new global marine gravity model from cryosat 2 and jason 1 reveals buried tectonic structure gravity models are powerful tools for mapping tectonic structures especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment we combined new radar altimeter measurements from satellites cryosat 2 and jason 1 with existing data to construct a global marine gravity model that is two times more accurate than previous models we found an extinct spreading ridge in the gulf of mexico a major propagating rift in the south atlantic ocean abyssal hill fabric on slow spreading ridges and thousands of previously uncharted seamounts these discoveries allow us to understand regional tectonic processes and highlight the importance of satellite derived gravity models as one of the primary tools for the investigation of remote ocean basins

a geodynamic model of mantle density heterogeneity using cenozoic and mesozoic plate motion reconstructions we derive a model of present day mantle density heterogeneity under the assumption that subducted slabs sink vertically into the mantle the thermal buoyancy of these slabs is estimated from the observed thermal subsidence cooling of oceanic lithosphere slab velocities in the upper mantle are computed from the local convergence rate we assume that slabs cross the upper lower mantle interface and continue sinking into the lower mantle with a reduced velocity for a velocity reduction factor between 2 and 5 our slab heterogeneity model is as correlated with current tomographic models as these models are correlated with each other we have also computed a synthetic geoid from our density model for a viscosity increase of about a factor of 40 from the upper to lower mantle our model predicts the first 8 spherical harmonic degrees of the geoid with statistical confidence larger than 95 and explains 84 of the observed geoid assuming that the model c21 and s21 terms are absent due to a long relaxation time for earth s rotational bulge otherwise 73 of the geoid variance is explained the viscosity increase is consistent with our velocity reduction factor for slabs entering the lower mantle since downwelling velocities are expected to scale roughly as the logarithm of viscosity loge 40 3 7 these results show that the history of plate tectonics can explain the main features of the present day structure of the mantle the dynamic topography induced by this heterogeneity structure consists mainly of about 1 km amplitude lows concentrated along the active continental margins of the pacific basin our model can also be used to predict the time variation of mantle heterogeneity and the gravity field we find that the age of the geoid defined as the time in the past before which the geoid becomes uncorrelated with the present geoid is about 50 m y our model for the history of the degree 2 geoid which is equivalent to the history of the inertia tensor should give us a tool to study the variations in earth s rotation pole indicated in paleomagiietic studies

cenozoic tectonic evolution in the central andes in northern chile and west central bolivia implications for paleogeographic magmatic and mountain building evolution a review of available stratigraphic structural and magmatic evolution in northernmost chile and adjacent peru and bolivia shows that in this region 1 compression on the paleogene intra arc during the middle eocene incaic phase formed the nne ssw oriented incaic range along the present day precordillera and western cordillera and 2 post incaic tectonic conditions remained compressive until present contrasting with other regions of the andes where extensional episodes occurred during part of this time lapse a late oligocene early miocene peak of deformation caused further uplift the incaic range formed a pop up structure bounded by two thrusts systems of diverging vergencies it represented a major paleogeographic feature that separated two domains with different tectonic and paleogeographic evolutions and probably formed the andean water divide this range has been affected by intense erosion and was symmetrically flanked by two major basins the pampa del tamarugal and the altiplano magmatic activity remained located along the previous late cretaceous early eocene arc with slight eastward shift further compression caused westvergent thrusting and uplift along the western eastern cordillera bounding the altiplano basin to the east by another pop up shaped ridge eastward progression of deformation caused eastvergent thrusting of the eastern cordillera and subandean zone

seismicity related to the glacier of cotopaxi volcano ecuador 1 significant seismic activity is generally recorded on volcanoes covered by an icecap this work was carried out in order to quantify the role of the glaciers in the generation of seismicity for cotopaxi volcano we compared the seismic activity registered on the glacier and on the rock near the snout of the north flank glacier we focused on the analysis of low frequency events 5 hz similar to volcanic lp events when recorded on rock base the particle motion analysis helps to estimate source locations which are distributed in crevasses areas high incident angles suggest a superficial origin these events are interpreted as icequakes for which we propose as source mechanism a fluid driven crack model triggered by ice cracking or hydraulic transients the low quality factor values estimated are consistent with the resonance of an ice crack filled with water this work shows that low frequency icequakes can be confusingly taken as volcanic lp events

constraints on dynamic topography from asymmetric subsidence of the mid ocean ridges abstract stresses from mantle convection deflect earth s surface vertically producing dynamic topography that is important for continental dynamics and sea level change but difficult to observe due to overprinting by isostatic topography for long wavelengths 10 4 km the amplitude of dynamic topography is particularly uncertain with mantle flow models typically suggesting larger amplitudes 1000 m than direct observations here we develop a new constraint on the amplitude of long wavelength dynamic topography by examining asymmetries in seafloor bathymetry across mid ocean ridges we compare bathymetric profiles across the mid atlantic ridge mar and the east pacific rise epr and we find that the south american flank of both ridges subsides faster than its opposing flank this pattern is consistent with dynamic subsidence across south america supported by downwelling in the lower mantle to constrain the amplitude of dynamic topography we compare bathymetric profiles across both ridges after correcting bathymetry for several different models of dynamic topography with varying amplitudes and spatial patterns we find that long wavelength dynamic topography with an amplitude of only 500 m explains the observed asymmetry of the mar a similar model can explain epr asymmetry but is complicated by additional asymmetrical topography associated with tectonic crustal thickness and or asthenospheric temperature asymmetries across the epr after removing 500 m of dynamic topography both the mar and epr exhibit a slower seafloor subsidence rate 280 290 m myr 1 2 than previously reported our finding of only 500 m of long wavelength dynamic topography may indicate the importance of thermochemical convection and or large viscosity variations for lower mantle dynamics

effects of latent heat release at phase boundaries on flow in the earth s mantle phase boundary topography and dynamic topography at the earth s surface abstract mantle flow models that do not consider the effects of latent heat on phase boundaries typically predict dynamic surface topography too large to be compatible with observations here these effects were implemented in a mantle flow model and resulting changes in dynamic topography and topography of phase boundaries were computed inclusion of these effects was found to reduce the rms amplitude of dynamic topography by about 50 60 m still leaving a substantial misfit from observations in most cases considered generally it also leads to a slight improvement of correlation with dynamic surface and phase boundary topography constrained by observations results thus indicate that the model implemented here is applicable to the earth but that other effects need to be considered as well in order to fully explain phase boundary and dynamic surface topographies

palaeoclimatic implications of mio pliocene sedimentation in the high altitude intra arc lauca basin of northern chile abstract this paper examines the late miocene to pliocene sedimentary succession in the high altitude intra arc lauca basin of northern chile and discusses the palaeoclimatic evidence recorded within the basin fill sedimentological and geochronological data allow the reconstruction of four stages of the fluvial to lacustrine basin fill from the late miocene 6 4 ma to the late pleistocene we interpret the sedimentary evolution to reflect changes in precipitation during a time interval of general aridity climatic changes exerted the dominant control on sediment accumulation volcanism tectonism changes in morphology and sediment supply were factors of subordinate importance stage 1 comprises a clastic red bed sequence developed during the late miocene under relatively humid conditions an abrupt change in depositional style occurred around 6 4 ma when ephemeral saline lake sedimentation prevailed stage 2 this change in depositional style is considered to document the begin of a phase of desiccation that lasted until the early pliocene 3 7 ma and which was succeeded by less arid climatic conditions during the late pliocene and pleistocene stages 3 and 4 the transition between stages 1 and 2 and the subsequent dry period is assumed to coincide with a global cooling event during the latest miocene to early pliocene comparable sedimentary responses to this climatic change can be expected in adjacent basins of the central andes

analysis of time series of glacier speed columbia glacier alaska during the summers of 1984 and 1985 laser measurements were made of the distance from a reference location to markers on the surface of the lower reach of columbia glacier alaska the data have numerous gaps mostly because of inclement weather the laser measurements were corrected for variations in atmospheric temperature and pressure and for the trajectory of the marker the marker speed was calculated by using a combination of cubic splines and digital filters to arrive at a data set with 1 hour time intervals the speed varies from 7 to 15 m d and has three noteworthy components 1 a low frequency perturbation in speed with a time scale of days related to increased precipitation 2 semidiurnal and diurnal variations related to sea tides and 3 diurnal variations related to glacier surface melt the low frequency and tidal period variations are separated by low pass filtering and subtracting the filtered data from the original data the variations from melt runoff and tides have the same frequency range and are examined using harmonic analysis and multiple regression with the various forcing functions the high frequency portion of the ice speed signal is dominated by tidal influences and to a lesser extent by meltwater influences the low frequency portion of the signal is dominated by the effects of precipitation

metallogeny structural evolution post mineral cover distribution and exploration in concealed areas of the northern chilean andes abstract mineral exploration of prospective areas concealed by extensive post mineralization cover is growing being very complex and expensive the projection of rich and giant paleocene to early oligocene porphyry cu mo belts in northernmost chilean andes 17 5 19 5 s has major exploration potential but only a few minor deposits have been reported to date due to the fact that the area is largely covered by post mineral strata we integrate the cenozoic stratigraphic structural and metallogenic evolution of this sector in order to identify the most promising regions related to lesser post mineral cover and the projection of different metallogenic belts the paleocene to early eocene metallogenic belt extends along the precordillera with ca 30 km wide and includes porphyry cu prospects and small cu mo au ag vein and breccia pipe deposits geochronological data indicate an age of 55 5 ma for an intrusion related to one deposit and ages from 69 5 to 54 5 ma for hydrothermal alteration in one porphyry cu prospect and largest known cu deposits the middle eocene to early oligocene porphyry belt in the western cordillera farther east is associated with 46 44 ma intrusions it is estimated to be 40 km wide but is largely concealed by thick post mineral cover the youngest miocene to early pliocene metallogenic belt also in the western cordillera is well exposed and includes au ag epithermal and polymetallic veins and manto type deposits the oligocene holocene cover consists of a succession of continental sedimentary and volcanic rocks that overall increase in thickness from 0 to 5000 m from west to east these strata are subhorizontal in the west and folded faulted towards the east miocene gentle anticlines and monocline flexures extend along strike for 30 60 km in the precordillera and were generated by propagation of high angle east dipping blind reverse faults with at least 300 900 m of oligocene bedrock offset the thickness of cover exceeds 2000 m in the eastern central depression whereas it is generally less than 1000 m in the precordillera along the paleocene to early eocene porphyry cu belt and it can reach locally up to 5000 m in the western cordillera above the middle eocene to early oligocene belt in the studied andean segment the miocene to early pliocene metallogenic belt is superimposed on the paleocene to oligocene belts in a 40 50 km wide zone this overlap may be explained by an accentuated migration of the magmatic front from east to west since ca 25 ma as a consequence of subduction slab steepening after a period of magmatic lull and flat subduction from ca 30 35 to 25 ma the identified areas of lesser cover thickness are prone to exploration for concealed deposits especially along the projection of major porphyry cu mo belts

on the amplitude of dynamic topography at spherical harmonic degree two abstract two large seismically slow regions in the lower mantle beneath africa and the pacific ocean are sometimes referred to as superplumes this name evokes images of large scale active upwellings however it remains unclear whether these features are real or represent collections of multiple regular mantle plumes here we investigate the implications of these upwellings for dynamic topography we combine detailed measurements of oceanic residual topography from hoggard et al 2016 with continental constraints derived from crust1 0 to produce a global model expanded in spherical harmonics observed dynamic topography is subsequently compared to predictions derived from mantle flow following steinberger 2016 using tomographic density models results yield relatively good overall agreement and amplitude spectra with similar slopes except for degree two i e 10 000 km wavelengths where predicted amplitude is more than two times as large and is dominated by contributions from the lower mantle predictive models suggest two large scale uplifted regions above the superplumes that are barely seen in the observed topography we suggest that this mismatch can only partly be reconciled by altering the seismic velocity to density conversion factor or by including the effects of lower mantle chemical heterogeneity in addition it may be important to consider more significant revisions to the lower mantle flow patterns such as those possibly induced by different radial viscosity profiles and laterally varying or anisotropic lower mantle viscosity

spatial extent of a hydrothermal system at kilauea volcano hawaii determined from array analyses of shallow long period seismicity 2 results we present a probabilistic method to locate the source of seismic events using seismic antennas the method is based on a comparison of the event azimuths and slownesses derived from frequency slowness analyses of array data with a slowness vector model several slowness vector models are considered including both homogeneous and horizontally layered half spaces and also a more complex medium representing the actual topography and three dimensional velocity structure of the region under study in this latter model the slowness vector is obtained from frequency slowness analyses of synthetic signals these signals are generated using the finite difference method and include the effects of topography and velocity structure to reproduce as closely as possible the behavior of the observed wave fields a comparison of these results with those obtained with a homogeneous half space demonstrates the importance of structural and topographic effects which if ignored lead to a bias in the source location we use synthetic seismograms to test the accuracy and stability of the method and to investigate the effect of our choice of probability distributions we conclude that this location method can provide the source position of shallow events within a complex volcanic structure such as kilauea volcano with an error of 200 m

tectonics and climate of the southern central andes the history of the southern central andes including the world s second largest plateau and adjacent intermontane basins and ranges of the eastern cordillera and the northern sierras pampeanas of argentina and bolivia impressively documents the effects of tectonics and topography on atmospheric circulation patterns the development of orographic barriers and their influence on erosion and landscape evolution at various timescales protracted aridity in the orogen interior has facilitated the creation and maintenance of the puna altiplano plateau contraction and range uplift filling of basins and possibly wholesale uplift of the plateau increased gravitational stresses in the orogen interior which caused the eastward migration of deformation into the foreland and successive aridification the uplift of the andean orogen has also had a far reaching influence on atmospheric and moisture transport patterns in south america this is documented by the onset of humid climate conditions on the eastern side of the andes in late miocene time which was coupled with the establishment of dramatic precipitation gradients perpendicular to the orogen and changes in tectonic processes in the andean orogenic wedge

the epithermal gold silver deposit of choquelimpie northern chile the choquelimpie gold silver deposit is located at an elevation of 4 860 m above sea level 115 km due east of arica in northern chile a 5 500 metric ton day open pit mine heap leach operation was brought on stream in 1988 by the sociedad contratual minera vilacollo whose shareholders are shell chile westfield minera and citibank the deposit is located near the arica bend of the south american continent where the earth s crust has a thickness of more than 70 km it lies in a belt of calc alkalic to alkali calcic miocene to recent volcanism which runs parallel to the pacific coast and contains a series of volcanic hosted precious metal deposits these have been worked in peru chile and bolivia since the time of the spanish conquest usually for ag but also with locally important au values these deposits are characterized by ag au pb zn the volcano hosting the mineralization is a subalkalic stratovolcano of late miocene age a late magmatic event has been dated at 6 60 or 0 20 ma the volcano is located at the intersection of a major n 60 degrees e trending lineament with a n 35 degrees e fault active from the late miocene to the recent the volcano consists of dacitic and andesitic volcanic flows and breccias and is intruded by dacite domes erosion of its central part has exposed a zone of hydrothermal alteration and mineralization centered upon an andesitic feldspar porphyry which is probably a dome most of the mineralization worked until recently came from narrow argentiferous veins but the present operation is centered on a series of hydrothermal breccia bodies emplaced in a n 60 degrees e trending zone 2 km long peripheral to the mineralized zone propylitic alteration exists grading inward to a sericite pyrite assemblage toward the breccia bodies this assemblage is overprinted by silicification associated with base metals pyrite kaolinite and barite the breccias themselves and some adjacent lithologies contain precious metal species including native au and ag electrum and argentite a final stage of mineralization is represented by base and precious metals in veins which cut the breccias oxidation has produced supergene enrichment of ag but probably not of au limited fluid inclusion data from structures peripheral to the breccia bodies indicate homogenization temperatures ranging from 213 degrees to 305 degrees c salinities are below 5 wt percent nacl equiv samples from one location show evidence of boiling at a minimum depth estimated as 300 m below the paleowater table based on the available evidence choquelimpie is interpreted as a volcanic hosted acid sulfate epithermal deposit it is associated with an ag au pb zn metallogenic province which contrasts with the maricunga and el indio au ag cu as provinces of central chile

dynamic topography gravity and the role of lateral viscosity variations from inversion of global mantle flow lateral viscosity variations lvvs in the mantle influence geodynamic processes and their surface expressions with the observed long wavelength geoid free air anomaly gravity gradient in three directions and discrete high accuracy residual topography we invert for depth and temperature dependent and tectonically regionalized mantle viscosity with a mantle flow model the inversions suggest that long wavelength gravitational and topographic signals are mainly controlled by the radial viscosity profile the pre cambrian lithosphere viscosity is slightly one order of magnitude higher than that of oceanic and phanerozoic lithosphere plate margins are substantially weaker than plate interiors and viscosity has only a weak apparent dependence on temperature suggesting either a balancing between factors or a smoothing of actual higher amplitude but short wavelength lvvs the predicted large scale lithospheric stress regime compression or extension is consistent with the world stress map thrust or normal faulting both recent compiled high accuracy residual topography and the predicted dynamic topography yield 1 km amplitude long wavelength dynamic topography inconsistent with recent studies suggesting amplitudes of 100 to 500 m such studies use a constant positive admittance transfer function between topography and gravity in contrast to the evidence which shows that the earth has a spatially and wavelength dependent admittance with large negative admittances between 4000 and 10 4 km wavelengths

tidal and spatial variability of flow speed and seismicity near the grounding zone of beardmore glacier antarctica gps measurements of tidal modulation of ice flow and seismicity within the grounding zone of beardmore glacier show that tidally induced fluctuations of horizontal flow are largest near the grounding line and decrease downstream seismic activity is continuous but peaks occur on falling and rising tides beamforming methods reveal that most seismic events originate from two distinct locations one on the grid north side of the grounding zone and one on the grid south side the broad pattern of deformation generated as beardmore glacier merges with the ross ice shelf results in net extension along the grid north side of the grounding zone and net compression along the grid south side during falling tides seismic activity peaks on both sides because of increased vertical flexure across the grounding line during rising tides seismic activity in the region of extension on the grid north side is relatively low because the tidal influence on both horizontal strain rate and vertical flexure is small on the grid south side during rising tides however tidally induced horizontal strain rates promote increased seismicity in regions of long term compressional flow paths our study highlights how concurrent geodetic and seismic measurements provide insight into grounding zone mechanics and their influence on ice shelf buttressing

digital isochrons of the world s ocean floor we have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self consistent set of global isochrons and associated plate reconstruction poles the age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models we have constructed an age grid with error estimates for each grid cell as a function of 1 the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid 2 the distance of a given grid cell to the nearest magnetic anomaly identification and 3 the gradient of the age grid i e larger errors are associated with high age gradients at fracture zones or other age discontinuities future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere the heat loss of the earth ridge push forces through time asymmetry of spreading and providing constraints for seismic tomography and mantle convection models

global dynamic topography observations reveal limited influence of large scale mantle flow mantle flow causes earth s surface to uplift and subside global analysis of dynamically generated topography suggests that temperature induced small scale mantle flow has a bigger influence on surface topography than large scale mantle flow

a 15 year record of frontal glacier ablation rates estimated from seismic data we present a unique time series of continuous glacier frontal ablation rates with weekly resolution over 15 years estimated from seismic calving observations at kronebreen svalbard using linear statistical models we calibrate the seismic record with seven years of satellite derived frontal ablation measurements the two basic input parameters required for our models are the cumulative duration of individual seismic calving events and the incompleteness of the seismic record to correct for the effect of seismic background noise frontal ablation follows the seasonal glacier speed up peaking 1 2 months after the melt season maximum short lived peaks are associated with melt and rain events cumulative frontal ablation of kronebreen between 2001 and 2015 is about 4 0 km3 3 7 gt with the greatest annual loss 0 45 km3 between 2013 and 2014 at the onset of the recent accelerated retreat of the glacier our approach provides a potential method for monitoring tidewater glaciers worldwide that have sufficiently close seismic instrumentation

renormalisation of global mantle dynamic topography predictions using residual topography measurements for normal oceanic crust abstract we compare mantle dynamic topography predicted from mantle convection modelling with residual topography measurements for oceanic regions where crustal basement thickness is 10 0 km or less measurements of residual topography calculated by removing the isostatic effects of crustal thickness variation bathymetry sediments ice and lithosphere thermal anomalies from the observed topography are inaccurate for continents and oceanic plateaus due to uncertainties in determining their crustal thickness and density as a consequence residual topography measurements for these regions are unsuitable for testing mantle dynamic topography predictions residual topography is more accurately determined for oceanic crust we use global mapping of crustal basement thickness using gravity anomaly inversion to identify oceanic crust of 10 0 km thickness or less to select measured residual topography for comparison with predicted mantle dynamic topography for these oceanic regions we compare mantle dynamic topography and residual topography and using amplitude histogram matching and grid searches compute the amplitude rescaling and shift which needs to be applied to predicted mantle dynamic topography to fit the observed residual topography we examine three global compilations which use different approaches to determine mantle dynamic topography i steinberger 2007 which uses seismic topography deeper than 220 km to determine mantle density ii flament et al 2013 which uses plate velocity and subduction history and iii steinberger et al 2017 which uses seismic tomography including that above 220 km to determine shallow upper mantle densities our analysis shows that for the steinberger 2007 and flament et al 2013 compilations the predicted mantle dynamic topography for oceanic regions requires a rescaling of approximately 0 5 and a negative shift of approximately 500 m to match the observed residual topography in contrast steinberger et al 2017 which includes shallow upper mantle densities above 220 km requires only a small shift 50 m but a greater scaling of 0 375 maps of renormalised rescaled and shifted mantle dynamic topography for steinberger et al 2017 show a close resemblance to measured residual topography

the source of infrasound associated with long period events at mount st helens 1 during the early stages of the 2004 2008 mount st helens eruption the source process that produced a sustained sequence of repetitive long period lp seismic events also produced impulsive broadband infrasonic signals in the atmosphere to assess whether the signals could be generated simply by seismic acoustic coupling from the shallow lp events we perform finite difference simulation of the seismo acoustic wavefield using a single numerical scheme for the elastic ground and atmosphere the effects of topography velocity structure wind and source configuration are considered the simulations show that a shallow source buried in a homogeneous elastic solid produces a complex wave train in the atmosphere consisting of p sv and rayleigh wave energy converted locally along the propagation path and acoustic energy originating from the source epicenter although the horizontal acoustic velocity of the latter is consistent with our data the modeled amplitude ratios of pressure to vertical seismic velocity are too low in comparison with observations and the characteristic differences in seismic and acoustic waveforms and spectra cannot be reproduced from a common point source the observations therefore require a more complex source process in which the infrasonic signals are a record of only the broadband pressure excitation mechanism of the seismic lp events the observations and numerical results can be explained by a model involving the repeated rapid pressure loss from a hydrothermal crack by venting into a shallow layer of loosely consolidated highly permeable material heating by magmatic activity causes pressure to rise periodically reaching the pressure threshold for rupture of the valve sealing the crack sudden opening of the valve generates the broadband infrasonic signal and simultaneously triggers the collapse of the crack initiating resonance of the remaining fluid subtle waveform and amplitude variability of the infrasonic signals as recorded at an array 13 4 km to the nw of the volcano are attributed primarily to atmospheric boundary layer propagation effects superimposed upon amplitude changes at the source

seismicity within a propagating ice shelf rift the relationship between icequake locations and ice shelf structure iceberg calving is a dominant mass loss mechanism for antarctic ice shelves second only to basal melting an important process involved in calving is the initiation and propagation of through penetrating fractures called rifts however the mechanisms controlling rift propagation remain poorly understood to investigate the mechanics of ice shelf rifting we analyzed seismicity associated with a propagating rift tip on the amery ice shelf using data collected during the austral summers of 2004 2007 we apply a suite of passive seismological techniques including icequake locations back projection and moment tensor inversion we confirm previous results that show ice shelf rifting is characterized by periods of relative quiescence punctuated by swarms of intense seismicity of 1 to 3 h even during periods of quiescence we find significant deformation around the rift tip moment tensors calculated for a subset of the largest icequakes mw 2 0 located near the rift tip show steeply dipping fault planes horizontal or shallowly plunging stress orientations and often have a significant volumetric component they also reveal that much of the observed seismicity is limited to the upper 50 m of the ice shelf this suggests a complex system of deformation that involves the propagating rift the region behind the rift tip and a system of rift transverse crevasses small scale variations in the mechanical structure of the ice shelf especially rift transverse crevasses and accreted marine ice play an important role in modulating the rate and location of seismicity associated with the propagating ice shelf rifts

glacier generated earthquakes from prince william sound alaska analysis of seismic records from stations near the prince william sound supports the association of monochromatic low frequency signals with tidewater glaciers in the area thirty three of the larger better recorded signals with corresponding earthquake magnitudes of ml 1 5 to 2 5 were located using routine seismological techniques epicenters for these glacierquakes clustered in the vicinity of the harvard columbia yale and barry glaciers monthly counts from one station for 1975 1979 and part of 1976 range from less than 4 to 248 events a sudden decrease in the number of events per month in mid 1979 raises the possibility of a single source or a common source mechanism for these glacier related signals the monochromatic nondispersive waveforms which characterize these 1 to 2 hz signals may result from harmonic resonance of the glaciers in the epicentral region we speculate that a variety of source mechanisms within or near the glaciers may provide the initial impulse for these events however the characteristic observed waveform is most likely the result of seismic energy which is internally reflected within the ice at fundamental resonant frequencies boundary conditions associated with tidewater glaciers may also allow the ice body to act as a wave guide for shear or surface waves the signal we observe therefore appears to be a source site phenomenon

automated recognition of quasi planar ignimbrite sheets as paleosurfaces via robust segmentation of digital elevation models an example from the central andes quasi planar morphological surfaces may become dissected or degraded with time but still retain original features related to their geologic geomorphic origin to decipher the information hidden in the relief recognition of such features is required possibly in an automated manner in our study using shuttle radar topography mission srtm digital elevation model dem an existing algorithm has been adapted to recognize quasi planar features fulfilling specified criteria the method has been applied to a study area of the central andes with miocene to quaternary volcanic edifices tilted ignimbrite surfaces and basin filling sediments the result is a surface segmentation whereas non planar features gullies tectonic faults etc are sorted out the main types of geomorphic features that can be distinguished and interpreted are as follows 1 the west dipping western margin of the altiplano is differentiated into segments of the lower sedimentary cover that of increased erosion by tectonic steepening at intermediate levels and an upper plane with limited erosion 2 in the central part of the western cordillera the oxaya ignimbrite block shows a striped bulging pattern that results from a smoothly changing surface dip this pattern is due to continuous folding warping of the ignimbrite block possibly related to gravitational movements 3 to the west large uniform planes correspond to flat smooth tectonically undisturbed surfaces of young sedimentary cover of the central basin 4 the evolution of taapaca volcanoes with sector collapse events and cone building phases is shown by several segments with overlapping clastic aprons 5 to the east on the western margin of the altiplano young intermontane basins filled by upper miocene sediments show progressively increasing dip toward basin margins reflected by a circular pattern of the segmentation planes we show that the segmentation models provide meaningful images and additional information for geomorphometric analysis that can be interpreted in terms of geological and surface evolution models copyright 2014 john wiley sons ltd

eruption dynamics at mount st helens imaged from broadband seismic waveforms interaction of the shallow magmatic and hydrothermal systems 1 the current eruption at mount st helens is characterized by dome building and shallow repetitive long period lp earthquakes waveform cross correlation reveals remarkable similarity for a majority of the earthquakes over periods of several weeks stacked spectra of these events display multiple peaks between 0 5 and 2 hz that are common to most stations lower amplitude very long period vlp events commonly accompany the lp events we model the source mechanisms of lp and vlp events in the 0 5 4 s and 8 40 s bands respectively using data recorded in july 2005 with a 19 station temporary broadband network the source mechanism of the lp events includes 1 a volumetric component modeled as resonance of a gently nnw dipping steam filled crack located directly beneath the actively extruding part of the new dome and within 100 m of the crater floor and 2 a vertical single force attributed to movement of the overlying dome the vlp source which also includes volumetric and single force components is 250 m deeper and nnw of the lp source at the sw edge of the 1980s lava dome the volumetric component points to the compression and expansion of a shallow magma filled sill which is subparallel to the hydrothermal crack imaged at the lp source coupled with a smaller component of expansion and compression of a dike the single force components are due to mass advection in the magma conduit the location geometry and timing of the sources suggest the vlp and lp events are caused by perturbations of a common crack system

evolution of the west andean escarpment at 18 s n chile during the last 25 ma uplift erosion and collapse through time abstract the geological record of the western andean escarpment warp reveals episodes of uplift erosion volcanism and sedimentation the lithological sequence at 18 s comprises a thick pile of azapa conglomerates 25 19 ma an overlying series of widespread rhyodacitic oxaya ignimbrites up to 900 m thick ca 19 ma which are in turn covered by a series of mafic andesite shield volcanoes between 19 and 12 ma the surface of the oxaya ignimbrites evolved into a large monocline on the western slope of the andes a giant antithetically rotated block oxaya block 80 km 20 km formed on this slope at about 10 12 ma and resulted in an easterly dip and a reversed drainage on the block s surface morphology topography and stratigraphic observations argue for a gravitational cause of this rotation a secondary gravitational collapse 50 km3 extending 25 km to the west occurred on the steep western front of the oxaya block alluvial and fluvial sediments 11 2 7 ma accumulated in a half graben to the east of the tilted block and were later thrust over by the rocks of the escarpment wall indicating further shortening between 8 and 6 ma flatlying upper miocene sediments

source mechanics for monochromatic icequakes produced during iceberg calving at columbia glacier ak 1 seismograms recorded during iceberg calving contain information pertaining to source processes during calving events however locally variable material properties may cause signal distortions known as site and path effects which must be eliminated prior to commenting on source mechanics we applied the technique of horizontal vertical spectral ratios to passive seismic data collected at columbia glacier ak and found no dominant site or path effects rather monochromatic waveforms generated by calving appear to result from source processes we hypothesize that a fluid filled crack source model offers a potential mechanism for observed seismograms produced by calving and fracture processes preceding calving

miocene to recent history of the western altiplano in northern chile revealed by lacustrine sediments of the lauca basin 18 15 18 40 s 69 30 69 05 w the intramontane lauca basin at the western margin of the northern chilean altiplano lies to the west of and is topographically isolated from the well known plio pleistocene lake system of fluvio lacustrine origin that covers the bolivian altiplano from lake titicaca to the north for more than 800 km to the salar de uyuni in the south the lauca basin is filled by a sequence of some 120 m of mainly upper miocene to pliocene elastic and volcaniclastic sediments of lacustrine and alluvial origin volcanic rocks partly pyroelastic provide useful marker horizons in the first period 6 4 ma of its evolution the lago lauca was a shallow ephemeral lake evaporites indicate temporarily closed conditions after 4 ma the lake changed to a perennial water body surrounded by alluvial plains in the late pleistocene and holocene 2 0 ma there was only marginal deposition of alluvial and glacial sediments the basin formed as a half graben or by pull apart between 10 and 15 ma tectonic displacement of the basal ignimbrite sequence during the quechua phase and 6 2 ma maximum k ar ages of biotites of tuff horizons in the deepest part of the basin apart from this early basin formation there has been surprisingly little displacement during the past 6 ma close to the western cordillera of the altiplano also climate indicators pollen evaporites sedimentary facies suggest that an arid climate has existed for the past 6 ma on the altiplano together these pieces of evidence indicate the absence of large scale block faulting tilt and major uplift during the past 5 6 ma in this area

models of isostatic and dynamic topography geoid anomalies and their uncertainties knowledge of the dynamic topography at earth s surface caused by sublithospheric density contrasts would provide crucial constraints on models of mantle dynamics we calculate global models of this dynamic topography by subtracting from the observed topography estimates of the topography caused by assumed isostatically compensated density variations in the crust the oceanic lithosphere and the continental tectosphere we also calculate the isostatic geoid anomaly that would result from these compensated near surface density anomalies because there is controversy about the thermal structure of old oceanic lithosphere we investigate two models of the cooling of the oceanic lithosphere half space and plate and calculate the effect of each on the inferred dynamic topography peak amplitudes of dynamic topography from sublithospheric sources expanded to spherical harmonic degree 6 are approximately 1 km we estimate the uncertainties in the calculated dynamic topography and geoid by combining the errors in the data and systematic errors to obtain the spectral coefficients of the fields we use weighted least squares inversions the calculated dynamic topography arising from sublithospheric sources residual geoid and errors associated with these fields can be used in studies of mantle dynamics

the nevados de payachata volcanic region 18 s 69 w n chile subduction related volcanism in the nevados de payachata region of the central andes at 18 s comprises two temporally and geochemically distinct phases an older period of magmatism is represented by glaciated stratocones and ignimbrite sheets of late miocene age the pleistocene to recent phase 0 3 ma includes the twin stratovolcanoes volcan pomerape and volcan parinacota the nevados de payachata volcanic group and two small centers to the west i e caquena and vilacollo both stratovolcanoes consist of an older dome and flow series capped by an andesitic cone the younger cone i e v parinacota suffered a postglacial cone collapse producing a widespread debris avalanche deposit subsequently the cone reformed during a brief second volcanic episode a number of small relatively mafic satellitic cinder cones and associated flows were produced during the most recent activity at v parinacota at the older cone i e v pomerape an early dome sequence with an overlying isolated mafic spatter cone and the cone forming andesitic dacitic phase mostly flows have been recognized the two nevados de payachata stratovolcanoes display continuous major and trace element trends from high k2o basaltic andesites through rhyolites 53 76 sio2 that are well defined and distinct from those of the older volcanic centers petrography chemical composition and eruptive styles at v parinacota differ between pre and post debris avalanche lavas precollapse flows have abundant amphibole at sio2 59 wt and lower mg numbers than postcollapse lavas which are generally less silicic and more restricted in composition compositional variations indicate that the magmas of the nevados de payachata volcanic group evolved through a combination of fractional crystallization crustal assimilation and intratrend magma mixing isotope compositions exhibit only minor variations pb isotope ratios are relatively low 206pb 204pb 17 95 18 20 and208pb 204pb 38 2 38 5 87sr 86sr ratios range 0 70612 0 70707 143nd 144nd ratios range 0 51238 0 51230 and 18osmow values range from 6 8 o to 7 6 o smow a comparison with other central volcanic zone centers shows that the nevados de payachata magmas are unusually rich in ba up to 1800 ppm and sr up to 1700 ppm and thus represent an unusual chemical signature in the andean arc these chemical and isotope variations suggest a complex petrogenetic evolution involving at least three distinct components primary mantle derived melts which are similar to those generated by subduction processes throughout the andean arc are modified by deep crustal interactions to produce magmas that are parental to those erupted at the surface these magmas subsequently evolve at shallower levels through assimilation crystallization processes involving upper crust and intratrend magma mixing which in both cases were restricted to end members of low isotopic contrast

tidal and seasonal variations in calving flux observed with passive seismology the seismic signatures of calving events i e calving icequakes offer an opportunity to examine calving variability with greater precision than is available with other methods here using observations from yahtse glacier alaska we describe methods to detect locate and characterize calving icequakes we combine these icequake records with a coincident manually generated record of observed calving events to develop and validate a statistical model through which we can infer iceberg sizes from the properties of calving icequakes we find that the icequake duration is the single most significant predictor of an iceberg s size we then apply this model to 18 months of seismic recordings and find elevated iceberg calving flux during the summer and fall and a pronounced lull in calving during midwinter calving flux is sensitive to semidiurnal tidal stage large calving events are tens of percent more likely during falling and low tides than during rising and high tides consistent with a view that deeper water has a stabilizing influence on glacier termini multiple factors affect the occurrence of mechanical fractures that ultimately lead to iceberg calving at yahtse glacier seismology allows us to demonstrate that variations in the rate of submarine melt are a dominant control on iceberg calving rates at seasonal timescales on hourly to daily timescales tidal modulation of the normal stress against the glacier terminus reveals the nonlinear glacier response to changes in the near terminus stress field

geomorphology on geologic timescales evolution of the late cenozoic pacific paleosurface in northern chile and southern peru abstract the atacama desert on the western margin of the central andes is one of the driest and oldest deserts in the world it is defined by a distinct and ancient surface known as the pacific paleosurface pps or atacama paleosurface the age of this surface is determined as the time at which sediment deposition ceased and the surface was effectively abandoned early studies suggested that this abandonment took place between 14 and 10 ma and was related to both the uplift of the andes and the onset of hyperaridity in the region here we provide a regional re examination of the pps compiling existing work on the underlying geology sedimentology surface exposure dating and seismic profiling we also present new multispectral satellite maps of the pps and 45 new cosmogenic 3he and 21ne surface exposure ages in order to constrain the formation age and the preservation and incision history of the paleosurface we conclude that the pps is not a single paleosurface but instead is a mosaic of smaller surfaces that were formed by aggradational and degradational processes over 19 million years or more and should be termed collectively as the pacific paleosurfaces the time at which individual paleosurfaces formed is related to regional climate where the location of each is controlled by regional tectonic activity cosmogenic surface exposure ages suggest that the surfaces are a record of regional scale climate events

glacial long period seismic events at katla volcano iceland repeating long period lp earthquakes are commonly8 observed in volcanic regions worldwide they are usually9 explained in terms of a volcanic source effect or anomalous10 propagation through the

geological constraints on the emplacement mechanism of the parinacota debris avalanche northern chile the holocene parinacota volcanic debris avalanche ca 8 000 years b p is located in the central andes of northern chile the avalanche formed by the sector collapse of a major stratovolcano adjacent to a lake basin in a single catastrophic event the deposit has an estimated volume of ca 6 km3 a run out of over 22 km and covers more than 140 km2 of the surrounding terrain the values of the heim coefficient 0 08 and the ratio a v 2 3 ca 50 where a is the area covered and v the volume of the deposit indicate high mobility of the avalanche debris in transport two avalanche units can be distinguished the lower unit consists mainly of blocks of rhyodacitic lavas and domes and pyroclastic flow deposits and glacial fluvial and lacustrine sediments the upper unit consists of a coarse grained breccia with little matrix largely composed of andesite blocks which are angular with little or no rounding by abrasion the avalanche displays pronounced hummocky topography in which hummock volume and amplitude as well as maximum block size within individual hummocks tends to decrease with transport distance and towards the lateral margins of the avalanche deposit some surfaces of individual breccia blocks are covered by tens to thousands of small scale impact marks indicating that neighbouring blocks were vibrating and colliding without significant shearing motion most of the deformation and shearing was instead accommodated in a basal layer of wet structureless sediments incorporated into the avalanche debris from the inundated lake basin we propose that the ancestral parinacota stratovolcano collapsed because of loading of underlying fluvioglacial and lacustrine sediments the edifice disintegrated during collapse along existing fractures into large rock domains volumes from 10 to greater than 1 106 m3 which were transported with little internal deformation and then fragmented into hummocks of breccia as they were deposited the decrease of hummock volume with distance suggests that material that travelled further broke up and had an initial greater kinetic energy

characteristics of seismic and acoustic signals produced by calving bering glacier alaska 1 we recorded 126 calving and iceberg breakup events from the terminus of the bering glacier during five days in august 2008 using seismometers and three small aperture arrays of infrasound sensors the seismic signals were typically emergent narrow band and lower frequency similar to records at other glaciers the acoustic records were characterized by shorter duration higher frequency signals with more impulsive onsets we demonstrate that triangular infrasound arrays permit improved locations of calving events over seismic arrivals that rely on a relatively complicated poorly known velocity model twenty six of 35 well located events occurred on icebergs in vitus lake rather than the glacier face while our data do not permit a complete description of the source process the distinctive frequency contents and durations in the seismic and infrasound data suggest that the two data types record different aspects of the same process

the origin of brines and salts in chilean salars a hydrochemical review abstract northern chile is characterized by a succession of north south trending ranges and basins occupied by numerous saline lakes and salt crusts collectively called salars fossil salt crusts are found to the west in the extremely arid central valley while active salars receiving permanent inflows fill many intravolcanic basins to the east in the semiarid cordillera sea salts and desert dust are blown eastward over the cordillera where they constitute an appreciable fraction of the solute load of very dilute waters salt content evaporative concentration of inflow waters leads to sulfate rich or calcium rich near neutral brines alkaline brines are almost completely lacking the alkalinity calcium ratio of inflow waters is lowered by the oxidation of native sulfur reducing alkalinity and the deposition of eolian gypsum increasing ca concentration theoretically so4 rich inflow waters and their derived so4 rich brines should be found in the intravolcanic basins of the cordillera because of the ubiquity of native sulfur while ca rich brines should prevail in sedimentary basins where ca rich minerals are abundant this relation is perfectly observed in the salar de atacama the largest in chile however several salars located within the volcanic cordillera belong to the ca rich group inflows and brines may have acquired their ca rich composition in pleistocene time when their drainage basins were mainly sedimentary later on recent lava flows and ignimbrites covered the sedimentary formations underground waters may have kept their early sedimentary signature by continuous recycling however the weathering of volcanic rocks tend to slowly shift the water compositions from the ca rich to the so4 rich type

a simple global model of plate dynamics and mantle convection cooling and thickening of lithospheric plates with age and subduction result in large scale horizontal density contrasts tending to drive plate motions and mantle flow we quantify the driving forces associated with these density contrasts to determine if they can drive the observed plate motions first two dimensional models are computed to evaluate the effects of assumed rheologies and boundary conditions we are unable to obtain platelike behavior in viscous models with traction free boundary conditions the piecewise uniform velocities distinctive of plate motion can be imposed as boundary conditions and the dynamic consistency of the models evaluated by determining if the net force on each vanishes if the lithosphere has a newtonian viscous rheology the net force on any plate is a strong function of the effective grid spacing used leading to ambiguities in interpretation incorporating a rigid plastic lithosphere which fails at a critical yield stress into the otherwise viscous model removes these ambiguities the model is extended to the actual three dimensional spherical plate geometry the observed velocities of rigid plastic plates are matched to the solution of the viscous stokes equation at the lithosphere asthenosphere boundary body forces from the seismically observed slabs from the thickening of the lithosphere obtained from the actual lithospheric ages and from the differences in structure between continents and oceans are included interior density contrasts such as those resulting from upwellings from a hot bottom boundary layer are assumed to occur on a scale small compared to plate dimensions and are not included the driving forces from the density contrasts within the plates are calculated and compared to resisting forces resulting from viscous drag computed from the three dimensional global return flow and resistance to deformation at converging boundaries the rms residual torque is 30 of the driving torque the density contrasts within the plates themselves can reasonably account for plate motions body forces from convection in the interior may provide only a small net force on the plates at converging boundaries the lithosphere has a yield stress of 100 bars drag at the base of the plates is 5 bars and resists plate motion the net driving forces from subducting slabs and collisional resistance are localized and approximately balance driving forces from lithospheric thickening are distributed over the areas of the plates as is viscous drag the approximate balance of these two forces predicts plate velocities uncorrelated with plate area as observed the model represents a specific case of boundary layer convection the dynamical results are consistent with either upper mantle or mantle wide convection

icequake locations and discrimination of source and path effects with small aperture arrays bering glacier terminus ak 1 the complex source processes associated with both glacier calving and the breakup of icebergs combined with commonly heterogeneous periglacial seismic velocity structure can result in complicated seismic records key features of the waveforms which are typically characterized by low amplitude or emergent first arrivals and long duration narrow band codas have been attributed to either source processes or propagation path effects this uncertainty must be addressed in order for seismic data to be effective for studying the calving process as it relates to terminus dynamics in this study we use sets of 3 element arrays of 3 component geophones and infrasound sensors to locate calving and iceberg breakup events and isolate path effects in the seismic records obtained near the bering glacier terminus in the summer of 2010 using waveform correlation we treat each array as an antenna and determine the direction to the source and apparent velocity of the wavefield across the array the initial few 3 cycles ofpwaves recorded from an array beam formed to identify coherent arrivals for each event are useful for deriving a propagation azimuth and apparent velocity allowing for location of events using a small number of similar arrays we locate 125 calving and iceberg breakup events near the terminus with this method we also demonstrate that the longer lived narrow band coda is not coherent across individual arrays suggesting that the narrow band coda observed at the bering glacier is attributable to a path effect rather than to the source process the large number of iceberg breakup events that we located has important implications for other calving glaciers where icebergs are present and calving rates may be erroneously overestimated from the seismic data if their contribution is not taken into account

tectonic signatures in arid continental basins an example from the upper miocene pleistocene calama basin andean forearc northern chile abstract the calama basin a transtensional basin situated within the andean forearc and its extension to the pampa del tamarugal central depression is filled with 700 m of sediments detailed sedimentary logging and 40ar 39ar dates from interbedded volcanic deposits have established a lithostratigraphic and chronostratigraphic framework for the upper 95 m thick upper miocene pleistocene succession five facies associations fluvio lacustrine diatomite palustrine carbonate massive anhydrite fluvial and alluvial fan have been identified within this part of the basin fill the following events are recognised in the basin evolution 1 deposition of diatomaceous lacustrine sediments in two separate depocentres in the pampa del tamarugal and the central calama basin with alluvial fan accumulation along the basin margins at 8 ma 2 localised deformation within the central calama basin between 7 and 6 ma but continuous sedimentation elsewhere 3 palustrine carbonate deposition across the entire area from 6 to 3 ma except in the pampa del tamarugal where diatomaceous sedimentation continued until 5 ma before being replaced by palustrine carbonate deposition 4 widespread folding after 3 ma and entrenchment as the drainage system cut down to reach a new base level caused by the rio loa breaching the coastal cordillera and reaching the sea localised lacustrine deposition in topographic lows or tectonically created dams also occurred during this period comparison with similar age facies elsewhere in northern chile has shown changes such as these to be localised and diachronous indicating that tectonic controls on accommodation space and drainage patterns are the primary influence on sedimentation in this tectonic setting the lacustrine deposits do not appear to be a reliable recorder of low frequency climatic change this is exemplified by the change from lacustrine to palustrine deposition at 6 5 ma which would appear to record a drying of the climate however a synchronous change from ephemeral alluvial fan deposition to more permanent fluvial deposition at the basin margins indicates increased run off

lacustrine sedimentation in active volcanic settings the late quaternary depositional evolution of lake chungara northern chile lake chungara 18 15 s 69 09 w 4520 m above sea level is the largest 22ae5 km2 and deepest 40 m lacustrine ecosystem in the chilean altiplano and its location in an active volcanic setting provides an opportunity to evaluate environmental volcanic vs climatic controls on lacustrine sedimentation the late quaternary depositional history of the lake is reconstructed by means of a multiproxy study of 15 kullenberg cores and seismic data the chronological framework is supported by 10 14c ams dates and one 230th 234u dates lake chungara was formed prior to 12ae8 cal kyr bp as a result of the partial collapse of the parinacota volcano that impounded the lauca river the sedimentary architecture of the lacustrine succession has been controlled by i the strong inherited palaeo relief and ii changes in the accommodation space caused by lake level fluctuations and tectonic subsidence the first factor determined the location of the depocentre in the nw of the central plain the second factor caused the area of deposition to extend towards the eastern and southern basin margins with accumulation of high stand sediments on the elevated marginal platforms synsedimentary normal faulting also increased accommodation and increased the rate of sedimentation in the northern part of the basin six sedimentary units were identified and correlated in the basin mainly using tephra keybeds unit 1 late pleistocene early holocene is made up of laminated diatomite with some carbonate rich calcite and aragonite laminae unit 2 mid holocene recent is composed of massive to bedded diatomite with abundant tephra lapilli and ash layers some carbonate rich layers calcite and aragonite occur unit 3 consists of macrophyte rich diatomite deposited in nearshore environments unit 4 is composed of littoral sediments dominated by alternating charophyterich and other aquatic macrophyte rich facies littoral carbonate productivity peaked when suitable shallow platforms were available for charophyte colonization clastic deposits in the lake are restricted to lake margins units 5 and 6 diatom productivity peaked during a lowstand period unit 1 and subunit 2a and was probably favoured by photic conditions affecting larger areas of the lake bottom offshore carbonate precipitation reached its maximum during the early to mid holocene ca 7ae8 and 6ae4 cal kyr bp this may have been favoured by increases in lake solute concentrations resulting from evaporation and calcium input because of the compositional changes in pyroclastic supply diatom and pollen data from offshore cores suggest a number of lake level fluctuations a late pleistocene deepening episode ca 12ae6 cal kyr bp four shallowing episodes during the early to mid holocene ca 10ae5 9ae8 7ae8 and 6ae7 cal kyr bp and higher lake levels since the mid holocene ca 5ae7 cal kyr bp until the present explosive activity at parinacota volcano was very limited between c 12ae8 and 7ae8 cal kyr bp mafic rich explosive eruptions from the ajata satellite cones increased after ca 5ae7 cal kyr bp until the present

origin of the high plateau in the central andes bolivia south america the bolivian altiplano in the central andes of south america is part of the second largest high plateau on earth it is an elongate region of subdued relief 1 2 105 km2 and 4 km above sea level bounded by the eastern cordillera and volcanic arc western cordillera here the crust is up to 75 km thick we describe the cenozoic geological evolution of this region using a revised chronostratigraphy and an analysis of the crustal and lithospheric structure crustal shortening and magmatic addition and locally sedimentation are the main mechanisms of cenozoic crustal thickening leading to nearly 4 km of surface uplift since the paleocene addition of mafic melts appears to be a first order mechanism of cenozoic crustal growth contributing 40 of the crustal thickening beneath the volcanic arc removal of the basal part of the lithosphere may have caused two episodes of widespread arc and behind arc mafic volcanism at 23 ma and 0 5 ma contributing to the surface uplift the altiplano originated as a sedimentary basin several hundred kilometers wide between the proto western cordillera and a narrow zone of uplift proto eastern cordillera farther east the latter zone formed by inversion of the center of a wide lacustrine or marine cretaceous paleocene basin close to sea level at 45 ma a thickness of 2 4 km of paleogene continental elastics accumulated in the proto altiplano basin subsequently in the oligocene we estimate that this region and the western margin of the eastern cordillera were technically shortened 22 65 km resulting in 9 km of average crustal thickening the altiplano basin was rejuvenated at 25 ma and subsequently flooded with up to 8 km thickness of detritus eroded from the uplifting eastern and western cordilleras between 25 and 5 ma folding and thrusting in the western margin of the eastern cordillera migrated westward into the center of the altiplano basin essentially terminating deposition except in local subbasins and accommodating 13 30 km of shortening and an estimated 7 km of average crustal thickening subsequently there has been strike slip deformation and limited local thrusting 5 km of shortening geomorphological and geochronological evidence for 1 5 2 km of surface uplift of this region since the late miocene suggests 14 km of lower crustal thickening beneath an essentially rigid lid and can be explained by 100 150 km of underthrusting of the brazilian shield and adjacent regions beneath the eastern margin of the central andes the present subdued relief in the altiplano may be a result of ductile flow in the lower crust and sedimentation and erosion in an internal drainage basin

impact of hydrodynamics on seismic signals generated by iceberg collisions full glacier thickness icebergs are frequently observed to capsize as they calve into the ocean as they capsize they may collide with the glaciers termini previous studies have hypothesized that such collisions are the source of teleseismic glacial earthquakes we use laboratory scale experiments force balance modeling and theoretical arguments to show that 1 the contact forces during these collisions are strongly influenced by hydrodynamic forces and 2 the associated glacial earthquake magnitudes expressed as twice integrated force histories are related to the energy released by the capsizing icebergs plus a hydrodynamic term that is composed of drag forces and hydrodynamic pressure our experiments and first order modeling efforts suggest that due to hydrodynamic forces both contact force and glacial earthquake magnitudes may not be directly proportional to the energy released by the capsizing icebergs as might be expected most importantly however our results highlight the need to better understand the hydrodynamics of iceberg capsize prior to being able to accurately interpret seismic signals generated by iceberg collisions

seismic detection and analysis of icequakes at columbia glacier alaska 1 contributions to sea level rise from rapidly retreating marine terminating glaciers are large and increasing strong increases in iceberg calving occur during retreat which allows mass transfer to the ocean at a much higher rate than possible through surface melt alone to study this process we deployed an 11 sensor passive seismic network at columbia glacier alaska during 2004 2005 we show that calving events generate narrow band seismic signals allowing frequency domain detections detection parameters were determined using direct observations of calving and validated using three statistical methods and hypocenter locations the 1 3 hz detections provide a good measure of the temporal distribution and size of calving events possible source mechanisms for the unique waveforms are discussed and we analyze potential forcings for the observed seismicity

maar diatreme volcanoes a review maar diatreme volcanoes are produced by explosive eruptions that cut deeply into the country rock a maar is the crater cut into the ground and surrounded by an ejecta ring while the diatreme structure continues downward and encloses diatreme and root zone deposits here we attempt an evenhanded review of maar diatreme volcanology that extends from mafic to kimberlitic varieties and from historical maar eruptions to deeply eroded or mined diatreme structures we conclude that maar diatreme eruptions are episodic ejecta rings provide invaluable insight into eruption processes and sequence but are incomplete records of diatreme formation deposits within the diatreme structure include in varying proportions lower unbedded deposits sometimes typified by subvertical contacts among domains of debris emplaced sequentially and upper bedded deposits formed by sedimentation on surfaces open to the atmosphere a basal root zone comprises the transition from coherent magmatic feeder dike to clastic deposits formed by fragmentation of magma and enclosing country rock root zones are irregular in form and the clastic deposits are typically intruded by contorted dikes irregular root zone like chaotic breccias cut by contorted dikes are also present within diatreme deposits where they represent intra diatreme fragmentation zones and record changes in the location of the explosion locus during eruption

geochemistry of ash leachates from the 1993 lascar eruption northern chile implication for recycling of ancient evaporites abstract volcanic formations in the central andes overlie extensive amounts of ancient evaporites of cenozoic age recycling of buried salts in present closed basins through the hydrological cycle is a well known process another salt recycling process through volcanic activity has been detected in a recent eruption of the lascar volcano in northern chile about 10 9 metric tons of air fall tephra was deposited over the surrounding closed basins leaching experiments were carried out on ashes deposited near the summit and in a lower neighbouring valley summit ash leachates are almost pure caso 4 solutions whereas the valley ashes leachates are enriched in minor components leachates of the summit ash are near neutral whereas those of the valley ash have ph as high as 10 5 sulfur isotope composition of the leached sulfate is consistent with the volcanic recycling of tertiary gypsum present in the sedimentary section beneath the volcanic cordillera as a rough estimate about 700 000 tons of easily soluble caso 4 were added in only three days to the surrounding closed basins the high ph of the valley ash leachates is due to the hydration of alkali and alkaline earth metal oxides formed during pyrolysis of vegetation by hot ash efflorescent salts encrusted on plants and dissolution of volcanic glass provided some of the minor components the almost pure caso 4 composition of the leach waters is compositionally distinct from any present inflow waters in the central andes addition of caso 4 may explain some of the differences between the observed brine compositions and those predicted by simulating the evaporation of regular inflows the recycling of sedimentary gypsum is probably not restricted to lascar volcano the recycling of ancient salts and possibly also the pyrolysis of vegetation may have been crucial processes in the salt balance of closed basins during the intense volcanic activity of the tertiary

seismic observations of glaciogenic ocean waves micro tsunamis on icebergs and ice shelves seismometers deployed over a 3 year period on icebergs in the ross sea and on the ross ice shelf antarctica reveal that impulsive sources of ocean surface waves are frequent e g 200 events per year in the ross sea in the ice shelf and iceberg covered environment of coastal antarctica the 368 events recorded by our field deployment suggest that these impulsive events are generated by glaciological mechanisms such as 1 small scale calving and edge wasting of icebergs and ice shelf fronts 2 edge on edge closing and opening associated with iceberg collisions and 3 possibly the impulsive opening of void space associated with ice shelf rifting and basal crevasse formation the observations described here provide a background of glaciogenic ocean wave phenomena relevant to the ross sea and suggest that these phenomena may be exploited in the future using more purposefully designed observation schemes to understand iceberg calving and ice shelf disintegration processes

analysis of low frequency seismic signals generated during a multiple iceberg calving event at jakobshavn isbrae greenland 1 we investigated seismic signals generated during a large scale multiple iceberg calving event that occurred at jakobshavn isbrae greenland on 21 august 2009 the event was recorded by a high rate time lapse camera and five broadband seismic stations located within a few hundred kilometers of the terminus during the event two full glacier thickness icebergs calved from the grounded or nearly grounded terminus and immediately capsized the second iceberg to calve was two to three times smaller than the first the individual calving and capsize events were well correlated with the radiation of low frequency seismic signals 0 1 hz dominated by love and rayleigh waves in agreement with regional records from previously published glacial earthquakes these low frequency seismic signals had maximum power and or signal to noise ratios in the 0 05 0 1 hz band similarly full waveform inversions indicate that these signals were also generated by horizontal single forces acting at the glacier terminus the signals therefore appear to be local manifestations of glacial earthquakes although the magnitudes of the signals twice time integrated force histories were considerably smaller than previously reported glacial earthquakes we thus speculate that such earthquakes may be a common if not pervasive feature of all full glacier thickness calving events from grounded termini finally a key result from our study is that waveform inversions performed on low frequency calving generated seismic signals may have only limited ability to quantitatively estimate mass losses from calving in particular the choice of source time function has little impact on the inversion but dramatically changes the earthquake magnitude accordingly in our analysis it is unclear whether the smaller or larger of the two calving icebergs generated a larger seismic signal

calving event detection by observation of seiche effects on the greenland fjords with mass loss from the greenland ice sheet accelerating and spreading to higher latitudes the quantification of mass discharge in the form of icebergs has recently received much scientific attention here we make use of very low frequency 0 001 0 01 hz seismic data from three permanent broadband stations installed in the summers of 2009 10 in northwest greenland in order to monitor local calving activity at these frequencies calving seismograms are dominated by a tilt signal produced by local ground flexure in response to fjord seiching generated by major iceberg calving events a simple triggering algorithm is proposed to detect calving events from large calving fronts with potentially no user interaction our calving catalogue identifies spatial and temporal differences in calving activity between jakobshavn isbrae and glaciers in the uummannaq district similar to 200 km to the north the uummannaq glaciers show clear seasonal fluctuations in seiche based calving detections as well as seiche amplitudes in contrast the detections at jakobshavn isbrae show little seasonal variation which may be evidence for an ongoing transition to winter calving activity the results offer further evidence that seismometers can provide efficient and inexpensive monitoring of calving fronts

calving icebergs a source of low frequency seismic signals from columbia glacier alaska low frequency icequakes produced by columbia glacier alaska are caused by large icebergs which break off the glacier terminus into prince william sound occasionally many ice seracs fall in rapid succession producing complex low frequency icequake signals with durations sometimes exceeding 10 min an empirical relationship v 4000 t between the volume v of an iceberg in cubic meters and the duration t of the seismic signal in seconds can be used to estimate the calving rate of columbia glacier from seismological data alone during 1984 and 1985 a period of rapid retreat of the glacier the calculated number of icequakes per month showed seasonal fluctuations that corresponded to variations in calving rate determined by photogrammetry it is likely that most previously reported low frequency icequakes in southern alaska are produced by calving tidewater glaciers

a global isostatic gravity model of the earth the long wavelength features of the external gravity field of the earth contain the gravitational signal from deep seated lateral mass and density inhomogeneities sustained by dynamic earth mantle processes to interpret the observed gravity field with respect to mantle dynamics and structures it is essential first to remove the lithosphere induced anomalous gravitational potential which is generated by the topographic surface load and its isostatically compensating masses based upon the most recent global compilation of crustal thickness and density data and the age distribution of cooling oceanic lithosphere residual topography and gravity are calculated by subtracting the known crustal and oceanic lithosphere compensating masses and gravitational effects from the surface fields empirical admittances between residual topography and gravity are then computed to estimate the effective depths of the remaining compensating masses which are not explained by the initial data and model assumptions this additional compensation is eventually placed by adjusting the density in the uppermost mantle between the moho and on average 70 km depth with a maximum of 118 km under tibet the lithospheric mass distribution is used in a subsequent forward computation to create a global model of the lithosphere induced gravitational potential the resulting isostatic model is considered to be valid for spatial wavelengths longer than 500 km the isostatic lithosphere model field expressed in terms of both gravity and geoid heights is subtracted from the observed free air gravity field to yield a global set of 1 1 isostatic gravity disturbances and from a satellite derived long wavelength geoid to yield the isostatic residual geoid the comparison of residual mantle gravity residual topography and isostatic corrected gravity allows us to identify the main characteristics of the underlying mantle for example dynamic support by mantle flow of the north atlantic topographic high applying the isostatic correction the overall pattern of the geoid becomes smoother and the most pronounced features which are separated in the observed geoid tend to get connected to larger structures these results stress the importance of separation of the lithospheric gravitational impact for a correct interpretation of the external gravity field even in its very long wavelength constituents also the isostatic corrected geoid spectrum reveals a stronger decrease in power from degree 3 to degree 4 and degree 5 to degree 6 which is in accordance with seismological models of deep mantle structures

volcanic eruptions observed with infrasound 1 infrasonic airwaves produced by active volcanoes provide valuable insight into the eruption dynamics because the infrasonic pressure field may be directly associated with the flux rate of gas released at a volcanic vent infrasound also enhances the efficacy of volcanic hazard monitoring and continuous studies of conduit processes here we present new results from erebus fuego and villarrica volcanoes highlighting uses of infrasound for constraining quantitative eruption parameters such as eruption duration source mechanism and explosive gas flux

cenozoic stratigraphic development in the north chilean forearc implications for basin development and uplift history of the central andean margin abstract analysis of the cenozoic stratigraphic development of the forearc of northern chile between 18 s and 23 30 s allows constraints to be placed on the timing and nature of basin formation and the uplift history of the central andes chronostratigraphic charts have been constructed from 20 lithostratigraphic sections distributed throughout the forearc sections were taken from the longitudinal valley central depression calama basin salar de atacama precordillera and the western flank of the western cordillera correlation and timing of events is largely based on the presence of dated volcanic horizons in all the studied sections three chronostratigraphic units are defined based upon the presence of regional unconformities deposition of the late eocene to early miocene chronostratigraphic unit 38 19 ma commenced across an irregular unconformity surface between 38 and 30 ma with alluvial fan and fluvial sediments derived from the east interbedded with rhyolitic ignimbrites aggradation after 25 ma resulted in development of a large broad basin over much of northern chile that expanded eastwards through onlap onto basement deposition terminated around 19 ma with the development of an angular unconformity over much but not all of the study area during deposition of the early to late miocene chronostratigraphic unit 18 10 ma emergent volcanic source areas to the east provided catchments for large fluvial systems that drained westwards into endorheic ephemeral lacustrine basins fold growth affected sedimentation restricting accommodation space to small intra thrust basins in the precordillera and localised disruption and unconformity development in the longitudinal valley the late miocene to present day chronostratigraphic unit 10 0 ma followed the development of a regional angular unconformity at 10 ma sedimentation was restricted to a series of thrust bounded endorheic basins in both the central depression and the precordillera sourced from the east with volcanic activity limited to the periodic eruption of extensive ignimbrite sheets alluvial fan fluvial and lacustrine sedimentation dominated within the endorheic basins from 8 to 3 ma after development of a regional unconformity at 3 ma a change to isolated evaporite sub basins took place in the central depression with small lacustrine basins developed along the flank of the western cordillera the scale and grain size recorded in the sedimentary systems indicates that a substantial source area was located in the present day area of the western cordillera by 30 ma and that this has persisted to the present day this area also shed material eastwards into the altiplano the presence of such a topographic feature by 30 ma suggests that a significant proportion of andean uplift had occurred prior to the late miocene this important uplift phase should be incorporated into any model of andean uplift the evidence from the basin fill succession suggests that sediments accumulated in a basin developed in front of a broad monocline between 38 and 19 ma and that a transition to a thrust bounded foreland style basin took place after the development of the unconformity at 19 ma

seismic and hydroacoustic tremor generated by colliding icebergs 1 iceberg harmonic tremor iht emanating from tabular icebergs in the southern ocean and along calving margins of the antarctic ice sheet is a complex evolving signal at frequencies above approximately 0 5 hz iht has been observed as t phases on islands in the equatorial pacific as hydroacoustic signals in the indian ocean and by local and regional antarctic seismic networks to identify the iht source mechanism and to understand its relevance to iceberg calving evolution and breakup we deployed seismometers on a giant 25 by 50 km tabular iceberg called c16 in the ross sea antarctica during a uniquely accessible period austral summer 2003 2004 when it was aground against the northern shore of ross island during the deployment period c16 was in sporadic contact with another giant tabular iceberg b15a that was moving under the influence of local ocean currents this study reveals that the c16 associated iht was a manifestation of extended episodes of discrete repeating stick slip icequakes typically thousands of individual subevents per hour produced when the cliff like edges of the tabular icebergs underwent glancing strike slip collisions the iht signal that we observed is thus not a phenomenon associated with iceberg elastic or fluid resonance modes but is instead the consequence of long sequences of very regularly spaced and similar pulses of seismic radiation from these constituent stick slip subevents iht represents a newly identified glaciogenic source of seismicity that can be used to improve our understanding of iceberg dynamics and possibly of ice shelf disintegration processes

three dimensional gravity inversion for moho depth at rifted continental margins incorporating a lithosphere thermal gravity anomaly correction summary this paper describes a method for determining moho depth lithosphere thinning factor 1 1 and the location of the ocean continent transition at rifted continental margins using 3 d gravity inversion which includes a correction for the large negative lithosphere thermal gravity anomaly within continental margin lithosphere the lateral density changes caused by the elevated geotherm in thinned continental margin and adjacent ocean basin lithosphere produce a significant lithosphere thermal gravity anomaly which may be in excess of 100 mgal and for which a correction must be made in order to determine moho depth accurately from gravity inversion we describe a method of iteratively calculating the lithosphere thermal gravity anomaly using a lithosphere thermal model to give the present day temperature field from which we calculate the lithosphere thermal density and gravity anomalies for continental margin lithosphere the lithosphere thermal perturbation is calculated from the lithosphere thinning factor 1 1 obtained from crustal thinning determined by gravity inversion and breakup age for thermal re equilibration time for oceanic lithosphere the lithosphere thermal model used to predict the lithosphere thermal gravity anomaly may be conditioned using ocean isochrons from plate reconstruction models to provide the age and location of oceanic lithosphere a correction is made for crustal melt addition due to decompression melting during continental breakup and seafloor spreading we investigate the sensitivity of the lithosphere thermal gravity anomaly and the predicted moho depth from gravity inversion at continental rifted margins to the methods used to calculate and condition the lithosphere thermal model using both synthetic models and examples from the north atlantic

glacier fjord and seismic response to recent large calving events jakobshavn isbrae greenland 1 the recent loss of jakobshavn isbrae s extensive floating ice tongue has been accompanied by a change in near terminus behavior calving currently occurs primarily in summer from a grounded terminus involves the detachment and overturning of several icebergs within 30 60 min and produces long lasting and far reaching ocean waves and seismic signals including glacial earthquakes calving also increases near terminus glacier velocities by 3 but does not cause episodic rapid glacier slip thereby contradicting the originally proposed glacial earthquake mechanism we propose that the earthquakes are instead caused by icebergs scraping the fjord bottom during calving

avalanching glacier instabilities review on processes and early warning perspectives avalanching glacier instabilities are gravity driven rupture phenomena that might cause major disasters especially when they are at the origin of a chain of processes reliably forecasting such events combined with a timely evacuation of endangered inhabited areas often constitute the most efficient action recently considerable efforts in monitoring analyzing and modeling such phenomena have led to significant advances in destabilization process understanding improving early warning perspectives the purpose of this paper is to review the recent progress in this domain three different types of instabilities can be identified depending on the thermal properties of the ice bed interface if cold 1 the maturation of the rupture is associated with a typical time evolution of surface velocities and passive seismic activity a prediction of the final break off is possible using these precursory signs for the two other types water plays a key role in the development of the instability if the ice bed interface is partly temperate 2 the presence of meltwater may reduce the basal resistance which promotes the instability no clear and easily detectable precursory signs are known in this case and the only way to infer any potential instability is to monitor the temporal evolution of the thermal regime the last type of instability 3 concerns steep temperate glacier tongues switching for several days weeks during the melting season into a so called active phase followed in rare cases by a major break off event although the prediction of such events is still far from being achievable critical conditions promoting the final instability can be identified

geoid anomalies in a dynamic earth in order to obtain a dynamically consistent relationship between the geoid and the earth s response to internal buoyancy forces we have calculated potential and surface deformation love numbers for internal loading these quantities depend on the depth and harmonic degree of loading they can be integrated as green functions to obtain the dynamic response due to an arbitrary distribution of internal density contrasts spherically symmetric self gravitating flow models are constructed for a variety of radial newtonian viscosity variations and flow configurations including both whole mantle and layered convection we demonstrate that boundary deformation due to internal loading reaches its equilibrium value on the same time scale as postglacial rebound much less than the time scale for significant change in the convective flow pattern by calculating relaxation times for a series of spherically symmetric viscous earth models for uniform mantle viscosity the geoid signature due to boundary deformations is larger than that due to internal loads resulting in net negative geoid anomalies for positive density contrasts geoid anomalies from intermediate wavelength density contrasts are amplified by up to an order of magnitude geoid anomalies are primarily the result of density contrasts in the interior of convecting layers density contrasts near layer boundaries are almost completely compensated layered mantle convection results in smaller geoid anomalies than mantle wide flow for a given density contrast viscosity stratification leads to more complicated spectral signatures because of the sensitivity of the dynamic response functions to model parameters forward models for the geoid can be used to combine several sources of geophysical data e g subducted slab locations seismic velocity anomalies surface topography to constrain better the structure and viscosity of the mantle

late cenozoic deformation and uplift of the western flank of the altiplano evidence from the depositional tectonic and geomorphologic evolution and shallow seismic activity northern chile at 19 30 s 1 we analyze the west vergent thrust system wts along the western flank of the altiplano in northern chile 18 s 21 s in our study area 19 20 s 19 50 s the wts consists of three thrust propagation monocline folds flexures developing growth strata the relative uplift accommodated by the flexures is rapid between 26 and 8 ma 0 1 mm yr diminishing to 0 02 mm yr after 8 ma approximately 2000 m of relative surface uplift was accommodated by the flexures since the late oligocene sedimentological and geomorphological analysis shows that westward tilting of the forearc occurred after 10 ma coeval with the shifting of deformation from the altiplano to the sub andean zone where the underthrusting of the brazilian craton would have resulted in crustal thickening surface uplift in the orogen and westward ductile subcrustal flow forearc tilting is accommodated by east vergent thrusts ets issued from the benioff zone beneath the central depression emerging into the western cordillera contributing 500 1400 m of surface uplift the wts connects the ets in the brittle ductile crustal transition 25 km depth continuing farther east as the altiplano low velocity zone configuring the western altiplano as a crustal scale fault bend fold forearc tilting would be caused by westward ductile flow in the lower crust pushing the rigid forearc in the ets meanwhile between 19 s and 21 s the wts accommodates dextral strike slip and 3 km of n s shortening occurred in the coastal cordillera transcurrence and strain partitioning are probably the result of slight plate convergence obliquity strong coupling within the interplate zone westward continental concavity and high elevation opposing horizontal contraction