bayesian source inference of the 1993 1997 deformation at mount etna italy by numerical solutions summary deformation data collected at mount etna from 1993 to 1997 show that the inflation of the volcano edifice is accompanied by instability of the eastern flank we propose a 3 d finite element model including topography and lateral variations of elastic constants source parameters of the inflating source are constrained by a direct search followed by an appraisal stage of the sampled solutions the instability of the eastern flank is addressed using a kinematic approach consisting of a rigid body translation over a prescribed area the aim is to evaluate how source parameters are affected by sliding of the eastern flank when sliding is accounted for the inferred source location shifts 1 km se and its strength decreases by 20 per cent

dike deflection modelling for inferring magma pressure and withdrawal with application to etna 2001 case abstract we studied the stress effects of the topography load on dike propagation by considering the results from analogue experiments in addition we refined the results by applying numerical simulations using the finite element method fem in order to also consider the medium rheology and real topography we investigated the dike deflection observed during the final dike emplacement accompanying etna s 2001 eruption we cross related the information on the position of the dike from ground deformation modelling with the numerical simulation results with the aim of estimating the final excess pressure of the dike when it started to deflect which proved to be about 4 8 mpa assuming that the pressure decreases linearly with the volume of magma moving from the chamber into the dike we estimated 7 15 mpa as the initial overpressure accumulated at the intermediate magma chamber before its breakout although the previous modelling overestimated the stress the approach presented here leads to infer a compatible stress with the strength of the rocks

effects of crustal layering on the inversion of deformation and gravity data in volcanic areas an application to the campi flegrei caldera italy 1 we study the effects of crustal layering on ground displacements and gravity changes due to a spheroidal expanding source soft superficial layers affect the deformation pattern giving an apparent shallower source if layering is not taken into account the ratio of horizontal to vertical displacements biasing the source shape and the subsurface mass redistribution effects on gravity changes retrieved intrusion density is biased toward very low values if the source is modelled as a penny shaped crack point and finite in a homogeneous half space and the resulting density misestimate can lead to a possibly incorrect assessment of volcanic hazard as an application we consider the 1982 1984 campi flegrei unrest we show that the large discrepancy between densities of spherical and penny shaped sources given in the literature and obtained inverting ground displacement and gravity data in a homogeneous half space is at least partially a consequence of the homogeneous half space assumption

modeling of surface deformation in volcanic areas the 1970 1972 and 1982 1984 crises of campi flegrei italy campi flegrei is a densely inhabited volcanic area within a caldera 12 14 km in diameter immediately west of naples italy in 1970 1972 and in 1982 1984 campi flegrei experienced considerable ground surface deformation producing a bulge about 3 5 m high at its peak in the two inflation episodes the point of maximum uplift did not change coinciding with the caldera center about which the displacements exhibited radial symmetry the 1982 1984 uplift was accompanied by considerable seismic activity gravity changes have been interpreted as reflecting the occurrence of a subvertical magmatic intrusion volcanological petrological and geophysical data point to the existence of a shallow magma chamber just beneath the center of the caldera we assume that the observed surface displacements are the response of an essentially elastic medium to a pressure increase in the magma chamber static deformation is calculated by using a finite element method assuming axial symmetry around a vertical axis through the caldera center the role played by various components of the model geometry boundary conditions elastic properties is analyzed it is shown that models assuming uniform elasticity are inadequate therefore the major volcanotectonic features as well as the influence of temperature and pressure on the elastic properties are taken into account the results of various more complex models are presented it is suggested that a progressively fractured zone whose size and shape depend also on the possible occurrence of magmatic intrusions may explain the observed surface displacements and the other data collected at campi flegrei it is suggested that the 1970 1972 uplift was possibly accompanied by larger scale changes in the stress field

a horizontal crack in a layered structure satisfies deformation for the 2004 2006 uplift of campi flegrei 1 sources responsible for volcanic unrest produce characteristic surface deformation given a sufficient number of distributed observation points inversion is the preferred procedure for retrieving the source parameters of location and volume or pressure change most often the solutions have been for point sources embedded in a homogeneous half space recent work indicates that layered structures particularly those with soft superficial layers significantly perturb the deformation pattern compared with that for the homogeneous medium we apply the methods of l crescentini and a amoruso to data for the most recent mini uplift in the campi flegrei caldera and show that models using a homogeneous medium cannot adequately fit all the data incorporating a layered structure appropriate for campi flegrei allows a significantly better fit avoiding characteristic discrepancies which are revealed by a synthetic test failure to use such structure results in incorrect source parameters possibly leading to misleading geophysical interpretations

modelling of surface ground deformations in the phlegraean fields volcanic area italy a preliminary finite elements model of the ground deformations observed at phlegraean fields is proposed the model assumes an oblate spheroid magma chamber at the depth of 5 4 km with major semiaxis of 1 5 km and minor semiaxis of 0 75 kin the dimensions of the magma chamber have been evaluated by using a thermal model based on the assumptions that a progressively cooling huge magmatic body is responsible for the volcanic activity at phlegraean fields in the last 35 000 years surface deformations caused by an overpressure of 30 mpa in the magma chamber have been calculated constant and temperature dependent elastic parameters of the surrounding medium have been considered vertical displacements of the order of those presently observed at phlegraean fields can be obtained only with temperature dependent elastic properties of the medium

thermal activity and ground deformation at phlegrean fields italy precursors of eruptions or fluctuations of quiescent volcanism a contribution of geochemical studies the ground uplift that occurred at phlegrean fields during the crisis of 1982 1984 is analyzed by taking into account the volcanological history of the area the available geophysical information and the data obtained through our systematic geochemical study the chemical composition of the products of a unique historical eruption in a d 1538 displays a strong evolved character and fits the hypothesis of a progressive reduction in size of the magma body which probably behaved as a closed system the bicarbonate contents of the thermal waters in the area has increased with time suggesting inputs of carbon dioxide into the shallow aquifers temperatures at the fumaroles have not changed for at least a hundred years indicating that boiling aquifer at depth feeds the surface manifestations significant variations in the ratios h2s co2 and h2 n2 observed at the same time suggest that both the rate of ground uplifting and the increase of seismic energy release may be related to the fluctuation of a convective flow from a deep heat source tectonic activity can modify the permeability of deep structures and thereby trigger increased activity in surface manifestations

magnetotelluric survey in the bradyseismic area of phlegraean fields a magnetotelluric survey was carried out in order to contribute to the definition of the deep structure of the phlegraean fields area affected by the bradyseismic crisis begun in the summer 1982 in a preliminary campaign carried out in autumn 1983 the mt measurements were made in eight sites located between 0 3 and 5 km from the harbour of pozzuoli and affected by different degrees of uplift

accurate fault mechanism determinations for a 1984 earthquake swarm at campi flegrei caldera italy during an unrest episode implications for volcanological research we have analyzed 42 microearthquakes 1 ml 3 that occurred at campi flegrei volcanic area during an intense swarm like activity more than 500 events in half a day in the last period of strong ground uplift 1982 1984 focal mechanisms of these earthquakes have been computed by a probability method which uses p wave polarity and s wave polarization data composite focal mechanisms for different groups of earthquakes have also been computed by the same technique results show a well defined fault plane in agreement with the elongation of the epicentral pattern the orientation and dip of this fault plane together with other observations about hypocenter locations and focal mechanisms of the whole seismicity accompanying the ground uplift episode suggest the presence of an elliptical fracture system at the caldera center this fracture system dipping toward the center of the caldera should represent the limit of the most recent caldera collapse which is also indicated by a negative bouguer gravity anomaly moreover an important differential feature among various groups of earthquakes has been shown namely a rotation up to about 30 of the strike of the compressive stress axis between the easternmost and the westernmost events the resulting pattern indicates that the axis is always oriented towards the town of pozzuoli which roughly represents the very center of the caldera and also the center of symmetry of the ground deformation these observations strongly suggest that earthquakes are generated by the variation of the stress field associated with the deformation along prefractured zones because of their greater weakeness this study provides then the first direct evidence that both seismicity and ground deformations have a common origin

a fluid filled fracture as possible mechanism of ground deformation at phlegraean fields italy two uplift episodes have recently been recorded at phlegraean fields a volcanic region near naples south central italy the first episode occurred in 1970 and lasted up to 1972 the second has begun at the end of 1982 and is still in progress an attempt to model the ground deformations which occurred during the 1970 1972 event is made in this paper the source has been assumed to be a two dimensional fluid filled fracture similar to a sill a good fit with experimental data has been obtained for a short 1 2 km long shallow 3 km deep source and a driving pressure ranging from 60 to 210 bars rigidity values have been fixed at 3 5 4 0 1010 c g s with poisson ratio equal to 0 3 this solution which differs from previous approaches bymogi 1958 andwalsh anddecker 1971 is non unique but the present results are in good agreement with observed horizontal and vertical displacements notwithstanding the oversimplification made in assuming a homogeneous elastic semi infinite medium the predicted stress field seems to be in agreement with the fault plane solutions and the pattern of epicenters determined for the uplift seismic swarm episode that is still in progress

intrusion and deformation at campi flegrei southern italy sills dikes and regional extension 1 the campi flegrei volcanic district in southern italy has been uplifted since 1968 by a net maximum of 3 m during the intervals 1968 1972 and 1982 1984 the uplift represents a permanent deformation against a background rate of subsidence of about 17 mm a 1 previous models have reproduced the observed vertical deformation but not the full pattern of horizontal movements the 1982 1983 deformation is here reanalyzed in terms of a penny shaped sill on its own with a tabular surface protrusion or in an extensional stress field it can be explained best by the intrusion of a sill of 0 03 0 04 km3 at a depth of 2 75 km in a crust that is being stretched ese wnw at a strain rate of about 5 6 10 5 a 1 the sill s volume is similar to the common volumes of campi flegrei s eruptions since the neapolitan yellow tuff nyt caldera was formed 15 6 ka ago this similarity and the permanent nature of the uplift favor magmatic intrusion as the primary source of unrest sill formation may thus reflect the spreading of magma at a level of neutral buoyancy or along lateral discontinuities in the crust the southern part of the caldera has been shielded from post nyt eruptions despite some 33 m of permanent uplift since roman times precursors to eruptions may thus be related not to caldera wide uplift but to the preceding conditions that determine whether magma ascends beneath the southern part of the caldera favoring sill intrusion or elsewhere favoring an eruption

magma chamber volume changes associated with ring fault initiation using a finite sphere model application to the aira caldera japan abstract we have derived an analytical solution expressing the magma chamber volume change required for ring fault caldera initiation in terms of a finite sphere model we consider the conditions by which magma chamber contraction volume reduction could contribute to the initiation of a ring fault at the surface above the chamber using the elastic plastic theory of host rock behaviour the model does not consider underpressure pressure less than lithostatic in the chamber but only magma chamber volume reduction or shrinkage the model is heuristic in the sense that we do not explore the detailed mechanical condition for the volume reduction apart from its being related to magma flow out of the chamber but rather focus on the consequences of the reduction for ring fault initiation and dip the solution obtained for the finite sphere model consists of a leading term that is proportional to the cube of the magma chamber depth and a second term that is proportional to the cube of the magma chamber radius the second term reflects explicitly the effects of a finite source radius whereas the first term corresponds to a solution for a point source model this follows because in a point source model the magma chamber radius is zero so that the second term drops out the equation that plays the key role in obtaining this solution is a linear function relating the radius of the caldera to the magma chamber depth the proportionality coefficient of this equation is dimensionless and depends not only on the elastic constants of the medium but also on the depth d and radius a of the magma chamber given by e a d in addition because this coefficient controls a geometric parameter related to the overall form of the ring fault our results indicate that the ring fault shape and size is decided by the magma chamber depth and size as well as by the host rock elastic properties and angle of internal friction the results indicate that the associated ring fault is inward dipping and that the magma chamber radius can be estimated from the fault radius and dip we applied the analytical solution to the ring fault of the aira caldera in southern kyushu japan the calculations indicate that the aira ring fault could have been initiated at the surface as a result of 2 8 reduction in the volume of a magma chamber with a radius of 4 7 km and at a depth of 9 1 km these results agree with independent information on the aira magma chamber we conclude that the present solution yields useful first order information on magma chambers associated with ring faults

eruptive versus non eruptive behaviour of large calderas the example of campi flegrei caldera southern italy caldera eruptions are among the most hazardous of natural phenomena many calderas around the world are active and are characterised by recurrent uplift and subsidence periods due to the dynamics of their magma reservoirs these periods of unrest are in some cases accompanied by eruptions at campi flegrei caldera cfc which is an area characterised by very high volcanic risk the recurrence of this behaviour has stimulated the study of the rock rheology around the magma chamber in order to estimate the likelihood of an eruption this study considers different scenarios of shallow crustal behaviour taking into account the earlier models of cfc ground deformation and caldera eruptions and including recent geophysical investigations of the area a semi quantitative evaluation of the different factors that lead to magma storage or to its eruption such as magma chamber size wall rock viscosity temperature and regional tectonic strain rate is reported here for elastic and viscoelastic conditions considering the large magmatic sources of the cfc ignimbrite eruptions 400 2 000 km3 and a wall rock viscosity between 1018 and 1020 pa s the conditions for eruptive failure are difficult to attain smaller source dimensions a few cubic kilometres promote the condition for fracture eruption rather than for the flow of wall rock we also analyse the influence of the regional extensional stress regime on magma storage and eruptions and the thermal stress as a possible source of caldera uplift the present study also emphasises the difficulty of distinguishing eruption and non eruption scenarios at cfc since an unambiguous model that accounts for the rock rheology magma source dimensions and locations and regional stress field influences is still lacking

axi symmetric deformation of a thermo poro elastic half space inflation of a magma chamber summary the deformation observed at phlegraean fields italy during the recent 1982 1984 crisis is interpreted in terms of overpressure in a shallow magma chamber and migration of hot pressurized fluids elastic effects are studied first and previous results obtained from maruyama s strain nuclei are corrected poro elastic and thermo elastic effects are found to be as important as the elastic ones in a semi pervious medium the three terms are typically of the same magnitude results are applied to interpreting the bradyseismic crisis of 1982 84 at phlegraean fields pf near naples italy the concave shape of the first phase of the deformation history at pf can be reproduced by linearly increasing fluid pressure and or temperature at the boundary of a spherical cavity the convex shape of the second phase is interpreted in terms of a gradual return to normal conditions the late phase of slow subsidence is interpreted as the effect of diffusional dissipation of temperature and pressure excess the deconvolution of the real source time history at pf is largely non unique but in any case the importance of fluids in the deformation history is assessed furthermore the inclusion of fluid migration in the deformation model allows simple explanations of several geochemical and geophysical observations made during the bradyseismic crisis

a study of the hydrothermal alteration in paleoproterozoic volcanic centers sao felix do xingu region amazonian craton brazil using short wave infrared spectroscopy abstract hypogene hydrothermal minerals have been identified by short wave infrared spectroscopy in hydrothermally altered rocks from the sobreiro and santa rosa formations which belong to a paleoproterozoic volcano plutonic system in amazonian craton three clay minerals are spectrally recognized montmorillonite kaolinite and illite the integration of these data with those available in the literature including gold occurrences suggests that those rocks are hydrothermal products of both volcanic thermal sources and later crustal intrusions as evidenced by variable styles of propylitic sericitic potassic and intermediate argillic alteration the influence of meteoric fluids is emphasized this low cost exploratory technique which can be applied to hand samples seems to be promising in the separation of hydrothermally altered volcano plutonic centers in regions submitted to severe weathering conditions in addition to aid elaborating models for prospecting mineral deposits

analytical models of deformation and residual gravity changes due to a mogi source in a viscoelastic medium abstract the popular mogi model describing deformation due to a small pressurized spherical cavity embedded in a homogeneous elastic half space is shortly reviewed similarities and differences with other isotropic deformation models are discussed and the interpretation of the different volume changes accompanying source inflation is provided the model is then generalized to viscoelastic rheology the overpressure needed within the source to reproduce the large deformation sometimes observed in volcanic regions is found to be strongly dependent on rheological parameters so that reasonably low values may be obtained if the relaxation time of the medium surrounding the source is short months instead of the extremely high values inferred from the elastic theory if the inflation of the source is due to the input of new magma from remote distance the resulting residual gravity change g may be easily computed thanks to the spherical geometry of the source and the density of the newly emplaced material may be inferred from the ratio of g w between the gravity change and the uplift this ratio is independent of the overpressure and the radius of the source which are generally ill defined parameters and is slightly dependent on the relaxation time in the transient phase explicit solutions are shown for a step like overpressure history and for a constant magma supply rate a more realistic model is also proposed in which the viscoelastic properties are restricted to a small spherical volume around the source surrounded by an elastic medium even if an accurate interpretation of deformation and gravity changes in volcanic areas generally requires taking into account topography elastic layering and the triaxial geometry of the inflation source values computed according to the generalized mogi model are compared with observations made during the 1982 84 uplift episode at campi flegrei caldera italy for the sake of illustration

the deep magmatic system of the campi flegrei caldera italy 1 melt inclusions in phenocrysts of the minopoli2 shoshonite and fondo riccio latite eruptive products campi flegrei caldera 10 2 to 9 5 ka bp constrain the nature of deep phlegraean magmatic fluids their role in volcanism and give new insights into the magmatic plumbing system the analyzed melt inclusions show that co2 is an abundant gaseous species confirming the results of geochemical studies on the magmatic gas fraction involved in present day fumarolic emissions volatile concentrations within the melt inclusions require gas melt equilibria between 8 and 9 km depth and closed system degassing in presence of ascending co2 rich fluids of deep provenance magmas later re equilibrate at depths up to 3 2 km i e above the top of the carbonate basement these observations correlate well with independent geophysical and geochemical evidence and are useful constraints for volcanic hazards assessment at campi flegrei

thermomechanics of shallow magma chamber pressurization implications for the assessment of ground deformation data at active volcanoes abstract in this study we utilize thermomechanical models to investigate how magma chambers overpressurize as the result of either magmatic recharge or volatile exsolution by implementing an adaptive reservoir boundary condition we are able to track how overpressure dissipates as the magma chamber expands to accommodate internal volume changes we find that the size of the reservoir greatly impacts the resultant magma chamber overpressure in particular overpressure estimates for small to moderate sized reservoirs 1 10 km 3 are up to 70 lower than previous analytical predictions we apply our models to santorini volcano in greece where recent seismic activity and ground deformation observations suggested the potential for eruption the incorporation of an adaptive boundary condition reproduces mogi flux estimates and suggests that the magma reservoir present at santorini may be quite large furthermore model results suggest that if the magma chamber is 100 km 3 overpressures generated due to the high magma flux may not exceed the strength of the host rock thus requiring an additional triggering mechanism for eruption although the adaptive boundary condition approach does not calculate the internal evolution of the magma reservoir it represents a fundamental step forward from elastic mogi models and fixed boundary solutions on which future investigations of the evolution of the magma can be built

recent ground movement and seismic activity in campi flegrei southern italy episodic growth of a resurgent dome leveling surveys in campi flegrei an active volcanic caldera in southern italy show that this caldera has undergone both subsidence and uplift of a few meters during the past 85 years a single source located at a depth of about 3 km beneath the center of the caldera can account for almost all elevation changes recorded in campi flegrei since the first leveling survey conducted in 1905 1907 this includes leveling surveys that span periods of subsidence such as between 1905 1907 and 1919 and between january 1985 and october 1986 and periods of rapid uplift between march 1970 and october 1971 and between january 1981 and december 1984 a possible geometry for the source of uplift and subsidence beneath campi flegrei is a rectangular horizontal sheet located at a depth of about 3 km and centered a few hundred meters east of the city of pozzuoli the horizontal dimensions of this sheet are about 1 5 km by 3 0 km the long axis is oriented n70 w this sheet lies adjacent to the most intense area of seismicity that occurred from mid 1983 to december 1984 during an uplift episode this sheet may represent the top of a magma body undergoing internal pressure changes possibly by intrusion of additional magma subsidence is caused by groundwater removal from the water saturated deposits that fill this caldera to a depth of a few kilometers a temporary increase in subsidence rate after an uplift episode is caused by increased rate of groundwater removal from newly fractured regions that lie immediately above the magma body the close proximity of this water saturated region and the magma body makes it impossible to separate the depth to these two sources from the results of leveling surveys two observations indicate that uplift has occurred in the center of campi flegrei for at least the past several thousand years first marine deposits in the center of campi flegrei were uplifted at least 40 m between 4000 and 8000 years ago second continuous seismic profiles of the undersea portion of campi flegrei have identified only one region where rocks are fractured and faulted adjacent to the uplifted marine deposits that surround the point of maximum uplift indicated by recent leveling surveys on the basis of these observations and the historical record of activity we suggest that campi flegrei caldera is in a stage of growing a resurgent dome the present diameter of the resurgent dome is about 4 km and the maximum amount of vertical uplift during the past 10 000 years has probably not exceeded 100 m the episodes of rapid uplift and shallow earthquake swarms during the past 20 years are probably related to the growth of this resurgent dome

dual reservoir structure at soufriere hills volcano inferred from continuous gps observations and heterogeneous elastic modeling 1 most inversions of geodetic data for volcanic systems assume homogeneous media here we examine the effect of inhomogeneous media using axisymmetric finite element models of soufriere hills volcano shv to show that homogeneous elastic crustal models underestimate both the depth and excess pressure of the deformation source continuous gps data from 1999 to 2009 are then used to infer that the shv system has multiple crustal pressure sources for a dual reservoir volcanic model a deep reservoir located within the mid crust undergoes volume changes approximately an order of magnitude larger than those of the shallow reservoir

magma chambers modeled as cavities explain the formation of rift zone central volcanoes and their eruption and intrusion statistics the volcanic rift zone in iceland is characterized by elongate volcanic systems consisting of tension fractures normal faults and volcanic fissures where most of the volcanotectonic activity takes place most volcanic systems develop central volcanoes the formation of which is still poorly understood there is great difference in the eruption and intrusion statistics of the volcanic systems inside and outside the central volcanoes in the central volcanoes eruptions are frequent typically one every several hundred years of small volume normally less than 0 1 km3 and fed mainly by thin average thickness of 0 5 m inclined sheets outside central volcanoes the eruptions are rare typically one every several thousand years but of large volume typically more than 1 km3 and fed mainly by thick average thickness of 4 5 m subvertical dikes using the results of a boundary element study of magma chambers modeled as a cavities or holes in a semi infinite plate these empirical relations as well as the formation of specific central volcanoes in the volcanic systems can be explained once a cavity like magma chamber has formed its existence in the rift zone concentrates tensile stress this stress concentration causes the segment containing the magma chamber to rupture much more frequently than the other parts of the volcanic system which partly explains the formation of central volcanoes and their high eruption frequencies this concentration also gives rise to a local stress field that encourages injection of small volume sheets in all directions and at various dips from their source magma chamber the magma chamber acts as a trap for upward propagating dikes from mantle reservoirs and channels magma through inclined sheets toward a limited area at the surface where the central volcano gradually forms the inverse relationship between eruption frequency and eruption volume when the central volcano is compared with other parts of the volcanic system is also partly due to the trap like nature of the magma chamber the chamber is normally much smaller than its source mantle reservoir so that a single magma flow through a dike from the reservoir lasting perhaps many years may trigger tens of magma flows through sheets from the chamber many of which would reach the surface in the central volcano

the restless resurgent campi flegrei nested caldera italy constraints on its evolution and configuration abstract we have collected new stratigraphic data in the campi flegrei caldera through surface geological mapping and study of cores drilled to various depths we integrate these data with geological geochronological and geophysical constraints available in the literature to reconstruct the volcanic and deformational history of the caldera the caldera is a resurgent nested structure resulting from two main collapses related to the campanian ignimbrite 37 ka and the neapolitan yellow tuff 12 ka eruptions while the structure is affected by a broad subsidence ongoing local resurgence and unrest occur inside the younger nested caldera structure although most of the caldera floor consists of multiple structural blocks due to long term deformations magmas were able to erupt only in one sector of the resurgent part the caldera has shown signs of unrest during the past 25 years with short term deformations that have generated a net uplift of 3 5 m the short term deformations are related to the neapolitan yellow tuff caldera resurgence and interpreted as the net result of brittle and ductile components the long term deformations likely represent the sum of the permanent brittle component of each short term deformational event

the effect of collapse structures on ground deformations in calderas ground deformations related to unrest episodes in calderas are generally interpreted like in other volcanic environments in terms of increased pressure within a magma chamber embedded in a continuous elastic medium in this framework the depth of the pressure source is inferred from the size of the deformed area this scheme works quite well for individual volcanoes for instance hawaiian shields where a good correspondence between inflation events and eruptive episodes has been observed ground deformation in calderas however show unusual features that are difficult to interpret within such a scheme because considerable positive deformation in the order of several meters and microfracturing i e intense seismicity may occur without eruptions altough the estimated depth for the magma source is sometime very shallow less than 1 2 km it has been recently suggested that the contact zones at the border of collapsed calderas could act as stress strain discontinuity zones and thus bias modeling results obtained for continuous elastic media we use both observations and theoretical modeling based on 3 d finite element techniques to show that ground deformations in collapsed calderas are strongly influenced by the caldera structure giving a new perspective in related geological and geophysical observations in such areas

the phlegraean fields structural evolution volcanic history and eruptive mechanisms abstract the main event within the volcanic history of the phlegraean fields was the eruption about 35 000 years ago of a huge alkali trachytic ignimbrite 80 km 3 dre followed by caldera collapse the pre caldera activity evidence from geothermal wells and surface outcrops changed from submarine to subaerial shortly before the ignimbrite eruption the caldera was subsequently invaded by the sea and became progressively filled with tuffites and subordinate submarine flows in its northern half the last submarine explosive activity dates back to 12000 10500 yr with the eruption of mostly hydroplinian yellow tuffs recent mostly subaerial activity consists of a series of explosive eruptions whose volume decreases with time until the last eruption of mt nuovo in 1538 a d two peaks in recent activity occur at 10000 8000 and 4700 3000 years ago during post caldera activity eruptive vents migrated from the caldera rim toward the center where there are two distinct zones of recent vents minor collapses occurred within the caldera after the main eruptions often they are eccentric to the vent and displaced toward the caldera center phlegraean explosive activity is characterized by water magma interaction eruptive events without a hydromagmatic component are extremely rare in most cases the evolved trachytic magmas interacted with surface water either the sea or intracaldera lakes however there is evidence of interaction of magma with deep seated aquifers for some plinian events explosivity i e the efficiency of the transformation of thermal into kinetic energy during magma water interaction is largely controlled by the primary fragmentation of the magmatic melt

on the effects of 3 d mechanical heterogeneities at campi flegrei caldera southern italy 1 campi flegrei caldera located near the highly populated city of naples southern italy is characterized by long term subsidence punctuated by fast uplift phases most of the interpretations of the ground deformation are still based on standard models that assume the lithosphere to behave as a homogeneous half space however several geophysical investigations show the presence of vertical and lateral heterogeneities especially in the shallow subsurface which might have an effect on the interpretation of the surface displacements our 3 d finite element models constrained by seismic tomography to take into account the realistic distribution of mechanical heterogeneities demonstrate that at campi flegrei the assessment of the source location is independent of the consideration of 3 d heterogeneities while the evaluation of its strength is overestimated thus we propose an approach that still allows use of standard homogeneous half space models but accounts for 3 d heterogeneity effects this procedure applied to the deformation field revealed by differential synthetic aperture radar interferometry dinsar over the past 16 years provides new insights for the understanding of the ground displacements observed at campi flegrei caldera this work provides an approach for a quantitative evaluation of the effects of mechanical heterogeneities on surface deformation analogous procedures can be also applied in other volcanic areas where similar to campi flegrei caldera a priori information on the mechanical heterogeneities distribution is available

source parameters and three dimensional attenuation structure from the inversion of microearthquake pulse width data qp imaging and inferences on the thermal state of the campi flegrei caldera southern italy the three dimensional p wave attenuation structure of the campi flegrei caldera and the estimate of source parameters for 87 local microearthquakes is obtained by the nonlinear inversion of pulse width and rise time measurements by using the method described by zollo and de lorenzo this issue source radii represent the better resolved parameters with values ranging from 70 m to 230 m the dip and strike angles defining fault orientations are usually affected by larger uncertainties and are well constrained only for 11 events the dip fault is usually confined in the range 30 60 with an average uncertainty of 12 the fault strikes mainly range between 60 and 60 and seem to define preferential directions oriented radially from the symmetry axis of the ground deformation stress drop estimates indicate rather low values 0 01 1 mpa which suggest low strength properties of the incoherent and brittle materials filling the caldera primarily yellow tuffs the three dimensional qp images obtained from the inversion of p pulse durations show two significant low qp anomalies between 0 and 1 km of depth in the north eastern sector and at 2 3 km of depth in the central eastern sector of the caldera the high degree of spatial correlation of the low qp zone and low vs as inferred by aster and meyer 1988 at 0 1 km in depth and other geophysical and geochemical observations suggest that this anomaly can be related to the presence of densely fractured porous and fluid filled rocks in the ne sector of the caldera the deeper low qp anomaly is interpreted as being related to a dominant thermal effect we used the surface and deep borehole temperature measurements available in the area to obtain a local calibration curve to convert qp in temperature at campi flegrei the retrieved t qp map shows a high thermal deep disturbance 450 500 c at depths between 2 and 3 km in the eastern sector of the caldera where the most recent eruptive activity is concentrated the present day temperature field retrieved by qp images has been interpreted by using a three dimensional thermal conduction model assuming an extended heat source initial temperature of 800 c located underneath the attenuation anomalous region the results indicate that the qp inferred temperature field can be related to the heat conduction effect of one or more molten bodies whose top should be at about 4 km depth consistent with recent seismic estimates of the magma chamber top at campi flegrei ferrucci et al 1992 this study suggests that the present thermal state and rock rheology of the inner caldera could be controlled by the cooling of molten bodies that originally intruded at depths of 1 4 1 6 km during one or more recent time of 10 kyr eruptive events

u pb age and hf o isotopes of detrital zircons from hainan island implications for mesozoic subduction models abstract a compilation of magmatic ages from the mesozoic south china block suggests a number of magmatic quiescence periods at ca 205 195 ma ca 150 140 ma and ca 125 115 ma casting doubt on tectonic models that suggest ongoing andean type subduction along the south china continental margin however sims u pb analyses on two detrital zircon samples from the cretaceous lumuwan formation on hainan island southeast china reveal three major age peaks at ca 120 ma ca 155 ma and ca 235 ma zircons of these ages are mostly euhedral and show typical magmatic oscillatory zoning suggesting short distance transport from nearby magmatic sources the extremely rare occurrence of ca 120 ma magmatic records onshore suggests that detrital zircons of this age population may be derived from a source proximal to hainan island but presently missing therefore our data provide new evidence for ongoing magmatic activity in late mesozoic south china in situ hf and o isotope analyses of the mesozoic detrital zircons reveal large variations in both ehf t 21 2 to 10 5 and 18o 4 4 to 13 6 values a general negative correlation between them suggests the reworking of old supracrustal materials average crustal residence age of ca 2 0 ga by juvenile mantle derived magmas the progression of increasing ehf t and decreasing 18o values of zircons from the triassic to the cretaceous suggests progressive crustal growth during the mesozoic the results are consistent with hybridization at an active continental margin we briefly review tectonic models for the indosinian orogeny and suggest that the petrologic evidence indicates that mesozoic magmatism was part of the circum pacific accretionary orogens that formed along the continental margin of east asia no later than ca 250 ma and continued at least to the late cretaceous

geodetic constraints to the source mechanism of the 2011 2013 unrest at campi flegrei italy caldera campi flegrei caldera italy was affected by a new unrest phase during 2011 2013 we exploit two cosmo skymed data sets to map the deformation field obtaining displacement rates reaching 9 cm yr in 2012 in the caldera center the resulting data set is fitted in a geophysical inversion framework using finite element forward models to account for the 3 d heterogeneous medium the best fit model is a north dipping mixed mode dislocation source lying at 5 km depth the driving mechanism is ascribable to magma input into the source of the large 1982 1984 unrest since similar source characteristics were inferred that generates initial inflation followed by additional shear slip accompanying the extension of crack tips the history and the current state of the system indicate that campi flegrei is able to erupt again and the advanced techniques adopted provide useful information for short term forecasting

p sv conversions at a shallow boundary beneath campi flegrei caldera italy evidence for the magma chamber seismograms from an active seismic experiment carried out at campi flegrei caldera near naples italy show a large amplitude 5v polarized shear wave following by less than 1 5 s p waves reflected at wide angle from a deep crustal interface early arriving sv polarized waves with the same delay to direct p waves are also observed in seismograms from a regional 280 km deep magnitude 5 1 earthquake such short delays of s to p waves are consistent with a p sv conversion on transmission occurring at a shallow boundary beneath the receivers the large amplitude of the converted sv phase along with that the p waves are near vertical requires a boundary separating a very low rigidity layer from the upper caldera fill the converted phases are interpreted as a seismic marker of a magma chamber the top of this magma chamber is located slightly deeper than the deepest earthquakes observed during the 1982 1984 unrest of campi flegrei

modeling the effect of layered volcanic material on magma reservoir failure and associated deformation with application to long valley caldera california abstract elastic gravitationally loaded finite element models of an ellipsoidal magma reservoir in mechanically layered host rock yield new insight into the effect of layer stiffness thickness and spatial configuration on the resulting surface displacement curve and tensile rupture of the reservoir wall decreasing layer stiffness enhances surface and subsurface deformation focusing pressure across a narrow area and generally decreases the likelihood of vertical magma intrusion and surface eruption in contrast increasing layer stiffness impedes uplift and distributes strain across a broad area enhancing the likelihood of vertical magma intrusion application of the model to deformation that occurred between 1985 and 1999 at the long valley caldera california shows that the predicted reservoir radius and depth change by 16 and 12 respectively when mechanical layers inferred to be present are included in the model highlighting the importance of explicitly incorporating mechanical layering analysis of rupture conditions for the reservoirs modeled in the present paper indicates that vertical intrusions are likely in addition analysis of rupture conditions for long valley magma reservoirs recently inferred from surface displacement inversions indicates that they will fail before achieving sufficient pressure to reproduce measured surface displacement

heat diffusion and size reduction of a spherical magma chamber an analytical solution is derived for the size reduction of a spherical magma chamber cooling by conduction the use of moving boundary conditions and the constraint of a spherical symmetry allow one to ignore the details of the heat redistribution processes which take place within the magma chamber the dependence of the solution on the initial conditions is investigated a simple solution is found for short time which is shown to be valid for times long enough to make it useful in the volcanological context moreover the general solution confirms that the hydrothermal contribution to heat transfer in phlegraean fields cannot be extremely important

the large scale surface uplift in the altiplano puna region of bolivia a parametric study of source characteristics and crustal rheology using finite element analysis 1 this paper focuses on the driving mechanism behind a 70km wide region of ground uplift centered on uturuncu volcano in the altiplano puna region of southern bolivia we present a series of forward models using finite element analysis to simultaneously test for first order parameters that help constrain a viable model for the observed maximum line of sight uplift rate of 1 2cm yr between 1992 and 2006 stresses from pressure sources with finite geometries are solved numerically accounting for both homogeneous and heterogeneous mechanical rock properties in elastic and viscoelastic rheologies crustal heterogeneity is constrained by seismic velocity data that indicate the presence of a large low velocity zone the altiplanopuna magma body at depths of 17km below the surface a viscoelastic rheology is employed to account for time dependent deformation and an inelastic crust comparing homogeneous and heterogeneous models demonstrates the significant impact of a mechanically weak source depth layer which alters surface displacement patterns by buffering subsurface deformation elastic model results guide the source parameters tested in the viscoelastic models and demonstrate a range of possible causative source geometries our preferred model suggests that pressurization of a magma source extending upward from the altiplano puna magma body is causing the observed surface uplift and alludes to a continued increase in this pressure to explain both the spatial and temporal patterns we also demonstrate how a pressure time function plays a first order role in explaining the observed temporal deformation pattern

effect of mechanical heterogeneity in arc crust on volcano deformation with application to soufriere hills volcano montserrat west indies 1 analyses of volcano surface deformation are commonly based on models that assume mechanical homogeneity of rocks surrounding the causative pressure source here we present a detailed study that shows the differences in deduced surface deformation caused by source pressurization accounting for either mechanical homogeneity or mechanical heterogeneity of encasing rocks in a volcanic arc setting using finite element models accounting for crustal heterogeneity from seismic data we test for a range of source geometries and intermediate crustal depths and explore the misfits of deduced source parameters from the two families of models in the second part of this study we test the results from the generic study against cgps data from two deformation periods the 2003 2005 ground inflation and the 2005 2007 ground deflation at soufriere hills volcano montserrat west indies to inform on source parameters accounting for a variable crustal rigidity with depth as deduced by seismic analysis beneath montserrat we find the data to be best explained by pressurization and depressurization of a slightly prolate midcrustal magma chamber that is centered between 11 5 and 13 km below sea level about 640 m ne of the active vent considering source dimension and source pressure changes we demonstrate that magma compressibility and viscoelasticity of host rocks considerably affect dynamics in the midcrustal magmatic system of soufriere hills volcano and need to be accounted for as first order effects in geodetic data analyses and modeling

structural and rheological constraints on source depth and overpressure estimates at the campi flegrei caldera italy ingv gruppo nazionale per la vulcanologia ministero dell istruzione universita e ricerca firb project

a model of the phlegraean fields magma chamber in the last 10 500 years volcanological and petrological data suggest that the phlegraean fields volcanic activity has been fed at least in the last 10 500 years by a not refilled magma chamber where trachytic residual liquids were produced by fractionation of a trachybasaltic magma using estimated volumes of the erupted products andp t data obtained through petrological studies a conductive thermal model of the chamber was built up in order to estimate its past and present size results suggest a volume decrease from approximately 14 to 1 4 km3 of the trachybasaltic magma in 10 500 years trachytic liquid would also be present in the chamber in a minimum amount of 0 4 km3 the model allowed some insights on the petrogenesis of the phlegraean trachytes suggesting that they were erupted as liquids because thermally buffered within the magma chamber

genesis and evolution of unrest episodes at campi flegrei caldera the role of thermal fluid dynamical processes in the geothermal system we develop a model for describing water flow in a porous medium under the effect of thermal and pressure gradients the model simulates geothermal systems in calderas given the boundary conditions and the fluid dynamical properties of the medium the model allows computation in fluid dynamical stationary states of parameters characterizing the flow such as flow velocity and temperature and pressure distributions at depth the model is applied to investigate the effects of the local geothermal system on the unrest episodes at campi flegrei caldera using experimentally determined fluid dynamical parameters for the caldera rocks we show that changes of water flow in shallow aquifers under the effect of pressure and or temperature variations within the geothermal system can be very important in the genesis and evolution of unrest crises in particular they can strongly amplify the effect of pressure increase in the magma chamber on ground uplift they can also explain the timescales of evolution of ground movements in terms of transit times of the water front and of the connected temperature fronts due to advective transport on such grounds an integrated mechanic thermal fluid dynamical model was built allowing us to give a semiquantitative global explanation to the genesis and evolution of unrest phenomena results obtained here can be generalized to other similar calderas

the interdisciplinary use of overpressure abstract overpressure is a polysemic word that has a variety of meanings within and across different disciplines this is likely to be a particular problem in analysis of geothermal resources where reservoir engineers volcanologists and structural geologists may each confidently use overpressure but mean different things we suggest that to avoid confusion the term should be carefully and accurately defined whenever used and ideally only used to mean fluid pressure in excess of hydrostatic pressure

4d gravity response of compacting reservoirs analytical approach abstracttime lapse gravity is a technique sensitive to subsurface change in mass and in mass distribution we attempted to devise a method to predict gravity effects caused by redistribution of subsurface mass induced by reservoir compaction first displacements and strains due to compaction were modeled using a geomechanical model then 4d gravity effects were derived from the displacements and the volumetric strains computed in and around the reservoir a sensitivity study was carried out for geomechanical parameters such as poisson s ratio as well as for geometrical parameters such as reservoir radius and depth finally changes in gravity due to compaction were compared to changes induced by reservoir fluid substitution given a rigid basement close below a strongly compacting reservoir our modeling case showed that the deformation itself could give gravity changes comparable to changes caused by reservoir fluid density changes which are the changes traditionally targeted by gravity monitoring

effects of topography on the interpretation of the deformation field of prominent volcanoes application to etna we have investigated the effects of topography on the surface deformation field of volcanoes our study provides limits to the use of classical half space models considering axisymmetrical volcanoes we show that interpreting ground surface displacements with half space models can lead to erroneous estimations of the shape of the deformation source when the average slope of the flanks of a volcano exceeds 20 tilting in the summit area is reversed to that expected for a flat surface thus neglecting topography may lead to misinterpreting an inflation of the source as a deflation comparisons of mogi s model with a three dimensional model shows that ignoring topography may lead to an overestimate of the source volume change by as much as 50 for a slope of 30 this comparison also shows that the depths calculated by using mogi s solution for prominent volcanoes should be considered as depths from the summit of the edifices finally we illustrate these topographic effects by analyzing the deformation field measured by radar interferometry at mount etna during its 1991 1993 eruption a three dimensional modeling calculation shows that the flattening of the deflation field near the volcano s summit is probably a topographic effect