monitoring ash emission episodes at mt etna the 16 november 2006 case study abstract mt etna in sicily italy is one of the best monitored basaltic volcanoes in the world due to the frequent eruptions from its summit and flanks routine monitoring carried out by istituto nazionale di geofisica e vulcanologia sezione di catania for surveillance purposes permits following the evolution of volcanic events in this paper a description of the ash monitoring system as occurred during the august december 2006 summit eruption at the southeast crater sec is shown this eruption was characterized by lava flow effusions and vigorous strombolian activity eighteen paroxysmal episodes occurred up to the end of november forming weak ash plumes accompanied by moderate tephra fallout over etna s slopes during these events we applied a multidisciplinary approach to promptly monitor the paroxysmal activity and the associated tephra fallout through analysis from seismic tremor and observation from live cameras sampling operations mapping and analysis of the deposit during the most significant episodes we carried out textural and grain size analysis on tephra samples and evaluated the total grain size deposit and the erupted volume while numerical simulations of tephra dispersal allowed better understanding eruptive dynamics an example of this methodology is applied to the 16 november episode during which seismic tremor furnished important constraints on the chronology this paroxysmal eruption produced light fallout on the north east sector of the volcano for about ten hours and a number of debris avalanches over the slopes of the sec cone the erupted deposit was composed for the most part of lithic components and characterized by a total size distribution centered on 2 2 while its total mass was evaluated 7 10 6 kg on the whole such integrated studies help to obtain information on magma fragmentation and eruptive mechanisms to characterize the explosive styles shown by etna and finally to better approach the monitoring of imminent eruptions

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

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

spatiotemporal gravity variations to look deep into the southern flank of etna volcano 1 a 14 year long microgravity data set october 1994 to september 2007 collected along a 24 km east west trending profile of 19 stations was analyzed to detect underground mass redistributions related to the volcanic activity involving the southern flank of mt etna italy a multiresolution wavelet analysis was applied to separate the volcano related anomalies from the unwanted components the residual image having both spatial extension and temporal duration evidenced two complete gravity increase decrease cycles mainly affecting the central and eastern stations of the profile the first gravity increase early 1995 to the end of 1996 and decrease end of 1996 to late in 1998 cycle reached a maximum amplitude of approximately 90 gal the second gravity increase mid 1999 to mid 2000 and decrease mid 2000 to early 2004 cycle attained an amplitude of about 80 gal after about 5 years of a persistent negative gravity anomaly a new semicycle started at the end of 2006 and continued during the last survey carried out in september 2007 the density changes modeled over time since 1994 using a quadratic programming algorithm are mainly located at a depth of 2 4 km bsl in a region recognized to be a preferential pathway of magma rising and an intermediate zone of magma storage withdrawal the computed positive mass variations of about 105 109 kg were interpreted as magma accumulation while negative mass changes of about 120 109 kg were associated with either magma drainage or opening of new voids by tectonic stresses within a source volume where tensional earthquakes occurred

source scaling of microearthquakes at mt etna volcano and in the calabrian arc southern italy microearthquake data recorded at mt etna volcano and in the calabrian arc southern italy have been used to study the scaling of the main source parameters after correction of the p wave displacement spectra for both path attenuation and the site amplification effects an inverse method has been applied to compute spectral parameters low frequency spectral level corner frequency and high frequency roll off results show that seismic moments m0 range from ca 1016 to 1021 dyne cm at mt etna and from ca 1017 to 1020 dyne cm in southern calabria corner frequencies range from ca 3 to 15 hz in both areas we found that the stress drop decreases from ca 100 to few bars with decreasing seismic moment a simple brune source model is not able to explain the source scaling because the typical fall off observed at higher frequencies 3 as an average is larger than that of brune s theory furthermore the relation between the seismic moment and the corner frequency points to a scaling law behaving as m0 c 4 5 and m0 c 3 6 on average at mt etna and in southern calabria respectively and higher for smaller events in both areas therefore the cube law m0 3 generally accepted for large earthquakes does not hold true for the analysed microearthquakes neither for those which occur along the tectonic structures of southern calabria or along those hosting the roots of the feeding system of the largest european volcano

intrusive mechanisms at mt etna forerunning the july august 2001 eruption from seismic and ground deformation data in this work we present seismological and ground deformation evidence for the phase preparing the july 18 to august 9 2001 flank eruption at etna the analysis performed through data from the permanent seismic and ground deformation networks highlighted a strong relationship between seismic strain release at depth and surface deformation this joint analysis provided strong constraints on the magma rising mechanisms we show that in the last ten years after the 1991 1993 eruption an overall accumulation of tension has affected the volcano then we investigate the months preceding the 2001 eruption in particular we analyse the strong seismic swarm on april 20 24 2001 comprising more than 200 events mmax 3 6 with prevalent dextral shear fault mechanisms in the western flank the swarm showed a ca ne sw earthquake alignment which in agreement with previous cases can be interpreted as the response of the medium to an intrusive process along the approximately nnw sse volcano genetic trend these mechanisms leading to the july 18 to august 9 2001 flank eruption are analogous to ones observed some months before the 1991 1993 flank eruption and more recently in january 1998 before the february november 1999 summit eruption

late quaternary slip rates on the acireale piedimonte normal faults and tectonic origin of mt etna sicily abstract mt etna is located along the east coast of sicily near the boundary between the continental crust of the hyblean plateau and the mesozoic oceanic crust of the ionian basin the main active faults near mt etna cut the base of its eastern flank forming a 30 km long system of nne and nnw trending ene chelon fault segments the acireale piedimonte system showing dip slip and oblique right lateral motion most segments are associated with shallow depth seismicity and all have late pleistocene to holocene vertical slip rates ranging between 1 and 2 mm yr typical of major active normal faults worldwide eruptive fissures arranged in nne to ne trending zones cut the highest slopes of the volcano on the footwall of the normal fault system structural analysis suggests that current motions along both the active faults and eruptive fissures are kinematically compatible and simply linked with ongoing wnw ese directed regional extension such extension characterizes at a greater scale the active tectonics of southern italy where all large shallow historical earthquakes have remained confined within a narrow normal fault belt or rift zone stretching from the northern calabrian arc to southeastern sicily the southernmost west dipping faults of that rift zone in calabria aspromonte cut across the calabro peloritan thrust belt to join the mostly east dipping acireale piedimonte faults along the western boundary of ionian oceanic lithosphere which continues southwards as the malta escarpment we thus relate magmatism at etna to dilational strain on the footwall of an east facing crustal scale normal fault at the bend where the siculo calabrian rift zone veers 60 eastwards as it begins to cross the calabrian arc leaving the east facing margin of the ionian sea to catch up with the west facing margin of the tyrrhenian sea farther north

very shallow earthquakes and brittle deformation in active volcanic areas the eatnean region as an example abstract some aspects of the stress field acting in active volcanic areas were investigated by studying the relationship between surficial seismicity h 1 2 km and the brittle deformation pattern of the etna volcano the magmatic composition and structural character of mt etna are described together with its geodynamic regional context after a discussion of the problem of the state of stress in active volcanoes and a definition of very shallow seismicity the high level of surficial seismicity the morphology of the sedimentary basement and the kinematic behaviour of the faults suggest that the eastern flank of mt etna is a shallow seismotectonic domain structurally decoupled from the rest of the volcanic body this flank shows a tendency to slide in an eastern direction and is bound to the north by a left lateral oblique slip normal fault trending e w and in the south by an arcuate fault system with right lateral features right lateral oblique slip normal faults

analytical and 3 d numerical modelling of mt etna italy volcano inflation summary since 1993 geodetic data obtained by different techniques gps edm sar levelling have detected a consistent inflation of the mt etna volcano the inflation culminating with the 1998 2001 strong explosive activity from summit craters and recent 2001 and 2002 flank eruptions is interpreted in terms of magma ascent and refilling of the volcanic plumbing system and reservoirs we have modelled the 1993 1997 edm and gps data by 3 d pressurized sources to infer the position and dimension of the magma reservoir we have performed analytical inversions of the observed deformation using both spheroidal and ellipsoidal sources embedded in a homogeneous elastic half space and by applying different inversion methods solutions for these types of sources show evidence of a vertically elongated magma reservoir located 6 km beneath the summit craters the maximum elevation of topography is comparable to such depth and strong heterogeneities are inferred from seismic tomography in order to assess their importance further 3 d numerical models employing source parameters extracted from analytical models have been developed using the finite element technique the deformation predicted by all the models considered shows a general agreement with the 1993 1997 data suggesting the primary role of a pressure source while the complexities of the medium play a minor role under elastic conditions however major discrepancies between data and models are located in the se sector suggesting that sliding along potential detachment surfaces may contribute to amplify deformation during the inflation for the first time realistic features of mt etna are studied by a 3 d numerical model characterized by the topography and lateral variations of elastic structure providing a framework for a deeper insight into the relationships between internal sources and tectonic structures

estimates of stress directions by inversion of earthquake fault plane solutions in sicily summary the tectonic stress orientation is estimated in the lithosphere of northern sicily the southern tyrrhenian sea and southern calabria and in the wadati benioff zone below the tyrrhenian by inversion of fault plane solutions of earthquakes covering a magnitude range from 2 5 to 7 1 focal mechanisms of 97 earthquakes are taken from the literature after a critical evaluation of their data quality an average misfit of f 13 indicates that the set of all shallow 50 km earthquakes is generated by a heterogeneous stress field for three subsets based on regional and magnitude separation f was small enough 2 8 lfs5 9 to support the assumption of a homogeneous stress direction for an additional subset with f 7 4 such a condition is close to being fulfilled even though some heterogeneity appears to be present the number of earthquakes in these subsets ranged from nine to 22 and the uncertainties of the principal stress directions were generally of the order of 20 at the 90 per cent confidence level the earthquakes with a425 define a regional stress field with the greatest principal stress ul dipping at a shallow angle to the south in north eastern sicily and south western calabria the stress field estimated by earthquakes is extensional with o3 in a direction of wnw and a near vertical ol in agreement with the graben tectonics mapped geologically in this area in western sicily the c1 direction is oriented wnw but this result is judged less reliable than the others based on the broader confidence limits of the solution and the average misfit of 7 4 the earthquakes in the wadati benioff zone define ol dipping at about 70 to the nw subparallel to the zone with o2 horizontal and striking parallel to the zone

recent seismicity and tomographic modeling of the mount etna plumbing system the monitoring of seismic activity in eastern sicily southern italy has been recently improved in the framework of the poseidon project to investigate both tectonics and volcanic processes of mount etna this effort has produced a homogeneous and complete data set which we use to image the deep structure of the volcano and to define the space and time distribution of the recent seismicity encompassing the 1995 eruption diffuse eruptions between 1995 and 1997 a further magma intrusion started in 1997 and an increase of volcanic activity in july 1998 we inverted p wave arrival times from 307 selected local earthquakes to obtain a three dimensional velocity model of the volcano with a simultaneous inversion for hypocenters and velocity parameters the new tomographic images permit us to define the structure beneath the volcano from the surface down to 18 km depth the main structural feature revealed by our inversion is a high velocity body located beneath the central craters whose lateral extent increases from 6 km between 18 and 9 km depth to 12 km between 9 and 3 km depth near the surface the fast anomaly branches in two separate high vp regions which are located below the summit craters and the eastern flank valle del bove respectively the high velocity features are interpreted as high density cumulates of solidified magma that intruded the shallow crust we hypothesize that magma ascends the crust within the relatively small high velocity conduit below 9 km depth and is stored at depth shallower than 9 km within the broad high velocity region as also suggested by petrological data a sharp increase of seismicity in 1997 with earthquakes occurring at the border of the high velocity body suggests that mount etna sustained recent episodes of intrusions which possibly herald future eruptions no large low velocity anomaly interpretable as a melted magma chamber is imaged in the upper 18 km of the crust while a broad low velocity anomaly in the uppermost mantle revealed by regional seismic data possibly indicates the magma source region at depth earthquake occurrence from the deep source to the shallow intrusive area helps to trace the magma migration and the feeding of the volcanic system

seismic heterogeneity of mt etna structure and activity a dense seismic array maintained temporarily for 7 weeks provides an approach to deducing the 3 d heterogeneity of the structure of the upper crust beneath mt etna volcano from the inversion of p and s wave arrivals of local earthquakes independent data from a different source array geometry using waves generated by distant shots at sea confirm a main lateral variation a high velocity body underlies part of the volcano its contrast with the surrounding thick sedimentary pile and its location extending from the present summit to the southeast suggests that it may have been built by the development and migration of past eruptive centres followed by caldera collapse local low velocity anomalies near its sharp western edge may be associated with presently active features

dispersion of gaseous volcanogenic fluoride island of hawaii abstract fluoride was measured in samples of lichen collected in 1990 from 68 sites on the island of hawaii in addition fluoride levels were measured in 8 rainfall samples collected at the same time the levels of fluoride in the lichens range from 6 to 332 g g 1 which are similar to the levels measured on etna the highest levels of fluoride were detected close to kilauea and the concentration generally decreases with increasing distance from this volcano this overall pattern of distribution is modified by local variations in wind direction which relate to the topographic features of the island close to kilauea there are more localised controls on the fluoride levels caused by circulating groundwaters and degassing lavas

evidence of multiple strain fields beneath the eastern flank of mt etna volcano sicily italy deduced from seismic and geodetic data during 2003 2004 we carried out a study of the seismicity and ground deformation occurring on mt etna volcano after the end of the 2002 2003 eruption and before the onset of the 2004 2005 eruption data were recorded by the permanent local seismic network run by istituto nazionale di geofisica e vulcanologia sezione di catania and by geodetic surveys carried out in july 2003 and july 2004 on the gps network most earthquakes were grouped in two main clusters located in the northeastern and southeastern sectors of the volcano the areal distribution of seismic energy associated with the recorded earthquakes allowed us to highlight the main seismogenic areas of mt etna in order to better understand the kinematic processes of the volcano 3d seismic locations were used to compute fault plane solutions and a selected dataset was inverted to determine stress and strain tensors the focal mechanisms in the northeastern sector show clear left lateral kinematics along an e w fault plane consistent with events occurring along the pernicana fault system the fault plane solutions in the southeastern sector show mainly right lateral kinematics along a nne and ene fault plane and left lateral kinematics along nw fault planes that together suggest roughly e w oriented compression surface ground deformation affecting mt etna measured by gps surveys highlighted a marked inflation during the same period and exceptionally strong seawards motion of its eastern flank the 2d geodetic strain tensor distribution was calculated and the results show mainly ene wsw extension coupled with wnw ese contraction indicating right lateral shear along a nw se oriented fault plane the different deformation of the eastern sector of the volcano as measured by seismicity and ground deformation must be interpreted by considering the different depths of the two signals seismic activity in the southeastern sector of volcano is located between 3 and 8 km b s l and can be associated with a very strong additional e w compression induced by a pressurizing source just westwards and at the same depth located by inverting gps data ground deformation in contrast is mainly affected by the shallower dynamics of the fast moving eastern flank which produces a shallower opposing e w extension the entire dataset shows that two different processes affect the eastern flank at the same time but at different depths the boundary is clearly located at a depth of 3 km b s l and could represent the decollement surface for the mobile flank

vsp normal moveout stretch the vertical seismic profiling common depth point vspcdp transformation is a technique used to image the reflected waves in an offset vsp this coordinate transformation procedure maps reflection amplitudes from receiver depth and reflection times to lateral offset and reflector depth wyatt and wyatt 1981 the process involves the application of moveout correction followed by stacking this moveout correction results in a distortion of the original waveform and a smear of the reflection event that consequently degrades the lateral resolution of the transformation owusu 1991 therefore to determine the optimum processing parameters for the transformation we need to understand the effects of the vsp moveout stretch

nonstretch moveout correction of long offset multichannel seismic data for subbasalt imaging example from the north atlantic we have developed a pragmatic new processing strategy to enhance seismic information obtained from long offset multichannel seismic data the conventional processing approach which treats data on a sample by sample basis is applied at a coarser scale on groups of samples using this approach a reflected event and its vicinity remain unstretched during the normal moveout correction isomoveout curves lines of equal moveout in the time velocity panel are employed to apply a constant moveout correction to selected individual events leading to a nonstretch stack a zigzag stacking velocity function is introduced as a combination of segments of appropriate isomoveout curves by employing a zigzag velocity function stretching of key events is avoided and thus information at far offset is preserved in the stack the method is also computationally cost effective however the zigzag stacking velocity field must be consistent with target horizons this method of horizon consistent nonstretch moveout has been applied to a wide angle data set from the north atlantic margin providing improved images of the basement interface which was previously poorly imaged

stress strain and mass changes at mt etna during the period between the 1991 93 and 2001 flank eruptions abstract during the 8 year period between the 1991 93 and 2001 flank eruptions the eruptive activity of mt etna was confined to the summit craters deformation and tomography studies indicate that this activity was fed by a magma accumulation zone centered ne of the summit at a depth of 5 to 9 km below sea level the most significant gravity changes measured during the same period were induced by mass redistributions at shallower depth below the southeastern flank of the volcano where minor ground deformation was observed i e vertical displacements within 2 cm the mismatch between the position of pressure and mass sources is difficult to explain under the assumption that both are directly related to magma dynamics past studies have suggested that the gravity changes observed during 1994 2001 may primarily reflect changes in the rate of microfracturing along the nnw sse fracture weakness zone fwz that crosses the se slope of etna we use the finite element method to shed new light on the complex relations between stress strain and mass changes that occurred at etna during the studied period in particular following previous results on the degradation of the mechanical properties of rocks we perform a set of simulations assuming that the part of the medium containing the fwz is characterized by a lower young s modulus than would be expected from interpolation of tomographic data we find that the presence of the fwz creates a distortion of the displacement field induced by the deeper pressure source locally resulting in a weak extensional regime this finding supports the hypothesis of a cause effect relationship between pressurization beneath the nw flank and tensile extension beneath the se slope of the volcano we propose that this extensional regime enhanced the propagation of pressurized gas that in turn amplified the tensile strain across the fwz we also find that decreasing the value of young s modulus in the fwz allows for a larger amount of extension at depth with no change in the magnitude of surface displacements this result provides an indication of how the changes in the rate of microfracturing at depth which are needed to induce the observed gravity changes might have occurred without large ground deformation

how to cope with volcano flank dynamics a conceptual model behind possible scenarios for mt etna abstract volcano flank dynamics poses a serious hazard also involving the inhabited lower slopes mt etna is a well studied unstable volcano and a significant amount of data has been collected on the dynamics of its eastern and southern flanks we first propose a conceptual model to describe and explain flank dynamics at etna we identify the preconditions as due to the differential unbuttressing conditions at the volcano base and the triggering factors as shallow magmatic sources dikes reservoirs evidence and parameters and or observations for flank dynamics are listed summarizing the 1994 2010 period of activity based on this we then propose a set of scenarios possibly occurring in case of unrest of the unstable flanks of mt etna flank unrest is a variation in the steady state condition of the volcano flanks possibly accompanied by significant ground deformation seismicity and eruptions the scenarios may provide a general reference and recommendation in case of five types of multi hazard processes related either as a cause or effect to flank dynamics 1 edifice inflation 2 emplacement of dikes along the ne and or s rifts 3 seismicity along pernicana fault system 4 seismicity on the s sector 5 seismicity along timpe fault system each scenario is analyzed and recommendations are given the scenarios may or may not be related to each other in the sense that the probability of occurrence of one scenario may or may not be contingent or dependent upon the prior occurrence of another these scenarios provide a qualitative analysis of the multi hazard processes related to flank dynamics a more quantitative i e probabilistic characterization is under consideration

long term record of co2 degassing along mt etna s flanks and its relationship with magma dynamics and eastern flank instability a record of soil co2 flux data on the lower flanks of mt etna measured from 1989 to 2008 is discussed in the framework of multidisciplinary observations including seismicity ground deformations and flank instability a huge increase in soil co2 fluxes appears to be related to the dynamics of magma ascent in the upper portions of the volcano 0 3 km and the intrusion of dykes along the southern rift as mainly observed before the 1991 93 eruption even after the 1991 93 eruption the recharge of the shallow central reservoir was accompanied by a long term increase in soil co2 degassing mainly in the southwestern area the 2001 eruption marked dramatic changes in the areal distribution of seismicity the deformation pattern and the soil co2 degassing indeed while the soil co2 degassing showed background values in the southwestern area it progressively increased in the eastern sector and along the pernicana fault this has been related to the marked sliding of the eastern flank since the 2002 03 eruption and the associated seismicity this study provides evidence that the extent of soil co2 degassing on the lower flanks of mt etna is controlled by 1 the volume of involved magma 2 the intrusion of dykes in the upper parts of the volcano and 3 fault movement and seismicity this implies that different degassing structures must be monitored simultaneously when attempting to understand the behavior of the volcano as a whole

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

nmo stretch and subtle traps introductory note the following paper shows the impact of cmp stacking on the search for subtle traps it appears that 14 years after the publication of aapg memoir 32 the search for the subtle trap is alive and well

ground deformation patterns at mt etna from 1993 to 2000 from joint use of insar and gps techniques abstract combined gps measurements and radar interferometry insar have been applied at mt etna to study the ground deformation affecting the volcano both over the long 1993 2000 and short term 1997 1998 and 1998 2000 the aim was to better understand the dynamics of the volcano during the magma recharging phase following the 1991 93 eruption since 1993 insar and gps data indicate that mt etna has undergone an inflation a deep intrusion was detected by insar on the western flank of the volcano between march and may 1997 in the following months this intrusion rose up leading to a seismic swarm occurring in january 1998 in the western sector this now shallow intrusion is confirmed by gps data from 1998 to 2000 a general deflation affecting the upper part of the volcano was detected over the whole study period a continuous eastward to south eastward motion of the eastern sector of the volcano was also evidenced the analytical inversions of gps data inferred a plane dipping about 12 ese located beneath the eastern flank of the volcano at a depth of 1 4 km b s l the movement along this plane is able to reproduce the observed south eastward motion of a sector bounded northward by the pernicana fault westward by the north east rift and the south rift and southward by the mascalucia tremestieri trecastagni fault system insar data have validated this model

first application of asdp software a case study at mt etna volcano and in the acri region southern italy abstract the pc based automatic seismic data processing asdp software module uses a multi algorithm approach and a new procedure msa for signal detection phase grouping and event identification and location it is designed for an efficient and accurate processing of local earthquakes records provided by single site and array stations results from asdp processing of two different data sets are analysed to evaluate its performance by comparing of asdp pickings with those revised manually the detection and subsequently the location capabilities of this software are assessed the first data set is composed of 330 local microearthquakes 1 7 m 3 8 recorded in the mt etna volcano area by a telemetered analog seismic network digital data conversion of data is performed at the network centre operated by the istituto internazionale di vulcanologia of c n r the second data set comprises 40 ultra microearthquakes 0 5 m 2 0 recorded by a temporary array of four digital three component stations deployed in the acri region southern calabria for the etnean earthquakes a comparison of the automatic results with the manual picks indicates that the asdp module can accurately pick 80 of the p waves differences are within 0 15 s and 65 of the s waves differences are within 0 3 s a peculiarity for these events is that the majority of the 3 three component station records do not exhibit distinct s waves this statistics includes records with a strong noise ground tremors and or system electronic disturbances but does not include false alarms due to non seismic signals conversely if we consider high dynamic recordings of seismic digital data in a low noise environment acri temporary array the asdp module can accurately pick 93 of the p waves differences with manual estimations are less than 0 1 s and 87 of the s waves differences with manual estimations are less than 0 2 s for this type of data with a favourable signal to noise ratio the automatic back azimuths estimates are also extremely accurate in the 87 of the cases differences estimations with those revised by an analyst and deriving from hypocenter solutions are generally within 10 in general our results indicate that both automatic asdp and manual hypocenter locations are comparable within the estimated errors bounds furthermore the comparison of asdp automatic locations with those performed by xrtp iaspei software routinely used for automatic locations at the mt etna seismic network indicates a better performance of the asdp module

nonstretching nmo correction of prestack time migrated gathers using a matching pursuit algorithm abstractwide azimuth long offset surveys are becoming increasingly common in unconventional exploration plays where one of the key routine processes is maintaining data fidelity at far offsets the conventional nmo correction that processes the data sample by sample results in the well known decrease of frequency content and amplitude distortion through stretch which lowers the seismic resolution and hinders and amplitude variation with offset and azimuth avaz analysis of the long offset signal to mitigate the stretch typically associated with large offsets we use a matching pursuit based normal moveout correction mpnmo to reduce nmo stretch effects in long offset data mpnmo corrects the data wavelet by wavelet rather than sample by sample thereby avoiding stretch we apply our technique 1 to a set of synthetic gathers and 2 as part of a residual velocity analysis workflow to a prestack time migrated data volume acquired over the northern chicontepec basin mexico test results show th

mount etna geochemical signals of magma ascent and unusually extensive plumbing system fiveyearsofgasmonitoringfromselectedsitessuggestthatmtetna splumbingsystemismuchmoreextensivethanpreviously reported it extends at least 40 km sw from thevolcano s boundary along the ne sw regional fault whereit discharges about 200 tons day of gas containing heliumwith mantle type isotopic composition synchronousvariations of

roots of etna volcano in faults of great earthquakes abstract results from several seismic methods allow us to sketch the deep structure of etna and its ionian margin under etna a volume of high velocity material is found in a structurally high position the emplacement of this suggests spreading of the surrounding medium just offshore down to the east normal faults penetrate through the upper crust the deeper crustal structure beneath appears upwarped from the basin towards etna juxtaposed with the crust of sicily a thinner crust reaches from the ionian basin under etna and the mantle is upwarped in such a structure magma can then be viewed as a melted lens capping a mantle upwarp at shallow depth rather than in an intracrustal chamber this reduces the conflict between estimates of its volume from excess output of volatiles and short residence times a link in time is indicated between volcanic and seismic activity at a large scale over the millennium the reported ends of episodes of high output rates of magma are followed by the reported occurrences of magnitude 7 earthquakes which caused destruction in southeastern sicily several steep active normal fault have been imaged to a depth of 10 km the crust up to 30 km offshore of the cities of catania and augusta which may be fault planes for such large earthquakes they expand and prolongate the system of the timpe faults on the eastern flank of etna thus linking large scale tectonics offshore with the volcano etna developed together with normal faulting upwarp and spreading during the recent evolution of the former ionian subduction activation of the material at depth at the lateral edge of the slab by vertical motion with extension above could produce the peculiar type of etna magmatism

normal moveout in focus improving the accuracy of nmo corrections and of the corresponding interval velocities entails implementing a better approximation than the formula used since the beginning of seismic processing the exact equations are not practical as they include many unknowns the approximate expression has only two unknowns the reflection time and the rms velocity but becomes inaccurate for large apertures of the recording system and heterogeneous vertical velocities several methods of improving the accuracy have been considered but the gains do not compensate for the dramatic increase in computing time two alternative equations are proposed the first containing two parameters the reflection time and the focusing time is not valid for apertures much greater than is the standard formula but has a much faster computing time and does not stretch the far traces the other containing three parameters the reflection time like focusing time and the tuning velocity retains high frequencies for apertures about twice those allowed by the standard equation its computing time can be kept within the same limits nmo equations old and new are designed strictly for horizontal layering but remain reliable as long as the rays travel through the same layers in both the down and up directions more an equation similar to dix s formula is given to compute the interval velocities the entire scheme can be automated to produce interval velocity sections without manual picking less

toward one meter resolution in 3d seismic high resolution 3d hr3d seismic data are important for hydrocarbon exploration of shallow reservoirs site characterization and geohazard assessments the goal of this contribution is to identify and quantify the parameters to increase the resolution of hr3d seismic data to meter scale the main acquisition parameters controlling the resolution of the collected data are the spectrum of the seismic source source receiver offset range and trace density an evolution to one meter scale resolution of 3d seismic will rely on combining a reproducible seismic source with high frequencies up to at least 600 hz a high uniform trace density of more than 4 million traces per square kilometer and an offset range shorter than approximately 200 m the resulting 3d seismic data volume will reach meter scale resolution for water and target depths of less than 600 m the proposed hr3d system will be suitable for 3d and 4d characterization of seabed properties and shallow stratigraphy the identification of geohazards and hydrocarbon leakage and monitoring the environmental impact of offshore activities the p cable 3d system is an excellent starting point for achieving one meter scale resolution due to its flexible and tight meter scale shot and receiver spacing

horizon based semiautomated nonhyperbolic velocity analysis abstractwith higher capacity recording systems long offset surveys are becoming common in seismic exploration plays long offsets provide leverage against multiples have greater sensitivity to anisotropy and are key to accurate inversion for shear impedance and density there are two main issues associated with preserving the data fidelity contained in the large offsets 1 nonhyperbolic velocity analysis and 2 mitigating the migration nmo stretch current nonhyperbolic velocity analysis workflows first estimate moveout velocity vnmo based on the offset limited gathers then pick an effective anellipticity eff using the full offset gathers unfortunately estimating vnmo at small aperture may be inaccurate with picking errors in vnmo introducing errors in the subsequent analysis of effective anellipticity we have developed an automated algorithm to simultaneously estimate the nonhyperbolic parameters instead of directly seeking an effective stacking model the algorithm finds an interval model t

dynamic deformation of etna volcano observed by satellite radar interferometry satellite radar interferometry of mt etna volcano sicily italy reveals a sequence of deformation characterized by deflation during the end of the 1993 eruption inflation from 1993 1995 with an increase in the inflation rate immediately before its resumed eruptive activity in late 1995 this was followed by very low deformation levels during the following year the source of the deformation changed from a depth of 9 km during deflation to more than 11 14 km during the subsequent inflation consistent with a model in which deflation at shallower levels is followed by inflation at greater depth as the volcano system recharges from below before its next eruption this study demonstrates that radar interferometry provides an important contribution towards understanding the dynamic deformation of volcanoes by revealing large scale changes in their pre eruption deformation rates radar interferometry could play an important role in volcano eruption monitoring

continental subduction and three dimensional crustal structure the northern south island new zealand the three dimensional vp and vp vs structure of a region where subduction transitions to oblique transform faulting has been determined using arrival times from 579 local earthquakes recorded during a temporary deployment and 3146 earthquakes have been relocated between 40 km and 100 km depth the subducted plate is imaged as a relatively low velocity feature in the uppermost mantle reflecting the continental nature of the subducted crust in this region an increase in amplitude of this low velocity feature from northeast to southwest can be related to an increase in the thickness of the crust of the subducted plate in this direction velocity variations within the subducted and overlying plates show some spatial correlation this suggests an interaction between the plates which extends well beyond the plate interface and is consistent with other geophysical and geological evidence that the plate interface beneath marlborough is currently not accommodating much active subduction in the overlying plate the awatere fault is a major structural feature associated with a low velocity zone extending to 23 km depth there is a marked change in structure near this fault with seismic velocities being lower to the southeast a relatively high level of seismicity occurs in this region of lower seismic velocities suggesting a relationship between the two a possible explanation for this is elevated pore pressures caused by fluids derived from dehydration of the continental subducted crust the low velocity region in the overlying plate coincides with the region of most intense active deformation suggesting it is relatively weak

instantaneous spectral attributes to detect channels channels filled with porous rock and encased in a nonporousmatrixconstituteoneofthemoreimportantstratigraphic exploration plays although attributes such as coherence can be used to map channel width they are relatively insensitive to channel thickness in contrast spectral decomposition can beusedtomapsubtlechangesinchannelthickness thepeak spectral frequency derived by using the short window discrete fourier transform swdft is an excellent tool for mapping such changes along an interpreted horizon we show that by use of instantaneous spectral attributes we can generateequivalentmapsforcompleteseismicvolumes because we are often interested in mapping high reflectivity channelsencasedinalower reflectivitymatrix wefindthata composite plot of the peak frequency and the above average peak amplitude accentuates highly tuned channels finally by generating a composite volume using peak frequency peakamplitude andcoherence wecanestablishnotonlythe channelthickness butalsoitswidth wedemonstratethevalueofsuch3dvolumetricestimatesthroughapplicationto1 a marine survey acquired over tertiary channels from the gulfofmexicoand2alanddatasurveyacquiredoverpaleozoic channels from the central basin platform west texas united states the channels in both marine and land surveys canbehighlightedthroughcomposite volumeanalysis

bayesian inversion of 1994 1998 vertical displacements at mt etna evidence for magma intrusion summary we have developed a bayesian method for the inversion of static ground deformations at volcanic areas the method allows inference of the conditional probability density on the location and mechanism of point sources representing volcanic phenomena isotropic strain nuclei tensile faults embedded in homogeneous elastic media the method has been tested with simulated and real data from volcanic areas we have then analysed vertical displacements recorded at mt etna southern italy from 1994 to 1998 by high precision levelling measurements in this period had been carried out yearly so resulting displacements have been analysed both in consecutive periods and in the cumulative one measurement periods 1994 1995 and 1997 1998 show significant uplift of several centimetres the maximum cumulative displacement amounts to 6 5 cm with a trend similar to each of the two periods 1994 1995 and 1997 1998 the shape of displacement is well approximated by a circular symmetry thus allowing one to hypothesize an isotropic overpressure model as the source simulating magma intrusion at shallow depth the application of the inverse method gives the most probable location at about 4 5 km of depth b s l at about 1 5 km north of the central craters the 95 per cent of probability density is concentrated within a radius of about 0 5 km on the horizontal 1 km on depth the obtained results give important insight on the interpretation of recent eruptive episodes

buoyant melting instabilities beneath extending lithosphere 2 linear analysis 1 in a companion paper numerical models reveal that buoyant melting instabilities can occur beneath extending lithosphere for a sufficiently small mantle viscosity extension rate and rate of melt percolation however in some cases instabilities do not develop during extension but only occur after extension slows or stops these results are suggestive of a critical behavior in the onset of these kinds of instabilities and motivate a linear analysis to study the onset of instability in a partially melting passively upwelling plane layer of mantle beneath extending lithosphere the model we employ includes the effects of buoyancy arising from thermal expansion the presence of a retained fraction of partial melt and depletion of the solid by melt extraction we find a critical behavior in the onset of instability controlled by melt retention buoyancy that is characterized by a rayleigh number m such that m must exceed some critical value mcrit which depends on the efficiency of stokes rise of a partially molten body relative to the rate of background percolation comparison of this theory to the numerical results in the companion paper yields a close quantitative agreement we also find that solid depletion buoyancy can either stabilize or destabilize a partially melting layer depending upon both the distribution of preexisting depletion and the magnitude of density changes with depth this theory is compared with previous studies of buoyant melting instabilities beneath mid ocean ridges where similar behavior was reported and it suggests that the stability of passively upwelling partially melting mantle underlying both narrow and wide rift settings is controlled by similar processes

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

volcanic unrest leading to the july august 2001 lateral eruption at mt etna seismological constraints abstract a close relationship between earthquake swarms volcanic eruptions and ground deformation at mt etna was well documented shortly before the beginning of the july august 2001 eruption past experiences at this volcano suggest how magma dike intrusion in the shallow crust or in the upper part of the volcanic pile normally occurs after several years months of internal recharging since seismic investigations provide a means to study the scale and origin of stress perturbations at active volcanoes allowing to better investigating the preparation phase of an eruption in this paper we performed a close examination of the seismic activity recorded at mt etna in the months preceding the 2001 eruption and in particular between november 2000 and july 2001 after integrating data recorded by the two networks operating during that time and run by the istituto internazionale di vulcanologia and sistema poseidon we relocated 522 earthquakes by using the tomodd code in a 3d velocity model and then we computed their fault plane solutions the application of different selection criteria enabled obtaining a good quality revised data set consisting of 111 fault plane solutions the high precision locations identified well defined seismic clusters in different periods suggesting a link with the magma migration from a depth of 8 13 km b s l towards shallower zones moreover the computed maximum compressive stress axis as inferred from earthquake focal mechanisms indicated a roughly w e oriented 1 this findings reflect an overpressure of the mid to shallow crust due to the progressive magma uprising in central portion of the volcano and also highlighted a rotation of the local stress field with respect to the regional one n s trending in addition p axis distribution pointed out the presence of a center of pressure located to the south of the central craters these results provide particularly compelling evidence for a direct causal link between pressurization of the mid level volcanic plumbing system by ascending magma and precursory local stress field reorientations demonstrating that seismological analysis can be used to detect subtle local stress changes that herald eruptive activity

ground deformations and volcanic processes as imaged by cgps data at mt etna italy between 2003 and 2008 1 we analyze the kinematic and crustal deformations of mt etna from 2003 to 2008 as imaged by the mt etna continuous gps cgps network etn net through a careful analysis of gps time series six coherent phases of crustal deformations have been identified three inflation phases and three deflation phases superimposed on a major inflation of the volcanic edifice since 2001 the inversions of gps velocities have enabled 1 a better understanding of the evolution of the volcanic sources acting beneath the volcano 2 analysis of the strain rate patterns and 3 a delineation of potential coupling between volcanic sources and the observed ground deformations the modeling of the pressure sources has shown a separation between inflation and deflation sources the deflation sources show an upward migration from 5 5 toward 2 0 km b s l while the inflation sources are located within 5 5 and 4 0 km b s l our results indicate that the kinematic and ground deformations of the mid upper eastern flank are driven by the interplay between the effect of the magmatic sources and a southeastward motion furthermore clockwise rotations have been detected that prevailed over the eastern motion of the flank during the inflation phases preceding the 2004 2005 and 2006 eruptions finally the accordance between the higher geodetic shear strain rates and the area with the highest seismic energy release shows that measured geodetic shear strain rates can provide useful information on the potential occurrence of seismic activity

evidence of deep magma degassing and ascent by geochemistry of peripheral gas emissions at mount etna italy assessment of the magmatic reservoir pressure 1 five gas discharges in the area of mount etna volcano italy and in the near hyblean plateau have been monitored since 1996 all the emissions displayed low contributions from crustal fluids whereas magmatic gases were the main component selective dissolution of these gases into hydrothermal aquifers has been recognized and modeled allowing us to calculate the original composition of the magma released gases the inferred composition of the magmatic gases exhibits synchronous variations of he ne and he co2 ratios which are coherent with the magma degassing process on the basis of numerical simulations of volatile degassing from etnean basalts we have computed the initial and final pressures of the magma batches feeding the emissions we thus can define the levels of the etna plumbing system where magmas are stored pressure values were around 360 and 160 mpa for initial and final stages respectively meaning related depths of about 10 and 3 km below sea level matching those obtained by geophysical investigations for the deep and shallow magma reservoirs in addition we have been able to recognize episodes of magma migration from the deeper reservoir toward the shallow one an important magma injection into the shallow storage volume was detected during the onset of the 2001 eruption 17 july no further injection had taken place during this period until september 2001 providing a possible reason for the quick exhaustion of the eruption in view of this we suggest that the sampled emissions are a powerful geochemical tool to investigate the etna s plumbing system and its magma dynamics as well as the development of eruptive events

magma dynamics in the shallow plumbing system of mt etna as recorded by compositional variations in volcanics of recent summit activity 1995 1999 describe the reactivation and the successive evolution of the shallow plumbing system of mt etna between the end of the largest flank eruption of the last three centuries 1991 1993 and the subterminal eruption from south east crater sec which occurred between february and mid november 1999 our analysis is based on observations of the volcanic activity and petrological studies of the erupted volcanics bulk rock mineral and glass compositions have been determined for more than 80 samples erupted from the four summit craters between october 1995 and february 1999 these data allow us to recognise significant compositional variations among the products of different craters in particular volcanics produced between 1995 and 1999 by bocca nuova bn voragine vor and north east crater nec show limited compositional variations and are similar to those observed during recent eruptions e g 1991 93 more primitive magmas have been produced during the more vigorous fire fountains episodes on the contrary the south east crater produced slightly more differentiated volcanics than those of the other summit craters following its reactivation november 1996 until the end of 1998 whole rock compositions of products from this crater show low cao al 2 o 3 whereas interstitial glasses have lower mgo and higher alkali contents than those from the other craters however since the beginning of 1999 and just before the start of the subterminal eruption from sec the volcanics erupted from this crater progressively changed in composition becoming similar to those of the other craters this trend indicates that within the conduits of the summit craters distinct thermal and fluid dynamical regimes can evolve controlling the cooling and crystallisation of etna magmas

dynamics of mount etna volcano inferred from static and kinematic gps measurements 1 ground deformations measured on mount etna from late 1995 to mid 1998 using gps observations are analyzed four gps surveys were carried out during the considered period in 1995 the gps network consisted of 18 stations on the volcanic edifice and 6 stations around it during the 1996 survey 22 new monuments were added along a n s profile crossing the summit craters area this profile was surveyed by a semikinematic method allowing greater spatial detail to be achieved on the uppermost part of the volcano the comparisons between the gps surveys are reported here in terms of horizontal and vertical displacements for each station and also in terms of areal dilatation and strain distribution this last parameter continues its ascending trend at a rate of 5 strain yr 1 already shown in the previous period after the end of the 1991 1993 flank eruption inversion of the ground deformation patterns permits investigation of the evolution of both the position and dynamics of magma reservoirs beneath the volcano consistently associated with a general eastward sliding of its eastern sector this study allows us to define the nonuniqueness of ground deformation sources through the investigated period suggesting that the plumbing system of the volcano is made up of a complex system of single intrusions occurring at different times

mapping of the b value anomalies beneath mt etna italy during july august 2001 lateral eruption 1 the pattern of b value of the frequency magnitude relation or mean magnitude has been analyzed as function of space beneath mt etna during the intense lateral eruption of july august 2001 the data used august 1999 august 2001 subdivided in the pre eruptive and eruption period show significant space variations in the b value for each of the two periods a volume of anomalously high b value can be observed in the southeastern flank of the volcano the anomalies located at 3 1 km b 1 84 0 20 and at about 1 1 km b 2 11 0 29 depth are interpreted as two different steps of a magma migration process ended with the july august 2001 eruption all the available geophysical evidences such as geodetic deformation measurements focal mechanism and tomographic studies support this interpretation

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

spatial mapping of the b value at mount etna italy using earthquake data recorded from 1999 to 2005 1 the spatial pattern of the b value of the frequency magnitude relation has been analyzed using gridding techniques beneath mount etna italy a regional data set of 2900 events with md duration magnitude 1 5 up to 15 km depth occurring between august 1999 and december 2005 has been used two regions with an abnormally high b value have been found one centered beneath the southern part of the valle del bove above the 6 km below sea level bsl deep basement and the other beneath the summit region 2 km bsl east of the central craters we can infer that these high b value anomalies are regions of increased crack density and or high pore pressure related to the presence of nearby magma storage this interpretation is supported by all the available geophysical evidence such as tomographic studies and geodetic deformation measurements the data set has also been subdivided into five periods corresponding to different phases of volcanic activity 2001 preeruption 2001 eruptive 2002 2003 preeruption 2002 2003 eruptive and 2002 2003 posteruption the minimum magnitude of completeness mc and the b value were computed for each period a volume of anomalously high b values can be observed in each of these periods except for the 2002 2003 preeruption interval this approach has allowed the detection of the transient presence of magmatic intrusions during the various periods evaluated

seismic data processing in vertically inhomogeneous ti media the first and most important step in processing data in transversely isotropic ti media for which velocities vary with depth is parameter estimation the multilayer normal moveout nmo equation for a dipping reflector provides the basis for extending the ti velocity analysis of alkhalifah and tsvankin to vertically inhomogeneous media this nmo equation is based on a root mean square rms average of interval nmo velocities that correspond to a single ray parameter that of the dipping event therefore interval nmo velocities including the normal moveout velocity for horizontal events vnmo 0 can be extracted from the stacking velocities using a dix type differentiation procedure on the other hand which is a key combination of thomsen s parameters that time related processing relies on is extracted from the interval nmo velocities using a homogeneous inversion within each layer time migration like dip moveout depends on the same two parameters in vertically inhomogeneous media namely vnmo

shear response to an intrusive episode at mt etna volcano january 1998 inferred through seismic and tilt data abstract the space time evolution of a seismic swarm m d max 3 7 occurring on 9 14 january 1998 at mt etna volcano is analysed the hypocentral pattern and most reliable focal mechanisms indicate that seismic activity during 10 14 january mainly occurred within a fault zone located in the volcano s western flank the fault showed an approximately ne sw overall trend and shallow rupture mode of right lateral strike slip type it is noteworthy that earthquakes occurring during the initial phase 9 january of the swarm showed prevalent dip slip rupture mechanisms which are consistent with tensile opening of an approximately nnw sse trending fault zone this nnw sse structural lineament belongs to a regional lithospheric structure which has also been identified as a main volcano genic structural trend of mt etna the observed continuous tilt data are not explainable by the seismic slip associated with strain released along the ne sw structure however an intrusive source would be compatible with the rupture mechanisms observed during the initial phase of the swarm and could explain the observed tilt therefore we evidence that an intrusive episode occurred along the nnw sse structure starting 9 january and during the following days it forced the ne sw fault system to work in a right lateral mode these mechanisms leading to the february november 1999 summit eruption are analogous to the ones observed before the 1991 93 eruption

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

the feeding of the eruptive activity of etna volcano the regional stress field as a constraint to magma uprising and eruption an analysis of the structural lineaments as observed on the middle and upper slopes of etna volcano was made with the aim of checking stress distribution within the volcanic structure

insights into magma and fluid transfer at mount etna by a multiparametric approach a model of the events leading to the 2011 eruptive cycle 1 since the second half of the 1990s the eruptive activity of mount etna has provided evidence that both explosive and effusive eruptions display periodic variations in discharge and eruption style in this work a multiparametric approach consisting of comparing volcanological geophysical and geochemical data was applied to explore the volcano s dynamics during 2009 2011 in particular temporal and or spatial variations of seismicity volcano tectonic earthquakes volcanic tremor and long period and very long period events ground deformation gps and tiltmeter data and geochemistry so2 flux co2 flux co2 so2 ratio were studied to understand the volcanic activity as well as to investigate magma movement in both deep and shallow portions of the plumbing system feeding the 2011 eruptive period after the volcano deflation accompanying the onset of the 2008 2009 eruption a new recharging phase began in august 2008 this new volcanic cycle evolved from an initial recharge phase of the intermediate shallower plumbing system and inflation followed by i accelerated displacement in the volcano s eastern flank since april 2009 and ii renewal of summit volcanic activity during the second half of 2010 culminating in 2011 in a cyclic eruptive behavior with 18 lava fountains from new southeast crater nsec furthermore supported by the geochemical data the inversion of ground deformation gps data and the locations of the tremor sources are used here to constrain both the area and the depth range of magma degassing allowing reconstructing the intermediate and shallow storage zones feeding the 2011 cyclic fountaining nsec activity