differentiating flow melt or fossil seismic anisotropy beneath ethiopia ethiopia is a region where continental rifting gives way to oceanic spreading yet the role that pre existing lithospheric structure melt mantle flow or active upwellings may play in this process is debated measurements of seismic anisotropy are often used to attempt to understand the contribution that these mechanisms may play in this study we use new data in afar ethiopia along with legacy data across ethiopia djibouti and yemen to obtain estimates of mantle anisotropy using sks wave splitting we show that two layers of anisotropy exist and we directly invert for these we show that fossil anisotropy with fast directions oriented northeast southwest may be preserved in the lithosphere away from the rift beneath the main ethiopian rift and parts of afar anisotropy due to shear segregated melt along sharp changes in lithospheric thickness dominates the shear wave splitting signal in the mantle beneath afar away from regions with significant lithospheric topography melt pockets associated with the crustal and uppermost mantle magma storage dominate the signal in localized regions in general little anisotropy is seen in the uppermost mantle beneath afar suggesting melt retains no preferential alignment these results show the important role melt plays in weakening the lithosphere and imply that as rifting evolves passive upwelling sustains extension a dominant northeast southwest anisotropic fast direction is observed in a deeper layer across all of ethiopia this suggests that a conduit like plume is lacking beneath afar today rather a broad flow from the southwest dominates flow in the upper mantle

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

correction for the static shift in magnetotellurics using transient electromagnetic soundings shallow inhomogeneities can lead to severe problems in the interpretation of magnetotelluric mt data by shifting the mt apparent resistivity sounding curve by a scale factor which is independent of frequency on the standard log apparent resistivity versus log frequency display the amount of parallel shift commonly referred to as the mt static shift can not be determined directly from conventionally recorded mt data at a single site one method for measuring the static shift is a controlled source measurement of the magnetic field unlike the electric field the magnetic field is relatively unaffected by surface inhomogeneities the controlled source sounding which may be a relatively shallow sounding made with lightweight equipment can be combined with a deep mt sounding to obtain a complete undistorted model of the earth inversions of the static shift corrected mt data provide a much closer match to well log resistivities than do inversions of the uncorrected data the particular controlled source magnetic field sounding which we used was a central induction transient electromagnetic tem sounding correction for the static shift in the mt data was made by jointly inverting the mt data and the tem data a parameter which allowed vertical shifts in the mt apparent resistivity curves was included in the computer inversion to account for static shifts a simple graphical comparison between the mt apparent resistivities and the tem apparent resistivities produced essentially the same estimate of the static shift within 0 1 decade as the joint computer inversion central induction tem measurements were made adjacent to over 100 mt sites in central oregon the complete data base of over 100 sites showed an average static shift between 0 and 0 2 decade however in the rougher topography and more complex structure of the cascade mountain range the majority of the sites had static shifts of the order of 0 3 to 0 4 decade the static shifts in this area are probably due to a combination of topography and surficial inhomogeneities the tem apparent resistivity which is used to estimate the unshifted mt apparent resistivity does not necessarily agree with either the transverse electric te or the transverse magnetic tm mt polarization tem apparent resistivity may occur between the two or may agree with one of the two polarizations or may lie outside the mt polarizations

discovery of a magma chamber and faults beneath a mid atlantic ridge hydrothermal field crust at slow spreading ridges is formed by a combination of magmatic and tectonic processes with magmatic accretion possibly involving short lived crustal magma chambers the reflections of seismic waves from crustal magma chambers have been observed beneath intermediate and fast spreading centres but it has been difficult to image such magma chambers beneath slow spreading centres owing to rough seafloor topography and associated seafloor scattering in the absence of any images of magma chambers or of subsurface near axis faults it has been difficult to characterize the interplay of magmatic and tectonic processes in crustal accretion and hydrothermal circulation at slow spreading ridges here we report the presence of a crustal magma chamber beneath the slow spreading lucky strike segment of the mid atlantic ridge the reflection from the top of the magma chamber centred beneath the lucky strike volcano and hydrothermal field is approximately 3 km beneath the sea floor 3 4 km wide and extends up to 7 km along axis we suggest that this magma chamber provides the heat for the active hydrothermal vent field above it we also observe axial valley bounding faults that seem to penetrate down to the magma chamber depth as well as a set of inward dipping faults cutting through the volcanic edifice suggesting continuous interactions between tectonic and magmatic processes

oceanic propagation of a potential tsunami from the la palma island 1 the likelihood of a large scale tsunami from the la palma island is considered small by most nevertheless the potential catastrophic consequences call for attention here we report on numerical simulations of a tsunami that might result from the extreme case of a flank collapse of the cumbre vieja volcano at the la palma island done by combining a multimaterial model for the wave generation with boussinesq models for the far field propagation our simulations show that the slide speed is close to critical effectively generating an initial wave of several hundred meters height our main focus is the wave propagation which is genuinely dispersive in the far field propagation becomes increasingly complex due to the combined effects of dispersion refraction and interference in the direction of propagation constructive interference of the trailing waves are found to decrease the decay of the maximum amplitude with distance compared to classical asymptotic theory at transatlantic distances thus the commonly used hydrostatic models fail to describe the propagation consequences of the la palma scenario would be largest at the canary islands but our findings also suggests that the whole central atlantic would face grave consequences however the largest surface elevations are smaller than the most pessimistic reports found in literature we also find undular bores towards the shorelines of america

electrical image of passive mantle upwelling beneath the northern east pacific rise sea floor magnetotelluric soundings along a portion of the east pacific rise reveal a symmetric high conductivity triangular region at depths of 20 90 kilometres that is consistent with partial melting of passively upwelling mantle the east pacific rise is a fast spreading mid ocean ridge where sea floor volcanoes and hydrothermal vents result from a robust mantle melt supply to explore how this magma is supplied to the surface kerry key and colleagues use sea floor magnetotelluric soundings to image mantle electrical structure to a depth of about 160 km along the northern east pacific rise the images reveal a symmetrical high conductivity anomaly beneath the ridge consistent with partial melting of passively upwelling mantle they explain a deeper conductor observed east of the ridge by asymmetric upwelling due to viscous coupling across two nearby transform faults these findings suggest that plate driven passive upwelling dominates this ridge segment while dynamic forces are negligible melt generated by mantle upwelling is fundamental to the production of new oceanic crust at mid ocean ridges yet the forces controlling this process are debated1 2 passive flow models predict symmetric upwelling due to viscous drag from the diverging tectonic plates but have been challenged by geophysical observations of asymmetric upwelling3 4 5 that suggest anomalous mantle pressure and temperature gradients2 6 7 and by observations of concentrated upwelling centres8 consistent with active models where buoyancy forces give rise to focused convective flow2 here we use sea floor magnetotelluric soundings at the fast spreading northern east pacific rise to image mantle electrical structure to a depth of about 160 kilometres our data reveal a symmetric high conductivity region at depths of 20 90 kilometres that is consistent with partial melting of passively upwelling mantle9 10 11 the triangular region of conductive partial melt matches passive flow predictions suggesting that melt focusing to the ridge occurs in the porous melting region rather than along the shallower base of the thermal lithosphere a deeper conductor observed east of the ridge at a depth of more than 100 kilometres is explained by asymmetric upwelling due to viscous coupling across two nearby transform faults significant electrical anisotropy occurs only in the shallowest mantle east of the ridge axis where high vertical conductivity at depths of 10 20 kilometres indicates localized porous conduits this suggests that a coincident seismic velocity anomaly12 is evidence of shallow magma transport channels13 14 rather than deeper off axis upwelling we interpret the mantle electrical structure as evidence that plate driven passive upwelling dominates this ridge segment with dynamic forces being negligible

variations in δ13c values of sedimentary organic matter since late miocene time in the indus fan iodp site 1457 of the eastern arabian sea

numerical simulation of waves generated by landslides using a multiple fluid navier stokes model abstract this work reports on the application and experimental validation for idealized geometries of a multiple fluid navier stokes model of waves generated by rigid and deforming slides with the purpose of improving predictive simulations of landslide tsunamis in such simulations the computational domain is divided into water air and slide regions all treated as newtonian fluids for rigid slides a penalty method allows for parts of the fluid domain to behave as a solid with the latter method the coupling between a rigid slide and water is implicitly computed rather than specifying a known slide kinematics two different volume of fluid algorithms are tested for tracking interfaces between actual fluid regions the simulated kinematics of a semi elliptical block moving down a water covered plane slope is first compared to an earlier analytical solution results for the vertical fall of a rectangular block in water are then compared to earlier experimental results finally more realistic simulations of two and three dimensional wedges sliding down an incline are compared to earlier experiments overall in all cases solid block velocities and free surface deformations are accurately reproduced in the model provided that a sufficiently resolved discretization is used the potential of the model is then illustrated on more complex scenarios involving waves caused by multi block or deformable slides

a numerical study of the run up generated by three dimensional landslides 1 a large set of numerical experiments are designed to examine the maximum run up generated by three dimensional 3 d submerged and subaerial solid body landslides a depth integrated numerical model is utilized allowing for the efficient simulation of landslides in shallow and intermediate water six dimensionless parameters are introduced the slide thickness the slide wave number a slide shape parameter the horizontal aspect ratio of the slide the specific gravity of the slide mass and the slope of the beach six sets of simulations are first presented wherein one of the six dimensionless parameters are singularly varied this allows for the identification of parameter dependence on maximum run up after combining the dependencies a number of relationships appear most notably a very clear division between the near and far field is observed where here the far field is defined as the region displaced from the projection of the landslide on the nearby beach where edge waves may dominate the wave pattern for submerged slides a nondimensional estimation of the maximum run up just landward of the slide is found as well as the location and magnitude of the secondary run up peak this secondary peak is due to the propagation of edge waves and is in some cases larger than the peak immediately landward of the slide the results presented in this paper may be useful for preliminary hazard assessment where a simple and quick estimation of the maximum run up height and locations are required additionally the formulas developed will be particularly beneficial to those developing 3 d landslide experiments

numerical modeling of tsunami waves generated by the flank collapse of the cumbre vieja volcano la palma canary islands tsunami source and near field effects 1 in this work we study waves generated by the potential collapse of the west flank of the cumbre vieja volcano cvv la palma canary island spain through numerical simulations performed in two stages i the initial slide motion and resulting free surface elevation are first calculated using a 3d navier stokes model ii generated waves are then input into a 2d horizontal boussinesq model to further simulate propagation to the nearby islands unlike in earlier work on cvv besides a similar extreme slide volume scenario of 450 km3 in our simulations i we consider several slide scenarios featuring different volumes i e 20 40 80 km3 which partly result from a geotechnical slope stability analysis ii we use a more accurate bathymetry and iii an incompressible version of a multiple fluid material navier stokes model we find wave trains for each scenario share common features in terms of wave directivity frequency and time evolution but maximum elevations near cvv significantly differ ranging from 600 to 1200 m for increasing slide volume additionally our computations show that significant energy transfer from slide to waves only lasts for a short duration order 200 s which justifies concentrating our best modeling efforts on the early slide motion phase the anticipated consequences of such wave trains on la palma and other canary islands are assessed in detail in the paper

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

the ramesses experiment iii controlled source electromagnetic sounding of the reykjanes ridge at 57 45 n summary a controlled source electromagnetic sounding survey centred on an axial volcanic ridge avr segment of the reykjanes ridge at 57 45aen was performed as part of the ramesses experiment low frequency 0 35 11 hz electromagnetic signals were transmitted through the crust to an array of horizontal electric field recorders at the seafloor to ranges of 15 km from the source which was a 100 m long horizontal electric dipole towed at heights of 50 80 m from the seafloor coincident seismic and magnetotelluric studies were conducted during the rest of the ramesses experiment data were interpreted using a combination of 1 d forward modelling and inversion and iterative forward modelling in two dimensions on the axis of the avr the resistivity at the seafloor is 1 v m there is a steep resistivity gradient in the upper few hundred metres of the crust with the resistivity reaching approximately 10 v ma t a depth of 500 m in order to explain the low resistivities the upper layer of the crust must be heavily fractured and saturated with sea water the resistivity increases with distance from the axis as the porosity decreases with increasing crustal age the most intriguing feature in the data is the large diverence in amplitude between fields transmitted along and across the avr axis a significant zone of low resistivity material is required at approximately 2 km depth beneath the ridge crest in order to explain this diverence it is coincident with the low velocity zone required by the seismic data and has a total electrical conductance in excellent agreement with the results of the magnetotelluric study the low resistivity zone can be explained by the presence of a body of partially molten basalt in the crust taken together these results provide the first clear evidence for a crustal magma chamber at a slow spreading mid ocean ridge the data constrain the melt fraction within the body to be at least 20 per cent with a melt volume suycient to feed crustal accretion at this segment of the ridge for of the order of 20 000 years since this body would freeze in the order of 1500 years this finding lends support to the hypothesis that at slow spreading rates crustal accretion is a cyclic process accompanying periodic influxes of melt from the mantle to a crustal melt reservoir

scaling properties of normal faults in the central afar ethiopia and djibouti implications for strain partitioning during the final stages of continental breakup abstract the central afar depression offers an opportunity for quantitative analysis of the final stages of continental breakup at a divergent triple junction here quaternary faulting dissects plio pleistocene flood basalts providing a regionally pervasive datum to quantify the regional finite strain and fault scaling laws to this end we mapped and measured more than 8500 normal faults using remote sensing products fault length generally follows a power law distribution but exponential distributions are found in areas of magmatic extension fault throw and fault length scale following a power law relationship where t 0 031 l 0 96 similar to previous studies in afar and elsewhere in the world combining the power law distribution with this throw scaling enables a comprehensive assessment of quaternary finite strain throughout the region strain is greatest near manda inakir lake asal and the dobe hanle accommodation zone the makarassou fault zone shows low strain suggesting it does not kinematically link the manda inakir and asal rift segments the presence of moderate to high strain in the amagmatic portions of the central afar rift suggests that those areas accommodate a significant proportion of plate motion this may provide a future path for propagation between the gulf of aden rift and the red sea rift

the lateral growth and coalesence of magma systems thermal and mechanical models of magma reservoir growth need to be reconciled with deformation patterns and structural relationships observed at active magma systems geophysical observations provi

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

magnetotelluric study of the mechanism of the abaga and dalinor volcanic groups in central inner mongolia china abstract central inner mongolia is one of the areas with intense volcanic activity in the cenozoic in order to better understand the origin of these volcanoes a study of magnetotelluric sounding mt was carried out this study aims to learn about the mechanism of deep volcanic areas from the electrical point of view broadband and long period mt data were collected on a 500 kilometer section at central inner mongolia two dimensional inversion was applied since the data show no obvious three dimensional effect impedance tensor decomposition and phase tensor analysis show that the electric strike angle of the study area is n45 e a 2 d resistivity model was obtained with a depth range from surface to the uppermost mantle 0 150 km the resistivity model imaged the ascending channels and the sources of the magma beneath the abaga and the dalinor volcanic groups there are low resistivity anomalies c1 and c2 related to volcanic activities at depths of 60 100 km below the two volcanic groups the percentage of melt in the low resistivity areas below the abaga volcanic group and the dalinor volcanic group are as high as 5 10 and 3 5 respectively this difference in terms of melt fraction explains why the volcanic activity of the abaga volcanic group is larger than that of the dalinor volcanic group two magma chambers were found in the lower crust of the dalinor volcanic group and no magma chamber was found beneath the abaga group based on the resistivity model it is further speculated that the formation mechanism of volcanic activity in central inner mongolia is that the partial molten asthenosphere in an extensive environment flowed up to the surface through structural fissures and formed a large area of basalt platform the magmatic body imaged at the depths of 60 100 km may be the source of volcanic eruptions of the study area

combinations of volcanic flank and seafloor sediment failure offshore montserrat and their implications for tsunami generation recent seafloor mapping around volcanic islands shows that submarine landslide deposits are common and widespread such landslides may cause devastating tsunamis but accurate assessment of tsunami hazard relies on understanding failure processes and sources here we use high resolution geophysical data offshore from montserrat in the lesser antilles to show that landslides around volcanic islands may involve two fundamentally different sources of sediment island flank and larger seafloor sediment failures and can occur in multiple stages a combination of these processes produces elongate deposits with a blocky centre associated with island flank collapse surrounded by a smoother surfaced deposit that is dominated by failed seafloor sediment the failure of seafloor sediment is associated with little marginal accumulation and involves only limited downslope motion submarine landslide deposits with similar blocky and smooth surfaced associations are observed in several locations worldwide but the complex emplacement processes implied by this morphological relationship can only be revealed by high resolution geophysical data such complexity shows that the volume of landslide deposits offshore of volcanic islands cannot simply be used in tsunami models to reflect a single stage collapse of primary volcanic material by applying predictive equations for tsunami amplitude to investigate general scenarios of volcanic island landslide generation we show that the tsunami hazard associated with volcanic island collapse remains highly significant volcanic flank failures even if relatively small may generate large local tsunamis but associated seafloor sediment failures even if they have a much greater volume have a substantially lower potential for tsunami generation

numerical modelling of the tsunami triggered by the guimar debris avalanche tenerife canary islands comparison with field based data abstract some tsunami deposits have been previously identified 41 188 m asl in the agaete valley on the northwest coast of the island of gran canaria in the canary islands in this paper the guimar sector collapse tenerife 0 83 ma and its expected associated tsunami that is thought to be at the origin of these tsunami deposits are tentatively reproduced using a two fluid numerical code two failure processes are considered 1 the whole 44 km 3 volume is released in one go or 2 the 44 km 3 are released in five retrogressive failures of equal volume occurring each 120 s in both cases two rheologies are used to simulate the landslide propagation the mohr coulomb frictional law and a constant retarding stress two hypotheses concerning the origin of the offshore mapped deposits are also considered 1 the mapped deposits are the direct result of a single collapse event occurring either in one go or by near retrogressive failures or 2 the mapped deposits result from a collapse followed by later partial remobilization of its deposits in all scenarios the subaerial destabilisation spreads out eastwards into the sea triggering waves 390 500 m high when considering a collapse in one go and 225 380 m when considering successive retrogressive failures the first wave reaches the coast of gran canaria located at 70 km from the scar 495 560 s after the collapse onset whatever the scenario considered water enters the agaete valley on gran canaria 555 690 s after the onset of collapse reaching up to 9 1 km inland for a collapse in one go and 5 0 km when considering five retrogressive failures in this valley the simulated waves inundate all the locations where tsunami deposits were identified with the flow depth measured reaching a maximum of 50 m collapse by retrogressive failures to 150 m collapse in one go at these particular places the directions of maximum kinetic energy as a function of time for the simulated waves are consistent with the current directions recorded by the cobble fabrics present in the run up and backwash layers of the tsunami deposits at one outcrop this study shows that the major source of uncertainty when reproducing landslide triggered tsunamis is linked to the way the landslide happens failure mechanisms that should be thus more precisely taken into account for landslide triggered tsunamis hazard assessment the rheology chosen to simulate the landslide propagation has only a second order impact on the produced waves

post rifting relaxation in the afar region ethiopia 1 crustal accretion at divergent plate boundaries typically occurs via the periodic intrusion of dikes but their emplacement and the associated deformation are rarely observed the few existing observations at subaerial rifts show that these diking events are followed by a decadal scale period with extension rates faster than the secular divergent plate motion this transient accelerated deformation has been explained by continued subsurface magma injection or by relaxation in the viscoelastic mantle of the stress changes imparted by dike opening for the first time gps measurements were collected within a few months of a rifting event at a major plate boundary the september 2005 60 km long dike intrusion in the dabbahu segment afar ethiopia extension rates for the first 3 years greatly exceed the plate motion nubia arabia secular divergence rate even at sites located more than 60 km from the rift axis here we show that these observations are consistent with stress relaxation in a viscoelastic upper mantle with a viscosity of about 5 1018 pa s overlain by a 12 14 km thick elastic crust the alternative model of continued diking requires continuous opening well below the moho and is therefore unlikely instead magma injection in afar since june 2006 has taken the form of smaller discrete diking events tapping into a mid crustal melt reservoir under the segment center

application of wavelet transform analysis to landslide generated waves the aim of this paper is to illustrate the results of a preliminary study on aerial landslide generated waves which has been mainly intended to establish a method for analyzing water surface records some simple physical experiments reproducing the scott russell s wave generator were carried out in a small two dimensional wave flume the wavelet transform wt is applied to analyze wave measurements and it is shown that useful information can be obtained by means of this technique the celerity of impulsively generated waves reflection by an overflow structure and seiching phenomena of the flume are studied a discussion of the results along with some remarks about ongoing research is also given

evolution of seaward dipping reflectors at the onset of oceanic crust formation at volcanic passive margins insights from the south atlantic seaward dipping reflectors sdrs have long been recognized as a ubiquitous feature of volcanic passive margins yet their evolution is much debated and even the subject of the nature of the underlying crust is contentious this uncertainty significantly restricts our understanding of continental breakup and ocean basin forming processes using high fidelity reflection data from offshore argentina we observe that the crust containing the sdrs has similarities to oceanic crust albeit with a larger proportion of extrusive volcanics variably interbedded with sediments densities derived from gravity modeling are compatible with the presence of magmatic crust beneath the outer sdrs when these sdr packages are restored to synemplacement geometry we observe that they thicken into the basin axis with a nonfaulted diffuse termination which we associate with dikes intruding into initially horizontal volcanics our model for sdr formation invokes progressive rotation of these horizontal volcanics by subsidence driven by isostasy in the center of the evolving sdr depocenter as continental lithosphere is replaced by more dense oceanic lithosphere the entire system records the migration of 10 km thick new magmatic crust away from a rapidly subsiding but subaerial incipient spreading center at rates typical of slow oceanic spreading processes our model for new magmatic crust can explain sdr formation on magma rich margins globally but the estimated crustal thickness requires elevated mantle temperatures for their formation

constraints on melt distribution from seismology a case study in ethiopia low seismic velocities and or strong seismic anisotropy are often interpreted as being caused by partial melt to better understand this we used numerical modelling varying the shape and amount of melt to show how seismic phases are affected by melt we observed that seismic waves are more sensitive to the shape than to the amount of melt rayleigh wave velocities were almost always reduced in the presence of melt while pn wide angle p wave refraction and love wave velocities showed low velocity anomalies for vertically aligned melt but little anomaly for horizontally aligned melt these data can therefore be used to determine the alignment of melt shear wave splitting receiver functions showed strong anisotropy and can be used to constrain the strike of vertically aligned partial melt we showed that melt in the mantle beneath ethiopia is probably stored in low aspect ratio disc like inclusions suggesting that the melt is not in textural equilibrium we estimated that 2 7 of the vertically aligned melt is stored beneath the main ethiopian rift 6 of the horizontally and vertically aligned melt is stored beneath the red sea rift and 1 6 of the horizontally aligned melt is stored beneath the danakil microplate this supports the idea of strong shear derived segregation of melt in the narrow main ethiopian rift compared with that observed beneath afar

three dimensional conductivity model of the tendaho high enthalpy geothermal field ne ethiopia abstract tendaho is one of the high enthalpy geothermal fields at advanced stage of exploration which is located in the afar depression in north eastern ethiopia six deep and shallow geothermal wells were drilled in the field between 1993 and 1998 here we present the first 3d conductivity model of the tendaho high enthalpy geothermal field obtained from 3d inversion of magnetotelluric mt data mt data from 116 sites at 24 selected periods in the period range from 0 003 s to 1000 s were used for the 3d inversion the 3d conductivity model reveals three main resistivity structures to a depth of 20 km the surface conductive structure 10 m and 1 km thick is interpreted as sediments geothermal fluids or hydrothermally altered clay cap the underlying high resistivity structure in the afar stratiod basalts is associated with the deep geothermal reservoir at a depth 5 km a high conductivity is observed across the whole of the tendaho geothermal field this structure is inferred to be the partial melt heat source of the geothermal system the most striking feature in the 3d model is a fracture zone upflow zone in the afar stratoid basalts at the dubti area which acts as a pathway for geothermal fluids targeting the inferred fracture zone by directional drilling will likely increase the permeability and temperature of the deep reservoir in the basalts hence the inferred presence of a fracture zone and shallow magma reservoir suggest that there is a huge potential with temperature exceeding 270 c at 2 km depth at tendaho for conventional hydrothermal geothermal energy development

experimental investigation of impact generated tsunami related to a potential rock slide western norway abstract two dimensional experiments of wave generation from the possible akneset rock slide have been performed using solid block modules in a transect with a geometric scaling factor of 1 500 the width of the slide model was kept fixed at 0 45 m the length of the blocks spanned from 1 to 2 m the thickness was either 0 12 or 0 16 m and the front angle was 45 maximum water depth was 0 6 m with the slide plane having an angle of 35 three different scenarios were studied only the run out side was modelled surface elevations at three locations outside the sloping region were measured with ultra sonic wave gauges and discussed in light of hydrodynamic wave theory particle image velocimetry piv was used to extract instantaneous velocity fields comparison is made between experimental velocity profiles and profiles consistent with a boussinesq theory high speed video of the impact was recorded and used to determine qualitative aspects of the forward collapse of the impact crater backfill wave

magnetotelluric imaging of lower crustal melt and lithospheric hydration in the rocky mountain front transition zone colorado usa we present an electrical resistivity model of the crust and upper mantle from two dimensional 2d anisotropic inversion of magnetotelluric data collected along a 450 km transect of the rio grande rift southern rocky mountains and high plains in colorado usa our model provides a window into the modern day lithosphere beneath the rocky mountain front to depths in excess of 150 km two key features of the 2d resistivity model are 1 a broad zone 200 km wide of enhanced electrical conductivity 20 m in the mid to lower crust that is centered beneath the highest elevations of the southern rocky mountains and 2 hydrated lithospheric mantle beneath the great plains with water content in excess of 100 ppm we interpret the high conductivity region of the lower crust as a zone of partially molten basalt and associated deep crustal fluids that is the result of recent less than 10 ma tectonic activity in the region the recent supply of volatiles and or heat to the base of the crust in the late cenozoic implies that modern day tectonic activity in the western united states extends to at least the western margin of the great plains the transition from conductive to resistive upper mantle is caused by a gradient in lithospheric modification likely including hydration of nominally anhydrous minerals with maximum hydration occurring beneath the rocky mountain front this lithospheric hydration front has implications for the tectonic evolution of the continental interior and the mechanisms by which water infiltrates the lithosphere

constraining melt geometries beneath the afar depression ethiopia from teleseismic receiver functions the anisotropic h κ stacking technique understanding the nature of the crust has long been a goal for seismologists when imaging the earth this is particularly true in volcanic regions where imaging melt storage and migration can have important implications for the size and nature of an eruption receiver functions and the h stacking h technique are often used to constrain crustal thickness h and the ratio of p to s wave velocities in this paper i show that it is essential to consider anisotropy when performing h i show that in a medium with horizontally transverse isotropy a strong variation in with back azimuth is present which characterizes the anisotropic medium in a vertically transverse isotropic medium no variation in with back azimuth is observed but is increased across all back azimuths thus estimates of are more difficult to relate to composition than previously thought i extend these models to melt induced anisotropy and show that similar patterns are observed but with more significant variations and increases in based on these observations i develop a new anisotropic h stacking technique which inverts h data for melt fraction aspect ratio and orientation of melt inclusions i apply this to data for the afar depression and show that melt is stored in interconnected stacked sills in the lower crust which likely supply the recent volcanic eruptions and dike intrusions this new technique can be applied to any anisotropic medium where it can provide constraints on the average crustal anisotropy

uppermost mantle pn velocity model for the afar region ethiopia an insight into rifting processes the afar depression ethiopia offers unique opportunities to study the transition from continental rifting to oceanic spreading because the process is occurring onland using traveltime tomography and data from a temporary seismic deployment we describe the first regional study of uppermost mantle p wave velocities vpn we find two separate low vpn zones as low as 7 2 km s 1 beneath regions of localized thinned crust in northern afar indicating the existence of high temperatures and potentially partial melt the zones are beneath and off axis from contemporary crustal magma intrusions in active magmatic segments the dabbahu manda hararo and erta ale segments this suggests that these intrusions can be fed by off axis delivery of melt in the uppermost mantle and that discrete areas of mantle upwelling and partial melting thought to characterize segmentation of the uppermost mantle at seafloor spreading centres are initiated during the final stages of break up

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

partial melt or aqueous fluid in the mid crust of southern tibet constraints from indepth magnetotelluric data summary the indepth project has applied modern geophysical techniques to the study of the crustal structure and tectonic evolution of the tibetan plateau in the lhasa block seismic reflection surveys in 1994 detected a number of bright spots at 15 20 km depths that indicate zones of crustal fluids aqueous fluids or partial melt coincident magnetotelluric mt data collected in 1995 detected a major zone of high electrical conductivity at the same depth as the brightspots using constrained inversion the mt data require a minimum crustal conductance of 6000 s this abnormally high electrical conductance can be best explained by a layered model with fluids partial melt aqueous fluids or a combination of partial melt and aqueous fluids the non uniqueness of the mt method means that a wide range of melt fraction thickness combinations for the above models could all explain the 6000 s conductance to distinguish between these three models other geophysical and geological data are required reflection seismic data suggest that a high fluid content 15 per cent is present at the top of the layer the amplitude versus offset data suggest that the top of this layer may be aqueous fluids rather than partial melt passive seismic data imaged a 20 km thick layer of lower fluid content that is probably partial melt petrological studies suggest that concentrations of aqueous fluids above 0 1 per cent at mid crustal depth cannot be sustained taken together these data show that the high conductivity in southern tibet is most probably the result of a relatively thin layer of aqueous fluids 100 200 m overlying a thicker zone of partial melt 10 km

plate tectonics magma for 50 000 years intrusions of magma into the crust help accommodate the divergence between tectonic plates a magnetotelluric survey of the crust and mantle beneath afar ethiopia has identified enough magma to accommodate plate separation there for about 50 000 years

use of a high precision gravity survey to understand the formation of oceanic crust and the role of melt at the southern red sea rift in afar ethiopia the red sea arm of the triple junction in northeastern ethiopia provides an opportunity to investigate rift forming processes at divergent boundaries in an attempt to study the subsurface especially the distribution and role of melt in the rifting process we carried out a high precision gravity survey with a mean square error of 0 011 mgal assisted by differential global positioning system measurements the profile is 162 km long and strikes ene wsw across the southern part of the red sea rift at a latitude of approximately 11 75 n modelling of the bouguer anomaly constrained by a priori information showed detailed in rift variations in the crustal structure and the distribution of melt beneath the rift axis our interpretation suggested that the process of continental break up is governed by crustal stretching and rifting accompanied by the emplacement of melt into the lower crust above a lower density upper mantle in addition we interpreted the thickness of the crust beneath this part of the rift axis to be 25 km the subsurface distribution of density beneath the profile shows that the south central part of the red sea rift has modified thinned crust intruded by high density material which resembles the crust formed during seafloor spreading

magmatic rifting and active volcanism introduction a major rifting episode began in the afar region of northern ethiopia in september 2005 over a 10 day period c 2 5 km3 of magma were intruded into the upper crust along a 60 km long dyke separating the arabian and nubian plates there was an intense seismic swarm and a small rhyolitic eruption extension of up to 10 m occurred across the rift segment over the next five years a further 13 dyke intrusions caused continued extension eruptions and seismicity the activity in afar led to a renewed international focus on the role of magmatism in rifting with major collaborative projects involving researchers from ethiopia the uk the usa france italy and new zealand working in afar and ethiopia to study the ongoing activity and to place it in a broader context this book brings together articles that explore the role of magmatism in rifting from the initiation of continental break up through to full seafloor spreading we also explore the hazards related to rifting and the associated volcanism this renewed focus on magmatism and its role in rifting has implications for our understanding of how continents break up and the associated distribution of resources in rift basins and continental margins

thermal models of dyke intrusion during development of continent ocean transition a consensus has emerged in recent years from a variety of geoscientific disciplines that extension during continental rifting is achieved only partly by plate stretching dyke intrusion also plays an important role magma intrusion can accommodate extension at lower yield stresses than are required to extend thick strong unmodified continental lithosphere mechanically thereby aiding the breakup process dyke intrusion is also expected to heat and thereby weaken the plate but the spatial extent of heating and the effect of different rates of magmatic extension on the timescales over which heating occurs are poorly understood to address this issue a numerical solution to the heat flow equation is developed here to quantify the thermal effects of dyke intrusion on the continental crust during rifting the thermal models are benchmarked against a priori constraints on crustal structure and dyke intrusion episodes in ethiopia finite difference models demonstrate that magmatic extension rate exerts a first order control on the crustal thermal structure once dyke intrusion supersedes faulting and stretching as the principal extensional mechanism the crust will heat and weaken rapidly less than 1 ma in the main ethiopian rift mer the majority of present day extension is focused on 20 km wide quaternary recent axial magmatic segments that are mostly seismogenic to mid crustal depths and show p wave seismic velocities characteristic of heavily intruded continental crust when reviewed in light of our models these observations require that no more than half of the mer s extension since 2 ma has been achieved by dyke intrusion magmatic heating and weakening of the crust would have rendered it aseismic if dyke intrusion accounted for the entire 6 mm yr extension rate in the older faster extending 16 mm yr red sea rift rsr in afar dyke intrusion is expected to have had a more dramatic impact on crustal rheology accordingly effective elastic plate thickness and moho depth in the danakil region of northernmost afar are markedly reduced and seismicity is shallower than in the mer thermally driven variations in crustal rheology over time in response to dyke intrusion thus play an important role in the development of continent ocean transition

physical modeling of tsunamis generated by three dimensional deformable granular landslides 1 tsunamis generated by deformable granular landslides are physically modeled in a three dimensional tsunami wave basin based on the generalized froude similarity the dynamic landslide impact characteristics were controlled by means of a novel pneumatic landslide generator the wave amplitudes periods and wavelengths are related to the landslide parameters at impact with the landslide froude number being a dominant parameter between 1 and 15 of the landslide kinetic energy at impact is converted into the wave train energy the wave amplitudes decay in radial and angular directions from the landslide axis the first wave crest mostly travels with speeds close to the theoretical approximation of the solitary wave speed the measured tsunami wave profiles were either of the nonlinear oscillatory or nonlinear transition type depending primarily on the landslide froude number and relative slide thickness at impact the generated waves range from shallow to deep water depth regimes with the majority being in the intermediate water depth regime wave characteristics are compared with other two and three dimensional landslide tsunami studies and the results are discussed

improved landslide tsunami prediction effects of block model parameters and slide model 1 subaerial landslide tsunamis and impulse waves are caused by mass movements impacting into a water body and the hazards they pose have to be reliably assessed empirical equations developed with physical froude model studies can be an efficient method for such predictions the present study improves this methodology and addresses two significant shortcomings in detail for the first time these are the effect of three commonly ignored block model parameters and whether the slide is represented by a rigid block or a deformable granular material a total of 144 block slide tests were conducted in a wave flume under systematic variation of three important block model parameters the slide froude number the relative slide thickness and the relative slide mass empirical equations for the maximum wave amplitude height and period as well as their evolution with propagation distance are derived for most wave parameters remarkably small data scatter is achieved the combined influence of the three block model parameters affects the wave amplitude and wave height by up to a factor of two the newly derived equations for block slides are then related to published equations for granular slides this comparison reveals that block slides do not necessarily generate larger waves than granular slides as often argued in the technical literature in fact it is shown that they may also generate significant smaller waves the new findings can readily be integrated in existing hazard assessment methodologies and they explain a large part of the discrepancy between previously published data

mantle dynamics beneath the east pacific rise at 17 s insights from the mantle electromagnetic and tomography melt experiment 1 the electromagnetic data from the mantle electromagnetic and tomography melt experiment are inverted for a two dimensional transversely anisotropic conductivity structure that incorporates a correction for three dimensional topographic effects on the magnetotelluric responses the model space allows for different conductivity values in the along strike cross strike and vertical directions along with imposed constraints of model smoothness and closeness among the three directions anisotropic models provide a slightly better fit to the data for a given level of model smoothness and are more consistent with other geophysical and laboratory data the preferred anisotropic model displays a resistive uppermost 60 km thick mantle independent of plate age except in the vicinity of the ridge crest in most inversions a vertically aligned sheet like conductor at the ridge crest is especially prominent in the vertical conductivity its presence suggests that the melt is more highly concentrated and connected in the vertical direction immediately beneath the rise axis the melt zone is at least 100 km wide and is asymmetric having a greater extent to the west off axis and to the east of the ridge the mantle is more conductive in the direction of plate spreading at depths greater than 60 km the flat resistive conductive boundary at 60 km agrees well with the inferred depth of the dry solidus of peridotite and the deeper conductive region is consistent with the preferred orientation of olivine inferred from seismic observations this suggests that the uppermost 60 km represents the region of mantle that has undergone melting at the ridge and has been depleted of water dissolved hydrogen by contrast the underlying mantle has retained a significant amount of water

the nature of the crust beneath the afar triple junction evidence from receiver functions the afar depression is an ideal locale to study the role of extension and magmatism as rifting progresses to seafloor spreading here we present receiver function results from new and legacy experiments crustal thickness ranges from 45 km beneath the highlands to 16 km beneath an incipient oceanic spreading center in northern afar the crust beneath afar has a thickness of 20 26 km outside the currently active rift segments and thins northward it is bounded by thick crust beneath the highlands of the western plateau 40 km and southeastern plateau 35 km the western plateau shows vp vs ranging between 1 7 1 9 suggesting a mafic altered crust likely associated with cenozoic flood basalts or current magmatism the southeastern plateau shows vp vs more typical of silicic continental crust 1 78 for crustal thicknesses 2 0 can only be explained by significant amounts of magmatic intrusions in the lower crust this suggests that melt emplacement plays an important role in late stage rifting and melt in the lower crust likely feeds magmatic activity the crust between the location of the miocene red sea rift axis and the current rift axis is thinner 2 0 than beneath the eastern part of afar 26 km vp vs 1 9 this suggests that the eastern region contains less partial melt has undergone less stretching extension and has preserved a more continental crustal signature than west of the current rift axis the red sea rift axis appears to have migrated eastward through time to accommodate the migration of the afar triple junction

magnetotelluric imaging of upper crustal partial melt at tendaho graben in afar ethiopia we report on a recent magnetotelluric mt survey across the manda hararo magmatic segment mhms within the tendaho graben in the afar depression in northeastern ethiopia twenty two broadband mt sites with 1 km station spacing were deployed along a profile with the recorded data covering a period range from 0 003 s to 1000 s a two dimensional 2 d resistivity model reveals an upper crustal fracture zone fault and partial melt with resistivity of 1 10 m at a depth of 1 km the partial melt has a maximum horizontal width of 15 km and extends to a depth of 15 km within the afar stratoid series basalts we estimate a melt fraction of about 13 based on geochemical and borehole data and bulk resistivity from the 2 d mt inversion model the interpreted upper crustal partial melt may have been formed by either a magma intrusion from mantle sources or a large volume of continental crust that has been fluxed by a small amount of mantle melt and heat within the mhms and tendaho graben a magma intrusion is a plausible explanation for the upper crustal conductor the inferred presence of a conductive fracture zone or fault with hydrothermal fluid and shallow heat sourcing magma reservoir also makes the tendaho graben a promising prospect for the development of conventional hydrothermal geothermal energy

magmatism on rift flanks insights from ambient noise phase velocity in afar region during the breakup of continents in magmatic settings the extension of the rift valley is commonly assumed to initially occur by border faulting and progressively migrate in space and time toward the spreading axis magmatic processes near the rift flanks are commonly ignored we present phase velocity maps of the crust and uppermost mantle of the conjugate margins of the southern red sea afar and yemen using ambient noise tomography to constrain crustal modification during breakup our images show that the low seismic velocities characterize not only the upper crust beneath the axial volcanic systems but also both upper and lower crust beneath the rift flanks where ongoing volcanism and hydrothermal activity occur at the surface magmatic modification of the crust beneath rift flanks likely occurs for a protracted period of time during the breakup process and may persist through to early seafloor spreading

probing the status of felsic magma reservoirs constraints from the p t h 2 o dependences of electrical conductivity of rhyolitic melt electrical conductivity of rhyolitic melts combined with magnetotelluric data can provide important constraints for the physicochemical conditions of active felsic magma reservoirs previous experimental investigations are limited to low h2o concentration 3 wt h2o and low pressure 0 2 gpa for hydrous melts we here report new results from electrical conductivity measurements of peralkaline rhyolitic melts with 4 7 wt na2o and 0 1 7 9 wt h2o at 868 1665 k and 0 5 1 0 gpa in piston cylinder apparatuses using sweeping frequency impedance analyses logarithmic electrical conductivity is found to correlate linearly with h2o concentration and reciprocal temperature and the influence of h2o has been considerably underestimated by previous work the negative pressure effect on electrical conductivity appears to attenuate with increasing h2o concentration based on the new data we develop the following electrical conductivity model for peralkaline rhyolitic melts under conditions up to 1665 k 1 0 gpa and 8 wt h2o log 2 983 0 0732w 3528 233 8w 763 7 5w2 pt where is electrical conductivity in s m t is temperature in k w is h2o concentration in wt and p is pressure in gpa according to the nernst einstein relation this conductivity model can also be applied to metaluminous and peraluminous rhyolitic melts by scaling down according to the diffusivity and concentration of na the primary charge carrier with the new model we suggest that the highest electrical anomaly beneath the tianchi volcano corresponds to a melt fraction of 9 if the melt contains 5 wt h2o or to a melt fraction of 32 for 2 wt h2o similarly the magma reservoir beneath the taupo volcanic zone new zealand is inferred to contain a fully molten rhyolite with 7 5 wt h2o or 36 water saturated melt with 10 wt h2o

compositional variability of the serenitatis tranquillitatis region of the moon from telescopic multispectral imaging and spectroscopy abstract we present results from a combined ccd multispectral imaging and near ir spectroscopic study of a region near the border between the mare serenitatis and mare tranquillitatis lunar impact basins we have detected and spatially mapped variations in mare tio 2 abundance in the degree of spectral maturity of impact craters and their ejecta blankets and in the level of fresh highlands contamination within mare units techniques employed include color ratio images image oriented linear mixing models and spectral band analyses specific findings include the detection of relatively fresh highlands materials in the craters tacquet and sulpicius gallus and in the central peak and floor of the crater plinius the detection of low tio 2 serenitatis like mare materials in a confined region of the ejecta from the crater dawes and the determination of immaturity rather than composition as the origin of the high albedo in the rectangular deposit surrounding dawes the combination of high spatial resolution imaging and high spectral resolution spectroscopy and the use of synthesizing techniques such as mixture modeling will provide valuable tools to optimize the scientific return from telescopic galileo clementine and other future lunar data sets

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

correction to transient rift opening in response to multiple dike injections in the manda hararo rift afar ethiopia imaged by time dependent elastic inversion of interferometric synthetic aperture radar data 1 interferometric synthetic aperture radar insar data spanning the time intervals separating thirteen dike intrusions in the manda hararo dabbahu rift afar ethiopia from 2005 to 2009 show that transient deformation occurs in the inter diking period this deformation can be explained by the presence of seven inflating or deflating pressure sources by combining the data acquired on four different insar tracks through time dependent elastic models we are able to track these deformation modes with a time resolution smaller than 1 month sustained deflation of a deep magma reservoir at dabbahu in the 6 months following the main rifting event of 2005 and slow decelerating post eruptive re inflation of two shallow magma reservoirs below dabbahu and gabho volcanoes are monitored a deflation signal of deep origin on the neighboring rift system is also detected possibly caused by outflow of material from a preexisting reservoir into the deep plate boundary in contrast rapidly evolving deformation is observed at the center of the manda hararo rift segment transient deformation events are monitored in the weeks months following the diking events with pulses of localized rift opening after the dike intrusions followed by an exponential like decay of opening rate this signal may be associated with the replenishment of the central magma reservoir involved in feeding the 2005 2009 dikes alternatively the predominantly horizontal mode of deformation suggests an interaction between the response of the lithosphere to tectonic strain accumulation and the process of hydraulic connectivity within the central magma plumbing system

on the characteristics of landslide tsunamis this review presents modelling techniques and processes that govern landslide tsunami generation with emphasis on tsunamis induced by fully submerged landslides the analysis focuses on a set of representative examples in simplified geometries demonstrating the main kinematic landslide parameters influencing initial tsunami amplitudes and wavelengths scaling relations from laboratory experiments for subaerial landslide tsunamis are also briefly reviewed it is found that the landslide acceleration determines the initial tsunami elevation for translational landslides while the landslide velocity is more important for impulsive events such as rapid slumps and subaerial landslides retrogressive effects stretch the tsunami and in certain cases produce enlarged amplitudes due to positive interference in an example involving a deformable landslide it is found that the landslide deformation has only a weak influence on tsunamigenesis however more research is needed to determine how landslide flow processes that involve strong deformation and long run out determine tsunami generation

composite modelling of subaerial landslide tsunamis in different water body geometries and novel insight into slide and wave kinematics this article addresses subaerial landslide tsunamis with a composite experimental numerical modelling approach a shortcoming of generic empirical equations used for hazard assessment is that they are commonly based on the two idealised water body geometries of a wave channel 2d or a wave basin 3d a recent systematic comparison of 2d and 3d physical block model tests revealed wave amplitude differences of up to a factor of 17 the present article investigates two of these recently presented 2d 3d test pairs in detail involving a solitary like wave scenario 1 and stokes like waves scenario 2 results discussed include slide and water particle kinematics and novel pressure measurements on the slide front instantaneous slide water interaction power graphs are derived and potential and kinetic wave energies are analysed solitary wave theory is found most appropriate to describe the wave kinematics associated with scenario 1 whereas stokes theory accurately describes the tsunami in scenario 2 the data of both scenarios are further used to calibrate the smoothed particle hydrodynamics sph code dualsphysics v3 1 which includes a discrete element method dem based model to simulate the slide ramp interaction five intermediate geometries lying between the ideal 2d and 3d cases are then investigated purely numerically for a channel geometry with a diverging side wall angle of 7 5 the wave amplitudes along the slide axes were found to lie approximately halfway between the values observed in 2d and 3d at 45 the amplitudes are practically identical to those in 3d the study finally discusses the implications of the findings for engineering applications and illustrates the potential and current limitations of dualsphysics for landslide tsunami hazard assessment

on numerical modelling of impulse water waves generated by submarine landslides an algorithm is presented for numerical modelling of impulse water waves generated by submarine landslides moving along irregular bottom profiles a spatially nonuniform submarine landslide moving on a spatially nonuniform slope is modelled by a quasi deformed rigid body in addition a simplified model is studied for the particular case of landslide and bottom profiles dependent on one spatial coordinate only both models are used for the comparative analysis of numerical and experimental data for submarine rigid landslides moving along a plane slope the simplified model is applied to analyse the dependences of wave characteristics on various parameters for submarine landslides moving along a sea bottom slope with monotonically increasing depth and in a bounded reservoir the full model is used to study the landslide trajectories and the wave patterns for the model submarine landslide of a spatially irregular shape moving in the model reservoir with a spatially irregular bottom all numerical computations are performed using the nonlinear shallow water equations with moving bottom and the time stepping algorithm provided by a predictor corrector scheme on adaptive grids

forecasting impulse waves generated by subaerial landslides 1 subaerial landslides falling into reservoirs or open seas generate impulsive water waves that are usually referred to as a class of tsunami waves it is important to study landslide generated waves occurring both in closed water basins where the waves interact with the shorelines and eventually the dam and in open seas where the generated waves can travel and deliver devastating damages hundreds of kilometers away in order to gain insight on subaerial landslide generated waves the italian national dam office recently funded an experimental and numerical research program geared to better understand and forecast tsunamis waves this paper introduces the experimental work which has been carried out in order to define empirical formulations able to forecast the principal features of the generated waves in a three dimensional water body as a function of the landslide movement wave types observed during the experiments are here characterized using a wavelet analysis approach new forecasting formulations named rid formulas are defined on the basis of the experimental study and tested using an artificial neural network model results are finally compared to those presented in past experimental studies

episodic melt transport at mid ocean ridges inferred from magnetotelluric sounding oceanic crust is generated at mid ocean ridges by decompression melting of upwelling mantle at depths of between 50 and 120 km geodynamic and geochemical models of upwelling melt extraction and melt emplacement into crustal magma reservoirs present a variety of possible migration geometries most of which assume steady state or near steady state processes here we present results from marine magnetotelluric mt measurements carried out as part of the ramesses experiment on the slow spreading reykjanes ridge which support a model of melt extraction and migration that is episodic rather than steady state

magnetotelluric image of transcrustal magmatic system beneath the tulu moye geothermal prospect in the ethiopian rift

lithospheric rheological heterogeneity across an intraplate rift basin linfen basin north china constrained from magnetotelluric data implications for seismicity and rift evolution abstract we take the linfen basin which is the most active segment of the cenozoic intraplate shanxi rift as an example showing how to use magnetotelluric data to constrain lithospheric rheological heterogeneities of intraplate tectonic zones electrical resistivity models combined with previous rheological numerical simulation show a good correlation between resistivity and rheological strength indicating the mechanisms of enhanced conductivity could also be reasons of reduced viscosity the crust beneath the linfen basin shows overall stratified features in both electrical resistivity and rheology the uppermost crustal conductive layer is dominated by friction sliding type brittle fracturing the high resistivity mid crust is inferred to be high viscosity metamorphic basement being intersected by deep fault the plastic lower crust show significantly high conductivity feature seismicity appears to be controlled by crustal rheological heterogeneity micro earthquakes mainly distribute at the brittle ductile transition zones as indicated by high to low resistivity interfaces or the high pore pressure fault zones while the epicenters of two giant destructive historical earthquakes occur within the high resistivity and therefore high strength blocks near the inferred rheological interfaces the lithosphere scale lateral rheological heterogeneity along the profile can also be illustrated the crust and upper mantle beneath the ordos block luliang mountains and taihang mountains are of high rheological strength as indicated by large scale high resistivity zones while a significant high conductivity lithosphere scale weak zone exists beneath the eastern margin of the linfen basin according to previous geodynamic modeling works we suggest that this kind of lateral rheological heterogeneity may play an essential role for providing driving force for the formation and evolution of the shanxi rift regional lithospheric deformation and earthquake activities under the far field effects of the india eurasian collision

discussion of experimental investigation of impact generated tsunami related to a potential rock slide western norway by g saelevik a jensen g pedersen coastal eng 56 2009 897 906 this paper is a discussion of saelevik et al 2009 their comparison between block and granular model results is described in more detail along with a discussion of five parameters which may be in general responsible for deviations between block and granular models new small scale physical model tests have been performed to support some of the statements made finally it is argued that the use of physical model testing based on simplified geometries are justified in practice and normally produce results that are considerably better than an order of magnitude

3 d analysis and interpretation of magnetotelluric data from the aluto langano geothermal field ethiopia the main ethiopian rift valley encompasses a number of volcanoes which are known to be actively deforming with reoccurring periods of uplift and setting one of the regions where temporal changes take place is the aluto volcanic complex it hosts a productive geothermal field and the only currently operating geothermal power plant of ethiopia we carried out magnetotelluric mt measurements in early 2012 in order to identify the source of unrest broad band mt data 0 001 1000 s have been acquired at 46 sites covering the expanse of the aluto volcanic complex with an average site spacing of 1 km based on this mt data it is possible to map the bulk electrical resistivity of the subsurface down to depths of several kilometres resistivity is a crucial geophysical parameter in geothermal exploration as hydrothermal and magmatic reservoirs are typically related to low resistive zones which can be easily sensed by mt thus by mapping the electrical conductivity one can identify and analyse geothermal systems with respect to their temperature extent and potential for production of energy 3 d inversions of the observed mt data from aluto reveal the typical electrical conductivity distribution of a high enthalpy geothermal system which is mainly governed by the hydrothermal alteration mineralogy the recovered 3 d conductivity models provide no evidence for an active deep magmatic system under aluto forward modelling of the tippers rather suggest that occurrence of melt is predominantly at lower crustal depths along an off axis fault zone a few tens of kilometres west of the central rift axis the absence of an active magmatic system implies that the deforming source is most likely situated within the shallow hydrothermal system of the aluto langano geothermal field

a mantle magma reservoir beneath an incipient mid ocean ridge in afar ethiopia the buoyancy of magma should cause it to rise into the crust preventing it from ponding in the uppermost mantle magnetotelluric data from the dabbahu rift segment ethiopia identify a magma reservoir that extends well into the mantle beneath the rift and is so large that it should persist for thousands of years

seismic structure across the rift valley of the mid atlantic ridge at 23 20 mark area implications for crustal accretion processes at slow spreading ridges the results from a 53 km long wide angle seismic profile across the rift valley of the mid atlantic ridge south of the kane transform near 23 20 n mark area provide new constraints on models of tectonic extension and magmatic accretion along slow spreading mid ocean ridges anomalously low middle and lower crustal p wave velocities beneath the neovolcanic snake pit ridge are consistent with elevated axial temperatures and with the presence of 4 1 partial melt evenly distributed within the lower crust in preferentially oriented elongated thin films if the melt inclusions have larger aspect ratios melt fractions can be up to 17 3 this and other geological observations suggest that the study area is presently in a magmatically active period the igneous crust is anomalously thin beneath both flanks of the median valley 2 3 2 5 km thus the mantle rocks observed along the western rift valley wall at pink hill were probably emplaced at shallow levels within the valley floor during a period of very low magma supply and were later exposed on the valley walls by normal faulting the crust within the eastern rift valley and flanking rift mountains is seismically heterogeneous with igneous crustal thickness variations of 2 2 km over horizontal distances of 5 km this heterogeneity indicates that the magma supply in the area has fluctuated during the last 2 m y thus magmatic and amagmatic periods at slow spreading ridges may alternate over much shorter temporal scales that previously inferred from sea surface gravity data