change

kinematic models of plate boundary deformation in southwest iceland derived from gps observations 1 we use data from gps campaign and continuous measurements from 1992 to 2004 in sw iceland to map the surface velocity field from the reykjanes peninsula to the eastern volcanic zone we divide the time series into preseismic july 1992 to june 2000 and postseismic june 2000 to may 2004 time intervals and we estimate gps station velocities for each interval as well as coseismic offsets due to the june 2000 earthquake sequence in the south iceland seismic zone sisz in addition to the plate spreading the preseismic velocity field shows the effects of inflation at hengill and hekla volcanoes whereas the postseismic velocities show deformation following the june 2000 earthquakes we consider several kinematic models to explain the preseismic velocities our preferred model includes several dislocations and point sources in an elastic half space with left lateral slip along the plate boundary on the reykjanes peninsula and below the sisz opening across the reykjanes peninsula and the western and eastern rift zones the optimal model has a locking depth of about 8 km in the central and eastern part of the reykjanes peninsula with a deep slip rate of about 17 mm yr and an opening of about 9 mm yr this locking depth is in agreement with the thickness of the seismogenic crust on the reykjanes peninsula which appears to vary between 7 and 9 km for the sisz we obtain a deep slip rate of about 19 mm yr below 16 km depth which is considerably deeper than the earthquake hypocenter depths in the area

extension across a divergent plate boundary the eastern volcanic rift zone south iceland 1967 1994 observed with gps and electronic distance measurements the average spreading rate in south iceland 19 mm yr is distributed over two parallel rift zones we measured a global positioning system gps network of 42 stations in the eastern zone in 1994 this network consists of stations measured with gps in 1986 and 1992 stations in a 60 km long distance profile measured several times since 1967 and a few new stations the 1994 gps data were processed using the bernese software version 3 5 and the average position uncertainties are about 3 mm in horizontal components and about 8 mm in the vertical component for baselines up to 100 km comparison with results of former gps campaigns gives a uniform extension steady in time perpendicular to the spreading axis a strain rate of 0 12 0 01 strain yr is observed across the 100 km wide network or an extension of about 12 mm yr minor deformation is observed in direction parallel to the spreading axis observations along the distance profile which lies across the rift zone gave a significant contraction during the period 1967 1977 but gave an extension during 1977 1994 this extension is about 138 47 mm and is mainly accommodated in the western part of the profile the observed extension across the rift zone during 1986 1994 can be simulated with a simple model of infinitely long dike intrusions into an elastic layer overlying a viscous layer this model is not able to simulate observed contraction along the distance profile 1967 1977 the observed irregularities along the western part of the distance profile coincide in space and time with volcanic and tectonic unrest near the hekla volcano the disturbances are probably caused by some common underlying process leading to crustal deformation eruptions and earthquakes

kinematic model of the south icelandic tectonic system summary due to the hot spot ridge interaction the tectonical situation in the southern part of iceland is quite complex within this investigation it is shown that the western volcanic zone is in spite of missing recent volcanic activity still an active spreading zone its annual widening of 8 1 1 0 mm yr 1 represents more than 45 per cent of the spreading of the southern part of iceland the full spreading rate of the investigated region amounted to 17 1 3 0 mm yr 1 these are the results of a constrained linear multiepoch deformation analysis of six gps measurement campaigns which have been carried out between 1986 and 1999 in the southwest of iceland the presented solution combines the motion information of 79 stations to yield a linear velocity field which is a snapshot of the medium term motion the used gps measurement campaigns had changing network geometries with a lack of point identities

diversity in deep sea benthic macrofauna the importance of local ecology the larger scale history and the antarctic abstract high diversity in macrobenthos in the deep sea still lacks satisfactory explanation even if this richness may not be exceptional compared to that in coastal soft sediments explanations have assumed a highly ecologically interactive saturated local community with co existence controlled by either niche heterogeneity or spatio temporal heterogeneity embodying disturbance all have failed to provide convincing support local regional scale biodiversity relationships support the idea of local richness in macrobenthos being predominantly dependent on the larger rather local scale local scale ecological interactions seem unlikely to have overriding importance in co existence of species in the deep sea even for relatively abundant core species with wide distributions variety in observed larger scale pattern and the strong inter regional pattern particularly in the poorly known southern hemisphere seem to have a pluralistic causation these include regional scale barriers and extinctions e g arctic and ongoing adaptive zone re colonisation e g mediterranean along with other historical constraints on speciation and migration of species caused by changes in ocean and ocean basin geometry at the global scale lack of knowledge of the antarctic deep sea for example blocks coherent understanding of latitudinal species diversity gradients we need to reconcile emerging understanding of large scale historical variability in the deep sea environment with massive extinctions among microfossil indicators as recently as the pliocene to results from cladistic studies indicating ancient lineages such as asellote isopods that have evolved entirely within the deep sea the degree to which the great age diversity and high degree of endemism in antarctic shelf benthos might have enriched biodiversity in the adjacent deep seas basins remains unclear basin confluence with the atlantic indian and pacific oceans may have encouraged northwards dispersion of species from and into the deep antarctic basins so that any regional identity is superficial interpretation of the antarctic deep sea as a diversity pump for global deep sea biodiversity may simply reflect re colonisation via basin confluence of northern hemisphere areas impoverished by the consequences of rapid environmental change during the quaternary

surface effects of triggered fault slip on reykjanes peninsula sw iceland three large earthquakes mw 4 5 were triggered within 5 min 85 km west of a mw 6 5 earthquake in the south iceland seismic zone sisz we report on surface effects of these triggered earthquakes which include fresh rupture widespread rockfall disrupted rockslides and block slides field data confirm that the earthquakes occurred along n striking right lateral strike slip faults field data also support the conclusion from modeling of insar data that deformation from the second triggered event was more significant than for the other two a major hydrological effect was the draining of water through an open fissure on a lake bed lowering the lake level by greater than 4 m field relationships suggest that a component of aseismic slip could have been facilitated by water draining into the fault zone d 2003 elsevier science b v all rights reserved