plate boundary geometry to moho depths within the 9 03 n and 12 54 n overlapping spreading centers of the east pacific rise abstract multichannel seismic reflection data from the east pacific rise provide a three dimensional view of overlapping spreading centers oscs at 9 03 n and 12 54 n previous studies of the 9 03 n osc based on position of the axial magma chamber top are extended to the base of the crust using the observation that the moho reflection is disrupted in the vicinity of the ridge axis the smaller 12 54 n osc is investigated for comparison like the shallower features the moho disruption is offset within the oscs at the larger 9 03 n osc misalignment between the morphologic ridge axis and the axial magma body extends to the base of the crust where the axial gap in the reflection moho does not consistently underlay the shallower structures spatial relationships within the oscs between axial topography axial magma chamber and axial gap in reflection moho suggest that ridge tips propagate first by brittle fracturing of the upper crust followed by intracrustal magma residence followed finally by establishment or capture of magma pathways from the mantle interpreting all three features as demarcating the axial zone of weakness along which new magma enters the crust the axial plane within the 9 03 n osc appears to dip and to rotate with depth the sense of overlap in the shallow crust is dextral while the sense of offset in the deep crust is sinistral spatial relationships within the 9 03 n osc suggest that the northern propagating ridge tip has already captured a portion of the deep crustal magma conduit connected with the southern ridge

east pacific rise 8 10 30 n evolution of ridge segments and discontinuities from seamarc ii and three dimensional magnetic studies magnetic bathymetric and seamarc ii side scan sonar data from the ridge flanks adjoining the overlapping spreading center osc at 9 03 n on the east pacific rise epr are used to establish the evolution of this ridge axis discontinuity and adjacent ridge segments within the past 2 4 m y a three dimensional inversion for magnetization shows the discontinuity evolved from one of small offset 2 km to an 8 km offset osc within the past approximately 1 0 m y the osc has left a v shaped discordant zone indicating an average southward migration of 42 km m y since the beginning of anomaly 2 time 1 8 m y the west flank discordant zone consists of discrete abandoned overlap basins bounded by highly magnetized ridge tips with anomalous lineations while the east flank discordant zone is a broad swath of high magnetization anomalous lineations and greater depths kinematic modelling indicates that southward migration has not been steady but has been accomplished by a series of episodic propagation events with rates ranging from 500 mm yr ridge tips have been abandoned at intervals of approximately 50 000 100 000 years both by linkage of neighboring ridge segments and by self decapitation magnetic modelling suggests rotations of overlap basins of 25 consistent with predictions of kinematic modelling orientation of magnetic isochrons indicate a 3 6 counterclockwise change in pacifie cocos plate motion within the past 1 m y assuming orthogonal spreading throughout this time although the discontinuity currently located at 9 03 n existed prior to this change in plate motion its growth into a right stepping 8 km offset osc may be causally related to this change the current configuration of intratransform spreading within the siqueiros has developed since onset of the brunhes anomaly 0 73 m y possibly in response to this recent counterclockwise change in plate motion in addition to the osc there is evidence for several small discontinuities offsetting the ridge during anomaly 2 time which have since migrated along the ridge and vanished an axial magnetization high is observed along the crest of the epr change in the magnitude of the axial magnetization high or shifts in its location relative to the bathymetric axis coincide with several devals within the area magnetization maxima are found at ridge transform intersections and the osc these highs may reflect presence of highly fractionated feti basalts erupted from magma chambers with restricted supply located adjacent to both large and short offset ridge axis discontinuities discrete magnetization highs are found off axis adjacent to clipperton and siqueiros fracture zones indicating that production of feti basalts at ridge transform intersections is episodic magnetizations are higher north of clipperton than south of it possibly reflecting a long lived starvation in magma supply north of clipperton and more abundant supply to the south most seamounts within the area have the same magnetization polarity as surrounding seafloor indicating that seamount formation occurs near the ridge axis the exceptions lie near magnetic reversal boundaries and are consistent with seamount formation as close as 10 km from the ridge axis few pronounced magnetization highs are associated with seamounts indicating that the magnetized source layer is no thicker beneath them than surrounding seafloor or that seamount basalts are substantially less magnetic than normal mid ocean ridge basalts

geochemical evidence for low magma supply and inactive propagation at the galapagos 93 25 w overlapping spreading center 1 major and trace element concentrations sr nd and pb isotopic ratios and plagioclase and olivine compositions of samples from 92 35 w to 94 10 w on the galapagos spreading center gsc constrain magmatic processes associated with the 93 25 w overlapping spreading center osc significant variations in parental magma compositions and extent of low pressure fractionation over short along axis distances suggest small discontinuous or poorly mixed magma chambers mineralogical petrological and geochemical data indicate this osc is characterized by low overall melt supply regional along axis geochemical gradients along the western gsc e g in 206pb 204pb nb zr and la 8 sm 8 are interrupted by increased variability within the osc consistent with less efficient mixing of melts in this region despite a long term history of westward propagation bathymetric and geochemical data are inconsistent with recent propagation of this offset the eastern limb appears to have recently retreated and left behind a series of abandoned ridges within the overlap zone the eastern limb shows two progressive westward trends of decreasing ratios of highly to moderately incompatible elements one outside and one within the overlap zone the overlapping portion of the western limb also has low ratios of these elements these patterns are consistent with previously depleted mantle being preferentially melted beneath this offset

significance of widespread low effusion rate eruptions over the past two million years for delivery of magma to the overlapping spreading centers at 9 n east pacific rise abstract ever since the discovery that the mid ocean ridge axis deepens at most axial discontinuities there has been vigorous debate about whether ridge axis depth and shape reflect magma supply here we report evidence from one of the most thoroughly studied ridge discontinuities on a fast spreading mid ocean ridge that volcanic eruption effusion rates have been low relative to nearby segment centers throughout its two million year history this pattern of low volcanic effusion rates is inferred from the fields of constructional volcanic mounds on the seafloor which are much more abundant in the off axis discordant zone of the east pacific rise epr 9 n overlapping spreading centers osc than on typical epr seafloor detailed seafloor mapping in 2007 shows that these mound fields consist of concentrations of large pillow mounds that formed within the current osc basin and ridge tips rather than off axis pillow lava erupted at approximately an order of magnitude lower effusion rate than lobate or sheet flows primarily builds mounds on the seafloor crustal thickness a proxy for long term magma supply does not decrease in spite of the decreased lava effusion rates implied by widespread pillow eruptions to resolve the problem of achieving the same magma emplacement rate with lower effusion rates without violating our observations by requiring drastically increased eruption frequency or unreasonably long eruption durations we propose that eruptions occur across the entire osc basin the current configuration of mid crustal melt sills within the osc as resolved by multichannel seismic reflection surveys have neither the correct location nor appropriate size to deliver magma to these eruptive vents in the osc basin via vertically propagating dikes instead we propose that magma delivery to eruptions occurs via laterally propagating dikes from robust mid crustal melt sills outside of the overlap zone

solidification and morphology of submarine lavas a dependence on extrusion rate the results of recent laboratory experiments with wax extruded beneath relatively cold water may be extrapolated to predict the surface morphology of submarine lavas as a function of the extrusion rate and melt viscosity the experiments with solidifying wax indicated that the surface morphology was controlled by a single parameter the ratio of the time taken for the surface to solidify and a time scale for lateral flow for submarine basalts a solution of the cooling problem which is dominated by conduction in the lava but convective heat transfer in the water and estimates of lava viscosities place this parameter within the empirically determined pillowing regime over a wide range of extrusion rates this result is consistent with the observation that pillow basalts are the most common products of submarine eruptions smoother surfaces corresponding to the various types of submarine sheet flows are predicted for sufficiently rapid extrusions of basaltic magma still higher eruption rates in regions of low topographic relief may produce submarine lava lakes minimum emplacement times can be calculated for submarine volcanic constructs of a single lava flow type

fault slip triggering healing and viscoelastic afterworking in sediments in the mexicali imperial valley crackmeter data from the southern tip of the imperial fault in the mexicali imperial valley in northern baja california mexico show slip events that tend to group in episodes or suites that last over a few days with months of quiescence between them the events in these suites are apparently triggered and stopped by ground strain related to temperature changes a characteristic decrease in peak extension velocities during the slip event suites indicates the presence of viscoelastic afterworking which contributes the strain necessary for succeeding events with diminishing driving stresses and which can be roughly modeled as a series of kelvin voigt viscoelastic solids occurrence of very small events towards the end of the suites plus gaps between suites indicate that for the sediments significant fault healing requires a minimum of several days without slip

development and application of a pseudo 3d pit slope displacement map derived from ground based radar slope monitoring plays an important role in the risk management of large open pit slopes historically displacement data derived from measuring geodetic prisms have been relied upon to delineate the boundaries of potential slope hazards however that data can be limited by its point measurement nature localized displacements at each prism may be misinterpreted when extended to the behavior of the entire slope and important displacements between prisms may be overlooked new technologies like ground based radar can provide high resolution full area coverage of a slope in combination with near real time acquisition and millimeter precision as a line of sight instrument these tools provide data on displacement magnitudes and rates but not true direction hence limiting their use in gaining understanding of the kinematics and behavior of the moving slope this paper describes a novel experiment in which two ground based synthetic aperture radar systems were simultaneously deployed to record continuous line of sight displacements of an open pit slope in stereo the displacement vectors were combined to create a pseudo 3 d displacement map for the slope which was subsequently used to interpret the influence of a major fault and the rock mass fabric in promoting different kinematic responses the data collected demonstrates that an improved understanding of the 3 d kinematics of a large rock slope can be achieved using advanced state of the art monitoring techniques to aid mine design

viscous type sliding laws for landslides sliding of a moving soil mass along a basal surface is analyzed and viscous type sliding laws are presented they relate the relative sliding velocity at the base or at an interface to the state of stress at this surface examples of practical parameter determination illustrate the suitability of this approach two landslides in switzerland and in france provide the data for this purpose a third site la frasse switzerland serves as an example of three dimensional analysis of creeping slopes using the proposed formulation comparison of computed and measured velocity distributions shows the method to be promising key words landslides creep sliding law time dependence interface

modelling tailings dams and mine waste dumps failures this paper presents a depth integrated model that can be used to simulate the flowslides mudflows and debris flows that are caused by the failure of tailing dams mining waste dumps and other similar structures the sliding mass is first determined using a coupled elastoplastic finite element code and a suitable constitutive equation once failure has been triggered propagation of the mobilised material is analysed considering flow properties averaged over depth a simple law of pore pressure dissipation is postulated for cases in which the consolidation and propagation times are of the same order of magnitude

volcanic mound fields on the east pacific rise 16 19 s low effusion rate eruptions at overlapping spreading centers for the past 1 myr 1 volcanic mound fields identified on seamarc ii and hmr1 12 khz side scan data from the southern east pacific rise sepr occur near overlapping spreading centers oscs and migration traces of oscs the volcanic mound fields appear as a distinctive hummocky seafloor fabric due to side scan backscatter reflections from clusters of mound shaped reflectors the lack of growth of the mound fields away from the ridge axis and their occurrence in association with osc traces suggests that mound fields form along the ridge crest near oscs volcanic mound fields are found where 120 khz side scan and visual observations find fields of pillow mounds since pillow mounds are constructed by low effusion rate eruptions the volcanic mound fields found near the oscs and in their migration traces indicate that volcanic effusion rates tend to be lower near ridge discontinuities than midsegment regions this tendency for low effusion rate eruptions at oscs is documented for the past 1 myr three independent measurements of ridge segmentation 1 volcanic segment boundaries marked by the low effusion rate eruptions 2 tectonic segments defined by oscs and 3 magmatic segment boundaries based on continuity of parental magma composition all coincide in the study area high backscatter off axis lava fields not associated with seamounts are found on seafloor younger than 0 2 ma the 0 2 ma corridor corroborates previous results from the distribution of small isolated volcanoes that indicates randomly distributed off axis eruptions mainly occur on crust younger than 0 2 ma

fault slip seismicity and deformation in mexicali valley baja california mexico after the m 7 1 1999 hector mine earthquake a local small deformation network in mexicali valley baja california mexico recorded fault slip seismicity and deformation produced by the 16 october 1999 m 7 1 hector mine earthquake 260 km away the network consists of two crackmeters two biaxial surface tiltmeters and one broadband seismograph all recording continuously these instruments are complemented by other seismological instruments within the valley local microearthquakes with clear p and s phases began 2 hours after arrival of the hector mine p wave and earthquakes with m 2 5 large enough to be located started about 33 hours after the earthquake local seismicity continued with decreasing frequency for about 2 weeks after the hector mine earthquake vertical and horizontal slip and tilt began on the imperial fault simultaneously with the hector mine earthquake seismic wave arrival which is clearly recorded by the tiltmeters deformation recorded by a tiltmeter on the cerro prieto geothermal field began about 30 hours after the main event and ended 13 hours later after the occurrence of the largest local earthquake m 4 1 in this episode the temporal pattern of seismicity and deformation suggests that deformation is the main process triggered by the hector mine earthquake waves in the study area and the transient local seismicity increase is a response to the triggered deformation

problems in predicting the mobility of slow moving landslides abstract this paper discusses problems in predicting the mobility of slow moving landslides three case studies are presented here where research has been carried out by the utrecht university the la valette landslide complex in the french alps the la mure landslide in the french pre alps near grenoble and the hau landslide in switzerland to predict field velocities of these slow moving landslides the viscosity parameters of the material of these landslides were determined by strain controlled tests in a ring shear apparatus based on bishop s design at utrecht university the viscosity parameters from the laboratory proved to be 10 to 1000 times lower than viscosities obtained from back analyses on the observed velocities in the field this discrepancy may be explained by the development of negative pore pressures when the plastic material slides over a rigid wavy slip surface and or by convergent flow effects the associated gain in strength results in a higher apparent viscosity a more detailed analysis is made for the movements of the la valette landslide observed velocities at the la valette landslide are difficult to describe by one parameter set as the response to a change in groundwater level is not the same during a rise or fall in the piezometric level this deviation may be explained by rapid changes in total stresses and consequently changes in pore pressure under partly undrained conditions the emerging hysteresis with local and temporal variations in pore pressure makes it difficult to predict in detail the moving pattern of landslides

constructing the crust along the galapagos spreading center 91 3 95 5 w correlation of seismic layer 2a with axial magma lens and topographic characteristics the seafloor and narrow 0 5 1 5 km cross axis width we also image a thin seismic layer 2a 0 24 0 42 km that thickens away from the ridge axis by as much as 150 west of 92 7 w the magma lens is deeper 2 5 4 5 km and wider 0 7 2 4 km and layer 2a is thicker 0 36 0 66 km and thickens off axis by 40 the positive correlation between layer 2a thickness and magma lens depth supports the interpretation of layer 2a as the extrusive volcanic layer with thickness controlled by the pressure on the magma lens and its ability to push magma to the surface our findings also suggest that narrower magma lenses focus diking close the ridge axis such that lava flowing away from the ridge axis will blanket older flows and thicken the extrusive crust off axis flow of lava away from the ridge axis is probably promoted by the slope of the axial bathymetric high which is largest east of 92 5 w west of 94 wt he transitional axial morphology lacks a prominent bathymetric high and layer 2a no longer thickens off axis we detect no magma lens west of 94 7 w where a small axial valley appears the above changes can be linked to the westward decrease in the magma and heat flux associated with the fading influence of the galapagos hot spot on the galapagos spreading center index terms 3035 marine geology and geophysics midocean ridge processes 7220 seismology oceanic crust 0935 exploration geophysics seismic methods 3025

small slope tilts caused by meteorological effects and vital processes of trees on a wooded slope in hidegviz valley hungary abstract long term measurements were carried out to investigate the relationship between ground tilts and variations of meteorological temperature precipitation and hydrological soil moisture content parameters in the area of the sopron mountains on a wooded slope of the hidegviz valley hungary the connection between surface tilts and the vital processes of the trees was also studied on the basis of the reference evapotranspiration calculated for the study area long and short term variations were separated a long term ground temperature change of 1 c caused a 4 rad tilt in the se direction short term temperature effects can be neglected the fluctuation of temperature around the freezing point caused tilts of about 10 rad c 1 the soil water content variation had the largest effect on the ground tilt 0 5 rad mm 1 its contribution to the total ground tilt in the investigated period was about 70 rad 65 of the total tilt of 107 rad toward the sse the contribution of the wind speed to the ground tilt was about 20 rad m s 1 toward the sse depending on the water content of the soil the wind did not cause a permanent ground tilt the magnitude of the daily tilt variations in the active growing period of trees from march to october is 1 2 rad while in the dormant period with no canopy the tilt variations were less than 0 4 rad the admittances between the evapotranspiration and the ground tilts were 0 3 0 5 rad mm 1 and 0 1 0 2 rad mm 1 in the active and dormant period of the trees respectively these small effects superimposed on each other can significantly contribute to slope failures the results of this study provide information which can be useful in the modelling of landslide movements and for the mitigation of landslide hazards

quantification of submarine lava flow morphology through analog experiments we developed a technique for determining paleoeffusion rates and emplacement times for submarine lava flows using observations of flow morphology and estimates of eruption volume eruption temperature lava viscosity and preflow topography using laboratory simulations and correlating these results with sea floor observations four submarine lava flow morphologies are considered to be diagnostic of specific effusion rates jumbled folded and lineated sheets and striated pillows we applied this approach to the coaxial flow emplaced in less than 14 days on the juan de fuca ridge in early summer 1993 and we calculated an effusion rate of 100 m3 s giving an emplacement time of 10 days

investigating landslides with space borne synthetic aperture radar sar interferometry abstract this paper is addressed to readers without advanced knowledge of remote sensing it illustrates some current and potential uses of satellite synthetic aperture radar interferometry insar for landslide assessment data acquired by sar systems can provide 3d terrain models and be used to assist in regional scale investigations e g aimed at evaluation of susceptibility of slopes to failure under favourable environmental conditions the innovative permanent scatterers ps technique which overcomes several limitations of conventional sar differential interferometry dinsar applications in landslide studies is suitable for monitoring slope deformations with millimetric precision the ps technique combines the wide area coverage typical of satellite imagery with the capability of providing displacement data relative to individual image pixels with the currently available radar satellites however only very slow ground surface displacements can be reliably detected and measured the presented case study of a landslide from the liechtenstein alps indicates that the most attractive and reliable contribution provided by this remote sensing technique lies in the possibility of i wide area qualitative distinction between stable and unstable areas and ii qualitative relative hazard zonation of large slow landslides based on the identification of segments characterised by different movement rates since only the radar line of sight projection of the displacements can be detected a quantitative exploitation of the ps data is possible only where sufficient ground truth is available in site specific or single landslide investigations the ps data can represent a very useful complementary data source with respect to the information acquired through ground based observations and in situ surveying however the difficulties associated with the feasibility assessments of the applicability of sar data to local scale problems as well as with the interpretation of ps results require a close collaboration between landslide experts and specialists in advanced processing of radar satellite data the interpretation of the exact geotechnical significance of small radar sensed ground surface deformations is challenging especially where ground truth is lacking although any ground deformation is potentially of interest to an engineering geologist detection of movements in both vertical and horizontal directions is needed in the case of landslides to evaluate slope failure mechanisms with their high radar viewing angles however the current space borne systems can detect only a fraction of the horizontal component of movement it is expected that the upcoming sar dedicated missions with new sensors and different acquisition geometries combined with the rapid developments in the field of advanced radar data processing will allow a full 3d reconstruction of deformation data and help to further reduce the current limitations of the ps and similar dinsar approaches

inconsistent correlation of seismic layer 2a and lava layer thickness in oceanic crust the oceanic crust makes up two thirds of the earth s surface and has been studied for many years yet the processes by which it is formed are still not fully understood one problem is inaccessibility only a tiny fraction of it has been subjected to drilling and sampling the tools of geology so much relies on remote sensing techniques such as seismic exploration the tools of geophysics these two approaches have led to some confusion over crustal structure christeson et al set out to reconcile the two by a direct comparison between seismic interpretations and geologic mapping the new data question the idea that seismic layer 2a correlates with lava layer thickness instead the layer 2a reflection seems to correspond to an alteration boundary within the lava layer at mid ocean ridges with fast to intermediate spreading rates the upper section of oceanic crust is composed of lavas overlying a sheeted dyke complex these units are formed by dykes intruding into rocks overlying a magma chamber with lavas erupting at the ocean floor seismic reflection data acquired over young oceanic crust commonly image a reflector known as layer 2a which is typically interpreted as defining the geologic boundary between lavas and dykes1 2 3 an alternative hypothesis is that the reflector is associated with an alteration boundary within the lava unit4 5 6 many studies have used mapped variability in layer 2a thickness to make inferences regarding the geology of the oceanic crust including volcanic construction dyke intrusion and faulting7 8 9 10 however there has been no link between the geologic and seismological structure of oceanic crust except at a few deep drill holes here we show that although the layer 2a reflector is imaged near the top of the sheeted dyke complex at fast spreading crust located adjacent to the hess deep rift it is imaged significantly above the sheeted dykes section at intermediate spreading crust located near the blanco transform fault although the lavas and underlying transition zone thicknesses differ by about a factor of two the shallow seismic structure is remarkably similar at the two locations this implies that seismic layer 2a cannot be used reliably to map the boundary between lavas and dykes in young oceanic crust instead we argue that the seismic layer 2a reflector corresponds to an alteration boundary that can be located either within the lava section or near the top of the sheeted dyke complex of oceanic crust

surface displacement and groundwater level changes associated with the 24 may 2006 mw 5 4 morelia fault earthquake mexicali valley baja california mexico on 24 may 2006 a moderate size m w 5 4 earthquake occurred in the mexicali valley mexico the event created 5 km of surface rupture associated deformation was recorded by geotechnical instruments leveling profile and synthetic aperture radar interferometry a coseismic steplike groundwater level change was detected at seven wells the surface rupture consisted of up to 30 cm of primarily normal displacement 20 25 cm of vertical offset was recorded by a crackmeter and 20 cm on leveling line we created envisat c band interferograms spanning the 24 may 2006 earthquake to image the coseismic displacement although the coherence of the interferometric images is low the images clearly show a spatial displacement field centered on the known surface rupture that is consistent with the expected sense of motion the interferograms and leveling line also include subsidence related to geothermal production this anthropogenic subsidence component was estimated using a pre event interferogram source parameters for the earthquake were estimated using forward modeling of both surface deformation data and static volume strain change inferred from coseismic changes in groundwater level modeling was based on finite rectangular fault embedded in an elastic media the preferred fault model has a strike rake and dip of 48 89 45 and has a length of 5 2 km width of 6 7 km and 34 cm of uniform slip the geodetic moment based on the modeled fault parameters is graphic 1 the model matched the observed surface deformation expected groundwater changes and teleseismic moment reasonably well 1 embed inline graphic 1 gif

the 1998 eruption of axial seamount new insights on submarine lava flow emplacement from high resolution mapping 1 axial seamount an active submarine volcano on the juan de fuca ridge at 46 n 130 w erupted in january 1998 along 11 km of its upper south rift zone we use ship based multibeam sonar high resolution 1 m bathymetry sidescan sonar imagery and submersible dive observations to map four separate 1998 lava flows that were fed from 11 eruptive fissures these new mapping results give an eruption volume of 31 106 m3 70 of which was in the northern most flow 23 in the southern most flow and 7 in two smaller flows in between we introduce the concept of map scale submarine lava flow morphology observed at a scale of hundreds of meters as revealed by the high resolution bathymetry and an interpretive model in which two map scale morphologies are produced by high effusion rate eruptions inflated lobate flows are formed near eruptive vents and where they drain downslope more than 0 5 1 0 km they transition to inflated pillow flows these two morphologies are observed on the 1998 lava flows at axial a third map scale flow morphology that was not produced during this eruption pillow mounds is formed by low effusion rate eruptions in which pillow lava piles up directly over the eruptive vents axial seamount erupted again in april 2011 and there are remarkable similarities between the 1998 and 2011 eruptions particularly the locations of eruptive vents and lava flow morphologies because the 2011 eruption reused most of the same eruptive fissures 58 of the area of the 1998 lava flows is now covered by 2011 lava

analysis of the evolution of ground movements in a low densely urban area by means of dinsar technique abstract this paper presents an application example of the use of the differential interferometry synthetic aperture radar technique dinsar for monitoring ground movements in a geologically complex area around the village of suria ebro basin catalonia ne spain associated to underground mining activities and to the presence of a salt dome the analysis has been mostly performed in a rural environment affected by ground movements with different patterns magnitudes and causes a total of fifty sar images recorded between 1995 and 2007 were processed to generate the interferograms in order to study the non linear trends or changes of the ground surface behavior the dinsar technique was applied in two sets of images the interferometric results in the form of vertical displacement rate maps were checked against conventional surveying and gps measurements the results present a significant discrepancy in some location due to the wrapping of the phase when both fast and significant deformations occur in order to avoid the latter effect and improve the accuracy of the results all sar images were reprocessed using topographic leveling and gps data of different monitored points to support the dinsar interpretation a detailed geological reconnaissance of the study area was carried out as well as an inventory of ground movement indicators four different patterns of ground movement have been identified active shifting subsidence associated to the progression of the mining exploitation fronts residual subsidence on abandoned galleries with a decreasing rate of closure uplifting due to the intrusion of the salt dome and sudden ground collapses sinkholes caused by the dissolution of soluble materials laying close to the ground surface

continuous mantle melt supply beneath an overlapping spreading center on the east pacific rise tomographic images of upper mantle velocity structure beneath an overlapping spreading center osc on the east pacific rise indicate that this ridge axis discontinuity is underlain by a continuous region of low p wave velocities the anomalous structure can be explained by an approximately 16 kilometer wide region of high temperatures and melt fractions of a few percent by volume our results show that oscs are not necessarily associated with a discontinuity in melt supply and that both osc limbs are supplied with melt from a mantle source located beneath the osc we conclude that tectonic segmentation of the ridge by oscs is not the direct result of magmatic segmentation at mantle depths

a sliding consolidation model for flow slides a model is proposed for the behaviour of flow slides in loose cohesionless materials in which the debris spreads out as a uniform sheet excess pore fluid pressures are assumed to be generated for example by undrained loading arising from the collapse of metastable structure in the source area of the flow slide under the influence of these the leading element of the debris moves downslope by basal sliding consolidating as it does so by single upward drainage as a result the pore pressure at the base of the element eventually decays to a value that brings the element to rest hence defining the run out of the flow slide the model is applicable in principle to subaqueous and subaerial flow slides and to pore fluids consisting of water gas or both of these the predictions of the model are tested against the observed behaviour and measured properties of the 1966 flow slide at aberfan south wales the results show that a sliding consolidation model provides a possible mechanism for that event

integration of ground based radar and satellite insar data for the analysis of an unexpected slope failure in an open pit mine abstract on 17 november 2016 an unexpected slope failure occurred in an undisclosed copper open pit mine the nature of the event urged for a thorough back analysis of slope monitoring data in order to assess its size and temporal evolution and to determine whether precursors potentially able to anticipate the failure were present to this aim satellite insar data spanning over the final 9 months before the event were in retrospect acquired and coupled with measurements from a ground based radar that was in use at the time of the failure although progressive deformation was detected by the ground based radar in correspondence of the two uppermost benches in the pit the satellite insar data revealed that the vast majority of the instability actually involved a large part of natural slope above the mine crest this sector was not visible by the ground based radar thanks to the short revisit time of the sentinel 1 mission clear slope accelerating creep was observed for the first time in satellite insar measurements over an open pit mine the delimitation of the area featuring accelerating creep behavior matched remarkably the source area of the failure as mapped in the field after the event considerations on the volume of the instability and on the development of the failure process both in space and time were consequently derived the results provided a clear example of the value of jointly using ground based and satellite interferometry to reduce the uncertainties inherent to the identification and characterization of impending catastrophic slope failures

controls on extrusion at mid ocean ridges a magma lens can erupt to form extrusives only if it is under greater pressure than the static pressure in a column of magma reaching from the lens to the surface the excess pressure results partly from overburden pressure caused by the presence of high and low density rocks dikes and extrusives respectively above the lens the thicker the pile of low density extrusives the lower the average overburden density thus extrusion above a lens should be self regulating in that thickening the extrusive layer reduces the driving pressure for subsequent eruptions flexural stresses may affect extrusion by altering the pressure on a magma chamber for ridges lacking an axial valley we predict that deeper magma lenses should correlate with thicker extrusive layers consistent with recent observations

numerical analysis of a landslide in soils with strain softening behaviour the results of an analysis concerning a landslide of great dimensions which occurred at senise southern italy on 26 july 1986 are presented the landslide was of a translational type and the failure developed within a thin clayey silt layer interbedded by a slightly cemented sand formation both these soils experienced a pronounced strain softening behaviour during laboratory tests from the analyses performed using the traditional limit equilibrium approach it has been found that the average operational resistance along the sliding surface was less than that of the peak and greater than the residual resistance deduced from the laboratory tests as a consequence it has been postulated that a progressive failure had occurred such a failure process can be appropriately studied using methods that are capable of simulating the formation and development of shear zones where strain is localised from a computational point of view this presents many difficulties because the numerical procedures current

geochemical studies of abyssal lavas recovered by dsrv alvin from eastern galapagos rift inca transform and ecuador rift 2 phase chemistry and crystallization history a diverse suite of lavas recovered by dsrv alvin from the eastern galapagos rift and inca transform includes mid ocean ridge tholeiitic basalts morb iron and titanium enriched basalts feti basalts and abyssal andesites rock types transitional in character ferrobasalts and basaltic andesites were also recovered the most mafic glassy basalts contain plagioclase augite and olivine as near liquidus phases whereas in more fractionated basalts pigeonite replaces olivine and iron titanium oxides crystallize plagioclase crystallizes after pyroxenes and iron titanium oxides in andesites possibly due to increased water contents or cooling rates apatite phenocrysts are present in some andesitic glasses ovoid sulfide globules are also common in many lavas compositional variations of phenocrysts in glassy lavas reflect changes in magma chemistry temperature of crystallization and cooling rate the overall chemical variations parallel the chemical evolution of the lava suite and are similar to those in other fractionated tholeiitic complexes elemental partitioning between plagioclase pyroxene and olivine glass pairs suggests that equilibration occurred at low pressure in a rather restricted temperature range various geothermometers indicate that the most primitive morb began to crystallize between 1150 and 1200 c with fo2 10 7 atm coexisting iron titanium oxides in more evolved lavas yield temperatures 1025 c to as low as 910 c withfo2 from 10 8 to 10 12 atm ph 2 o could have been as high as 1 kbar during andesite crystallization compositions of the lavas from the galapagos rift follow the experimentally determined 1 atm qfm liquid line of descent least squares calculations for the major elements indicate that the entire suite of lavas can be produced by fractional crystallization of successive residual liquids from a morb parent magma feti basalts represent 30 65 cumulative weight percent crystallization of plagioclase augite and olivine an additional 30 50 fractionation of pyroxenes plagioclase titanomagnetite and possible apatite is required to generate andesite from feti basalt liquids the presence of partially resorbed mafic xenocrysts in some andesites feti basalt inclusions in these xenocrysts high silica glass inclusions in basaltic andesites and the transitional chemistry of basaltic andesites are evidence that some magma mixing occurred during crystal fractionation the diversity of lava types recovered at single dive sites suggests that low pressure fractional crystallization is a very efficient process beneath the eastern galapagos rift and that isolated magma bodies must be present at shallow levels beneath the accretionary locus voluminous feti basalts erupted at the rift transform intersection are genetically related to the rift lavas but their restricted chemistry reflects different thermal and tectonic controls on their petrogenesis

the east pacific rise near 21 n 13 n and 20 s inferences for along strike variability of axial processes of the mid ocean ridge abstract data obtained along various segments of the mid ocean ridge mor are used to construct an idealized model for crustal accretion the model seeks to predict the topographic volcanic tectonic and hydrothermal characteristics of any given spreading segment of the mor as a function of distance away from the bounding transform faults this model is based on a series of detailed mapping efforts carried out on segments of the mor having a broad range of spreading rates between 2 and 16 cm yr this paper includes the results of the french searise program carried out during the summer of 1980 aboard the n o jean charcot and two american cruises conducted in 1981 aboard the r v melville

localization of volcanic activity topographic effects on dike propagation eruption and conduit formation magma flow in a dike rising in a crack whose strike runs from a highland or a ridge to an adjacent lowland has been modeled to determine the effect of topography on the flow it is found that there is a distinct tendency for the flow to be diverted away from the highland end of the strike toward the lowland separation of the geometric effect of the topography from its effect on lateral confining stresses on the crack indicates that both contribute to the effect but that the effect of stress is less important although this analysis explains a tendency for volcanic eruptions to occur in low lands it does not preclude eruptions on highlands the particular configuration modeled mimics topography around the proposed nuclear waste repository at yucca mountain nevada so that the results may indicate some reduction in the volcanic hazard to the site

sinkhole monitoring and early warning an experimental and successful gb insar application abstract sinkholes represent a natural risk that may hit catastrophically without clearly detectible precursors however they are often overlooked by people and administrators therefore sinkhole monitoring and associated early warnings constitute important research topics but currently only a few papers about sinkhole prediction can be found in this paper an experience of sinkhole monitoring and early warning with gb insar is described the latter is a highly precise instrument that is able to produce displacement maps with metric spatial resolution the described activities were carried out on elba island central italy where karstified limestone set off the occurrence of nine sinkholes since 2008 all within less than 3000 m2 causing major damage to an important road and many indirect losses in 1 year of monitoring two deforming areas were detected and the point where a sinkhole was about to propagate to the street level was predicted thus permitting the preventive closure of the road the deformation area was larger than the hole generated by the sinkhole thus showing a subsidence that continued for a prolonged time even after the cavity was filled up the occurrence of a 1 5 m wide sinkhole undetected by the gb insar also showed the lower detection limit of the instrument

atmospheric effects in interferometric synthetic aperture radar surface deformation and topographic maps interferogram images derived from repeat pass spaceborne synthetic aperture radar systems exhibit artifacts due to the time and space variations of atmospheric water vapor other tropospheric variations such as pressure and temperature also induce distortions but the effects are smaller in magnitude and more evenly distributed throughout the interferogram than the wet troposphere term spatial and temporal changes of 20 in relative humidity lead to 10 cm errors in deformation products and perhaps 100 m of error in derived topographic maps for those pass pairs with unfavorable baseline geometries in wet regions such as hawaii these are by far the dominant errors in the spaceborne imaging radar c and x band synthetic aperature radar sir c x sar interferometric products the unknown time delay from tropospheric distortion is independent of frequency and thus multiwavelength measurements such as those commonly used to correct radar altimeter and global positioning system gps ionospheric biases cannot be used to rectify the error in the topographic case the errors may be mitigated by choosing interferometric pairs with relatively long baselines as the error amplitude is inversely proportional to the perpendicular component of the interferometer baseline for the sir c x sar hawaii data we found that the best longest baseline pair produced a map supporting 100 m contouring whereas the poorest baseline choice yielded an extremely noisy topographic map even at this coarse contour interval in the case of deformation map errors the result is either independent of baseline parameters or else very nearly so here the only solution is averaging of independent interferograms so in order to create accurate deformation products in wet regions many multiple passes may be required rules for designing optimal data acquisition and processing sequences for interferometric analyses in nondesert parts of the world are 1 to use the longest radar wavelengths possible within ionospheric scintillation and faraday rotation limits 2 for topography maximize interferometer baseline within decorrelation limits and 3 for surface deformation use multiple observations and average the derived products following the above recipe yields accuracies of 10 m for digital elevation models and 1 cm for deformation maps even in very wet regions such as hawaii

evidence of rock slope breathing using ground based insar ground based interferometric synthetic aperture radar gb insar campaigns were performed in summer 2011 and 2012 in the romsdalen valley more romsdal county western norway in order to assess displacements on mannen bora rock slope located 1 km northwest a second gb insar system continuously monitors the large mannen rockslide the availability of two gb insar positions creates a wide coverage of the rock slope including a slight dataset overlap valuable for validation a phenomenon of rock slope breathing is detected in a remote and hard to access area in mid slope millimetric upward displacements are recorded in august 2011 analysis of 2012 gb insar campaign combined with the large dataset from the continuous station shows that the slope is affected by inflation deflation phenomenon between 5 and 10 mm along the line of sight the pattern is not homogenous in time and inversions of movement have a seasonal recurrence these seasonal changes are confirmed by satellite insar observations and can possibly be caused by hydrogeological variations in addition combination of gb insar results in situ measurements and satellite insar analyses contributes to a better overview of movement distribution over the whole area

new insights into mid ocean ridge volcanic processes from the 2005 2006 eruption of the east pacific rise 9 46 n 9 56 n digital seafloor imagery collected on 37 camera tows and alvin dives in which we identify 186 contacts between new and old lava are used to create the most detailed map of a mid ocean ridge mor eruption to date lava flows erupted in 2005 2006 at the east pacific rise epr covered an area of 14 6 km2 along 18 km of the epr crest between 9 46 and 9 56 n the 2005 2006 lava is characterized by inflated lobate and sheet morphologies in the flow interiors and pillow forms at terminal flow fronts numerous lava channels 10 50 m wide and 1 5 m deep trending approximately east west served as distributory pathways eruptions were sourced from fissures within the epr axial summit trough as well as fissures located on an off axis fissure mound 600 m east of the epr axis between 9 52 and 9 56 n portions of the lava flow reached as far as 2 km east of the axis near 9 51 2 n using a conservative estimate of 1 5 m for the average flow thickness implies that the 2005 2006 eruptions produced 22 106 m3 of lava 4 5 times larger than estimated volumes of 1991 1992 epr lava flows estimated lava volume for the 2005 2006 eruptions represents 15 of the magma available in the axial magma chamber

an assessment of bottom current controlled sedimentation in pacific ocean abyssal environments the effect of the circulation of polar sourced dense waters on the deep seafloor is still largely unknown this paper presents multibeam bathymetric evidence for the existence of present day contourite drifts on the central pacific ocean at depths ranging between 4000 and 5000 m based on the identification of their diagnostic erosive moats linear moats furrows and abyssal sinuous channels and depositional plastered elongated separated and abyssal contourite fan drifts contourite morphological features these contourite drifts display a patchy distribution sculpted by the secondary flows of the lower circumpolar water lcpw and the north pacific deep waters npdw as well as local dynamics of the flow in the form of internal waves and bottom currents modulated by tides which are capable of accelerating the typically sluggish bottom currents and contribute to the erosion transport and deposition of sediments the formation of contourites is also predominantly controlled by the presence of large scale tectonic and volcanic features ridges seamounts and deep elongated valleys which affect the morphology and distribution of the basins and induce the acceleration of bottom currents overall this study allows to re assess the effects distribution and significance of bottom current controlled sedimentation in abyssal environments where examples of contourite features are still rather scarce in part because of the technical challenges and their remote location but also because the effect of bottom currents is not well known in the central oceanic basins and only capable of marginally affecting their sedimentological record

the montaguto earthflow a back analysis of the process of landslide propagation abstract earthflow and mudflow processes represent a class of landslides that owing to their typical long run out may generally induce huge damages to infrastructure lines with negative economic impacts therefore the analysis of the landslide propagation with time in such cases can provide useful information to mitigate landslide risk the present paper discusses the case history of a huge earthflow developed in 2005 2006 in the area of montaguto town southern apennines italy that produced significant damages to a national road and a national railway at the slope toe the average displacement rate during the first critical stage of propagation was of some m day the aim of this contribution is the reconstruction of the propagation stage of this landslide during the first high mobility stage a detailed geomorphological analysis aimed at defining the main features of the in situ landslide propagation is firstly described later on a back analysis of the kinematical features of the same landslide process based on a simple infinite slope sliding consolidation model is presented to investigate the role of different factors in the process of landslide propagation the application of this analytical solution suggests that the development of high excess pore water pressures due to undrained loading processes and the consequent consolidation process can represent a reasonable way to explain the earthflow mobility the application of the analytical model to the specific case study is also supported by the field evidence of the existence of excess pore water pressures in the landslide mass which have been measured in situ during the recent monitoring campaign and the corresponding data are also discussed in the work

a performance based method for the design of drainage trenches used to stabilize slopes abstract drainage trenches are widely used as a measure for slope stabilization their effect is generally quantified in terms of a safety factor against a possible collapse mechanism of the slope a more rational and economical design approach consists in admitting the occurrence in some time intervals of limit conditions in the slope and evaluating the performance of the slope in terms of accumulated permanent displacements of the unstable soil mass the resulting displacements should avoid the occurrence of significant damage and preserve the serviceability of existing structures in this context a new method is proposed in the present paper for the design of drainage trenches used to control the mobility of translational landslides periodically activated by rainfall this method is based on some analytical equations that relate rain to the groundwater regime as modified by the trenches and a simple sliding block model to evaluate the landslide displacements the proposed method also accounts for the delay of the hydraulic response at different depths the above mentioned equations are validated by several comparisons with numerical results obtained using a finite element code or published in the literature finally the method is applied to some case studies to show the effectiveness of the drainage trenches to control the landslide mobility owing to rainfall

mechanical decoupling and thermal structure at the east pacific rise axis 9 n constraints from axial magma chamber geometry and seafloor structures abstract we study the relationships between the seafloor structures and the axial magma chamber geometry in the 9 n overlapping spreading center osc area on the fast spreading east pacific rise epr our observations are based on a new high resolution bathymetric map of the 9 n osc area derived from picks of the seafloor arrival on 3d seismic data and on previously published data that constrain the presence and distribution of melt below the 9 n osc differences in the orientation of structures between the seafloor and the magma chamber indicate a sharp change in principal stress directions with depth suggesting that the brittle crust above the melt sill is decoupled from the melt sill itself and the ductile crust underlying it the stress field within the brittle upper crust results from a local interaction of the two overlapping spreading centers whereas the stress field in the crust below the melt sill corresponds to the regional stress field imposed by plate separation given this mechanical structure of the crust the melt sill shape and location appear to be controlled by the following factors the location of the deep melt source below the melt sill the ambient stress field at the depth of the melt sill and the stress field in the brittle upper crust above the melt sill which thermally shapes the roof of the melt sill through repeated eruptions

asymmetric melt sills and upper crustal construction beneath overlapping ridge segments implications for the development of melt sills and ridge crests a new three dimensional tomographic velocity model and depth converted reflection images of the melt sills beneath the 9 03 n overlapping spreading center on the east pacific rise show that the upper crustal construction at this ridge discontinuity is highly asymmetric with reference to the bathymetric ridge crests of the overlapping limbs despite the similarly curved ridge crests the asymmetries are markedly different under the two limbs and appear to be related to the contrasting evolutionary history of the limbs the overlap basin is closely related to the propagating eastern limb in terms of its seismic structure by contrast the western limb forms a distinct morphologic region that displays little structural relationship to the adjacent overlap basin and other relict basins as the overlapping spreading center is migrating southward the differential development of melt sills and ridge crests may be inferred from the results of this study ridge propagation appears to involve two major processes the advancement of the melt sill at the ridge tip and the development of ridge crest morphology and the neovolcanic axis to the north of the overlap basin region near the existing propagating limb the latter process may result in the abandonment of the current neovolcanic axis leading to the self decapitation of the propagating limb by contrast the self decapitation of the western limb is related to the receding melt sill which lags behind the anticlockwise rotational motion of the ridge crest

the spreading rate dependence of three dimensional mid ocean ridge gravity structure we analyze over 1300 km of high resolution along axis gravity profiles at ridges with half spreading rates ranging from 1 2 to 5 5 cm yr the results show consistently higher along axis gradients of mantle bouguer anomaly at the slow spreading mid atlantic ridge mar 0 3 1 2 mgal km than at the intermediate to fast spreading cocos nazca ridge and east pacific rise epr 0 1 0 2 mgal km the regional peak to trough amplitude of mantle bouguer anomaly is also greater along the mar 30 60 mgal than the cocos nazca ridge and the epr 10 20 mgal with increasing spreading rate the regional peak to trough amplitude of axial seafloor depth decreases from 1000 1700 m to 200 700 m 3 d numerical experiments suggest that mantle contributions to the gravity can be significant only near large offset transforms at the more commonly observed non transform offsets gravity anomalies will reflect crustal thickness variations the along axis gravity data thus indicate that the amplitude of along axis crustal thickness variation decreases with increasing spreading rate we propose that this spreading rate dependent crustal accretion style may originate in the mantle finite amplitude mantle upwelling is intrinsically plume like 3 d beneath a slow spreading ridge but more sheet like 2 d beneath a fast spreading ridge such a transition in mantle upwelling may occur if the relative importance of passive upwelling over buoyant upwelling increases with increasing spreading rate small amplitude 3 d upwellings may occur at a fast spreading ridge but their effects on crustal thickness variations will be significantly reduced by along axis melt flows along a persistent low viscosity crustal magma chamber in contrast the large crustal thickness variations due to 3 d mantle upwellings will be maintained at a slow spreading ridge because less along axis melt flows can occur in the colder and more rigid crust there

incorporation of seawater into mid ocean ridge lava flows during emplacement evidence for the interaction between seawater and lava during emplacement on the deep seafloor can be observed in solidified flows at a variety of scales including rapid quenching of their outer crusts and the formation of lava pillars through the body of the flow recently an additional interaction incorporation of heated seawater vapor into the body of a flow has been proposed large voids and vesicles beneath the surface crusts of mid ocean ridge crest lobate and sheet lava flows and lava drips found within those cavities have been cited as evidence for this interaction the voids resulting from this interaction contribute to the high porosity of the shallow ocean crust and play an important role in crustal permeability and hydrothermal circulation at mid ocean ridges and thus it is important to understand their origin we analyze lava samples from the fast spreading east pacific rise and intermediate spreading galapagos spreading center to characterize this process identify the source of the vapor and investigate the implications this would have on submarine lava flow dynamics we find that lava samples that have interacted with a vapor have a zone of increased vesicularity on the underside of the lava crust and a coating of precipitate minerals i e crystal fringe that are distinct in form and composition from those crystallized from the melt we use thermochemical modeling to simulate the reaction between the lava and a vapor and find that only with seawater can we reproduce the phase assemblage we observe within the crystal fringes present in the samples model results suggest that large scale contamination of the lava by mass exchange with the vapor is unlikely but we observe local enrichment of the lava in cl resulting from the incorporation of a brine phase separated from the seawater we suggest that high eruption rates are necessary for seawater incorporation to occur but the mechanism by which seawater enters the flow has yet to be resolved a persistent vapor phase may be important in inhibiting the collapse of lava flow roofs during natural waxing and waning of lava levels during emplacement allowing lava pathways to be maintained during long lived eruptions in addition we illustrate the potential for a persistent vapor layer to increase local flow rates within submarine flows by up to a factor of three thereby influencing how lava is distributed across the ridge crest

a comparison between theoretical and measured creep profiles of landslides abstract continuous creep contributes to the movements of a landslide in varved clays the creep models developed in this paper are based on the bingham rheological behaviour of the soil in this bingham model the yield strength value and the viscosity coefficient can be defined in different ways as was done by ter stepanian 1963 and yen 1969 the yield strength can be defined as a residual strength value for overconsolidated clays yen or as a fixed fraction of the peak strength parameters cp and p ter stepanian and the viscosity coefficient can be considered as a constant yen or as a flow factor which depends on the effective normal stress ter stepanian creep tests reversal direct shear tests and triaxial tests were carried out on varved clay samples in order to determine yield strength values and the viscosity parameter according to different definitions four creep models have been evaluated these are based on four possible combinations of the different definitions of yield strength and the viscosity parameter yen s definition of the yield strength in combination with a flow factor which depends on the effective stress ter stepanian is found to give the best prediction of the creep velocity data that were measured in the field

numerical modelling of the hydrogeological and geomechanical behaviour of a large slope movement the triesenberg landslide liechtenstein using advanced hydrogeological and geomechanical finite element modelling it has been possible to model the mechanical behaviour of a large slope movement the triesenberg landslide this slope is located along the rhine valley in the principality of liechtenstein and covers an area of around 5 km 2 which includes two villages pore water pressure fields calculated by the hydrogeological model were used as input for the geomechanical model the results obtained through numerical simulation agree fairly well with field measurements of peak velocity spatial and temporal distribution of velocity and total displacements such results were obtained using a modified cam clay elastoplastic constitutive model for which the required material parameters were obtained through careful geotechnical tests these finite element models were carried out in two and three dimensions to gradually improve the understanding of the physical phenomena governing the hydrogeological conditions and the movements of the slope

three dimensional shallow crustal emplacement at the 9 03 n overlapping spreading center on the east pacific rise correlations between magnetization and tomographic images we report a three dimensional 3 d seismic reflection and tomographic survey conducted at the 9 03 n overlapping spreading center osc on the east pacific rise to understand crustal accretion at this feature inversions of travel time data from 19 ocean bottom hydrophones provide a 3 d image of the shallow velocity structure beneath the nontransform offset and associated discordance zone seismic analysis indicates that layer 2a thickness varies between 100 and 900 m and averages 430 m throughout the study area the heterogeneous upper crustal structure at the osc region contrasts with the simpler symmetric structure flanking the midsegments of the east pacific rise the crust affected by the osc migration carries evidence for the complex accretion at the axial discontinuity where the overlap basin may act as a lava pond an area of thick layer 2a covers the southern half of the overlap basin and the propagating ridge tip and shows good correlation with a high magnetization region comparison of the magnetic field anomaly derived from the seismic structure model with the observed sea surface magnetic anomaly suggests that a significant portion of the high magnetization can be related to magnetic source thickness variation rather than solely to the geochemistry of the volcanic rocks

geochemical studies of abyssal lavas recovered by dsrv alvin from eastern galapagos rift inca transform and ecuador rift 1 major element variations in natural glasses and spacial distribution of lavas fifty three major element chemical analyses of volcanic glasses collected by alvin from the eastern gapalagos rift inca transform ecuador rift plate boundary are used to assess tectonic controls on petrogenesis and subrift magma chamber evolution these lavas span a compositional range that includes mid ocean ridge basalts morb feti basalts basaltic andesites and andesites this entire chemical spectrum of rocks was recovered on each of several dives within the eastern galapagos rift along short 2 km traverses of the seafloor at the axis of accretion this juxtapositon of chemically diverse lavas supports the idea that very small shallow level isolated magma bodies are the eruptive sources for fractionated accretionary lavas in this rift segment a distinct difference in chemical diversity occurs between two of the dives 1002 and 998 in the eastern rift lavas recovered east of the break exhibit high degrees of fractionation while rocks from west of this divide have only morb compo sitions this break occurs approximately 60 km west of the galapagos rift inca transform intersection and it is believed to mark an important east to west transition in subrift accretionary dynamics east of this break accretion is perturbed by transform cold edge plus attempted rift propagation effects while west of it a more stable accretionary environment large buffered magma chambers which erupt only morb spectrum lavas prevails only extremely fe and ti enriched lavas were recovered from the southern intersection of the inca transform with the galapagos rift the abundance of feti basalts at this locale is considered to be an effect of attempted rift propagation through thick cold nazca plate lithosphere rocks from the ecuador rift northern inca transform intersection have similar morb chemistries and are among the least fractionated basalts recovered from the cocos nazca plate boundary

spatial analysis of stream length gradient sl index for detecting hillslope processes a case of the gallego river headwaters central pyrenees spain abstract a morphometric analysis of drainage networks and relief using geomorphic indices and geostatistical analyses of topographical data are useful tools for discussing the morphoevolution of a given area among the geomorphic indices the stream length gradient sl index represents a practical tool to highlight anomalous changes in river gradients perturbations of sl are usually indicative of 1 differences in the resistance of outcropping lithological units to erosion 2 sub surface processes such as active faulting and 3 slope failures that directly reach the stream channels particularly in small catchments in this work the sl index was calculated for the upstream sector of the gallego river basin in the central spanish pyrenees to test its accuracy and sensitivity for detecting the imprints of different surface processes a geostatistical procedure is proposed to obtain sl index maps through the interpolation and filtering of the values estimated along the drainage network this method allows computing of sl validation and assessing of its spatial distribution with robust statistical accuracy and objectively defining the anomalies in sl the anomalies in the sl map of the study area which coincide with knickpoints and knickzones were analyzed in detail the results indicate 1 perturbation in the drainage network caused by differences in the resistance to erosion of outcropping lithological units and 2 hillslopes affected by large landslides earth flows and rock falls directly reaching the stream bed this study indicates that the sl index has strong potential to solve geomorphological problems in different geological settings especially in detecting the role of active large scale features that influence landscape evolution

analytical method for predicting the mobility of slow moving landslides owing to groundwater fluctuations this paper deals with the active landslides that are controlled by pore water pressure changes owing to groundwater fluctuations these landslides are usually characterized by low displacement rate with deformations essentially concentrated within a narrow shear zone above which the unstable soil mass moves as a rigid body taking advantage of some original analytical solutions a method is developed for a preliminary prediction of the landslide mobility this method is based on a simple sliding block model and allows the landslide velocity to be readily evaluated once pore water pressure measurements are available an application to a case study documented in the literature is also shown

geomagnetic excursions and paleointensities in the matuyama chron at ocean drilling program sites 983 and 984 iceland basin 1 we report natural remanent magnetization nrm directions and geomagnetic paleointensity proxies for part of the matuyama chron 0 9 2 2 ma interval from two sites located on sediment drifts in the iceland basin at ocean drilling program sites 983 and 984 mean sedimentation rates in the late matuyama chron are 15 9 and 11 5 cm kyr 1 respectively for the older part of the record 1 2 ma oxygen isotope data are too sparse to provide the sole basis for age model construction the resemblance of the volume susceptibility record and a reference 18o record led us to match the two records to derive the age models this match based on site 983 984 susceptibility is consistent with available site 983 984 benthic 18o data paleointensity proxies were derived from the slope of the nrm versus anhysteretic remanent magnetization plot for alternating field demagnetization in the 30 60 mt peak field range paleointensity lows correspond to polarity reversals at the limits of the jaramillo olduvai cobb mountain and reunion subchrons and to seven excursions in nrm component directions magnetic excursions defined here by virtual geomagnetic polar latitudes crossing the virtual geomagnetic equator are observed at 932 1048 1115 1190 1215 cobb mountain subchron 1255 1472 1480 1567 1575 gilsa subchron and 1977 ka the results indicate that geomagnetic directional excursions associated with paleointensity minima are a characteristic of the matuyama chron and probably of polarity chrons in general

deep tow studies of the overlapping spreading centers at 9 03 n on the east pacific rise the deeply towed instrument package of the scripps institution of oceanography was used to study for the first time the fine scale structure of an overlapping spreading center osc system the 9 03 n osc on the east pacific rise epr the eastern and western limbs of this osc system which are 8 km apart and overlap by 27 km show marked differences away from the tips the spreading centers are highly tectonized and differ greatly from the ridge tips the western ridge tip exhibits a few fissures but no sign of recent volcanic activity whereas the eastern ridge tip is highly fissured and has experienced more recent volcanic episodes which are confined to a narrow zone within this highly fissured area in both cases the ridge tip fissures are 10 15 oblique to the strike of the faults that occur on the flanks of the adjacent portion of the opposite spreading axis indicating a recent change in the direction of deviatoric tension and suggesting that the eastern and western spreading centers have been propagating southward and northward respectively the eastern ridge tip fissures are transecting the flank of the western spreading axis suggesting that the eastern spreading center is about to become the through going trace of the east pacific rise in contrast the western spreading center disappears into abyssal hill terrain that was presumably created at the eastern ridge axis some of the very few tectonic features observed in the overlap basin may reflect the existence of a short lived shear couple due to the interaction of the two overlapping spreading centers sediment cover over the whole area and especially in the overlap basin is relatively thick supporting the idea of a time averaged deficit in the magmatic budget at this osc we suggest that the 9 03 n osc developed where two magmatic pulses independent in space and time and propagating along the strike of the east pacific rise away from the loci of melt emplacement failed to meet misalignment of the magmatic conduits resulted in the propagation of the two spreading centers past each other and the development of the ensuing osc geometry independent lines of evidence derived from the three dimensional inversion of the magnetic field at the 9 03 n osc sempere et al 1984 from numerical modelling of the growth of two en echelon elastic cracks in a tensile stress field sempere and macdonald 1986 and from geochemical data langmuir et al 1986 support our interpretation of the deep tow data we suggest that deviations from axial linearity of the spreading centers devals langmuir et al 1986 and small nonoverlapping offsets snoos batiza and margolis 1986 are simply local lows or saddle points along the axial depth profile that arise when two magmatic pulses propagating toward one another meet head on oscs and some saddle points i e devals snoos are all small rapidly evolving ridge axis discontinuities which may represent the surficial expression of the distal ends of small scale longitudinal convection cells beneath the east pacific rise

eruption styles of basalt in oceanic spreading ridges and seamounts effect of magma temperature and viscosity basalts erupted along oceanic zones of spreading and on intraplate seamounts at depths where hydroexplosions are not likely follow various styles of eruption quiet eruptions produce a variety of forms including lava lakes and sheet pillow and pavingstone lavas reactive eruptions occur instead when the lava is thermally shattered as in the formation of hyaloclastites the stresses induced in a rapidly cooling lava flow are important in determining the different lava forms with lava lakes and sheet flows resulting from low stresses pillows from higher stresses and hyaloclastites from even higher stresses which cause rupture calculations show that if we consider basaltic lavas of the same composition the intensity of the stresses induced in the cooling lava increases proportionally to the initial viscosity and inversely to the temperature and rate of discharge of the lava at eruption the viscosity is strongly dependent on the crystal liquid ratio of the magma at eruption the temperature and viscosity of the lava at eruption are related ultimately to the thermal regime of the lithosphere below viscosity tends to increase going from fast to slow spreading ridges and to intraplate seamounts within a given ridge segment temperature tends to decrease and viscosity to increase approaching a transform or overlapping boundary thus the model predicts that going from fast to slow spreading ridges i e from east pacific rise to mid atlantic ridge the probability of forming lava lakes and sheet flows decreases and the probability of forming pillow flows increases moreover within a given ridge segment the areal sheet to pillow ratio should decrease as a transform or overlapping boundary is approached sheet flows should be significant only in the earliest stages of the growth of large intraplate seamounts pillows and hyaloclastites in later stages the probability of forming hyaloclastites should be low in spreading ridges higher in intraplate seamounts recent high resolution observations on the east pacific rise the galapagos rift the mid atlantic ridge and the red sea are consistent with the model because they show that 1 the areal ratio of lava lakes and sheet flows over pillows decreases going from fast to slow spreading ridges 2 within a given ridge segment it decreases approaching a transform and 3 hyaloclastites are important on seamounts only

variation in cross sectional area of the axial ridge along the east pacific rise evidence for the magmatic budget of a fast spreading center along the fast and ultrafast spreading east pacific rise the cross sectional area of the axial ridge varies significantly over length scales similar to its morphologic segmentation using an automated method we measure the ridge area volume per kilometer along axis where there is complete bathymetric coverage along 3500 km of the northern and southern east pacific rise our two study areas encompass numerous transform faults large overlapping spreading centers small overlapping spreading centers and smaller discontinuities first second third and fourth order discontinuities the cross sectional area variation mimics the undulation of the ridge crest depth local area maxima occur toward the middle of segments and the axial area decreases by 40 or more at first and second order discontinuities third order discontinuities are generally marked by smaller disruptions in the ridge area and fourth order offsets do not systematically correspond with features of the cross sectional area profile the correlation between shallower ridges and larger ridge areas breaks down at some locations because axial cross sectional area represents a longer term average of the ridge s magmatic state than axial depth a correlation between large ridge areas and negative residual gravity anomalies indicates that inflated ridges are underlain by low density crust and mantle also a correlation between larger area and higher mgo content of axial basalts suggests that inflated areas generally erupt hotter magmas which are presumably supplied more rapidly to the neovolcanic zone the cross sectional area of the axial ridge appears to correlate with the width of the axis centered low velocity zone in the crust these observations as well as the absence of large relict axial ridges off axis indicate that the axial ridge originates from buoyancy due to thermal expansion and the presence of melt in the crust and mantle within about 10 km of the rise axis portions of the northern east pacific rise underlain by a magma chamber reflector generally occur where the ridge cross sectional area is greatest this supports the connection between processes which inflate the axial ridge and those which heat the crust and upper mantle and produce melt thus while the axial high on fast spreading centers resembles a constructional volcano in cross section it is more like a long narrow balloon whose cross sectional area is a sensitive indicator of magma supply using this relationship we predict with 75 confidence that at least 45 of the unsurveyed northern east pacific rise 18 n to 13 n and 9 n to 5 n and at least 60 of the southern east pacific rise 4 s to 23 s is underlain by a magma chamber reflector

direct observation of a submarine volcanic eruption from a sea floor instrument caught in a lava flow our understanding of submarine volcanic eruptions has improved substantially in the past decade owing to the recent ability to remotely detect such events and to then respond rapidly with synoptic surveys and sampling at the eruption site but these data are necessarily limited to observations after the event in contrast the 1998 eruption of axial volcano on the juan de fuca ridge was monitored by in situ sea floor instruments one of these instruments which measured bottom pressure as a proxy for vertical deformation of the sea floor was overrun and entrapped by the 1998 lava flow the instrument survived being insulated from the molten lava by the solidified crust and was later recovered the data serendipitously recorded by this instrument reveal the duration character and effusion rate of a sheet flow eruption on a mid ocean ridge and document over three metres of lava flow inflation and subsequent drain back after the brief two hour eruption the instrument also measured gradual subsidence of 1 4 metres over the next several days reflecting deflation of the entire volcano summit as magma moved into the adjacent rift zone these findings are consistent with our understanding of submarine lava effusion as previously inferred from seafloor observations terrestrial analogues and laboratory simulations

a landslide forecasting model using ground based sar data the portalet case study this paper presents a kinematic study of the portalet landslide sallent de gallego central spanish pyrenees which was triggered by the construction of a big parking area at the toe of the slope a description of the landslide from a geomorphological point of view is first introduced the measurements of displacement performed by conventional total station inclinometers and differential gps and advanced gb sar ground monitoring techniques are presented and gb sar and dgps datasets are compared the correlation between measured displacements and rainfall series indicates that the landslide is very sensitive to rainfall the continuous gb sar measurements from the 5th of october 2006 to the 21st of november 2006 at a rate of 1 h were used to calibrate a simple 1d infinite model by back analysis the model includes a viscoplastic behaviour and takes into account directly the known daily rainfall intensity and the dissipation of the excess pore fluid through a simple consolidation equation prediction was made in an extended period of time from may 2006 to july 2007 and compared to the dgps measurements

reconciling geochemical and geophysical observations of magma supply and melt distribution at the 9 n overlapping spreading center east pacific rise 1 early studies of mid ocean ridge discontinuities such as transform faults and overlapping spreading centers suggested a lower magma supply compared to ridge segment centers this is reflected in bathymetrically deeper ridge axes decreased hydrothermal activity and the eruption of more evolved lava compositions while many signatures of lower magma supply are observed at the 9 n overlapping spreading center on the east pacific rise geophysical studies indicate extensive sub surface melt in the region suggesting that the present magmatic system is not diminished here major and trace element concentrations of erupted lavas are used to better understand magma supply at a large second order ridge discontinuity we show that the wide range of lava compositions erupted at the 9 n overlapping spreading center is generally consistent with early petrologic models of ridge propagation and require variable degrees of fractional crystallization extensive magma mixing and in some instances crustal assimilation moderately evolved ferrobasalts and feti basalts erupted at the osc indicate that crustal residence times are long enough for significant crystallization of all magmas within the region but the presence of dacitic lavas reflects periods of even lower magma supply where melt replenishment is subordinate to cooling and crystallization the geophysical observations of extensive melt within the shallow crust are reconciled with the geochemistry of the lavas if melts are supplied intermittently to the propagating ridge over relatively short timescales

overlapping spreading centers implications from crack growth simulation by the displacement discontinuity method overlapping spreading centers osc s are a fundamental aspect of accretionary processes at intermediate and fast spreading centers and typically occur at deep points along the axial depth profile they have a characteristic geometry consisting of two en echelon overlapping curving ridges separated by an elongated depression the length to width ratio of this overlap basin is typically 3 1 we have been successful in reproducing the overlapping spreading center geometry by modelling the growth of two initially parallel elastic cracks of given length and offset in a tensile stress field at infinity a boundary element displacement discontinuity method was used to solve this problem our calculated results are compared with seafloor observations in terms of the size and shape of the overlap region for small osc s there is a very good agreement between calculations and observations but for large ones the overlap basin tends to be longer than our predicted results indicate this suggests that the assumptions made in the model i e perfectly elastic isotropic and homogeneous medium are perhaps valid for the brittle lid above the magma chamber that underlies osc s with small offsets 2 km but oversimplified for osc s with large offsets our modelling shows that the initial interaction of closely spaced surface ruptures along spreading centers is to deflect away from one another as they approach the deflection will be the greatest for small misalignments of the fracture systems thus even minor misalignments of the spreading centers may result in the development of osc s where the misalignment is less than the width of the cracking front the fracture systems may meet head on creating a saddle point along the axial depth profile our results support the hypothesis suggested by macdonald et al 1984 in which overlapping spreading centers develop where two magmatic pulses migrate toward each other along the strike of the spreading center following fracture systems and magmatic conduits which are imperfectly aligned

gravity anomalies isostasy and mantle flow at the east pacific rise crest bathymetry and gravity data obtained during a detailed hydrosweep survey of the southern east pacific rise from 7 s to 9 s are used to investigate isostasy at the axis of a fast spreading mid ocean ridge in particular we examine the manner in which the bathymetric crestal high is supported and how this support varies along the axis within the 160 km long 7 12 s 8 38 s ridge segment the crestal high stands about 400 m above the adjacent ridge flanks and has a nearly constant minimum axial depth for a distance of 140 km the summit is broad and flat and an axial summit caldera is present for the entire length of the ridge segment however the width and cross sectional shape of the crestal high vary systematically along the axis it is broad with gentle slopes in the center of the segment but becomes progressively narrower and steeper toward the ends of the ridge segment the ridge crest is marked by a free air gravity anomaly high about 15 20 km wide with an amplitude of 10 15 mgal relative to the ridge flanks mantle bouguer anomalies vary systematically along the axis with minimum values found near the center of the segment the axial mantle bouguer anomalies thus do not reflect the axial depth but are correlated with changes in the cross sectional area of the crestal bathymetric high the effects of cooling and subsidence away from the axis were removed from the bathymetry and free air anomalies to isolate residual topographic and gravity anomalies associated with the ridge crest the residual crestal bathymetric high was modeled as a flexural feature resulting from the upward buoyant load of a region of low density material centered beneath the axis the lithosphere was treated as a broken plate either with a constant flexural rigidity or an effective elastic thickness te which grows at a rate proportional to the square root of distance from the axis the best fitting values of te for the constant rigidity case are in the range of 0 3 0 6 km for the growing plate model te increases at a rate of 0 2 0 3 km the gravity constrains the mass deficiency to extend to a depth of 20 30 km for both lithospheric models we interpret this low density material as a region of partial melt feeding magma to the ridge axis the best fitting density anomalies imply that a 4 9 melt fraction is present beneath the crestal high upwelling of melt to the axis is thus confined to a narrow zone within about 10 km of the axis the mass deficiency and thus the upwelling partial melt are not distributed evenly along the ridge axis but rather are concentrated in the central portion of the ridge segment it thus appears that differences between the along axis gravity and depth patterns observed at slow spreading and at fast spreading ridges are not the result of a change from three dimensional focused upwelling at slow spreading ridges to two dimensional sheetlike upwelling at fast spreading ridges rather the differences in axial gravity and depth between fast and slow spreading ridges reflect differences in the efficiency of the shallow along axis magma distribution

monitoring very slow slope movements by means of sar interferometry a case study from a mass waste above a reservoir in the otztal alps austria the application of radar interferometry to detect slope movements on the order of millimeters to centimeters per year is demonstrated the deformation field of a slope above a hydropower reservoir in the austrian alps was derived from sar interferometric pairs of the satellites ers 1 and ers 2 acquired between july 1992 and august 1998 above the treeline it was possible to map the motion from interferograms covering time spans up to three years whereas ground based geodetic measurements focussed on the movements of the lower slope section the interferometric analysis shows that the mass wasting processes affect the entire slope of 1000 m vertical extent significant interannual differences of the displacement rates became apparent which were found to be related to the pattern of summer rainfall

global positioning system constraints on fault slip rates in southern california and northern baja mexico we use global positioning system gps estimates of horizontal site velocity to constrain slip rates on faults comprising the pacific north america plate boundary in southern california and northern mexico we enlist a simple elastic block model to parameterize the distribution and sum of deformation within and across the plate boundary we estimate a pacific north america relative plate motion rate of 49 3 mm yr one standard deviation consistent with nuvel 1a estimates we are able to resolve robust slip rate estimates for the southernmost san andreas san jacinto and elsinore faults 26 2 9 2 and 6 2 mm yr respectively and for the imperial and cerro prieto faults 35 2 and 42 1 mm yr respectively accounting for about 86 of the total plate motion the remaining 14 appears to be accommodated to the west of these fault systems probably via slip along the san clemente fault and or the san miguel vallecitos rose canyon and newport inglewood fault systems these results are highly consistent with paleoseismic estimates for slip rates implying that off fault strain accumulation within the deforming zone of the plate boundary is largely elastic we estimate that the seismically quiescent southernmost san andreas fault has incurred about 8 2 m of slip deficit over the last few hundred years presumably to be recovered during a future large earthquake

segment scale variations in the crustal structure of 150 300 kyr old fast spreading oceanic crust east pacific rise 8 15 n 10 5 n from wide angle seismic refraction profiles summary we have simultaneously inverted seismic refraction and wide angle moho reflection traveltimes for the 2 d crustal thickness and velocity structure of 150 300 kyr old crust along the east pacific rise epr between the siqueiros and clipperton fracture zones fzs our results show a strong correlation between ridge segmentation and upper and mid crustal seismic velocities with higher velocities near segment centres and lower velocities near segment ends low crustal velocities at the clipperton and siqueiros fzs are interpreted as fracturing resulting from brittle deformation of the crust in the transform domain a relict overlap basin left on the pacific plate by the 9 03 n overlapping spreading centre osc as it propagated southward is associated with a large 1 km s 1 negative upper and mid crustal velocity anomaly this anomaly is consistent with the presence of an unusually thick extrusive section within the basin and with tectonic alteration fracturing and shearing arising from rotation of the basin as it was formed the discordant zone left by this osc on the cocos plate is characterized by moderately low crustal velocities probably because of crustal fracturing as the osc propagated into older crust higher crustal velocities near segment centres may reflect a higher ratio of dikes to extrusives in the upper crust and lower intensity tectonic alteration of the crust than near segment ends the mean crustal thickness along the epr between the siqueiros and clipperton fzs is 6 7 6 8 km the thickest crust is found beneath the lamont seamounts 9 km and in a southward pointing v shaped band located just north of the off axis trace of the 9 03 n osc 7 3 7 8 km the thinnest crust 6 km is found proximal to the clipperton and siqueiros fzs the crust associated with the off axis trace of the 9 03 n osc is not anomalously thin suggesting that magma supply beneath the osc is similar to that of the northern and southern segments we see a similar pattern of crustal thickness variation to that determined using multichannel reflection data including a gradual thickening of the crust from north to south along the northern ridge segment and the location of the thickest crust just north of the 9 03 n osc however the magnitude of the along axis crustal thickness variation we observe along the northern ridge segment between 9 50 n and 9 15 n 1 3 1 8 km excluding the lamont seamounts is significantly less than the 2 3 km of variation previously reported weakening the case for the existence of a low density mantle diapir at 9 50 n inferred from gravity data the band of thick crust located just north of the off axis trace of the 9 03 n osc suggests a close genetic link between this feature and the osc thus we attribute the pattern of crustal thickness variations along the northern segment to the kinematics of the southward propagating 9 03 n osc over the past 0 5 myr and not to along axis melt migration away from a mantle diapir as previously proposed

estimation of seismic and aseismic deformation in mexicali valley baja california mexico in the 2006 2009 period using precise leveling dinsar geotechnical instruments data and modeling ground deformation and seismicity in mexicali valley baja california mexico the southern part of the mexicali imperial valley are influenced by active tectonics and human activity in this study data from two successive leveling surveys in 2006 and 2009 2010 are used to estimate the total deformation occurred in mexicali valley during 2006 2009 the leveling data span more than 3 5 years and include deformation from several natural and anthropogenic sources that acted at different temporal and spatial scales during the analyzed period because of its large magnitude the aseismic anthropogenic deformation caused by fluid extraction in the cerro prieto geothermal field obscures the deformation caused by other mechanisms and sources the method of differential interferograms stacking was used to estimate the aseismic interseismic tectonic and anthropogenic components of the observed displacement using sar images taken in 2007 during a period when no significant seismicity occurred in the study area after removing the estimated aseismic signal from the leveling data residual vertical displacement remained and to identify possible sources and mechanisms of this displacement a detailed analysis of records from tiltmeters and creepmeters was performed the results of this analysis suggest that the residual displacement is mainly caused by moderate sized seismicity in the area of study modeling of the vertical ground deformation caused by the coseismic slip on source fault primary mechanism of the two most important earthquakes may 24 2006 mw 5 4 and december 30 2009 mw 5 8 was performed the modeling results together with the analysis of geotechnical instruments data suggests that this moderate sized seismicity influences the deformation in the study area by coseismic slip on the source fault triggered slip on secondary faults and soft sediments deformation

multi channel seismic imaging of a crustal magma chamber along the east pacific rise a reflection observed on multi channel seismic profiles along and across the east pacific rise between 8 50 n and 13 30 n is interpreted to arise from the top of a crustal magma chamber located 1 2 2 4 km below the sea floor the magma chamber is quite narrow 4 6 km wide but can be traced as a nearly continuous feature for tens of kilometres along the rise axis

influence of enhanced melt supply on upper crustal structure at a mid ocean ridge discontinuity a three dimensional seismic tomographic study of 9 n east pacific rise we present a three dimensional upper crustal model of the 9degrees03 n overlapping spreading center osc on the east pacific rise that assists in understanding the relationship between melt sills and upper crustal structure at a ridge discontinuity with enhanced melt supply at crustal levels our p wave velocity model obtained from tomographic inversion of similar to 70 000 crustal first arrival travel times suggests that the geometry of extrusive emplacement are significantly different beneath the overlapping spreading limbs extrusive volcanic rocks above the western melt sill are inferred to be thin similar to 250 m more extensive accumulation of extrusives is inferred to the west than to the east of the western melt sill the extrusive layer inferred above the eastern melt sill thickens from similar to 350 at the neovolcanic axis to 550 m to the west of the melt sill volcanic construction is likely to be significant in the formation of ridge crest morphology at the osc particularly at the tip of the eastern limb on the basis of our interpretation of the velocity model we propose that enhanced magma supply at crustal levels at the osc may provide an effective mechanism for the migration of ridge discontinuities this dynamic magma supply model may explain the commonly observed nonsteady migration pattern of ridge discontinuities by attributing this to the temporal fluctuations in melt availability to the overlapping spreading limbs

tomographic imaging of the shallow crustal structure of the east pacific rise at 9 30 n compressional wave travel times from a seismic tomography experiment at 9 30 n on the east pacific rise are analyzed by a new tomographic method to determine the three dimensional seismic velocity structure of the upper 2 5 km of oceanic crust within a 20 18 km2 area centered on the rise axis the data comprise the travel times and associated uncertainties of 1459 compressional waves that have propagated above the axial magma chamber a careful analysis of source and receiver parameters in conjunction with an automated method of picking p wave onsets and assigning uncertainties constrains the prior uncertainty in the data to 5 to 20 ms the new tomographic method employs graph theory to estimate ray paths and travel times through strongly heterogeneous and densely parameterized seismic velocity models the nonlinear inverse method uses a jumping strategy to minimize a functional that includes the penalty function horizontal and vertical smoothing constraints and prior model assumptions all constraints applied to model perturbations are normalized to remove bias we use the tomographic method to reject the null hypothesis that the axial seismic structure is two dimensional three dimensional models reveal a seismic structure that correlates well with cross and along axis variations in seafloor morphology the location of the axial summit caldera and the distribution of seafloor hydrothermal activity the along axis segmentation of the seismic structure above the axial magma chamber is consistent with the hypothesis that mantle derived melt is preferentially injected midway along a locally linear segment of the rise and that the architecture of the crustal section is characterized by an en echelon series of elongate axial volcanoes approximately 10 km in length the seismic data are compatible with a 300 to 500 m thick thermal anomaly above a midcrustal melt lens such an interpretation suggests that hydrothermal fluids may not have penetrated this region in the last 103 years asymmetries in the seismic structure across the rise support the inferences that the thickness of seismic layer 2 and the average midcrustal temperature increase to the west of the rise axis these anomalies may be the result of off axis magmatism alternatively the asymmetric thermal anomaly may be the consequence of differences in the depth extent of hydrothermal cooling

volcanic eruptions on mid ocean ridges new evidence from the superfast spreading east pacific rise 17 19 s uniform sediment cover were recovered from lava that buries older faulted terrain the boundary in lava composition coincides with a change in depth to the top of an axial magma lens seismic reflector consistent with magmas from two separate reservoirs being erupted in the same event chemical compositions from throughout the area indicate that lavas with identical compositions can be emplaced in separate volcanic eruptions within individual segments a comparison of our results to global data on submarine mid ocean ridge eruptions suggests consistent dependencies of erupted volume activated fissure lengths and chemical heterogeneity with spreading rate consistent with expected eruptive characteristics from ridges with contrasting thermal properties and magma reservoir depths index terms 3035 marine geology and geophysics midocean ridge processes 8414 volcanology eruption mechanisms 8439 volcanology physics and chemistry of magma bodies 3655 mineralogy and petrology major element composition keywords lava flow chemical heterogeneity erupted volume lava morphology side scan sonar

simplified approach for the analysis of rainfall induced shallow landslides this paper presents a simplified approach for the analysis of shallow landslides triggered by heavy rainfalls which occur after a rainy period on the basis of some analytical solutions this approach combines a simple infiltration model to calculate the change in pore water pressure caused by rain infiltration within the slope with a sliding block model to assess whether a slope failure occurs owing to a prescribed rainfall if this is the case the method also allows the time at which the landslide is triggered and the subsequent slope movements to be readily evaluated

lava deposition history in odp hole 1256d insights from log based volcanostratigraphy a log based volcanic stratigraphy of ocean drilling program hole 1256d provides a vertical cross section view of in situ upper crust formed at the east pacific rise epr with unprecedented resolution this stratigraphy model comprises ten electrofacies principally identified from formation microscanner images in this study we build a lava flow stratigraphy model for the extrusive section in hole 1256d by correlating these electrofacies with observations of flow types from the modern epr such as sheet flows and breccias and pillow lavas and their distribution the resulting flow stratigraphy model for the hole 1256d extrusive section represents the first realization of detailed in situ epr upper oceanic crust construction processes that have been detected only indirectly from remote geophysical data we correlated the flow stratigraphy model with surface geology observed from the southern epr 14 s by shinkai 6500 dives in order to obtain the relationship between lava flow types and ridge axis ridge slope morphology this dive information was also used to give a spatial time reference frame for modeling lava deposition history in hole 1256d in reconstructing the lava deposition history we interpreted that the origins of the 100 m thick intervals with abundant pillow lavas in hole 1256d are within the axial slope where pillow lavas were observed during the shinkai 6500 dives and previous epr surveys this correlation could constrain the lava deposition history in hole 1256d crust using the lateral scale of ridge axis ridge slope topography from the shinkai 6500 observations and assuming the paleospreading rate was constant 50 of the extrusive rocks in hole 1256d crust were formed within 2000 m of the ridge axis whereas nearly all of the remaining extrusive section was formed within 3000 m of the ridge axis these results are consistent with the upper crustal construction model previously suggested by seismic studies

integration between ground based and satellite sar data in landslide mapping the san fratello case study abstract the potential use of the integration of psi persistent scatterer interferometry and gb insar ground based synthetic aperture radar interferometry for landslide hazard mitigation was evaluated for mapping and monitoring activities of the san fratello landslide sicily italy intense and exceptional rainfall events are the main factors that triggered several slope movements in the study area which is susceptible to landslides because of its steep slopes and silty clayey sedimentary cover in the last three centuries the town of san fratello was affected by three large landslides developed in different periods the oldest one occurred in 1754 damaging the northeastern sector of the town in 1922 a large landslide completely destroyed a wide area in the western hillside of the town in this paper the attention is focussed on the most recent landslide that occurred on 14 february 2010 in this case the phenomenon produced the failure of a large sector of the eastern hillside causing severe damages to buildings and infrastructures in particular several slow moving rotational and translational slides occurred in the area making it suitable to monitor ground instability through different insar techniques ps insar permanent scatterers sar interferometry techniques using ers 1 ers 2 envisat radarsat 1 and cosmo skymed sar images were applied to analyze ground displacements during pre and post event phases moreover during the post event phase in march 2010 a gb insar system able to acquire data continuously every 14 min was installed collecting ground displacement maps for a period of about three years until march 2013 through the integration of space borne and ground based data sets ground deformation velocity maps were obtained providing a more accurate delimitation of the february 2010 landslide boundary with respect to the carried out traditional geomorphological field survey the integration of gb insar and psi techniques proved to be very effective in landslide mapping in the san fratello test site representing a valid scientific support for local authorities and decision makers during the post emergency management

seismic evidence of a complex multi lens melt reservoir beneath the 9 n overlapping spreading center at the east pacific rise the crustal structure at fast spreading ridges is characterized by the presence of an axial melt lens along a significant part of the ridge axis over a partially molten lower crust using three dimensional seismic reflection data and waveform inversion here we show the existence of two to three stacked melt lenses beneath both limbs of the 9 n overlapping spreading center on the east pacific rise which we suggest are the source of the very evolved lavas locally observed on the seafloor the melt lenses are 2 4 km wide and lie in a 900 m depth range we suggest that the presence of a complex multi lens melt reservoir in the crust is due to the reduced ambient stress regime hence cracking resulting from the overlap of the two segments of the ridge allowing melt to stay longer in the crust at different depths

multi sensor advanced dinsar monitoring of very slow landslides the tena valley case study central spanish pyrenees abstract in this work it is demonstrated how the combination of multi sensor and multi temporal sar data improves the monitoring capacity of very slow landslides the study area is the upper tena valley central spanish pyrenees where mostly very slow earth flows have caused direct damage estimated at approximately 15 m in the last decade the advanced dinsar processing of ascending orbit alos palsar images 2006 2010 and descending orbit ers envisat 2001 2007 and terrasar x 2008 datasets has provided heterogeneous displacement velocity measurements the projection along the steepest slope of los displacements reduces the geometrical differences introduced by each satellite these results were compared and validated with available d gps measurements in a second step ps displacement data are combined with a landslide inventory increasing the number of monitored landslides with sufficient ps from 4 to 19 obtained from c and x band data to 38 of the total 294 finally the retrieved multi sensor landslides velocities are classified with respect to the magnitude of road damages that occurred in the 2008 2010 period at local scale the combination of multi sensor data was useful to differentiate different landslide displacement directions to measure different velocity patterns within the same moving mass and to distinguish the slower natural and faster human induced landslides the analysis of displacement time series permitted to evaluate the acceleration caused by a destabilising anthropogenic change and the correlation between displacement variability and seasonal precipitation and melting

rapid emplacement of a mid ocean ridge lava flow on the east pacific rise at 9 46 51 n in april 1991 during a submersible diving expedition to the east pacific rise epr crest at 9 46 51 n a new volcanic eruption on the sea floor was discovered here we report results from numerical modeling of that eruption which indicate that 4 106 6 106 m3 of lava was emplaced in 1 2 h with an average eruption rate of 103 106 m3 s 1 comparable to rates observed in hawaii at kilauea s east rift zone if the rapid emplacement of the 1991 epr lava and its short eruption duration are typical of volcanic events at fast spreading mid ocean ridge crests these characteristics have broad implications for our ability to detect monitor and understand the evolution of magmatic and volcanic processes within the axial zone

sill to surface linking young off axis volcanism with subsurface melt at the overlapping spreading center at 9 03 n east pacific rise abstract no young off axis mid ocean ridge lavas have yet been directly linked to underlying off axis melt bodies in this study we present new measurements of 238 u 230 th 226 ra 210 pb isotope compositions for a suite of lavas from the overlapping spreading center osc at 9 03 n on the east pacific rise epr these lavas span a large range of compositions from basalt to dacite and include both axial and off axis samples recovered from a prominent axis parallel pillow ridge and a flat topped seamount that overlie the westernmost extent of a 4 km wide melt lens kent et al 2000 we report 210 pb excesses in axial basalts and basaltic andesites which we suggest results from gas magma fractionation of 222 rn from 226 ra beneath dacite magmas in addition our u series ages agree with visual observations indicating that while most recent volcanic activity occurs at the spreading axis active volcanism also occurs away from the axis specifically the off axis pillow ridge and seamount samples overlying the off axis subsurface melt body have eruption ages of less than 8 ka and likely as young as 1 ka despite being located on crust that has a spreading age of 75 ka the young ages of these lavas combined with existing geological geochemical and geophysical constraints provide evidence for a genetic link between the pillow ridge and seamount lavas and the seismically imaged underlying off axis melt lens this link demonstrates that off axis volcanism does not necessarily come from a sub axial magma body and can be sourced directly from off axis magma bodies

seafloor photo geology and sonar terrain modeling at the 9 n overlapping spreading center east pacific rise 1 a fundamental goal in the study of mid ocean ridges is to understand the relationship between the distribution of melt at depth and seafloor features building on geophysical information on subsurface melt at the 9 n overlapping spreading center on the east pacific rise we use terrain modeling dsl 120a side scan and bathymetry photo geology jason ii and whoi towcam and geochemical data to explore this relationship terrain modeling identified four distinct geomorphic provinces with common seafloor characteristics that correspond well to changes in subsurface melt distribution visual observations were used to interpret terrain modeling results and to establish a relative seafloor age scale calibrated with radiometric age dates to identify areas of recent volcanism on the east limb recent eruptions in the north are localized over the margins of the 4 km wide asymmetric melt sill forming a prominent off axis pillow ridge along the southern east limb recent eruptions occur along a neovolcanic ridge that hugs the overlap basin and lies several kilometers west of the plunging melt sill our results suggest that long term southward migration of the east limb occurs through a series of diking events with a net southward propagation direction examining sites of recent eruptions in the context of geophysical data on melt distribution in the crust and upper mantle suggests melt may follow complex paths from depth to the surface overall our findings emphasize the value of integrating information obtained from photo geology terrain modeling lava geochemistry and petrography and geophysics to constrain the nature of melt delivery at mid ocean ridges

correlation between volcanic and tectonic segmentation of fast spreading ridges evidence from volcanic structures and lava flow morphology on the east pacific rise at 9 10 n 1 combined analyses of volcanic features in dsl 120 sonar data and argo i images along the ridge crest of the east pacific rise 9 09 54 n reveal a consistent decrease in inferred lava effusion rate toward the ends of third order segments the correlation of tectonic segmentation and volcanic style suggests that third order segmentation corresponds to the volcanic segmentation of the ridge along axis changes in volcanic structures from collapse troughs to basaltic lava domes and lava morphology from sheet to pillow flows coincide with the boundaries of morphologically defined third order tectonic segments of the ridge crest visible in shipboard multibeam bathymetry pillow lava flows cover 25 of the surveyed area of the ridge crest and are closely associated with small lava domes that occur primarily at third order segment ends an additional 25 of the surveyed area of the ridge crest is covered by sheet lava flows found in close association with an axial collapse trough the remaining terrain consists of lobate lava flows we interpret the spatial correlations of morphologic structural seismic and petrologic data as evidence that individual volcanic plumbing systems are organized at 20 km spacing along the ridge axis third order segment scale in agreement with the hypothesis that volcanic and tectonic segmentations are correlated for fast spreading ridges we estimate that the longevity of volcanic segments is 104 105 years 1 3 orders of magnitude longer than fourth order segments 102 103 years this implies the present pattern of hydrothermal activity may reorganize tens or hundreds of times while volcanic segmentation remains fairly stable

using gb sar technique to monitor slow moving landslide a ground based sar gb sar interferometer was employed to measure the surface displacements of a landslide occurring in the carnian alps north eastern italy which has affected a national road and seriously damaged a road tunnel still under construction moreover since the landslide is located on the left bank of the tagliamento river valley it is feared that this mass movement might dam the river creating a basin that would increase natural hazard for the valley inhabitants the data collected from december 2002 to july 2005 by a conventional monitoring system consisting of a gps network and boreholes equipped with inclinometric tubes showed that the landslide was moving at a quasi constant rate of about 3 cm per year due to the slow deformation rate of the landslide a recently developed gb sar technique based on the analysis of a restricted ensemble of coherent points was used two surveys each lasting two days were planned in december 2004 and july 2005 in order to map and measure the surface displacements that occurred over time the results from the radar were compared with the ones derived from the gps monitoring network an agreement was achieved among the data collected showing the capability of the gb sar technique to measure displacements even within a time span of several months between the surveys

a review of terrestrial radar interferometry for measuring surface change in the geosciences this paper presents a review of the current state of the art in the use of terrestrial radar interferometry for the detection of surface changes related to mass movement different hardware types and acquisition concepts are described which use either real or synthetic aperture for radar image formation we present approaches for data processing procedures paying special attention to the separation of high resolution displacement information from atmospheric phase variations recent case studies are used to illustrate applications in terrestrial radar interferometry for change detection applications range from detection and quantification of very slow moving millimeters to centimeters per year displacements in rock walls from repeat monitoring to rapid processes resulting in fast displacements 50 m yr acquired during single measurement campaigns with durations of only a few hours fast and episodic acting processes such as rockfall and snow avalanches can be assessed qualitatively in the spatial domain by mapping decorrelation caused by those processes a concluding guide to best practice outlines the necessary preconditions that have to be fulfilled for successful application of the technique as well as in areas characterized by rapid decorrelation empirical data from a ku band sensor show the range of temporal decorrelation of different surfaces after more than two years for rock surfaces and after a few seconds to minutes in vegetated areas during windy conditions the examples show that the displacement field can be measured for landslides in dense grassland ice surfaces on flowing glaciers and snowpack creep copyright 2014 john wiley sons ltd

channelized lava flows at the east pacific rise crest 9 10 n the importance of off axis lava transport in developing the architecture of young oceanic crust 1 submarine lava flows are the building blocks of young oceanic crust lava erupted at the ridge axis is transported across the ridge crest in a manner dictated by the rheology of the lava the characteristics of the eruption and the topography it encounters the resulting lava flows can vary dramatically in form and consequently in their impact on the physical characteristics of the seafloor and the architecture of the upper 50 500 m of the oceanic crust we have mapped and measured numerous submarine channelized lava flows at the east pacific rise epr crest 9 10 n that reflect the high effusion rate and high flow velocity end member of lava eruption and transport at mid ocean ridges channel systems composed of identifiable segments 50 1000 m in length extend up to 3 km from the axial summit trough ast and have widths of 10 50 m and depths of 2 3 m samples collected within the channels are n morb with mg indicating eruption from the ast we produce detailed maps of lava surface morphology across the channel surface from mosaics of digital images that show lineated or flat sheets at the channel center bounded by brecciated lava at the channel margins modeled velocity profiles across the channel surface allow us to determine flux through the channels from 0 4 to 4 7 103 m3 s and modeled shear rates help explain the surface morphology variation we suggest that channelized lava flows are a primary mechanism by which lava accumulates in the off axis region 1 3 km and produces the layer 2a thickening that is observed at fast and superfast spreading ridges in addition the rapid high volume flux eruptions necessary to produce channelized flows may act as an indicator of the local magma budget along the epr we find that high concentrations of channelized lava flows correlate with local across axis ridge morphology indicative of an elevated magma budget additionally in locations where channelized flows are located dominantly to the east or west of the ast the ridge crest is asymmetric and layer 2a appears to thicken over a greater distance from the ast toward the side of the ridge crest where the channels are located

major element constraints on melting differentiation and mixing of magmas from the galapagos 95 5 w propagating rift system projections in the pseudo quaternary system diopside plagioclase olivine quartz di pl ol q are used in this paper as a base on which to plot additional compositional petrologic or tectonic variables used in this manner the projections provide a sensitive means of displaying and evaluating the chemical variability of mid ocean ridge basalt morb suites such as that of the galapagos 95 5 w propagating rift system and allow mantle controls on the chemical variability of morb to be distinguished from the predominant effects of shallow level crystal fractionation and mixing primitive lavas mg 63 from the 95 5 w region form a broadly linear array within the di pl ol q tetrahedron parallel to the di ol join in terms of two recent high pressure studies of morb petrogenesis stolper 1980 takahashi and kushiro 1983 the primitive liquids in this array are not primary but have evolved by less than 10 olivine fractionation from an array of primary liquids which separated from residual mantle over a range of pressures between 10 20 kb with appropriate assumptions as to residual lithology and mg of residual olivine the nature and origin of 95 5 w primary magmas can be deduced 1 lavas of the normal rift are derived from a broad range of primary magmas that separated from compositionally uniform in terms of major elements mantle over a pressure range of 10 20 kb 2 beneath the newly forming propagating rift melting is initiated perhaps by pressure release at shallow depth 9 11 kb degree of melting and source composition appear similar to those for the normal rift within a few km of the propagating rift tip this shallow source is joined by a second deeper 11 12 kb more iron rich source both sources persist for at least 100 km along the propagating rift but the deeper source appears to become dominant farther behind the tip maximum pressure for melt separation anywhere beneath the propagating rift is less than 15 kb in addition to these source effects the projections allow a more complete description of the shallow level fractionation and mixing effects along the propagating rift primitive lavas of restricted composition erupted near the rift tip give way within 2 3 km to an increasingly diverse suite of lavas characterized by variable extents of fractionation and by numerous single mixing events consistent with magmatic evolution in small only occasionally interconnected magma bodies beyond 15 km the diversity gradually declines toward a restricted population of cpx saturated lavas which characterizes the propagating rift beyond 75 km and is consistent with the presence of a large well mixed magma chamber in this region

a physical model predicting instability of rock slopes with locked segments along a potential slip surface abstract better understanding the evolutionary mechanism of landslides is very important to predict their occurrence based on firm scientific grounds the stability of a rock slope is often dominated by one or more locked segments along a potential slip surface with a large bearing capacity to resist instability we propose three preliminary categories for locked segments and develop a physical model for predicting the instability of rock slopes with locked segments by coupling a one dimensional renormalization group model with a strain softening constitutive model based on the weibull distribution we found that the ratio of the strain at the peak strength point of a locked segment to the strain at its volume dilation point is exclusively dependent on the weibull shape parameter m and is approximately constant at 1 48 the accelerating displacement of the slope can be observed from the volume dilation point of the locked segment due to unstable fracture propagation the physical model for slopes with multiple locked segments is only related to the displacement corresponding to the volume dilation point of the first locked segment and the number of locked segments applying this model to two typical cases the yanchihe rockslide in china and the wedge rockslide in libby dam usa the results are in agreement with field records this work will help to better understand the failure mechanism of slopes with locked segments and may provide guidelines for disaster mitigation and prevention

seismic mapping of a magma chamber beneath the valu fa ridge lau basin we analyze a dense grid of seismic normal incidence and wide angle data collected over an active back arc spreading center in the lau basin of the southwest pacific our survey area covers the whole of a 35 km long morphological segment and a small overlapping spreading center a bright reflector which is coincident with a velocity inversion at a depth of 3 2 0 2 km below the seafloor is observed on every one of the 40 across axis profiles we interpret this reflector as being the roof of a crustal magma chamber the widest magma chamber reflector occurs beneath the overlapping spreading center where it extends up to 4 km being imaged beneath both ridges and in places beneath the overlap basin elsewhere the width of the reflector varies between 0 6 and 2 3 0 4 km the narrowest reflectors are observed beneath deviations devais of the ridge axis in addition to being observed on each of the kilometer spaced across axis profiles the reflector is also seen as a continuous event for at least 10 km on a profile along the ridge axis the reflection coefficient of the event is between 0 34 and 0 65 this requires the melt at the top of the chamber to have a p wave velocity less than 2 7 km s if the interface is planar or less than 3 8 km s if the interface is layered

landslide monitoring by using ground based sar interferometry an example of application to the tessina landslide in italy abstract an innovative technique based on radar interferometry and implemented using ground based instrumentation has been applied for monitoring the tessina landslide italy belluno the technique has allowed us to derive multitemporal surface deformation maps of the entire depletion zone of the landslide with a high spatial resolution and accuracy the portable device used in this application is known as linear sar lisa and it is able to provide measurements at 17 ghz with a synthetic aperture of up to 2 8 m the results have been validated by comparing the recorded pixel displacements with independent measurements carried out by a motorized theodolite and electronic distance meter edm on two benchmarks

using global positioning system techniques in landslide monitoring the precise determination of point coordinates with conventional global positioning system gps techniques often required observation times of one to several hours in the last few years new gps methods have been developed among them the fast static and real time kinematic with higher productivity and good theoretical precision the main objective of this paper is to ascertain the performance of these methods in landslide monitoring practice we present first of all the basic principles of the gps the equipment and working procedures we discuss afterwards the applicability of the gps to the monitoring of landslide surface displacements compared with the classical surveying methods the gps allows a larger coverage and productivity with similar accuracy furthermore it can work in all kinds of weather conditions and a direct line of sight between stations is not required finally we present an example of the performance of the gps equipment in the landslide of vallcebre eastern pyrenees spain this landslide has been periodically monitored since 1987 with terrestrial photogrammetry and geodetic measurements theodolite electronic distance metres edm the movement extends over an area of 0 8 km2 and has experienced displacements as large as 1 6 m during the period 1996 1997 14 campaigns over a period of 26 months using both static and kinematic gps methods have been carried out the gps measurements have been compared with the results obtained with the edm inclinometers and wire extensometers and checked against fixed stable points the precision achieved with the gps measurements is 12 to 16 mm in the horizontal plane and 18 to 24 mm in elevation 2000 elsevier science b v all rights reserved