structural analysis of a transform fault rift zone junction in north iceland abstract on the north coast of iceland the rift zone in north iceland is shifted about 120 km to the west where it meets with and joins the mid ocean kolbeinsey ridge this shift occurs along the tjornes fracture zone an 80 km wide zone of high seismicity which is an oblique non perpendicular transform fault there are two main seismic lineaments within the tjornes fracture zone one of which continues on land as a 25 km long wnw trending strike slip fault this fault referred to as the husavik fault meets with and joins north trending normal faults of the theistareykir fissure swarm in the axial rift zone the most clear cut of these junctions occurs in a basaltic pahoehoe lava flow of holocene age where the husavik fault joins a large normal fault called gudfinnugja at this junction the husavik fault strikes n55 w whereas gudfinnugja strikes n5 e so that they meet at an angle of 60 the direction of the spreading vector in north iceland is about n73 w which is neither parallel with the strike of the husavik fault nor perpendicular to the strike of the gudfinnugja fault during rifting episodes there is thus a slight opening on the husavik fault as well as a considerable dextral strike slip movement along the gudfinnugja fault consequently in the holocene lava flow there are tension fractures collapse structures and pressure ridges along the husavik fault and pressure ridges and dextral pull apart structures subparallel with the gudfinnugja fault the 60 angle between the husavik strike slip fault and the gudfinnugja normal fault is the same as the angle between the tjornes fracture zone transform fault and the adjacent axial rift zones of north iceland and the kolbeinsey ridge the junction between the faults of husavik and gudfinnugja may thus be viewed as a smaller scale analogy to the junction between this transform fault and the nearby ridge segments using the results of photoelastic and finite element studies a model is provided for the tectonic development of these junctions the model is based on an analogy between two offset cuts mode i fractures loaded in tension and segments of the axial rift zones or parts thereof in the case of the husavik fault the results indicate that the tjornes fracture zone in general and the husavik fault in particular developed along zones of maximum shear stress furthermore the model suggests that as the ridge segments propagate towards a zero underlapping configuration the angle between them and the associated major strike slip faults gradually increases this conclusion is supported by the trends of the main seismic lineaments of the tjornes fracture zone

dike fault interaction during the 2004 dallol intrusion at the northern edge of the erta ale ridge afar ethiopia received 17 july 2012 revised 29 august 2012 accepted 4 september 2012 published 12 october 2012 1 during continental rifting the interaction between faulting and magmatic intrusions is not well understood using insar and seismicity we show that a 0 06 km 3 dike was intruded along the dallol segment ethiopia and was accompanied by a mw 5 5 earthquake and associated fault slip along the western flank of the rift the intrusion was fed by a previously unidentified magma chamber under dallol the total seismic moment release was 2 3 10 17 nm 10 of the geodetic moment this is a higher proportion than during the 2005 2009 dabbahu rifting episode which ranged between 1 4 of the geodetic moment a larger component of faulting occurs at dallol than at dabbahu segment a feature we interpret to be related to the proximity 10 km of the dallol segment to the rift margin where welldeveloped faults facilitate slip citation nobile a c pagli d keir t j wright a ayele j ruch and v acocella 2012 dike fault interaction during the 2004 dallol intrusion at the northern edge of the erta ale ridge afar ethiopia geophys res lett 39 l19305 doi 10 1029 2012gl053152

glacial rebound and plate spreading results from the first countrywide gps observations in iceland iceland is one of the few places on earth where a divergent plate boundary can be observed on land direct observations of crustal deformation for the whole country are available for the first t

effective tension shear relationships in extensional fissure swarms axial rift zone of northeastern iceland abstract the geometry of fracture systems in selected areas of the active krafla fissure swarm mid atlantic ridge northeastern iceland is analysed based on geodetic analysis of the present day topography at the top of holocene basaltic lava flows which fill the axial rift zone the deformation of this initially horizontal surface can be reconstructed extensional deformation is localised at all scales and block tilting though present remains minor using simple models of the surface expression of normal faults the geometrical characteristics of the topographic features related to active deformation during tectonic volcanic events are quantitatively analysed at crustal depths of about 1 km normal faults are present and have an average 70 dip comparison with the dip data of older normal faults observed in the uplifted and eroded shoulders of the rift zone at palaeodepths of 1 2 km indicates that this dip determination is valid comparisons between the local case study and structural analyses of active fissure swarms on a larger scale suggest that normal faulting plays a major role in the middle section of the thin newly formed brittle crust of the rift zone in the axial oceanic rift zone of ne iceland the extensional deformation in the upper crust is dominated by horizontal tension and shear of normal sense their relative importance depending on depth absolute tension dominates in the uppermost several hundred metres of the crust resulting in the development of fissure swarms effective tension plays an important role at a deeper level 2 5 km because of the presence of magmatic fluid pressure from magma chambers which feed dyke injections at crustal depths of about 1 km normal shear prevails along fault planes which dip 60 75 this importance of normal shear at moderate depth between upper and lower crustal levels where tension prevails is pointed out within the extensional context of rifting these variations of tectonic behaviour with depth are controlled by both the lithostatic pressure and the effective tension induced by the presence of magmatic fluid pressure

propagation of rifting along the arabia somalia plate boundary into afar it is generally accepted that the aden ridge has propagated westward from 58 e to the western tip of the gulf of aden tadjoura at the edge of afar here we use new tectonic and geochronological data to examine the geometry and kinematics of deformation related to the penetration of that ridge on dry land in the republic of djibouti we show that it veers northward forming a narrow zone of dense faulting along the northeastern edge of the afar depression the zone includes two volcanic rifts asal ghoubbet and manda inakir connected to one another and to the submarine part of the ridge by transfer zones both rifts are composite divided into two or three disconnected parallel nw se striking subrifts all of which appear to have propagated northwestward in asal ghoubbet as in manda inakir the subrifts appear to have formed in succession through north directed jumps from subrifts more farther south at present the northernmost subrifts manda and dirko koma of the manda inakir rift form the current tip of the northward propagating arabia somalia plate boundary in afar we account for most observations by a mechanical model similar to that previously inferred for the gulf of aden in which propagation is governed by the intensity and direction of the minimum horizontal principal stress 3 we interpret the northward propagation on land almost orthogonal to that in the gulf to be related to necking of the central afar lithosphere where it is thinnest such necking may be a consequence of differential magmatic thickening greater in the center of the afar depression where the ethiopian hot spot enhanced profuse basaltic effusion and underplating than along the edges of the depression the model explains why the aden ridge foregoes its wsw propagation direction constant from 58 e to asal ghoubbet at a smaller scale individual rifts and subrifts keep opening perpendicular to the arabia somalia or danakil somalia motion vector and propagate northwestward concurrently such lithospheric cracks are forced to jump northward such that the plate boundary remains inside the regional n s necking zone changes of obliquity between the directions of overall and local propagation may account for different segmentation patterns a small angle promoting long en echelon subrifts and a high angle smaller nested subrifts within subrifts the propagation mechanism is thus similar whether in oceanic or continental lithosphere the principal change being the overall propagation path here governed by thickness changes rather than by the geometry in map view as previously inferred for the rest of the aden ridge finally because the same mechanism has led rifting along the red sea to propagate southward and jump to the western edge of afar the arabia somalia and arabia nubia plate boundaries tips have missed each other and keep overlapping further leading to strain transfer by large scale bookshelf faulting

seismicity of the galapagos 95 5 w propagating rift an array of ocean bottom seismometers was deployed for 21 days about the 95 5 w galapagos propagating rift tip to obtain seismic evidence for the propagating rift hypothesis and to investigate the dynamic effects of rift propagation seismicity was fairly constant 10 17 events per day with no indication of swarm activity hypocenters were determined for 304 earthquakes the largest of which is estimated to be mb 2 3 with a seismic moment of 2 9 1020 dyn cm the cumulative seismic moment released by all local earthquakes is estimated to be 6 6 1020 dyn cm a b value of 0 77 0 08 was estimated for the region implying a stress regime dominated by a broad tectonic stress field the distribution of earthquakes is consistent with the propagating rift hypothesis most earthquakes occurred south of the propagating rift within the de steiguer deep seismicity within the transform zone is clustered in such a way as to suggest that two or three discrete fault segments may be active at the same time the seismicity observed along the propagating rift is diffuse earthquakes were observed at the propagating rift tip but not in front of it almost all earthquakes occur south of the northern pseudofault and its extension west of the rift tip that is earthquakes occur almost exclusively in lithosphere that has been or is being overtaken by the propagating rift six composite focal mechanisms are consistent with the propagating rift hypothesis first motions from earthquakes located on the propagating rift indicate extension whereas motions associated with the failing rift area indicate compression a compressional regime is also indicated west of the transform zone twelve earthquakes from the transform zone produce a poorly constrained focal mechanism consistent with right lateral strike slip motion along a fault plane that is roughly parallel to the isochrons of the transferred lithosphere

migration of mid ocean ridge volcanic segments the propagation of small offset volcanic spreading centre segments along mid ocean ridge crests may reflect absolute motion of the plate boundary relative to the underlying mesospheric frame such a relationship could be caused by a purely vertical flow of the mantle under spreading centres and would have value in constraining past plate motions from non transform trends generated during along ridge propagation and in linking the major element variability of oceanic crust and upper mantle to the bulk composition and temperatures of mantle ascending under mid ocean ridges

plate boundary deformation in north iceland during 1992 2009 revealed by insar time series analysis and gps abstract in north iceland extensional plate motion is accommodated by the northern volcanic zone a set of en echelon volcanic systems and the tjornes fracture zone a transform offset in the mid atlantic ridge consisting of two parallel transform lineaments the southern lineament the husavik flatey fault is a 100 km long right lateral strike slip fault that has not ruptured for more than 140 years and poses a significant seismic hazard to husavik a fishing town located by the fault and to other coastal communities we present results of insar time series analysis data spanning almost two decades 1992 2009 that show extensional and interseismic deformation within the northern volcanic zone and the on shore part of the tjornes fracture zone the results also exhibit transient inflation at theistareykir volcano deflation at krafla central volcano and a broad uplift north of krafla the current plate extension is not uniform across the northern volcanic zone but concentrated at the western fissures of the theistareykir volcanic system and the outermost fissures of the krafla fissure swarm we combine a back slip plate boundary model with a set of point pressure sources representing volcanic changes to describe the current extensional plate boundary deformation and update the previous estimations of the locking depth and slip rate of the husavik flatey fault that were based on gps data alone using different combinations of input data we find that the husavik flatey fault has a locking depth of 6 10 km and with a slip rate of 6 9 mm yr is accommodating about a third of the full transform motion we furthermore show that while the insar data provide important constraints on the volcanic deformation within the nvz they do not significantly improve the model parameter estimation for the hff as the dense gps network appears to better capture the deformation across the fault

experiments of dike induced deformation insights on the long term evolution of divergent plate boundaries the shallow transport of magma occurs through dikes causing surface deformation our understanding of the effects of diking at the surface is limited especially on the long term for repeated intrusive episodes we use analogue models to study the upper crustal deformation induced by dikes we insert metal plates within cohesive sand with three setups in setup a the intrusion rises upward with constant thickness and in setups b and c the intrusion thickens at a fixed depth with final rectangular setup b or triangular setup c shape in section setup a creates a doming delimited by reverse faults with secondary apical graben without close correspondence in nature in setups b and c a depression flanked by two uplifted areas is bordered by inward dipping normal faults propagating downward and for deeper intrusions in setup b also by inner faults reverse at the surface this deformation is similar to what is observed in nature suggesting a consistent physical behavior dikes in nature initially propagate developing a mode i fracture at the tip subsequently thickened by magma intrusion without any host rock translation in the propagation direction as in setup a the deformation pattern in setups b and c depends on the intrusion depth and thickness consistently to what is observed along divergent plate boundaries the early deformation in setups b and c is similar to that from a single rifting episode i e lakagigar iceland and dabbahu afar whereas the late stages resemble the structure of mature rifts i e krafla iceland confirming diking as a major process in shaping divergent plate boundaries

insar observations of 2007 tanzania rifting episode reveal mixed fault and dyke extension in an immature continental rift summary in the early stages of continental rifting extension takes place by normal faulting while in mature continental rifts dyke intrusion dominates little is known about the nature of the transition between fault controlled and dyke controlled extension or about the processes in an intermediate setting here we present observations of the temporal and spatial evolution of surface displacements during the 2007 july 14 august 4 rifting episode in northern tanzania an immature section of the east african rift the ground deformation initiated with subsidence that can be attributed to 40 cm of normal motion on a ne striking fault following july 17 deformation was dominated by the intrusion of 7 km long dyke dyke opening increased gradually to a total of 2 4 m from july 21 the collapse of a shallow graben above the fault dominated the near field displacements comparison to the 2007 dabbahu dyke afar which occurred in a more mature rift shows an order of magnitude scale difference in dyke length using numerical models of dyke propagation we attribute this to the size and depth of the magma chamber in immature rifts the thick crust and slow spreading rate favour small deep magma chambers forming short buried dykes whereas in mature rifts the thinner crust and faster spreading rate favour large shallow magma chambers and long erupting dykes observing the pattern of active processes in the east african rift is key to understanding the development of rift systems and passive margins elsewhere

strain localisation and weakening of the lithosphere during extension we explore the sensitivity of extensional systems to the thermal structure of the lithosphere using numerical simulations that fully couple the energy momentum and continuity equations the rheology of the lithosphere is controlled by weakening processes such as shear heating that localises strain into shear zones and faults numerical models show that during extension of an initially unpatterned lithosphere structures develop spontaneously out of basic thermodynamic energy fluxes and without the imposition of ad hoc rules on strain localisation this contrasts with the classical mohr coulomb theory for brittle localisation which prescribes the angles of faults by a mathematical rule our results show that the mode of extension is sensitive to subtle changes in rheology heat flux and geometry of the system this sensitivity lies at the core of the variety and complexity observed in extensional systems localisation processes make the lithosphere weaker than previously estimated from the brace goetze quasi static approach consequently typical estimates for plate tectonic forces are capable of splitting the lithosphere under extension even without the role of active magmatism

the development of divergent margins insights from the north volcanic zone iceland abstract iceland is a natural laboratory where plate separation and mid ocean ridge formation can be studied directly in the field in this setting it is not fully understood how magma interacts with faulting and fissuring and how rift zones propagate in order to improve the understanding of how these processes operate we conducted a detailed field study about the kinematics and propagation of 33 holocene faults along the n s theistareykir rift north volcanic zone and mapped all tension fractures this rift hosts the holocene theistareykir central volcano for which ground deformation data insar and gps indicate an inflating shallow magma chamber throughout 2006 2008 analyses of the cumulative fault slip distribution at 696 sites show two opposite directions of fault rift propagation the first more developed is directed northwards and affects the area located north of theistareykir volcano whereas south of the volcano the rift propagates southwards tension fractures increase in frequency with respect to faults outwards from the volcano along a n s to nne ssw direction the presence of aligned vents dykes and topographic bulging along some of the n s structures and the active magma chamber below theistareykir volcano suggest that faults and tension fractures propagate following repeated dyke intrusions from the magma chamber outward along the plate margin the fact that the rift is more developed north of the volcano than south of it is interpreted as the effect of buttressing from another coterminous magma chamber sitting below a neighbouring central volcano other causes for the general observed pattern such as tectonic stresses mechanical interaction of faults and changes in the rheological characteristics of rocks are discussed as well

geometry of propagating continental rifts reconstruction of past plate configurations through palinspastic restoration of continental margins1 4 requires a detailed knowledge of the geometries of horizontal continental extension extension is often restricted to discrete linear zones termed rifts5 6 and rift models that invoke propagating vertical dykes and cracks7 10 are useful for assessing the relative significance and timing of uplift subsidence and extension in the tectonic evolution of rift basins however many models do not adequately account for the observed asymmetry of rifts i describe here the general three dimensional character of young and aborted continental rifts which can be used to derive a structural model for the propagation of rifts in continental lithosphere the rifts become asymmetric as a consequence of the role played by low angle normal faults in the overall rift geometry

deformation in the northern volcanic zone of iceland 2008 2014 an interplay of tectonic magmatic and glacial isostatic deformation gps measurements spanning 2008 to 2014 are used to derive the surface velocity field across the northern volcanic zone nvz of iceland a subaerial part of the divergent boundary between the north american and eurasian plates no volcanic activity nor magmatic intrusions were detected in the zone during this time period we infer an extensional rate of 17 4 0 3 0 2 mm yr in direction 292 0 0 6 0 5 consistent with the results of previous studies and current plate motion models including morvel2010 and geodvel2010 the horizontal velocity field reveals about 50 km wide stretching zone caused by the divergent plate movements glacial isostatic adjustment gia induces uplift of over 20 mm yr at the northern edge of vatnajokull ice cap and 3 4 mm yr horizontal motion directed away from the ice cap deformation in the nvz between 2008 and 2014 can be reproduced by a combination of models relating to several different processes i mogi sources for volcanic and geothermal deformation at the askja and krafla volcanoes ii scaled version of a velocity field derived from a glacial isostatic model and iii simple arctangent based model for secular plate spreading we find the approximate location of the plate boundary spreading axis as well as its locking depth the spreading axis lies through the krafla fremrinamar and askja central volcanoes the most active ones in the nvz it does not appear to follow the general direction of each fissure swarm but rather to change direction at the central volcanoes the locking depth is on average within the 7 9 km range

deformation partitioning inside a fissure swarm of the northern icelandic rift abstract extension in an oceanic rift domain is accommodated by fissuring and faulting processes the fissuring including dike injection involves extension and an increase in crustal volume consistent with magma supply as in oceanic ridge and hot spot contexts the faulting mainly involves thinning and extension the relationship between these two deformation modes is analysed in the northern rift of iceland in the active rift zone deformation and volcanism occur within 2 3 km wide fissure swarms separated by 10 km wide zones where deformation is minor based on topographic and geological mapping the local structure in a major fissure swarm was analysed the fracture density increases near the faults but also beyond their tips the geometrical analysis of structures revealed that for the last 10 000 years block faulting and tilting accommodated about one half of the extension the other half resulting from fissuring this distribution shows that even in an active volcanic zone with widespread magmatism the stretching resulting from normal shear can play an important role as estimated from the ages of eroded surfaces and lava flows the deformation rates range between 1 5 and 15 cm year these values are compared with other rates estimated for different time intervals in the same area

history of rift propagation and magnetization intensity for the cocos nazca sspreading center analysis of magnetic anomaly profiles collected nearly parallel to tectonic flow lines allows detailed interpretation of the complicated tectonic history of the cocos nazca spreading center forward models of the magnetic anomalies accounting for spreading rate variations ridge jumps asymmetric spreading magnetization intensity variations and bathymetry show excellent agreement with observed anomalies spreading rates can be constrained to a common finite rotation history through anomaly 4a with three changes in rates rate changes at about 1 5 ma and 4 1 ma correspond to changes in rate gradients and occur during the well calibrated part of the reversal timescale so they can unquestionably be identified as true changes in plate motion a 15 rate decrease at about 5 2 ma could be interpreted either as a change in plate motion or as an artifact of poor calibration of the older part of the timescale the change at 4 1 ma is especially important because many timescales are based on the assumption of constant spreading rate for this plate pair for 0 6 ma rift propagation has played a dominant role in the continuous reorganization of the geometry of the ridge axis propagation has been predominantly away from the hotspot with jumps predominantly south ward propagation rates have ranged from 30 to 120 mm yr commonly near 70 mm yr origin of most propagation sequences is difficult to interpret but many appear to involve discrete southward ridge jumps forming a new segment near the hotspot magnetic anomaly amplitude appears to be a reliable tracer of fe content of lavas several generalizations can be drawn about along axis variations in magnetization intensities since 8 ma high magnetizations are only observed at the far ends relative to the galapagos hotspot of segments at least 150 km long offset at the end of a high magnetization segment is at least 15 km and there are no offsets larger than 30 45 km between high magnetization segments and the reconstructed position of the hotspot we interpret these patterns to indicate that fractionated lavas erupt where gradients in magma supply cause along axis flow of evolved magma the gradients in supply result from subaxial flow of hotspot derived asthenosphere in a narrow conduit this flow is only partly obstructed by an offset of 20 30 km but entirely blocked by an offset of 50 km

analogue modelling of orthogonal and oblique rifting abstract the three dimensional progressive development of orthogonal and oblique rift systems has been simulated using scaled analogue sandbox models the orientation of the zone of rifting where angle between the rift axis and the extension direction was varied systematically from 90 orthogonal rifting to 75 60 and 45 oblique rifting completed models were impregnated and sectioned both vertically and horizontally orthogonal rift models are characterized by long straight rift border faults and intra rift faults perpendicular to the extension direction oblique rift models are characterized by shorter segmented rift border faults and intrarift faults in the oblique models the rift border faults formed en echelon arrays parallel to the inderlying zone of basement stretching whereas the intra rift faults formed at a high angle to the extension vector increased extension in the moderately oblique and oblique rift systems 60 and 45 caused the intra rift faults to rotate towards parallelism with the rift border faults no strike slip or oblique slip transfer faults were found in any experiments rift border faults and intra rift faults in the models are segmented along strike with relay ramp structures formed between overlapping fault tips along the strike of the rift variations in half graben polarities and offsets of depocentres are accomplished by accommodation zones formed by interlocking conjugate fault arrays the experimental fault patterns compare well with the fault architectures found in those modern or relatively young rift systems where well defined basement controlled strike slip or oblique slip transfer faults are absent an accommodation zone model consisting of interlocking conjugate extension faults is proposed for the along strike switching of half graben asymmetries and offsetting of depocentres in rift systems the fault geometries in the analogue models can be used as templates for recognition of fault styles in both orthogonal and in oblique rift environments

interaction and linkage of extension fractures and normal faults examples from the rift zone of iceland abstract field and photogeological studies were made of 90 zones of interacting fracture segments along the rift zone of iceland each zone consists of a pair of extension fractures or a pair of normal faults with lengths from metres to kilometres these zones evolve from an underlapping stage through an overlapping stage the most common configuration and finally to a linkage stage of all the zones only 7 are underlapping whereas 93 are overlapping with hook shaped fracture pairs the length width ratios of the overlapping zones have a mean value of 3 5 the preferred geometry of the overlapping zones depends upon the initial configuration of the interacting fractures length overstep and the development of the interaction in the overlapping zones most fracture pairs show moderate shear strike slip components related to local variations in the extension opening directions vertical displacements on normal faults decrease as the overstep and length of overlapping zones increase both in turn are proportional to the total lengths of the faults forming the pair the geometrical and kinematic features of overlapping spreading centres at mid ocean ridges show close similarities to those reported here these similarities indicate that the architecture and evolution of overlapping zones are scale independent

linking rift propagation barriers to excess magmatism at volcanic rifted margins break up related extrusive magmatism imaged in reflection seismic data as seaward dipping reflectors sdrs extends symmetrically along the volcanic margins of the atlantic ocean recent research found distinct along margin variations in the distribution of sdrs and abundance of volcanic material was found to be spatially linked to transfer fault systems these segmented the propagating rift that later developed into the ocean and are interpreted as rift propagation barriers based on these observations we develop a numerical model which shows that rift parallel mantle flow and locally enhanced rates of volcanism are the result of delays in rift propagation and segmented opening our model suggests that segmentation is one of the major factors in the distribution and localization of riftrelated extrusive magmatism we conclude that in addition to mantle temperature and inherited crustal structures e g weaknesses from previous rift episodes rift propagation delay plays an important role in the distribution of extrusive volcanism at volcanic passive margins by controlling the mantle flow beneath the rift axis

magma influence on propagation of normal faults evidence from cumulative slip profiles along dabbahu manda hararo rift segment afar ethiopia abstract measuring displacement length profiles along normal faults provides crucial information on fault growth processes here based on satellite imagery and topography we analyze 357 normal faults distributed along the active rift of dabbahu manda hararo dmh afar which offers a unique opportunity to investigate the influence of magmatism on fault growth processes our measurements reveal a large variety of slip profiles that are not consistent with elastic deformation their analysis contributes towards a better understanding of the lateral propagation of faults especially when nucleation points and existence of barriers are included using the fault growth model of manighetti et al 2001 we determine the preferred direction of lateral propagation for each fault our results suggest that lateral propagation of faults is easier away from areas where magma has been stored for long time at crustal depth and has thus modified the thermo mechanical properties of the host rock however these areas correspond also to areas where the initiation of fault growth appears as easiest along the rift in combining these results with the analysis of rift width and the position of magma reservoirs along dmh rift we show that fault growth keeps track of the magma presence and or movement in the crust

mechanical models for dikes a third school of thought abstract geological and geophysical data from continental volcanic centers and giant radial swarms and from oceanic shield volcanoes and rift zones indicate that dikes propagate laterally for distances that can be 10 to over 100 times their height what traps dikes within the shallow lithosphere and promotes these highly eccentric shapes gravity induced stress gradients in the surrounding rock and pressure gradients in the magma are the primary loading mechanisms pressure gradients due to magma flow are secondary to insignificant because the flow direction is dominantly horizontal this configuration of vertical blade shaped dikes with horizontal dike propagation and magma flow is fundamentally different from the two dike model configurations described in a recent review paper as two schools of thought for mechanical models of dikes in school i a dike is disconnected from its source and ascends under the influence of buoyancy in school ii a dike is connected to a magma reservoir and is driven upward by magma flux from the source we review the geological and geophysical data supporting the vertical dike horizontal flow propagation configuration and suggest the abundance and veracity of these data in many different geological settings and the modeling results that address this physical process warrant adding this as a third school of thought a new analytical solution for the boundary value problem of a homogeneous isotropic and linear elastic solid with a vertical fluid filled crack is used to investigate the effects of gravitationally induced stress and pressure gradients on the aperture distribution dike tip stress intensity and stable height model results indicate that in a homogeneous crust dikes can achieve stable heights greater than a kilometer only if the host rock fracture toughness k ic 100 mpa m 1 2 however density stratification of the crust is an effective mechanism for trapping kilometer scale dikes even if the host rock is very weak k ic 0 this analysis may explain why vertical dikes propagate laterally for great distances but reside within a narrow range of depths in the crust

dem based morphometry of range front escarpments in attica central greece and its relation to fault slip rates in this paper we apply current geological knowledge on faulting processes to digital processing of digital elevation models dem in order to pinpoint locations of active faults the analysis is based on semiautomatic interpretation of 20 and 60 m dem and their products slope shaded relief in northern eastern attica five normal fault segments were recognized on the 20 m dem all faults strike wnw ese the faults are from west to east thriassion thfs fili fifs afidnai affs avlon avfs and pendeli pefs and range in length from 10 to 20 km all of them show geomorphic evidence for recent activity such as prominent range front escarpments v shaped valleys triangular facets and tilted footwall areas however escarpment morphometry and footwall geometry reveal systematic differences between the bexternalq segments pefs thfs and avfs and the binternalq segments affs and fifs which may be due to mechanical interaction among segments and or preexisting topography in addition transects across all five escarpments show mean scarp slope angles of 22 18f0 78 for both carbonate and metamorphic bedrock the slope angle equation for the external segments shows asymptotic behaviour with increasing height we make an empirical suggestion that slope angle is a function of the long term fault slip rate which ranges between 0 13 and 0 3 mm yr the identified faults may rupture up to magnitude 6 4 6 6 earthquakes the analysis of the 60 m dem shows a difference in fault patterns between western and northern attica which is related to crustal rheology variations d 2004 elsevier b v all rights reserved

earthquakes in the ductile regime pseudotachylytes from a crustal scale shear zone in central australia have developed in a cyclical manner once developed an individual pseudotachylyte is deformed in a ductile manner only to be overprinted at a later stage by a new generation of pseudotachylytes such cyclic generation and deformation of pseudotachylyte has been interpreted in the past as representing conditions at the brittleductile transition a different interpretation however is presented here it is proposed that psuedotachylytes and associated ultramylonites can develop entirely within the ductile regime as ductile instabilities such instabilities are different in nature to those previously discussed at length in the geophysical literature but are identical in principle with the instabilities that develop for velocity weakening frictional behavior in spring slider systems at a given strain rate a critical temperature tc is defined at which the transient work hardening equals the product of stress relaxation due to a thermal fluctuation and the heat generated by shearing a necessary condition for ductile instability at a given strain rate is that the temperature is belowtc then the rate of change of stress with respect to strain is negative an additional requirement is that this rate of change exceeds in magnitude the effective elastic stiffness of the loading system ductile instabilities are marginally possible at geological strain rates in quartzites but are possible at mid crustal temperatures in other rock types on the basis of these observations a new interpretation is presented for the base of the seismogenic zone in crustal regions

uav based surveying in volcano tectonics an example from the iceland rift abstract in the present work we applied the use of an unmanned aerial vehicle uav a quadcopter and the aerial structure from motion digital photogrammetry image processing technique asfm to study volcano tectonics and tectonic features in an active icelandic rift data have been collected in order to evaluate the holocene deformation in the northern volcanic zone of iceland we mapped 397 structures mainly related to extension fractures and subordinately normal faults in the theistareykir fissure swarm obtaining 1098 and 21 structural data respectively this allowed to reconstruct an overall spreading direction of n108 during holocene times and to calculate a stretch of 1 013 regarding 8 10 ka old lava units deformation in the area is related to both dyke intrusions and extensional tectonics furthermore detailed geological structural field and uav surveys were also performed in two test areas in order to determine data accuracy and the associated reliability of this approach in addition to the above different flight heights were tested suggesting that photo collection with a 12 4 mpx camera at 100 m is efficient to study fracture dilation and kinematics

slip accumulation and lateral propagation of active normal faults in afar we investigate fault growth in afar where normal fault systems are known to be currently growing fast and most are propagating to the northwest using digital elevation models we have examined the cumulative slip distribution along 255 faults with lengths ranging from 0 3 to 60 km faults exhibiting the elliptical or bell shaped slip profiles predicted by simple linear elastic fracture mechanics or elastic plastic theories are rare most slip profiles are roughly linear for more than half of their length with overall slopes always 0 035 for the dominant population of nw striking faults and fault systems longer than 2 km the slip profiles are asymmetric with slip being maximum near the eastern ends of the profiles where it drops abruptly to zero whereas slip decreases roughly linearly and tapers in the direction of overall aden rift propagation at a more detailed level most faults appear to be composed of distinct shorter subfaults or segments whose slip profiles while different from one to the next combine to produce the roughly linear overall slip decrease along the entire fault on a larger scale faults cluster into kinematically coupled systems along which the slip on any scale individual fault or fault system complements that of its neighbors so that the total slip of the whole system is roughly linearly related to its length with an average slope again 0 035 we discuss the origin of these quasilinear asymmetric profiles in terms of initiation points where slip starts and barriers where fault propagation is arrested in the absence of a barrier slip apparently extends with a roughly linear profile tapered in the direction of fault propagation

tectonics of the thingvellir fissure swarm sw iceland abstract the thingvellir fissure swarm dissects 9000 year old pahoehoe lava and contains about 100 fractures of average orientation n29 3e the average length of fractures is 620 m the minimum being 57 m and the maximum 7 7 km the maximum width and throw on a single fracture are 68 m and 40 m respectively most fractures are vertical at the surface and must be the result of an absolute tensile stress the geometry and arrangement of the fractures indicate that they have grown by coalescence of initially offset small fractures it is concluded that most fractures attain depths of the order of several hundred meters or less but that the largest faults attain depths of many kilometers comparison with the vogar fissure swarm on the reykjanes peninsula suggests that the thingvellir swarm may have the greater rate of dilation the total maximum postglacial dilation of the vogar swarm is only 15 m whereas the corresponding figure for the thingvellir swarm is about 100 m

analogue experiments of propagation of oblique rifts abstract we present the results of analogue models of oblique rifting which were carried out using a isostatically compensated two layered small scale models the experiments show that structures formed in the brittle layer under oblique extension comprise a series of lenticular rifted basins set en echelon along the axial zone of the experiment box in time the basins propagate lengthways to merge and form a unified composite rift however traces of the initial en echelon rifts expressed in deeper axial basins separated by shallower threshold zones are clearly discernible in the mature rifts both the basins and the threshold zones are located within the composite rift so that the rift margins are abrupt and steep along the basins and more diffuse along the threshold zones the thinning in the brittle layer along the rift is enhanced by diapirs that ascend from the ductile layer and penetrate the rift floor model experiments of nearly orthogonal extension showed a single unified rift which differed conspicuously from the composite oblique rifts the results of the experiments suggest that oblique extension forms en echelon rift segments the axes of which are perpendicular to the extension direction separated by threshold zones therefore there is ground to presume that occurrence of a series of alternating basins and threshold zones inside the axial section of a major rift could suggest a regime of oblique tectonic extension

surface deformation and strike slip faulting controlled by dyking and host rock lithology a compendium from the krafla rift iceland abstract in the present work we have obtained a detailed complete view of surface deformation at a volcano tectonic structure belonging to the krafla fissure swarm ne iceland through the integration of field mapping and the aerial structure from motion technique asfm as well as through orthomosaics and digital surface models dsms the documented 2 5 km long deformation zone is marked by a range of features such as topographic bulging parallel extension fractures and narrow grabens affected by local floor uplift which we have explained as the effect of the northward shallow propagation of a dyke from the krafla magma chamber our lithostratigraphic field survey of the area at a 1 5000 scale indicates that major changes in the pattern of surface deformation take place across the contacts between deposits with different rheological properties the transition from very stiff lavas to softer hyaloclastites produces changes from extensional fracturing to normal faulting though the width of the deformation zone does not change we have also documented a number of ne sw left lateral and nnw sse right lateral strike slip fault zones that are rotated in clockwise and anticlockwise sense to the main nne ssw graben trend and extend outwards as much as about 17 m the graben zone terminates to the north by splitting into two strike slip fault zones these were likely generated at the front of the dyke tip during its propagation and were later on bypassed by the advancement of the dyke as the dyke entered the soft hyaloclastites propagation was slowed down and the dyke became thicker

magma induced strain localization in centrifuge models of transfer zones abstract scaled centrifuge experiments have been used to investigate the dynamic relations between deformation and magma distribution in rift related transfer zones the physical models were built using suitable analogue materials such as sand to represent the brittle upper crust various kinds of silicone mixtures to simulate the lower crust and upper mantle and glycerol to reproduce magma models simulated the development of transfer zones across pre existing glycerol reservoirs placed at the base of the analogue continental crust in plan view different geometries dimensions and positions of subcrustal reservoirs were reproduced in three different sets of experiments to compare results models were also performed without magma simulating glycerol set 1 experiments incorporating a narrow rectangular glycerol reservoir show that the low viscosity material is able to localise deformation into the overlying crust giving rise to discrete transfer zones this concentrated surface deformation corresponds at depth to major magma accumulation set 2 experiments with an initial wide squared glycerol reservoir show instead that deformation is distributed across the whole model surface corresponding at depth to relatively minor magma accumulation set 3 experiments explored various positions of a small squared reservoir that invariably localised faulting in the overlying analogue brittle crust at the onset of model deformation the overall model behaviour suggests that magma distribution at depth can effectively control the strain distribution in the overlying crust and the deformative pattern of transfer zones strain distribution in turn may control magma emplacement as localized deformation would favour major accumulation of magma at transfer zones coupled to a strong thermal weakening of the country rocks this process may ultimately lead to a positive feedback interaction between magma and deformation

real world based immersive virtual reality for research teaching and communication in volcanology direct outcrop observation and field data collection are key techniques in research teaching and outreach activities in volcanic areas however very often outcrops are of difficult or impossible access such as in areas with active volcanoes or steep cliffs classical remote sensing surveys by satellites or airplanes are expensive rarely reach sufficient resolution to allow high quality 3d visualisation of volcanic features and do not facilitate mapping of vertical cliffs we describe a novel approach that uses immersive virtual reality vr based on real world 3d digital outcrop models doms from images surveyed by unoccupied aerial system uas 3d doms are built up using the structure from motion sfm photogrammetry technique and a vr scene is created using game engine technologies immersive real time exploration of the environment is possible through a head mounted display e g oculus rift tools embedded in the vr environment allow the user to map polygons lines and point features tools also allow to measure orientation dip inclination azimuth area and thickness and even take virtual photographs using three examples of volcanic areas with different geological features we demonstrate the potential of our approach to allow users to be able to virtually map and measure remotely and to collect data for research and teaching our approach is of paramount importance also for outreach as it allows non specialist audiences e g common citizens to experience and appreciate highly complex volcanic features through customised hands on immersive vr tools

tectonics of nisyros island greece by field and offshore data and analogue modelling abstract we use new on land and offshore structural data and scaled analogue models to analyse the fault tectonic pattern at nisyros island greece which has an active caldera that shows a complicated network of faults fractures and volcano tectonic structures we measured 157 faults that show dominant dip slip normal motions along planes mainly striking ne sw nne ssw and nnw sse inside the caldera dykes necks and morphometric parameters of volcanic domes explosion craters and fumarole pits indicate the control by ne striking discontinuities on magma and gas paths the nnw and ne striking faults bound a major block that underwent repeated downthrow and uplift movements during the late pleistocene holocene experiments with scaled models of caldera resurgence and two magma chambers indicate the formation of an hourglass shaped fault pattern as seen in plan view with an asymmetric increase in the fault offset and a widening of the fault divergence towards the volcano flank all these data suggest that regional fault tectonics and stress state strongly guided magma upwelling and the emplacement of volcanic centres whereas periodical bulging due to the overpressure of a second magma chamber located northwest of the caldera combined with faulting due to tectonic stresses can account for the overall deformation field

the role of off fault damage in the evolution of normal faults abstract recent measurements of slip profiles on normal faults have found that they are usually triangular in shape this has been explained to be a consequence of on fault processes such as slip dependent friction however the recent observation that cumulative slip profiles on normal faults and fault systems in afar are both triangular and self similar excludes this explanation and requires some form of off fault deformation here we use elastic modelling to show that large triangular zones of off fault damage can explain the observed triangular slip profiles provided damage is anisotropic in the form of cracks sub parallel to the fault our modelling suggests that these triangular damage zones result from the enlargement of the crack tip damage area as the fault or system lengthens our modelling also demonstrates that different types of barriers can cause the slip profiles to terminate abruptly at one or both fault ends as observed in afar and elsewhere

relocation of m 2 events of the 1989 dobi seismic sequence in afar evidence for earthquake migration the ethiopian side of central afar was struck in august 1989 by the largest seismic sequence three 6 1 ms 6 3 events 15 with ms or mb 5 0 since that of serdo in 1969 using the djibouti seismological network we relocated 297 of the events of that sequence as most of the large events took place outside the network we assessed the accuracy and stability of earthquake relocations by using three different velocity models and two relocation codes to try to relate individual shocks to distinct faults and surface breaks a majority of the events apparently occurred underneath the floor of the dobi graben an area about 45 km long and 15 km wide rupturing boundary and inner floor faults in agreement with the surface cracks and scarps that we mapped in the area the relocation shows that the principal events propagated about 50 km northwestwards along the graben in the first 40 hr a day and a half after the beginning of the sequence smaller events m 4 started to propagate more than 55 km eastwards towards asal lake using two three component stations installed near the ethiopian border we could determine reliable depths for 21 events the depths are compatible with a seismogenic crust about 14 km thick in the dobi and hanle graben area although the dobi sequence ruptured about 50 km of the fault array extending from serdo to asal where the regional stress was released by earthquakes in 1969 and 1978 respectively a seismic gap about 50 km long still subsists along the northern part of the gaggade region der ela half graben

the offshore east african rift system structural framework at the toe of a juvenile rift the cenozoic east african rift system ears extends from the red sea to mozambique here we use seismic reflection and bathymetric data to investigate the tectonic evolution of the offshore branch of the ears the data indicate multiple and time transgressive neotectonic deformations along 800km of the continental margin of northern mozambique we observe a transition from a mature rift basin in the north to a juvenile fault zone in the south the respective timing of deformation is derived from detailed seismic stratigraphy in the north a 30km wide and more than 150km long n s striking symmetric graben initiated as half graben in the late miocene extension accelerated in the pliocene causing a continuous conjugate border fault and symmetric rift graben coevally the rift started to propagate southward which resulted in a present day 30km wide half graben approximately 200km farther south since the pleistocene the rift has continued to propagate another 300km where the incipient rift is reflected by subrecent small scale normal faulting estimates of the overall brittle extension of the matured rift range between 5 and 12km with an along strike southward decrease of the extension rate the offshore portion of the ears evolves magma poor similar to the onshore western branch the structural evolution of the offshore ears is suggested to be related to and controlled by differing inherited lithospheric fabrics preexisting fabrics may not only guide and focus extension but also control rift architecture

interannual extremes in new zealand precipitation linked to modes of southern hemisphere climate variability abstract interannual extremes in new zealand rainfall and their modulation by modes of southern hemisphere climate variability are examined in observations and a coupled climate model north island extreme dry wet years are characterized by locally increased reduced sea level pressure slp cold warm sea surface temperature sst anomalies in the southern tasman sea and to the north of the island and coinciding reduced enhanced evaporation upstream of the mean southwesterly airflow during extreme dry wet years in south island precipitation an enhanced reduced meridional slp gradient occurs with circumpolar strengthened weakened subpolar westerlies and an easterly westerly anomaly in zonal wind in the subtropics as a result via ekman transport anomalously cold warm sst appears under the subpolar westerlies while anomalies of the opposite sign occur farther north the phase and magnitude of the resulting sst and evaporation anomalies cannot account for the rainfall extremes over t

along rift propagation of pleistocene holocene faults from a central volcano abstract the mechanisms of rift propagation are still not fully understood especially at mid oceanic ridges owing to the inherent difficulty in collecting submarine data here we investigate the fault slip profiles of the 60 km long theistareykir rift northern iceland that may suggest the direction of along axis rift propagation this is one of the few places on earth where rifting processes and mid oceanic ridge formation can be studied directly moreover this rift hosts an active central volcano and this enables to fully understand the relations between rift propagation and magma systems we reconstructed the slip profiles of all the 281 main pleistocene holocene faults that compose this n s rift by merging measurements performed in the field collected by unmanned aerial vehicle surveys and derived from digital surface models results indicate that north of the volcano 75 of the asymmetric faults propagated northward the value increases to 82 if the cumulated fault length is considered south of the volcano 47 of the asymmetric faults propagated southward 54 if the cumulated fault length is considered these data point to a dominant mechanism of along axis propagation of the rift outward from the volcano suggesting a genetic link with the underlying magma chamber two possible processes are suggested which can also occur in combination i faults develop following lateral dyke propagation outward from the magma chamber and ii faults nucleate near the volcano as a consequence of the different crustal rock rheology produced by a higher heat flux the rift architecture is complicated by the presence of tectonic zones with different dominant fault dips separated by transversal accommodation zones the latter also play the role of barriers guiding local fault propagation

widespread inclination shallowing in permian and triassic paleomagnetic data from laurentia support from new paleomagnetic data from middle permian shallow intrusions in southern illinois usa and virtual geomagnetic pole distributions abstract recent paleomagnetic work has highlighted a common and shallow inclination bias in continental redbeds the permian and triassic paleomagnetic records from laurentia are almost entirely derived from such sedimentary rocks so a pervasive inclination error will expectedly bias the apparent polar wander path of laurentia in a significant way the long standing discrepancy between the apparent polar wander paths of laurentia and gondwana in permian and triassic time may be a consequence of such a widespread data pathology here we present new middle permian paleomagnetic data from igneous rocks and a contact metamorphosed limestone from cratonic laurentia the exclusively reversed middle permian magnetization is hosted by low ti titanomagnetite and pyrrhotite and yields a paleomagnetic pole at 56 3 s 302 9 e a95 3 8 n 6 this pole which is unaffected by inclination shallowing suggests that a shallow inclination bias may indeed be present in the laurentian records to further consider this hypothesis we conduct a virtual geomagnetic pole distribution analysis comparing theoretical expectations of a statistical field model tk03 gad against published data sets this exercise provides independent evidence that the laurentian paleomagnetic data is widely biased likely because of sedimentary inclination shallowing we estimate the magnitude of this error from our model results and present and discuss several alternative corrections

dynamics of continental rift propagation the end member modes abstract an important aspect of continental rifting is the progressive variation of deformation style along the rift axis during rift propagation in regions of rift propagation specifically transition zones from continental rifting to seafloor spreading it has been observed that contrasting styles of deformation along the axis of rift propagation are bounded by shear zones the focus of this numerical modeling study is to look at dynamic processes near the tip of a weak zone in continental lithosphere more specifically this study explores how modeled rift behavior depends on the value of rheological parameters of the crust a three dimensional finite element model is used to simulate lithosphere deformation in an extensional regime the chosen approach emphasizes understanding the tectonic forces involved in rift propagation dependent on plate strength two end member modes are distinguished the stalled rift phase is characterized by absence of rift propagation for a certain amount of time extension beyond the edge of the rift tip is no longer localized but occurs over a very wide zone which requires a buildup of shear stresses near the rift tip and significant intra plate deformation this stage represents a situation in which a rift meets a locked zone localized deformation changes to distributed deformation in the locked zone and the two different deformation styles are balanced by a shear zone oriented perpendicular to the trend in the alternative rift propagation mode rift propagation is a continuous process when the initial crust is weak the extension style does not change significantly along the rift axis and lengthening of the rift zone is not accompanied by a buildup of shear stresses model predictions address aspects of previously unexplained rift evolution in the laptev sea and its contrast with the tectonic evolution of for example the gulf of aden and woodlark basin

geometry oblique kinematics and extensional strain variation along a diverging plate boundary the example of the northern theistareykir fissure swarm ne iceland abstract the boundary between the american and european plates emerges in iceland an outstanding natural laboratory where it is possible to analyse ongoing rifting processes in the north volcanic zone we studied with unprecedented detail an active rift known as the theistareykir fissure swarm thfs we surveyed an area of 85 km2 with 694 measurement sites along 1537 post late glacial maximum extension fractures in the southern sector of the study area fractures strike n30 40 with opening directions about n120 fractures in the central sector strike about n00 and opening directions are n90 100 in the northern sector fractures strike about n30 with opening directions about n125 through a comparison with older faults cropping out in the substrate at the shoulder of the thfs we are able to suggest that variations in fracture strike are the effect of substrate structural inheritance as well as the possible interaction with the tjornes fracture zone with regard to kinematics we highlight that most fractures show a small but systematic strike slip component a more frequent right lateral component and a less common left lateral one this cannot be explained as the result of fracture strike rotation relative to the regional tectonic least principal stress we conclude that the net opening directions can result from the combination of tectonic offsets and events caused by shallow magma chamber inflation and or dyke intrusions the latter can produce transcurrent components of displacement along new or already existing fractures

growth of faults by accumulation of seismic slip the accommodation of large strains in the upper crust is largely achieved by the accumulation of displacement on faults observation shows that as a fault accumulates displacement it grows in size i e its surface area and its length increase here we address the question for an increase in the amount of displacement on a fault by how much would the length of the fault change it is argued by cowie and scholz 1992a that the displacement on a fault is linearly related to the length of the fault this simple result is expanded upon in this paper by assuming that a fault accumulates displacement by repeated earthquakes two different approaches are presented the first approach considers the balance that must be achieved between the energy available for deformation and the work involved in creating new fault surface area as the fault grows the available energy is provided by changes in strain energy when the fault slips the second approach is to construct a geometrical model for fault growth using the scaling relationship between the slip during a single earthquake and the length of the rupture the total displacement on a fault is the sum of the slips contributed by many earthquakes the usefulness of these two approaches is that the growth of a fault over geologic time can be described by parameters that can be obtained from earthquake and fault data the models presented here predict that 1 the maximum amount a fault can grow in a single earthquake that ruptures the entire fault is of the order of 1 of its previous length and 2 the work of faulting may account for 10 of the total energy available during an earthquake the energy lost from the system is accounted for by work done against friction and seismic radiation consequences of fault growth for the segmentation and thus seismogenic potential of a fault over geologic time are discussed using predictions of the theory

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

fracturing and earthquake activity within the prestahnukur fissure swarm in the western volcanic rift zone of iceland the prestahnukur fissure swarm is located within the ultraslowly spreading western volcanic zone in iceland the fissure swarm is characterized by normal faults open fractures and evidence of subglacial fissure eruptions tindars in this study fractures and faults within the prestahnukur fissure swarm were mapped in detail from aerial photographs to determine the extent and activity of the fissure swarm earthquakes during the last 23 years were relocated to map the subsurface fault planes that they delineate the prestahnukur fissure swarm is 40 80 km long and up to 20 km wide most of the areas of the fissure swarm have been glacially eroded although a part of it is covered by postglacial lava flows the fissure swarm includes numerous faults with tens of meters vertical offset within the older glacially eroded part whereas open fractures are found within postglacial lava flows comparison of relocated earthquakes and surface fractures indicates that some of the surface fractures have been activated at depth during the last 23 years although no dike intrusions have been ongoing the existence of tindars nevertheless indicates that dike intrusions and rifting events do occur within the prestahnukur fissure swarm the low fracture density within postglacial lava flows and low density of postglacial eruptive fissures indicate that rifting episodes occur less often than in the faster spreading northern volcanic zone

rift nucleation rift propagation and the creation of basement micro plates within active rifts abstract in this contribution we study the dynamics of rift nucleation and the interaction of propagating rift segments we use the east african rift system ears as a case study with special emphasis on the albertine rift system situated within the western branch of the ears with the 5000 m high rwenzori horst a basement block that was captured by two rift segments fieldwork in the rwenzori mountains shows that the range is not only affected by range parallel faults but that major fault sets cut across the rwenzoris in order to understand these complex fault patterns and the dynamics of the process that leads to the capturing of basement blocks within the extending rift system we developed a two dimensional visco elasto plastic spring model the model shows that propagating rift faults commonly capture micro plates with shapes similar to the rwenzori mountains these micro plates rotate during successive rift opening in a clockwise or anti clockwise sense depending on the direction of the rift segment overstep a left lateral overstep as is the case for the albertine rift system produces a clockwise rotation of the associated micro plate indicating that the rwenzori mountains rotate clockwise during the rotation of the micro plate the local stress field at the rift segment tips is perturbed so that the rifts turn 70 to 90 and propagate towards each other to capture the plates completely this perturbed stress field produces an extensional fault set that is oriented almost parallel to the far field extension direction and explains the range cutting faults that we find in the rwenzori mountains the large scale geometry of the rift system seems to be strongly controlled by rigid cratons in the lithosphere leading to a curvature of the western branch of the ears and a sinistral wrench component in the lake albert rift north of the rwenzori mountains capturing of micro plates of various sizes within the rift system is a common phenomenon and leads to strong perturbations of the local stress field during micro plate rotation the resulting structures are normal and strike slip faults that cut through the micro plates and local reverse faults

the krafla fissure swarm iceland and its formation by rifting events fissure swarms at divergent plate boundaries are activated in rifting events during which intense fracturing occurs in the fissure swarm accompanied by intrusion of magma to form dikes that sometimes lead to eruptions to study the evolution of fissure swarms and the behaviour of rifting events detailed mapping was carried out on fractures and eruptive fissures within the krafla fissure swarm kfs fracture densities of dated lava flows ranging from 10 000 years bp to 30 years old were studied and the fracture pattern was compared with data on the historical m vatn rifting episode 1724 1729 and the instrumentally recorded krafla rifting episode 1975 1984 additionally the interaction of transform faults and fissure swarms was studied by analysing the influence of the husavik transform faults on the kfs during the historical rifting episodes eruptions on the fissure swarm occurred within 7 km from the krafla central volcano although faults and fractures were formed or activated at up to 60 70 km distance this is consistent with earlier rifting patterns as holocene eruptive fissures within the kfs are most common closer to the central volcano most fractures within the central krafla caldera are parallel to the overall orientation of the fissure swarm this suggests that the regional stress field is governing in the krafla central volcano while the local stress field of the volcano is generally weak a sudden widening of the graben in the northern kfs and a local maximum of fracture density at the junction of the kfs and the extrapolation of the husavik transform fault zone indicates possible buried continuation of the husavik transform fault zone which extends to the kfs eruptive fissures are found farther away from the krafla central volcano in the southern kfs than in the northern kfs this is either due to an additional magma source in the southern kfs the hei arspor ur volcanic system or caused by the husavik transform faults transferring some of the plate extension in the northern part fracture density within particular lava flow fields increases with field age indicating that repeated rifting events have occurred in the fissure swarm during the last 10 000 years bp the fracture density in the kfs is also generally higher closer to the krafla central volcano than at the ends of the fissure swarm this suggests that rifting events are more common in the parts of the fissure swarm closer to the krafla central volcano

locking depth and slip rate of the husavik flatey fault north iceland derived from continuous gps data 2006 2010 summary located at the northern shore of iceland the tjornes fracture zone tfz is a 120 km offset in the mid atlantic ridge that connects the offshore kolbeinsey ridge to the on land northern volcanic zone this transform zone is seismically one of the most active areas in iceland exposing the population to a significant risk however the kinematics of the mostly offshore area with its complex tectonics have not been adequately resolved and the seismic potential of the two main transform structures within the tfz the grimsey oblique rift gor and the husavik flatey fault hff in particular is not well known in summer 2006 we expanded the number of continuous gps cgps stations in the area from 4 to 14 the resulting gps velocities after four years of data collection show that the tfz accommodates the full plate motion as it is predicted by the morvel plate motion model in addition envisat interferograms reveal a transient uplift signal at the nearby theistareykir central volcano with a maximum line of sight uplift of 3 cm between summers of 2007 and 2008 we use a combination of an interseismic backslip and a mogi model in a homogeneous elastic half space to describe the kinematics within the tfz with a non linear optimization approach we fit the gps observations and estimate the key model parameters and their uncertainties which are among others the locking depth the partition of the transform motion between the two transform structures within the tfz and the slip rate on the hff we find a shallow locking depth of 6 3 1 7 1 2 km and transform motion that is accommodated 34 3 per cent by the hff and 66 3 per cent by the gor resulting in a slip velocity of 6 6 0 6 mm yr 1 for the hff assuming steady accumulation since the last two large m6 5 earthquakes in 1872 the seismic potential of the fault is equivalent to a mw6 8 0 1 event

a new look for the southern hemisphere jet stream a new jet stream description defined as the geostrophic streamline of maximum average velocity is proposed an objective algorithm for detecting and tracking the jet has been developed tested and applied to the ncep ncar 200 hpa geopotential height in the southern hemisphere for the period 1958 2002 the results show the variability of the double character of the southern hemisphere jet with a marked seasonality during the warm season a single jet can be found around 40 s while autumn and winter are characterized by a clear double jet structure with a strong and dominant subtropical jet located around 30 s and a polar front jet progressively displaced toward southern latitudes and reaching 60 s by the end of the cold season in general a trend toward slower subtropical jets and stronger polar front jets has been detected during the study period the southern annular mode appears as a main modulator of the latitude and strength of the polar front jet influencing to a minor extent its subtropical counterpart the enso cycle strongly modifies the latitude and specially the strength of the subtropical jet affecting its preferred wavenumber as well nevertheless the effect of this oscillation seems fairly restricted in the pacific thus limiting the ability of this jet to drive the el nino teleconnections along the southern hemisphere the consistency of the results when compared with previous jet climatologies suggests that the new approach is a reliable jet tracking method thus providing a new tool to analyze climatic variability at hemispheric scales

fabric development in syn tectonic intrusive sheets as a consequence of melt dominated flow and thermal softening of the crust the temperature dependence of ductile deformational processes suggests that the thermal anomaly associated with a cooling syn tectonic intrusion will produce a crustal low viscosity horizon that will concentrate deformation in the vicinity of the pluton during cooling this effect should be most prominent when magma is present but should also occur after solidification of the magma when flow is by solid state processes this paper evaluates this hypothesis for sheet like intrusions using one dimensional time dependent thermal models and accompanying predictions of viscosity vs time history based on experimental flow laws these models predict that for systems with an initial normal geothermal gradient e g extensional systems strike slip systems or thrust systems with low displacement rates the base of a large plutonic sheet cools more slowly than the top and fabric development should be most pronounced on the floor of the pluton in contrast in megathrust systems where displacements are sufficiently rapid to produce temperature inversions cooling is also upside down and fabric development should preferentially occur along the top of plutonic sheets moreover when a pluton is emplaced within a zone of inverted isotherms the heat may be trapped within the inversion a natural system characterized by this history should show a sharp thermal front coincident with the top of a paleo temperature inversion if a pluton is weaker than its country rock it will form a weak horizon in the crust throughout its cooling history and the plutonic sheet should take up the bulk of the deformation throughout its cooling history if a pluton is stronger than its country rock under conditions of solid state flow however models predict a two phase deformational history prior to solidification the deformation should be concentrated in the pluton with the magma representing a weak horizon in the crust but upon crystallization the pluton should become relatively rigid with respect to its country rock and deformation should be concentrated in the wall rocks these two cases predict markedly different structural histories and the history could easily be misinterpreted in the first case static mineral growth might be prominent in the wall rocks and these textures could be misinterpreted as evidence for post tectonic emplacement in the second case the extensive high t deformation of the wall rocks could be readily ascribed to non tectonic emplacement related deformation rather than a consequence of syn tectonic emplacement the model predictions are tested with three examples of well exposed plutonic sheets a neogene extensional system in death valley california and two megathrust systems in southern alaska border ranges fault system and mclaren metamorphic belt structural observations from these systems are broadly consistent with the model predictions and lend support to first order characteristics of the models nonetheless more sophisticated 2 d models of the coupled thermal mechanical system are needed to thoroughly test the hypothesis

enso sam interactions during the middle and late holocene a new chronology of large magnitude rainfall events derived from the continuous high resolution lake tutira storm sediment record covers the last 6800 years and provides the first insight into changes in el nino southern oscillation enso teleconnections to the higher southern latitudes to be obtained from new zealand synthesis with independent paleoclimate records from the tropical pacific and antarctica also reveals a millennial scale waxing and waning of the teleconnections that were not visible in the narrow historical window previously used to view interactions between enso and the southern annular mode sam consistent with modern enso behaviour we find teleconnections to the southwest pacific varied throughout the middle and late holocene depending on the strength and phase of enso and the phase of the sam we suggest that precession driven changes in the seasonal cycle of solar radiation exert a first order control on the interaction between the two climate modes consequently their present

ascent and emplacement of buoyant magma bodies in brittle ductile upper crust 1 the emplacement of silicic magma bodies in the upper crust may be controlled by density such that there is no buoyancy to drive further ascent or temperature such that surrounding rocks are too cold to deform significantly over geological timescales evidence for the latter control is provided by negative gravity anomalies over many granitic plutons conditions of diapir ascent and emplacement in this case are studied with a numerical model for deformation and heat transport allowing for ductile elastic and brittle behavior a large strain formulation is used to solve for temperature stress strain and strain rate fields as a function of time for a range of diapir sizes density contrasts and background geotherms the method allows for large viscosity contrasts of more than 6 orders of magnitude and determines the dominant deformation mechanism depending on the local values of temperature strain and strain rate emplacement depth and final deformation characteristics depend on diapir size and buoyancy small diapirs less than about 5 km in diameter cannot reach shallow crustal levels and do not involve brittle deformation in the ductile regime the diapir flattens significantly upon emplacement due to stiff roof rocks and to the free surface above late stage deformation proceeds by horizontal spreading with little upward displacement of roof rocks and is likely to be interpreted as ballooning large diapirs more than about 5 km in diameter rapidly rise to shallow depths 1 5 km and induce brittle faulting in the overlying rocks in this regime buoyancy forces may lead to faulting in roof rocks in this case late stage ascent proceeds by vertical intrusion of a plug of smaller horizontal dimensions than the main body buoyant diapirs keep on rising after solidification long after the relatively short lived high temperature magmatic stage this may account for some phases of late caldera resurgence in extinct volcanic systems

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

dikes minor faults and mineral veins associated with a transform fault in north iceland abstract the tjornes fracture zone is a transform fault connecting the axial rift zone in north iceland with that of the kolbeinsey ridge off the north coast of iceland on the north coast of the flatcyjarskagi peninsula there is a 3 5 km wide zone of intense deformation which we interpret as the main on land part of this transform fault this transform zone strikes n64 w and is characterized by unusually steeply dipping lavas 25 44 wnw extensive secondary mineralization numerous slickensided surfaces normal faults 1 20 m throw dikes that strike parallel to the zone and occasional 3 20 m wide subzones of crushed rocks striking parallel to the transform fault in a 17 km long continuous coastal profile south of the transform zone there is a 30 clockwise change from south to north in the lava strike the dike strike also changes clockwise north along this profile but only by 4 this indicates that the clockwise change in the lava strike is original and not due to subsequent tectonic rotation when the axial rift zones of north iceland and the kolbeinsey ridge are modelled as single offset mode i cracks finiteelement results show that the tjornes fracture zone developed between these mode i cracks in a region of maximum shear stress the underlap between these axial rift zones has apparently decreased during the past several million years the model predicts that as this underlap decreased the angle between the husavik flatey fault and that of the associated axial rift zones increased and the activity of the husavik flatey fault decreased both these predictions are borne out by the available data

structure from motion photogrammetry a low cost effective tool for geoscience applications abstract high resolution topographic surveying is traditionally associated with high capital and logistical costs so that data acquisition is often passed on to specialist third party organisations the high costs of data collection are for many applications in the earth sciences exacerbated by the remoteness and inaccessibility of many field sites rendering cheaper more portable surveying platforms i e terrestrial laser scanning or gps impractical this paper outlines a revolutionary low cost user friendly photogrammetric technique for obtaining high resolution datasets at a range of scales termed structure from motion sfm traditional softcopy photogrammetric methods require the 3 d location and pose of the camera s or the 3 d location of ground control points to be known to facilitate scene triangulation and reconstruction in contrast the sfm method solves the camera pose and scene geometry simultaneously and automatically using a highly redundant bundle adjustment based on matching features in multiple overlapping offset images a comprehensive introduction to the technique is presented followed by an outline of the methods used to create high resolution digital elevation models dems from extensive photosets obtained using a consumer grade digital camera as an initial appraisal of the technique an sfm derived dem is compared directly with a similar model obtained using terrestrial laser scanning this intercomparison reveals that decimetre scale vertical accuracy can be achieved using sfm even for sites with complex topography and a range of land covers example applications of sfm are presented for three contrasting landforms across a range of scales including an exposed rocky coastal cliff a breached moraine dam complex and a glacially sculpted bedrock ridge the sfm technique represents a major advancement in the field of photogrammetry for geoscience applications our results and experiences indicate sfm is an inexpensive effective and flexible approach to capturing complex topography

high temperature experiments on the elastic and anelastic behaviour of magmatic rocks measurements of the complex shear modulus have been performed on various ultrabasic and basic rocks dunite peridotite gabbro and basalts and a synthetic forsterite at temperatures between 600 and 1500 c depending on the sample material and in the frequency range from 0 003 to 30 hz under forced torsional oscillations the maximum shear stress was 0 3 mpa and the strains were of the order 5 10 6 to 5 10 5 measurements of the electrical resistivity as a function of temperature have been carried out together with the mechanical experiments to indicate the beginning of partial melting the absolute values of the shear modulus below tm are comparable with the results of other authors the onset of melting shows up in a rapid decrease of both shear modulus and electrical resistivity at high temperatures t 0 8 tm the absorption factor q 1 follows a power law q 1 exp a rt with 0 15 0 30 and a between 100 and 200 kj mol 1 towards lower temperatures this high temperature background is superimposed by a flat absorption peak which shifts from high to low frequencies with falling temperature this peak can often be described by a lognormal distribution of simple relaxation processes with a standard deviation of about three and a mean relaxation time exp a rt with a 400 600 kj mol 1 above tm a third contribution to q 1 is observed that can be regarded as independent of frequency between 1 and 30 hz this last component which contributes 50 to the total absorption is attributed to the melt phase in the samples an explanation for the high temperature background and the peak is proposed which is based on the relaxation of pinned dislocation lines by some coupling mechanism via the reorganisation of the stress field with increasing deformation this process may be responsible for both features at very high temperatures and low frequencies a small influence of steady state flow on q 1 is observed and below t 0 6 tm thermal cracking or thermoelastic losses may contribute to q 1 the influence of lithostatic pressure on q 1 is estimated and the extrapolation of the experimental data to the p t conditions of the uppermost mantle are in good agreement with published earth models an attempt is made to establish a general q t relationship from the experimental data

surface deformation in volcanic rift zones abstract the principal conduits for magma transport within rift zones of basaltic volcanoes are steeply dipping dikes some of which feed fissure eruptions elastic displacements accompanying a single dike emplacement elevate the flanks of the rift relative to a central depression concomitant normal faulting may transform the depression into a graben thus accentuating the topographic features of the rift if eruption occurs the characteristic ridge trough ridge displacement profile changes to a single ridge centered at the fissure and the erupted lava alters the local topography a well developed rift zone owes its structure and topography to the integrated effects of many magmatic rifting events to investigate this process we compute the elastic displacements and stresses in a homogeneous two dimensional half space driven by a pressurized crack that may breach the surface a derivative graphical method permits one to estimate the three geometric parameters of the dike height inclination and depth to center and the mechanical parameter driving pressure rock stiffness from a smoothly varying displacement profile direct comparison of measured and theoretical profiles may be used to estimate these parameters even if inelastic deformation notably normal faulting creates discontinuities in the profile geological structures open cracks normal faults buckles and thrust faults form because of stresses induced by dike emplacement and fissure eruption theoretical stress states associated with dilation of a pressurized crack are used to interpret the distribution and orientation of these structures and their role in rift formation

4 d evolution of rift systems insights from scaled physical models the four dimensional 4 d evolution of brittle fault systems in orthogonal oblique and offset rift systems has been simulated by scaled sandbox models using dry cohesionless fine grained quartz sand extensional deformation in the models was controlled by the orientation and geometry of a zone of stretching at the base of the model the results of these analog model studies are compared with natural examples of rift fault systems rift basins produced by orthogonal and oblique rifting are defined by segmented border fault systems parallel to the rift axes and by intrarift fault systems that are subperpendicular to the extension direction segmentation of the rift margin increases with increase in obliquity of the rift axis resulting in a consequent increase in displacement on intrarift fault systems offset rift models are characterized by highly segmented border faults and offset subbasins in the rift zone along strike displacement transfer in the model rifts occurred as a result of formation of two types of accommodation zones high relief extension parallel accommodation zones typically are found in 60 degrees rifts and above left steps in offset rift systems changes in fault polarities in these accommodation zones were achieved by interlocking arrays of conjugate extensional faults the second type of accommodation zone was generally oblique to the extension direction and consisted of conjugate fault arrays having rotated tips that bounded a low relief oblique slip zone or grabens these typically are found in highly oblique rift systems 45 degrees and above right steps in offset rift models