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

circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

segmented lateral dyke growth in a rifting event at barðarbunga volcanic system iceland crust at many divergent plate boundaries forms primarily by the injection of vertical sheet like dykes some tens of kilometres long1 previous models of rifting events indicate either lateral dyke growth away from a feeding source with propagation rates decreasing as the dyke lengthens2 3 4 or magma flowing vertically into dykes from an underlying source5 6 with the role of topography on the evolution of lateral dykes not clear here we show how a recent segmented dyke intrusion in the bar arbunga volcanic system grew laterally for more than 45 kilometres at a variable rate with topography influencing the direction of propagation barriers at the ends of each segment were overcome by the build up of pressure in the dyke end then a new segment formed and dyke lengthening temporarily peaked the dyke evolution which occurred primarily over 14 days was revealed by propagating seismicity ground deformation mapped by global positioning system gps interferometric analysis of satellite radar images insar and graben formation the strike of the dyke segments varies from an initially radial direction away from the bar arbunga caldera towards alignment with that expected from regional stress at the distal end a model minimizing the combined strain and gravitational potential energy explains the propagation path dyke opening and seismicity focused at the most distal segment at any given time and were simultaneous with magma source deflation and slow collapse at the bar arbunga caldera accompanied by a series of magnitude m 5 earthquakes dyke growth was slowed down by an effusive fissure eruption near the end of the dyke lateral dyke growth with segment barrier breaking by pressure build up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries

surface deformation and stress interactions during the 2007 2010 sequence of earthquake dyke intrusion and eruption in northern tanzania s u m m a r y magma movement and fault slip alter the magnitude and orientation of the stress in the surrounding crust observations of a sequence of events clustered in space and time provide information about the triggering mechanism and stress interactions between magma intrusion earthquakes and eruptions we investigate the synand post intrusion stress changes associated with the 2007 gelei dyke intrusion episode and subsequent eruption of nearby oldonyo lengai previous studies produced a kinematic model of the 2007 june august sequence involving 1m slip on a normal fault followed by the intrusion of the 7 10 km long gelei dyke collapse of a shallow graben and the deflation of the gelei magma chamber immediately following this the volcano oldoinyo lengai 10 km away experienced a new phase of explosive activity lasting for several months here we present new geodetic observations covering gelei and oldoinyo lengai in 2008 september 2010 we show continued slip on graben bounding faults above the gelei dyke the eruption of oldoinyo lengai was accompanied by the intrusion of a 4 km long e w trending dyke followed by deflation of a shallow source directly below the summit of the volcano next we use stress calculations to investigate a number of hypotheses linking these events 1 before the onset of surface deformation a dyke sufficiently deep and narrow to be geodetically undetectable could still have produced sufficient stress changes to trigger slip on the normal fault i e the sequence could have been magmatically driven 2 stresses at the dyke tip would have been sufficient to overcome the effect of continued slip on the normal fault allowing the dyke to propagate upwards into a region of clamping 3 the gelei sequence would have produced a significant stress change on the chamber beneath oldoinyo lengai these static stress calculations allow us to discuss the roles played by dynamic stress deeper magmatic changes and background stresses throughout the sequence with implications for the stress triggering of both seismic and volcanic hazards

flow hydrography turbulent mixing and dissipation at fieberling guyot examined with a primitive equation model 1 the extensive set of measurements previously taken at fieberling guyot provides a backdrop for model results on flow hydrography turbulent mixing and derivative variables a z level primitive equation model driven at subinertial and superinertial tidal frequencies allows the nonlinear interaction of free and topographically trapped motions to jointly determine model outcomes model residual flows mean hydrographic features topographic amplification of oscillatory currents turbulent dissipation and vertical diffusivity kv profiles are all examined in the light of the observations azimuthal residual flows are toroidal above the summit with maximum speed 20 cm s 1 diurnal flow over the summit is intensified by a factor 20 downward vertical flow as a time mean w t occurs from 150 m above the summit apex to summit rim depth with radially inward flow above the apex and radial outward flow below upward w t rings the summit at larger r the existence of the observed cold dome is shown to depend on w t in the summit circulation cell vertical current shear is concentrated in a 150 m thick cap above the summit accounting for a domed distribution of and kv with maxima of 10 7 w kg 1 and 30 cm2 s 1 respectively profiles most like the observations of kv are obtained with a subgrid scale parameterization in which the turbulent prandtl number pr depends on the shear richardson number ri

creep dike intrusion and magma chamber deflation model for the 2000 miyake eruption and the izu islands earthquakes 1 analysis of global positioning system data shows shrinkage of miyake island and the widening between nijima and kozu islands during the period of the miyake island volcanic activity and the ensuing izu islands earthquakes in 2000 the estimated time evolution of a model consisting of a dike creeping faults and a mogi source suggests that a crack opening on miyake island occurred immediately after the start of the seismic activities on 26 june and ended within several days at the west coast of miyake island after the seabed eruption on 27 june magma migrated from miyake island to kozu and nijima islands within several days the estimated volume of intruded magma totals around 1 2 109 m3 associated with the magma intrusion between miyake and kozu islands left lateral and right lateral creep motions occurred in regions off the west coast of miyake island and near kozu island the accumulated moment energy is equivalent to an earthquake of mw 6 6 and 6 6 for right lateral and left lateral creeping faults respectively the estimated magma chamber continued deflation beneath the southwestern part of miyake island from 26 june totaling around 0 12 109 m3 in volume change in addition to the collapse volume of 0 6 109 m3 at the summit of mount oyama on miyake island the volume change on miyake island can be compensated by the migrated magma toward kozu island from the deflation source beneath miyake island the deflation speed of the magma chamber beneath miyake island decreased and increased before and after the eruption of 14 15 july and 18 august suggesting a change in balance of mass influx and draining out rate of the magma chamber

stress transfer between thirteen successive dyke intrusions in ethiopia large earthquakes are known to trigger subsequent earthquakes in nearby regions but similar triggering has not been confirmed for volcanic hazards analysis of the progressive deformation associated with 13 volcanic dykes intruded in ethiopia between 2005 and 2009 indicates that magmatic intrusions can help to trigger subsequent intrusions

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

tensile rock mass strength estimated using insar 1 the large scale strength of rock is known to be lower than the strength determined from small scale samples in the laboratory however it is not well known how strength scales with sample size i estimate kilometer scale tensional rock mass strength by measuring offsets across new tensional fractures joints formed above a shallow magmatic dike intrusion in western arabia in 2009 i use satellite radar observations to derive 3d ground displacements and by quantifying the extension accommodated by the joints and the maximum extension that did not result in a fracture i put bounds on the joint initiation threshold of the surface rocks the results indicate that the kilometer scale tensile strength of the granitic rock mass is 1 3 mpa almost an order of magnitude lower than typical laboratory values

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

shallow earthquake inhibits unrest near chiles cerro negro volcanoes ecuador colombian border magma movement or reservoir pressurisation can drive swarms of low magnitude volcano tectonic earthquakes as well as occasional larger earthquakes m5 on local tectonic faults earthquakes m5 near volcanoes are challenging to interpret in terms of evolving volcanic hazard but are often associated with eruptions and in some cases enhance the ascent of magma we present geodetic observations from the first episode of unrest known to have occurred near chiles and cerro negro de mayasquer volcanoes on the ecuador colombian border a swarm of volcano tectonic seismicity in october 2014 culminated in a mw 5 6 earthquake south of the volcanoes satellite radar data spanning this earthquake detect displacements that are consistent with dextral oblique slip on a reverse fault at depths of 1 4 3 4 km within a ssw nne trending fault zone that last ruptured in 1886 gps station measurements capture 20 days of uplift before the earthquake probably originating from a pressure source 10 15 km south of volcan chiles at depths exceeding 13 km after the mw 5 6 earthquake uplift ceased and the rate of seismicity began to decrease potential mechanisms for this decline in activity include a decrease in the rate of movement of magma into the shallow crust possibly caused by the restriction of fluid pathways our observations demonstrate that an earthquake triggered during volcanic unrest can inhibit magmatic processes and have implications for the hazard interpretation of the interactions between earthquakes and volcanoes

dike propagation energy balance from deformation modeling and seismic release magma is transported in the crust mainly by dike intrusions in volcanic areas dikes can ascend towards the free surface and also move by lateral propagation eventually feeding flank eruptions understanding dike mechanics is a key to forecasting the expected propagation and associated hazard several studies have been conducted on dike mechanisms and propagation however a less in depth investigated aspect is the relation between measured dike induced deformation and the seismicity released during its propagation we individuated a simple equation that can be used as a proxy of the expected mechanical energy released by a propagating dike and is related to its average thickness for several intrusions around the world afar japan mt etna we correlate such mechanical energy to the seismic moment released by the induced earthquakes we obtain an empirical law that quantifies the expected seismic energy released before arrest the proposed approach may be helpful to predict the total seismic moment that will be released by an intrusion and thus to control the energy status during its propagation and the time of dike arrest

abyssal mixing where it is not abstract a parameterization based on internal wave wave interaction theory which infers turbulence production from finescale internal wave shear is applied to 114 full water depth velocity profiles in the sargasso sea an average eddy diffusivity of 0 1 10 4 m2 s 1 independent of depth is inferred this value is consistent with full water depth microstructure measurements from abyssal basins in the eastern north atlantic and eastern north pacific it is an order of magnitude smaller than the values inferred from a simple vertical advection diffusion balance or bulk budgets thus the mixing needed to close deep global water mass budgets does not appear to occur over midlatitude abyssal plains this suggests that ocean mixing is either i confined to boundary layers as in ideal thermocline theory or ii localized to hotspots such as over rough topography or restrictive passages abyssal diffusivities do not display any dependence on bottom slope for slopes less than 7 10 2 based on 5 10 km bathy

analogue modeling of flank instability at mount etna understanding the driving factors 1 mount etna is characterized by significant flank instability whose triggering factors are still a matter of debate we use analog models to investigate the role of different factors in the models a cone and base of granular material simulate the volcanic edifice and its basement the asymmetric geometry of the basement simulates the topographic gradient around the volcano injections of silicone sets a and b and low viscosity vegetable oil set c simulate the pressurization of plutonic complex deep reservoirs and the emplacement of dikes respectively other experiments set d reproduce regional extensional tectonics in the last 105 years within layers with different cohesion simulating strength differences in the basement laser scanner and control points allow the tracking of surface deformation with submillimeter precision the asymmetric topography enhances flank instability on the side with the weakest confinement i e seaside providing the preparing factor for instability in sets a and b any type of pressurized reservoir enhances up to 10 times the amount of flank instability toward the seaside with respect to the other flanks of the volcano in set c dike emplacement enhances seaside flank instability up to 8 times regional tectonics and crustal layering in set d enhance flank instability up to 2 and 1 3 times respectively considering the duration and frequency of the simulated processes in nature we propose a semiquantitative evaluation and hierarchy of the factors controlling flank instability at etna magmatic activity point like source inflation and dike emplacement provides the most important triggering factor extensional tectonics in the last 105 years and crustal layering are more than 10 times less effective this study shows the importance of differential buttressing at the volcano base for flank instability this condition is an important indication to expect asymmetric activity in any volcano flank eruptions and deformation

evidence that coupling to magma chambers controls the volume history and velocity of laterally propagating intrusions 1 in this paper i present a simple analytical solution for the unsolved problem of a propagating dike coupled to a magma chamber as recognized by segall et al 2001 the flow of the magma from a chamber to a dike is described by an ordinary differential equation for the unknown pressures of chamber and dike the most intuitive assumption on magma exchange is that the volume gained by the intrusion equals the volume lost by the chamber this constraint however implies a chamber so large that its pressure does not drop during the feeding process and an incompressible magma that does not expand or vesiculate as it intrudes models assuming constant driving pressure fail to explain observations here mass conservation constrains pressure as magma flows from the chamber to the dike and the compressibilities of magma and sources control volume changes these assumptions allow me to decouple the equations and solve the system analytically the model predicts that chamber and dike volume change exponentially with time as v t v 1 exp t the asymptotic volume v and the timescale are found to be functions of rock magma chamber and dike parameters and of the initial pressure conditions assuming that the intrusion is shaped as an elongating cuboid its velocity is found to change as v v0exp t where v0 is the initial dike velocity the model is successfully tested against the best observations available for lateral dike propagation events the volume history of chamber and dike during the 2000 miyakejima intrusion japan and dike velocity during the 1978 krafla event iceland and during some intrusions following the 2005 event in afar ethiopia this paper confirms and extends the results of a previous study by rivalta and segall 2008 who found the final ratio between dike volume and the volume withdrawn from the chamber to be rv 1 4 m 3 1 where is the host rock rigidity and m is the magma compressibility here i demonstrate that the formula for rv holds at any time during the intrusion not just at the end this model confirms that some magma chambers behave as stiff magma tanks able to inflate large dikes as balloons and demonstrates that high volume ratios are unlikely if the chamber has a pure sill shape fitting observations with the model allows us to estimate several dike chamber magma and rock parameters

magmatic architecture within a rift segment articulate axial magma storage at erta ale volcano ethiopia abstract understanding the magmatic systems beneath rift volcanoes provides insights into the deeper processes associated with rift architecture and development at the slow spreading erta ale segment afar ethiopia transition from continental rifting to seafloor spreading is ongoing on land a lava lake has been documented since the twentieth century at the summit of the erta ale volcano and acts as an indicator of the pressure of its magma reservoir however the structure of the plumbing system of the volcano feeding such persistent active lava lake and the mechanisms controlling the architecture of magma storage remain unclear here we combine high resolution satellite optical imagery and radar interferometry insar to infer the shape location and orientation of the conduits feeding the 2017 erta ale eruption we show that the lava lake was rooted in a vertical dike shaped reservoir that had been inflating prior to the eruption the magma was subsequently transferred into a shallower feeder dike we also find a shallow horizontal magma lens elongated along axis inflating beneath the volcano during the later period of the eruption edifice stress modeling suggests the hydraulically connected system of horizontal and vertical thin magmatic bodies able to open and close are arranged spatially according to stresses induced by loading and unloading due to topographic changes our combined approach may provide new constraints on the organization of magma plumbing systems beneath volcanoes in continental and marine settings

estimating source parameters from deformation data with an application to the march 1997 earthquake swarm off the izu peninsula japan we have applied two monte carlo optimization techniques simulated annealing and random cost to the inversion of deformation data for fault and magma chamber geometry these techniques involve an element of randomness that permits them to escape local minima and ultimately converge to the global minimum of misfit space we have tested the monte carlo algorithms on two synthetic data sets we have also compared them to one another in terms of their efficiency and reliability we have applied the bootstrap method to estimate confidence intervals for the source parameters including the correlations inherent in the data additionally we present methods that use the information from the bootstrapping procedure to visualize the correlations between the different model parameters we have applied these techniques to gps tilt and leveling data from the march 1997 earthquake swarm off of the izu peninsula japan using the two monte carlo algorithms we have inferred two sources a dike and a fault that fit the deformation data and the patterns of seismicity and that are consistent with the regional stress field

investigating the p wave velocity structure beneath harrat lunayyir northwestern saudi arabia using double difference tomography and earthquakes from the 2009 seismic swarm 1 in 2009 a swarm of more than 30 000 earthquakes occurred beneath the harrat lunayyir lava field in northwest saudi arabia this event was just one of several seismic swarms to occur in this region over the past decade surface deformation associated with the seismicity modeled in previous studies using interferometric synthetic aperture radar insar data is best attributed to the intrusion of a 10 km long dyke however little is known about the velocity structure beneath harrat lunayyir making assessment of future seismic and volcanic hazards difficult in this study we use local double difference tomography to generate a p wave velocity model beneath harrat lunayyir and to more precisely locate earthquakes from the 2009 seismic swarm a pronounced fast velocity anomaly centered at 15 km depth with a shallower extension to the n nw is interpreted as an area of repeated magmatic intrusion the crust surrounding the fast intrusion is slower than that suggested by broader scale models for the arabian shield the largest magnitude events occurred early in the swarm concentrated at shallow depths 2 8 km beneath northern harrat lunayyir and these events are associated with the dyke intrusion later deep earthquakes 15 km beneath the southern end of the study region as well as a group of intermediate depth events connecting the shallow and deep regions of seismicity occurred these later events likely represent responses to the local stress conditions following the intrusion our results are unique since harrat magma systems are rarely imaged and our observations coupled with the seismic history in this region suggest that future volcanic intrusions beneath harrat lunayyir are likely

comparison of deep ocean finescale shear at two sites along the mid atlantic ridge abstract four drifting floats were used to measure the magnitude of the vertical derivative of horizontal velocity in waters above the rough bathymetry of the mid atlantic ridge this derivative is typically the dominant component of the velocity gradient the shear two floats were at the site of the brazil basin tracer release experiment bbtre in the south atlantic and two were near the site of the guiana abyssal gyre experiment gage in the north atlantic floats operated for 1 year except for one bbtre float which operated for 100 days shear was measured over a vertical span of 9 5 m using drag elements that caused the floats to rotate slowly in response to shear for each float the first second and fourth moments of shear were elevated above levels associated with the garrett munk model internal wave spectrum three of the four floats were tracked as they moved over mountainous terrain allowing shear intensity to be measured as a function of height above the bottom a deep bbtre float showed enhancement of rms shear near the bottom floats at both areas provided measurements at 2000 m above the bottom with differing results the gage site had a lower fourth moment of shear diapycnal diffusivity proxy than the bbtre site however application of normalization factors accounting for differences between the sites in bottom roughness latitude dependent internal wave dynamics and tidal current speeds brings the results into agreement

the effect of localized mixing on the ocean circulation and time dependent climate change observations indicate that intense mixing in the ocean is localized above complex topography and near the boundaries model experiments presented here illustrate that accounting for this fact can be important in particular it is found that in the case of localized mixing the rate of overturning circulation is proportional to the net rate of generation of potential energy by the vertical mixing linked to the net downward heat diffusion rather than to the value of the mean vertical diffusivity coefficient furthermore it is shown that two climate models having the same vertical profile of diffusivity but differing in their distribution horizontally uniform versus topography boundary intensified can simulate significantly different meridional oceanic circulations vertical heat transfers and responses of simulated climate to atmospheric co2 increase this is found for relatively large o 1 0 cm 2 s 1 horizontal mean values of vertical diffusivity in the pycnocline however in cases of relatively small o 0 1 cm 2 s 1 mean diffusivity in the pycnocline the simulated integral quantities such as meridional mass and heat transports do not depend much on the details of the mixing distribution even so it is found that the deep western boundary currents are more localized near the boundaries in the case of topography boundary intensified mixing also the stratification in the deep ocean is set through the localized regions of intense vertical mixing in addition it is shown that reconciling the observed basin mean values of diffusivity in the abyssal ocean of o 10 cm 2 s 1 with realistic stratification can be problematic unless the regions of enhanced vertical mixing are localized

september 2005 manda hararo dabbahu rifting event afar ethiopia constraints provided by geodetic data faults the volume of the 2005 dike 1 5 2 0 km 3 is not balanced by sufficient volume loss at dabbahu and gabho volcanoes 0 42 and 0 12 km 3 respectively taking into account the deflation of a suspected deep midsegment magma chamber simultaneously to dike intrusion produces a smoother opening distribution along the southern segment above the dike faults slipped by an average 3 m yielding an estimated geodetic moment of 3 5 10 19 nm one order of magnitude larger than the cumulative seismic moment released during the earthquake swarm between dabbahu and ado ale volcanic complexes significant opening occurred on the western side of the dike the anomalous location of the dike at this latitude offset to the east of the axial depression may explain this phenomenon a two stage intrusion scenario is proposed whereby rifting in the northern manda hararo rift was triggered by magma upwelling in the dabbahu area at the northern extremity of the magmatic segment although vigorous dike injection occurred during the september 2005 event the tectonic stress deficit since the previous rifting episode was not fully released leading to further intrusions in 2006 2009

dike induced faulting in rift zones of iceland and afar geodetic data and field observations demonstrate that the emplacement of dikes in volcanic rift zones frequently generates normal faulting and graben subsidence at the earth9s surface elastic modeling of the vertical ground surface displacements above dikes and faults indicates that the extent of graben subsidence can be achieved only if fault slip extends virtually to or beyond the dike plane at depth a mechanical model that includes dikes and frictional faults shows that dike opening tends to compress and lock faults located to either side of the dike therefore slip extending into or beyond the dike cavity must occur either 1 on faults that intersect the dike near its top above the zone of dike induced compression or 2 on faults that slip ahead of the dike as it propagates laterally data from iceland indicate that slip occurred on deep faults that presumably slipped in advance of the laterally propagating dike

long period seismicity in the shallow volcanic edifice formed from slow rupture earthquakes volcanic eruptions are often preceded by long period seismic events that were thought to be generated by the resonance of cracks filled with magmatic fluid analysis and modelling of long period seismicity at volcanoes in italy costa rica and peru shows that it could instead be caused by slow rupture along faults in the upper volcanic edifice

length and timescales of rift faulting and magma intrusion the afar rifting cycle from 2005 to present although fault and magmatic processes have achieved plate spreading at mid ocean ridges throughout earth s history discrete rifting episodes have rarely been observed this paper synthesizes ongoing seismic structural space based geodetic and petrologic studies from the subaerial red sea rift in ethiopia where a major rifting episode commenced in september 2005 our aims are to determine the length and timescales of magmatism and faulting the partitioning of strain between faulting and magmatism and their implications for the maintenance of along axis segmentation most of the magma for the initial and subsequent 12 intrusions was sourced from the center of the dabbahu manda hararo rift segment strain is accommodated primarily by axial dike intrusions fed from mid segment magma chamber s these findings show that episodic approximate century interval rapid opening of discrete rift segments is the primary mechanism of plate boundary deformation the scale 65 km 8 km and intensity of crustal

inferences and observations of turbulent dissipation and mixing in the upper ocean at the hawaiian ridge abstract the hawaiian ridge is one of the most energetic generators of internal tides in the pelagic ocean the density and current structure of the upper ocean at the hawaiian ridge were observed using seasoar and doppler sonar during a survey extending from oahu to brooks banks and up to 200 km from the ridge peak survey observations are used to quantify spatial changes in internal wave induced turbulent dissipation and mixing the turbulent dissipation rate of kinetic energy e and diapycnal eddy diffusivity k are inferred from an established parameterization using internal wave shear as input at the kauai channel kc and french frigate shoals brooks banks sites e and k decay away from the ridge with maxima exceeding minima by 5 times at both sites average k is everywhere greater than the canonical open ocean value of 10 5 m2 s 1 along the ridge e and k vary by up to 100 times and are largest at sites of largest numerical model internal tide energy density in the eastern kc k 10 3 m2 s

modelling of surface stresses and fracturing during dyke emplacement application to the 2009 episode at harrat lunayyir saudi arabia abstract correct interpretation of surface stresses and deformation or displacement during volcanotectonic episodes is of fundamental importance for hazard assessment and dyke path forecasting here we present new general numerical models on the local stresses induced by arrested dykes in the models the crustal segments hosting the dyke vary greatly in mechanical properties from uniform or non layered elastic half spaces to highly anisotropic layers with strong contrast in young s modulus the shallow parts of active volcanoes and volcanic zones are normally highly anisotropic and some with open contacts the numerical results show that for a given surface deformation non layered half space models underestimate the dyke overpressure thickness needed and overestimate the likely depth to the tip of the dyke also as the mechanical contrast between the layers increases so does the stress dissipation and associated reduction in surface stresses and associated fracturing in the absence of open contacts the distance between the two dyke induced tensile and shear stress peaks and fractures if any at the surface is roughly twice the depth to the tip of the dyke the width of a graben if it forms should therefore be roughly twice the depth to the tip of the associated arrested dyke when applied to the 2009 episode at harrat lunayyir the main results are as follows the entire 3 7 km wide fracture zone graben formed during the episode is far too wide to have been generated by induced stresses of a single arrested dyke the eastern part of the zone graben may have been generated by the inferred arrested dyke but the western zone primarily by regional extensional loading the dyke tip was arrested at only a few hundred metres below the surface the estimated thickness of the uppermost part of the dyke being between about 6 and 12 m for the inferred dyke length strike dimension of about 14 km this yields a dyke length thickness ratio between 2400 and 1200 similar to commonly measured ratios of regional dykes in the field

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

dyke emplacement in fractured media application to the 2000 intrusion at izu islands japan summary we use a boundary element approach to study the problem of a large magma filled dyke embedded in a fractured damaged medium the numerical simulations show that the dyke opening and the crack extension force at the dyke tip increases with increasing fracture density we show that this behaviour can at moderate fracture densities be predicted by an effective media model simple analytical formulae are given for the increasing average opening of the dyke and the decreasing fracture toughness as functions of increasing fracture density the numerical and the theoretical results are found to be in good agreement in a first application we tested the model by using gps deformation and seismicity data from a recent lateral magma intrusion in izu islands japan this shows that a simple comparison of the distance change and the cumulative earthquake number enables the study of the stability of the dyke intrusion the method seems to distinguish whether the dyke opening is actively driven by magma influx or passively driven by an expansion due to fracturing

vertical diffusivity of the western arctic ocean halocline a nearly year long series of upper ocean temperature conductivity and temperature microstructure profiles were collected from an ice camp drifting in the beaufort gyre as part of the 1997 1998 surface heat budget of the arctic experiment sheba geographically the record includes portions over the deep canada basin and the steep bathymetry of the chukchi borderlands region hydrographically the record includes cool pacific origin haloclines which contain a variety of subsurface temperature maxima and cold haloclines typical of the eurasian basins we present estimates of the vertical turbulent diffusivity derived from the dissipation rate of thermal variance and calculations of the associated vertical heat fluxes we find that vertical diffusion proceeds at molecular rates in the deep basins and away from topographic features while still relatively small diffusivity is enhanced by 1 order of magnitude near and above the chukchi borderlands the enhanced diffusivity is correlated to an increase in water column strain variance above the borderlands providing a linkage between bathymetry internal wave activity and turbulence the chukchi borderlands play a significant role in heat transport in the western arctic they are a pathway for horizontal heat transport and a hot spot for vertical heat transport vertical fluxes make a substantial contribution to the energy balance of the sea ice cover in this region heat fluxes between the halocline and underlying atlantic water are shown to be small and lacking vertical connection near surface waters

stress changes focal mechanisms and earthquake scaling laws for the 2000 dike at miyakejima japan faulting processes in volcanic areas result from a complex interaction of pressurized fluid filled cracks and conduits with the host rock and local and regional tectonic setting often volcanic seismicity is difficult to decipher in terms of the physical processes involved and there is a need for models relating the mechanics of volcanic sources to observations here we use focal mechanism data of the energetic swarm induced by the 2000 dike intrusion at miyakejima izu archipelago japan to study the relation between the 3 d dike induced stresses and the characteristics of the seismicity we perform a clustering analysis on the focal mechanism fm solutions and relate them to the dike stress field and to the scaling relationships of the earthquakes we find that the strike and rake angles of the fms are strongly correlated and cluster on bands in a strike rake plot we suggest that this is consistent with optimally oriented faults according to the expected pattern of coulomb stress changes we calculate the frequency size distribution of the clustered sets finding that focal mechanisms with a large strike slip component are consistent with the gutenberg richter relation with a b value of about 1 conversely events with large normal faulting components deviate from the gutenberg richter distribution with a marked roll off on its right hand tail suggesting a lack of large magnitude events mw 5 5 this may result from the interplay of the limited thickness and lower rock strength of the layer of rock above the dike where normal faulting is expected and lower stress levels linked to the faulting style and low confining pressure

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

subsurface imaging of the harrat lunayyir 2007 2009 earthquake swarm zone western saudi arabia using potential field methods abstract the harrat lunayyir hl 2007 2009 earthquake swarm has attracted much scientific interest mainly due to its occurrence within the large igneous province lip of saudi arabia qualitative interpretation of aeromagnetic anomalies is suggestive of linear dike like anomalies striking nw se across the earthquake swarm zone esz residual bouguer anomaly data for hl range between 4 3 and 1 5 mgal and show a 20 km wide gravity low flanked by lateral gravity highs the axial zone of low gravity corresponds to the esz cluster employing a three dimensional 3d inversion of the residual gravity field with a one dimensional 1d p wave velocity model as a proxy for background density variations with depth we imaged a mid to upper crustal low density zone 10 km depth we interpret this zone as the source area of ascending magma that intruded into the upper crust underlying the hl during the 2009 seismic crisis the inversion also highlights lower than average density rocks beneath the western parts of the hl whereas its eastern part is composed of rocks of higher density the 3d magnetic inversions lead us to infer magmatic intrusion of lower magnetic susceptibility at this locality extending vertically from 1 57 km altitude above sea level to its bottom edge at 10 8 km depth below sea level based on these results the 2007 2009 esz is likely associated with rift related extension associated with the red sea spreading where a trans crustal magmatic plumbing system extends to depths of about 10 km beneath the centre of hl

conditions for the arrest of a vertical propagating dyke magma ascent towards the earth s surface occurs through dyke propagation in the vast majority of cases we investigate two purely mechanical effects unrelated to cooling or solidification that lead to the arrest of propagation so that no eruption occurs the first is that the input of magma from the source is not maintained continuously such that a fixed volume of magma is released laboratory experiments show that in this case the dyke stops at a finite distance from the source this behaviour is specific to the fracturing process in 3 d we derive a relationship for the minimum magma volume required for an eruption as a function of magma buoyancy and source depth when large magma volumes are available eruption may also be prevented by a thick low density layer in the upper crust numerical studies of dyke propagation show that the dyke continues to rise even though it is negatively buoyant magma accumulates in a swollen nose region at the interface between the low density layer and the dense basement magma overpressure is largest at this interface and increases with increasing penetration into the upper layer it may become large enough to induce horizontal fractures in the dyke walls and lateral intrusion of a sill which prevents eruption this requires that the thickness of the low density layer exceeds a threshold value that depends on the density contrast between magma and host rock if the magma volume is smaller than a threshold value neither sill intrusion nor eruption are possible and magma gets stored in a horizontal blade shaped dyke straddling the interface scaling laws for variations of ascent rate and for the minimum magma volume allow diagnosis of a failed eruption

fault slip distribution of the 1999 mw 7 1 hector mine california earthquake estimated from satellite radar and gps measurements we use a combination of satellite radar and gps data to estimate the slip distribution of the 1999 m w 7 1 hector mine earthquake a right lateral strikeslip earthquake that occurred on a northwest southeast striking fault in the southern california mojave desert the data include synthetic aperture radar interferograms insar from both ascending and descending orbits radar amplitude image offset fields sario for both ascending and descending azimuth directions and campaign gps observations from 55 stations provided by agnew et al 2002 we model the fault with nine segments derived from the field mapped fault rupture the sario data and aftershock locations we first estimate the dip of each fault segment as well as a single constant strike slip component across each segment resulting in an average dip of 83 to the northeast and slip of up to 5 6 m then we fix the optimal fault segment dip discretize the fault segments into 1 5 km 1 5 km patches and solve for the variable slip distribution using a nonnegative least squares method that includes an appropriate degree of smoothing our preferred solution has both right lateral strike slip and reverse faulting the estimated geodetic moment is 5 93 10 19 n m m w 7 1 similar to seismological estimates indicating that there are insignificant interseismic and postseismic deformation signals in the data we find strike slip displacements of up to 6 0 m and reverse faulting of up to 1 6 m with the maximum slip located just northwest of the epicenter most of the slip is concentrated northwest and south of the epicenter little slip is found on the northeastern branch of the fault the sario data and our modeling indicate that the amount and extent of surface fault rupture were underestimated in the field

dike induced stresses and displacements in layered volcanic zones abstract during a volcanic unrest period with dike injection one of the main scientific tasks is to assess the geometry and the propagation path of the dike and in particular the likelihood of the dike reaching the surface to erupt currently the dike path and geometry including depth and opening aperture are both partly determined from geodetic surface data using mostly dislocation models that assume the volcanic zone volcano to be an elastic half space of uniform mechanical properties by contrast field observations of volcanic zones volcanoes active and extinct show that they are composed of numerous layers whose mechanical properties primarily young s modulus vary widely and whose contacts commonly arrest dikes here we provide field observations and numerical models on the effects of a typical variation in young s modulus in an active volcanic zone on the internal and surface stresses and displacements induced by a dike whose tip is arrested at 0 5 km depth below the surface of the volcanic zone above the layer or unit hosting the dike are four layers of equal thickness we vary the young s modulus or stiffness of the fourth layer the one adjacent to the layer or unit hosting the dike from 10 gpa to 0 01 gpa while all the other layers units maintain their young s moduli in the model runs the results show that as the fourth layer becomes more compliant or soft 0 1 0 01 gpa dike induced stresses and displacements lateral and vertical above the layer including those at the surface become suppressed but the stresses and displacements of the layer unit hosting the dike increase and their peaks do not coincide in location or magnitude with those of the other layers thus the dike induced internal deformation of the volcanic zone increases as the fourth layer becomes softer also the tensile and shear stress peaks at the surface occur at locations widely different from those of maximum surface uplift more specifically for a comparatively stiff fourth layer 1 10 gpa the surface tensile and shear stresses peak at lateral distances of 0 5 0 7 km from the projection of the dike to the surface essentially no tensile shear stresses reach the surface when the fourth layer is as soft as 0 1 0 01 gpa so that there are no stress peaks by contrast the maximum surface displacements uplift peak at lateral distances of 2 8 3 3 km from the dike projection to the surface if tension fractures or faults in particular the boundary faults of a graben are induced by the dike they should form at the tensile shear stress peaks and not as is commonly suggested at the location of the surface displacement peaks our results thus suggest that any dike induced graben is likely to be of a width about twice the depth to the tip top of the arrested dike the results demonstrate that elastic half space models overestimate the dike induced surface stresses and thus the depth to the tip top of the associated dike in particular the models presented here indicate that for typical dikes little or no dike induced surface deformation would be expected until the dike tip propagates to depths below the surface of less than a kilometre

on the mechanisms governing dike arrest insight from the 2000 miyakejima dike injection abstract magma stored beneath volcanoes is sometimes transported out of the magma chambers by means of laterally propagating dikes which can lead to fissure eruptions if they intersect the earth s surface the driving force for lateral dike propagation can be a lateral tectonic stress gradient the stress gradient due to the topographic loads the overpressure of the magma chamber or a combination of those forces the 2000 dike intrusion at miyakejima volcano izu arc japan propagated laterally for about 30 km and stopped in correspondence of a strike slip system sub perpendicular to the dike plane then the dike continued to inflate without further propagation abundant seismicity was produced including five m 6 earthquakes one of which occurred on the pre existing fault system close to the tip of the dike at approximately the time of arrest it has been proposed that the main cause for the dike arrest was the fault induced stress here we use a boundary element numerical approach to study the interplay between a propagating dike and a pre stressed strike slip fault and check the relative role played by dike fault interaction and topographic loading in arresting the miyakejima dike we calibrate the model parameters according to previous estimates of dike opening and fault displacement based on crustal deformation observations by computing the energy released during the propagation our model indicates whether the dike will stop at a given location we find that the stress gradient induced by the topography is needed for an opening distribution along the dike consistent with the observed seismicity but it cannot explain its arrest at the prescribed location on the other hand the interaction of dike with the fault explains the arrest but not the opening distribution the joint effect of the topographic load and the stress interaction with strike slip fault is consistent with the observations provided the pre existing fault system is pre loaded with a significant stress released gradually during the dike fault interplay our results reveal how the mechanical interaction between dikes and faults may affect the propagation of magmatic intrusions in general this has implications for our understanding of the geometrical arrangement of rift segments and transform faults in mid ocean ridges and for the interplay between dikes and dike induced graben systems

imaging the dynamics of magma propagation using radiated seismic intensity 1 at shallow depth beneath the earth s surface magma propagates through strongly heterogeneous volcanic material inversion of buoyancy and or solidification have strong impacts on the dynamics of propagation without any change of magma supply in this paper we study the spatial and time evolution of magma intrusions using induced seismicity we propose a new method based on ratio analysis of estimates of radiated seismic intensities recorded at different stations during seismic swarms by applying this method to the january 2010 piton de la fournaise volcano eruption we image complex dike propagation dynamics which strongly differ from a model of constant velocity dike propagation we provide a new method to image in real time the dynamics of dike propagation and to infer the position of eruptive fissures

global abyssal mixing inferred from lowered adcp shear and ctd strain profiles abstract internal wave wave interaction theories and observations support a parameterization for the turbulent dissipation rate e and eddy diffusivity k that depends on internal wave shear vz2 and strain z2 variances its latest incarnation is applied to about 3500 lowered adcp ctd profiles from the indian pacific north atlantic and southern oceans inferred diffusivities k are functions of latitude and depth ranging from 0 03 10 4 m2 s 1 within 2 of the equator to 0 4 0 5 10 4 m2 s 1 at 50 70 diffusivities k also increase with depth in tropical and subtropical waters diffusivities below 4500 m depth exhibit a peak of 0 7 10 4 m2 s 1 between 20 and 30 latitudes where semidiurnal parametric subharmonic instability is expected to be active turbulence is highly heterogeneous though the bulk of the vertically integrated dissipation e is contributed from the main pycnocline hotspots in e show some correlation with small scale bottom roughness and near bottom flow at sites where st

strain accommodation by slow slip and dyking in a youthful continental rift east africa continental rifts begin and develop through repeated episodes of faulting and magmatism but strain partitioning between faulting and magmatism during discrete rifting episodes remains poorly documented in highly evolved rifts tensile stresses from far field plate motions accumulate over decades before being released during relatively short time intervals by faulting and magmatic intrusions1 2 3 these rifting crises are rarely observed in thick lithosphere during the initial stages of rifting here we show that most of the strain during the july august 2007 seismic crisis in the weakly extended natron rift tanzania was released aseismically deformation was achieved by slow slip on a normal fault that promoted subsequent dyke intrusion by stress unclamping this event provides compelling evidence for strain accommodation by magma intrusion in addition to slip along normal faults during the initial stages of continental rifting and before significant crustal thinning

graben formation and dike arrest during the 2009 harrat lunayyir dike intrusion in saudi arabia insights from insar stress calculations and analog experiments

a nonplanar slow rupture episode during the 2000 miyakejima dike intrusion magmatic intrusions release extensional strain in the earth s crust upon availability of magma intrusions are typically accompanied by earthquake swarms and by surface faulting that is often larger than what is expected from the magnitude of the induced earthquakes the 2000 miyakejima dike intrusion triggered the largest volcanic earthquake swarm monitored so far with five ml 6 earthquakes we analyze the seismicity and deformation induced by the miyakejima dike with the aim of constraining the timescale and mechanisms of slow strain release during the episode in six earthquake bursts lasting few hours and migrating at 1 km h 1 we find candidates for slow earthquakes each burst nucleated at the tips of previous bursts suggesting stress interaction the variability of fault plane solutions indicates that the bursts occurred on a complex system of fractures consistent with weakly consolidated surface layers strained by spatially inhomogneous stresses that change in time such as those induced by a dike based on dislocation models we find that deformation is best explained by aseismic slip in addition to the seismic burst with a moment 1 3 to 2 3 times larger than the earthquakes seismic moment and opening of 0 20 0 07 m on the dike the aseismic slip occurred over a few hours with moment duration and migration velocity consistent with that of previously observed slow slip events we argue that the seismic bursts are likely driven by slow slip sharing most properties with tectonic slow slip events and swarms but occurring on a set of nonaligned faults

form and growth of an embryonic continental rift insar observations and modelling of the 2009 western arabia rifting episode summary a magma driven rifting episode occurred at the harrat lunayyir harrat al shaqa volcanic field western arabia between 2009 april and july it was accompanied by a swarm of more than 4000 m 2 earthquakes the largest ever documented in that region with a peak mw 5 7 shock on may 19 we combine interferometric synthetic aperture radar insar measurements and elastic modelling with seismic moment calculations to resolve the evolution of surface deformation associated with this event phase discontinuities and low coherence lineaments are used to infer the location of the main active structures during the various deformation stages and descending track interferograms that span the entire period are inverted to resolve the slip and opening distributions along two graben bounding normal faults and a dyke respectively assuming negligible rift parallel displacements we combine ascending and descending track interferograms to derive the vertical and rift perpendicular deformation which add up to a maximum surface extension of 1 5 m across the rift and subsidence of 0 8 m the far field deformation is dominated by the dyke opening whereas the near field displacements are mostly associated with movements along the faults the cumulative seismic moment released during the entire swarm period accounts for about 14 per cent of the total geodetic moment compared to about 55 per cent at the 2007 gelai tanzania and about 8 per cent at the 2005 manda hararo dabbahu afar events we propose that the differences in moment partitioning ratios are due to the different crustal and seismogenic layer thicknesses in the three regions and represent different stages in the evolution of a volcanic rift the gelai event represents the most juvenile stage of rifting the dabbahu event represents the most evolved and the harrat lunayyir event represents a rift that is intermediate between the two in its degree of maturity

determination of diapycnal diffusion rates in the upper thermocline in the north atlantic ocean using sulfur hexafluoride 1 the apparent diapycnal diffusivity below the wind driven surface mixed layer of the ocean was determined in an anticyclonic eddy in the eastern north atlantic using sulfur hexafluoride sf6 tracer data collected in june 1998 in this tracer experiment the downward penetration of sf6 was measured for 3 weeks following the deliberate injection of sf6 in the surface mixed layer the resulting data were used to constrain the one dimensional fickian diffusion model to estimate the diapycnal diffusivity the model also includes the lateral diffusion component so that it can more accurately represent the time evolution of the sf6 concentrations along the isopycnal surface this affects the estimation of the diapycnal diffusivity for the upper thermocline immediately below the surface mixed layer we estimated the diapycnal diffusivity for the 3 week period as 0 3 0 2 cm2 s 1 at a buoyancy frequency of 8 2 cph

structural cause of a missed eruption in the harrat lunayyir basaltic field saudi arabia in 2009 harrat lunayyir is one of the most volcanically active recent basaltic fields in western saudi arabia a period of substantial seismic unrest featuring more than 30 000 local events occurred in harrat lunayyir in april june 2009 although this crisis was presumably related to ongoing magma activity it ended without any surface volcanic activity we create new tomographic models of p and s velocities v p and v s and use them to explain the causes of this unrest and the reasons the eruption failed a large seismic anomaly of high v p v s ratio below 7 km depth coincides with the locations of more than 50 recent cinder cones with ages of older than 100 ka and is interpreted as a steady state magma reservoir we also identify another seismic anomaly at depths below 15 km which is interpreted as a conduit for fluids and melts from deeper sources because the location of this conduit is slightly outside the main reservoir some of the incoming material was dispersed as a result the activation of the crustal reservoir was not sufficiently strong to pierce the rigid basaltic cover and cause an actual eruption dur ing the crisis in 2009

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

interaction of ascending magma with pre existing crustal fractures in monogenetic basaltic volcanism an experimental approach 1 magma transport through dikes is a major component of the development of monogenetic volcanic fields these volcanic fields are characterized by numerous volcanic centers each typically resulting from a single eruption therefore magma must be transported from source to surface at different places which raises the question of the relative importance of 1 the self propagation of magma through pristine rock and 2 the control exerted by pre existing fractures to address this issue we have carried out a series of analogue experiments to constrain the interaction of a propagating dike through a medium with pre existing fractures the experiments involved the injection of air into an elastic gelatin solid which was previously cut into its upper part to simulate pre existing fractures the volume of the dikes their distance from the fractures and the ambient stress field were systematically varied to assess their influence on potential dike fracture interactions the results show that distance and angle between dikes and fractures influence these interactions and the dike trajectory dike geometry and dynamics are also affected by both the presence of the fractures and the dike volume dikes propagating in between fractures tend to decelerate in nature interactions are expected for dikes and fractures separated by less than about 200m and dikes with a volume less than about 10 2 km 3 would experience a velocity decrease these results highlight the influence of pre existing fractures on the mechanics and dynamics of dikes these heterogeneities must be considered when studying the transport of magmas within the crust

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

geodetic constraints on present day motion of the arabian plate implications for red sea and gulf of aden rifting 1 five years of continuously recording gps observations in the kingdom of saudi arabia together with new continuous and survey mode gps observations broadly distributed across the arabian peninsula provide the basis for substantially improved estimates of present day motion and internal deformation of the arabian plate we derive the following relative geodetic euler vectors latitude n longitude e rate myr counterclockwise for arabia nubia 31 7 0 2 24 6 0 3 0 37 0 01 arabia somalia 22 0 0 5 26 2 0 5 0 40 0 01 arabia india 18 0 3 8 87 6 3 3 0 07 0 01 arabia sinai 35 7 0 8 17 1 5 0 0 15 0 04 and arabia eurasia 27 5 0 1 17 6 0 3 0 404 0 004 we use these euler vectors to estimate present day stability of the arabian plate the rate and direction of extension across the red sea and gulf of aden and slip rates along the southern dead sea fault south of the lebanon restraining bend 4 5 4 7 0 2 mm yr left lateral 0 8 1 1 0 3 mm yr extension and the owens fracture zone 3 2 2 5 0 5 mm yr right lateral increasing from north to south 1 2 mm yr extension on a broad scale the arabian plate has no resolvable internal deformation weighted root mean square of residual motions for arabia equals 0 6 mm yr although there is marginally significant evidence for n s shortening in the palmyride mountains syria at 1 5 mm yr we show that present day arabia plate motion with respect to eurasia is consistent within uncertainties i e 10 with plate tectonic estimates since the early miocene when arabia separated from nubia we estimate the time of red sea and gulf of aden rifting from present day arabia motion plate tectonic evidence for a 70 increase in arabia nubia relative motion at 13 ma and the width of the red sea and gulf of aden and find that rifting initiated roughly simultaneously 2 2 myr along the strike of the red sea from the gulf of suez to the afar triple junction as well as along the west gulf of aden at 24 2 2 ma based on the present kinematics we hypothesize that the negative buoyancy of the subducted ocean lithosphere beneath the makran and the zagros fold thrust belt is the principle driver of arabia eurasia convergence and that resisting forces associated with arabia eurasia continental collision have had little impact on plate motion

dike induced contraction along oceanic and continental divergent plate boundaries the axis of divergent plate boundaries shows extension fractures and normal faults at the surface here we present evidence of contraction along the axis of the oceanic ridge of iceland and the continental main ethiopian rift contraction is found at the base of the tilted hanging wall of dilational normal faults balancing part of their extension our experiments suggest that these structures result from dike emplacement multiple dike injection induces subsidence above and uplift to the sides of the dikes the transition in between is accommodated by reverse faults and subsequent peripheral inward dipping normal faults our results suggest that contraction is a direct product of magma emplacement along divergent plate boundaries at various scales marking a precise evolutionary stage and initiating part of the extensional structures extension fractures and normal faults

imaging ruptured lithosphere beneath the red sea and arabian peninsula abstract the red sea rift an archetype of a newly formed ocean basin is an ideal environment in which to study the controversial processes associated with continental rifting different models have been proposed to explain how rifting in the red sea evolved however accurate constraints on lithospheric structure have not been available to discriminate rifting models we use the s wave receiver function technique to produce the first images of the lithosphere asthenosphere boundary lab structure along the red sea and throughout the arabian peninsula lithospheric thickness varies considerably with thin lithosphere centered on the rift axis thickening toward the arabian interior gravity data are well fit by our structural model and indicate that high surface topography along the rift flank is not in isostatic equilibrium requiring dynamic compensation for its support while our derived structure is consistent with active rifting processes previous studies demonstrated that the red sea initiated as a passive rift therefore our results suggest a two stage rifting history where extension and erosion by flow in the underlying asthenosphere are responsible for variations in lab depth lab topography guides asthenospheric flow beneath western arabia and the red sea demonstrating the important role lithospheric variations play in the thermal modification of tectonic environments

sequence of rifting in afar manda hararo rift ethiopia 2005 2009 time space evolution and interactions between dikes from interferometric synthetic aperture radar and static stress change modeling thirteen dike intrusions in the manda hararo rift afar ethiopia from september 2005 to june 2009 studied using an extensive interferometric synthetic aperture radar insar data set provide insight into the mechanics of a major active rift kinematic inversions of insar data reveal that dikes opened by 0 8 3 5 m at an average 5 km depth with volumes of 0 04 0 2 km 3 with up to 12 m opening and a volume greater than 1 km 3 for the september 2005 megadike dikes have their source in a midsegment magma reservoir which induces a local shallowing of the brittle ductile boundary presumably due to thermal weakening of the lithosphere the smaller dikes in 2006 2009 were emplaced in regions of minimum opening of the september 2005 megadike above the central magma reservoir in contrast the most voluminous dike intrusions in 2006 2009 occurred near the locus of the peak of maximum opening of the september 2005 megadike 10 km north of the magma source this may suggest that tension on the plate boundary was highest there both prior to 2005 and possibly also after 2005 evolution and distribution of normal stress on the plate boundary throughout the rifting episode may indicate that tension near to the magma reservoir is lower than toward segment ends average relief of normal stresses of tectonic origin coeval to dike intrusions is comparable with shear stress drops for earthquakes presumably because dikes in the manda hararo rift are intruded at low magma pressure and high tectonic stress time space evolution and interactions between dikes from interferometric synthetic aperture radar and static stress change modeling

radar interferogram filtering for geophysical applications the use of sar interferometry is often impeded by decorrelation from thermal noise temporal change and baseline geometry power spectra of interferograms are typically the sum of a narrow band component combined with broad band noise we describe a new adaptive filtering algorithm that dramatically lowers phase noise improving both measurement accuracy and phase unwrapping while demonstrating graceful degradation in regions of pure noise the performance of the filter is demonstrated with sar data from the ers satellites over the jakobshavns glacier of greenland

the madinah eruption saudi arabia magma mixing and simultaneous extrusion of three basaltic chemical types during a 52 day eruption in 1256 a d 0 5 km3 of alkali olivine basalt was extruded from a 2 25 km long fissure at the north end of the harrat rahat lava field saudi arabia the eruption produced 6 scoria cones and a lava flow 23 km long that approached the ancient and holy city of madinah to within 8 km three chemical types of basalt are defined by data point clusters on variation diagrams i e the low k high k and hybrid types all three erupted simultaneously their distribution is delineated in both scoria cones and lava flow units from detailed mapping and a petrochemical study of 135 samples six flow units defined by distinct flow fronts represent extrusive pulses the high k type erupted during all six pulses the low k type during the first three and the hybrid type during the first two

kinematic analysis of vertical collapse on volcanoes using experimental models time series 1 volcanoes are often associated with vertical collapse due to deeper magma withdrawal calderas are the most notable type of vertical collapse on the summit of volcanoes caldera collapse has been observed and monitored only at miyakejima japan 2000 dolomieu reunion 2007 and fernandina galapagos 1968 highlighting our limited knowledge on its kinematic behavior here we use experimental models to investigate the kinematic evolution of calderas and vertical collapses in general we extract velocity and strain fields using the particle image velocimetry piv technique generating time series experimental vertical collapses undergoing constant subsidence velocity show three main kinematic behaviors 1 continuous collapse whose velocity is similar to the source subsidence velocity 2 incremental collapse with episodic stepwise accelerations along pre existing ring structures 3 sudden collapse resulting from the upward migration of a cavity only for t d 2 t and d are the depth and width of the magma chamber respectively and without ring structures the velocity in the collapsing column may increase up to four orders of magnitude with regard to the constant subsidence velocity of the source comparison to nature suggests that 1 there are close kinematic similarities with monitored collapse calderas explaining their incremental subsidence after the development of ring structures 2 sudden pit crater formation is induced by the upward propagation of cavities due to magma removal at depth and in absence of ring structures 3 all these types of vertical collapses have a consistent mechanism of formation and kinematic behavior function of t d and the presence absence of ring structures

surface deformation and shallow dike intrusion processes at inyo craters long valley california the inyo craters are the two largest of four phreatic craters that lie within a 2 5 km long 500 to 700 m wide n s trend of faults and fissures at the south end of the inyo volcanic chain in eastern california the alignment of these features with dike fed silicic volcanic centers of the same age a few kilometers to the north suggests that they were produced during intrusion of a dike at about 650 550 yr b p e w extension south of south inyo crater is ten to several tens of meters suggesting that the dike is at least that thick to understand how the faults and fissures developed we mapped and studied the fault and fissure pattern used a theoretical boundary element model to determine the surface strain profile above a shallow dike in a purely elastic medium and conducted physical model experiments of fault and fissure growth results of the field studies and experiments indicate that deformation develops according to the following sequence 1 extension fractures and perhaps other inelastic deformation develop immediately above the dike top and on the limbs of a shallow syncline which forms above the dike 2 fissures form along two parallel trends at the surface on opposite sides of the dike plane leaving a relatively unfractured region in between 3 dip slip movement on subsurface fractures and linkage of these fractures with surface fissures produces inward facing normal fault scarps that bound a nested graben above the dike experimental graben widths are up to several times narrower than predicted from the locations of theoretical strain maxima above a dilating crack in a linearly elastic medium this fact is apparently due to the growth of a zone of inelastic deformation above the experimental dike top in the subsurface if the ratio between the depth to the dike top and the distance between the outermost surface fissures at inyo craters is within the range of ratios measured experimentally then the depth to the dike top is between 250 m and several times that a slant hole drilled in the summer of 1987 by the department of energy office of basic energy sciences intersected three breccia bodies of possibly intrusive origin directly below the center of south inyo crater between 550 m and 610 m below the crater rim no intact juvenile igneous rock was intersected suggesting that the hole passed above the magma filled dike top perhaps passing through the zone of inelastic deformation which is inferred to exist from our model results

a basinwide estimate of vertical mixing in the upper pycnocline spreading of bomb tritium in the north pacific ocean abstract the vertical diffusivity kv in the upper half kilometer of the north pacific subtropical pycnocline is estimated from observations of the spreading rate of anthropogenic tritium the calculation is based on approximately 300 ocean tritium profiles made since tritium was introduced to the atmosphere via bomb testing in the 1960s the data coverage does not permit detailed mapping of tritium penetration especially in the sparsely sampled western pacific for this reason and to minimize advective effects the spreading rate is averaged within the closed streamlines of the subtropical gyre spanning 5 n to 40 n the result kv 1 5 0 7 10 5 m2 s 1 is consistent with inferences from microstructure and purposefully released tracer measurements in the north atlantic confirming that the spatially averaged rate of mixing in the upper pycnocline is substantially lower than the canonical munk estimate for the lower pycnocline

broad accommodation of rift related extension recorded by dyke intrusion in saudi arabia volcanic fields at the eastern margin of the red sea rift were regarded as seismically quiet until a swarm of 30 000 earthquakes struck in 2009 geological analyses reveal the intrusion of a volcanic dyke and indicate that rift related extension is spread over a broad region far from the rift axis