rift transform junction in north iceland rigid blocks and narrow accommodation zones revealed by gps 1997 1999 2002 summary the current tectonics of north iceland are characterized by rifting episodes along fissure swarms and by ml 6 7 earthquakes in the transform zone between the northern rift zone and the kolbeinsey ridge north of iceland the last rifting period 1975 1984 was associated with an average opening of 5 m along the krafla fissure swarm post rifting deformation has been revealed by gps investigations in northern iceland a gps network was occupied in 1997 1999 and 2002 to quantify present day displacements and their variation with time on

crustal accretion model for iceland predicts cold crust we present a self consistent crustal accretion model of iceland that includes heat and mass transfer between an upwelling melting mantle and an accreting cooling crust this models predicts sub solidus crustal temperatures that are consistent with seismic estimates of the maximum depth of earthquake hypocenters and mid crustal shear wave quality factors and with geothermal estimates of surface heatflow

the magmatic plumbing system of the askja central volcano iceland as imaged by seismic tomography the magmatic plumbing system beneath askja a volcano in the central icelandic highlands is imaged using local earthquake tomography we use a catalog of more than 1300 earthquakes widely distributed in location and depth to invert for the p wave velocity vp and the vp vs ratio extensive synthetic tests show that the minimum size of any velocity anomaly recovered by the model is 4 km in the upper crust depth 8 km below sea level bsl increasing to 10 km in the lower crust at a depth of 20 km bsl the plumbing system of askja is revealed as a series of high vp vs ratio bodies situated at discrete depths throughout the crust to depths of over 20 km we interpret these to be regions of the crust which currently store melt with melt fractions of 10 the lower crustal bodies are all seismically active suggesting that melt is being actively transported in these regions the main melt storage regions lie beneath askja volcano concentrated at depths of 5 km bsl with a smaller region at 9 km bsl their total volume is 100 km3 using the recorded waveforms we show that there is also likely to be a small highly attenuating magmatic body at a shallower depth of about 2 km bsl

anatomy of an extinct magmatic system along a divergent plate boundary alftafjordur iceland recent rifting episodes highlight the role of magmatic systems with propagating dikes on crustal spreading however our knowledge of magmatic systems is usually limited to surface observations and geophysical data eastern iceland allows direct access to extinct and eroded deeper magmatic systems here we collected field structural and ams anisotropy of magnetic susceptibility data on 187 and 19 dikes respectively in the 10 12 ma old alftafjordur magmatic system at a paleodepth of 1 5 km the extension due to diking is at least 1 2 orders of magnitude larger than that induced by regional tectonics confirming magmatism as the key mechanism for crustal spreading this magma induced extension inferred from the aspect ratio of the magmatic system was of 8 mm yr lower than the present one ams data suggest that most of dikes have geometrically normal fabric at least at the margins consistent with prevalent subvertical magma flow and propagation

magma reflection imaging in krafla iceland using microearthquake sources the details of magma plumbing beneath active volcanoes remain a major challenge in geochemistry geophysics and volcanic hazard evaluation here we apply a relatively novel variation of seismic interferometry which we call virtual reflection seismic profiling vrsp to produce a high resolution image of a known crustal magma body the technique takes advantage of recent advances in both seismic instrumentation dense arrays and seismic analysis seismic interferometry we have applied this technique to data recently acquired at an iconic volcanic system krafla which lies on the mid atlantic ridge as exposed in northern iceland what make this particular site exceptional are encounters with rhyolitic magma in two drillholes k 39 and iceland deep drilling project 1 iddp 1 these known magma bodies represent a unique calibration opportunity for surface geophysical measurements of magma distribution at depth in this study we produced a stacked seismic reflection section by applying common depth point processing techniques to virtual shot gathers derived from interferometry of p waves from microearthquakes generated by tectonic magmatic and or geothermal activity we observe a strong coherent reflection on the seismic section at a travel time corresponding to the depth at which magma was encountered in the iddp 1 wellbore we interpret this reflection to be from magma or magma related fluids additional coherent reflections may correspond to other components of the magma plumbing beneath krafla these results represent a promising new technique for structural imaging with natural sources that can be applied to a wide array of geologic and energy problems that involve natural or induced seismic clusters

the accretion of oceanic crust by episodic sill intrusion seismic refraction data from mature oceanic regions show remarkable consistency in crustal thickness between sites yet the characteristics of different spreading centers show great variation this leads to the paradox that the similarity in mature oceanic crust suggests that the igneous processes in crustal accretion are the same across a range of spreading rates but that the differences in the spreading centers themselves imply the opposite we have developed a simple two dimensional model for crustal accretion at oceanic spreading centers by the episodic addition of sills at a high level within the crust as implied by recent geophysical studies of spreading centers using our model we have calculated velocity and temperature fields in the crust including the effects of hydrothermal cooling we show that oscillations in the temperature field due to episodicities of 200 20000 years have an effect localized to the region within 50 500 m of the intrusion by assuming that all latent heat and excess specific heat introduced by the injection of sills is convected away by hydrothermal circulation we estimate that the maximum heat transfer associated with hydrothermal cooling in the upper crust is of the order of 10 times greater than the conductive flux we have calculated seismic velocities associated with the model temperature field in the crust and we show that these are consistent with results from both seismic refraction and reflection experiments the model may be applied to both fast and slow spreading ridges and it accounts for the apparent increases in both the mean crustal temperature and the frequency of presence of melt with increasing spreading rate hence resolving the paradox we also show that the implications of this model are consistent with geological observations of layering in ophiolites

volcano tectonic implications of 3 d velocity structures derived from joint active and passive source tomography of the island of hawaii 1 we present a velocity model of the onshore and offshore regions around the southern part of the island of hawaii including southern mauna kea southeastern hualalai and the active volcanoes of mauna loa and kilauea and loihi seamount the velocity model was inverted from about 200 000 first arrival traveltime picks of earthquakes and air gun shots recorded at the hawaiian volcano observatory hvo reconstructed volcanic structures of the island provide us with an improved understanding of the volcano tectonic evolution of hawaiian volcanoes and their interactions the summits and upper rift zones of the active volcanoes are characterized by high velocity materials correlated with intrusive magma cumulates these high velocity materials often do not extend the full lengths of the rift zones suggesting that rift zone intrusions may be spatially limited seismicity tends to be localized seaward of the most active intrusive bodies low velocity materials beneath parts of the active rift zones of kilauea and mauna loa suggest discontinuous rift zone intrusives possibly due to the presence of a preexisting volcanic edifice e g along mauna loa beneath kilauea s southwest rift zone or alternatively removal of high velocity materials by large scale landsliding e g along mauna loa s western flank both locations also show increased seismicity that may result from edifice interactions or reactivation of buried faults new high velocity regions are recognized and suggest the presence of buried and in some cases previously unknown rift zones within the northwest flank of mauna loa and the south flanks of mauna loa hualalai and mauna kea

intense seismicity during the 2014 2015 barðarbunga holuhraun rifting event iceland reveals the nature of dike induced earthquakes and caldera collapse mechanisms

tectonics and magma dynamics coupling in a dyke swarm of iceland abstract to study the dynamics of dyke and fissure swarms in iceland we analyse the distribution of the dykes across the tertiary alftafjordur dyke swarm and that of open fissures and faults across the active krafla fissure swarm within these narrow 5 to 10 km wide and long length width ratio 10 swarms deformation is accommodated both by tectonics and magmatism the dyke swarm built during the westward regional tilting of the host rock lava pile the populations of dykes suggest that a characteristic thickness at about 3 m is involved during dyking dykes show a quasi periodic distribution across the swarm and form clusters spaced by about 2 5 km the analysis of the fissure distribution in the krafla volcanic system reveals a cluster spacing of about half of that of the dyke clusters we discuss the potential origins of these features as a result of magma dynamics host rock properties and tectonics clustering possibly reflects the intrinsic mechanical response to stretching of the upper levels of the brittle crust we propose a three dimensional model of dyke swarms in which magma likely migrates laterally within the upper crust from igneous centres where high magmatic supply rates locally perturb the regional stress field

from feeder dykes to scoria cones the tectonically controlled plumbing system of the rauðholar volcanic chain northern volcanic zone iceland the rau holar volcanic chain located in the northern volcanic zone of iceland has been variably eroded such that in the northern part the original scoria cones are preserved while the central and southern parts expose their shallow feeders the chain thus offers insight into the inner workings of the near surface feeder system of scoria cones the volcanic chain was mapped in 3d using gps the en echelon arranged volcanic chain can be divided into three parts the southernmost part contains only plugs and necks with a thin pyroclastic cover as well as multi tiered lava flows the central part combines partially eroded scoria cones feeder dyke intersections and welded scoria interbedded within rootless and clastogenic lava flows the welded scoria is composed of different kinds of lithics and bombs the northern part preserves almost intact overlapping scoria cones with voluminous lapilli sized scoriaceous deposits the overall dyke trend is orthogonal but shows radial patterns in individual cone complexes feeder dykes observed to depths of about 200 m below the volcanic chain are up to 8 m thick and flare in to conduits in the uppermost 20 50 m the exposed shallow plumbing system shows that magma pathways through the volcanic edifice are very complex with incremental repeated intrusions we interpret the arcuate shape to be the result of a local change in the orientation of the stress field because the rau holar volcanic chain is located within a major relay structure between volcanoes on the eastern fremrinamur rift arm and a rift extension with grabens on the western periphery

origin and evolution of the kolbeinsey ridge and iceland plateau n atlantic variations in crustal structure along the 700 km long krise7 refraction reflection and gravity profile straddling 66 5 n across the iceland shelf iceland plateau and western norway basin confirm that extinct spreading centers coexisted with the now extinct aegir ridge prior to the initiation of the kolbeinsey ridge at 26 ma the western 300 km of the profile across the iceland shelf formed by rifting at the kolbeinsey ridge whereas the eastern 400 km across the iceland plateau and the western norway basin formed by earlier rifting possibly containing slivers of older oceanic or continental crust rifted off the central e greenland margin along with the jan mayen ridge crustal thickness increases gradually across the iceland shelf from 12 to 13 km near the kolbeinsey ridge to 24 28 km near the eastern shelf edge decreasing abruptly across the shelf edge to 12 13 km the iceland plateau has crustal thickness ranging from 12 to 15 km decreasing to 5 8 km across the western norway basin and 4 5 km at the aegir ridge we suggest that high velocity lower crustal domes and corresponding gravity highs across the iceland plateau mark the location of extinct rift axes that coexisted with the aegir ridge similar lower crustal domes are associated with the currently active rift segments within iceland and the kolbeinsey ridge

capturing magma intrusion and faulting processes during continental rupture seismicity of the dabbahu afar rift continental rupture models emphasize the role of faults in extensional strain accommodation extension by dyke intrusion is commonly overlooked a major rifting episode that began in 2005 september in the afar depression of ethiopia provides an opportunity to examine strain accommodation in a zone of incipient plate rupture earthquakes recorded on a temporary seismic array 2005 october to 2006 april direct observation of fault patterns and geodetic data document ongoing strain and continued dyke intrusion along the 60 km long dabbahu rift segment defined in earlier remote sensing studies epicentral locations lie along a 3 km wide 50 km long swath that curves into the se flank of dabbahu volcano a second strand continues to the north toward gab ho volcano considering the 8 m of opening in the september crisis we interpret the depth distribution of microseismicity as the dyke intrusion zone the dykes rise from 10 km to the near surface along the 60 km long length of the tectono magmatic segment focal mechanisms indicate slip along nnw striking normal faults perpendicular to the arabia nubia plate opening vector the seismicity insar continuous gps and structural patterns all suggest that magma injection from lower or subcrustal magma reservoirs continued at least 3 months after the main episode persistent earthquake swarms at two sites on dabbahu volcano coincide with areas of deformation identified in the insar data 1 an elliptical northwestward dipping zone of seismicity and subsidence interpreted as a magma conduit and 2 a more diffuse 8 km radius zone of shallow seismicity 2 km above a shadow zone interpreted as a magma chamber between 2 5 and 6 km subsurface insar and continuous gps data show uplift above a shallow source in zone 2 and uplift above the largely aseismic gab ho volcano the patterns of seismicity provide a 3 d perspective of magma feeding systems maintaining the along axis segmentation of this incipient seafloor spreading segment

deep crustal melt plumbing of barðarbunga volcano iceland understanding magmatic plumbing within the earth s crust is important for understanding volcanic systems and improving eruption forecasting we discuss magma plumbing under bar arbunga volcano iceland over a 4 year period encompassing the largest icelandic eruption in 230 years microseismicity extends through the usually ductile region of the earth s crust from 7 to 22 km depth in a subvertical column moment tensor solutions for an example earthquake exhibits opening tensile crack behavior this is consistent with the deep 7 km seismicity being caused by the movement of melt in the normally aseismic crust the seismically inferred melt path from the mantle source is offset laterally from the center of the bar arbunga caldera by 12 km rather than lying directly beneath it it is likely that an aseismic melt feed also exists directly beneath the caldera and is aseismic due to elevated temperatures and pervasive partial melt under the caldera

seismic imaging of the geothermal field at krafla iceland using shear wave splitting abstract shear wave splitting is emerging as a useful exploration method for geothermal reservoirs as it can detect the geometry of the fracture system the intensity of cracking and possibly changes in fluid pressure within the reservoir the method is based on the analyses of polarizations and time delays of shear waves that have been distorted by the anisotropy of the medium through which the seismic waves have propagated observations of shear wave splitting within the krafla leirhnukur geothermal field iceland using a 20 station 3 component portable seismic array have provided evidence for at least two major crack systems of microfractures oriented approximately n s and e w located microearthquakes align roughly along the e w direction of the geothermal field with shallow focal depths mostly around the injection well probably related to the ongoing injection this unexpected direction is however consistent with results from a simultaneous mt magnetotelluric survey

magma bright spots mapped beneath krafla iceland using rvsp imaging of reflected waves from microearthquakes abstract the geometry and distribution of magma in the crust remain controversial topics with recent studies questioning the role of large magma chambers in this investigation high resolution 3d reflection images of crustal discontinuities beneath the krafla geothermal field in northern iceland were generated by applying vertical seismic profiling vsp techniques adapted from reflection seismology to microearthquake data exceptionally large amplitude reflections bright spots at a depth of 2 1 km correlate with rhyolitic magma encountered in the iddp 1 borehole although similarly bright reflectors at about 4 km correspond in depth to the top of an inferred magma chamber from previous seismic studies the scattered reflectivity that persists beneath this deeper reflector argues for a distributed magma system rather than a large feeder chamber

deep crustal reflectors under reydarfjordur eastern iceland crustal accretion above the iceland mantle plume summary deep seismic reflection profiling on the faroe iceland ridge experiment fire imaged a sequence of dipping events in the upper to crust beneath the tertiary lava pile in reydarfjordur eastern iceland these events dip towards the spreading centre at which the crust was formed and continue down to 6 s two way time corresponding to depths down to 15 18 km similar crustal reflections have been observed previously within the crust in other areas of iceland although the reflective events located by previous surveys have not been interpreted rigorously in this study we calculate synthetic seismograms from modelled sequences of lava flows to examine the reflective character of a lava le the synthesized lava pile sections are based on field measurements made in the reydarfjordur area the 1 km vertical exposures on the sides of the fjord are composed of lava flows within stratigraphic units which have a range of compositions and some intercalated tuffaceous clastic horizons we compare the synthetic seismograms with our seismic reflection data to test the interpretation that the deep dipping reflections are caused by a gently dipping sequence of subaerially erupted lavas we conclude that the upper and mid crustal reflections that we observe can be interpreted as lava flow sequences similar to those seen at the surface with the main reflections resulting from packets of flows of similar thicknesses the reflectors that we have imaged beneath iceland are similar to those defining the seaward dipping reflectors on the volcanic continental margins and we therefore suggest that the seaward dipping reflections commonly result from packets of lavas with similar distributions of thicknesses the occurrence of lavas down to 15 18 km beneath reydarfjordur can be explained partly by multiple episodes of accretion of the upper crust although the volcanic processes forming the crust in iceland generally lead to advection of extrusive material to mid crustal levels the production of an average extrusive layer totalling 15 km thickness is within reasonable estimates of the current volcanic productivity the advection of frozen lava flows to mid crustal levels contributes to the maintenance of the subsolidus crust that is observed on iceland and the zeolite minerals within the extrusive sequence may be responsible for the crustal low resistivity zone that has been observed using magnetotelluric techniques

rheologic controls on inter rifting deformation of the northern volcanic zone iceland article i nfo extensional rifts are characterized by significant lateral variations in crustal rheology as lithospheric material cools and advects away from the rift axes nevertheless most models used for modeling of crustal movements consist of horizontal layers with uniform properties this paper explores the role spatial variation of rheological properties play in modifying the style of surface deformation at rifts by comparing finite element model predictions to inferred inter rifting surface deformation in iceland s northern volcanic zone crustal deformation has been observed by satellite radar interferometry insar and gps measurements extension is observed across the entire northern rift zone whereas subsidence occurs in two distinct areas corresponding to mapped fissure swarms where major rifting took place in 1975 1984 and 1874 1876 respectively our models indicate that the observed inter rifting plate spreading deformation field is controlled by rheological variations within the en echelon arrangement of fissure segments and that a central ridge axes model does not apply uniform stretching across a plate boundary zone where fissure swarms are weaker than the surrounding crust and reflect the surface expression of the rift reproduces the characteristics of the deformation field the most realistic fissure swarm structure consists of a wedge of

volcanism on the rockall continental margin continental break up in the northern north atlantic was accompanied by massive volcanism this produced sequences of basalt flows erupted close to sea level which are imaged as seaward dipping reflectors on seismic reflection profiles they comprise the upper 4 5 km of transitional crust in both the edoras bank and hatton bank areas of the rockall continental margin detailed surveys show that the reflectors are convex upward on dip lines but are sub horizontal on strike lines they are probably produced by aerially extensive basalt flows extruded from linear fissure vents aligned parallel to the rift axis along the rockall margin two sequences of seaward dipping reflectors occur separated by an 9outer high9 near the foot of the continental margin the landward set of basalt flows are emplaced above stretched and intruded continental crust while the seaward set span the region from highly distended continental crust to fully oceanic crust the outer high is capped by basalt flows but exhibits little coherent internal reflectivity we discuss possible origins of the outer high as a residual block of thinned and intruded continental crust or as a central volcano cut by fissure vents similar to those found in the neovolcanic zones of iceland

thin low velocity zone within the krafla caldera ne iceland attributed to a small magma chamber we examine seismograms from microearthquakes recorded at krafla central volcano in the northern volcanic zone of iceland during a short inflation period in 1988 we produce record sections for propagation both to the north and to the south of the center of the caldera by combining seismograms from many earthquakes the northern record section contains clear evidence of a low velocity zone lvz including a low amplitude diffraction of the p wave as it impinges on top of the lvz and high amplitude reflections from beneath the lvz the absence of clear shear waves indicates that the lvz is at least partially molten and should be interpretated as a magma chamber the magma chamber is less than 1 km thick with a top approximately 3 km beneath the surface we find no evidence for a lvz in the southern part of the caldera

tomographic image of the axial low velocity zone at 12 50 n on the east pacific rise the 1982 magma seismic refraction experiment yielded a large set of accurate p wave travel times corrected for bathymetry and anisotropy which sample the structure of the east pacific rise epr at 12 50 n the arrivals were recorded using ocean bottom seismographs at three sites on axis and at 7 km and 16 km east of the axis we invert 2320 travel times for the twodimensional crustal seismic velocity structure across the epr axis assuming that the velocity structure is invariant along strike the travel times provide strong evidence for compressional velocity anisotropy in the upper crust corresponding to 10 faster velocities for propagation parallel to the axis than perpendicular to the axis the travel tunes used for the tomography are corrected for the effects of this azimuthal anisotropy our preferred model contains only the structure clearly required by the data structure which is stable under excessive smoothing and achieves a variance reduction of 81 relative to the laterally homogeneous starting model we resolve a substantial zone beneath the rise axis in which the velocity is reduced by 0 4 to 0 7 km s this low velocity zone lvz is about 7 km wide and extends from a depth of about 1 5 2 0 km down to moho at a depth of 5 5 km the lvz is slightly asymmetric extending 1 km further to the east than to the west of the axis in the shallow 1 0 km depth crust a pattern of velocity variations is imaged in which velocities are high at the spreading axis decrease between 3 km and 7 km east of the axis and then increase again between 10 and 15 km east of the axis we investigate the resolution of the inversion using an impulse response method the lvz and off axis upper crustal variations are well resolved in addition the travel time data indicate that an axial high velocity anomaly less than 2 km wide exists in the upper crust but is not resolved by the inversion the small velocity reductions of the lvz are consistent with hot rock containing only a small quantity of melt these results combined with the multichannel seismic reflection lines and expanded spread profiles from the northern epr suggest that the zone of high melt fraction under the spreading center is confined to a narrow thin lens capping a broad zone of hot plutonic rocks the upper crustal velocity reduction within 1 km of the axis reflects near axial thickening of the extrusive layer and the later reduction probably reflects porosity increases due to near axial tectonism the upper crustal velocity increase beyond 15 km off axis is attributed to porosity decreases associated with hydrothermal alteration

vegetation and climate changes during the late pliocene and early pleistocene in sw turkey comment to the published paper by jimenez moreno et al quaternary research 84 2015 448 456

widening of the krafla fissure swarm during the 1975 1981 volcano tectonic episode frequent distance measurements across the krafla fissure swarm north iceland recorded the extension accompanying the sequence of rifting events which started in december 1975 and lasted for 6 years an 80 to 90 km long section of the fissure swarm extended during this sequence of rifting and volcanic events maximum widening of about 8 m occurred 10 to 12 km north of leirhnjukur which is located above the center of the krafla magma reservoir from that location the amount of widening decreased north wards and is estimated to exceed 2 m where the seismicity indicated the northern termination of the present rifting off the north coast about 70 km north of leirhnjukur the amount of widening also decreased southwards and approached zero at 15 to 20 km south of leirhnjukur the ground deformation associated with these rifting events can be summarised as a narrow strip 1 to 2 km wide along the fissure swarm is heavily fractured with numerous open cracks parallel to the fissure swarm this fractured strip has subsided 2 to 3 m relative to its flanks the flanks of the fractured zone have been uplifted relative to regions farther away the uplift is not well constrained but tilt observations at several locations indicate about 1 m uplift the flanks of the rift zone have contracted perpendicular to the fissure swarm the maximum contractional strain exceeds 300 mm per km the amount of areal expansion windening of the fissure swarm times the length of the fractured zone associated with these rifting events is estimated to be about 0 30 km2 for individual events the area of expansion has been roungly proportional to the volume of subsidence above the krafla magma reservoir if the width of a new dike is equal widening of surface fissures the ratio of the subsidence volume to the area of expansion for the best observed events indicated a height of a new dike system as 2 4 to 2 8 km this ratio is significantly less for events of large lava production but even during these events the majority of magma leaving the krafla reservoir was apparently emplaced in subsurface fissures

the krafla spreading segment iceland 1 three dimensional crustal structure and the spatial and temporal distribution of local earthquakes the geothermal seismicity of the krafla volcanic system ne iceland was monitored for 3 months in 1985 using a dense local seismometer network the seismicity was continuous and the spatial and temporal distributions were roughly known prior to monitoring the instruments could thereby be deployed in a well positioned array a total of 489 locatable events were recorded within the network and 1771 arrival times were inverted to calculate the three dimensional p wave velocity structure and hypocentral locations low velocity volumes were imaged beneath the krafla and namafjall geothermal areas and indicate zones of hydrothermal alteration high velocity bodies beneath the krafla caldera rim are interpreted as gabbroic intrusions using a three dimensional velocity structure instead of a refraction based one dimensional model to locate the hypocenters significantly improves their location quality and illustrates the shortcomings of using refraction based models to locate earthquakes in local anomalous areas seismic activity was concentrated within the krafla and namafjall geothermal areas and in a narrow zone where dike injections had occurred 8 and 5 years earlier the activity occurred in the depth range 0 3 km the seismic rate for the whole area was one magnitude 3 2 event per year and the b value was 0 77 0 10 most of the seismicity appears to result from geothermal processes in the manner proposed for other icelandic areas foulger and long 1984 foulger 1988b seismicity directly beneath the bjarnarflag well field within the namafjall area is probably induced partly by geothermal exploitation considerable seismicity also occurred immediately below leirhnjukur a site of intense geothermal activity in the center of the krafla caldera that overlies a roof pendant in the magma chamber below this volume of high seismicity is probably highly fractured and may provide a conduit for magma escaping from the magma chamber

fault and graben growth along active magmatic divergent plate boundaries in iceland and ethiopia recent studies highlight the importance of annual scale dike induced rifting episodes in developing normal faults and graben along the active axis of magmatic divergent plate boundaries mdpb however the longer term 102 105 years role of diking on the cumulative surface deformation and evolution of mdpb is not yet well understood to better understand the longer term normal faults and graben along the axis of mdpb we analyze fissure swarms in iceland and ethiopia we first focus on the simplest case of immature fissure swarms with single dike fed eruptive fissures these consist of a 1 km wide graben bordered by normal faults with displacement up to a few meters consistent with theoretical models and geodetic data a similar structural pattern is found with asymmetric and multiple graben within wider mature fissure swarms formed by several dike fed eruptive fissures we then consider the lateral termination of normal faults along these grabens to detect their upward or downward propagation most faults terminate as open fractures on flat surface suggesting downward fault propagation this is consistent with recent experiments showing dike induced normal faults propagating downward from the surface however some normal faults also terminate as open fractures on monoclines which resemble fault propagation folds this suggests upward propagation of reactivated buried faults promoted by diking these results suggest that fault growth and graben development as well as the longer term evolution of the axis of mdpb may be explained only through dike emplacement and that any amagmatic faulting is not necessary

why meter wide dikes at oceanic spreading centers abstract numerical models show that maximum dike width at oceanic spreading centers should scale with axial lithospheric thickness if the pre diking horizontal stress is close to the andersonian normal faulting stress and the stress is fully released in one dike intrusion dikes at slow spreading ridges could be over 5 m wide and maximum dike width should decrease with increasing plate spreading rate however data from ophiolites and tectonic windows into recently active spreading ridges show that mean dike width ranges from 0 5 m to 1 5 m and does not clearly correlate with plate spreading rate dike width is reduced if either the pre diking horizontal stress difference is lower than the faulting stress or the stress is not fully released by a dike partial stress release during a dike intrusion is the more plausible explanation and is also consistent with the fact that dikes intrude in episodes at iceland and afar partial stress release can result from limited magma supply when a crustal magma chamber acts as a closed source during dike intrusions limited magma supply sets the upper limit on the width of dikes and multiple dike intrusions in an episode may be required to fully release the axial lithospheric tectonic stress the observation of dikes that are wider than a few meters such as the recent event in afar indicates that large tectonic stress and large magma supply sometimes exist

seismic constraints on magma chambers at hekla and torfajokull volcanoes iceland hekla and torfajokull are active volcanoes at a rift transform junction in south iceland despite their location next to each other they are physically and geologically very different hekla is an elongate stratovolcano built mainly of basaltic andesite torfajokull is a prominent rhyolitic centre with a 12 km diameter caldera and extensive geothermal activity the scope of this study is to examine the propagation of body waves of local earthquakes across the hekla torfajokull area and look for volumes of anomalous s wave attenuation which can be evidence of magma chambers so far the magma chamber under hekla has been modelled with various geophysical means and its depth has been estimated to be 5 9 km a data set of 118 local earthquakes providing 663 seismic rays scanning hekla and torfajokull was used in this study the major part 650 seismograms did not show evidence for s wave attenuation under these volcanoes only six seismograms had clear signs of s wave attenuation and seven seismograms were uncertain cases the data set samples hekla well at depths of 8 14 km and south part of it also at 4 8 km and 14 16 km western torfajokull is sampled well at depths of 4 14 km eastern and southern torfajokull at 6 12 km conclusions cannot be drawn regarding the existence of magma beyond these depth ranges also magma volumes of smaller dimensions than about 800 m cannot be detected with this method if a considerable molten volume exists under hekla it must be located either above 4 km or below 14 km the former possibility seems unlikely because hekla lacks geothermal activity and persistent seismicity usually taken as expressions of a shallow magma chamber an aseismic volume with a diameter of 4 km at the depth of 8 km in the west part of torfajokull has been inferred in earlier studies and interpreted as evidence for a cooling magma chamber our results indicate that this volume cannot be molten to a great extent because s waves travelling through it are not attenuated intense geothermal activity and low frequency earthquakes are possibly signs of magma in the south part of torfajokull but a magma chamber was not detected there in the areas sampled by this study

performance of the short period geophones of the iris passcal array we calibrated 64 mark products l22 d short period geophones of the iris passcal array using a mass displacement test the mean natural frequency of the 192 components was 2 1 hz slightly larger than the nominal value of 2 hz with a standard deviation of about 0 15 hz the standard deviation of the voltage sensitivity is about 5 per cent variability of both sensitivity and natural period are within the manufacturer s published specifications three types of nonlinearities were noted a 5 per cent difference in parameters determined by positive and negative mass displacements possibly due to a nonlinear spring observed on more than 90 per cent of the 192 components tested apparent cross axis errors in wide 1 to 2 hz bands near 10 hz and spurious resonance peaks at frequencies between 22 and 29 hz observed on about 20 per cent of the components array equalization of seismograms from the loma prieta earthquake aftershock survey indicate that the root mean square misfit between two seismograms recorded by different geophones at the same site can be reduced from 10 per cent to 5 per cent by application of the calibration results

crustal accretion and dynamic feedback on mantle melting of a ridge centred plume the iceland case abstract a major consequence of the interaction of a plume with an oceanic ridge is the enhanced melt production and associated crust generation in the case of iceland crustal thickness as large as 20 to 40 km has been reported crustal seismic velocities are high and have to be explained by thermal or chemical effects in the first part of the paper we address the question whether extraction of melt out of the plume beneath a slowly spreading ridge and deposition of extracted basalt volumes at the surface produces a dynamic feedback mechanism on mantle melting to study this question we solve the convection equations for a ridge centred plume with non newtonian rheology including melting melt extraction associated with deposition of cold crust at the surface of the model and using a simplified approach for compaction the assumption of cold crust is justified if the thickness of each deposited basaltic layer is less than roughly 1 km depending on the buoyancy flux of the plume crustal thicknesses between 10 and 40 km are modelled showing characteristic dipping structures resembling the rift ward dipping basaltic layers of east and western iceland comparing the resulting crustal thickness and magma generation rate with models in which the dynamic effect of crust deposition has been suppressed indicates that melt generation beneath a slowly spreading ridge is considerably damped by the dynamic feedback mechanism if the plume buoyancy flux exceeds 400 to 600 kg s based on the observed crustal thickness of iceland our models predict a plume buoyancy flux of 1140 kg s in the second part we study the accretion of the icelandic crust by a thermo mechanical model in more detail based on the navier stokes the heat transport and the mass conservation equations including volumetric sources hot 1200 c molten crustal material is injected into the newly forming crust with a constant rate at different crustal source regions a deep widespread emplacement of dykes and sills including crustal underplating b magma chambers at shallow to mid crustal level and c surface extrusions and intrusions in fissure swarms at shallow depth connected to volcanic centres we identify the material from the different source regions by a marker approach varying the relative dominance of these source regions characteristic crustal structures evolve showing shallow dipping upper crustal layers with dip angles between 10 and 15 the thermal structure of the crust varies between cold crust shallow source region dominating and hot crust deep source region dominating we use observations of maximum depth of seismicity to constrain the depth of the 650 c isotherm and seismological inferences on the lower crust to constrain temperatures in that region the best agreement with our models is achieved for crust formation dominated by deep dykes and underplating with a considerable influence of magma chamber accretion

joint inversion of multichannel seismic reflection and wide angle seismic data improved imaging and refined velocity model of the crustal structure of the north ecuador south colombia convergent margin 1 improving seismic imaging of the crust is essential for understanding the structural factors controlling subduction zones processes we developed a processing work flow based on the combined analysis of multichannel seismic reflection mcs and wide angle wa reflection refraction data to derive both shallow and deep velocities suitable for prestack depth migration and to construct a blocky velocity model integrating all identifiable seismic phases contained in mcs and wa data we apply this strategy to the study of the north ecuador sw colombia subduction margin to improve the imaging and geostructural interpretation of a splay fault and surrounding outer and inner margin wedges results show improvements over tomographic inversion of wa data only such as 1 sediment velocity variation across the trench and margin slope that correlates with lateral lithologic changes tectonic compaction and effect of mass wasting processes 2 a two layer velocity structure of the inner wedge basement that is consistent with the crust of an oceanic plateau 3 a complex velocity structure of the outer wedge basement that consists of a deep high velocity 5 0 5 5 km s 1 core and a low velocity zone 3 8 5 0 km s 1 associated with the major splay fault 4 a 1 3 km thick low velocity 3 5 4 0 km s 1 subduction channel that extends beneath the margin outer wedge both the splay fault and subduction channel are expected to direct fluid flows and 5 downdip velocity increase 5 6 km s 1 in the subducting oceanic crust associated with a low 7 8 km s 1 upper mantle velocity possibly reflecting changes in rock nature or properties

lithology and structure of the volcanic sequence in eastern iceland the reydarfjordur drill hole penetrated 1919 m of section with a recovery of 99 7 subaerial lava flows comprise 54 of the core dikes 41 and clastic rocks about 5 in addition a 1 3 km thick section of lava flows and clastic rocks exposed above the drill site was measured and sampled the lava flows are chiefly low magnesia basalts and ferrobasalts with lesser amounts of icelandite basaltic andesite and olivine tholeiite in the drill core complete flows range from 1 2 to 19 7 m in vertical thickness and average 7 1 m in the exposed section flow thicknesses range from 1 to 30 m and average 5 2 m most of the flows are characterized by an upper scoriaceous zone 1 3 meters thick grading downward through a zone of fractured basalt into a massive flow interior some flows also have a thin basal breccia olivine tholeiites and some low magnesia basalts are commonly mottled whereas ferrobasalts and icelandites have well developed flow banding most of the flows are fine to medium grained aphyric to sparsely phyric and moderately vesicular a few are moderately plagioclase phyric others have scattered phenocrysts of clinopyroxene and olivine over 100 intrusive units are recognized in the core and they span approximately the same compositional range as the flows they are characterized by having steeply inclined chilled contacts a uniform massive aspect and an absence of vesicles or brecciation most are less altered than the intruded lava flows and contain secondary minerals only along sparse high angle fractures many of the dikes are also aphyric but some contain notable plagioclase or olivine phenocrysts groundmass textures range from fine grained intersertal to coarse grained ophitic clastic units occur typically as thin varicolored layers between lava flows rarely exceeding 0 5 m in thickness these are chiefly fine to coarse grained poorly to well bedded lithic tuffs showing varying degrees of reworking most are silicic to intermediate in composition but basaltic units are also present two rhyolitic ash flow tuffs occur in the section one of which is 30 m thick we interpret the lavas to be the flanking portions of broad low angled central volcanoes centered on silicic complexes some of the flows may have erupted from central vents but most probably represent flank eruptions from rift zones represented by the dike swarms most of the dikes were probably intruded laterally into the lava pile thus they do not represent direct vertical feeders from deep magma bodies

comparison of dike intrusions in an incipient seafloor spreading segment in afar ethiopia seismicity perspectives 1 oceanic crust is accreted through the emplacement of dikes at spreading ridges but the role of dike intrusion in plate boundary deformation during continental rupture remains poorly understood between 2005 and 2009 the 70 km long dabbahu manda hararo rift segment in ethiopia has experienced 14 large volume dike intrusions 9 of which were recorded on temporary seismic arrays a detailed comparison of the seismic characteristics of the seismically monitored dikes is presented with implications for dike intrusion processes and magmatic plumbing systems all of the migrating swarms of earthquakes started from a 80 of energy is released during the propagation phase with minimal seismic energy release after the dike propagation ceases we interpret that faulting and graben formation above the dikes occurs hours after the passage of the dike tip coincident with the onset of low frequency earthquakes dike lengths show no systematic reduction in length with time suggesting that topographic loading and stress barriers influence dike length as well as changes in tectonic stress the propagation velocities of all the dikes follow a decaying exponential northward propagating dikes had faster average velocities than those that propagated southward suggesting preconditioning by the 2005 megadike or ongoing heating from a subcrustal magma source north of the midsegment

seismic properties density and composition of the icelandic crust near reydarfjordur compressional and shear wave velocities densities and porosities have been measured to confining pressures of 6 kbar for 135 samples from a deep borehole in eastern iceland the measurements are from a random sampling of dikes and sills through the 2 km hole velocities within the flow units are relatively low at the tops reach maximum values within central portions and decrease near the bases this systematic variation correlates well with variations in porosity and bulk density the dike units on the other hand have relatively uniform velocities which are approximately equivalent to maximum velocities measured within flow units below 700 m the dike and flow velocities show systematic increases with depth which are related to changes in mineralogy and independent of porosity the velocity gradient dvp dz t within this region is well defined by the laboratory velocities and approximates 0 6 s 1 in good agreement with field refraction measurements high velocities near the base of the hole are related to increasing alteration with depth and in particular an increase in epidote content the abundance of epidote in the rocks recovered from the lower portion of the drillhole supports a metamorphic origin for the layer 2 layer 3 boundary in this region

faroe iceland ridge experiment 2 crustal structure of the krafla central volcano the seismic velocity structure of the krafla central volcano is characterized by large variations in compressional velocity a 40 km wide high velocity dome extends from the lower crust 11 14 km depth beneath the volcano narrowing upward a magma chamber sits at its top near 3 km depth it is defined by both 0 2 0 3 s compressional wave delays and shear wave shadowing to be 2 3 km n s 8 10 km e w and 0 7 1 8 km thick the near surface structure uppermost 2 5 km of the krafla caldera is approximately flat lying with only minor lateral heterogeneities the crust beneath the magma chamber has low shear wave attenuation and anomalously high compressional and shear wave velocities shear waves reflected from a 19 km deep moho are clearly visible for some paths through the crustal volume below the magma chamber even though the more shallow diving s waves are severely attenuated the midcrust beneath the shallow magma chamber cannot contain partial melt or even be at near solidus temperatures the krafla central volcano plays a major role in crustal genesis along the plate boundary the high velocity dome in our view represents crust generated in and around the magma chamber which has subsequently been advected to greater depths

sources of crustal deformation associated with the krafla iceland eruption of september 1984 a decade long plate boundary rifting episode in northern iceland ended with the september 1984 fissure eruption of krafla volcano we apply a nonlinear inversion method to geodetic data collected before and after the eruption to infer the location geometry and strengths of deformation sources associated with the eruption the net outflow of magma from a 3 km deep magma chamber beneath the krafla caldera was 30 120 106 m a similar volume of magma 50 70 106 m was emplaced in a 1 meter wide 9 km long dike extending from the surface to 7 km depth furthermore at least 110 106 m of magma erupted accordingly a surplus of magma must have been expelled from a second reservoir the location of which although uncertain is likely to lie at depths greater than 5 km beneath krafla volcano it would be difficult to detect this deeper source because of the narrow aperture of the geodetic networks

imaging rapidly deforming ocean island volcanoes in the western galapagos archipelago ecuador using local body wave arrival time tomography methods to determine 3 d seismic velocity structure we imaged the plumbing system of sierra negra volcano galapagos this hot spot volcanic chain includes some of the fastest deforming volcanoes in the world making this an ideal location to study shield volcano plumbing systems we inverted p and s wave arrivals recorded on a 15 station temporary array between july 2009 and june 2011 using an a priori 1 d velocity model constrained by offshore refraction studies with local seismicity from nearby volcanoes as well as the ring fault system the model resolution is good between depths of 3 and 15 5 km the propagation of s waves throughout this volume argues against any large high melt accumulations although a shallow melt sill may exist above 5 km we image a broad low velocity region 25 km laterally below sierra negra at depths 8 15 km no large regional velocity increase is found within the limits of good resolution suggesting that crust is thicker than 15 km beneath the western galapagos archipelago our results are consistent with crustal accretion of mafic cumulates from a large volume magma chamber that may span the boundary between preplume and accreted crust the similarity between our results and those of hawaii leave open the possibility that the crust has also been thickened by under plating

the northern mid atlantic and reykjanes ridges spreading center morphology between 55 50 n and 63 00 n seamarc ii and hydrosweep acoustic imagery and bathymetry reveal that the northern mid atlantic ridge mar and reykjanes ridge between 55 50 n and 63 00 n are segmented seafloor spreading centers that exhibit structural morphologies that vary with distance from iceland the northern 100 km of the mar 55 50 n 56 47 n is oriented 005 perpendicular to the spreading azimuth and contains four third order spreading segments separated along strike by right and left stepping axial discontinuities the boundary between mar and reykjanes ridge occurs at 56 47 n where the bight transform fault offsets the neo volcanic axis 15 km right laterally across a single linear fault oriented 092 this is the only transform fault between 55 50 n and 63 00 n and is inferred to have generated the bight fracture zone the reykjanes ridge lies between the bight transform and iceland s reykjanes peninsula and is oriented 30 oblique to the spreading orthogonal direction axial faults and volcanic systems on the reykjanes ridge are arranged in a right stepping en echelon pattern and display strikes intermediate between the spreading orthogonal direction and the strike of the ridge which is compatible with experimental models of oblique extension spreading segments on the northern mar and reykjanes ridge are defined structurally and bathymetrically at the smallest scale the volcanic axis is segmented into individual volcanic systems 4 45 km long which are separated along strike by intervolcano gaps or offsets these features are analogous to fourth order spreading segments documented elsewhere on the mar axial volcanic systems are superimposed on intermediate wavelength 13 65 km axial topographic highs that constitute third or second order spreading segments segment boundaries occur at axial depth maxima which correspond to offsets in the volcanic axis four primary characteristics of the spreading axis axial valley depth axial boundary fault throw relief along the neovolcanic axis and degree of inter segment structural discontinuity decrease toward the north this variation is consistent with higher crustal temperatures near iceland due to either thicker crust or elevated mantle temperatures

formation of lunar highlands anorthosites abstract the lunar magma ocean lmo model was proposed after the discovery of anorthosite in apollo 11 samples however the chemical and isotopic compositions of lunar anorthosites are not fully consistent with its lmo origin we have analyzed major and trace elements in anorthositic clasts from ten lunar feldspathic meteorites which are related to the solidification of the lmo the plagioclase rare earth element ree abundances and patterns are not correlated with the mg of coexisting mafic minerals in anorthosites implying that mafic minerals and plagioclase may not be in chemical equilibrium consistent with their textural differences the ree abundances in plagioclase range approximately fortyfold which cannot be produced by fractional crystallization of a single magma combining plagioclase trace element data from apollo and meteoritic anorthosites we propose that plagioclases derived from the lmo floated to the surface to form the primordial crust which then may have been metasomatized by incompatible element rich kreep potassium rare earth element phosphorus melts and mantle derived partial melts the lunar anorthosites may represent this metasomatized crust rather than solely a derivative from the lmo furthermore silicate melts similar to the metasomatic agents may also have melted the crust to form the mg suite rocks this hypothesis is consistent with overlapping ranges of age and initial end between lunar anorthosites and mg suite rocks these events are consistent with an overturn event of the cumulate mantle very early after primordial crust formation to produce the partial melts that metasomatized the crust

uppermost mantle velocity beneath the mid atlantic ridge and transform faults in the equatorial atlantic ocean seismic rays travelling just below the moho provide insights into the thermal and compositional properties of the upper mantle and can be detected as pn phases from regional earthquakes such phases are routinely identified in the continents but in the oceans detection of pn phases is limited by a lack of long term instrument deployments we present estimates of upper mantle velocity in the equatorial atlantic ocean from pn arrivals beneath and flanking the mid atlantic ridge and across several transform faults we analyzed waveforms from 50 earthquakes with magnitude mw 3 5 recorded over 12 months in 2012 2013 by five autonomous hydrophones and a broadband seismograph located on the st peter and st paul archipelago the resulting catalog of 152 ray paths allows us to resolve spatial variations in uppermantle velocities which are consistent with estimates from nearby wide angle seismic experiments we find relatively high velocities near to the st paul transform system 8 4 km s 1 compared to lower ridge parallel velocities 7 7 km s 1 hence this method is able to resolve ridge transform scale velocity variations ray paths in lithosphere younger than 10 myr have mean velocities of 7 9 0 5 km s 1 which is slightly lower than those sampling lithosphere older than 20 myr 8 1 km 0 3 s 1 there is no apparent systematic relationship between velocity and ray azimuth which could be due to thickened lithosphere or complex mantle upwelling although uncertainties in our velocity estimates may obscure such patterns we also do not find any correlation between pn velocity and shear wave speeds from the global sl2013sv model at depths 150 km our results demonstrate that data from long term deployments of autonomous hydrophones can be used to obtain rare and insightful estimates of uppermost mantle velocities over hundreds of kilometers in otherwise inaccessible parts of the deep oceans

shear wave splitting a diagnostic tool to monitor fluid pressure in geothermal fields an experiment on the uses of shear wave splitting as an imaging tool in fracture controlled geothermal reservoirs was conducted at krafla iceland fifteen days after the beginning of the seismic recording the injection was stopped for eleven days and then restarted a sequence designed to determine whether shear wave splitting measurements can detect the transient response of the subsurface crack system to changes in fluid pressure it was observed that time delays between the fast and slow split shear waves changed significantly and promptly with the stoppage and resumption of injection large time delays occurred only during injection decreased substantially during the stoppage phase and increased again as injection restarted comparisons of these results with similar observations at the coso geothermal field in california strongly suggest that the time delay of split shear waves can be a useful proxy to monitor fluid pressure in the cracks and changes in crack density

crustal structure of the cocos ridge northeast of cocos island panama basin 1 the submarine cocos ridge in the northwestern panama basin pacific ocean is generally interpreted as the trace of the galapagos hotspot a 278 km long seismic wide angle transect was carried out across a comparatively narrow ridge segment 150 km northeast of cocos island the results indicate a huge thickened crust where crustal thickening is mainly achieved by the lower crust which makes up 75 of the crustal thickness and is tripled compared to normal oceanic lower crust the velocities are comparable to normal lower crust and suggest no differences to a gabbroic composition the moho deepens from 10 to 18 km depth below the ridge similarities to other hotspot related oceanic ridges and plateaus with massive lower crusts and velocities below 7 4 km s suggest the formation of this cocos ridge segment near or at the plate boundary

kerguelen plateau crustal structure and basin formation from seismic and gravity data we use multichannel seismic data gravity and subsidence modeling in conjunction with plate reconstructions to evaluate the crustal origin and composition of the kerguelen plateau predominantly oceanic crust of the southern and parts of the central kerguelen plateau appears to include continental fragments related to the breakup of india and antarctica these fragments may have been metamorphosed during emplacement of the main plateau the upper crust is basaltic the middle crust is intrusive mafic rock and intruded continental crust and the lower crust is a plagioclase rich metamorphic rock the labuan basin crust is predominantly oceanic with stranded kerguelen plateau fault blocks high density lower crust in the labuan basin is probably composed of serpentinized peridotites formed during slow rifting and spreading plate reconstruction models indicate opening between eastern broken ridge and southern kerguelen plateau at 90 ma heralding the formation of the labuan basin and diamantina zone crustal attenuation and slow accretion of oceanic crust continued until the australian and antarctic plates separated at ci8 time 40 ma plate reconstructions of the free air gravity field indicate that the naturaliste plateau fits against antarctica and that elan bank and india were juxtaposed until 110 ma both naturaliste plateau and elan bank are probable microcontinents a 1 km positive residual depth anomaly in the oceanic basins adjacent to the plateau along with the positive geoid anomaly centered beneath the northern kerguelen plateau imply that the lithosphere is partially dynamically supported by an upwelling hot asthenosphere of the kerguelen hot spot

along axis structure and crustal construction processes of spreading segments in iceland implications for magmatic rifts magmatic rift systems are composed of discrete spreading segments defined by morphologic structural and volcanic features that vary systematically along strike in iceland structural features mapped in the glaciated and exhumed miocene age upper crust correlate with analogous features in the seismically and volcanically active neovolcanic zone integrating information from both the active rift zones and ancient crust provides a three dimensional perspective of crustal structure and the volcanic and tectonic processes that construct crust along spreading segments crustal exposures in the skagi region of northern iceland reveal significant along strike variations in geologic structure the upper crust at exhumed magmatic centers segment centers is characterized by a variety of intrusive rocks high temperature hydrothermal alteration and geologic evidence for kilometer scale subsidence in contrast the upper crust along segment limbs which extend along strike from magmatic centers is characterized by thick sections of gently dipping lava flows cut by varying proportions of subvertical dikes this structure implies relatively minor upper crustal subsidence and lateral dike intrusion the differing modes of subsidence beneath segment centers and segment limbs require along axis mass redistribution in the underlying upper middle and lower crust during crustal construction this along axis material transport is accomplished through lateral dike intrusion in the upper crust and by along axis flow of magmatic to high temperature solid state gabbroic material in the middle and lower crust these processes inferred from outcrop evidence in skagi are consistent with processes inferred to be important during active rifting in iceland and at analogous magmatic oceanic and continental rifts

new constraints on dike injection and fault slip during the 1975 1984 krafla rift crisis ne iceland correlation of kh9 spy and spot5 satellite images airphotos digital elevation model differencing electronic distance measurement and leveling survey data is used to constrain the deformation resulting from the 1975 1984 krafla rifting crisis we find that diking typically extends to depths of 5 km while the dike tops range from 0 km in the caldera region to 3 km at the northern end of the rift extension is accommodated by diking at depth and normal faulting in the shallowest crust in the southern section of the krafla rift surface opening is 80 of the dike opening at depth over the 70 80 km length of the rift the average dike opening was 4 3 5 4 m from these estimates we calculate the total geodetic moment released over the krafla rift crisis 4 4 9 0 10 19 nm which is an order of magnitude higher than the seismic moment released over the same time period 5 8 10 18 nm the total volume of magma added to the upper crust was 1 1 2 1 10 9m 3 this study highlights how optical image correlation using inexpensive declassified spy satellite and airphotos combined with simple models of crustal deformation can provide important constraints on the deformation resulting from past earthquake and volcanic events

crustal drift in iceland summary there are indications that tertiary and post tertiary volcanism in iceland has been confined to the present main belt of active volcanism the geological structure of the tertiary lava piles in the east and west of iceland and results of geophysical studies may be explained by invoking an appreciable amount of crustal drift since the beginning of the tertiary the rocks in the extreme east and west of the island may have been carried apart by 400 km or more the crustal drift is believed to result mainly from crustal extension through the injection of dykes the structure of iceland and possibly that of other flood basalt areas is believed to be closely related to the world wide rift system

propagation and arrest of dikes under topography models applied to the 2014 bardarbunga iceland rifting event dikes along rift zones propagate laterally downslope for tens of kilometers often becoming arrested before topographic reliefs we use analogue and numerical models to test the conditions controlling the lateral propagation and arrest of dikes exploring the presence of a slope in connection with buoyancy and rigidity layering a gentle downslope assists lateral propagation when combined with an effective barrier to magma ascent e g gelatin stiffness contrasts while antibuoyancy alone may be insufficient to prevent upward propagation we also observe that experimental dikes become arrested when reaching a plain before opposite reliefs our numerical models show that below the plain the stress field induced by topography hinders further dike propagation we suggest that lateral dike propagation requires an efficient barrier rigidity to upward propagation assisting antibuoyancy and a lateral pressure gradient perpendicular to the least compressive stress axis while dike arrest may be induced by external reliefs

long period interferograms reveal 1992 1998 steady rate of deformation at krafla volcano north iceland we formed interferograms of ers sar scenes covering the area of krafla n iceland with time span values of up to six years 1992 1998 our data reveals a steady deformation rate at krafla and within its fissure swarm with values reaching 2 1 cm y in the ground to satellite direction at the volcano the area affected by deformation extends 20 km both north and south of the volcano the best fit dislocation model consists of sills to the north and south of the volcano and a magma chamber located below the volcano all of them undergoing contraction

seismic anisotropy in the crust at the mid atlantic plate boundary in south west iceland summary seismograms of microearthquakes recorded on stations of the sil network in south western iceland exhibit strong shear wave splitting and are consistent with being caused by aligned parallel cracks in the uppermost crust splitting times of 0 1 0 3 s are observed with the larger values 0 2 0 3 s occurring beneath stations in the highly heated western volcanic zone and the smaller values 0 1 s in the younger less fractured south iceland seismic zone five of the stations have a fast shear wave polarization azimuth of n30 e n40 e7 parallel to the axis of the western volcanic zone i e the mid atlantic ridge in iceland and in the direction of maximum horizontal compression defined by fault dyke and fissure strikes and microearthquake focal mechanisms station gyg in the north western part of the network has the significantly different azimuth of n70 e this is parallel to one of the local strike slip fault trends and is probably due to a heated rock fabric caused by those faults

volcanoes as elastic inclusions their effects on the propagation of dykes volcanic fissures and volcanic zones in iceland mechanically many volcanoes may be regarded as elastic inclusions either softer with a lower young s modulus or stiffer with a higher young s modulus than the host rock matrix for example many central volcanoes stratovolcanoes composite volcanoes are composed of rocks that are softer than the crustal segments that host them this is particularly clear in iceland where central volcanoes are mostly made of soft rocks such as rhyolite pyroclastics hyaloclastites and sediments whereas the host rock is primarily stiff basaltic lava flows most active central volcanoes also contain fluid magma chambers and many have collapse calderas fluid magma chambers are best modelled as cavities in three dimensions or holes in two dimensions entire calderas as holes and the ring faults themselves which commonly include soft materials such as breccias as soft inclusions many hyaloclastite basaltic breccias mountains partly buried in the basaltic lava pile also function as soft inclusions modelling volcanoes as soft inclusions or holes we present three main numerical results the first using the hole model shows the mechanical interaction between all the active central volcanoes in iceland and in particular those forming the two main clusters at the north and south end of the east volcanic zone evz the strong indication of mechanical interaction through shared dykes and faults in the northern cluster of the evz is supported by observations the second model using a soft inclusion shows that the torfajokull central volcano which contains the largest active caldera in iceland suppresses the spreading generated tensile stress in its surroundings we propose that this partly explains why the proper rift zone northeast of torfajokull has not managed to propagate through the volcano apparently torfajokull tends to slow down the rate of southwest propagation of the rift zone part of the evz the third model again using a soft inclusion indicates how the lateral propagation of a segment of the 1783 laki fissure became arrested in the slopes of the hyaloclastite mountain laki

upper crustal structure of newberry volcano from p wave tomography and finite difference waveform modeling 1 seismic tomography combined with waveform modeling constrains the dimensions and melt content of a magma body in the upper crust at newberry volcano we obtain a p wave tomographic image by combining travel time data collected in 2008 on a line of densely spaced seismometers with active source data collected in the 1980s the tomographic analysis resolves a high velocity intrusive ring complex surrounding a low velocity caldera fill zone at depths above 3 km and a broader high velocity intrusive complex surrounding a central low velocity anomaly at greater depths 3 6 km this second upper crustal low velocity anomaly is poorly resolved and resolution tests indicate that an unrealistically large low velocity body representing 60 km3of melt could be consistent with the available travel times the 2008 data exhibit low amplitude first arrivals and an anomalous secondary p wave phase originating beneath the caldera two dimensional finite difference waveform modeling through the tomographic velocity model does not reproduce these observations to reproduce these phases we predict waveforms for models that include synthetic low velocity bodies and test possible magma chamber geometries and properties three classes of models produce a transmittedp phase consistent with the travel time and amplitude of the observed secondary phase and also match the observed lower amplitude first arrivals these models represent a graded mush region a crystal suspension region and a melt sill above a thin mush region the three possible magma chamber models comprise a much narrower range of melt volumes 1 6 8 0 km3 than could be constrained by travel time tomography alone

the effect of the large scale mantle flow field on the iceland hotspot track abstract fluid dynamical simulations were carried out in order to investigate the effect of the large scale mantle flow field and the depth of the plume source on the structure of the iceland plume through time the time dependent location and shape of the plume in the earth s mantle was calculated in a global model and it was refined in the upper mantle using a 3d cartesian model box global flow was computed based on density heterogeneities derived from seismic tomography plate motion history served as a velocity boundary condition in both models hotspot tracks of the plume conduits and the plume head were calculated and compared to actual bathymetry of the north atlantic if a plume source in the lowermost mantle is assumed the calculated surface position of the plume conduit has a southward component of motion due to southward flow in the lower mantle depending on tomography model assumed plume age and buoyancy the southward component is more or less dominating plume models having a source at the 660 km discontinuity are only influenced by flow in the upper mantle and transition zone and hence rather yield westward hotspot motion many whole mantle plume models result in a v shaped track which does not match the straight greenland iceland faroe ridge models without strong southward motion such as for a plume source at 660 km depth match actual bathymetry better plume tracks were calculated from both plume conduits and plume heads a plume head of 120 k anomalous temperature gives the best match between plume head track and bathymetry

magmatic fissures and their systems in iceland a tectonomagmatic model 1 volcanic systems in iceland comprise a central volcano linked to magmatic fissures whose subsurface architecture remains enigmatic the surface dimensions and trends of active fissures show their spatial relation with fault systems structure of the fremri namur and hengill volcanic systems was analyzed the linear vent arrays marking recent fissures are tightly bound by vertical segmented faults while normal faults accommodating extension are common on the flanks of the fissure swarm evidence of normal frictional slip on the fissure bounded faults suggests that failure occurred in response to subsidence with subsequent dilation this is supported by inward tilting of strata adjacent to faults compatible with a downsag phase we propose that magmatic fissures have vertical feeders with lateral offshoots extending along the rift zone their inflation deflation during an eruptive cycle causes subsidence such magmatically generated faults can be subsequently modified by tectonic extension

magma chamber properties from integrated seismic tomography and thermal modeling at montserrat it is widely believed that andesitic magmas erupted at arc volcanoes are stored in shallow reservoirs prior to eruption but high resolution images of focused regions of magma in the shallow crust are rare we integrate seismic tomography with numerical models of magma chamber growth to constrain the magma chamber beneath soufriere hills volcano montserrat our approach reveals the characteristics and dynamics of the magmatic system with a level of detail that no single method has yet achieved the integrated analysis suggests that a magma chamber of 13 km3 with over 30 melt fraction formed between 5 5 and at least 7 5 km depth a significantly higher melt fraction than inferred from the seismic data alone the magma chamber may have formed by incremental sill intrusion over a few thousand years and is likely to be a transient geologically short lived feature these volume and geometry estimates are critical parameters to model eruption dynamics which in turn are key to hazard assessment and eruption forecasting

imaging the high temperature geothermal field at krafla using vertical seismic profiling abstract geophysical exploration and in particular active source seismic imaging of geothermal fields is important to assess and optimize the exploitation of natural heat sources for energy production and direct use the first multi offset moving source vertical seismic profiling vsp experiment over the high temperature geothermal field in krafla iceland was carried out in spring 2014 with the aim to test whether vsp is a suitable method to map volcanic stratigraphy fractures dykes steam zones and magmatic bodies at this site and for volcanic environments in general in this study we present a workflow for processing the sparse krafla vsp dataset recorded with receivers in either of two boreholes the analysis involved first arrival traveltime inversion and seismic reflection processing the seismic velocity model obtained by traveltime tomography reveals structural information between the two boreholes and can be linked to an existing geological model showing that the seismic velocities are mainly controlled by lithology the zero offset seismic reflection data were processed into two corridor stacks walk away vsp reflection data were migrated with a novel multicomponent kirchhoff migration algorithm that includes p and s wave isolation to obtain separate pp ps and ss migrated images the reflections imaged in the corridor stacks can be linked to the main lithological units known from borehole logging information migrated images from the walk away data reveal reflectors below and to the sides of the two boreholes considering a priori information such as hypocenter locations from earthquake seismology studies the reflectors can be related to changes in lithology fault zones dykes and possibly the top of the krafla magma chamber we found that vsp is potentially a useful method to image the key lithological boundaries and volcanic stratigraphy in the complex magmatic environment at krafla but a priori information proved to be essential to constrain the processing and interpretation of the sparse array dataset

the crustal structure of the cocos ridge off costa rica 1 the submarine cocos ridge in the northwestern panama basin a bathymetric feature more than 1000 km long and 250 500 km broad is about 2 km shallower than the adjacent basin it is generally interpreted as the trace of the galapagos hot spot two 127 and 260 km long seismic wide angle sections were recorded along and across this ridge offshore the osa peninsula costa rica crustal thickening is seen everywhere along the sections on the northwestern outer ridge flank increased thickness is exclusively attributed to the upper crust and expressed by 2 km thick flow basalts the quepos plateau caps the upper crust in this area toward the center of the cocos ridge the moho deepens from 11 12 to 21 km depth and crustal thickening is almost entirely attributed to the lower crust which makes up 80 of the crust and is three times the thickness of normal oceanic lower crust it is homogeneously structured and the velocities which range from 6 5 km s at the top to 7 35 km s at the base are comparable to normal lower crust under these depth conditions and suggest no differences to a gabbroic rock composition similarities to the crustal velocity structure of iceland central kerguelen plateau and broken ridge are consistent with a formation of this 13 15 ma old cocos ridge segment by excessive magmatism in a near plate boundary setting

contemporaneous phreatomagmatic and effusive activity along the hverfjall eruptive fissure north iceland eruption chronology and resulting deposits abstract the 2500 bp hverfjall eruption in northern iceland produced pyroclastic and effusive deposits of widely different characteristics along the length of the eruptive fissure the southern half of the fissure was located in a shallow lake whereas the northern part of the fissure extended onto dry land this specific setting with overlapping periods of activity at the different vents resulted in various mingling features between fine grained phreatomagmatic deposits and lava flows here we reconstruct the course of events during this eruption based on field observations and granulometric analyses of the resulting deposits the eruption can be divided into three main phases depending on the main depositional characteristics and vent locations the initial phase is dominated by phreatomagmatic fall deposits which are attributed to an overall high eruption rate in a shallow lacustrine setting the second phases involved opening of two new vents on dry ground and deposition of scoria and lava flows the third and final phase of the eruption is associated with a lowering of the eruption rate in the southernmost vent with a shift in the activity from continuous uprush and fall deposits to discrete explosions and emplacement of base surges these surges display features consistent with drying up with increasing distance from the vent suggesting that their dynamics changed during emplacement most wet surges were channelized within a preexisting graben structure close to the vent but some more dilute i e dry surges were able to flow over this obstacle and continued to flow for more than 5 km away from the vent and 100 m uphill before stopping

a comparison between airguns and explosives as wide angle seismic sources the relative merits of a 48 gun 9324 cu in 153 litre airgun array and a 200 kg explosive source are considered for the purposes of long range 0 400 km refraction seismic work with particular reference to traveltime modelling theoretical source calculations indicate that in the frequency range 2 5 12 0 hz the airgun source will produce an rms pressure 8 of that produced by the explosive source and an initial burst pressure 17 of that produced by the explosive source observed data support these calculations at short ranges and illustrate the greater attenuation of the airgun signal with range due to its lack of very low frequency 5 hz content at short offsets the airgun array provides a preferable seismic source to the explosives due to densely spaced shots and a consistent waveform resulting in excellent trace to trace coherence with increasing offsets it may be necessary to stack the airgun data to enhance its signal to noise ratio here we use a 4 fold stack large explosive shots although more powerful produce a less consistent waveform and are more widely spaced due to operational constraints the offset at which airguns provide a preferable source is dependent on the ambient noise this practical comparison of real sources demonstrates that even without advanced processing a well tuned airgun array may provide a preferable source to explosives at offsets up to 160 km under favourable experimental conditions

integration of micro gravity and geodetic data to constrain shallow system mass changes at krafla volcano n iceland new and previously published micro gravity data are combined with insar data precise levelling and gps measurements to produce a model for the processes operating at krafla volcano 20 years after its most recent eruption the data have been divided into two periods from 1990 to 1995 and from 1996 to 2003 and show that the rate of deflation at krafla is decaying exponentially the net micro gravity change at the centre of the caldera is shown using the measured free air gradient to be 85 gal for the first and 100 gal for the second period after consideration of the effects of water extraction by the geothermal power station within the caldera the net gravity decreases are 73 17 gal for the first and 65 17 gal for the second period these decreases are interpreted in terms of magma drainage following a mogi point source model we calculate the mass decrease to be 2 1010 kg year reflecting a drainage rate of 0 23 m3 s similar to the 0 13 m3 s drainage rate previously found at askja volcano n iceland based on the evidence for deeper magma reservoirs and the similarity between the two volcanic systems we suggest a pressure link between askja and krafla at deeper levels at the lower crust or the crust mantle boundary after the krafla fires co rifting pressure decrease of a deep source at krafla stimulated the subsequent inflow of magma eventually affecting conditions along the plate boundary in n iceland as far away as askja we anticipate that the pressure of the deeper reservoir at krafla will reach a critical value and eventually magma will rise from there to the shallow magma chamber possibly initiating a new rifting episode we have demonstrated that by examining micro gravity and geodetic data our knowledge of active volcanic systems can be significantly improved

small scale crustal variability within an intraplate structure the crozet bank southern indian ocean summary the crozet bank the easternmost region of the crozet plateau austral indian ocean is capped by two groups of islands which form the crozet archipelago terres australes and antarctiques francaises a n s trending 2 km deep basin the indivat basin extends between the two groups of islands and bisects the crozet bank into two separate domains the interpretation of the keobs8 seismic refraction profile shot during the keobs md66 cruise january february 1991 over the eastern crozet plateau was carried out by ray tracing and the computation of synthetic seismograms this interpretation leads to a rather complex seismic structure and outlines a pro nounced eastward crustal thinning from 16 5 to 10 km at the expense of layer 2 the thinning of the crust is abrupt east of the indivat basin unlike below the hawaiian islands and the marquesas islands no underplated mantle material underlies the crust of the crozet bank moreover this deep seismic sounding has further revealed that a high velocity feature outcropping the seabed 30 km east of ile aux cochons could be a major structural feature deeply rooted within the lower crust the occurrence of this feature a submarine volcano is associated with a mantle dyke causing a steep shallowing of the lower crustal interfaces gravity modelling was performed along line keobs8 with a density structure deduced from the seismic section to model free air anomalies derived from altimetry data this modelling confirms that the indivat basin underlined by a gravity low running roughly n s between the two groups of islands is a major structural boundary as the model generates medium wavelength anomalies of adequate amplitude it also confirms that the volcano located west of the indivat basin is a deeply rooted feature the crozet bank clearly appears as a plume avected structure which may have originated from a deep thermal anomaly within the lithosphere more recent volcanic episodes related to a still active plume activity under the crozet bank could have uplifted upper mantle material and caused the emplacement of the newly discovered feature and of the western group of islands

precise hypocentre relocation of microearthquakes in a high temperature geothermal field the torfajokull central volcano iceland the torfaj okull volcanic system is one of approximately 30 active volcanoes comprising the neovolcanic zones of iceland the central volcano of the system is the largest silicic centre in iceland with a caldera of approximately 12 km diameter its high temperature geothermal system is one of the most powerful in iceland torfaj okull is a source of persistent seismicity where both high and low frequency earthquakes occur to study this microseismicity in detail a temporary array of 20 broad band seismic stations was deployed between 2002 june and november these temporary stations were embedded in the permanent south iceland lowland sil network and data from nine adjacent sil stationswere included in this study aminimum one dimensional 1 d velocity model with station corrections was computed for earthquake relocation by inverting manually picked p and s wave arrival times from events occurring in the torfaj okull volcanic centre and its surroundings high frequency earthquakes from the torfaj okull volcanic centre were then relocated calculating a non linear probabilistic solution to the earthquake location problem subsequently we correlated the waveforms of these 121 events 2000 observations to define linked events calculated the relative traveltime difference between event pairs and solved for the hypocentral separation between these events the resulting high resolution pattern shows a tighter clustering in epicentre and focal depth when compared with original locations earthquakes are mainly located beneath the caldera with hypocentres between 1 and 6 km depth and lie almost exclusively within the geothermal system a sharp cut off in seismicity at 3 km suggests either that there is a marked temperature increase or that this is a structural boundary no seismic activity was observed in the fissure swarms to the northeast ne and southwest sw of the volcanic centre

mantle thermal structure and active upwelling during continental breakup in the north atlantic seismic reflection and refraction data acquired on four transects spanning the southeast greenland rifted margin and greenland iceland ridge gir provide new constraints on mantle thermal structure and melting processes during continental breakup in the north atlantic maximum igneous crustal thickness varies along the margin from s 30 km in the near hotspot zone 6 500 km from the hotspot track to v18 km in the distal zone 500 1100 km magmatic productivity on summed conjugate margins of the north atlantic decreases through time from 1800 300 to 600 50 km 3 km ma in the near hotspot zone and from 700 200 to 300 50 km 3 km ma in the distal zone comparison of our data with the british faeroe margins shows that both symmetric and asymmetric conjugate volcanic rifted margins exist joint consideration of crustal thickness and mean crustal seismic velocity suggests that along margin changes in magmatism are principally controlled by variations in active upwelling rather than mantle temperature the thermal anomaly vt at breakup was modest v100 125 c varied little along the margin and transient data along the gir indicate that the potential temperature anomaly 125 50 c and upwelling ratio v4 times passive of the iceland hotspot have remained roughly constant since 56 ma our results are consistent with a plume impact model in which 1 a plume of radius v300 km and vt of v125 c impacted the margin around 61 ma and delivered warm material to distal portions of the margin 2 at breakup 56 ma the lower half of the plume head continued to feed actively upwelling mantle into the proximal portion of the margin and 3 by 45 ma both the remaining plume head and the distal warm layer were exhausted with excess magmatism thereafter largely confined to a narrow 6 200 km radius zone immediately above the iceland plume stem alternatively the warm upper mantle layer that fed excess magmatism in the distal portion of the margin may have been a pre existing thermal anomaly unrelated to the plume fl 2001 elsevier science b v all rights reserved

multiple volcano deformation sources in a post rifting period 1989 2005 behaviour of krafla iceland constrained by levelling tilt and gps observations abstract the krafla rifting episode which occurred in north iceland in 1975 1984 was followed by inflation of a shallow magma chamber until 1989 at that time gradual subsidence began above the magma chamber and has continued to the present at a declining rate pressure decrease in a shallow magma chamber is not the only source of deformation at krafla as other deformation processes are driven by exploitation of two geothermal fields together with plate spreading in addition deep seated magma accumulation appears to take place with its centre 10 km north of the krafla caldera the relative strength of these sources has varied with time new results from a levelling survey and gps measurements in 2005 allow an updated view on the deformation field deformation rates spanning 2000 2005 are the lowest recorded in the 30 year history of geodetic studies at the volcano the inferred rate of 2000 2005 subsidence related to processes in the shallow magma chamber is less than 0 3 cm yr whereas it was 5 cm yr in 1989 1992 currently the highest rate of subsidence takes place in the leirbotnar area within the krafla caldera and appears to be a result of geothermal exploitation

seismic imaging in the krafla high temperature geothermal field ne iceland using zero and far offset vertical seismic profiling vsp data abstract among geothermal exploration methods active surface seismic methods have played only a minor role to date especially in high temperature volcanic systems reflection seismic data often reveal poor delineation of volcanic features due to the internal heterogeneity of volcanic sequences to enhance the vertical resolution one possibility is the application of downhole seismic methods like vertical seismic profiling vsp a test experiment was carried out in the krafla high temperature geothermal field ne iceland to assess the ability of vsp to image subsurface structures such as fractures zones of high permeability magmatic bodies and zones of supercritical fluids and steam logging in such hostile environments is technical challenging in many aspects but mainly due to the high temperature impact on the downhole electronic components of the measuring equipment this requires a thorough pre examination and implementation of the measurement especially to avoid delays and tool failures this paper presents results of zero and far offset vsp data from the k 18 borehole from within the krafla caldera which reveal good correlation with the surrounding lithology the raw three component seismic data display a good signal to noise ratio and dominant signal frequencies between 20 and 40 hz down to c 2200 m depth for air gun and explosive sources respectively a zero offset source comparison was also conducted to assess the use of different impulsive sources for future vsp surveys in similar settings by applying a standard vsp processing we identified stratigraphic boundaries between lavas hyaloclastites and intrusions which are in good agreement with existing well data for the zero offset vsp both p and s wave velocity models were calculated and a depth converted corridor stack was determined in addition multicomponent kirchhoff depth migration and fresnel volume migration were tested around the borehole the 3d results are promising but the specific shape and lateral extent of the reflectors could not be determined due to the restriction to only two sources and the insufficient spatial coverage aperture our study demonstrates that vertical seismic profiles can clearly detect variations in the subsurface volcanic stratigraphy in high temperature geothermal fields a more detailed reservoir characterization can be achieved by further data integration enhanced survey design including more source positions and improved processing and imaging techniques such as full waveform inversion

unravelling the magma feeding system of a young basaltic oceanic volcano abstract a multidisciplinary approach combining petrological geochemical and fluid inclusion studies with seismic monitoring data was used to build a model of the magma feeding system of pico volcano azores islands north atlantic ocean we explore how magma has ascended to the surface in the last 10 ka and how this ascent is associated with the selective activation of the three tectonic systems intersecting the volcano the deepest and most important ponding level for all ascending magmas is located at 17 3 17 7 km and corresponds to the moho transition zone mtz which marks the transition from mantle rocks to ultramafic cumulates at shallower depth ascending magmas carry 30 vol of clinopyroxene and olivine each magma ascent followed a distinct path and ponded often for a limited period ponding levels common to all feeding systems are present at 16 3 16 7 km 12 1 14 5 km 9 4 9 8 km and 7 7 8 1 km these depths mark important discontinuities where magmas formed stacked sills and evolved through fractional crystallisation dense and un decrepitated fluid inclusions show rapid ascent from the mtz along the lomba do fogo sao joao fault n150 system and along the n120 regional transtensive system despite multiple intrusions magma ponding at 5 6 6 8 km occurs where the n150 and n60 tectonic systems intersect each other here magma evolves towards plagioclase rich and is only erupted at the summit crater and subterminal vents this region is the source of the frequent microseismicity recorded at 4 to 7 km beneath the southern flank of pico volcano which might be associated with the early stages of formation of a more complex magma reservoir the local and regional tectonics are of paramount importance in the activation of the different magma feeding systems over time this new information is fundamental to improve the knowledge on the future eruptive behaviour of pico volcano and can have significant implications on the mitigation of volcanic risk this multidisciplinary approach can be applied not only to other volcanoes of the azores but also to poorly monitored oceanic volcanoes where magma ascent strongly depends on the activation of tectonic systems