the mid norwegian margin a discussion of crustal lineaments mafic intrusions and remnants of the caledonian root by 3d density modelling and structural interpretation the high density lower crustal body lcb on the mid norwegian margin is almost universally interpreted to represent magmatically underplated material added to the crust during early tertiary opening of the ne atlantic the thickness of the lcb is uneven and its distribution along the margin is sharply limited by margin perpendicular lineaments three dimensional density modelling constrained by petrophysical and seismic data was performed to investigate the expression of the various lineaments bivrost jan mayen gleipne etc in the crustal architecture with and without the lcb the bivrost lineament separating the voring and lofoten margin segments is clearly expressed and so is arguably a lineament in the sw voring margin notably most of the lineaments can be interpreted as offshore prolongations of major onshore detachments stemming from late caledonian orogenic collapse an alternative interpretation of the lcb is thus that it represents high grade metamorphic rocks remnant from the caledonian root determining the nature of the lcb has profound effects for the volume estimate of magmatic rocks in the north atlantic igneous province and consequently also for the degree of crustal thinning and heat flow

aftershock decay productivity and stress rates in hawaii indicators of temperature and stress from magma sources 1 we examined dozens of aftershock sequences in hawaii in terms of gutenberg richter and modified omori law parameters we studied p the rate of aftershock decay ap the aftershock productivity defined as the observed divided by the expected number of aftershocks and c the time delay when aftershock rates begin to fall we found that for earthquakes shallower than 20 km p values 1 2 are near active magma centers we associate this high decay rate with higher temperatures and faster stress relaxation near magma reservoirs deep earthquakes near kilauea s inferred magma transport path show a range of p values suggesting the absence of a large deep magma reservoir aftershock productivity is 4 0 for flank earthquakes known to be triggered by intrusions but is normal 0 25 to 4 0 for isolated main shocks we infer that continuing post main shock stress from the intrusion adds to the main shock s stress step and causes higher ap high ap in other zones suggests less obvious intrusions and pulsing magma pressure near kilauea s feeding conduit we calculate stress rates and stress rate changes from pre main shock and aftershock rates stress rate increased after many intrusions but decreased after large m7 8 earthquakes stress rates are highest in the seismically active volcano flanks and lowest in areas far from volcanic centers we found sequences triggered by intrusions tend to have high ap high 0 10 day c values a stress rate increase and sometimes a peak in aftershock rate hours after the main shock we interpret these values as indicating continuing intrusive stress after the main shock

aseismic slip during the 1996 earthquake swarm in and around the onikobe geothermal area ne japan abstract in august 1996 an earthquake swarm including 4 earthquakes of magnitudes greater than 5 occurred in and around the onikobe geothermal area northeast japan while earlier studies detected ground displacements by l band jers radar interferograms there remained certain puzzling discrepancies between the observations and the predictions from a seismologically inferred model and no satisfactory models have yet been proposed here by identifying that a steep gradient in the radar line of sight changes exists in seismicity gaps to the east and west of the torage area just to the north of the onikobe caldera we propose two aseismic reverse faults which turn out to contribute to a local topographic growth as well as explaining the pre existing discrepancies another significant signal is detected in a region in which no large earthquakes occurred we account for this signal by another aseismic fault this fault adds to another evidence for the recent hypothesis that aseismic fault motion drives earthquake swarm

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

observations on a debris covered polar glacier whisky glacier james ross island antarctic peninsula antarctica on etudie la structure d un glacier polaire dans lequel des couches de debris atteignent la surface pour generer une aire tres vaste de glace couverte de debris

estimation of distant relief effect in gravimetry we analyze gravitational effects of distant topographic and bathymetric relief beyond the earth centered angular distance of 1 29 58 i e beyond the outer limit of the hayford bowie zone o or approximately 167 km using a spherical earth model our results support current procedures that neglect distant relief effects for most local gravity surveys but show their potential importance for continental and global scale surveys the distant relief can produce horizontal gradients as large as 0 3 e 0 03 mgal km in mountainous areas the gravitational effect of the distant relief is significant even for local surveys although the vertical gradient of the distant relief effect never exceeds 30 e 3 mgal km on the earth s surface

direct observation of basal sliding and deformation of basal drift at sub freezing temperatures in a tunnel at the base of sub polar urumqi glacier no 1 china three new mechanisms of glacier flow at sub freezing temperatures have been observed taken individually or in combination these modes of flow can account for nearly all 60 80 of the overall glacier motion and yet they act only within the lowermost 1 2 of the effective glacier thickness these mechanisms are 1 enhanced deformation of the frozen and ice laden subglacial drift 2 motion across discrete shear planes or shear bands within the frozen drift or at the ice drift interface and 3 basal sliding at an ice rock interface at a temperature of nearly 5 c the ice laden drift has an effective viscosity of more than one hundred times less than that measured in the overlying ice thus allowing very rapid shear deformation the observed rate or basal sliding at the ice rock interface agrees favorably with that predicted by the recent work of shreve 1984 if proper account is taken of the measured surface roughness and reduced ice viscosity

the structure evolution and symmetry of the magma poor rifted margins of the north and central atlantic a synthesis abstract magma poor rifted margins consistently show extreme crustal thinning accompanied by normal faulting the serpentinization of the mantle beneath crust thinned to less than 8 2 km and the unroofing of a broad zone of mantle within the continent ocean transition accompanied by the development of detachment and other large offset faults these observations are the logical result of the progressive extension of cool lithosphere away from thermal anomalies such as plumes although the paucity of magmatism may be explained by depth dependent extension of the lithosphere and by pre depleted sub crustal lithosphere rifting above initially cool sub lithospheric mantle also may explain the subsidence deficit observed at some margins synrift subsidence is buffered by the simultaneous influx of warmer oceanic asthenosphere as it extends thins and cools ductile creeping layers in the mid and deep crust become progressively more brittle resulting in increased coupling between the upper and lower crust and eventually the embrittlement of the entire crust faults cutting from the surface across the moho bringing water into the mantle and causing its serpentinization increased coupling and the development of serpentine detachments predict the development of late stage asymmetry once the entire crust is brittle such detachments are imaged on some margins and inferred on others analysis of the crustal structure across conjugate margins shows that these are approximately symmetric until this late stage when they become markedly asymmetric similar analyses show that depth dependent stretching of the crust is insufficient to explain the discrepancy between the amount of the visible extension along faults and the amount of crustal thinning instead this extension discrepancy may be related to the complex evolution of brittle deformation through multiple phases and styles of faulting related to the changes in the rheological character and strength of the lithosphere as it is thinned complex polyphase faulting continues after complete crustal separation resulting in the exhumation of broad expanses of peridotitic basement the top of which is everywhere marked by an exhumed slip surface similar to the corrugated surface observed at mid ocean ridges the similarity in processes between mantle unroofing and seafloor spreading makes the distinction between the cot and true oceanic crust difficult and possibly moot

earthquake clusters in southern california i identification and stability 1 we use recent results on statistical analysis of seismicity to present a robust method for comprehensive detection and analysis of earthquake clusters the method is based on nearest neighbor distances of events in space time energy domain the method is applied to a 1981 2011 relocated seismicity catalog of southern california having 111 981 events with magnitudes m 2 and corresponding synthetic catalogs produced by the epidemic type aftershock sequence etas model analysis of the etas model demonstrates that the cluster detection results are accurate and stable with respect to 1 three numerical parameters of the method 2 variations of the minimal reported magnitude 3 catalog incompleteness and 4 location errors application of the method to the observed catalog separates the 111 981 examined earthquakes into 41 393 statistically significant clusters comprised of foreshocks mainshocks and aftershocks the results reproduce the essential known statistical properties of earthquake clusters which provide overall support for the proposed technique in addition systematic analysis with our method allows us to detect several new features of seismicity that include 1 existence of a significant population of single event clusters 2 existence of foreshock activity in natural seismicity that exceeds expectation based on the etas model and 3 dependence of all cluster properties except area on the magnitude difference of events from mainshocks but not on their absolute values the classification of detected clusters into several major types generally corresponding to singles burst like and swarm like sequences and correlations between different cluster types and geographic locations is addressed in a companion paper

birth of a volcanic margin off argentina south atlantic 1 based on a dense grid of multichannel reflection seismic lines we study the evolution of a volcanic rifted margin segment off argentina the segment under study is located between 44 s and 41 s we describe in detail the facies of the extrusive basaltic complexes across the margin these include single and multiple inner seaward dipping reflectors sdrs with varying architecture along the margin outer highs and outer sdr wedges a detailed interpretation of a transitional zone between the inner and outer sdr wedges is presented multiple inner sdrs are concentrated at the southern part of the margin segment while in the north only one steeply dipping wedge is present the dip of the inner sdr wedges changes along the margin and we propose subsidence by loading as main cause the transitional zone between the inner and outer sdr wedges becomes narrower toward the north by correlating with magnetic data we conclude that the emplacement of the 30 100 km wide multiple inner sdrs occurred episodically we propose an injection center which migrated in a seaward direction with proceeding extension as the origin for the multiple inner sdrs a scissor like opening of the margin segment resulted in different amounts of stretching along strike of the margin segment and is likely the cause for the varying distribution of the extrusive basaltic complexes the varying extension rates within the margin segment contribute to decreasing volumes of melts generated in a northward direction within this rift segment

evidence of cryostatic desiccation processes associated with sand intraclasts within diamictons southern ontario canada shore bluffs at mohawk bay southern ontario reveal within a complex melange of glacial sediments brecciated diamicton surrounding sand block intraclasts typically each intraclast has an aureo

sand intraclasts as evidence of subglacial deformation of middle pleistocene permafrost north norfolk uk sand intraclasts are common within the bacton green till member a glacitectonic mlange subjected to polyphase deformation during the middle pleistocene in north norfolk uk the intraclasts range from a few tens of centimetres to 10 m in length and have sharp contacts with the surrounding till sand within the intraclasts is unconsolidated and contains well preserved primary stratification the wrapping of glacitectonic foliation around the intraclasts and the development of folds relating to mechanical instabilities indicate that the intraclasts acted as competent masses within a more easily deformable fine grained till that accommodated the majority of the strain sharp contacts and distinctive heavymineral assemblages indicate little intermixing between the sand and till five hypotheses about the entrainment and evolution of the intraclasts are tested against sedimentological structural and mineralogical observations the most reasonable hypothesis attributes the intraclasts to glacitectonic deformation of warm permafrost initial ice advance caused large scale thrusting of proglacial permafrost that led to the stacking of pre glacial and ice marginal sediments that were subsequently deformed sub marginally to generate the intraclasts preservation of primary stratification within the intraclasts is attributed to deformation at temperatures slightly below the pressure melting point when pore ice cemented the intraclasts as rigid bodies at the same time deformation was concentrated into the surrounding finer grained till because of its significant liquid water content and ductile rheology it is concluded that the intraclasts provide a criterion to identify past glacierepermafrost interactions and a potential means of differentiating between subglacial deformation under unfrozen and partially frozen conditions

characteristics of three recent earthquake sequences in the taupo volcanic zone new zealand abstract we have analysed three recent earthquake sequences in the northern part of the taupo volcanic zone a 1998 sequence at haroharo with a largest event of ml 4 8 and a 2004 sequence near lake rotoehu largest event ml 5 4 had normal b values and displayed an aftershock decay pattern with most of the activity within the first few days in contrast a 2005 sequence a few tens of kilometres away at matata largest event ml 4 1 had very different characteristics with a slow development and decay no tendency for enhanced seismicity after the larger events and a very high b value the focal mechanisms of the rotoehu and matata events are normal and have stress patterns consistent with the geodetically observed extension of the taupo volcanic zone in a northwest southeast direction the extensive recent volcanism in the okataina volcanic centre does not seem to have affected the stress pattern in this area the rotoehu sequence showed a strong resemblance particularly in the time distribution of events to the well known swarm activity in the vogtland region on the german czech border in which larger events were followed by a burst of seismicity as in a normal aftershock sequence some of the arguments that have been advanced to explain the vogtland swarm as seismicity induced by fluid injection apply to rotoehu but there is no direct evidence of fluid involvement the matata sequence appears to have a continuing trigger mechanism either a slow injection of fluid or a slow slip event in an environment in which opening pore spaces prevent high overpressures developing the matata sequence occurred close to the area of the 1987 ml 6 3 edgecumbe earthquake so exhibiting two extremes of seismic temporal pattern namely mainshock aftershock and a swarm with many events of similar magnitude within a small area

influence of overconsolidation on the freezing characteristics of a clayey silt laboratory freezing tests were performed on a saturated clayey silt at various overconsolidation ratios ocr to establish the relationship between initial void ratio and stress history and the amount of moisture transfer during freezing the frost heave tests were analysed in terms of the segregation potential as well as a function of the temperature of ice lens formation and the overall hydraulic conductivity of the frozen fringe all other factors being the same the segregation potential was found to increase with increasing values of ocr decreasing initial void ratios however the combined effects of decreasing void ratio and increasing suction at the frost line all other factors being identical in all freezing tests resulted in decreasing segregation potentials this trend was the result of a decrease in the temperature of ice lens formation and the concomitant decrease in overall hydraulic conductivity of the frozen fringe a simple model showed that the capillary unfrozen water between clay

crustal earthquake bursts in california and japan their patterns and relation to volcanoes 1 we analyze 153 bursts of earthquakes in southern california and japan the burst patterns are similar in southern california and japan they fill a spectrum between swarm like sequences without obvious mainshocks and mainshocks with omori law abiding aftershocks in agreement with our previous work the swarm like sequences in japan have more events are more voluminous and tend to expand with time when compared to mainshock aftershock type sequences in both regions we find that the sequences starting with their largest events tend to be much shorter in duration bursts within 50 km of volcanoes are similar in character to those elsewhere except they tend to have longer duration we hypothesize that swarminess is a proxy for fluid pressure redistribution and or aseismic slip driving the seismicity bursts and conversely the mainshock aftershock style sequences have end member behavior that results solely from a cascade of elastic failures the complexity of the spatial seismicity distribution does not correlate with the style of swarm observed indicating that fluid conditions and composition are likely more influential than geometry in determining the patterns we observe

a common origin for aftershocks foreshocks and multiplets we demonstrate that the statistics of earthquake data in the global cen troid moment tensor cmt and national earthquake information center neic catalogs and local california council of the national seismic system cnss catalog are consistent with the idea that a single physical triggering mechanism is responsible for the occurrence of aftershocks foreshocks and multiplets specifically we test the hypothesis that tectonic earthquakes usually show clustering only as a result of an initial earthquake triggering subsequent ones and that the magnitude of each trig gered earthquake is entirely independent of the magnitude of the triggering earth quake therefore a certain percentage of the time as determined by the gutenberg richter magnitude frequency relationship an earthquake should by chance be larger than or comparable in size to the earthquake that triggered it this hypothesis predicts that the number of times foreshocks or multiplets are observed should be a fixed fraction of the number of aftershock observations we find that this is indeed the case in the global cmt and neic catalogs the average ratios between foreshock aftershock and multiplet rates are consistent with what would be predicted by the gutenberg richter relationship with b 1 we give special attention to the solomon islands where it has been claimed that unique fault structures lead to unusually high numbers of multiplets we use monte carlo trials to demonstrate that the solomon islands multiplets may be explained simply by a high regional aftershock rate and earthquake density we also verify our foreshock results from the more complete recordings of small earthquakes available in the california catalog and find that foreshock rates for a wide range of foreshock and mainshock magnitudes can be projected from aftershock rates using the gutenberg richter relationship with b 1 and the relationship that the number of earthquakes triggered varies with triggering earthquake magnitude m as c10m where c is a productivity constant and is equal to 1 finally we test an alternative model that proposes that foreshocks do not trigger their mainshocks but are instead triggered by the mainshock nucleation phase in this model the nucleation phase varies with mainshock magnitude so we would expect mainshock magnitude to be correlated with the magnitude number or spatial extent of the foreshocks we find no evidence for any of these correlations

sediment deformation beneath glaciers rheology and geological consequences experiments beneath breidamerkurjokull in iceland have led to development of flow laws for the subglacial till relating strain rate to shear stress and effective pressure and assuming either bingham fluid or nonlinearly viscous fluid behavior water pressures in the till are less than ice pressures and it is suggested that this may lead to infiltration of ice into the sediment which inhibits sliding at the ice sediment interface where water pressures are equal or near to ice pressures infiltration does not occur and sliding may result a one dimensional theory of subglacial deformation is developed in which the empirical flow law is coupled with a model of subglacial hydrology and consolidation this predicts stable states in which subglacial sediment either does not deform or a dilatant deforming horizon forms with positive effective pressures at the ice bed interface or unstable states where zero or negative effective pressures are predicted time dependent analyses show that response times following perturbations of the system may be of the order of 103 years and thus that unsteady behavior may be normal on glaciers flowing over unlithified sediment beds it is suggested that the natural variability of material properties in subglacial sediment beds leads to the development of drumlins on the glacier bed it is suggested that unstable deformation at zero or negative effective stress leads to piping in subglacial sediments at the glacier terminus and the growth of sediment floored subglacial tunnels their frequency is that which is sufficient to draw down subglacial water pressures so as to prevent unstable deformation where they discharge large water volumes subglacial sediments flow laterally toward them producing tunnel valleys this sediment is then removed by water flowing along the axial tunnel tunnel valleys can be regarded as the equivalent in soft sediment areas of eskers in bedrock areas

climate and paleo environmental change within the mannheim formation near heidelberg upper rhine valley germany a case study based upon microsedimentological analyses abstract microsedimentological analyses were used to examine the first 56 m of a 500 m core near heidelberg germany in the upper rhine valley this core chronostratigraphically stretches from present day to 450 ka and includes proxy evidence supporting the presence of wurmian eemian and likely components of the riss and ho kirch stages the sediment in the core reflects the geomorphic biotic pedogenic and climatic processes the sediments were deposited in a fluvial environment at times within a broad floodplain in the main channel and also at other times some distance from the main river these upper sediments act as indirect proxy evidence that indicate changes in climate over time illustrative of cool periglacial tundra like conditions and of milder forested temperate environments from ho kirch to present day times within the sediments evidence can be found of an interglacial fossil soil followed later by a holocene temperate climate up to present day a strong link can be ascertained between macro and micro stratigraphic evidence the latter revealing detailed and invaluable sources of information this analysis permits the reconstruction of past climate and paleoenvironmental conditions the application of microsedimentological analyses to the mannheim formation reveals a store of data that has been largely hidden when using only macro sedimentological methods

aseismic transient driving the swarm like seismic sequence in the pollino range southern italy tectonic earthquake swarms challenge our understanding of earthquake processes since it is difficult to link observations to the underlying physical mechanisms and to assess the hazard they pose transient forcing is thought to initiate and drive the spatio temporal release of energy during swarms the nature of the transient forcing may vary across sequences and range from aseismic creeping or transient slip to diffusion of pore pressure pulses to fluid redistribution and migration within the seismogenic crust distinguishing between such forcing mechanisms may be critical to reduce epistemic uncertainties in the assessment of hazard due to seismic swarms because it can provide information on the frequency magnitude distribution of the earthquakes often deviating from the assumed gutenberg richter relation and on the expected source parameters influencing the ground motion for example the stress drop here we study the ongoing pollino range southern italy seismic swarm a long lasting seismic sequence with more than five thousand events recorded and located since october 2010 the two largest shocks magnitude m w 4 2 and m w 5 1 are among the largest earthquakes ever recorded in an area which represents a seismic gap in the italian historical earthquake catalogue we investigate the geometrical mechanical and statistical characteristics of the largest earthquakes and of the entire swarm we calculate the focal mechanisms of the m l 3 events in the sequence and the transfer of coulomb stress on nearby known faults and analyse the statistics of the earthquake catalogue we find that only 25 per cent of the earthquakes in the sequence can be explained as aftershocks and the remaining 75 per cent may be attributed to a transient forcing the b values change in time throughout the sequence with low b values correlated with the period of highest rate of activity and with the occurrence of the largest shock in the light of recent studies on the palaeoseismic and historical activity in the pollino area we identify two scenarios consistent with the observations and our analysis this and past seismic swarms may have been passive features with small fault patches failing on largely locked faults or may have been accompanied by an active largely aseismic release of a large portion of the accumulated tectonic strain those scenarios have very different implications for the seismic hazard of the area

properties of aftershock sequences in southern california the temporal behavior of 39 aftershock sequences in southern california 1933 1988 was modeled by the modified omori relation minimum magnitudes for completeness of each sequence catalog were determined and the maximum likelihood estimates of the parameters k p and c with the standard errors on each were determined by the ogata algorithm the b value of each sequence was also calculated many of the active faults in the region both strike slip and thrust were sampled the p values were graded in terms of the size of the standard error relative to the p value itself most of the sequences were modeled well by the omori relation many of the sequences had p values close to the mean of the whole data set 1 11 0 25 but values significantly different from the mean as low as 0 7 and as high as 1 8 exist no correlation of p with either the b value of the sequence or the mainshock magnitude was found the results suggest a direct correlation of p values is with surface heat flow with high values in the salton trough high heat flow and one low value in the san bernardino mountains and on the edge of the ventura basin both low heat flow the large fraction of the sequences with p values near the mean are at locations where the heat flow is near the regional mean 74 mw m2 if the hypothesis that aftershock decay rate is controlled by temperature at depth is valid the effects of other factors such as heterogeneity of the fault zone properties are superimposed on the background rate determined by temperature surface heat flow is taken as an indicator of crustal temperature at hypocentral depths but the effects on heat flow of convective heat transport and variations in near surface thermal conductivity invalidate any simple association of local variations in heat flow with details of the subsurface temperature distribution the interpretation is that higher temperatures in the aftershock source volume caused shortened stress relaxation times in the fault zone materials leading to a faster decay rate higher p value in 1967 mogi proposed such a relation on the basis of japanese data seismic velocity distributions published for southern california generally support the hypothesis with low velocities higher temperatures corresponding to high p values and vice versa

till melange at amsdorf central germany sediment erosion transport and deposition in a complex soft bedded subglacial system abstract glacial melange in the open cast mine at amsdorf central germany consists of several square meters of large sorted sediment blocks embedded in till the blocks are composed of largely intact to slightly deformed glaciofluvial and glaciolacustrine sand silt and clay initially deposited in a proglacial lake 2 3 km up ice and subsequently overridden by a glacier the blocks typically have cuboid to subrounded outlines are randomly distributed in the till and the contacts with the surrounding till are distinctly sharp underneath the melange are varved clays which exhibit strong deformations occasionally intervening with entirely undisturbed areas it is suggested that the blocks were entrained into debris rich basal ice by bulk freeze on when the glacier sole was lowered onto the bottom of an overridden lake after entrainment the blocks were transported englacially and re deposited with far traveled till matrix as a melt out till from stagnant ice the glacier moved mainly by sliding enhanced by low permeability varved clays in the substratum the glacier is believed to have been of a polythermal type these results show that bulk freeze on can lead to entrainment of soft sediment blocks at least 20 m2 in size and that these blocks can be englacially transported with little or no deformation for several kilometers and more the occurrence of deformed and undeformed clays under the till melange indicates a possible mosaic of coupled and decoupled ice the latter caused by a thin transient subglacial water film separating the bed from the glacier

seismic and geodetic investigation of the 1996 1998 earthquake swarm at strandline lake alaska summary microearthquake swarms occur frequently in volcanic environments but do not always culminate in an eruption such non eruptive swarms may be caused by stresses induced by magma intrusion hydrothermal fluid circulation or possibly other tectonic processes such as slow slip earthquakes the strandline lake region of southcentral alaska located 30 km northeast of mt spurr volcano experienced an intense earthquake swarm between 1996 august and 1998 september a total of 2507 earthquakes were recorded by the alaska volcano observatory s permanent seismic network during the swarm period with a maximum magnitude of ml 3 6 the cumulative seismic moment of the swarm was 1 2 1015 n m equivalent to that of a single mw 4 0 earthquake because of the swarm s distance from the nearest holocene volcanic vent seismic monitoring was minimal and gas emission and gps data do not exist for the swarm period however combined waveforms from a dense seismic network on mt spurr and from several regional seismic stations allow reanalysis of a representative set of swarm and background earthquakes swarm hypocentres calculated using a newly formulated 1 d velocity model and station corrections indicate a roughly circular swarm volume with dimensions of approximately 5 km centred below 10 km below sea level bsl composite fault plane solutions for swarm earthquakes indicate oblique strike slip faulting with a northeast trending p axis orientation in contrast a composite fault plane solution for background earthquakes indicates a fundamentally different though poorly constrained local stress field orientation interferometric synthetic aperture radar images spanning the swarm period unambiguously show no evidence of surface deformation but do not rule out subcentimetre scale deformation during the swarm while a shallow 10 km bsl magma intrusion representing an intrusive or protovolcanic segment of the aleutian arc

intrusive and extrusive micro melange couplets as distal effects of tidal pumping by a marine ice sheet microscopic soft sediment deformation structures in a 30 x 25 x 12 mm hand specimen of glaciogenic silty mudstone from the permo carboniferous dwyka formation of northern natal in south africa are illustrated by serial sections the processes these structures imply are interpreted using palinspastically restored sections and isopachytes reconstructed from them the sedimentation of silts muds and microrhythmites is found to have been punctuated by episodes of hydraulic activity which resulted in thirteen bodies with the mixed fabrics of micromelanges these are divisible into five melange types 1 subconcordant intrusive 2 disconcordant intrusive 3 subconcordant extrusive 4 near surface with asymmetric internal structures and 5 conformable near surface with internal structures symmetric about the palaeovertical remarkable similarities between isopachs for pairs of micromelanges at different levels in the specimen suggest that intrusive melanges at depth fed contemporaneous extrusive melanges on the sea floor each couplet of melanges with matched isopachs is linked by faults which are interpreted as having acted as hydraulic vents despite only parts of them being infilled by intrusive melange a significant proportion of the succession could consist of sediment recycled from depth by hydraulic extrusion repeated hydraulic intrusions along and extrusions from the same disturbed interface suggest that this interface acted as the distal leaking end of one of the hydraulic sills recently described by von brunn talbot 1986 pulses of pressurized water were transmitted through a prograding marine slope of quickclay by the tidal pumping of a marine ice sheet periodically grounding upslope the results of this analysis are extrapolated to processes operative in subduction complexes all four fabrics described from large scale hydraulic melanges in modern and ancient accretionary prisms are matched on a much smaller scale in our sample from a proglacial submarine slope dismember ment by faults is the only fabric element described from accretionary complexes which is missing from the micro analogues described here

seismic clusters analysis in northeastern italy by the nearest neighbor approach abstract the main features of earthquake clusters in northeastern italy are explored with the aim to get new insights on local scale patterns of seismicity in the area the study is based on a systematic analysis of robustly and uniformly detected seismic clusters which are identified by a statistical method based on nearest neighbor distances of events in the space time energy domain the method permits us to highlight and investigate the internal structure of earthquake sequences and to differentiate the spatial properties of seismicity according to the different topological features of the clusters structure to analyze seismicity of northeastern italy we use information from local ogs bulletins compiled at the national institute of oceanography and experimental geophysics since 1977 a preliminary reappraisal of the earthquake bulletins is carried out and the area of sufficient completeness is outlined various techniques are considered to estimate the scaling parameters that characterize earthquakes occurrence in the region namely the b value and the fractal dimension of epicenters distribution required for the application of the nearest neighbor technique specifically average robust estimates of the parameters of the unified scaling law for earthquakes usle are assessed for the whole outlined region and are used to compute the nearest neighbor distances clusters identification by the nearest neighbor method turn out quite reliable and robust with respect to the minimum magnitude cutoff of the input catalog the identified clusters are well consistent with those obtained from manual aftershocks identification of selected sequences we demonstrate that the earthquake clusters have distinct preferred geographic locations and we identify two areas that differ substantially in the examined clustering properties specifically burst like sequences are associated with the north western part and swarm like sequences with the south eastern part of the study region the territorial heterogeneity of earthquakes clustering is in good agreement with spatial variability of scaling parameters identified by the usle in particular the fractal dimension is higher to the west about 1 2 1 4 suggesting a spatially more distributed seismicity compared to the eastern parte of the investigated territory where fractal dimension is very low about 0 8 1 0

insights from recent gravity satellite missions in the density structure of continental margins with focus on the passive margins of the south atlantic abstract we focus on new gravity and gravity gradient data sets from modern satellite missions goce grace and champ and their geophysical interpretation at passive continental margins of the south atlantic both sides south africa and south america have been targets of hydrocarbon exploration and academic research of the german priority program sample south atlantic margin processes and links with onshore evolution the achievable spatial resolution driven by goce is 70 80 km therefore most of the geological structures which cause a significant gravity effect by both size and density contrast can be resolved however one of the most important aspects is the evaluation of the omission error which is not always in the focus of interpreters it results from high frequency signals of very rough topographic and bathymetric structures which cannot be resolved by satellite gravimetry due to the exponential signal attenuation with altitude the omission error is estimated from the difference of the combined gravity model eigen 6c4 and the satellite only model goco05s it can be significantly reduced by topographic reductions simple 2d density models and their related mathematical formulas provide insights in the magnitude of the gravity effect of masses that form a passive continental margin they are contrasted with results from satellite only and combined gravity models example geophysical interpretations are given for the western and eastern margin of the south atlantic ocean where standard deviations vary from 25 to 16 mgal and 21 11 mgal respectively it could be demonstrated that modern satellite gravity data provide significant added value in the geophysical gravity data processing domain and in the validation of heterogeneous terrestrial data bases combined models derived from high resolution terrestrial gravity and homogeneous satellite data will lead to more detailed and better constrained lithospheric density models and hence will improve our knowledge about structure evolution and state of stress in the lithosphere

salt as a 3d element in structural modeling example from the central european basin system abstract based on a well constrained 3d structural model of the central european basin system 3d modeling has been carried out to understand the regional scale regularities between movements of the upper permian zechstein salt and the major post permian tectonic events the 3d reconstruction of the paleo thickness of upper permian salt at the end of the permian period demonstrates that areas of thickened upper permian salt correlate with the present day distribution of the largest salt structures within the central european basin system this spatial correlation implies that the distribution of salt thickness at the end of deposition partially controlled the structural style of the basin during post permian phases of salt tectonics moreover the results of 3d salt redistribution for post permian times indicate that the initiation of salt movements took place in the triassic the triassic extensional events triggered several phases of salt movements within the coeval depocenters of the central european basin system such as the glueckstadt graben the horn graben the norwegian danish basin the fjerritslev trough and the himmerland graben and the polish basin during the late jurassic early cretaceous extensional transtensional tectonic event the strongest salt movement occurred within the central graben the lower saxony basin and the pompeckj block the intensity of the late jurassic early cretaceous phase of salt tectonics is essentially declining from the marginal areas of the central european basin system towards the horn graben the glueckstadt graben and adjacent areas the late early cretaceous early late cretaceous is characterized by tectonic quiescence without strong salt movements over the entire study area the next regional phase of salt movements was triggered by late cretaceous early cenozoic inversion involving almost the entire central european basin system in terms of renewed salt movements inversion related thick skinned salt tectonics is observed along the nw se trending elbe fault system and the teisseyre tornquist zone where strongest compressional deformations were localized on the contrary a thin skinned character of salt movements was prevailing within the largest part of the north german basin post inversion cenozoic subsidence was also accompanied by salt activity related either to diapiric rise due to regional shortening and or to local roughly e w directed extension the cenozoic phase of salt movements was especially prominent within the marginal troughs of the glueckstadt graben

subglacial hydraulic conditions and their possible impact upon subglacial bed formation abstract in reviewing hypotheses of subglacial bed formation it becomes apparent that a close relationship must exist between the development of these bedforms and subglacial hydraulic conditions a speculative classification of subglacial temperate beds is presented subglacial beds are subdivided into h q and m beds h beds are typically hard beds in which upper interface meltwater activity dominates m beds are those in whichd soft mobile subglacial debris conditions prevail and in which advective pervasive f flow of saturated debris occurs in q beds both of the other bed types occur but are of a spatially and temporally transitory nature thus this latter bed type may be the most common beneath ice masses it is under an m bed state that many drumlin subglacial bedforms and associated forms are thought to develop discussion on the processes involved in mobile debris entrainment and the effect of changing rheological parameters are developed it is argued that such bedform initiation occurs due to anisotropic rheological variations within the mobile debris setting up a feedback effect such conditions are thought to be found most likely at the lower interface of a fast moving ice mass possibly typical of an ice stream in using empirical analyses of mobile debris conditions a limited set of relationships between subglacial meltwater flux rates basal ice velocity debris porosity and bed width are established with reference to mobile debris thicknesses using this relationship a set of possible parameter values that would allow bed formation to be achieved are presented the impact of bed formation under these conditions upon possible sedimentological facies and deformation structures is postulated the wider effect of m bedd conditionsd on subglacial sedimentology is introduced and the need to investigate subglacial hydraulic and bed conditions under past glaciations from the evidence of their glacial sediments and landforms emphasised

asperity generating upper crustal sources revealed by b value and isostatic residual anomaly grids in the area of antofagasta chile in our study we show that the locations of largest coseismic slip asperities on the fault plane of the m w 8 0 1995 antofagasta earthquake in northern chile can be mapped by the spatial distribution of the seismic b value obtained from the aftershock sequence of the megathrust earthquake these areas of high seismic moment release and concurrent high b values are congruent with anomalies of the gravity isostatic residual ir field in the antofagasta region they are superimposed on the seismogenic part of the north chilean subduction zone where the strongest coupling of the upper and lower plate is expected the ir anomalies are interpreted to be caused by large jurassic early cretaceous batholiths which intruded into the upper crust the observed positive correlations between high seismic b values ir anomalies and geologic structures enable us to propose a mechanical model for the generation of the asperities in the antofagasta region we suggest that the batholiths in conjunction with buoyant forces acting on the subducted slab of the nazca plate are responsible for locking the interface where the asperities are located this implies long term conditions for the existence of the asperity generating tectonic situation concequently the asperities around antofagasta could be stationary features at least for several seismic cycles hence we propose that the ir anomalies along the north chilean convergent margin can be used as an indicator for high moment release and slip in future large earthquakes

tectonic stress regime in the 2003 2004 and 2012 2015 earthquake swarms in the ubaye valley french alps we study two earthquake swarms that occurred in the ubaye valley french alps within the past decade the 2003 2004 earthquake swarm with the strongest shock of magnitude ml 2 7 and the 2012 2015 earthquake swarm with the strongest shock of magnitude ml 4 8 the 2003 2004 seismic activity clustered along a 9 km long rupture zone at depth between 3 and 8 km the 2012 2015 activity occurred a few kilometres to the northwest from the previous one we applied the iterative joint inversion for stress and fault orientations developed by vavrycuk 2014 to focal mechanisms of 74 events of the 2003 2004 swarm and of 13 strongest events of the 2012 2015 swarm the retrieved stress regime is consistent for both seismic activities the 3 principal axis is nearly horizontal with azimuth of 103 the 1 and 2 principal axes are inclined and their stress magnitudes are similar the active faults are optimally oriented for shear faulting with respect to tectonic stress and differ from major fault systems known from geological mapping in the region the estimated low value of friction coefficient at the faults 0 2 0 3 supports an idea of seismic activity triggered or strongly affected by presence of fluids

esa s satellite only gravity field model via the direct approach based on all goce data gravity field and steady state ocean circulation explorer goce gravity gradient data of the entire science mission and data from lageos 1 2 and gravity recovery and climate experiment grace were combined in the construction of a satellite only gravity field model to maximum degree 300 when compared to earth gravitational model 2008 it is more accurate at low to medium resolution thanks to goce and grace data when compared to earlier releases of european space agency goce models it is more accurate at high degrees owing to the larger amount of data ingested which was moreover taken at lower altitude the impact of orbiting at lower altitude in the last year of the mission is large a model based on data of the last 14 months is significantly more accurate than the release 4 model constructed with the first 28 months the calibrated cumulated geoid error estimate at 100 km resolution is 1 7 cm the optimal resolution of the goce model for oceanographic application is between 100 and 125 km

indications for a successively triggered rupture growth underlying the 2000 earthquake swarm in vogtland nw bohemia 1 the characteristics of earthquake swarms can neither be described by simple laws nor are the underlying mechanisms presently understood swarm activity is often assumed to be caused by an intrusion of fluids into the seismogenic zone we have studied the earthquake catalog of the large earthquake swarm that occurred in the year 2000 in vogtland se germany and nw bohemia an area well known for its episodic swarm generation we observe a significant decrease of the gutenberg richter b value during the swarm evolution as well as a fractal temporal clustering of the earthquakes the spatial spreading of the swarm s activity which is approximately confined to one plane cannot simply be explained by a process of fluid diffusion instead we observe a simple relationship between the spatial spreading and the seismic moment release which is in good agreement with empirical relationships derived for tectonically driven earthquakes and theoretical crack growth models this observation points to a progressively growing main fracture underlying the swarm activity in addition we find that the swarm earthquakes themselves trigger aftershocks near the border of their rupture area the stick slip behavior of the rupture propagation can be explained by stress transfers and induced fluid flows due to earthquakes in a fluid permeated critically loaded fault zone however during the first phase the temporal behavior is found to be different pointing to intrusion of fluids initiating the swarm activity

slip generated patterns of swarm microearthquakes from west bohemia vogtland central europe evidence of their triggering mechanism 1 we investigated space time relations between consecutive events of west bohemian 2000 swarm and their association with the coulomb stress changes induced on a fault plane by prior swarm events a few thousand m 3 3 strike slip swarm earthquakes clustered along a fault plane at depths 6 5 10 5 km and showed common rake angle of 30 in order to disclose earthquake interaction we investigated the space time relations between consecutive earthquakes we determined relative position vectors for each consecutive event pair the prior event and the immediate aftershock ia and we measured time lags between them the resulting cluster of relative position vectors shows a high density of aftershocks near the origin which decays with distance it points out a triggering effect of the prior event upon subsequent aftershocks the spatial distribution of the relative positions disclosed dominance of aftershocks in the slip parallel directions which is manifested by pronounced elongation of the cluster of the relative positions and of the angular dependence of the rate of ias the temporal distribution of the relative positions indicates that some aftershocks prove high interevent velocities and occur systematically at greater distances suggesting the existence of two distinct triggering mechanisms acting at large and small timescales we evaluated the complete coulomb stress change upon the fault plane due to the prior event and showed that the observed space time distribution of the relative positions can be explained by a common effect of both static and dynamic stress changes which act on different distance and timescale

reflections on soft subglacial beds as a mosaic of deforming and stable spots abstract much discussion regarding subglacial processes is centred around the question of how soft beds respond to ice overriding in particular how widespread and penetrative is their deformation how does it affect the ice stability and what are the consequences for large scale sediment redistribution patterns contrasting views have been proposed which are difficult to verify and reconcile in the light of scarcity of agreed criteria to identify deforming beds here we suggest that soft beds under warm based glaciers can be envisaged as a mosaic of deforming and stable spots transient in time and space according to changes in the control parameters at the ice bed interface the subglacial mosaic model is consistent with field data showing heavily deformed beds interspersed with largely undisturbed beds it is suggested that deformation found in tills is a cumulative effect of strain within a relatively thin ephemeral deforming spots under the ice sole affecting the till as it accretes during ice overriding in accord with the coulomb plastic rheology the role of clast ploughing in bed deformation is emphasised

the dynamics of plate tectonics and mantle flow from local to global scales plate tectonics is regulated by driving and resisting forces concentrated at plate boundaries but observationally constrained high resolution models of global mantle flow remain a computational challenge we capitalized on advances in adaptive mesh refinement algorithms on parallel computers to simulate global mantle flow by incorporating plate motions with individual plate margins resolved down to a scale of 1 kilometer back arc extension and slab rollback are emergent consequences of slab descent in the upper mantle cold thermal anomalies within the lower mantle couple into oceanic plates through narrow high viscosity slabs altering the velocity of oceanic plates viscous dissipation within the bending lithosphere at trenches amounts to 5 to 20 of the total dissipation through the entire lithosphere and mantle

reconstruction of the southwestern african continental margin by backward modeling abstract as the evolution of the southwestern african passive continental margin and in particular the vertical movements in this area are still a matter of debate this study aims to quantify the past vertical movements by reconstructing the paleobathymetric evolution of the southwestern african margin during the post rift phase to quantify the vertical movements inferred from paleobathymetries different subsidence components that have affected the passive continental margin are calculated and interpreted with respect to the generating processes our investigation takes advantage of information on the present day sedimentary thicknesses and the crustal configuration along the sw african margin by using this detailed information and modeling backward in time we attempt to separate different subsidence components such as the load induced subsidence and the thermal subsidence for different time intervals during the post rift phase calculating the amounts of each subsidence component and subtracting them from the present day configuration yields paleobathymetries which are interpreted with respect to the evolution of the southwestern african passive margin these restored paleobathymetries for different time steps during the post rift phase indicate spatial and temporal variations of vertical movements including phases of seafloor uplift as a result our investigation allows to give minimum estimates of the vertical movements that have occurred during the post rift phase in addition to predominant subsidence about 1000 m of seafloor uplift are deduced for the northern and southern parts of the sw african margin quantifying the amounts of vertical movements cannot finally clarify the generating processes behind these movements but the timing and magnitude of seafloor uplift indicate a deep mantle mechanism

penecontemporaneous non tectonic brecciation of unconsolidated silts and muds abstract at several localities sediments have been found which partly or completely consist of angular fragments from the geological context it is clear that the fine grained parent material was broken up after deposition this cannot be explained by endogenic forces so that sedimentary and diagenetic penecontemporaneous processes must be the cause occurrences from poland and the netherlands are described together with an analysis of the brecciation processes these breccias are the result of pressure which may have been cryostatic or caused by bioturbation flowage of liquified material or similar processes

the origin of soft sediment deformation structures in permo carboniferous glacial and proglacial beds south africa abstract soft sediment deformational structures in subsurface glacial and proglacial beds of the permo carboniferous dwyka formation include faults folds boudins sigmoidally shaped laminae and sandstone siltstone injections within specific zones ranging in thickness from 1 to 12 m the zones consist of rhythmite shale with ice rafted debris siltstone and minor sandstone and diamictite but often the original character of the sediments is completely destroyed by the deformation the deformation structures predominantly formed during extensional strain of the sediments and form part of complex shear zones diapiric structures load coasts and convolute lamination the deformation zones are lithologically controlled and intimately associated with debris flow deposits indicating that gravitational forces giving rise to slumping were the predominant cause of the deformation excess pore water pressures and subsequent liquefaction of the fine grained sediments on oversteepened depositional slopes apparently generated the sheetlike slumps but the possibility of grounded ice initiating slumps in the lowermost deformation zone cannot be excluded a new type of coarse grained matrix supported deposit designed melange diamictite which formed during slumping under a soft sediment slab is described for the first time

mechanism of the 1996 97 non eruptive volcano tectonic earthquake swarm at iliamna volcano alaska a significant number of volcano tectonic vt earthquake swarms some of which are accompanied by ground deformation and or volcanic gas emissions do not culminate in an eruption these swarms are often thought to represent stalled intrusions of magma into the mid or shallow level crust real time assessment of the likelihood that a vt swarm will culminate in an eruption is one of the key challenges of volcano monitoring and retrospective analysis of non eruptive swarms provides an important framework for future assessments here we explore models for a non eruptive vt earthquake swarm located beneath iliamna volcano alaska in may 1996 june 1997 through calculation and inversion of fault plane solutions for swarm and background periods and through coulomb stress modeling of faulting types and hypocenter locations observed during the swarm through a comparison of models of deep and shallow intrusions to swarm observations we aim to test the hypothesis that the 1996 97 swarm represented a shallow intrusion or failed eruption observations of the 1996 97 swarm are found to be consistent with several scenarios including both shallow and deep intrusion most likely involving a relatively small volume of intruded magma and or a low degree of magma pressurization corresponding to a relatively low likelihood of eruption

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

earthquakes triggered by silent slip events on kīlauea volcano hawaii silent earthquakes or slow slip events happen so slowly that they cannot be detected by conventional seismographs but now the availability of gps data means that they can be followed in detail segall et al report on a series of small earthquakes on k lauea volcano hawaii the earthquakes at depths of 7 to 8 km appear to be triggered by otherwise silent slow slips though small triggered earthquakes of this type can be used to help quantify the increased hazard due to slow slip events slow slip events or silent earthquakes have recently been discovered in a number of subduction zones including the nankai trough1 2 3 in japan cascadia4 5 and guerrero6 in mexico but the depths of these events have been difficult to determine from surface deformation measurements although it is assumed that these silent earthquakes are located along the plate megathrust this has not been proved slow slip in some subduction zones is associated with non volcanic tremor7 8 but tremor is difficult to locate and may be distributed over a broad depth range9 except for some events on the san andreas fault10 slow slip events have not yet been associated with high frequency earthquakes which are easily located here we report on swarms of high frequency earthquakes that accompany otherwise silent slips on k lauea volcano hawaii for the most energetic event in january 2005 the slow slip began before the increase in seismicity the temporal evolution of earthquakes is well explained by increased stressing caused by slow slip implying that the earthquakes are triggered the earthquakes located at depths of 7 8 km constrain the slow slip to be at comparable depths because they must fall in zones of positive coulomb stress change triggered earthquakes accompanying slow slip events elsewhere might go undetected if background seismicity rates are low detection of such events would help constrain the depth of slow slip and could lead to a method for quantifying the increased hazard during slow slip events because triggered events have the potential to grow into destructive earthquakes

emag2 a 2 arc min resolution earth magnetic anomaly grid compiled from satellite airborne and marine magnetic measurements 1 a global earth magnetic anomaly grid emag2 has been compiled from satellite ship and airborne magnetic measurements emag2 is a significant update of our previous candidate grid for the world digital magnetic anomaly map the resolution has been improved from 3 arc min to 2 arc min and the altitude has been reduced from 5 km to 4 km above the geoid additional grid and track line data have been included both over land and the oceans wherever available the original shipborne and airborne data were used instead of precompiled oceanic magnetic grids interpolation between sparse track lines in the oceans was improved by directional gridding and extrapolation based on an oceanic crustal age model the longest wavelengths 330 km were replaced with the latest champ satellite magnetic field model mf6 emag2 is available at http geomag org models emag2 and for permanent archive at http earthref org cgi bin er cgi s erda cgi n 970

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

temporal changes in stress drop frictional strength and earthquake size distribution in the 2011 yamagata fukushima ne japan earthquake swarm caused by fluid migration

advancements in satellite gravity gradient data for crustal studies in recent years global gravity models both based only on satellite data and from combination with terrestrial data are increasingly available and particularly useful to construct regional models before more local interpretations on the exploration scale are carried out often it is challenging to distinguish clearly between near surface and regional or even subcrustal signals in the gravity field applying simple techniques like wavelength filtering might lead to an incorrect estimate of the regional and residual field which may significantly alter estimates of the thickness of sedimentary basins or the size of mineral deposits an alternative is to use satellite gravity gradients to establish the regional components before studying local geology sampietro 2011 presented a global mohorovicic discontinuity moho depth map which sparked a discussion about the validity of such results especially the question remains about whether crustal thickness estimates based on gravity field and steady state ocean circulation explorer goce satellite data have a higher accuracy than models based on global gravity models or terrestrial data for example the density contrast between crust and mantle remains a main factor of uncertainty here we join this discussion by describing how satellite gravity gradients can be used in addition to terrestrial data sets or global models like egm2008 and how the combined use of data sets at multiple levels above the earth s surface can help confine the uncertainty in both regional and local modeling studies

swarms of repeating stick slip icequakes triggered by snow loading at mount rainier volcano we have detected over 150 000 small m 3000 m on the glacier covered edifice and occur primarily in weeklong to monthlong swarms composed of simultaneous distinct families of events each family contains up to thousands of earthquakes repeating at regular intervals as often as every few minutes mixed polarity first motions a linear relationship between recurrence interval and event size and strong correlation between swarm activity and snowfall suggest the source is stick slip basal sliding of glaciers the sudden added weight of snow during winter storms triggers a temporary change from smooth aseismic sliding to seismic stick slip sliding in locations where basal conditions are favorable to frictional instability coda wave interferometry shows that source locations migrate over time at glacial speeds starting out fast and slowing down over time indicating a sudden increase in sliding velocity triggers the transition to stick slip sliding we propose a hypothesis that this increase is caused by the redistribution of basal fluids rather than direct loading because of a 1 2 day lag between snow loading and earthquake activity this behavior is specific to winter months because it requires the inefficient drainage of a distributed subglacial drainage system identification of the source of these frequent signals offers a view of basal glacier processes discriminates against alarming volcanic noises documents short term effects of weather on the cryosphere and has implications for repeating earthquakes in general

how variable is the number of triggered aftershocks aftershock activity depends at first order on the mainshock magnitude but also shows important fluctuations between shocks of equal magnitude we here investigate these fluctuations by quantifying them and by relating them to the mainshock stress drop and other variables for southern california earthquakes a method is proposed in order to only count directly triggered aftershocks rather than secondary aftershocks i e triggered by previous aftershocks and to only quantify fluctuations going beyond the natural poisson variability testing of the method subjected to various model errors allows to quantify its robustness it is found that these fluctuations follow a distribution that is well fitted by a log normal distribution with a coefficient of variation of about 1 0 to 1 1 a simple model is proposed to relate this observed dependence to mainshock stress drop variability

δd δ18o relationships and the thermal history of basal ice near the margins of two glaciers in lyngen north norway les resultats des mesures combinees d et 18 o pour 2 glaciers en norvege du nord sont rapportes ainsi que leurs implications pour l histoire thermique de la glace et les variations observees dans l entrainement des debris

combined satellite gravity field model goco01s derived from goce and grace 1 the satellite only gravity field model goco01s is a combination solution based on 61 days of goce gravity gradient data and 7 years of grace gps and k band range rate data resolved up to degree order 224 of a harmonic series expansion the combination was performed consistently by addition of full normal equations and stochastic modeling of goce and grace observations the model has been validated against external global gravity models and regional gps leveling observations while low to medium degrees are mainly determined by grace significant contributions by the new measurement type of goce gradients can already be observed at degree 100 beyond degree 150 goce becomes the dominant contributor correspondingly with goco01s a global gravity field model with high performance for the complete spectral range up to degree order 224 is now available this new gravity model will be beneficial for many applications in geophysics oceanography and geodesy

deformation of till beneath ice stream b west antarctica the behaviour and possible instability of the west antarctic ice sheet depend fundamentally on the dynamics of the large ice streams which drain it model calculations show that most ice stream velocity arises at the bed1 2 and radar sounding has shown the bed to be wet3 but the basal boundary condition is not well understood seismic evidence from the upstream b camp upb on the siple coast of west antarctica4 shows that the ice stream there rests on a layer of unconsolidated sediment averaging 5 or 6 m thick in which the water pressure is only 50 kpa less than the overburden pressure because this thin layer occurs well inland beneath an active ice sheet and rests on a surface showing flutes4 characteristic of glacial erosion5 we presume that it is glacial till we propose here that deformation within the till is the primary mechanism by which the ice stream moves and we discuss implications of this hypothesis

mapping the mass distribution of earth s mantle using satellite derived gravity gradients the dynamics of earth s mantle are difficult to constrain analysis of goce satellite gravity data can be used to identify gravity anomalies to mid mantle depths and hence to identify regions of tectonic plate subduction and plume upwelling in the mantle

microstructures in diamictons evidence of subglacial bed conditions abstract examination of microstructures within diamictons from southern ontario canada and southern bavaria and baden wurttemburg germany reveal evidence illustrative of certain subglacial bed conditions the microstructures from ontario were obtained from a complex glacial melange unit that forms the internal structure of an isolated drumlin megaflute on the north shore of lake erie the evidence from germany was taken from individual drumlins within drumlin fields in the inn chiemsee iller rhein and salzach glacier areas the structures within the diamicton from ontario reveal clear evidence of massive shear associated with high externally applied strain there are kink band arrays high angle shear zones crenulation and sedimentary dyke and water escapes structures in the german diamictons there is a lack of evidence of high levels of bulk deformation there is however a very high carbonate content some evidence points to the possibility that these diamictons may contain intraclasts of paleosols interpretation of both sets of diamictons suggests that the ontario sediments were subject to conditions at the bed of an ice mass best typified as a deformable bed the german sediments may be interpreted as 1 being so saturated that any deformation must have been by inter grain slip pervasive deformation and thus no structures are recorded or 2 being already cemented by the carbonates and sufficiently rigid to cause strain to be taken up elsewhere or 3 were frozen prior to transposition and were again too rigid to suffer deformation or 4 suffered no deformation whatsoever the analyses of these two sets of sediments have important implications for subglacial conditions before and during drumlin and other subglacial bedform development

rates of aftershock decay and the fractal structure of active fault systems abstract aftershock activity on frequency decay against time is characterized by a power law the modified omori formula of an exponent p which differs with each aftershock sequence a theoretical study suggested that p which is a rate constant of aftershock decay is related to the fractal dimension of a pre existing fault system this has however never been checked aftershock activity on size distribution is also characterized by an exponential distribution against magnitude the gutenberg richter relation with a slope b although p is expected to be related to b which is related to the partitioning rate of earthquake energy the relationship has never been established here the relation between the p values and the fractal dimensions of the pre existing fault systems and that between the p values and the b values are explored using natural seismicity data and data of the observable fault systems the p and b values were estimated for fifteen aftershock sequences which occurred in japan in this paper aftershocks were identified on the basis of a phenomenological definition in the seismicity data the fractal capacity dimensions d0 are estimated for the pre existing active fault systems observed on the surface in the aftershock regions in the present paper the standard box counting method was adopted to get the d0 negative correlations between 1 p and d0 and 2 p and b were observed with some scattering observation 1 shows that the rate of aftershock decay p decreases systematically with increasing occupancy rate of the pre existing active fault system d0 and suggests that aftershock decay dynamics is constrained by the pre existing fracture field observation 2 shows that p certainly has a relation with b moreover we offer possible interpretation on these negative correlations and some scatters in both observations the scatters are interpreted as the scatter of the difference of two fractal dimensions between 3 d fracture construction in the crust and 2 d cross sectional surface observed active fault system supported by further tests this paper strongly suggests that the scaling for a natural fracture system is self affine with different fractal scalings in different directions rather than self similar which would be a manifestation of regional anisotropy of the fracture system and that the seismic parameters p and b depend on the 3 d construction of the fracture system in the crust

seismic and aseismic slip evolution and deformation associated with the 2009 2010 northern malawi earthquake swarm east african rift summary interferometric synthetic aperture radar insar measurements field observations and elastic modelling of the 2009 2010 karonga northern malawi earthquake swarm reveal widespread coseismic and localized post seismic deformation in a period of about 1 5 months starting on november 5 29 m 4 earthquakes struck the region culminating in an mw 6 peak event on december 19 the next few months were characterized by significant localized deformation with a very low seismic moment release we find a very good agreement between insar and field observations of surface ruptures our best fitted coseismic models indicate dip slip displacements on a fault dipping 40 to the southwest with maximum slip of about 120 cm at 3 5 km depth fault activity continued until 2010 august as shallow aseismic afterslip mostly above the maximum coseismic slip patches although the swarm occurred within a coastal plain covered by porous quaternary sediments and a high water table the effect of poroelastic relaxation on the post seismic deformation was found to be negligibly small in contrast with other recent earthquake swarms along the east african rift the karonga swarm shows no evidence for dike intrusion

complementary slip distributions of the largest earthquakes in the 2012 brawley swarm imperial valley california we investigate the finite rupture processes of two m 5 earthquakes in the 2012 brawley swarm by joint inversion of nearby strong motion and high rate gps data waveform inversions up to 3 hz were made possible by using a small event m w3 9 for path calibration of the velocity structure our results indicate that the first m w5 3 event ruptured a strong concentrated asperity with offsets of 20 cm centered at a depth of 5 km the subsequent m w5 4 event occurred 1 5 h later with a shallower slip distribution that surrounds and is complementary to that of the earlier event the second event has a longer rise time and weaker high frequency energy release compared to the m w5 3 event both events display strong rupture directivity toward the southwest and lack of very shallow 2 km coseismic slip the hypocenters for these events appear to be near or in the bedrock but most of the slip is distributed at shallower depths 6 km and can explain a large part of the gps offsets for the swarm the complementary slip distributions of the two events suggest a triggering relationship between them with no significant creep needed to explain the various data sets

high resolution 3 d p wave attenuation structure of the new madrid seismic zone using local earthquake tomography a three dimensional 3 d high resolution p wave seismic attenuation model for the new madrid seismic zone nmsz is determined using p wave path attenuation t values of small magnitude earthquakes md 3 9 events were recorded at 89 broadband and short period seismometers of the cooperative new madrid seismic zone network and 40 short period seismometers of the portable array for numerical data acquisition experiment the amplitude spectra of all the earthquakes are simultaneously inverted for source path t and site parameters the t values are inverted for qp using local earthquake tomography methods and a known 3 d p wave velocity model for the region the four major seismicity arms of the nmsz exhibit reduced qp higher attenuation than the surrounding crust the highest attenuation anomalies coincide with areas of previously reported high swarm activity attributed to fluid rich fractures along the southeast extension of the reelfoot fault the qp results are consistent with previous attenuation studies in the region which showed that active fault zones and fractured crust in the nmsz are highly attenuating

the argentine continental margin north of 48 s sedimentary successions volcanic activity during breakup abstract new seismic data and geophysical results from the outer argentine continental margin and from seismic flow line transects across the oceanic argentine brazil and cape angola basins are presented the results document that the early cretaceous south atlantic continental breakup and initial sea floor spreading were accompanied by large scale transient volcanism emplacing voluminous extrusive constructions on the conjugate outer continental margins of the south atlantic on the argentine margin we interpret three major tectono volcanic crustal units beneath a thick and tectonically undisturbed sedimentary succession of cretaceous and tertiary age 1 syn rift basins and even pre rift features are present on the outer shelf 2 a deeply buried 60 120 km wide and several thousand metres thick volcanic wedge occupies most of the slope the wedge is characterized by seaward dipping reflectors and is associated with the distinct magnetic anomaly g 3 the seaward adjacent oceanic crust of cretaceous age shows isochronous changes of the seismic images along our flow line transects suggesting some form of episodicity of rich magma and poor to moderate magma supply at the pre existing mid ocean ridge of the south atlantic during cretaceous time

seismicity in the outer rise offshore southern chile indication of fluid effects in crust and mantle we examine the micro earthquake seismicity recorded by two temporary arrays of ocean bottom seismometers on the outer rise offshore southern chile on young oceanic plate of ages 14 ma and 6 ma respectively the arrays were in operation from december 2004 january 2005 and consisted of 17 instruments and 12 instruments respectively approximately 10 locatable events per day were recorded by each of the arrays the catalogue which is complete for magnitudes above 1 2 1 5 is characterized by a high b value i e a high ratio of small to large events and the data set is remarkable in that a large proportion of the events form clusters whose members show a high degree of waveform similarity the largest cluster thus identified consisted of 27 similar events average inter event correlation coefficient 0 8 for a 9 5 s window and waveform similarity persists far into the coda inter event spacing is irregular but very short waiting times of a few minutes are far more common than expected from a poisson distribution seismicity with these features high b value large number of similar events with short waiting times is typical of swarm activity which based on empirical evidence and theoretical considerations is generally thought to be driven by fluid pressure variations because no pronounced outer rise bulge exists on the very young plate in the study region it is unlikely that melt is accessible from decompression melting or opening of cracks a fluid source related to processes at the nearby ridge is conceivable for the younger segment but less likely for the older one we infer that the fluid source could be seawater which enters through fractures in the crust most of the similar earthquake clusters are within the crust but some of them locate significantly below the moho if our interpretation is correct this implies that water is present within the mantle hydration of the mantle is also indicated by a decrease of pn velocities below the outer rise seen on a refraction profile through one of the arrays contreras reyes e grevemeyer i flueh e r scherwath m heesemann m 2007 alteration of the subducting oceanic lithosphere at the southern central chile trench outer rise geochem geophys geosyst 8 q07003 the deepest events within the array on the 6 ma old plate occur where the temperature reaches 500 600 c consistent with the value observed for large intraplate earthquakes within the mantle 650 c suggesting that the maximum temperature at which these fluid mediated micro earthquakes can occur is similar or identical to that of large earthquakes

colorado basin 3d structure and evolution argentine passive margin abstract this 3d structural model of the colorado basin provides new insights into the crustal geometry of the basin and its evolution in relation with the argentine passive margin three nw se segments oblique to the n30 e trending margin structure the basin the oldest infill is generally thought to be coeval with the rifting of the south atlantic margins in late jurassic early cretaceous this coeval development of the colorado basin and of the passive margin is still under debate and gives rise to several hypotheses that we investigate in the light of our observations we propose that reactivation of inherited structures is predominant in the evolution of the colorado basin 1 the western segment follows the continental continuation of the colorado transfer zone 2 the central segment consists in the continental continuation of the tona deformation zone 3 the eastern segment is superimposed over the palaeozoic claromeco basin in addition to the 3 segments the central high separating the central segment to the eastern segment corresponds to the palaeozoic sierras australes fold belt the direction of extension responsible for the south atlantic opening cannot explain the syn rift infill and thinning of the basin the structural analysis shows two phases of syn rift deformation with different directions thus we suggest that the colorado basin and the south atlantic margin are not coeval but that a first extensional event probably oblique predates the extension responsible for the south atlantic opening this event is then followed by the formation of the n30 trending distal margin and the reactivation of palaeozoic n70 trending faults occurs under the nw se opening of the south atlantic this two phase evolution is consistent with the fault chronology and the two directions of thinned crust observed in the distal margin

late wisconsin landform distribution and glacier bed conditions in wisconsin abstract the late wisconsin laurentide ice sheet advanced across permafrost and reached its maximum extent in wisconsin between about 18 000 and 15 000 years ago deep permafrost persisted in southern wisconsin until about 14 000 years ago and in northern wisconsin until about 13 000 years ago we suggest that during maximum glaciation a zone about 5 km wide in the south and 20 km wide in the north along the margin of the late wisconsin glacier was frozen to its bed meltwater from farther behind the margin where the bed was at least locally thawed cut a series of closely spaced tunnel channels through the frozen bed zone these channels most likely formed episodically and they were the source for much of the meltwater stream sediment deposited in broad outwash plains beyond the ice margin frozen bed conditions near the margin also likely contributed to increased upward shearing of sediment and the accumulation of thicl supraglacial sediment in northern areas up ice from the frozen bed zone the glacier bed was at least locally thawed in a zone about 75 km wide extensive drumlin fields formed in the area of the bed that was thawed by about 13 000 years ago permafrost melted in northern wisconsin and thawed bed conditions probably extended to the ice margin throughout wisconsin and adjacent areas after about 13 000 years ago in northern wisconsin the glacier was sliding on its bed and forming drumlins out to the ice margin and thick supraglacial sediment no longer accumulated

stress release process along an intraplate fault analogous to the plate boundary a case study of the 2017 m5 2 akita daisen earthquake ne japan stress accumulation and release in the crust remains poorly understood compared to that at the plate boundaries spatiotemporal variations in foreshock and aftershock activities can provide key con