dislocation modelling of the 1989 dike intrusion into the flank of mount etna sicily we have applied a dislocation model consisting of a dipping tabular body with constant dislocation perpendicular to the plane of the body to surface displacements related to an intrusion in the south flank of etna volcano sicily ground deformation was measured by a trilateration array and automatic tilt measurements during the 1989 eruption of the volcano significant line length changes and tilt were measured associated with an episodic 0 8 km propagation of the intrusion into the measurement array we incorporated the orientation and location of measured surface cracking into a bayesian nonlinear inversion of the data to determine the geometry of the intrusion we suggest the intrusion caused a 1 m wide opening of a vertical crack that extended from a depth of 1 km to within a few hundred meters of the surface we relate the distribution of surface cracking and seismicity associated with the fracture to stresses generated in the slip weakening zone associated with the crack edge

effects of the 1989 fracture system in the dynamics of the upper se flank of etna revealed by volcanic tremor data the missing link 1 fracture reactivation is a widespread process in nature even though evidence of magma induced reactivation is less documented here we provide evidence of the reactivation of a fracture system on the upper flank of the mt etna volcano and consider its possible implications in understanding the recent volcanic and tectonic activity a nnw sse trending fracture partly accompanied by magma emplacement in the form of a laterally propagating dike formed in 1989 on the upper se flank of etna lava effusions in 1991 1993 2001 and 2006 were associated with volcano tectonic vt seismicity and ground deformations on the upper part of the volcano which document the seismogenetic involvement of the 1989 fractures although without eruptive phenomena along the discontinuity in addition to the aforementioned episodes of vt seismicity differences in the characteristics of the background seismic radiation volcanic tremor were measured at stations close to these fractures during the eruptive activity on 24 november 2006 for which more detailed volcanological and seismological time histories are available moving on from these findings we analyze volcanic tremor data recorded close to the summit and along the s flank of the volcano to highlight the interactions between seismic radiation and the 1989 fracture system centroid location of volcanic tremor and wave field characteristics at stations of the permanent local seismic network of etna highlight the guidance role played by the 1989 fractures during the eruptive activity on 24 november 2006 in addition the collected data shed light on hitherto unknown structural features which appear to connect the volcano summit to the lower se slope and also play an important role in controlling the instability of the e flank more generally this study shows how 1 using an integrated approach it is possible to link apparently different features to a common structure showing uniform and distinct dynamics relevant at the volcano scale and 2 fracture reactivation can also occur by means of magma intrusion playing an important role in the transfer of magma within a volcanic edifice

deep magma body beneath the summit and rift zones of kilauea volcano hawaii a magnitude 7 2 earthquake in 1975 caused the south flank of kilauea volcano hawaii to move seaward in response to slippage along a deep fault since then a large part of the volcano s edifice has been adjusting to this perturbation the summit of kilauea extended at a rate of 0 26 meter per year until 1983 the south flank uplifted more than 0 5 meter and the axes of both the volcano s rift zones extended and subsided the summit continues to subside these ground surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones kilauea s magmatic system is therefore probably deeper and more extensive than previously thought the summit and both rift zones may be underlain by a thick near vertical dike like magma system at a depth of 3 to 9 kilometers

seismic activity accompanying the outbreak of the 1991 1993 eruption of mt etna italy abstract the character and location of seismic activity accompanying the onset of the 1991 1993 eruption at mt etna are compatible with the surface evidence of the volcanic pile rupture both the epicentral distribution and the focal mechanisms of a swarm that occurred on december 14 1991 agree with magma ascent occurring along the main nnw sse trending structure of the volcano and the consequent opening of a system of effusive fissures with the same trend a typical mainshock aftershock sequence recorded the day after and indicating transcurrent displacement occurring along the second principal structure of etna ne sw depicts the tectonic response of the volcanic pile and the underlying basement to major stresses applied by the magma push

dike propagation energy balance from deformation modeling and seismic release magma is transported in the crust mainly by dike intrusions in volcanic areas dikes can ascend towards the free surface and also move by lateral propagation eventually feeding flank eruptions understanding dike mechanics is a key to forecasting the expected propagation and associated hazard several studies have been conducted on dike mechanisms and propagation however a less in depth investigated aspect is the relation between measured dike induced deformation and the seismicity released during its propagation we individuated a simple equation that can be used as a proxy of the expected mechanical energy released by a propagating dike and is related to its average thickness for several intrusions around the world afar japan mt etna we correlate such mechanical energy to the seismic moment released by the induced earthquakes we obtain an empirical law that quantifies the expected seismic energy released before arrest the proposed approach may be helpful to predict the total seismic moment that will be released by an intrusion and thus to control the energy status during its propagation and the time of dike arrest

understanding etna flank instability through numerical models abstract as many active volcanoes mount etna shows clear evidence of flank instability and different mechanisms were suggested to explain this flank dynamics based on the recorded deformation pattern and character shallow and deep deformations mainly associated with both eruptive and seismic events are concentrated along recognised fracture and fault systems mobilising the eastern and south eastern flank of the volcano several interacting causes were postulated to control the phenomenon including gravity force magma ascent along the feeding system and a very complex local and or regional tectonic activity nevertheless the complexity of such dynamics is still an open subject of research and being the volcano flanks heavily urbanised the comprehension of the gravitative dynamics is a major issue for public safety and civil protection the present research explores the effects of the main geological features in particular the role of the subetnean clays interposed between the apennine maghrebian flysch and the volcanic products and the role of weakness zones identified by fracture and fault systems on the slope instability process the effects of magma intrusions are also investigated the problem is addressed by integrating field data laboratory tests and numerical modelling a bi and tri dimensional stress strain analysis was performed by a finite difference numerical code flac and flac 3d mainly aimed at evaluating the relationship among geological features volcano tectonic structures and magmatic activity in controlling the deformation processes the analyses are well supported by dedicated structural mechanical field surveys which allowed to estimate the rock mass strength and deformability parameters to take into account the uncertainties which inevitably occur in a so complicated model many efforts were done in performing a sensitivity analysis along a wnw ese section crossing the volcano summit and the valle del bove depression this was mainly devoted to evaluate the effect of topography geometry and rheological behaviour of the structural units the 3d numerical model extended 40 60 km was implemented to simulate the volcano deformation pattern first the role of the pleistocene subetnean clays was investigated then two structural weakness zones the pernicana fault system and the ne rift were introduced and their effects on the flank instability evaluated two extreme hydrogeological conditions drained and undrained were analysed the results are expressed in terms of stress strain field displacement pattern plasticity states and shear strain increments two main instability mechanisms were identified one at shallow depth with the sliding surface located inside the subetnean quaternary clay and another deep seated mechanism with a not continuous and less evident sliding surface developed inside the apennine maghrebian chain flysch bordered by active structures both mechanisms contribute to explain the present deformation pattern and some of the main structures of the etna flank the effect of magma pressure exerted on the active dyke walls during eruptions was then simulated and relations between magmatic activity and flank instability were preliminarily investigated

transient deformation following the 30 january 1997 dike intrusion at kīlauea volcano hawai i on 30 january 1997 an intrusion on k lauea volcano opened a new fissure within the east rift zone erz at n pau crater 3 km uprift from the ongoing eruptions at pu u the fissure eruption lasted 22 h and opened a 5 1 km long nearly vertical dike 1 9 m extending from the surface to a depth of 2 4 km owen et al 2000b during the eruption the lava pond at pu u drained and eruptions ceased there pu u eventually refilled in late february and eruptions resumed there on 28 march 1997 continuous gps data show a large transient following the 30 january 1997 dike intrusion after lengthening 40 cm during the initial eruption the baseline between two stations spanning the erz lengthened an additional 10 cm over the following 6 months a coastal station kaep also exhibited transient deformation as it continued to move southward 5 cm over the same 6 month period the baseline between two stations spanning k lauea s summit caldera contracted sharply during the eruption but gradually recovered to slightly longer than its previous length 2 months after the intrusion we use the extended network inversion filter mcguire and segall 2003 to invert continuous gps data for volume change of a spherical pressure source under k lauea s summit opening distribution on a nearly vertical dike in the erz and potential slip on a decollement 9 km beneath the south flank following the 30 january intrusion rift extension continued below the initial dike intrusion for the duration of the transient decollement slip regardless of its assumed depth is not required to fit the data the modeled transient summit reinflation and rift opening patterns under n pau crater coincide with changes in observed behavior of pu u s lava pond rift opening accelerated while pu u eruptions paused and began to decelerate after the lava pond reappeared nearly a month after the n pau eruption the transient deformation is interpreted as resulting from shallow accommodation of the new dike volume

paleoseismology and seismic hazards evaluations in extensional volcanic terrains extensional structures in volcanic terrains are the surface expression of shallow dike intrusion and can be misinterpreted as structures associated with major tectonic faults dike induced structures can be distinguished from their tectonic counterparts by their association with cogenetic volcanic rocks and by several geometric relationships tensile fissures with little or no vertical displacement fissure swarms flexural monoclines and normal faults are commonly symmetrically distributed about a central eruptive fissure sometimes forming a graben above shallow dikes the structures typically occur within broad zones not narrow belts near a main fault zone reflecting their origin by repeated dike injection colluvial wedges containing records of single large earthquakes generally do not form instead fault scarps with several meter vertical displacements in volcanic bedrock may reflect the cumulative effects of many decimeter scale displacement events from several dike injection episodes the mechanism of dike intrusion and the nature of cointrusive seismicity have important implications for determination of the maximum magnitude and recurrence of earthquakes in extensional volcanic terrains observational seismicity from volcanic rift zones worldwide suggests the maximum magnitudes of dike induced earthquakes are 3 8 0 8 earthquakes are generally small to moderate because downdip extents of faults and fissures are controlled by the depth to the top of the associated dike usually 5 km permitting only small rupture areas also rupture and displacement on faults and fissures migrate incrementally at about the velocity of propagating dikes 0 5 m s as dike dilation stresses the zone above and ahead of the dike earthquake recurrence is tied to recurrence of volcanic cycles based on the geochronology of the associated volcanic materials based on these concepts innovative approaches have led to estimates of the maximum magnitude and recurrence for magma induced seismicity in eastern snake river plain esrp volcanic rift zones the most conservative approach uses surface length fault width downdip extent and rupture areas of normal faults and fissures produced by dike injection to estimate a maximum m5 5 earthquake for an episode of rift zone volcanism chronology of volcanic rocks suggests annual probabilities of 10 4 to 10 5 for volcanic rift zones near idaho national engineering laboratory facilities probabilistic assessments show that ground motion hazard due to volcanic rift zone seismicity is lower than the hazard from other earthquake sources this is because of the relatively low magnitudes and long recurrence intervals of cointrusive earthquakes in volcanic rift zones

magnetic history of a dyke on mount etna sicily summary during the 1989 eruption of mount etna two fracture systems trending c n45 e and n150 e opened at the foot of its 3000 m high se crater and propagated quickly downslope to distances of 3 and 7 km respectively the northeastern fracture fed a flank eruption whereas the southeastern fracture remained dry and overed contrasting volcanological and geophysical evidence of the presence of magma at a shallow depth during the opening of this non eruptive fracture system a diverential magnetic network was set up on a short profile across its distant extremity initially the magnetic field did not display any change along the profile between frequent surveys however repeated measurements at intervals of about 3 months for two years revealed the slow build up of a 130 nt anomaly the anomaly vanishes laterally within 0 2 km of the surface expression of the fracture system this exceptional set of observations constrains the location and time of cooling of a shallow dyke the increase in magnetization of the dyke inferred by the rate of growth of the anomaly leads to the interpretation that the dyke was emplaced near the end of the eruption

activity along the osning thrust in central europe during the lateglacial ice sheet and lithosphere interactions abstract the osning thrust is one of the major fault systems in central europe with a length of approximately 115 km it underwent a polyphase tectonic evolution in the mesozoic that ranged from extensional movements in the jurassic to reverse faulting and thrusting during inversion in the late cretaceous a series of complex metre scale faults and related fold structures are developed within the upper pleistocene alluvial aeolian complex of the upper senne 1 km away from the thrust the faults dip towards the north and show offsets in a range of several decimetres growth strata indicate a two fold evolution of the structures the faults began as normal faults and were later transformed into reverse faults which resulted in the formation of small scale inversion structures with a typical harpoon shape glaciotectonics can be ruled out as the driving mechanism for these structures because new optically stimulated luminescence osl ages imply that the sedimentary succession was deposited during the late pleistocene between 29 3 2 9 ka and 13 1 1 5 ka at which time the ice margin was much further to the northeast we believe the inversion structures were caused by movement on the osning thrust due to generation of a forebulge of the late pleistocene weichselian ice sheet this led to normal faulting as a consequence of extension in the forebulge area during glaciation the osl ages for the normal fault related growth strata are in a range of 16 13 ka later reverse movements occurred during deglaciation due to the n s directed compressional stress field in northern germany numerical simulations of the deglaciation seismicity point to seismic events with a thrust mechanism in the study area between 15 5 and 12 3 ka bp although normal faulting is also possible in this time period numerous soft sediment deformation structures imply that movement on the osning thrust caused earthquakes with a significant magnitude in the autumn of 1612 an earthquake took place in this area it is very likely that this event is related to background seismicity on this fault although movement due to the influence of the ongoing glacial rebound in fennoscandia is also possible

surface deformation associated with a dipping hydrofracture crustal deformation associated with hydrofracture is modeled by a dipping rectangular dislocation beneath the surface of an elastic half space the burger s vector is taken normal to the rectangular surface analytical expressions for vertical displacements are obtained from integration of volterra s equation by using mindlin s point force solutions for the elastic halfspace in the limits of 0 and 90 dip the results agree with those obtained by maruyama 1964 for poisson s ratio 0 25 expressions for arbitrary poisson s ratio are given for elongate dislocations the displacement field agrees with curves given by pollard and holzhausen 1979 for two dimensional near surface fractures at various dips at dip 0 a deep square dislocation gives displacements indistinguishable from those of sun s 1969 model of a horizontal penny shaped crack beneath the surface of an elastic half space modifying his result for shallow depths shows that they correspond to a dislocation of semi elliptical cross section with the surface displacement field asymptotically approaching a semi elliptical shape as depth decreases to zero similarly the surface displacement field of the square dislocation approaches that of its rectangular cross section nonlinear inversion of surface tilt fields associated with hydrofracture of deep boreholes gives estimates of fracture geometry position and orientation along with their uncertainties two examples are presented one of a near horizontal and one of a near vertical fracture

progressive proglacial to subglacial deformation and syntectonic sedimentation at the margins of the mid pleistocene british ice sheet evidence from north norfolk uk abstract detailed analysis and interpretation of the stratigraphy and structures developed within polydeformed sediments exposed in the coastal section between west runton and sheringham eastern england has allowed the characterisation of the glacitectonic signature associated with the advance of a major mid pleistocene anglian ice sheet the sequence of pre glacial deposits and glacial sediments laid down during earlier southerly directed ice advances d1 d2 is deformed and disrupted by an ice advance from the west southwest that marks a major change in ice flow dynamics in northern east anglia the simplest interpretation of this deformation event d3 is in terms of a progressive proglacial to subglacial deformation model proglacial deformation occurred in advance of the ice margin and was dominated by thrusting positive topographic features which developed above the propagating thrusts controlled sediment dispersal patterns within outwash sandur leading to the formation of small sub basins between these morainic ridges the accretion of the wedge shaped proglacial thrust moraines to the main push moraine formed at the margin of the advancing glacier may have temporarily stalled forward motion of the ice thrusting and large scale folding associated with ice marginal deformation led to the stacking of material excavated from further up ice onto the stoss side of these accreted thrust related moraines that allowed the glacier to override the obstruction subglacial deformation was highly variable in its style and intensity ranging from heterogeneous folding and thrusting through to more pervasive ductile shearing associated with the formation of a subglacial shear zone the thickness and complexity of this shear zone increases up ice where it is characterised by a thick glacitectonic melange the pore water content of the deforming sediments controlled the pattern of deformation within the shear zone however an increase in the efficiency of the drainage system towards the front of the glacier would have led to a rapid thinning of this water enhanced zone of ductile shear evidence from north norfolk suggests that zones of preferential pore water flow within the glacier bed are a major controlling factor on the location of the subglacial shear zone consequently the bulk of the forward motion of the glacier may not be accommodated by shearing within the sediments immediately below its base but occur at a deeper level within the deforming bed

the march 1981 mount etna eruption inferred through ground deformation modelling abstract the march 1981 eruption of mt etna was characterised by the fast propagation of a long eruptive fissure approximately 7 km and by an unusually high eruption rate the continuous tilt recorded by a bore hole station located on the southern flank showed a small inflation 3 4 months before the eruption followed by a rapid deflation during the fissure opening the discrete deformation measurements electroptical distance measurements edm and levelling showed large horizontal changes in the volcano flanks and smaller vertical ones close to the eruptive fissure we modelled the deformation pattern associated with the 1981 eruption using horizontal 57 data and vertical 50 data measurements two geometric constraints were considered for the eruptive fissure the dislocation theory was used to model the intrusion by characterising it in two parts as a double tensile crack which represents the initial deeper intrusion first crack and then the final shallower part associated with the eruptive fissure second crack an analytic inversion was performed obtaining a very good solution and then the robustness of this result was verified through an accurate trial and error search the first deeper crack extends vertically from about 300 to 1700 m above sea level a s l it was widely opened opening 5 m dipping w and radiating from the summit of the volcanic edifice in the nnw direction for approximately 3 km in the shallowest part last 500 m the intrusion propagated radially in the northern sector along the nnw direction second crack matching the surface location of the observed eruptive fissure we interpret that the deeper crack formed during the 3 4 months preceding the eruption

geophysical investigations of the plumbing system of stromboli volcano aeolian islands italy abstract in this work we report the results of an integrated approach using both seismological and geodetic data provided by the ingv ct istituto nazionale di geofisica e vulcanologia sezione di catania stromboli volcano monitoring systems in order to improve the knowledge of its plumbing system in particular we investigated the relationships between the june 1999 seismic swarm occurring in the area of stromboli and the possible activation of the ne sw oriented volcano tectonic structure we analyzed this seismic swarm proposing new locations and a morphological analysis of the waveforms this approach allowed us to demonstrate that there are relationships between the tectonic activity near stromboli and the rising of magma this evidence supports the hypothesis that during the 1999 swarm an intrusive process started from a crustal level where earthquakes were located about 10 15 km b s l as already testified by other similar episodes deformation anomaly recorded between december 1994 and march 1995 after the november 1994 swarm months after the 1999 seismic activity the tiltmeters and the gps permanent stations deployed in stromboli showed slow variations over three months may july 2000 we performed an analytical inversion of these geodetic observations and found that the modelled sources are characterized by ne sw trend compatible with the regional faults cutting the volcano the modelled sources could represent the rising pathway connecting the deep plumbing system about 10 15 km b s l to the shallow one located in the body of the stromboli volcano about 500 m a s l these new evidences support the hypothesis of the existence of a simple plumbing system with different levels of magma storage where batches of magma are periodically pushed up along the main ne sw tectonic trend

early detection of large eruptions at piton de la fournaise volcano la reunion island contribution of a distant tiltmeter station we report a compilation of data recorded at a distant tiltmeter station rer during recent episodes of dyke emplacement and eruption 2003 2007 at piton de la fournaise volcano la reunion island this sensitive station provides useful information for evaluating the extent of deformation distinct responses of this station were recorded based on the eruption type dykes feeding summit eruptions did not significantly influence the rer tiltmeter signals whereas dykes feeding large distal eruptions with vents located more than 4 km from the summit generated up to 1 4 rad of tilt an amplitude 2 to 4 times greater than for proximal eruptions 0 3 0 7 rad on the flanks of the summit cone the distinct tilt amplitude is directly linked to the location depth and volume of the dyke comparison with summit tiltmeters reveals that up to one third to half of the rer tilt signal associated to dyke propagation is recorded when the dyke is still below the summit crater thus before large distal eruptions more than 0 5 rad of tilt is recorded in less than 20 min when the dyke is below the summit crater i e a few minutes hours before the beginning of the eruption we can thus propose for the rer station a threshold value of 0 5 rad which when reached as a dyke rises beneath the summit crater suggests a high likelihood of a large distal eruption the distant rer tiltmeter station thus appears to be a powerful tool for forecasting the type of eruption that is likely to occur and can contribute to the early detection of large distal eruptions at piton de la fournaise which are the most dangerous to inhabitants for volcano monitoring installation of high precision distant tiltmeters along the lower slopes of a volcano may provide warnings of large eruptions with enough lead time to allow for short term hazards mitigation efforts

three dimensional model of the feeder conduit of the 1983 eruption of mt etna volcano from ground deformation measurements a levelling network and a horizontal distance measuring network down mt etna s south flank were measured before during and after the 1983 eruption we analyse the large movements recorded using theoretical models of surface displacement to determine the shape and position of the feeder conduit that supplied magma to the eruption the results indicate that a dyke the top surface extending nearly horizontally connects the eruption site to a point near the southeast crater the top of the dyke lies at an altitude of 2400 m to 2500 m and dips between 75 and 90 to the west more tentative evidence indicates that the top of the active dyke dropped by about 150 m between the 25th and the 95th day of the eruption and that a small branching dyke 1 km long was emplaced to the east of the main dyke but did not attain the surface the implications of these observation are discussed

models of ground deformation from vertical volcanic conduits with application to eruptions of mount st helens and mount etna we present simple analytical models of ground deformation from inflation of vertical volcanic conduits or pipes we compare three cases corresponding to 1 a pressurized pipe with closed end at the top that resists the internal pressure 2 a pressurized pipe with top open for which the internal deformation is mainly dislocation of the cylindrical walls and 3 a pipe shaped region that dilates for the closed pipe we use eshelby s inclusion theory to model deformation from a thin pressurized elongated prolate ellipsoid in a full space which we express in terms of double forces to satisfy surface boundary conditions we superimpose image solutions by using double forces derived from mindlin s half space solution for the point force for the open pipe we apply the volterra integral to dislocation across a cylindrical surface and generalize it to the half space using mindlin s point force solution these two solutions show marked differences from the line of dilatation solution ratios of maximum horizontal deformation to maximum vertical deformation for the pipe models are significantly greater than values for the center or line of dilatation models this and the more gradual fall off of the deformation with distance may be used as diagnostics for discriminating between pipe like sources and dilatational sources on volcanoes where both components of the deformation field are available as examples we compare the closed pipe model with deformation associated with dome building on mount st helens volcano and tilt predicted by the open pipe model with tilt measured during a period of explosive eruptive activity on mount etna sicily in 1995 comparison between model values and the measurements suggests that the effective elastic moduli of the volcanic cones are very low

mechanical response of the south flank of kilauea volcano hawaii to intrusive events along the rift systems abstract increased earthquake activity and compression of the south flank of kilauea volcano hawaii have been recognized by previous investigators to accompany rift intrusions we further detail the temporal and spatial changes in earthquake rates and ground strain along the south flank induced by six major rift intrusions which occurred between december 1971 and january 1981 the seismic response of the south flank to individual rift intrusions is immediate the increased rate of earthquake activity lasts from 1 to 4 weeks horizontal strain measurements indicate that compression of the south flank usually accompanies rift intrusions and eruptions emplacement of an intrusion at a depth greater than about 4 km such as the june 1982 southwest rift intrusion however results in a slight extension of the subaerial portion of the south flank horizontal strain measurements along the south flank are used to locate the january 1983 east rift intrusion which resulted in eruptive activity the intrusion is modeled as a vertical rectangular sheet with constant displacement perpendicular to the plane of the sheet this model suggests that the intrusive body that compressed the south flank in january 1983 extended from the surface to about 2 4 km depth and was aligned along a strike of n66 e the intrusion is approximately 11 km in length extended beyond the january 1983 eruptive fissures which are 8 km in length and is contained within the 14 km long region of shallow rift earthquakes

structural and seismological features of the 1989 syn eruptive nnw sse fracture system at mt etna during the september october 1989 eruption at mt etna structural faults folds fractures and seismological data locations focal mechanisms shear wave splitting on the opening of a 6 5km long nnw sse fracture system were collected the fracture system reflected the surface deformation associated to the emplacement of a blade like dyke at shallow depth seismic activity occurred only at the southern tip of the fracture system and at about 1 1 5km depth i e at the interface between the less stiff clay basement and the stiffer volcanic pile structural data indicate that fractures formed in response to an ene wsw striking 3 hmin in contrast the nnw sse compressive structures which developed only at the southern tip of the main fracture system were related to an ene wsw hmax the inversion of focal mechanisms shows a thrust type deformation related to an ene wsw striking 1 hmax the association of compressive structures is consistent with experimental models of dykes stopping at a less stiff stiffer interface s wave splitting parameters have been measured during the fracture system propagation no change was observed in the qs1 polarization eigendirections ne sw while the td values seemed to vary with time the results of seismological and structural analyses suggest that the dyke stopping mechanism produces i a seismic swarm associated to a local compressive stress field and ii dyke induced stress generating shallow aligned secondary fractures eda cracks

geostatistical inverse modeling for the characterization of aquitard heterogeneity using long term multi extensometer data abstract the classical aquitard drainage model compac was used to simulate the deformation of a one dimensional vertically heterogeneous aquitard i e heter compac by coupling heter compac with the quasi linear geostatistical inversion approach the vertical heterogeneities of hydraulic conductivity k v elastic specific storage s ske and inelastic specific storage s skp fields could be characterized with the availability of long term multi extensometer data the methodology was first tested through a group of ten synthetic cases with randomly generated k v s ske and s skp fields results of the synthetic cases revealed that a geostatistical model could characterize the variability of aquitard hydraulic parameter fields and yields improved fits of simulated versus observed zone deformation than a geological model that treats each zone to be homogeneous subsequently the methodology was applied to a research site situated in changzhou city jiangsu province china where long term deformation behaviors of the strata within the aquifer aquitard system have been monitored vertical heterogeneities of k v s ske and s skp fields of the investigated aquitard at the site were characterized using the quasi linear geostatistical approach the correlation length of the three fields that yielded the best quality fit was assessed to be approximately 50 m and the fitting quality was slightly improved in comparison with that produced from calibrating a geological or zonation model through monte carlo analysis of aquitard deformation utilizing the inversed parameters and corresponding uncertainties the investigated aquitard is estimated to have compacted 914 8 42 6 mm before the rise in groundwater levels in adjoining aquifers

seismic vs geodetic moments at mt etna volcano a tool for a rapid understanding the eruptive behaviour abstract the seismic to geodetic moment ratio mo mg related to seven magma intrusion episodes occurring at mt etna volcano between 1981 and 2008 are considered the lateral eruptions show a moment ratio of 0 04 0 06 meaning that only about 5 of the stress energy accumulated with ground deformation was released by earthquakes significantly higher values instead characterized vertical 0 25 0 50 and non eruptive 0 17 dike intrusions this paper proposes a simple relationship in order to estimate during the early phases of an eruption the intruding magma volumes by the cumulative seismic moment of the ongoing seismicity and elapsed time

an investigation into shallow borehole tiltmeters shallow borehole tiltmeters are frequently used for ground deformation monitoring in volcanic areas where they are usually installed within a few meters of the surface a major problem concerns the noise affecting the installation at shallow depth where large tilt and strain are caused by temperature effects the long term stability of these instruments and the best shallow depth of installation in terms of best cost benefit are the crucial points we conducted an experiment in order to compare the signals of three shallow borehole electronic tiltmeters installed in the same place at different depths we verified the signal reliability in revealing the long term slow deformation and looked into the reduction of the temperature effects with depth we present three years of data and discuss the limits and the advantages of the different installation depths

sea level change glacial rebound and mantle viscosity fornorthern europe northwestern europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the last glacial maximum models for this rebound and associated sea level change require a detailed knowledge of the ice sheet geometry including the ice thickness through time existing ice sheet reconstructions are strongly model dependent and inversions of sea level data for the mantle response may be a function of the model assumptions thus inverse solutions for the sea level data are sought that include both ice and earth model parameters as unknowns sea level data from fennoscandia the north sea the british isles and the atlantic and english channel coasts have been evaluated and incorporated into the solutions the starting ice sheet for fennoscandia is based on a reconstruction of a model by denton hughes 1981 that is characterized by quasi parabolic cross sections and symmetry about the load centre both global northwestern europe as a whole and regional subsets of the data solutions have been made for earth model parameters and ice height scaling parameters the key results are as follows 1 the response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across scandinavia the north sea and the british isles 2 this response can be adequately modelled by an effective elastic lithosphere of thickness 65 85 km and by an effective upper mantle viscosity from the base of the lithosphere to the 670 km depth seismic discontinuity of about 3 4 1020 pa s the effective lower mantle viscosity is at least an order of magnitude greater 3 the ice thickness over scandinavia at the time of maximum glaciation was only about 2000 m much less than the 3400 m assumed in the denton hughes model 4 the ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin

dynamic inversion of ground deformation data for modelling volcanic sources etna 1991 93 the 1991 93 etna eruption that represented the most important recent eruptive event both in terms of duration 472 days and total volume of erupted lava ca 250 106 m caused marked ground deformation measured by using different geodetic techniques such as edm gps levelling and tiltmetry an inversion termed dynamic because it took into account the sequence of events considering both the separate and cumulative effects of two sources a shallow tensile crack and a deeper ellipsoidal deflating source was performed it was based on 163 data collected by the different techniques plus 2 geometrical conditions for constraining the geometry of the crack on the surface the final solution furnished a good fit for all measurements defining a shallow tensile crack located inside the volcanic edifice which represents the effect of the intrusion and a depressuring body with centre at ca 3000 m b s l which could represent the centre of a generalized and more complex deflation of the volcanic edifice during the course of the eruption

geodetic analysis of dike intrusion and motion of the magma reservoir beneath the summit of kilauea volcano hawaii 1970 1985 we use leveling and trilateration data collected on kilauea volcano to constrain the location of deformation sources caused by magma accumulation intrusion and eruption for the 13 inflationary epochs examined combinations of an expanding point source and one or two opening rectangular dislocations mimic inflation of the summit reservoir and formation of dike s respectively the combined model adequately accounts for the deformation data and is consistent with the seismicity observed during each epoch for 10 deflationary epochs however the data require only a contracting point source confidence in these results is gained by noting that locations of the sources of both inflation and deflation are coincident within the observed uncertainties of the data the function of network geometry and the inversion procedure it appears therefore that magma accumulation at kilauea volcano may be characterized by the growth of dikes during inflation of the summit reservoir drainage of the reservoir on the other hand is not accompanied by significant closure of dikes in contrast to previous studies e g fiske and kinoshita 1969 dvorak et al 1983 that do not include the dislocation or dike growth component of summit magma accumulation and concluded that the source of inflation migrates over a 5 km2 area we find that a single magmatic reservoir source accounts for data collected during all inflationary and deflationary epochs results which compare favorably with those obtained from the point ellipsoid model can be used to estimate the distribution of stresses within the volcano in the near field of the source

geometry of the september 1971 eruptive fissure at kilauea volcano hawaii a three dimensional model has been used to estimate the location and dimensions of the eruptive fissure for the 24 29 september 1971 eruption along the southwest rift zone of kilauea volcano hawaii the model is an inclined rectangular sheet embedded in an elastic half space with constant displacement on the plane of the sheet the set of best model parameters suggests that the sheet is vertical extends from a depth of about 2 km to the surface and has a length of about 14 km because this sheet intersects the surface where eruptive vents and extensive ground cracking formed during the eruption this sheet probably represents the conduit for erupted lava the amount of displacement perpendicular to the sheet is about 1 9 m in the middle range of values measured for the amount of opening across the september 1971 eruptive fissure the thickness of the eruptive fissure associated with the january 1983 east rift zone eruption was determined in an earlier paper to be 3 6 m about twice the thickness determined here for the september 1971 eruption because the lengths 12 km for 1983 and 14 km for 1971 and heights about 2 km of the sheet models derived for the january 1983 and september 1971 rift zone eruptions are nearly identical the greater thickness for the january 1983 eruptive fissure implies that the magma pressure was about a factor of two greater to form the january 1983 eruptive fissure because the september 1971 and january 1983 eruptive fissures extent to depths of only a few kilometers the region of greatest compressive stress produced along the volcano s flank by either of these eruptive fissures would also be within a few kilometers of the surface previous work has shown that rift eruptions and intrusions contribute to the buildup of compressive stress along kilauea s south flank and that this buildup is released by increased seismicity along the south flank because south flank earthquakes occur at significantly greater depths i e from 5 to 13 km than the vertical extent of the 1971 and 1983 eruptiv fissures the depth of emplacement of these eruptive fissures cannot be the main factor in controlling the hypocentral depths of south flank earthquakes two possible explanations for the occurrence of south flank earthquakes in the depth range of 5 13 km are 1 a deeper pressure source possibly related to deeper magma storage within the rift zone and 2 a lowstrength region located between 5 and 13 km beneath kilauea s south flank possibly at the interface between oceanic sediments and the base of the hawaiian volcanics

experimental study of the interplay between magmatic rift intrusion and flank instability with application to the 2001 mount etna eruption mount etna volcano is subject to transient magmatic intrusions and flank movement the east flank of the edifice in particular is moving eastward and is dissected by the timpe fault system the relationship of this eastward motion with intrusions and tectonic fault motion however remains poorly constrained here we explore this relationship by using analogue experiments that are designed to simulate magmatic rift intrusion flank movement and fault activity before during and after a magmatic intrusion episode using particle image velocimetry allows for a precise temporal and spatial analysis of the development and activity of fault systems the results show that the occurrence of rift intrusion episodes has a direct effect on fault activity in such a situation fault activity may occur or may be hindered depending on the interplay of fault displacement and flank acceleration in response to dike intrusion our results demonstrate that a complex interplay may exist between an active tectonic fault system and magmatically induced flank instability episodes of magmatic intrusion change the intensity pattern of horizontal flank displacements and may hinder or activate associated faults we further compare our results with the gps data of the mount etna 2001 eruption and intrusion we find that syneruptive displacement rates at the timpe fault system have differed from the preeruptive or posteruptive periods which shows a good agreement of both the experimental and the gps data therefore understanding the flank instability and flank stability at mount etna requires consideration of both tectonic and magmatic forcing

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

three dimensional numerical modeling of slip rate variations on normal and thrust fault arrays during ice cap growth and melting 1 changes in the volumes of ice caps considerably alter the stress state of the lithosphere by generating a transient signal that is added to the tectonic background stress field these stress field changes in turn affect crustal deformation and in particular the slip behavior of existing faults here we use three dimensional finite element models to investigate how arrays of normal and thrust faults near a growing and subsequently melting ice cap are influenced in their slip evolution the results show that regardless of fault dip both types of faults experience a decrease in their slip rate during ice cap advance and an increase in their slip rate during ice cap retreat if they are located beneath the ice cap in contrast faults outside the ice cap that are loaded on their footwall or hanging wall only show the opposite pattern their slip rate increases during glacial loading and decreases during subsequent unloading if the load is located along strike of the fault that is at one of its tips the slip behavior of normal and thrust faults is different the normal fault shows a slip rate increase during unloading the thrust fault during loading our results explain the location and timing of deglaciation induced paleoearthquakes in scandinavia and the contrasting slip histories reported from normal faults in the basin and range province which are located at different positions relative to the former yellowstone ice cap more generally our findings imply that a uniform slip behavior of faults in formerly glaciated regions should not be expected

time correlation analysis of the microseismicity of the low eastern flank of mt etna volcano italy an analysis in terms of time correlation functions has been applied to the time distribution of microseismicity we considered the single station detections m 2 recorded by each one of the four working stations of the network of the osservatorio sismologico di protezione civile acireale catania located on the active faults systems timpe of the low eastern flank of mt etna information obtained on the time regularity of seismic crisis and on the time correlation between the activities recorded by different stations allowed a better understanding of the role of the two main structures the timpa di santa tecla is the most seismogenic structure in the area and probably played a role in the magma transfer process for the 1989 eruption modifications of the local stress field by actions of this feature may have produced gravitational instability along a second structural system the timpa di s leonardello with a time delay of about 100 days by contrast magma penetration associated with the larger eruption of 1991 1993 had a deeper rise system and had no effect on local stress conditions consequently there was no correlation between volcanism and seismicity

ground deformation monitoring at mt etna evidence for dyke emplacement and slope instability ground deformation monitoring at mount etna has successfully enabled the sub surface paths of two shallow feeder dykes to be traced and their dimensional parameters depths and departures from the vertical to be constrained determinations of horizontal movement have recorded the displacement by 3 6 m maximum of a rim segment of the valle del bove flank caldera due to dilation associated with dyke emplacement adjacent to the rim over the period 1981 to 1989 small scale collapse along this rim segment associated with the opening of the 1989 fissure points to increasing slope instability and highlights the potential for major failure and debris avalanche generation

imaging composite dike propagation etna 2002 case 1 late on the night of 26 october 2002 a dike intrusion started suddenly at mount etna producing intense explosive activity and lava effusion on the southern flank five to six hours afterward a long field of eruptive fractures propagated radially along the northeastern flank of the volcano producing marked variations at the permanent tilt network the dike propagation velocity was inferred by the associated seismicity we modeled the temporal evolution of the continuously recorded tilt data both during the vertical dike propagation on the high south flank on 26 october and during the radial propagation along the northeast flank between 27 and 28 october the reproduction of the recorded tilt signal allowed us to describe the geometry and characteristics of the two dikes in greater detail than the previous static inversion we deduced that the eruption was characterized by an unusual composite mechanism clearly showing a transition from a nearly pure opening mode displacement to a mechanism characterized by an equally strong normal dip slip component and a smaller left lateral strike slip component in this study we demonstrate the interaction between the final segment of the dike and a preexisting structure that was reactivated in response to the intrusion we show that tilt and its modeling represent a powerful tool to verify and constrain dike intrusions in detail

evidence of a dyke sheet intrusion at stromboli volcano inferred through continuous tilt a tiltmeter installed in the northern sector of the island of stromboli aeolian archipelago tyrrhenian sea recorded a co seismic offset at the time of the main shock ml 3 7 of the 7 november 1994 swarm located 5 km north of the island during the three months following this event a transient tilt anomaly which was interpreted as due to a lateral intrusion and modelled through a dyke sheet dislocation was recorded the tilt data were used in an analytical inversion based on a propagating tensile source with length and width increasing in time the final result is consistent with the tectonic and structural framework of the volcano area

analysis of surface deformation data kilauea volcano hawaii october 1966 to september 1970 a least squares inversion technique has been applied to surface displacement measurements made at kilauea volcano hawaii in an attempt to locate centers of intrusive activity utilizing analytic expressions for the displacement field arising from dilatational sources in an elastic half space this technique allows for the simultaneous inversion of level tilt and horizontal distance measurements in terms of the location and volume of the intrusive body a variety of simple elastic model geometries representing possible shapes for intrusive bodies in the summit region of kilauea were examined none of the model geometries considered significantly improved the quality of the model fit to the available data over that obtained by a point source model calculations based on elastic models to consecutive level surveys were compared to available tilt data and horizontal distance measurements these comparisons indicate occasional departures from ideal elastic behavior the departure of measured tilt patterns from calculated tilt values may be the result of earthquake activity or episodic block movements superimposed on larger elastic displacements the departure of measured and calculated horizontal measurements reveals a gradual north south extensional strain across the summit caldera of kilauea in addition to the elastic uplift and subsidence patterns determined from level surveys a minimum estimate for the magma supply rate to kilauea is provided by the elastic models to the level data the average rate for the period from october 1966 to september 1970 was 0 07 km3 per year

magma reservoir subsidence mechanics theoretical summary and application to kilauea volcano hawaii an analytic model has been developed for the prediction of the three dimensional deformation field generated by the withdrawal of magma from a sill like storage compartment during an intrusion or eruption cycle the model is based on the work of berry and sales 1961 1962 and predicts the vertical displacement components over the areal plane model parameters are the depth of burial h the intrusion half width a the intrusion half length b the thickness of the magmatic interior at the moment of melt withdrawal tm and the planform aspect ratio a b the products of the model include areal deformation maps systematic variation in model parameters within the context of kilauea volcano hawaii have revealed that circular and elliptical deformation patterns result from the collapse of draining rectilinear intrusions at depth moreover the geometric parameters of a storage compartment may interact in complex ways to produce similar deformation patterns the model has been applied to kilauea volcano for three periods of pronounced summit subsidence 1 1921 1927 bracketing the steamblast eruptive phases of 1924 2 june 1972 to december 1972 and 3 december 1972 to may 1973 application of the model requires the simultaneous optimization of five predicted deformation features with respect to field measurements and the derivative deformation maps 1 the vertical displacement maxima 2 the vertical displacement gradients over the areal plane 3 the lateral extent of the deformation field 4 the aspect ratio of the subsidence pattern and 5 the strike of the major axis of the deformation field the constrained geometries and volumes of the inferred collapsed storage cavities for each period are 1 1921 1927 depth 3 km a 1500 m b 4500 m tm 20 m v 540 106 m3 2 june 1972 to december 1972 depth 3 3 km a 600 m b 2000 m tm 1 m v 4 8 106 m3 and 3 december 1972 to may 1973 depth 2 2 km a 500 m b 1612 m tm 1 m v 3 2 106 m3 for 2 and 3 calculated magmatic thicknesses tm happen to be in the range 3 48 0 15 m of measurements for sill like bodies in deeply dissected hawaiian shield volcanoes the fits obtained between calculated and observed deformation patterns allow quantification of the location overall dimensions orientation and volume of the discrete still molten interior of sill like compartments from which magma is tapped during eruption or intrusion

static shear crack with a zone of slip weakening summary as a prologue to our investigation of the nature of sequences of earthquake events we investigate the problem of a finite 2 d antiplane static shear crack for two different models of a slip weakening zone near the crack tip the crack is imbedded in an infinite elastic medium in the limit as the size of the slip weakening zone vanishes the problem becomes one considered by knopoff for a finite shear crack in a uniform field we solve for the displacement and the stress for representative values of dimension less stress drop for the two models our results indicate that these quantities are not strongly dependent on the details of the constitutive relation in the transition zone with decreasing dimensionless stress drop the crack length increases monotonically and the size of the slip weakening zone decreases monotonically these results can be interpreted as the critical conditions for the further extension of an initial earthquake fault in this interpretation these results imply that the initiation of an earthquake is not only controlled by the stress drop on the fault plane but also by the size of a pre existing fracture an earthquake can be initiated from a small pre existing fracture if the stress drop on the initial fault is large enough conversely it can be initiated under the influence of a lower stress drop if the initial fault is large enough no solution to the static problem exists if the dimensionless stress drop is greater than a certain value this maximum dimensionless stress drop corresponds to a minimum crack length for which the slip weakening zone occupies the entire crack in the small dimensionless stress drop or small scale yielding limit the dimensionless half length of the crack is inversely proportional to the square of the dimensionless stress drop the dimensionless length of the slip weakening zone has been calculated we generalize the formula for the effective shear fracture energy obtained by palmer rice and andrews to include the effect of the size of the slip weakening zone our results indicate that because the influence of the size of of the slip weakening zone has not been taken into account earlier estimates of the effective shear fracture energy may have been overestimated by as much as 67 per cent

fast deformation processes and eruptive activity at mount etna italy the seismic and deformation patterns observed on mount etna before and during the 1991 1993 eruption the third largest since the seventeenth century in terms of lava volume are consistent with the regional tectonic framework of eastern sicily the pattern of the stress field acting on the intermediate and lower crust was defined at the local scale by focal mechanisms of microearthquakes occurring at depths between 10 and 25 km beneath the volcano they provide evidence for a strike slip compressional stress regime with the maximum compressive component acting approximately n s the fault plane solutions and the spatial and temporal distribution of seismicity indicate that usually sinistral shear ruptures occur along approximately ne sw trending fault zones while dip slip ruptures affect approximately nnw sse trending fault zones the latter include the avenues along which magma ascended during the 1991 1993 eruption seismic observations indicate a local inversion of the stress field acting on the upper crust depth 10 km underlying mount etna which was initiated less than 2 months before the eruptive event and disappeared with its end this is consistent with a local tensile regime that favored the magma ascent through the shallow crust the events preceding the eruption and accompanying its onset tilt anomalies and seismic swarms and those occurring shortly after its beginning a mainshock aftershock seismic sequence and associated coseismic tilts provide important evidence for understanding the dynamics of the two main volcano tectonic structures ne sw and nnw sse trending fault zones and associated intrusive mechanisms on etna the shape and location of the eruption feeding dike have been modeled from ground deformation data this approximately nnw sse modeled dike the seismicity and the position of the fractures are consistent with the regional stress field characterized by 1 oriented approximately n s the geophysical data presented and analyzed in the present paper strongly suggest an overall regional tectonic control as well as an active role for the intruding magma in the dynamics of the volcano

mt etna volcano modelling of ground deformation patterns of recent eruptions and considerations on the associated precursors abstract the study of the ground deformation associated with the recent eruptions of the etna volcano 1981 1989 1991 93 furnished the opportunity to observe different behaviour relating to the eruptive activity and suggested different feeding and penetration mechanisms inside the volcano edifice in particular the analytical modelling of geodetic data was applied to study the strain sources of these eruptions by the application of single and multiple source models i e composed of two single sources in particular a single tensile dislocation was used to model the se fracture associated with the 1989 eruption a double tensile dislocation was adopted to interpret and model the deformation pattern of the 1981 eruption a double source composed of a tensile dislocation for the final eruptive fracture and a depressuring body for the deflation during the eruption course was considered for the 1991 93 eruption the results of this modelling show that however the final uprising system i e the tensile mechanisms inside the volcano edifice involved the same structure oriented approximately nnw sse this structure was activated by different eruption mechanisms with associated different deformation patterns during these three recent eruptions a review of the methodologies applied and main results obtained in modelling of different sources and mechanisms is presented here the analysis of the deformation data and the performed modelling evidence that the associated precursors can strongly change for the different eruptions in addition the implications both in terms of how the volcano works and in terms of ground deformation precursors are discussed

near field modifications of stress induced by dyke injection at shallow depth summary the deformation and stress fields accompanying dyke injection in rift zones are described in terms of a vertical crack opening in response to internal overpressure in plane strain configuration previous numerical computations of the displacement field induced by shallow dykes are found to be affected in some cases by significant distortion mainly due to the limited extension of the computational domain difficulties in handling the singularities in the proximity of the free surface and an incorrect choice of the reference frame in particular it is found that no subsidence can be ascribed to the mere opening of a tensile crack in a homogeneous elastic half space if analytical constant dislocation models are employed surface displacements compare reasonably well with crack model solutions if the upper tip is not too shallow however constant dislocation solutions present unphysical singularities along the tips which distort significantly the near field stress pattern with respect to crack solutions if the principal stress axes are computed from crack models a broad region is found on both sides of the dyke where the induced stress has a nearly vertical intermediate axis while the compressive axis is normal to the dyke plane strike slip earthquakes are expected to prevail in this region above the upper crack tip a small region is present where the tensile stress is dominant and the intermediate stress is still vertical in the proximity of the free surface typically within a few tens of metres of it induced tensile stresses are greater than the lithostatic pressure open fissures might then develop in cohesionless soil or pre faulted rock the induced pressure in the host rock is found to be negative suction in the proximity of the ground surface and positive at greater depth fluid flow within the aquifers can be significantly altered by this induced overpressure and by the anisotropic modification of the pre existing permeability according to the modified coulomb failure criterion in the short term the shallower region characterized by suction is strengthened while the deeper pressurized region is weakened these results can explain in a straightforward way the abundance of strike slip focal mechanisms in volcanic areas the switch between tensional and compressional axes inferred from focal mechanisms of earthquakes in connection with a dyke injection episode on mount etna en echelon fracture systems observed at piton de la fournaise above the feeding dyke and precursory geochemical anomalies

surface deformation in volcanic rift zones abstract the principal conduits for magma transport within rift zones of basaltic volcanoes are steeply dipping dikes some of which feed fissure eruptions elastic displacements accompanying a single dike emplacement elevate the flanks of the rift relative to a central depression concomitant normal faulting may transform the depression into a graben thus accentuating the topographic features of the rift if eruption occurs the characteristic ridge trough ridge displacement profile changes to a single ridge centered at the fissure and the erupted lava alters the local topography a well developed rift zone owes its structure and topography to the integrated effects of many magmatic rifting events to investigate this process we compute the elastic displacements and stresses in a homogeneous two dimensional half space driven by a pressurized crack that may breach the surface a derivative graphical method permits one to estimate the three geometric parameters of the dike height inclination and depth to center and the mechanical parameter driving pressure rock stiffness from a smoothly varying displacement profile direct comparison of measured and theoretical profiles may be used to estimate these parameters even if inelastic deformation notably normal faulting creates discontinuities in the profile geological structures open cracks normal faults buckles and thrust faults form because of stresses induced by dike emplacement and fissure eruption theoretical stress states associated with dilation of a pressurized crack are used to interpret the distribution and orientation of these structures and their role in rift formation

impulsive tilt variations on mount etna volcano 1990 1993 abstract this study was focussed on the analysis of the fast ground deformations impulsive anomalies recorded at the mt etna tilt array from 1990 to 1993 a period that preceded accompanied and followed the 1991 1993 eruption these fast deformations were recorded as transient anomalies ranging from a few hours to days 1 2 observed contemporaneously at several tilt stations and characterized by variations ranging from one to tens of microradians the signals evidenced volcanic dynamics characterized by tilt anomalies during the non eruptive periods 1990 1993 the pre eruptive period november december 1991 the beginning of the eruption 14 15 december 1991 and the eruption course 1992 in particular pre seismic co eruptive and co seismic anomalies were recorded during the pre eruptive period and the eruption onset in these cases interpretations of the phenomena and comparison to modelling studies are provided furthermore tilt variations affecting the global volcanic edifice were also observed one year before the eruption when they were followed by seismicity and during the eruption course without seismicity we interpreted this last class of tilt variations as due to the push of the magma uprising along the main nnw sse structure crossing mt etna