a nonlinear rheology model for mid ocean ridge axis topography this paper describes a mechanical model of the mid ocean ridge axis based on a nonlinear rheology the oceanic lithosphere is modeled as a strongly temperature dependent power law material with the byerlee s friction law describing the brittle behavior of the upper oceanic lithosphere we examined two simple models a mantle only model predicted an axial rift valley 1 2 km deep and 10 15 km wide at slow half rates of 5 25 mm yr which is in fair agreement with observations however the rift valley did not completely vanish at fast spreading rates even though its width and relief became much smaller thus the mantle only model failed to explain the observed transition in axial topography with spreading rate by including a uniform thickness oceanic crust with theological properties different from the mantle our second model produced the first order variation of axial topography with spreading rate a pronounced rift valley with 1 2 km relief at slow rates a smaller relief 500 m rift valley at intermediate rates and no rift valley at fast rates there are two additional results of the nonlinear rheology model which are distinctively different from the previous uniform viscosity mantle models first horizontal velocity at the seafloor changes sharply in a very narrow zone at the ridge axis i e the stresses are concentrated in a very narrow zone for the nonlinear rheology this conclusion is remarkably independent of the boundary conditions at the seafloor second the computed width of the axial plastic failure zone decreases with spreading rate a result very different from that of a uniform viscosity model this is caused by the strong temperature dependence of the power law rheology and the fact that the temperature of the oceanic lithosphere depends greatly on the spreading rate beyond some distance from the ridge axis the brittle plate roughly the region above the 750 c isotherm deforms very little both the horizontal strain rate 11 and the maximum shear strain rate max are less than 10 17 s 1 which is in good agreement with the 10 18 s 1 average for oceanic brittle plate deformation inferred from seismic moment data within the ductile region area beneath the 750 c isotherm the strain rates are in the range of 10 14 10 16 s 1 except within a narrow band near the ridge axis where higher strain rates are located we found that the thermal structure of the oceanic lithosphere is not very sensitive to the details of the mantle flow pattern or the rheology but is very sensitive to the cooling by hydrothermal circulation near the ridge axis axial structure is also influenced by factors other than the spreading rate within the range of slow and intermediate rates our calculations show that the size of an axial rift valley decreases with an increase in either the thickness of the oceanic crust or the mantle temperature in other words a thinner crust or a cooler mantle temperature will produce a more pronounced rift valley in the vicinity of hotspots the absence of an axial rift valley even at slow spreading rates such as the reykjanes ridge can be well explained by the anomalously thicker crust and higher mantle temperatures in contrast at the australian antarctic discordance a deeper than normal section of an intermediate spreading ridge has very rough topography not present on the adjacent sections of the ridge this can be explained by our model as due to an anomalously low mantle temperature as has been suggested or perhaps also due to a thinner oceanic crust

high thermal maturity in the lower saxony basin intrusion or deep burial abstract the lower saxony basin lsb is situated at the southern rim of the northern permian basin the most important hydrocarbon bearing province in europe in its southern part areas of high thermal maturation up to 6 rr occur which were previously explained as being caused by magmatic intrusions of turonian to santonian age that affected carboniferous to lower cretaceous rocks in this area 2d numerical basin modelling was carried out in order to reconstruct the temperature histories along two parallel n s trending seismic sections along these sections new data about maturity distribution and temperature history were obtained by vitrinite reflectance measurements and apatite fission track analysis for the areas with highest maturity values low coalification gradients were established which agree well with earlier published data on wells further towards the west this new information does not support previous hypotheses on high heat flows from magmatic intrusions even if lateral heat transport is taken into account instead comparisons with a recently published map of the subsurface structure of the lsb indicate that maturity distribution may be closely related to major tectonic structures deep burial of individual structures of the lsb which are bordered by deep e w to ese wnw trending faults is further suggested by a rapidly increasing thicknesses of preserved cretaceous strata towards the south and b structural restoration of one of the seismic sections to achieve a fit between measured and calculated palaeo temperature and vitrinite reflectance data deep burial of carboniferous source rocks during cretaceous time has to be assumed due to an inversion phase in the early and middle upper cretaceous major amounts of sediment were removed and further uplift occurred in tertiary times in contrast the northern part of the lsb experienced maximum burial and temperatures during tertiary times

constraining spatiotemporal characteristics of magma migration at piton de la fournaise volcano from pre eruptive seismicity volcano tectonic seismicity has been recorded for decades on various volcanoes and is linked with the magma transport and reservoir pressurization yet earthquakes often appear broadly distributed such that magma movement is difficult to infer from its analysis we explore the seismicity that occurred before eruptions at piton de la fournaise in the last 5 years using template matching and relocation techniques we produce a refined image of the summit seismicity demonstrating that most earthquakes are located on a ring structure however only a portion of this structure is activated before each eruption which provides an indication as to the direction of the future eruptive site furthermore we show that the delay between the pre eruptive swarm and the eruption onset is proportional to the distance of the eruptive fissures relative to the summit cone this reveals that the beginning of the intrusion already bears information regarding the future eruption location

permo carboniferous magmatism of the northeast german basin abstract variscan continent continent collision in central europe was followed by a period of syn to late tectonic magmatism involving the extrusion of large volumes of permosilesian age volcanic rocks particularly in the northeast german basin the volcanic suite up to ca 2000 m thick comprises rhyolites acid and basic andesites and tholeiitic and alkali basalts tectono geochemical analysis in conjunction with volume calculations and petrography reveals changes in volcanic activity over time a total of five eruptive stages are recognised beginning in the stephanian and extending up into the upper rotliegend permian these include the stephanian late carboniferous andesite pre ignimbrite stage i lower rotliegend permian age explosive ignimbrite stage ii post ignimbrite stage iii late rhyolite stage iv and upper rotliegend permian age late basalt stage v in addition several volcanic centres including at least two large caldera like structures are recognised the total calculated volume for the northeast german basin volcanics is ca 48 000 km3 comprising rhyolitic rocks and ignimbrites ca 70 andesitic rocks ca 26 and basalts with cogenetic dolerites ca 4 regional variations in composition and geochemistry are related to diverse crust mantle regimes which correlate with differing positions relative to the heterogeneous basement of the variscan foredeep or within the rhenohercynian orogenic zone the crustal thickening and increasing generation depth of the mafic magmas from north to south may reflect the presence of a pre existing subduction influenced basaltic magma source

basaltic calderas collapse dynamics edifice deformation and variations of magma withdrawal 1 the incremental caldera collapses of fernandina 1968 miyakejima 2000 and piton de la fournaise 2007 are analyzed in order to understand the collapse dynamics in basaltic setting and the associated edifice deformation for each caldera the collapse dynamics is assessed through the evolution of the 1 time interval t between two successive collapse increments 2 amount of vertical displacement during each collapse increment and 3 magma outflow rate during the whole collapse caldera process we show from the evolution of t that piton de la fournaise and fernandina were characterized by a similar collapse dynamics despite large differences in the caldera geometry and the duration of the whole collapse caldera process this evolution significantly differs from that of miyakejima where t strongly fluctuated throughout the whole collapse process quantification of the piston vertical displacements enables us to determine the magma outflow rates between each collapse increment displacement data tiltmeter and or gps for piton de la fournaise and miyakejima are used to constrain the edifice overall deformation and the edifice deformation rates these data reveal that both volcanoes experienced edifice inflation once the piston collapsed into the magma chamber such a deformation which lasts during the first collapse increments only is interpreted as the result of larger volume of piston intruded in the magma chamber than magma withdrawn before each collapse increment once the effect of the collapsing rock column vanishes edifice deflates we also determine for each caldera the critical amount of magma evacuated before collapse initiation and compare it to analog models the significant differences between models and nature are explained by the occurrence of preexisting weak zones in nature i e the ring faults that are not taken into account in analog models finally we show that t at piton de la fournaise and fernandina was equally controlled by the frictional resistance along the ring faults and the magma outflow rate in addition to these two parameters the collapse dynamics of miyakejima was also influenced by variations of the magma bulk modulus which changed after the influx of deep gas rich magma into the collapse related magma chamber altogether our results show that the dynamics of caldera collapse in basaltic volcanoes proceeds in two phases phase 1 starting with the first collapse is characterized by the largest collapse amplitude an incremental edifice inflation and a step by step increase of the rate of magma outflow phase 2 shows a rapid decrease of the magma discharge rate to a low level concomitant with the continuous edifice deflation if deep magma is injected into the magma chamber as at miyakejima an additional phase occurs phase 3

intermittent inflations recorded by broadband seismometers prior to caldera formation at miyake jima volcano in 2000 abstract very long period vlp pulses with widths of 20 s on velocity seismograms were observed during volcanic activity at miyake jima volcano japan in 2000 the vlp events occurred repeatedly during a few days prior to caldera formation and essentially vanished following the onset of caldera collapse waveform inversions of the pulse like signals point to a source offset 3 5 km beneath and 1 km south of the summit a candidate for the source mechanism is the inflation of an elliptical cylinder with axis tilted 20 30 from vertical and major axis of the elliptical cross section oriented northeast southwest the inferred mechanism appears consistent with a step like pressurization of a magma reservoir impacted by a falling rock mass in response to gravitational instability the repeated occurrences of the rock collapses lead to the caldera formation at miyake jima

three dimensional shear velocity anisotropic model of piton de la fournaise volcano la reunion island from ambient seismic noise we cross correlate 4 years of seismic noise from the seismic network of piton de la fournaise volcano la reunion island to measure the group velocity dispersion curves of rayleigh and love waves we average measurements from vertical and radial components to obtain 577 rayleigh wave dispersion curves the transverse components provided 395 love wave dispersion curves we regionalize the group velocities measurements into 2 d velocity maps between 0 4 and 8 s finally we locally inverted these maps for a pseudo 3 d anisotropic shear velocity model down to 3 km below the sea level using a neighborhood algorithm the 3 d isotropic shear wave model shows three distinct high velocity anomalies surrounded by a low velocity ring the anomaly located below the present plaine des sables could be related to an old intrusive body at the location of the former volcanic center before it migrated toward its present location the second high velocity body located below the summit of the volcano likely corresponds to the actual preferential dyke intrusion zone as highlighted by the seismicity the third high velocity anomaly located below the grandes pentes and the grand brule areas and is an imprint of the solidified magma chamber of the dismantled les alizes volcano radial anisotropy shows two main anomalies positive anisotropy above sea level highlighting the recent edifice of piton de la fournaise with an accumulation of horizontal lava flows and the second one below the sea level with a negative anisotropy corresponding to the ancient edifice of piton de la fournaise dominated by intrusions of vertical dykes

the tectonic evolution of the fennoscandian border zone in denmark abstract the fennoscandian border zone is a complex tectonic zone defining the border between the stable fennoscandian baltic shield and the metastable danish basin and polish trough it forms the northwestern part of the tornquist teisseyre lineament one of the major european tectonic sutures intricate tectonic movements took place within the fennoscandian border zone from early paleozoic to recent time it is postulated that its evolution was dominated during the early palaeozoic by tensional tectonics and during the late paleozoic by dextral wrench movements the latter led to the development of curvilinear faults and the subsidence of pull apart basins transtensional stresses governing the triassic to early cretaceous evolution of the fennoscandian border zone induced the differential subsidence of rift basins during the late cretaceous and early cenozoic dextral transpressional stresses induced the partial inversion of mesozoic basins associated with the fennoscandian border zone this is reflected by the uplift of a major anticlinorium over which cretaceous strata became progressively truncated whilst adjacent areas developed into late cretaceous early tertiary depocentres basin inversion diminishes to the northwest along the fennoscandian border zone and disappears in the skagerrak area

the collapse of barðarbunga caldera iceland lying below vatnajokull ice cap in iceland bar arbunga stratovolcano began experiencing wholesale caldera collapse in 2014 august 16 one of the largest such events recorded in the modern instrumental era simultaneous with this collapse is the initiation of a plate boundary rifting episode north of the caldera observations using the international constellation of radar satellites indicate rapid 50 cm d 1 subsidence of the glacier surface overlying the collapsing caldera and metre scale crustal deformation in the active rift zone anomalous earthquakes around the rim of the caldera with highly nondouble couple focal mechanisms provide a mechanical link to the dynamics of the collapsing magma chamber a model of the collapse consistent with available geodetic and seismic observations suggests that the majority of the observed subsidence occurs aseismically via a deflating sill like magma chamber

using centroid time delays to characterize source durations and identify earthquakes with unique characteristics the relationship between m 0 and the rupture duration is often difficult to establish this is particularly true for large earthquakes for which the moment rate functions mrf generally have complicated shapes and the estimated durations can vary considerably depending on the methodology used to evaluate the mrf in this work we show that the centroid time delay c provides an alternative estimate of the source duration inverted mrfs often end gradually making the end of coseismic rupture difficult to detect in such cases when the rupture duration is not well defined the time delay c is a useful quantity to represent the first order temporal characteristics of the rupture process variations in stress parameter can be investigated by assuming a standard scaling relationship between the seismic moment m0m0 and c this simple scaling relationship can also be used to identify unusual earthquakes with unique source properties such as events involving complicated rupture processes or earthquakes characterized by unusual rupture velocities stress drops or aspect ratios

physical explanation of the formation and evolution of inversion zones and marginal troughs inversion zones are elongate structures some tens of kilometers wide and up to hundreds of kilometers long that have deformed in response to compression and produced topography inversion zones in the alpine foreland are mainly associated with mesozoic grabens and troughs and although very important in the geologic picture the conditions of their formation and evolution and their regional geologic significance are not entirely understood the internal structure of inversion zones is variable and depends on details in the pre inversion setting the inversion inducing stress field and the sedimentary fill however on a larger scale most inversion zones share certain principal observational features which sample the physical structure and the rheologic properties of the lithosphere and thereby provide an opportunity to test hypotheses of lithospheric rheology and dynamics the quantitative model presented in this paper explains how inversion zones and the associated marginal troughs are related to lithospheric zones of differential shortening and regional isostatic compensation of the induced topography

crustal memory and basin evolution in the central european basin system new insights from a 3d structural model abstract the central european basin system cebs is composed of a series of subbasins the largest of which are 1 the norwegian danish basin 2 the north german basin extending westward into the southern north sea and 3 the polish basin a 3d structural model of the cebs is presented which integrates the thickness of the crust below the permian and five layers representing the permian cenozoic sediments structural interpretations derived from the 3d model and from backstripping are discussed with respect to published seismic data the analysis of structural relationships across the cebs suggests that basin evolution was controlled to a large degree by the presence of major zones of crustal weakness the nw se striking tornquist zone the ringkobing fyn high rfh and the elbe fault system efs provided the borders for the large permo mesozoic basins which developed along axes parallel to these fault systems the tornquist zone as the most prominent of these zones limited the area affected by permian cenozoic subsidence to the north movements along the tornquist zone the margins of the ringkobing fyn high and the elbe fault system could have influenced basin initiation thermal destabilization of the crust between the major nw se striking fault systems however was a second factor controlling the initiation and subsidence in the permo mesozoic basins in the triassic a change of the regional stress field caused the formation of large grabens central graben horn graben gluckstadt graben perpendicular to the tornquist zone the ringkobing fyn high and the elbe fault system the resulting subsidence pattern can be explained by a superposition of declining thermal subsidence and regional extension this led to a dissection of the ringkobing fyn high resulting in offsets of the older nw se elements by the younger n s elements in the late cretaceous the nw se elements were reactivated during compression the direction of which was such that it did not favour inversion of n s elements a distinct change in subsidence controlling factors led to a shift of the main depocentre to the central north sea in the cenozoic in this last phase n s striking structures in the north sea and nw se striking structures in the netherlands are reactivated as subsidence areas which are in line with the direction of present maximum compression the moho topography below the cebs varies over a wide range below the n s trending cenozoic depocentre in the north sea the crust is only 20 km thick compared to about 30 km below the largest part of the cebs the crust is up to 40 km thick below the ringkobing fyn high and up to 45 km along the teisseyre tornquist zone crustal thickness gradients are present across the tornquist zone and across the borders of the ringkobing fyn high but not across the elbe fault system the n s striking structural elements are generally underlain by a thinner crust than the other parts of the cebs the main fault systems in the permian to cenozoic sediment fill of the cebs are located above zones in the deeper crust across which a change in geophysical properties as p wave velocities or gravimetric response is observed this indicates that these structures served as templates in the crustal memory and that the prerift configuration of the continental crust is a major controlling factor for the subsequent basin evolution

the post triassic evolution of the sorgenfrei tornquist zone results from thermo mechanical modelling abstract the sorgenfrei tornquist zone stz is part of the fennoscandian border zone separating the danish basin from the fennoscandian shield the stz as a structural element is of palaeozoic origin and represents the north westerly segment of the tornquist teisseyre zone which separates the younger west european crust from the older east european platform and extends from the black sea to the eastern north sea area the stz was reactivated in triassic jurassic extension and late cretaceous and paleogene compression this paper investigates the regional geological consequences of the reactivations by quantitative modelling along a profile across the stz in the danish area the numerical model invokes elastic viscous and plastic deformations of the lithosphere as well as surface processes governed by erosion sedimentation and lateral transport under the influence of eustatic sea level variations and regional isostatic compensation surface processes and lithospheric mechanics are coupled through thermal blanketing effects and loading the results in general address the regional geological consequences of the existence of intracontinental zones of structural weakness more specifically the results show that the late cretaceous and paleogene chalk depocentres in the danish basin are a direct consequence of the inversion of the stz and that the stz inversion together with falling sea level in cenozoic time are amongst the principal controlling factors in the geological evolution in the eastern north sea area

evolution of the lower saxony basin abstract the lower saxony basin is a 300 km long and 65 km wide late jurassic and early cretaceous trough which parallels the northern margin of the rhenish massif this basin became inverted during the senonian and paleocene the lower saxony basin is the most important oil province of germany past production amounts to 200 10 6 t of oil 1 5 10 9 bbl the lower saxony basin is superimposed on the late carboniferous variscan foredeep basin and the frontal structures of the variscan fold belt during the permian to middle jurassic the area formed part of the northwest european basin differential subsidence of the lower saxony basin was initiated during the late jurassic and persisted till albian time this involved reactivation of permo carboniferous fracture systems by divergent wrenching a major aptian deep seated laccolith is evident in the western part of the lower saxony basin during the senonian and paleocene sinistral convergent wrenching induced uplift of the basin floor and folding of its sedimentary fill the margins of the inverted lower saxony basin are thrust over the adjacent stable platform areas the differential subsidence of the lower saxony basin can be related to a period of major crustal extension in the north sea rift basin inversion coincides with important orogenic events in the alpine system and is thought to have been induced by intra plate compressional stresses

edifice strength and magma transfer modulation at piton de la fournaise volcano 1 from 2003 to 2007 eruptive activity at piton de la fournaise was shown to follow cycles comprising many summit proximal eruptions and finishing by a distal eruption gps measurements evidenced striking asymmetric deformation between its western and eastern flanks horizontal displacements recorded during interdistal periods showed a characteristic amplitude at the top of the eastern flank displacements recorded at the base of the summit cone showed a bimodal distribution with low amplitudes during interdistal periods and large ones during distal eruptions to account for displacement asymmetry characteristic amplitude and large flank displacement we modeled the volcanic edifice using a drucker prager elastoplastic rheology friction angles of 15 and 30 were needed to model the displacements respectively during distal eruptions and interdistal periods this change shows that strain weakening occurred during distal events large plastic displacement that occurred in the eastern flank during distal eruptions relaxed the horizontal elastic stress accumulated during interdistal periods it triggered summit deflation horizontal magma transfer and distal flank eruption and reset the eruptive cycle our elastoplastic models also show that simple source geometries may induce large eastern flank displacements that would be explained by a complex geometry in a linear elastic edifice magma supply is often thought to control volcano s eruptive activity with surface deformation reflecting changes in magma supply rate the volcano s response being linear our results bring some evidences that on piton de la fournaise time space discretization of magma transfer may be the result of the edifice s nonlinear response rather than changes in magma supply

seismic source mechanism of degassing bursts at kilauea volcano hawaii results from waveform inversion in the 10 50 s band the current march 2008 to february 2009 summit eruptive activity at kilauea volcano is characterized by explosive degassing bursts accompanied by very long period vlp seismic signals we model the source mechanisms of vlp signals in the 10 50 s band using data recorded for 15 bursts with a 10 station broadband network deployed in the summit caldera to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous medium that takes topography into account the vlp signals associated with the bursts originate in a source region 1 km below the eastern perimeter of halemaumau pit crater the observed waveforms are well explained by the combination of a volumetric component and a vertical single force component for the volumetric component several source geometries are obtained which equally explain the observed waveforms these geometries include 1 a pipe dipping 64 to the northeast 2 two intersecting cracks including an east striking crack dike dipping 80 to the north intersecting a north striking crack another dike dipping 65 to the east 3 a pipe dipping 58 to the northeast intersecting a crack dipping 48 to the west southwest and 4 a pipe dipping 57 to the northeast intersecting a pipe dipping 58 to the west southwest using the dual crack model as reference the largest volume change obtained among the 15 bursts is 24 400 m3 and the maximum amplitude peak to peak of the force is 20 gn each burst is marked by a similar sequence of deflation and inflation trailed by decaying oscillations of the volumetric source the vertical force is initially upward synchronous with source deflation then downward synchronous with source reinflation followed by oscillations with polarity opposite to the volumetric oscillations this combination of force and volume change is attributed to pressure and momentum changes induced during a fluid dynamic source mechanism involving the ascent expansion and burst of a large slug of gas within the upper 150 m of the magma conduit as the slug expands upon approach to the surface and more liquid becomes wall supported by viscous shear forces the pressure below the slug decreases inducing conduit deflation and an upward force on the earth the final rapid slug expansion and burst stimulate vlp and lp oscillations of the conduit system which slowly decay due to viscous dissipation and elastic radiation consideration of the fluid dynamic arguments leads us to prefer the dual crack vlp source model as it is the only candidate model capable of producing plausible values of length scales and pressure changes the magnitudes of the vertical forces observed in the 15 bursts appear consistent with slug masses of 104 to 106 kg

regional patterns of tectonic stress in europe nearly 1500 stress orientation determinations are now available for europe the data come from earthquake focal mechanisms overcoring measurements well bore breakouts hydraulic fracturing measurements and young fault slip studies and sample the stress field from the surface to seismogenic depths three distinct regional patterns of maximum compressive horizontal stress shmax orientation can be defined from these data a consistent nw to nnw shmax stress orientation in western europe a wnw ese shmax orientation in scandinavia similar to western europe but with a larger variability of shmax orientations and a consistent e w shmax orientation and n s extension in the aegean sea and western anatolia the different stress fields can be attributed to plate driving forces acting on the boundaries of the eurasian plate locally modified by lithospheric properties in different regions on average the orientation of maximum stress in western europe is subparallel to the direction of relative plate motion between africa and europe and is rotated 17 clockwise from the direction of absolute plate motion the uniformly oriented stress field in western europe coincides with thin to medium lithospheric thickness approximately 50 90 km and high heat flow values 80 m w m2 in western europe a predominance of strike slip focal mechanisms implies that the intermediate principal stress is vertical the more irregular horizontal stress orientations in scandinavia coincide with thick continental lithosphere 110 170 km and low heat flow 50 m w m2 the cold thick lithosphere in this region may result in lower mean stresses associated with far field tectonic forces and allow the stress field to be more easily perturbed by local effects such as deglaciation flexure and topography the stress field of the aegean sea and western anatolia is consistent with n s extension in a back arc setting behind the hellenic trench subduction zone the stress field is influenced in places by regional geologic structures e g in the western alps where shmax directions show a slight tendency toward a radial stress pattern not all major geologic structures however appear to affect the shmax orientation e g in the vicinity of the rhine rift system horizontal stress orientations are continuous

post mid cretaceous eastern north sea evolution inferred from 3d thermo mechanical modelling abstract the late cretaceous cenozoic evolution of the eastern north sea region is investigated by 3d thermo mechanical modelling the model quantifies the integrated effects on basin evolution of large scale lithospheric processes rheology strength heterogeneities tectonics eustasy sedimentation and erosion the evolution of the area is influenced by a number of factors 1 thermal subsidence centred in the central north sea providing accommodation space for thick sediment deposits 2 250 m eustatic fall from the late cretaceous to present which causes exhumation of the north sea basin margins 3 varying sediment supply 4 isostatic adjustments following erosion and sedimentation 5 late cretaceous early cenozoic alpine compressional phases causing tectonic inversion of the sorgenfrei tornquist zone stz and other weak zones the stress field and the lateral variations in lithospheric strength control lithospheric deformation under compression the lithosphere is relatively weak in areas where moho is deep and the upper mantle warm and weak in these areas the lithosphere is thickened during compression producing surface uplift and erosion e g at the ringkobing fyn high and in the southern part of sweden observed late cretaceous early cenozoic shallow water depths at the ringkobing fyn high as well as cenozoic surface uplift in southern sweden the south swedish dome ssd are explained by this mechanism the stz is a prominent crustal structural weakness zone under compression this zone is inverted and its surface uplifted and eroded contemporaneously marginal depositional troughs develop post compressional relaxation causes a regional uplift of this zone the model predicts sediment distributions and paleo water depths in accordance with observations sediment truncation and exhumation at the north sea basin margins are explained by fall in global sea level isostatic adjustments to exhumation and uplift of the inverted stz this underlines the importance of the mechanisms dealt with in this paper for the evolution of intra cratonic sedimentary basins

size and volume evaluation of the caldera collapse on piton de la fournaise volcano during the april 2007 eruption using aster stereo imagery 1 the scale of summit collapse during the april 2007 eruption of piton de la fournaise volcano reunion island western indian ocean was evaluated using before and after differential digital elevation models dems derived from nadir and backward looking images from the advanced spaceborne emission and reflection radiometer aster instrument the dimensions of horizontal length and width volume and depth of the depression were estimated as 1 100 800 m 9 6 10 7 m 3 and 320 m respectively these estimates show excellent agreement with field survey data a ring shaped thermal anomaly diameter of about 500 m was found at dolomieu crater during or just after the collapse on nighttime aster swir image it may correspond to the high temperature areas associated with the cross section of a hydrothermal zone at a constant altitude inside the crater our analysis of aster orbital data documents topographic and related thermal changes as a result of the 2007 eruption and demonstrates the power of aster as a volcanological tool citation urai m n geshi and t staudacher 2007 size and volume evaluation of the caldera collapse on piton de la fournaise volcano during the april 2007 eruption using aster stereo imagery geophys

evolution of the northeast german basin inferences from a 3d structural model and subsidence analysis abstract a 3d structural model of the northeast german basin was evaluated with special emphasis on its evolution as an intracontinental depression the study includes investigations on subsidence history and structural setting of the basin thickness evolution and calculated tectonic subsidence volumes of permian to quaternary sediments in the northeast german basin indicate that the subsidence history was related to five stages of basin evolution which differ in their subsidence mechanisms for the initial rift phase in the late carboniferous to early permian a dominant thermal event and subordinate horizontal stresses were indicated by thickness variation evolution and by structural evidence the main part of basin subsidence occurred in a nw se oriented basin in the subsequent phase of thermal relaxation with maximum subsidence from early permian rotliegend to middle triassic muschelkalk from middle triassic the thermal subsidence pattern was superposed by further tectonic events in the middle triassic regional extension led to a reconfiguration of the southern part of the basin where new nne ssw trending troughs rheinsberg and gifhorn troughs developed in the jurassic the northwestern part of the basin was uplifted while in the south the keuper subsiding areas continued to sink and nw se trending depressions related to salt margins became important differentiation continued into cretaceous times when regional compression caused uplift of the southeastern part of the basin and basin margins a final subsidence phase occurred in the cenozoic this was accompanied by intensive salt movement recent basin configuration reflects the superposition of structural elements resulting from different evolution stages the main structural characteristics of the basin are 1 a vertical tectonic zonation in a pre zechstein succession which lacks significant internal structures and a strongly deformed post zechstein succession which was decoupled due to the thick zechstein salt and 2 a marked asymmetry of the basin with a shallow northern slope and a steep bounding fault at the southern margin elbe fault system the northwestern part of the basin shows the structural properties of an intracratonic sag basin with persisting subsidence and with minor salt mobilisation in contrast initial structures in the southeastern part are strongly overprinted by younger tectonic events including middle triassic to jurassic extension late cretaceous inversion and late to post cretaceous salt movements tectonic elements that deform the whole sedimentary succession are restricted to the basin s southern eastern and northeastern margins where salt thickness decreases combined volumetric and backstripping investigations show that 2 3 of the total subsidence was induced by the sediment load and 1 3 was caused by tectonics the tectonic subsidence history varies laterally across the basin while tectonic subsidence curves in the northwestern part of the basin show fast subsidence during the permian and early triassic decreasing exponentially with time subsidence curves in the southeastern part indicate repeated tectonic activity however the tectonic subsidence volume created during permian to late triassic is significantly higher than the tectonic subsidence during younger phases of basin history

basin evolution of the northern part of the northeast german basin insights from a 3d structural model abstract a 3d structural model for the entire southwestern baltic sea and the adjacent onshore areas was created with the purpose to analyse the structural framework and the sediment distribution in the area the model was compiled with information from several geological time isochore maps and digital depth maps from the area and consists of six post rotliegend successions the upper permian zechstein lower triassic middle triassic upper triassic jurassic cretaceous and cenozoic this structural model was the basis for a 3d backstripping approach considering salt flow as a consequence of spatially changing overburden load distribution isostatic rebound and sedimentary compaction for each backstripping step in order to reconstruct the subsidence history in the region this method allows determination of the amount of tectonic subsidence or uplifting as a consequence of the regional stress field acting on the basin and was followed by a correlation with periods of active salt movement in general the successions above the highly deformed zechstein evaporites reveal a thickening trend towards the gluckstadt graben which also experienced the highest amount of tectonic subsidence during the mesozoic and cenozoic two periods of accelerating salt movement in the area has been correlated with the e w directed extension during the late triassic early jurassic and later by the late cretaceous early cenozoic inversion suggesting that the regional stress field plays a key role in halokinesis the final part of this work dealt with a neotectonic forward modelling in an attempt to predict the future topography when the system is in a tectonic equilibrium the result reveals that many of the salt structures in the region are still active and that future coastline will run with a wnw ese trend arguing that the compressional stresses related to the alpine collision are the prime factor for the present day landscape evolution

late cretaceous cenozoic evolution of the north german basin results from 3 d geodynamic modelling abstract the late cretaceous cenozoic evolution of the north german basin has been investigated by 3 d thermomechanical finite element modelling the model solves the equations of motion of an elasto visco plastic continuum representing the continental lithosphere it includes the variations of stress in time and space the thermal evolution surface processes and variations in global sea level the north german basin became inverted in the late cretaceous early cenozoic the inversion was most intense in the southern part of the basin i e in the lower saxony basin the flechtingen high and the harz the lower crustal properties vary across the north german basin north of the elbe line the lower crust is dense and has high seismic velocity compared to the lower crust south of the elbe line the lower crust with high density and high velocity is assumed to be strong lateral variations in lithospheric strength also arise from lateral variations in moho depth in areas where the moho is deep the upper mantle is warm and the lithosphere is thereby relatively weak compression of the lithosphere causes shortening thickening and surface uplift of relatively weak areas tectonic inversion occurs as zones of preexisting weakness are shortened and thickened in compression contemporaneously the margins of the weak zone subside cenozoic subsidence of the northern part of the north german basin is explained as a combination of thermal subsidence and a small amount of deformation and surface uplift during compression of the stronger crust in the north the modelled deformation patterns and resulting sediment isopachs correlate with observations from the area this verifies the usefulness and importance of thermomechanical models in the investigation of intraplate sedimentary basin formation

centroid single force inversion of seismic waves generated by landslides the centroid moment tensor cmt waveform inversion method of dziewonski et al 1981 is modified to analyze long period seismic waves generated by single force events such as the gigantic landslides associated with the 1980 eruption of mount st helens we refer to the method as centroid single force csf inversion as the result of the inversion we obtain the spatio temporal centroid and three components of a vector we call the csf vector which is the seismic point source representation of a landslide and whose direction is the opposite of the direction of sliding the sealer magnitude of the csf vector measures the overall size of the landslide and is given by mcsf md where m is the mass of the sliding object and d is the sliding distance we apply csf inversion to the long period surface waves generated by the 1980 mount st helens event the 1975 kalapana earthquake and the 1974 mantaro landslide using seismograms from the gdsn ida and hglp networks the csf solution for the st helens event is remarkably consistent with the actual geological observations and proves the efficacy of csf inversion the csf solution for the kalapana event does not fit the overall waveforms better than the cmt solution does however because the cmt solution does not explain the observed love wave radiation pattern it may be necessary to invoke a combination of both types of mechanism for this event although the geometry of the csf solution the direction of the force for the mantaro event is consistent with the actual landslide mcsf is about 5 times smaller than that expected from the mass and travel distance of the landslide estimated by geological observations this discrepancy may suggest either the relatively aseismic nature of this landslide or that the total volume of the slide was overestimated by analogy to single station cmt inversion single station csf inversion also appears to be stable and useful

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

heat flow and thermal structure of the lithosphere across the baltic shield and northern tornquist zone abstract terrestrial heat flow data from archean and proterozoic provinces of the baltic shield its southwestern margin and the tectonic transition to the younger tectonic units of central europe northern segment of the european geotraverse are compiled and examined for local and regional variations a 2 d numerical lithospheric temperature and heat flux model is presented covering 1800 km of the deep seismic fennolora profile across the baltic shield and 500 km of eugeno s northern eugemi seismic lines across the northern tornquist zone and the danish and north german basins thermal lithosphere defined as the outer layer with relatively low temperatures t c in which heat transfer is dominantly by conduction is found to vary markedly in thickness from 85 110 km beneath basins and tornquist zone to about 150 km in central shield areas and 200 250 km in areas of low heat flow along the northern shield profile these results are in very good agreement with seismological information from surface wave dispersion analysis and the refraction wide angle seismic interpretation of fennolora data the combined thermal and seismologic evidence indicates that the uppermost mantle region stratified in seismic velocity is restricted to the upper relatively cold thermal layer which is interpreted to constitute shield lithosphere local and to some extent regional variations in surface heat flow are found to be closely related to variations in near surface radiogenic heat production for the southern baltic shield a heat flow heat production relationship of q 0 32 8 7 6 h 0 is derived regional increase in heat flow from northern and central shield provinces to the shield margin and the tornquist zone is interpreted to be related partly to differences in upper crustal heat generation partly and in southernmost areas mainly to an increased heat flux from the upper mantle upper mantle heat flux is estimated at 20 25 mw m 2 along the northern and central shield transect increasing to 30 40 mw m 2 beneath the shield margin basins and tornquist zone lithospheric thickness variations in this region of northern europe are found to be closely associated with variations in heat flux from the uppermost mantle and perhaps to a large extent controlled by geodynamically determined lateral differences in upper mantle heat flux earthquake focal depth data and information on crustal strength show baltic shield seismicity to be limited generally to the upper 20 25 km brittle part of the crust at temperatures less than 300 400 c maximum source depth of magnetic anomalies at temperatures near 600 c is in the deepest part of the crust near the crust mantle boundary in the southern region about 25 km depth along the tornquist zone and about 35 40 km in southern shield areas and in the uppermost mantle 60 70 km depth in the northern shield areas some petrologic implications are discussed the present deep crust is supposed to be at lower temperature pressure conditions than at early stages of formation however also the present deepest parts of the shield crust 35 40 km are within the stability field of eclogites the general absence of significant gravity anomalies in areas of marked crustal thickness variations indicate high density eclogites to be present in significant amounts in the deep shield crust

analysis of long period seismic waves excited by the may 18 1980 eruption of mount st helens a terrestrial monopole long period 100 to 260 s love and rayleigh waves excited by the eruption of mount st helens on may 18 1980 and recorded by ida sro and asro stations were analyzed to determine the mechanism of the eruption the amplitude radiation patterns of both rayleigh and love waves are two lobed with a nodal direction in e5 s for rayleigh waves and in n5 e for love waves these radiation patterns preclude any double couple mechanism the radiation pattern the initial phase the relatively large amplitude ratio of love to rayleigh waves and the existence of clear nodes in the radiation patterns of fundamental mode and higher mode rayleigh waves suggest that the source is represented by an almost horizontal less than 15 from the horizontal single force pointed toward s5 w the surface wave spectra fall off very rapidly at periods shorter than 75 s suggesting a very slow source process although the details of the source time history could not be determined a smooth bell shaped time function f o s t 1 2 f o l cos t for 0 t 2 and f o s t 0 for t 2 with 75 s is considered appropriate on the basis of comparison between synthetic and observed seismograms and of the shape of the source spectrum the peak value of the force f 0 is about 10 18 dynes the tailing end of the source time function could not be resolved and some overshoot may be added the magnitude and the time history of the force can be explained by a northward landslide followed by a lateral blast observed at the time of the eruption two distinct events about 110 s apart can be identified on body wave and short period surface wave records the first event may correspond to the earthquake which triggered the landslide and the lateral blast the second event appears to correspond to a second large earthquake and explosion which took place about 2 minutes after the first earthquake

cenozoic uplift and subsidence in the north atlantic region geological evidence revisited abstract the topographic evolution of the passive margins of the north atlantic during the last 65 myr is the subject of extensive debate due to inherent limitations of the geological geomorphological and geophysical methods used for studies of uplift and subsidence we have compiled a database of sign time and amplitude where possible of topographic changes in the north atlantic region during the cenozoic 65 0 ma our compilation is based on published results from reflection seismic studies aft apatite fission track studies vr vitrinite reflectance trends maximum burial sediment supply studies mass balance calculations and extrapolation of seismic profiles to onshore geomorphological features the integration of about 200 published results reveal a clear pattern of topographic changes in the north atlantic region during the cenozoic 1 the first major phase of cenozoic regional uplift occurred in the late palaeocene early eocene ca 60 50 ma probably related to the break up of the north atlantic between europe and greenland as indicated by the northward propagation of uplift it was preceded by middle palaeocene uplift and over deepening of some basins of the north sea and the surrounding areas 2 a regional increase in subsidence in the offshore marginal areas of norway the northern north sea the northern british isles and west greenland took place in the eocene ca 57 35 ma 3 the oligocene and miocene 35 5 ma were characterized by regional tectonic quiescence with only localised uplift probably related to changes in plate dynamics 4 the second major phase of regional uplift that affected all marginal areas of the north atlantic occurred in the plio pleistocene 5 0 ma its amplitude was enhanced by erosion driven glacio isostatic compensation despite inconclusive evidence this phase is likely to be ongoing at present

gravity structure of piton de la fournaise volcano and inferred mass transfer during the 2007 crisis abstract the structure and mass transfers at piton de la fournaise volcano are investigated using new on land and offshore measurements the structures are defined using 2 and 3d modelling short wavelength positive anomalies to the w and nw of the central area are interpreted as shallow piles of thick dense lava flows which have filled volcano tectonic depressions several hundreds of meters deep this finding provides a new insight into the evolution of the volcano conversely the currently active central zone is associated with a negative short wavelength anomaly explained by the presence of thin highly vesiculated and fractured lava flows building the central cone low density formations underlying the rivieres des remparts and langevin areas are tentatively interpreted as breccias related to erosion and or to southward directed mass wasting topographic offshore highs in the continuation of the se and ne rift zones of piton de la fournaise are characterized by negative gravity anomalies and reversed magnetic anomalies their interpretation as hyaloclastites and pillow lavas provides a coherent explanation for both types of signals if we admit that they were primarily constructed during the alizes stage two main deeper dense structures are also found the grand brule complex and a complex beneath the plaine des sables and the enclos fouque both are identified as hypovolcanic intrusive complexes the grand brule complex 10 18 km in plan view shows a marked ns elongated geometry unlike the other comparable complexes on the island the plaine des sables enclos fouque complex a more or less circular structure 5 km in diameter is attributed to the ancient shield stage it is centered on the enclos fault suggesting that the paleo center of the ancient shield was located about 1 5 km eastward of the previously proposed location an apparent contradiction was noted between the seismic and gravity images of the internal structure in particular a high velocity cylinder beneath the summit was not detected in the gravity models this contradiction was resolved by considering the relative sensitivity of each method finally the gravity dataset has allowed us to explore the gravity changes that accompanied the major eruptive and volcano tectonic crisis of april 2007 350 m collapse of the summit and emission of 120 106 m3 of lava the change in the mass distribution of the edifice was large enough to be detected in the survey data collected in the central area before and after the crisis however the accuracy was too low for the precise assessment of the mass transfers

cyclic magma storages and transfers at piton de la fournaise volcano la reunion hotspot inferred from deformation and geochemical data abstract piton de la fournaise is in a period of intense volcanic activity since 1998 to constrain the magma dynamics responsible for this activity we combined gps ground deformation monitoring interpreted through numerical modelling and geochemistry two cycles of continuous volcano inflation are evidenced for the may 2004 december 2005 period with a rest from march to october 2005 these inflations are consistent with two cycles of compatible major element enrichment in the emitted lavas numerical models indicate that the pressurization of a single magma reservoir may be responsible for the observed pre eruptive inflations of the volcano the reservoir located at 2300 m depth has a radius of 500 m at the beginning of each cycle dykes propagate from the roof of the reservoir and yield eruptions of differentiated basalt near the summit at the end of the cycle dykes propagate from the eastern sidewall of the reservoir and yield distal eruptions of primitive magmas away from the summit the volumes of magma emitted during the primitive eruptions seem too large to explain the surface deformations and therefore suggest some refill of the reservoir by deeper magmas our results may be used to predict the location and lava volume of future eruptions at piton de la fournaise volcano depending on the timing of these eruptions within a cycle of volcanic activity

real time monitoring of relative velocity changes using ambient seismic noise at the piton de la fournaise volcano la reunion from january 2006 to june 2007 we present the results of a real time method based on coda wave interferometry from seismic noise cross correlation functions for relative seismic velocity variations monitoring on a volcanic edifice the ambient seismic noise at the piton de la fournaise volcano on la reunion island is analyzed from january 2006 to june 2007 during this period five eruptions occurred showing a great diversity in eruption duration intensity and eruptive fissure location two different methods are used to compute the velocity variations in order to compare their stability in quasi real time routine we compare the obtained velocity variations with the surface deformation observed by gps and extensometers networks this allows us to identify and quantify three major processes at the origin of seismic wave velocity variations in the edifice firstly the observed pre eruptive summit inflation is accompanied by a decrease in seismic velocity secondly the edifice deflation following the opening of an eruptive fissure is characterized by an increase of the velocity finally the summit caldera collapse generates a strong velocity drop coda wave interferometry from seismic noise cross correlation functions in quasi real time may allow us to forecast eruption and constrain the processes taking place in the volcanic plumbing system

small scale diagenetic facies heterogeneity controls porosity and permeability pattern in reservoir sandstones the fluvial aeolian upper rotliegend sandstones from the bebertal outcrop flechtingen high germany are the famous reservoir analog for the deeply buried upper rotliegend gas reservoirs of the southern permian basin while most diagenetic and reservoir quality investigations are conducted on a meter scale there is an emerging consensus that significant reservoir heterogeneity is inherited from diagenetic complexity at smaller scales in this study we utilize information about diagenetic products and processes at the pore and plug scale and analyze their impact on the heterogeneity of porosity permeability and cement patterns eodiagenetic poikilitic calcite cements illite iron oxide grain coatings and the amount of infiltrated clay are responsible for mm to cm scale reservoir heterogeneities in the parchim formation of the upper rotliegend sandstones using the petrel e p software platform spatial fluctuations and spatial variations of permeability porosity and calcite cements are modeled and compared offering opportunities for predicting small scale reservoir rock properties based on diagenetic constraints

the mesozoic cenozoic structural framework of the bay of kiel area western baltic sea a dense grid of multichannel high resolution seismic sections from the bay of kiel in the western baltic sea has been interpreted in order to reveal the mesozoic and cenozoic geological evolution of the northern part of the north german basin the overall geological evolution of the study area can be separated into four distinct periods during the triassic and the early jurassic e w extension and the deposition of clastic sediments initiated the movement of the underlying zechstein evaporites the deposition ceased during the middle jurassic when the entire area was uplifted as a result of the mid north sea doming the uplift resulted in a pronounced erosion of upper triassic and lower jurassic strata this event is marked by a clear angular unconformity on all the seismic sections the region remained an area of non deposition until the end of the early cretaceous when the sedimentation resumed in the area throughout the late cretaceous the sedimentation took place under tectonic quiescence reactivated salt movement is observed at the cretaceous cenozoic transition as a result of the change from an extensional to compressional regional stress field the vertical salt movement influenced the cenozoic sedimentation and resulted in thin skinned faulting

relation of summit deformation to east rift zone eruptions on kilauea volcano hawaii an inverse relationship exists between the summit deflation of kilauea as recorded by summit tilt and the elevation of associated eruptive vents on the east rift zone this relationship implies that east rift eruptions drain the summit magma reservior to pressure levels that are dependent on the elevation of the eruptive vents

the april 2007 eruption and the dolomieu crater collapse two major events at piton de la fournaise la reunion island indian ocean abstract after 10 years of high activity and 24 eruptions piton de la fournaise pdf produced on april 2 to may 1 2007 one of its most voluminous and intense eruption since at least one century the eruption focused at 590 m elevation in the grand brule on the south east flank of piton de la fournaise 7 km away from summit it was located close to the southern cliff of the grand brule volcano tectonic collapse the rempart du tremblet and to the nearby village called le tremblet and it highly rattled and incommoded the inhabitants there eleven hours after the beginning of the eruption the lava flows reached the sea and created 0 45 km 2 of new land until the end of eruption in the night of april 5 the rock column beneath dolomieu crater started to collapse with a piston like mechanism into the magma chamber forming within less than 24 h the most recent and well documented caldera we report in this paper the chronology of these two related major events in the recent activity of pdf seen by the scientific networks of the volcanological observatory ovpf ipgp and field observations which allowed to back up the scenario of the caldera formation and to quantify these two exceptional episodes

the elbe fault system in north central europe a basement controlled zone of crustal weakness abstract the elbe fault system efs is a wnw striking zone extending from the southeastern north sea to southwestern poland along the present southern margin of the north german basin and the northern margin of the sudetes mountains although details are still under debate geological and geophysical data reveal that upper crustal deformation along the elbe fault system has taken place repeatedly since late carboniferous times with changing kinematic activity in response to variation in the stress regime in late carboniferous to early permian times the elbe fault system was part of a post variscan wrench fault system and acted as the southern boundary fault during the formation of the permian basins along the trans european suture zone sensu geol mag 134 5 1997 585 the teisseyre tornquist zone ttz most probably provided the northern counterpart in a pull apart scenario at that time further strain localisation took place during late mesozoic transtension when local shear within the elbe fault system caused subsidence and basin formation along and parallel to the fault system the most intense deformation took place along the system during late cretaceous early cenozoic time when the elbe fault system responded to regional compression with up to 4 km of uplift and formation of internal flexural highs compressional deformation continued during early cenozoic time and actually may be ongoing the upper crust of the elbe fault system which itself reacted in a more or less ductile fashion is underlain by a lower crust characterised by low p wave velocities low densities and a weak rheology structural seismic and gravimetric data as well as rheology models support the assumption that a weak stress sensitive zone in the lower crust is the reason for the high mobility of the area and repeated strain localisation along the elbe fault system

very long period seismic signals and caldera formation at miyake island japan over a period of roughly 40 days starting on 8 july 2000 a caldera structure 1 7 kilometers in diameter developed by means of gradual depression and expansion of the summit crater at miyake island japan at the same time very long period vlp seismic signals were observed once or twice a day source mechanism analyses of the vlp signals show that the moment tensor solutions are smooth step functions over a time scale of 50 seconds with dominant volumetric change components we developed a model to explain the caldera and the vlp signals in which a vertical piston of solid materials in the conduit is intermittently sucked into the magma chamber by lateral magma outflow this model offers potential for making quantitative estimations of the characteristic physical properties of magma systems

reflection seismic constraints on paleozoic crustal structure and moho beneath the ne german basin abstract a 330 km long ne sw trending seismic transect across the ne german basin combined with a 75 km long perpendicular cross line in the basin centre reveals the structure of this intracontinental basin between the stable precambrian baltic shield and the weaker mid european variscides the combination of high fold vibroseis and low fold explosive seismic profiling images both upper and lower crustal structures in detail distinct faults related to a rift stage are not observed below the permian sedimentary basin but there is evidence of lower crustal thinning a moho pattern less reflective below the basin centre than at the margins may be related to magmatic underplating the rather flat lying moho dips slightly towards the basin margins structures further north suggest a southern extent of baltica below the ne german basin the caledonian accretionary wedge may be outlined by sw dipping mid crustal reflectors beneath the basin

heat flow and lithospheric thermal regime in the northeast german basin abstract new values of surface heat flow are reported for 13 deep borehole locations in the northeast german basin negb ranging from 68 to 91 mw m 2 with a mean of 77 3 mw m 2 the values are derived from continuous temperature logs measured thermal conductivity and log derived radiogenic heat production the heat flow values are supposed free of effects from surface palaeoclimatic temperature variations from regional as well as local fluid flow and from thermal refraction in the vicinity of salt structures and thus represent unperturbed crustal heat flow two d numerical lithospheric thermal models are developed for a 500 km section along the dekorp basin 9601 deep seismic line across the basin with a north eastward extension across the tornquist zone a detailed conceptual model of crustal structure and composition thermal conductivity and heat production distribution is developed different boundary conditions for the thickness of thermal lithosphere were used to fit surface heat flow the best fit is achieved with a thickness of thermal lithosphere of about 75 km beneath the negb this estimate is corroborated by seismological studies and somewhat less than typical for stabilized phanerozoic lithosphere modelled moho temperatures in the basin are about 800 c heat flow from the mantle is about 35 to 40 mw m 2 in the southernmost part of the section beneath the harz mountains higher moho temperatures up to 900 to 1000 c are shown while the relatively high level of surface heat flow in the negb obviously is of longer wave length and related to lithosphere thickness changes in crustal structure and composition are responsible for short wave length anomalies

origin of the regional stress in the north german basin results from numerical modelling abstract we use a thin sheet approach to investigate the effects induced by the alpine collision on the deformation and regional stress in northern europe with special emphasis on the ne german basin here new seismic crustal studies indicate a flexural type basin which may have been induced by compressive forces transmitted from the south due to the alpine orogeny finite element techniques are used to solve the equations for the deformation of a continuum described by a linear creep rheology and a spatial resolution of about 0 5 the model has been constrained by stress and seismic data we show that a relatively strong lithosphere below the northern margin of the german basin at the transition with the baltic shield may explain the characteristic regional stress field in particular the fan like pattern which is observed within the region furthermore the predicted strain rate pattern resembles the seismically recognizable undeformed area of the north german basin

magma dynamics and collapse mechanisms during four historic caldera forming events 1 four historic caldera forming events were studied to understand the relationship of magma withdrawal processes and caldera subsidence mechanisms two calderas are silicic katmai in 1912 and pinatubo in 1991 and two are basaltic fernandina in 1968 and miyakejima in 2000 all events have sufficient geophysical geologic and petrologic data with which to examine and model magma withdrawal and caldera collapse the data reveal that the magmas erupted at katmai and pinatubo were in a bubbly state in the reservoir immediately before and during caldera collapse the bubbly magma allowed for its efficient extraction from the reservoir causing significant underpressures to develop rapidly particularly in the case of katmai where the erupted rhyolite was voluminous and nearly aphyric and has very low viscosity the rapidly developing underpressures at katmai and pinatubo caused sudden en masse caldera collapse halfway through the climactic eruptions thereby liberating large amounts of seismic energy at fernandina and miyakejima by contrast caldera collapse was initiated early and continued for an extended period of time from weeks to months consisting of a series of discrete subsidence events manifested by large earthquakes at fernandina and by very long period vlp signals at miyakejima systematic changes in earthquake magnitudes and quiescent intervals at both volcanoes reveal changes in friction as collapse took place during extended time intervals

geochemistry of marine sediments by david j burdige princeton nj princeton university press 2006 609 pages 110 line figures 33 tables 85 00 cloth

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

structure and evolution of the northeastern german basin and its transition onto the baltic shield abstract the post permian sequence stratigraphical and structural evolution of the northeastern german basin and its transition onto the baltic shield has been studied in the bay of mecklenburg sw baltic sea by means of seismic interpretation five major sequences have been identified middle triassic upper triassic jurassic cretaceous and cenozoic time isochore maps allowed the identification of several phases of salt pillow growth the contemporaneity of active salt tectonics and the well studied tectonic evolution of the northeastern german basin suggest a causative correlation the e w directed extension during the triassic early jurassic marking the beginning break up of pangaea is seen as the trigger process for the first period of salt movement a fault system outside the limit of the zechstein evaporates is understood as the consequence of thin skinned faulting and brittle thick skinned deformation that accompanied this extension the observed pronounced erosion of upper triassic and lower jurassic strata is considered to result from the uplift due to the mid north sea doming event in middle jurassic times the seismic data show an undisturbed late cretaceous succession which reflects a period of rising sea level tectonic quiescence and no salt movement in contrast to the salt pillows which emerged above triassic fault systems in the westernmost baltic and western north german basin the cenozoic salt movement activity is the most pronounced this period of reactivated salt pillow growth started coevally with the onset of the alpine orogeny at the cretaceous cenozoic transition when the africa arabian plate collided with eurasia generally no significant faults were identified in the overburden of the salt floored southern bay of mecklenburg where ductile zechstein salt decouples deep rooted faulting from supra salt deformation

cenozoic global sea level sequences and the new jersey transect results from coastal plain and continental slope drilling the new jersey sea level transect was designed to evaluate the relationships among global sea level eustatic change unconformity bounded sequences and variations in subsidence sediment supply and climate on a passive continental margin by sampling and dating cenozoic strata from coastal plain and continental slope locations we show that sequence boundaries correlate within 0 5 myr regionally onshore offshore and interregionally new jersey alabama bahamas implicating a global cause sequence boundaries correlate with 18o increases for at least the past 42 myr consistent with an ice volume glacioeustatic control although a causal relationship is not required because of uncertainties in ages and correlations evidence for a causal connection is provided by preliminary miocene data from slope site 904 that directly link 18o increases with sequence boundaries we conclude that variation in the size of ice sheets has been a primary control on the formation of sequence boundaries since 42 ma we speculate that prior to this the growth and decay of small ice sheets caused small amplitude sea level changes 20 m in this supposedly ice free world because eocene sequence boundaries also appear to correlate with minor 18o increases subsidence estimates backstripping indicate amplitudes of short term million year scale lowerings that are consistent with estimates derived from 18o studies 25 50 m in the oligocene middle miocene and 10 20 m in the eocene and a long term lowering of 150 200 m over the past 65 myr consistent with estimates derived from volume changes on mid ocean ridges although our results are consistent with the general number and timing of paleocene to middle miocene sequences published by workers at exxon production research company our estimates of sea level amplitudes are substantially lower than theirs lithofacies patterns within sequences follow repetitive predictable patterns 1 coastal plain sequences consist of basal transgressive sands overlain by regressive highstand silts and quartz sands and 2 although slope lithofacies variations are subdued reworked sediments constitute lowstand deposits causing the strongest most extensive seismic reflections despite a primary eustatic control on sequence boundaries new jersey sequences were also influenced by changes in tectonics sediment supply and climate during the early to middle eocene low siliciclastic and high pelagic input associated with warm climates resulted in widespread carbonate deposition and thin sequences late middle eocene and earliest oligocene cooling events curtailed carbonate deposition in the coastal plain and slope respectively resulting in a switch to siliciclastic sedimentation in onshore areas oligocene sequences are thin owing to low siliciclastic and pelagic input and their distribution is patchy reflecting migration or progradation of depocenters in contrast miocene onshore sequences are thicker reflecting increased sediment supply and they are more complete downdip owing to simple tectonics we conclude that the new jersey margin provides a natural laboratory for unraveling complex interactions of eustasy tectonics changes in sediment supply and climate change

some aspects of the late and post variscan development of the northwestern german basin abstract the crust of northern germany can be subdivided into three provinces that are evident by differences in crustal density seismic velocity reflectivity magnetic characteristics thermal history and electric conductivity these provinces are limited by the elbe river and the northern foothills of the mittelgebirge during the pre and post variscan evolution the tectonic setting of northern germany has changed repeatedly each of the three recognized basement provinces differs in the timing of basement consolidation caledonian variscan the sequence of basin development during permian mesozoic and cenozoic times and the timing and intensity of magmatic activity permian cretaceous cenozoic

source mechanism of long period events at kusatsu shirane volcano japan inferred from waveform inversion of the effective excitation functions abstract we investigate the source mechanism of long period lp events observed at kusatsu shirane volcano japan based on waveform inversions of their effective excitation functions the effective excitation function which represents the apparent excitation observed at individual receivers is estimated by applying an autoregressive filter to the lp waveform assuming a point source we apply this method to seven lp events the waveforms of which are characterized by simple decaying and nearly monochromatic oscillations with frequency in the range 1 3 hz the results of the waveform inversions show dominant volumetric change components accompanied by single force components common to all the events analyzed and suggesting a repeated activation of a sub horizontal crack located 300 m beneath the summit crater lakes based on these results we propose a model of the source process of lp seismicity in which a gradual buildup of steam pressure in a hydrothermal crack in response to magmatic heat causes repeated discharges of steam from the crack the rapid discharge of fluid causes the collapse of the fluid filled crack and excites acoustic oscillations of the crack which produce the characteristic waveforms observed in the lp events the presence of a single force synchronous with the collapse of the crack is interpreted as the release of gravitational energy that occurs as the slug of steam ejected from the crack ascends toward the surface and is replaced by cooler water flowing downward in a fluid filled conduit linking the crack and the base of the crater lake

simple scaling of catastrophic landslide dynamics catastrophic landslides involve the acceleration and deceleration of millions of tons of rock and debris in response to the forces of gravity and dissipation their unpredictability and frequent location in remote areas have made observations of their dynamics rare through real time detection and inverse modeling of teleseismic data we show that landslide dynamics are primarily determined by the length scale of the source mass when combined with geometric constraints from satellite imagery the seismically determined landslide force histories yield estimates of landslide duration momenta potential energy loss mass and runout trajectory measurements of these dynamical properties for 29 teleseismogenic landslides are consistent with a simple acceleration model in which height drop and rupture depth scale with the length of the failing slope

field observations of the 2008 summit eruption at piton de la fournaise ile de la reunion and implications for the 2007 dolomieu collapse abstract more than one year after the most important eruption ever observed at piton de la fournaise in april 2007 a new eruption started in 2008 at piton de la fournaise with three different eruptive phases in september november and december they were located within the 340 m deep dolomieu crater due to the steep dip angle 45 80 and unstable walls of the new crater formed in april 5 2007 no measurements in situ of the 2008 eruption had been possible only observations from the dolomieu crater rim and from helicopter were performed using an infrared camera a portable rangefinder and numerous photographs these field observations allowed precise monitoring of the setting up of the lava flows with time the total erupted volume of lava of the three phases was 2 2 106 m3 and the average flow rates ranged between 0 3 and 1 m3 s 1 lava temperatures of up to 1150 c have been measured by an infrared camera overall infrared images of the dolomieu crater illustrate the control of the eruptive vents by the structure of the april 2007 dolomieu collapse

rock mechanics observations pertinent to the rheology of the continental lithosphere and the localization of strain along shear zones emphasized in this paper are the deformation processes and rheologies of rocks at high temperatures and high effective pressures conditions that are presumably appropriate to the lower crust and upper mantle in continental collision zones much recent progress has been made in understanding the flexure of the oceanic lithosphere using rock mechanics based yield criteria for the inelastic deformations at the top and base at mid plate depths stresses are likely to be supported elastically because bending strains and elastic stresses are low the collisional tectonic regime however is far more complex because very large permanent strains are sustained at mid plate depths and this requires us to include the broad transition between brittle and ductile flow moreover important changes in the ductile flow mechanisms occur at the intermediate temperatures found at mid plate depths two specific contributions of laboratory rock rheology research are considered in this paper first the high temperature steady state flow mechanisms and rheology of mafic and ultramafic rocks are reviewed with special emphasis on olivine and crystalline rocks rock strength decreases very markedly with increases in temperature and it is the onset of flow by high temperature ductile mechanisms that defines the base of the lithosphere the thickness of the continental lithosphere can therefore be defined by the depth to a particular isotherm tc above which at geologic strain rates the high temperature ductile strength falls below some arbitrary strength isobar e g 100 mpa for olivine tc is about 700 800 c but for other crustal silicates tc may be as low as 400 600 c suggesting that substantial decoupling may take place within thick continental crust and that strength may increase with depth at the moho as suggested by a number of workers on independent grounds put another way the moho is a rheological discontinuity a second class of laboratory observations pertains to the general phenomenon of ductile faulting in which ductile strains are localized into shear zones ductile faults have been produced in experiments of five different rock types and is generally expressed as strain softening in constant strain rate tests or as an accelerating creep rate stage at constant differential stress a number of physical mechanisms have been identified that may be responsible for ductile faulting including the onset of dynamic recrystallization phase changes hydrothermal alteration and hydrolytic weakening microscopic evidence for these processes as well as larger scale geological and geophysical observations suggest that ductile faulting in the middle to lower crust and upper mantle may greatly influence the distribution and magnitudes of differential stresses and the style of deformation in the overlying upper continental lithosphere

european cenozoic rift system abstract the european cenozoic rift system extends from the coast of the north sea to the mediterranean over a distance of some 1100 km it finds its southern prolongation in the valencia trough and a plio pleistocene volcanic chain crossing the atlas ranges development of this mega rift was paralleled by orogenic activity in the alps and pyrenees major rift domes accompanied by subsidence reversal of their axial grabens developed 20 40 ma after beginning of rifting uplift of the rhenish shield is related to progressive thermal lithospheric thinning the vosges black forest and the massif central domes are probably underlain by asthenoliths emplaced at the crust mantle boundary evolution of this rift system is thought to be governed by the interaction of the eurasian and african plates and by early phases of a plate boundary reorganization that may lead to the break up of the present continent assembly

the 2015 gorkha earthquake a large event illuminating the main himalayan thrust fault the 2015 gorkha earthquake sequence provides an outstanding opportunity to better characterize the geometry of the main himalayan thrust mht to overcome limitations due to unaccounted lateral heterogeneities we perform centroid moment tensor inversions in a 3 d earth model for the main shock and largest aftershocks in parallel we recompute s top and p to s receiver functions from the hi climb data set inverted centroid locations fall within a low velocity zone at 10 15 km depth and corresponding to the subhorizontal portion of the mht that ruptured during the gorkha earthquake north of the main shock hypocenter receiver functions indicate a north dipping feature that likely corresponds to the midcrustal ramp connecting the flat portion to the deep part of the mht our analysis of the main shock indicates that long period energy emanated updip of high frequency radiation sources previously inferred this frequency dependent rupture process might be explained by different factors such as fault geometry and the presence of fluids

april 2007 collapse of piton de la fournaise a new example of caldera formation collapse calderas are frequent in the evolution of volcanic systems but very few have formed during historical times piton de la fournaise is one of the world s most active basaltic shield volcanoes the caldera collapse which occurred during the april 2007 lateral eruption is one of the few large documented collapse events on this volcano it helps to understand the mode and origin of caldera collapses in basaltic volcanoes field observations gps and seismic data show that the collapse occurred at an early stage of the eruption the cyclic seismic signal suggests a step by step collapse that directly influenced the lateral eruption rate likely the caldera results from the combined effect of i the progressive collapse of the plumbing system above the magma chamber since 2000 and ii the large amount of magma withdrawal during the early stage of the eruption by both a significant intrusion within the edifice and an important emission rate

an integrated study of the ne german basin abstract the ne german basin is part of the southern permian basin south of the transeuropean suture zone tesz here we report an attempt to integrate a variety of geological and geophysical data in order to reveal the present day deep crustal structure of the ne german basin special focus is taken on detailed geological information available reflection seismic data wide angle refraction seismic data and gravity data based on this integrative approach a concise crustal model is developed which can be subject to further evaluation furthermore it is shown that the ne german basin is an outstanding feature quite different from classical basin types as the moho is flat below the basin neither a simple shear nor a pure shear extension model can be applied instead a thick high velocity lower crustal layer is present below the basin centre this high velocity lower crust is also observed in the western part of the basin and can be taken as characteristic for east avalonia results of gravity modelling indicate the presence of a high density lower crust thus supporting the wide angle data furthermore changes in crustal structure can be derived from changes in reflectivity pattern and from the gravimetric signature along the elbe fault system indicating the presence of different crustal domains north and south of the fault system an elastic plate model where the forces applied are the sediment load a vertical load at the southern margin accounting for the harz moutains and a nne ssw directed compression indicates a buckling of the crust during late cretaceous to tertiary inversion however the correlation between the observed crustal structure and the tectonic events that have affected the area remains a subject of discussion a permian thermal event affected the upper mantle and the lower crust and therefore may have modified the crustal memory with regard to caledonian and variscan events additional tectonic events affected the area during the mesozoic in conclusion it remains an open question whether the high velocity and high density lower crustal structure represents a remnant of east avalonia whether it is related to the formation of the permo triassic basin or is the cumulative result of a series of events during the palaeozoic and mesozoic

explosive activity of the summit cone of piton de la fournaise volcano la reunion island a historical and geological review summit explosive activity and collapses that form pit craters and calderas represent major volcanic hazards on a dominantly effusive frequently active volcano like piton de la fournaise only three summit collapse events 1986 2002 2007 have been recorded since the foundation of the piton de la fournaise volcano observatory ovpf in 1979 and two of them 1986 and 2007 were associated with weak phreatic activity at piton de la fournaise the normal explosive activity consists of short lived and mild 20 m high lava fountains which quickly evolve into strombolian activity during the eruptions based on comprehensive literature review and high resolution image analysis of surface outcrops and summit caldera walls we reconstructed the time distribution of recent explosive events phreatomagmatic phreatic and their link with summit collapses and lateral flank effusive eruptions in historical time post 1640 ce we recognise two main clusters of explosive events frequent and violent phreatomagmatic to phreatic explosions occurred during the oldest cluster 1708 1878 and alternated with long lasting periods years to decades of summit effusive activity in contrast scarce and on average weak explosions occurred during the youngest cluster 1897 2012 when discrete and short lived 6 months effusive eruptions represent the main eruptive dynamics historical summit collapses pit craters and caldera all localised at the top of the summit cone were related to voluminous lateral eruptions and were followed by a significant decrease in eruptive rate however magma draining during lateral eruptions was not systematically associated with summit collapses or explosions the long lasting occurrence of magma at very shallow depth below the volcano summit followed by a rapid lateral drainage apparently represents a critical condition favouring magma groundwater interaction to produce explosive activity the prehistoric growth of the piton de la fournaise summit cone results chiefly from long lasting to continuous activity centred below its western side bory crater containing lava lakes high lava fountains long lasting effusive activity lava lakes ash plumes and block ejections were common types of eruptive dynamics in the historical past between 1640 and 1878 in this perspective short lived small volume eruptions and long pauses up to six years during the last century of activity of piton de la fournaise can be considered as a lull despite the high frequency of eruption 1 eruption 9 months on average temporal and spatial variations in recurrence rate and eruptive dynamics of basaltic volcanism such as those recognised at piton de la fournaise should be considered in the formulation of hazard assessments and in the interpretation of precursory patterns

major crustal features between the harz mountains and the baltic shield derived from receiver functions major crustal features between the harz mountains and the baltic shield derived from receiver functions

high resolution seismic analysis of the coastal mecklenburg bay north german basin the pre alpine evolution the pre alpine structural and geological evolution in the northern part of the north german basin have been revealed on the basis of a very dense reflection seismic profile grid the study area is situated in the coastal mecklenburg bay germany part of the southwestern baltic sea from the central part of the north german basin to the northern basin margin in the grimmen high area a series of high resolution maps show the evolution from the base zechstein to the lower jurassic we present a map of basement faults affecting the pre zechstein the pre alpine structural evolution of the region has been determined from digital mapping of post permian key horizons traced on the processed seismic time sections the geological evolution of the north german basin can be separated into four distinct periods in the rerik study area during late permian and early triassic evaporites and clastics were deposited salt movement was initiated after the deposition of the middle triassic muschelkalk salt pillows which were previously unmapped in the study area are responsible for the creation of smaller subsidence centers and angular unconformities in the late triassic keuper especially in the vicinity of the fault bounded grimmen high in this area partly lower jurassic sediments overlie the keuper unconformably the change from extension to compression in the regional stress field remobilized the salt leading to a major unconformity marked at the base of the late cretaceous

the 2007 eruptions and caldera collapse of the piton de la fournaise volcano la reunion island from tilt analysis at a single very broadband seismic station seismic records from la reunion island very broadband geoscope station are investigated to constrain the link between the 2007 eruptive sequence and the related caldera collapse of the piton de la fournaise volcano tilt estimated from seismic records reveals that the three 2007 eruptions belong to a single inflation deflation cycle tilt trend indicates that the small volume summit eruption of 18 february occurred during a phase of continuous inflation that started in january 2007 inflation decelerated 24 days before a second short lived small volume eruption on 30 march almost simultaneous with a sudden large scale deflation of the volcano deflation rate which had stabilized at relatively low level increased anew on 1 april while no magma was erupted followed on 2 april by a major distal eruption and on 5 april by a summit caldera collapse long term tilt variation suggests that the 2007 eruptive succession was triggered by a deep magma input

source mechanism of seismic waves excited by pyroclastic flows observed at unzen volcano japan a number of pyroclastic flows have occurred at unzen volcano unzendake in kyushu japan since the end of may 1991 seismic waves which are excited by the pyroclastic flows contain low frequency components in their initial phases they were recorded by two long period seismographs in the seismic network deployed around the volcano this paper is an attempt to clarify the source mechanism of the seismic waves triggered by the pyroclastic flows visual data show that the pyroclastic flow which excites these seismic waves occurs in three successive steps first fall of a lava dome front dome collapse then its collision with the mountain slope and its fragmentation into small blocks and finally descent of the blocks along the slope we can build a simple mechanical model which gives theoretical time histories of vertical and horizontal components of a force acting on the spot of dome collapse on the mountain slope the model of a mechanism generating these seismic waves was constructed through analysis of the low frequency components with the aid of inversion methods which can estimate source time function of the force acting on the source the estimated time histories are close to those predicted by the simple mechanical model we conclude that the three steps mentioned above are essential in exciting the low frequency seismic signals this idea is supported by the fact that the volume of fallen material estimated from the visual data is proportional to the maximum vertical amplitude of seismic waves triggered by the pyroclastic flow this relation holds for the two pyroclastic flows of june 22 1991 and may 28 1992 which were studied in this paper these findings seismically confirm a visual observation that the pyroclastic flow is a result of dome collapse

geomechanical and geochemical effects on sandstones caused by the reaction with supercritical co2 an experimental approach to in situ conditions in deep geological reservoirs the geochemical and geomechanical behaviour of reservoir rocks from deep saline aquifers during the injection and geological storage of co2 is studied in laboratory experiments a combination of geochemical and geomechanical studies was carried out on various sandstones from the north german basin after the mineralogical geochemical and petrophysical characterization a set of sandstone samples was exposed to supercritical sc co2 and brine for 2 4 weeks in an autoclave system one sample was mineralogically and geochemically characterised and then loaded in a triaxial cell under in situ pressure and temperature conditions to study the changes of the geomechanical rock properties after treatment in the autoclaves geochemical alterations mainly in the carbonate but also in the sheet silicate cements as well as in single minerals of the sandstones were observed affecting the rocks granular structure in addition to partial solution effects during the geochemical experiments small grains of secondary carbonate and other mineral precipitations were observed within the pore space of the treated sandstones results of additional geomechanical experiments with untreated samples show that the rock strength is influenced by the saturation degree the confining pressure the pore fluid pressure and temperature the exposure to pure scco2 in the autoclave system induces reduced strength parameters modified elastic deformation behaviour and changes of the effective porosity in comparison to untreated sandstone samples experimental results show that the volume of pore fluid fluxing into the pore space of the sandstones clearly depends on the saturation level of the sample

the role of volatiles in magma chamber dynamics many andesitic volcanoes exhibit effusive eruption activity1 with magma volumes as large as 107 109 m3 erupted at rates of 1 10 m3 s 1 over periods of years or decades during such eruptions many complex cycles in eruption rates have been observed with periods ranging from hours to years2 3 4 5 6 7 longer term trends have also been observed and are thought to be associated with the continuing recharge of magma from deep in the crust and with waning of overpressure in the magma reservoir here we present a model which incorporates effects due to compressibility of gas in magma we show that the eruption duration and volume of erupted magma may increase by up to two orders of magnitude if the stored internal energy associated with dissolved volatiles can be released into the magma chamber this mechanism would be favoured in shallow chambers or volatile rich magmas and the cooling of magma by country rock may enhance this release of energy leading to substantial increases in eruption rate and duration

the legacy of the ne german basin reactivation by compressional buckling in contrast to previously published models for the area the seismic reflection moho is essentially flat beneath the ne german basin along the dekorp deep seismic profile basin 96 this raises the question whether the present structure of the crust and flat moho reflect the initial formation of the basin or modification by more recent processes a 2d flexural model developed for a thin elastic plate is presented together with lithospheric strength profiles calculated along the basin 9601 reflection seismic line the analysis shows a southward decrease of lithospheric strength below the basin with a lithospheric decoupling between the crust and the mantle the modelling supports the hypothesis that the present moho topography is caused by flexural buckling which caused subsidence of the ne german basin during the upper cretaceous early cenozoic inversion event this suggests that the basin is in isostatic disequilibrium and that compressive stresses are required to keep the present basin geometry

structures and evolution of the plumbing system of piton de la fournaise volcano inferred from clustering of 2007 eruptive cycle seismicity analysis of seismic activity associated with the eruptions of 2007 which led to the collapse of the dolomieu crater on april 5th reveals the link between the seismicity and the magma transfers at piton de la fournaise three eruptive phases occurred on february 18th march 30th and april 2nd 2007 at the summit 2 000 m and 600 m high on the south east flank respectively illustrating the three types of eruptions defined for the current piton de la fournaise activity we use cross correlation of seismic waveforms and clustering to improve the earthquake locations and determine the best constrained focal mechanisms with an average of 78 p phase polarities the pre eruptive seismicity of the february and march eruptions is composed of time extended clusters that also preceded other distal eruptions from 2000 to 2007 our analysis shows that the seismic swarm prior to the february eruption initiated the intrusion that led to the april 2007 eruption the seismicity preceding the dolomieu crater collapse consists of numerous but time limited clusters and specific seismic activity that accompanied the dolomieu crater collapse from april 1st to april 5th earthquakes with clvd mechanisms combined with normal faulting sources occurred between 0 8 and 0 km asl until the complete rupture of the shallow magma storage roof this collapse induced the propagation of a de pressurization front and triggered a migration of seismicity from 0 to 8 km along a very narrow path

the 2007 caldera collapse of piton de la fournaise volcano source process from very long period seismic signals abstract in april 2007 piton de la fournaise volcano experienced its largest caldera collapse in at least 300 yr this event consisted of a series of 48 subsidence increments characterized by very long period vlp seismic signals equivalent to m w 4 4 to 5 4 source analysis of vlp events suggests a piston like mechanism with a collapsing crack source corresponding to the contraction of the magma reservoir and a single force representing the collapse of the above rock column we show that the collapse dynamics is primarily controlled by magma withdrawal from the reservoir which was likely in a bubbly state at the time of the event similar to the 2018 kilauea collapse we observe a reduction of the time interval between successive subsidence increments which results from the acceleration of magma withdrawal and a progressive weakening of the edifice at the beginning of the sequence

analysis of seismic body waves excited by the mount st helens eruption of may 18 1980 seismic body waves which were excited by the may 18 1980 eruption of mount st helens and recorded by the global digital seismographic network stations are analyzed to determine the nature and the time sequence of the events associated with the eruption the polarity of teleseismic p waves period 20s is identical at six stations which are distributed over a wide azimuthal range this observation together with a very small s to p amplitude ratio at 20 s suggests that the source is a nearly vertical single force a simple model shows that for seismic radiation a volcanic eruption can be represented by a single force applied in the direction opposite to the blast direction the time history of the vertical force suggests two distinct groups of events about 2 min apart each consisting of several subevents with a duration of about 25 s the magnitude of the force is approximately 2 6 10 12 n this vertical force is in contrast with the long period 150 s southward horizontal single force which has been determined by a previous study and interpreted to be due to the massive landslide an m s 5 2 earthquake initiated the eruption sequence the direction of the p wave first motion of this event observed at two nearby stations is consistent with the radiation pattern expected for the landslide and suggests that it represents the onset of the landslide the ground motions observed at station lon 67 km are dominated by rayleigh waves i e lamb pulse and provide tight constraints on the time sequence of the events

toward continuous quantification of lava extrusion rate results from the multidisciplinary analysis of the 2 january 2010 eruption of piton de la fournaise volcano la reunion the dynamics of the 2 12 january 2010 effusive eruption at piton de la fournaise volcano were examined through seismic and infrasound records time lapse photography so2 flux measurements deformation data and direct observations digital elevation models were constructed for four periods of the eruption thus providing an assessment of the temporal evolution of the morphology the volume and the extrusion rate of the lava flow these data were compared to the continuous recording of the seismic and infrasonic waves and a linear relationship was found between the seismic energy of the tremor and the lava extrusion rate this relationship is supported by data from three other summit eruptions of piton de la fournaise and gives total volume and average lava extrusion rate in good agreement with previous studies we can therefore provide an estimate of the lava extrusion rate for the january 2010 eruption with a very high temporal resolution we found an average lava extrusion rate of 2 4 m3s 1 with a peak of 106 6 m3s 1 during the initial lava fountaining phase we use the inferred average lava extrusion rate during the lava fountaining phase 30 23 m3s 1 to estimate the value of the initial overpressure in the magma reservoir which we found to range from 3 7 106 pa to 5 9 106 pa finally based on the estimated initial overpressure the volume of magma expelled during the lava fountaining phase and geodetic data we inferred the volume of the magma reservoir using a simple mogi model between 0 25 km3 and 0 54 km3 which is in good agreement with previous studies

the tectonosedimentary evolution of the northern margin of the carboniferous foreland basin of ne germany abstract the geometry and evolution of the northern margin of the carboniferous foreland basin in ne germany was examined in terms of depositional environments petrographic and geochemical data lower carboniferous units are carbonate rich and predominantly marine by namurian times continental environments are established along the northern basin margin with turbiditic sedimentation persisting in the south the upper carboniferous succession is continental and clastic the sandstones were derived from a quartz rich source located to the north with subordinate sedimentary input basin evolution and the development of a characteristic marine to continental sedimentary succession while being predominantly controlled by flexure induced by the variscan orogen to the south was also influenced by eustatic sea level variations and more localised tectonic movements

the southern margin of the east european craton new results from seismic sounding and potential fields between the north sea and poland abstract the extension of eastern avalonia from britain through the ne german basin into poland is in some sense a virtual structure it is covered almost everywhere by late paleozoic and younger sediments evidence for this terrane is only gathered from geophysical data and age information derived from magmatic rocks during the last two decades much geophysical and geological information has been gathered since the european geotraverse egt which was followed by the babel lt 7 mona lisa dekorp basin 96 and polonaise 97 deep seismic experiments based on seismic lines a remarkable feature has been observed between the north sea and poland north of the elbe line el the lower crust is characterised by high velocities 6 8 7 0 km s a feature which seems to be characteristic for at least a major part of eastern avalonia far eastern avalonia in addition the seismic lines indicate that a wedge of the east european craton eec or baltica continues to the south below the southern permian basin spb a structure which resembles a passive continental margin the observed pattern may either indicate an extension of the baltic crust much farther south than earlier expected or oceanic crust of the tornquist sea trapped during the caledonian collision in either case the data require a reinterpretation of the docking mechanism of eastern avalonia and the elbe odra line eol as well as the elbe fault system together with the intra sudedic faults appear to be related to major changes in the deeper crustal structures separating the east european crust from the paleozoic agglomeration of middle european terranes

formation of the april 2007 caldera collapse at piton de la fournaise volcano insights from gps data abstract on april 5th 2007 a major collapse of the dolomieu summit crater occurred at piton de la fournaise volcano la reunion island to constrain the origin and the dynamics of the collapse we modelled continuous gps displacements preceding and accompanying this event our results reveal that the dolomieu collapse formed by a piston like mechanism in which the fast draining of the shallow magma reservoir at the beginning of the march 30th may 1st 2007 eruption caused a gravity driven downward displacement of its roof during the five days preceding the collapse summit deflation was caused by volume change through the fractured rock column above the shallow magma chamber due to the closure of voids or small scale cavities or the upward stoping and migration of an underground cavity since 2000 weakening of the rock column by repeated refilling and draining of the shallow magma chamber favoured its destabilization on april 5th 7 h before the onset of the collapse the deflation source was located at 300 m depth revealing the initiation of the collapse at very shallow depth the sudden collapse on april 5th was followed by continuous cyclic subsidence until april 6th each cycle was characterized by a progressive inward deflation of the summit zone and ended by sudden summit outward displacements caused by stress relaxation following a collapse event subsidence of the stoped column in the magma reservoir during the collapse of the crater on april 5th and 6th acted as a piston thus increasing the eruption rate the collapse occurred in only 24 h by successive events and increased the depth of the dolomieu crater by 340 m after april 6th only minor readjustments of the summit cone occurred with slight summit deflation and small landslides of the caldera walls

deep structure and evolution of the harz mountains results of three dimensional gravity and finite element modeling a new bouguer anomaly map is presented for the region of the entire harz mountains based on more than 60 000 gravity values the various gravity anomalies are discussed and interpretation is carried out by high resolution 3 d gravity modeling one of the main subjects of interest in the investigation is the northern boundary fault zone of the harz mountains separating the mesozoic sediments in the north from the palaeozoic rocks of the harz in the south dip and vertical displacement are determined for this fault zone mean values are 3400 m and 70 respectively gravity modeling shows that the brocken and the ramberg granites are distinctly different the brocken granite is shallow whereas the ramberg granite has a maximum depth of 8 5 km and a n s dimension of 37 km the prominent benneckenstein gravity high is explained by two different models one based on a granodioritic intrusion 2900 kg m3 with a center depth of 14 km and the other based on phyllites 2740 kg m3 on a depth of 3 4 km studies on the geodynamic evolution of the harz mountains are carried out using the finite element method on the basis of a 3 d model vertical displacements that can be related to horizontal forces are computed for the period of the variscan orogeny an uplift of 600 m in the harz area is calculated for late cretaceous and tertiary 400 m are determined the total amount of 1000 m is about 12 of the vertical displacement of the northern boundary fault zone of the harz mountains shown by the gravity modeling these results do not contradict geological ideas