the influence of fluid type on elastic wave velocity and attenuation in volcanic rocks abstract volcano seismic signatures are the convolution of source and path effects the source signature provides important information about the dynamic rock deformation and fluid resonance processes within the volcano but path effects are the result of the volcanic plumbing the edifice physical conditions and the complex geological structure complicating the inversion of seismic data further is the influence of fluid properties here we use ultrasonic experiments to understand the effect of variable fluid viscosity and bulk modulus on p wave attenuation and velocity for volcanic rocks from white island volcano whakaari new zealand our experimental conditions for high porosity ash tuff and low porosity lava resemble shallow and deep volcano facies respectively p wave velocity vp and quality factor qp increase with the viscosity and bulk modulus of the saturating fluid and decrease with porosity and fracture volume tuffs are highly sensitive to saturating fluid with variations in vp of up to 67 and qp of 383 vp and qp in fractured lavas are slightly less sensitive to fluids 24 and 296 respectively but vp can be used to identify lithology for these tuff vs lavas comparison of the experimental data with rock physics models suggests that squirt flow is the dominant attenuation mechanism for viscosities greater than that of water while scattering losses may be important in gas saturated rocks our results have significant implications for the interpretation of seismic tomography studies and for volcano hazard monitoring based on the characteristics of detected seismicity

comparison between the 1994 2006 seismic and gravity data from mt etna new insight into the long term behavior of a complex volcano abstract we investigate the relationship between changes of the gravity field and the release of the seismic energy at mt etna over a 12 year period 1994 2006 during which the volcano exhibited different eruptive patterns over the two sub periods when intense gravity decreases occur centered on the upper southeastern sector of the volcano late 1996 to mid 1999 and late 2000 to mid 2001 the strain release curve displays neat long term accelerations with many hypocenters clustered in the volume containing the gravity source various evidences suggest that since 1994 and until the breakout of the 2001 eruption the eastern flank of etna remained peripheral to the lines of rise of the magma from the deep storage to the surface accordingly we hypothesize that rather than being directly associated to the migration of the magma the joint anomalies we found image phases of higher tensile stress on the upper southeastern sector associated to increase in the rate of microfracturing along the nnw sse fracture zone such an increase implies a local density gravity decrease and an increase in the release of seismic energy thus explaining the correlation we observe the second period of gravity decrease strain release increase culminated in the breakout of the 2001 flank eruption as a pressurized deeper magma accumulation used the inferred zone of increasing microfracturing as a path to the surface this eruption marks an important modification in the structure of etna s plumbing system as also testified by the absence of post 2001 long term gravity changes and accelerations in the strain release curve and the neat modification of the seismicity and ground deformation patterns we prove that joint microgravity and seismic studies can allow zones of the medium experiencing an increase in the rate of microfracturing to be identified months to years before a magma batch is conveyed through them to the surface setting off a lateral eruption

dynamics of surface currents over qingdao coastal waters in august 2008 1 surface currents measured by high frequency hf radar are used to investigate the dynamics in the coastal waters of qingdao china on the western coast of the yellow sea different factors affecting the surface currents are revealed by dynamical analysis harmonic tidal analysis shows that the coastal tidal currents are barotropic and their temporal evolution is mainly influenced by the semidiurnal tidal constitutes topography and geometry it is also found that their horizontal distribution represents the effect of local topography at sub tidal frequencies the high correlation between winds and the sub tidal surface currents indicates a crucial role of wind forcing in driving the currents varying wind direction coupled with small scale features of the coastal geometry results in complicated sub mesoscale circulation in addition the monthly coastal circulation is characterized by an eddy structure and is primarily determined by the outflow which is closely associated with the sea level slope along the coast the variability of the residual currents is studied by analyzing the cross shore momentum equation with wind stress sea level records and hf radar currents it is shown that both the barotropic pressure gradient and the nonlinear tidal stress contribute to the variations of the residual currents near the bay mouth and further govern the coastal monthly circulation in august 2008

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

high resolution aeromagnetic anomaly map of mount etna volcano southern italy abstract a high resolution aeromagnetic survey of mount etna volcano was carried out by the airborne geophysics science team of istituto nazionale di geofisica e vulcanologia ingv aimed at producing the most detailed magnetic anomaly map existing so far for this area two datasets of the total intensity of the earth s magnetic field were collected at different altitudes to take into account the huge topographic variations of etna volcano that reaches elevations above 3300 m asl one level was flown at the altitude of 2200 m whereas a second one over the central part at about 3500 m of altitude since the region is characterized by a large presence of strongly magnetized volcanic products the survey was carried out acquiring profile lines only in order to optimize the resources from the residual magnetic anomaly analysis we inferred two main trending lineaments 35 n and 0 n that are related to regional tectonic stress field and we interpret the main magnetic anomaly as the effect of thickness variation of magnetized volcanic products due to the complex pre volcanic basement morphology of etna

three dimensional attenuation tomography at loma prieta inversion of t for q three dimensional q 1 variations in the aftershock region of loma prieta are derived by tomographic inversion the data set consists of over 4000 aftershock recordings at 22 passcal program for array seismic studies of the continental lithosphere stations deployed after the loma prieta mainshock of 1989 estimates of attenuation are determined from nonlinear least squares best fits to the fourier amplitude spectrum of p and s wave arrivals the linear attenuation inversion is accomplished by using three dimensional velocity variations derived previously in nonlinear velocity inversions low q is observed near the surface and q generally increases with depth the southwest side of the san andreas fault exhibits lower q than does the northeast side and this feature apparently extends to approximately 7 km depth the fault zone as determined by the dipping plane of aftershock activity is characterized by slightly higher qp and lower qs compared to regions immediately adjacent to the fault these correlate with high velocity anomalies associated with seismicity at depth the results are in agreement with earlier observations regarding the association of high velocity anomalies seismicity and fault zone asperities

tomographic images and 3d earthquake locations of the seismic swarm preceding the 2001 mt etna eruption evidence for a dyke intrusion 1 on july 12 2001 mt etna experienced a sudden increase of seismic activity heralding one of the most intense eruptions of the past 30 years between july 12 and july 18 when the eruption started thousands of small magnitude earthquakes occurred and were recorded by a dense seismic network run by the istituto nazionale di geofisica e vulcanologia sezione di catania ingv ct hypocentral depths of earthquakes were very shallow mostly located above 3 km b s l and clustered near the summit area the high quality seismic dataset gives us the unique opportunity to study the process of magma migration before the eruption in this study we present the three dimensional earthquake locations and the velocity structure obtained by a tomographic inversion the shallowness of seismicity allowed us to enhance the details of the structure beneath the summit craters in a volume poorly defined by previous tomographic studies the presence of a high vp body previously observed at mt etna is confirmed at shallow depth beneath the southeastern part of the summit area the earthquakes preceding the eruption onset concentrated at its western border a low vp vs anomaly is found at 0 1 km depth just at the top of the volume where the magma intruded before the eruption this anomalous zone can be considered as molten material wealthy in gas the relocated seismicity occurs in a cylinder below the vents activated along the fracture system and exhibited an upward migration until the eruption all these results show evidence for the emplacement of a near vertical dyke striking about n s and a few kilometres south of the summit craters

seismological evidence for magmatic and hydrothermal structure in long valley caldera from local earthquake attenuation and velocity tomography we compare the results of six different tomographic inversions for the three dimensional seismic attenuation and velocity structure in long valley caldera california in order to constrain interpretations on the location and character of magmatic and geothermal structure in the caldera crust p and s wave amplitudes and arrival times obtained in previous studies from seismograms of local earthquakes recorded on vertical and three component seismographis were inverted for q sv 1 q sh 1 q s 1 q p 1 and v p v s in the upper 9 km of teh caldera crust detailed comparisons of the results of the inversions suggest significant locations of high temperatures and perhaps magma and hydrothermal zones in the caldera a region of low q s with locally variable q p and v p v s is imaged in the 7 9 km depth range beneath the resurgent dome overlying and adjacent to this anomaly are significant low q p and low v p v s anomalies as well as smaller zones of low q s and high v p v s together these suggest zones of high temperature magma below and adjacent to zones of supercritical hydrothermal fluids at 4 5 km depth along the southern rim of the caldera just east of mammoth mountain a significant anomaly with relatively low q p and relatively low v p v s is imaged and is interpreted as a supercritical hydrothermal zone poorly resolved relatively low q p and relatively high v p v s are seen at 4 5 km depth beneath the inyo craters suggesting possible high temperatures and perhaps magma because of lack of data in the individual inversions the resultant images have spatially variable error and resolution however by comparing multiple images of different seismic parameters we have improved our ability to determine the significance of an constrain interpretation of seismic structure anomalies

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

geophysical indications of magma uprising at mt etna during the december 2005 to january 2006 non eruptive period 1 during the december 2005 january 2006 non eruptive period the tremor amplitude at etna markedly increased and negatively correlated with the gravity signal from one of the two summit station over 2 3 hour periods no correlation was found with the signal from the other gravity station we locate the tremor source by inverting the spatial distribution of seismic amplitudes relying on the relative position of the two stations we define a volume within which the gravity source must lie during the period of marked anti correlation the tremor sources intersect this volume in a region located 1 km s se of the summit craters and about 2 km beneath the surface this finding suggests that the anti correlation marks the activation of a joint source process possibly related to the arrival of fresh magma and the consequent gas separation our study has implications for the early recognition of gas segregation processes at active volcanoes

analogue modeling of flank instability at mount etna understanding the driving factors 1 mount etna is characterized by significant flank instability whose triggering factors are still a matter of debate we use analog models to investigate the role of different factors in the models a cone and base of granular material simulate the volcanic edifice and its basement the asymmetric geometry of the basement simulates the topographic gradient around the volcano injections of silicone sets a and b and low viscosity vegetable oil set c simulate the pressurization of plutonic complex deep reservoirs and the emplacement of dikes respectively other experiments set d reproduce regional extensional tectonics in the last 105 years within layers with different cohesion simulating strength differences in the basement laser scanner and control points allow the tracking of surface deformation with submillimeter precision the asymmetric topography enhances flank instability on the side with the weakest confinement i e seaside providing the preparing factor for instability in sets a and b any type of pressurized reservoir enhances up to 10 times the amount of flank instability toward the seaside with respect to the other flanks of the volcano in set c dike emplacement enhances seaside flank instability up to 8 times regional tectonics and crustal layering in set d enhance flank instability up to 2 and 1 3 times respectively considering the duration and frequency of the simulated processes in nature we propose a semiquantitative evaluation and hierarchy of the factors controlling flank instability at etna magmatic activity point like source inflation and dike emplacement provides the most important triggering factor extensional tectonics in the last 105 years and crustal layering are more than 10 times less effective this study shows the importance of differential buttressing at the volcano base for flank instability this condition is an important indication to expect asymmetric activity in any volcano flank eruptions and deformation

integrating ambient noise with gis for a new perspective on volcano imaging and monitoring the case study of mt etna abstract the timely estimation of short and long term volcanic hazard relies on the availability of detailed 3d geophysical images of volcanic structures high resolution seismic models of the absorbing uppermost conduit systems and highly heterogeneous shallowest volcanic layers while particularly challenging to obtain provide important data to locate feasible eruptive centres and forecast flank collapses and lava ascending paths here we model the volcanic structures of mt etna sicily italy and its outskirts using the horizontal to vertical spectral ratio method generally applied to industrial and engineering settings the integration of this technique with web based geographic information system improves precision during the acquisition phase it also integrates geological and geophysical visualization of 3d surface and subsurface structures in a queryable environment representing their exact three dimensional geographic position enhancing interpretation the results show high resolution 3d images of the shallowest volcanic and feeding systems which complement 1 deeper seismic tomography imaging and 2 the results of recent remote sensing imaging the study recovers a vertical structure that divides the pre existing volcanic complexes of ellittico and cuvigghiuni this could be interpreted as a transitional phase between the two systems a comparison with recent remote sensing and geological results however shows that anomalies are generally related to volcano tectonic structures active during the last 17 years we infer that seismic noise measurements from miniaturized instruments when combined with remote sensing techniques represent an important resource to monitor volcanoes in unrest reducing the risk of loss of human lives and instrumentation

numerical simulation of stress induced piezomagnetic fields at etna volcano summary 3 d magneto elastic models based on finite element method fem have been developed to compute piezomagnetic fields caused by magmatic overpressure sources we solved separately i the elastostatic equation for the stress field and ii the coupled poisson s equation for magnetic potential field the numerical computations were focused on a more realistic modelling of etna volcano where remarkable magnetic changes have been observed during eruptive events we evaluated the effects of topography and medium heterogeneities considering different multilayered crustal structures constrained by seismic tomography and geological evidences when topography and magneto elastic heterogeneities are included in the numerical models the piezomagnetic field changes show significant deviations from the homogeneous half space solution generally it was found that the analytical model overestimates the expected magnetic changes the numerical models of the piezomagnetic field showed significant differences in presence of strong magnetization contrasts and in proximity of steep cliffs that is at the volcano summit the fem approach presented here allows considering a picture of a fully 3 d model of etna volcano which could advance the reliability of model based assessments of magnetic observations

p wave attenuation of the yellowstone caldera from three dimensional inversion of spectral decay using explosion source seismic data using explosion source seismic refraction data recorded in the 1978 and 1980 yellowstone snake river plain seismic experiments a three dimensional inversion of differential p wave attenuation was used to assess the relative variations in q 1 in and around the volcanically active 45 km by 70 km yellowstone caldera northwestern wyoming differential attenuation was derived from spectral decay of upper crustal pg phases observed from six explosions and recorded at 90 temporary stations because of the relatively short time windows used to determine the spectral content a maximum entropy technique was employed to estimate the spectra that yielded an optimally small variance differential p wave attenuation was calculated from least squares determinations of the spectral ratios corrected for source and path effects the observed differential attenuation parameters were then inverted using a weighted least squares technique for a discretized 70 105 km three dimensional surface and upper crustal q 1 model of the yellowstone caldera and surrounding region results showed that the surface layer to depths of 2 km within the yellowstone caldera is characterized by relatively high attenuation with low q values less than 30 compared to values of 38 to 50 outside the caldera the higher attenuation in the caldera s surface layer is thought to be associated with quaternary lake sediments highly altered rhyolites and the possible influence of steam in areas of hydrothermal activity in the crystalline upper crust at depths of 2 km to 12 km q values of 40 to 70 were observed in areas of thick sedimentary fill northwest of the caldera and in areas of hydrothermal activity within the caldera upper crustal attenuation generally corresponded to q of 200 in areas that are interpreted to be associated with hot but now solidified granitic material in comparison relatively high attenuation q 40 was observed in the upper crust of the northeastern yellowstone caldera in an area that also corresponds to a 20 reduction in pg velocity a prominent negative bouguer gravity low of 20 mgal near yellowstone s largest area of hydrothermal activity and near a quaternary volcanic resurgent dome on the basis of constitutive models of velocity and density this zone of high attenuation is likely a product of unusual hydrothermal activity highly altered upper crustal rocks a shallow magmatic source or a highly porous steam saturated body outside the caldera the upper crust is relatively unaffected by high temperatures and thermal alteration and the corresponding attenuation is low with q values greater than 200

tomographic inversion of p wave velocity and q structures beneath the kirishima volcanic complex southern japan based on finite difference calculations of complex traveltimes summary we estimate the p wave velocity and attenuation structures beneath the kirishima volcanic complex southern japan by inverting the complex traveltimes arrival times and pulse widths of waveform data obtained during an active seismic experiment conducted in 1994 in this experiment six 200 250 kg shots were recorded at 163 temporary seismic stations deployed on the volcanic complex we use first arrival times for the shots which were hand measured interactively the waveform data are fourier transformed into the frequency domain and analysed using a new method based on autoregressive modelling of complex decaying oscillations in the frequency domain to determine pulse widths for the first arrival phases a non linear inversion method is used to invert 893 first arrival times and 325 pulse widths to estimate the velocity and attenuation structures of the volcanic complex wavefronts for the inversion are calculated with a finite difference method based on the eikonal equation which is well suited to estimating the complex traveltimes for the structures of the kirishima volcano complex where large structural heterogeneities are expected the attenuation structure is derived using ray paths derived from the velocity structure we obtain 3 d velocity and attenuation structures down to 1 5 and 0 5 km below sea level respectively high velocity pipe like structures with correspondingly low attenuation are found under the summit craters these pipe like structures are interpreted as remnant conduits of solidified magma no evidence of a shallow magma chamber is visible in the tomographic images

a scattering image of campi flegrei from the autocorrelation functions of velocity tomograms summary we propose a new quantitative approach for the joint interpretation of velocity and attenuation tomography images performed through the lateral separation of scattering and intrinsic attenuation the horizontal p wave scattering attenuation structure below campi flegrei caldera cfc is imaged using the autocorrelation functions acf of p wave vertical velocity fluctuations cluster analysis ca is then applied to interpret the images derived from acf and the available p wave total attenuation images at 2000 m quantitatively the analysis allows the separation of intrinsic and scattering attenuation on a 2 d plane adding new geophysical constraints to the present knowledge about this volcanic area the final result is a new quantitative image of the past and present tectonic and volcanological state of cfc p wave intrinsic dissipation dominates in an area approximately located under the volcanic centre of solfatara as expected in a region with a large presence of fluids and gas a north south scattering attenuation region is mainly located below the zone of maximum uplift in the 1982 1984 bradiseismic crisis in the sea side of the pozzuoli bay but also extending below mt nuovo this evidence favours the interpretation in terms of a hard but fractured body contoured by strong s wave scatterers corresponding to the caldera rim the region is possibly a section of the residual magma body associated with the 1538 eruption of mt nuovo

seismic anisotropy time variations at mt etna this article has been accepted for publication in geophysical journal international the authors 2020 published by oxford university press on behalf of the royal astronomical society all rights reserved uploaded in accordance with the publisher s self archiving policy

new insights into magma dynamics during last two eruptions of mount etna as inferred by geochemical monitoring from 2002 to 2005 two distinct eruptive events characterize the volcanic activity at mount etna during the 2002 to 2005 period we identified signals of magma ascent preceding these eruptions by geochemical monitoring of both chemical composition and he isotope ratio of gas emissions from five locations in the peripheral area of the volcano the geochemical signals are interpreted using the models proposed by caracausi et al 2003a 2003b and allow identification of episodes of magma ascent and estimation of the pressures of degassing magma as observed for the 2001 eruption caracausi et al 2003b magma ascent probably triggered the onset of the 2002 2003 eruption and minor events of magma ascent were observed between may and december 2003 in contrast to the previous two eruptions the 2004 2005 eruption was not preceded by significant geochemical signals of volcanic unrest suggesting that this eruption was mainly triggered by the failure of the upper portion of the volcanic edifice under the magmatic hydrostatic pressure in the conduits high 3he 4he ratio revealed new volatile rich magma accumulation the 2002 2003 eruption was preceded by a much shorter period of new magma accumulation from deep levels of the feeding system few minor signals of magma migration were detected at some of the sites during the months preceding the 2004 2005 eruption suggesting that the degassed 3he depleted magma resident in the volcanic conduits was not replaced by new volatile rich magma this is in agreement with the lack of explosive activity during the 2004 2005 eruption and with petrologic observations that the parent magma probably erupted in 2000 and 2001 new geochemical signals of magma ascent from the deep reservoir have been identified since june 2005 indicating that the volcanic activity of mount etna is evolving toward new pre eruptive conditions

seismicity and velocity structures along the south alpine thrust front of the venetian alps ne italy abstract in this paper we show the seismicity and velocity structure of a segment of the alpine retro belt front along the continental collision margin of the venetian alps ne italy our goal is to gain insight on the buried structures and deep fault geometry in a silent area i e an area with poor instrumental seismicity but high potential for future earthquakes as indicated by historical earthquakes 1695 me 6 7 asolo and 1936 ms 5 8 bosco del cansiglio local earthquakes recorded by a dense temporary seismic network are used to compute 3 d vp and vp vs tomographic images yielding well resolved images of the upper crust underneath the south alpine front we show the presence of two main distinct high vp s verging thrust units the innermost coincides with the piedmont hill and the outermost is buried under a thick pile of sediments in the po plain background seismicity and vp vs anomalies interpreted as cracked fluid filled volumes suggest that the ne portion of the outermost blind thrust and its oblique lateral ramps may be a zone of high fluid pressure prone to future earthquakes three dimensional focal mechanisms show compressive and transpressive solutions in agreement with the tectonic setting stress field maps and geodetic observations the bulk of the microseismicity is clustered in two different areas both in correspondence of inherited lateral ramps of the thrust system tomographic images highlight the influence of the paleogeographic setting in the tectonic style and seismic activity of the region

qp structure of mount etna constraints for the physics of the plumbing system 1 in this study we present the three dimensional qp structure of the mount etna volcano italy obtained by using local earthquake data the attenuation along ray paths t computed from the high frequency decay of velocity spectra is used to reconstruct the deep structure of the volcano down to 15 km depth the tomographic images reveal two broad low qp anomalies at 0 and 3 km depth located to the south and southwest of the summit area and extending at depth to the west of a central high qp anomaly located between 6 and 15 km depth the joint analysis of p wave attenuation and velocity allows us to better constrain the physics of the plumbing system the shallow low qp anomalies are associated with high vp anomalies beneath the top of the volcano and normal low vp toward its western borders we interpret the regions of low qp and normal low vp as shallow volumes where magmatic fluids are stored conversely the low qp high vp region may indicate intensely fractured rock volumes filled by fluids surrounding the magma branches at depth the low qp anomaly defines the path of the magma ascent to the west of an extremely high qp high vp volume located beneath the southeastern side of the summit area the high qp high vp body is interpreted to be the compact solidified high density intrusive body formed by nonerupted material during past volcano activity

shear modulus and q of forsterite and dunite near partial melting from forced oscillation experiments an apparatus designed to determine the complex shear modulus of rock samples by forced torsion oscillations at high temperature and in the seismic frequency band 0 003 30 hz is briefly described measurements were performed on natural dunite from aheim norway up to 1400 c and on polycrystalline forsterite up to 1500 c at 1 atm pressure the two materials were chosen to study by comparison the effect of melt on the elasticity and anelasticity of mantle rocks between 1000 and 1200 c the absolute values of the shear modulus g are almost equal for both materials above 1200 c g for natural dunite decreases progressively with temperature and at 1400 c and 1 hz reaches 13 of its value at 1100 c in contrast g of pure forsterite depends little on temperature for petrological reasons supported by simultaneous measurements of the electric resistivity there is strong evidence that the decrease of g in dunite above 1200 c is due to melt from the lower melting components of the dunite based on different models estimates of the melt fraction are made at high temperature in both materials q 1 is characterized by a monotonic decrease with frequency according to with 0 25 an apparent activation energy of 38 5 kcal mol 1 for forsterite and 48 8 kcal mol 1 for dunite was found with no significant change in the regime of partial melting from this it is concluded that q 1 even at partial melting is dominated by solid state high temperature background absorption there is no indication from these experiments for a constant q band at low seismic frequencies or an increase of q proportional to frequency as suggested by some seismologists the present results are in good qualitative agreement with those for young s modulus obtained previously by strain retardation experiments

p wave attenuation structure in the fault area of the 1995 kobe earthquake the three dimensional 3 d p wave attenuation structure in the kobe epicentral area is determined using aftershock records from the 1995 kobe hyogo ken nanbu earthquake waveform data from both permanent seismic networks and portable stations set up following the kobe mainshock were used the observed p wave amplitude spectra were inverted for the spectral plateau value the source corner frequency and a frequency independent t operator assuming an 2 type source model the calculated t operators were subsequently used for the computation of the 3 d absorption structure using a 3 d velocity model only high quality amplitude spectra were used for the estimation of reliable attenuation parameters resulting in a final data set of 4100 t operators two regions of high absorption were found in the upper part of the crust one is below the northern part of awaji island and reaches down to a depth of 5 km the other region northeast of kobe city is along the arima takatsuki tectonic line and extends along the rokko kashiodani and yamada faults it extends northward to the hokusetsu sanchi area in both regions a high density of fault lineations is mapped and high poisson ratios are known this suggests that partially saturated cracks cause the observed high attenuation

a three dimensional image of shallow subduction crustal structure of the raukumara peninsula new zealand summary earthquake arrival time data from a 36 station deployment of portable seismographs on the raukumara peninsula have been used to determine the 3 d vp and vp vs structure of this region of shallow subduction a series of inversions have been performed starting with an inversion for 1 d structure then 2 d and finally 3 d this procedure ensures a smooth regional model in places of low resolution the subducted plate is imaged as a northwest dipping feature with vp consistently greater than 8 5 km s 1 in the uppermost mantle of the plate structure in the overlying plate changes significantly along strike in the northeast there is an extensive low velocity zone in the lower crust underlying the most rapidly rising part of the raukumara range it is bounded on its arcward side by an upwarp of high velocity a viable explanation for the low velocity zone is that it represents an accumulation of underplated subducted sediment while serpentinization of the uppermost mantle may be responsible for the adjacent high velocity region the low velocity zone decreases and the adjacent high velocity region is less extensive in the southwest this change is interpreted to be related to a change in the thickness of the crust of the overlying plate in the northeast the crust is thinner and subducted sediment ponds against relatively strong uppermost mantle while in the southwest the crust is thicker and the relatively weak lower crust allows sediment subduction to greater depths a narrow zone of high vp vs parallels the shallow part of the plate interface this suggests elevated fluid pressures with the distribution of earthquakes about this zone further suggesting that these pressures may be close to lithostatic the plate interface at 20 km depth beneath the raukumara peninsula may thus be a closed system for fluid flow similar to that

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

volcano topography structure and intrinsic attenuation their relative influences on a simulated 3d visco elastic wavefield the seismic wavefield recorded on volcanoes can be significantly influenced by path effects scattering from the topography and internal volcanic structure can play a dominant role in the recorded seismograms intrinsic attenuation is also thought to play an important role in the characteristics of volcano seismic signals we use 3d numerical modelling of wave propagation in elastic and visco elastic media including complex velocity models and topography to investigate the scattering and attenuation characteristics of synthetic seismograms we generate 5 distinct volcano models and simulate wave propagation through these models using shallow and deep double couple broadband sources we then analyse 129 synthetic seismograms calculated on the free surface the synthetic seismograms resemble vt a and vt b events the scattering effect of the topography alone is capable of producing complex seismograms the introduction of an internal velocity structure increases the duration of these seismograms while the introduction of intrinsic attenuation decreases the duration but not the complexity we fitted our synthetic seismograms to the diffusion in a half space model to quantify the scattering and attenuation coefficients the scattering quality factor measured on all 129 stations for all 5 volcano models was similar therefore we deduce that the topography appears to be the dominant scatterer the intrinsic attenuation quality factor for each of the specific models cannot be accurately recovered using the diffusion in a half space model the measured quality factor is not only sensitive to the attenuation properties but also to the structural properties in all cases the scattering is more dominant than the intrinsic attenuation

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

intrusive mechanism of the 2008 2009 mt etna eruption constraints by tomographic images and stress tensor analysis abstract since january 2008 several geophysical parameters have evidenced a recharging phase at mt etna volcano culminating with an effusive eruption that began on may 13 2008 seismic activity recorded at mt etna from january 2007 to may 2008 was analyzed in order to provide seismological constraints to the volcano dynamics leading to the eruption a total of 336 selected earthquakes with m l 1 5 were used as data source for this study specifically we calculated 3d velocity and attenuation tomography including a 3d relocation of the events and we computed 53 selected fault plane solutions fpss that were used for stress tensor inversion the most important result obtained from the joint analysis of v p v p v s and p wave attenuation is an anomalous zone with normal to high v p values between 3 5 and 4 5 km s and low v p v s values 1 64 which partially overlaps with a low q p values 50 volume located along a ns trending channel beneath the central crater this can be interpreted as a shallow volume characterized by high temperature where the magma is located with the presence of supercritical fluids the analysis of seismic stress tensor evidenced an extensional regime in the depth range 3 13 km with a vertically oriented 1 this finding may suggest an extensional stress regime probably related to the kinematic response of the volcanic edifice to both a deep magmatic intrusion and a condition of decreased regional compressive stress facilitated by sliding processes of the eastern flank of the volcano

geochemical evidence for mixing between fluids exsolved at different depths in the magmatic system of mt etna italy abstract a 4 year geochemical survey of some fumaroles at the voragine summit crater of mt etna was performed in combination with synchronous monitoring of peripheral gas emissions at the base of the volcano this was the first geochemical study at mt etna to have included the abundances of ar he and c isotopes once the effects of postmagmatic shallow processes were identified and quantitatively removed the he ar co 2 systematics of the voragine crater fumaroles and peripheral gas emissions described the same degassing path combining the carbon isotope composition with information about noble gases provided evidence that the crater fumaroles are fed from a two endmember mixture composed of a deep member coming from pressures between 200 and 400 mpa depending on time and a shallower one exsolved at 130 mpa similar mixing processes probably also occur in gases from peripheral vents the simultaneous assessment of 13 c co2 and he ar values of crater fumaroles over time has identified simple changes in the mixing proportion between the two endmembers and moreover periods during which the exsolution pressure of the deep fluid increased these periods seem to be linked to pre eruptive phases of the volcano the identified open system degassing processes are indicative of efficient bubble melt decoupling at depth whereas the mixing process requires a convective transfer of the deeply exsolved fluids toward shallower levels of magma where further vapor is exsolved in agreement with the most recent geophysical and petrological data from mt etna these observations allow inferences about a deep portion of the plumbing system 5 to 12 km b s l comprising sill like reservoirs connected by small vertical structures and a main reservoir at 2 3 km b s l that is probably fluxed by magmatic volatiles

the intrusive process leading to the mt etna 2001 flank eruption constraints from 3 d attenuation tomography 1 we have analyzed 291 shallow seismic events leading to the july 17 august 9 2001 flank eruption at mt etna volcano to obtain high resolution three dimensional 3 d images of seismic attenuation of p waves qp down to 2 km depth 2293 p wave spectra have been inverted for seismic attenuation to calculate t values considering a frequency independent q and a 2 type source model the 3 d tomographic images reveal an anomalous region of very low qp values between 10 and 30 located in the same place where the 2001 dike emplaced we interpret this anomaly as the effect of fluid intrusion magma rich in gas in the uppermost part of the etna volcano just before the 2001 eruption this confirms that attenuation is a physical parameter sensitive to the thermal state of crustal volumes through which seismic waves travel

the dyke swarm of mount calanna etna italy an example of the uppermost portion of a volcanic plumbing system a new multidisciplinary study combining geology petrography and geochemistry on the rocks of the isolated hill of mount calanna mount etna italy has provided evidence for the existence of a dyke swarm formed by more than 200 dykes distributed over an area of 0 7 km2 with an intensity of intrusion up to 40 all bodies are deeply altered and the geological and mesostructural surveying of 132 dykes revealed that they intruded in e w direction with an average dip of 60 the faults affecting the outcrop have in general an e w strike and dip of 55 these have all normal motion and have been interpreted as coeval with the dykes this interpretation contrasts with the previous hypothesis that considered mount calanna as a thrust resulting from compressive deformation resulting from the gravitational spreading of the volcanic edifice mount calanna is here interpreted as the uppermost portion of a vertically extensive magmatic plexus that fed the eruptive activity of one or more eruptive center s sited in the valle del bove area measurements of the apparent densities on 23 dykes and host rock samples give an average value of 2 420 kg m3 for the entire complex 15 lower than the density expected for hawaiitic magma placing an important constraint on the geophysical identification of similar structures considering that mount etna is not an old eroded edifice but an active and growing volcano the exposure of this subvolcanic structure can be regarded as exceptional its geometry and physical characteristics can be thus regarded as an interesting example of the present day shallow plumbing system of mount etna as well as of other basaltic volcanoes

temperature dependent viscoelastic modeling of ground deformation application to etna volcano during the 1993 1997 inflation period abstract we used the finite element method fem for modeling time dependent ground deformation due to volcanic pressure sources embedded in a viscoelastic medium especially in volcanic areas the presence of heterogeneous materials and high temperatures produce a lower effective viscosity of the earth s crust that calls for considering the thermal regime of crustal volume surrounding the magmatic sources we propose a thermo mechanical numerical model for evaluating the temperature dependency of the viscoelastic solution both temperature distributions and ground deformation are evaluated by solving an axi symmetric problem to estimate the effects of thermo viscoelastic response of the medium the thermo mechanical model permits to evidence that viscoelastic relaxation is responsible for significant time dependent variations in long term deformation these effects may be relevant for the interpretation and quantitative assessments of the pressure changes within magmatic sources with this in mind we reviewed the ground deformation observed on etna volcano during the 1993 1997 inflation period by setting up a fully 3d temperature dependent viscoelastic model since 1993 different geodetic measurements edm gps sar and leveling data identified an inflationary phase characterized by a uniform and continuous expansion of the overall volcano edifice that was not perturbed by eruptive activity the numerical model including significant viscoelastic material and reduced crustal rigidity around the magmatic source enables to produce deformation comparable with those obtained from elastic model requiring a significantly lower pressure for a purely elastic model with the same geometry and rigidity the pressure change necessary to describe the 1993 through 1997 inflation is around 320 mpa whereas for the viscoelastic model a pressure increase of about 200 mpa is required

chlorine partitioning between a basaltic melt and h2o co2 fluids at mount etna abstract partitioning experiments between a basaltic melt from mt etna and a low density hydrous fluid or vapor containing h 2 o or h 2 o co 2 were performed at 1200 1260 c at pressures between 1 and 200 mpa either near the nickel nickel oxide nno buffer or at two log units above it nno 2 and with different chloride concentrations most of the experiments were done at chloride brine undersaturated conditions although at the highest cl concentrations explored brine saturation might have been reached the average partition coefficients d cl fluid melt over the range of cl concentrations were derived on a weight basis by plotting the calculated concentrations of cl in the fluid phase versus the measured ones in the melt for h 2 o cl experiments in which the cl concentration in the melt was 0 4 wt a negative dependence between d cl f m and pressure is observed d cl fluid melt in h 2 o cl bearing experiments ranges between 11 14 at 1 and 25 mpa to 6 at 200 mpa at nno and between 4 at 50 mpa and 13 at 100 mpa at nno 2 addition of co 2 at nno yields lower partition coefficients than in co 2 free conditions over the pressure range investigated the negative pressure dependence observed for h 2 o cl experiments disappears when co 2 is present in the system overall once co 2 is introduced in the system cl fugacity in the silicate melt tends to increase thus resulting in a decrease of d cl f m application to mt etna shows that the composition of the volcanic plume in terms of cl records very shallow pressures of magma equilibration with its exsolved fluid

three dimensional seismic velocity structure and earthquake relocations at katmai alaska abstract we invert arrival time data from local earthquakes occurring between september 2004 and may 2009 to determine the three dimensional 3d upper crustal seismic structure in the katmai volcanic region waveforms for the study come from the alaska volcano observatory s permanent network of 20 seismic stations in the area predominantly single component short period instruments plus a densely spaced temporary array of 11 broadband 3 component stations the absolute and relative arrival times are used in a double difference seismic tomography inversion to solve for 3d p and s wave velocity models for an area encompassing the main volcanic centers the relocated hypocenters provide insight into the geometry of seismogenic structures in the area revealing clustering of events into four distinct zones associated with martin mageik trident novarupta and mount katmai the seismic activity extends from about sea level to 2 km depth all depths referenced to mean sea level beneath martin is concentrated near 2 km depth beneath mageik and lies mainly between 2 and 4 km depth below katmai and trident novarupta many new features are apparent within these earthquake clusters in particular linear features are visible within all clusters some associated with swarm activity including an observation of earthquake migration near trident in 2008 the final velocity model reveals a possible zone of magma storage beneath mageik but there is no clear evidence for magma beneath the katmai novarupta area where the 1912 eruptive activity occurred suggesting that the storage zone for that eruption may have largely been evacuated or remnant magma has solidified

seismic attenuation above 10 hz in southern california from coda waves recorded in the cajon pass borehole we estimate the attenuation around cajon pass southern california for frequencies above 10 hz and we find total q to exhibit only weak frequency dependence ranging from 800 at 10 hz to 1500 at 100 hz the intrinsic attenuation is approximately twice the level of the scattering attenuation measurements are made using earthquake seismograms recorded at 0 3 km depth using the multiple lapse time window method the results are not dependent on receiver depth and are consistent with previous estimates of q made from direct waves recorded at 2 5 km depth our q values are therefore thought to be representative of the seismogenic crust and the technique used is uncontaminated by the highly attenuating near surface at least above 10 hz we also calculate q from surface data between 1 and 10 hz and find a clear change in the frequency dependence of both intrinsic and scattering attenuation at 10 hz q exhibits strong frequency dependence below 10 hz 1 8 consistent with previous studies in active tectonic regions and only weak frequency dependence at higher frequencies 0 34 this change in behavior renders it unwise to extrapolate q measurements outside the frequency range from which they were derived for example in earthquake source studies possible factors responsible for the apparent change in frequency dependence of q are considered further work is required however to resolve the causes of this change

response of mount etna to dynamic stresses from distant earthquakes 1 influences of distant earthquakes on volcanic systems by dynamic stress transfer are well documented we analyzed seismic signals and volcanic activity at mount etna during two periods january 2006 and may 2008 that clearly showed variations coincident with distant earthquakes in the first period characterized by mild volcano activity the effect of the dynamic stress transfer caused by an earthquake in greece m 6 8 was twofold 1 banded tremor activity changed its features and almost disappeared 2 a swarm of volcano tectonic vt earthquakes took place the changes of the banded tremor were likely due to variations in rock permeability caused by fluid flows driven by dynamic strain the vt earthquake swarm probably developed as a secondary process promoted by the dynamically triggered activation of magmatic fluids the second period may 2008 showed an intense explosive activity during this interval the dynamic stress transfer associated with the arrival of the seismic waves of the sichuan earthquake m 7 9 affected the character of the seismo volcanic signals and on the following day triggered an eruption in particular we observed changes in volcanic tremor and increases of both occurrence rate and energy of long period events in this case we suggest that dynamic stress transfer caused nucleation of new bubbles in volatile rich magma bodies with consequent buildup of pressure highlighted by the increase of long period activity followed by the occurrence of an eruption we conclude that stresses from distant earthquakes are capable of modifying the state of the volcano

seismic tomography of compressional wave velocity and attenuation structure for makushin volcano alaska abstract located in the central portion of the alaska aleutian subduction zone makushin volcano is among the most active volcanoes in the united states and has been classified as a very high threat by the national volcano early warning system based on its eruptive history and proximity to the city of unalaska and international air routes in 2015 five standalone seismic stations and three mini seismic arrays of 15 stations each were deployed on unalaska island to supplement the alaska volcano observatory permanent seismic network this temporary array was operational for one year taking advantage of the increased azimuthal coverage and the array s increased earthquake detection capability we developed body wave vp and vp vs seismic images of the velocity structure beneath the volcano our results show a complex structure with the upper 4 km of the crust the shallow high vp features possibly delineate remnant magma pathways or conduits low vp regions are found east of the caldera at approximately 4 8 km depth this is in agreement with previous seismic tomographic work and insar based geodetic models which had identified this region as a possible long term source of magma a three dimensional compressional wave attenuation model complemented the velocity models in general we observe regions of corresponding low p wave velocity and high attenuation east of the summit caldera between 5 and 7 km depth supporting the presence of a melt rich zone the absolute vp values 5 5 6 0 km s in this region are consistent with the presence of a magma body with a mafic signature we suggest that a triggering mechanism that involves mafic injections into a more evolved shallow magma chamber is representative of the current magmatic system below the volcano similarly to what petrological studies have inferred for past eruptions

mount etna dense array local earthquake p and s tomography and implications for volcanic plumbing inversion for the three dimensional velocity structure of mount etna is performed with a data set of arrival times of p and s waves of local earthquakes from temporary dense arrays of three component seismographs a high v p body revealed by the original tomography without nearby stations is confirmed and its image is sharpened using new velocity constraints provided by refraction data synthetic tests of v p and v p v s and comparison with an independent artificial source tomography with a fundamentally different geometry consistently calibrate the significance threshold of the resolution indicators the trustworthy part of the image shows a high v p body centered under the southern part of valle del bove above the 6 km below sea level deep basement which extends towards sea level and may be rooted in or through the crust it has a large contrast of over 1 km s with the surrounding sediments and sharp lateral limits and can thus be regarded as made of intrusive material of magmatic origin the massive high v p body is heterogeneous in v p v s the regions inside it where v s is relatively low can then be suspected of containing a proportion of melt or be fractured and act as pressure links or transport zones such features may be structurally linked and appear to be activated in eruptive phenomena by taking into account the heterogeneities in structure and physical state retrieved by seismic tomography a succession of seismic events deformational episodes and geochemical variation in lavas can be discussed with respect to the well observed eruptions

attenuation and source parameters of earthquakes in the cascadia region digital ground motion data recorded by the western canada telemetered network wctn are used to examine the attenuation and source parameters of earthquakes in the cascadia region of southwestern british columbia and northwestern washington the data base is comprised of over 1000 vertical component fourier spectra from earthquakes of magnitude 3 to 7 at distances from 10 to 500 km regression analyses determine the shape and coefficients of the regional attenuation curve and source spectra for 68 earthquakes seismic moment and stress drop are inferred from the amplitudes of the source spectra shallow h 10 km earthquakes have an attenuation curve with a complex shape exhibiting significant flattening no apparent geometric spreading in the distance range from 75 to 230 km this shape is probably a result of strong reflected phases from mid crustal discontinuities and the subducting slab events within the subducting slab and the lower crust exhibit a simple r 1 attenuation curve the anelastic attenuation coefficient for the region as a whole is given by q 380 f 0 39 the duration of motion for each wctn record is determined as the value that yields the observed relationship between time domain and spectral domain amplitudes according to random process theory these durations are approximately constant within 50 km of the source then increase with distance as 0 07 r the high frequency ground motions from cascadia earthquakes are relatively weak cascadia source spectra are characterized by an average brune stress drop of about 30 bars this is significantly lower than the average california stress drop of 70 to 100 bars and dramatically lower than the average eastern stress drop of 150 to 200 bars it is concluded that there are significant regional variations in source parameters hazard estimates for the cascadia region based on california groundmotion relations may be overly conservative

attenuation of short period seismic waves at etna as compared to other volcanic areas codaq for etna volcano is frequency dependent and theq frequency pattern and the numerical values ranging from about 100 at 1 hz to about 300 at 18 hz are similar to the values obtained for other volcanoes campi flegrei aeolian islands and hawaii moreover the frequency pattern and the numerical values of coda quality factor for most of the seismically active zones of italy are very different from those of the volcanic zones

seismic attenuation imaging of campi flegrei evidence of gas reservoirs hydrothermal basins and feeding systems 1 passive high resolution attenuation tomography is used here to image the geological structure in the first upper 4 km of the shallow crust beneath the campi flegrei caldera southern italy the inverse q was estimated for each source receiver path using the coda normalization method s waves and the slope decay method p waves and s waves inversion was performed using a multi resolution method which ensures a minimum cell size resolution of 500 m the study of the resolution matrix as well as the synthetic tests guarantee an optimal reproduction of the input anomalies in the center of the caldera between 0 and 3 5 km in depth high attenuation vertical structures are connected at the surface with the main volcanological features e g the solfatara and mofete fumarole fields and depict vertical q contrast imaging important geological structures such as the la starza fault these high attenuation volumes extend between the surface and a depth of about 3 km where a hard rock layer is imaged by the sharp contrast of the quality factors the retrieved image of the campi flegrei has been jointly interpreted taking into account evidence from seismological geological volcanological and geochemical investigations this analysis has allowed an unprecedented view of the feeding systems in this area and in particular it recognizes the vertically extending high attenuation structures that correspond to gas or fluid reservoirs beneath pozzuoli solfatara solfatara mofete mt nuovo and agnano this high attenuation system is possibly connected with the magma sill revealed at about 7 km in depth by passive travel time tomography

a three dimensional qp imaging of the shallowest subsurface of campi flegrei offshore caldera southern italy to improve the knowledge of the shallowest subsurface of campi flegrei caldera a 3 d p wave attenuation tomography of the area was performed we analyzed about 18 000 active seismic traces which provided a dataset of 11 873 t measurements e g the differential traveltimes to quality factor ratios these were inverted through an adapted tomographic inversion procedure the 3 d tomographic images reveal an average qp about 70 interpreted as water saturated volcanic and marine sediments an arc like low qp structure at 0 5 1 km depths was interpreted as a densely fractured fluid saturated rock volume well matching the buried rim of campi flegrei caldera the spatial distribution of high and low qp bodies in the inner caldera is correlated with low vp values and may reflect either the differences in the percentage of fluid saturation of sediments or the presence of vapor state fluids beneath fumaroles manifestations

new evidence for the serpentinization of the palaeozoic basement of southeastern sicily from joint 3 d seismic velocity and attenuation tomography

three dimensional attenuation model of the shallow hikurangi subduction zone in the raukumara peninsula new zealand 1 the material properties of the shallow subduction zone are imaged with data from a passive seismic deployment in the raukumara peninsula attenuation images are obtained using t values measured from 2848 spectra of p wave arrivals the t values are inverted for frequency independent three dimensional 3 d qp using a 3 d velocity model linked nodes in a preliminary 2 d inversion are used to obtain the most reliable initial model for 3 d inversions the results show the benefits of obtaining 3 d q in addition to 3 d vp and vp vs q is related to localized permeability and heterogeneity and thus 3 d q is an important tool for interpreting active tectonic regions qp in the shallow overlying plate generally corresponds to the mapped geology two high qp features 600 represent subducted seamounts or cretaceous volcanics within the overlying plate the gradient above the subducting plate is the strongest feature in the qp model with the slab having high qp 600 900 below 20 km depth and above the plate interface there is a zone of 50 decrease in qp and high vp vs about 10 km thick which represents actively subducting sediment and has distributed microearthquake activity associated with active underplating

gravity steps at mt etna volcano italy instrumental effects or evidences of earthquake triggered magma density changes 1 on two occasions sudden gravity changes occurred simultaneously at two summit etna s stations during local low magnitude earthquakes a systematic coupling between earthquakes inducing comparable maximum acceleration and displacement at the observation points and gravity steps is missing implying 1 the non instrumental nature of the steps and 2 the need for particular underlying conditions for the triggering mechanism s to activate we review some of the volcanological processes that could induce fast underground mass redistributions resulting in gravity changes at the surface these processes involve bubbles and crystals present in the magma and require particular conditions in order to be effective as mass redistributing processes the gravity steps could be a geophysical evidence of the dynamical stress transfer between tectonic and magmatic systems at a local scale given the implications that these transfers may have on the volcanic activity routine volcano monitoring should include the observation of fast gravity changes

the role of long period ground motions on magnitude and damage of volcanic earthquakes on mt etna italy on october 2002 a seismic swarm occurred on mt etna one of the strongest events caused severe damage up to a european macroseismic scale inten sity of viii that contrasts with its local magnitude of 4 4 the occurrence of significant damage at such a small magnitude is repeatedly observed in the area and is tradition ally attributed to shallow source recorded strong motion accelerograms and broad band seismograms demonstrate that there is one more cause for the severe damage that is an anomalously strong low frequency 0 1 f 1 hz radiation deviating from the conventional brune 1970 spectral scaling therefore these earthquakes cause large ground displacements and long 20 sec durations of shaking the integration of digital accelerograms yields a maximum peak ground displacement as large as 1 8 cm at a distance of 18 km based on the sharp local attenuation of ground motion in the study area we infer that peak ground displacements near the epicenters did exceed 10 cm the occurrence of large displacements caused selective damage to medium rise 3 stories reinforced concrete buildings and elements like church facades the frequency cutoff below 1 25 hz in the wood anderson response attenuates the peak to peak amplitudes used to assess local magnitudes therefore ml values are not representative of the real strength of volcanic earthquakes because a prompt magnitude and damage potential assessment is crucial for civil protection actions a procedure is proposed which in near real time can be successful in identifying po tentially damaging earthquakes of mt etna through the computation of pseudove locity response spectra the procedure provides a magnitude value that is derived on a statistical basis from the housner 1952 spectral intensity computed in the low frequency band this parameter is a suitable near real time indicator of large earthquake induced building shaking and could also be applied for a preliminary es timate of the epicentral macroseismic intensity

attenuation tomography in the western central andes a detailed insight into the structure of a magmatic arc high quality data from 1498 local earthquakes recorded by the pisco 94 proyecto de investigation sismologica de la cordillera occidental 1994 and ancorp 96 andean continental research project 1996 temporary seismological networks allowed the detailed determination of the three dimensional 3 d attenuation structure qp 1 beneath the recent magmatic arc in the western central andes 20 to 24 s assuming a frequency independent qp 1 in a frequency band between 1 and 30 hz whole path attenuation t was estimated from the amplitude spectra of the p waves using spectral ratios and a spectral inversion technique the damped least squares inversion tomography of the data reveals a complex attenuation structure crust and mantle of the forearc and subducting slab are generally characterized by low attenuation qp 1000 crust and mantle beneath the magmatic arc show elevated attenuation the strongest anomaly of extremely low qp is found in the crust between 22 and 23 s beneath the recent volcanic arc qp 100 n s variations can be observed the western flank of the crustal attenuation anomaly follows the curved course of the volcanic front north of 21 s the attenuation is less developed in the northern part of the study area the low qp zone penetrates in the forearc mantle down to the subducting slab in the south a deeper zone of high attenuation is resolved between 23 and 24 s directly above the subducting slab low qp in the mantle correlates with earthquake clusters the strong crustal attenuation is confined to the distribution of young ignimbrites and silicic volcanism and is interpreted as a thermally weakened zone with partial melts the attenuation pattern in the upper mantle might reflect the variable extent of the asthenosphere and maps variations of subduction related hydration processes in the mantle wedge from slab derived fluids

seismic tomography of the crust underneath the etna volcano sicily abstract a new tomographic inversion of the velocity structure and hypocenter parameters has been carried out in the etna area using a remarkably larger seismic dataset than used in the previous investigations the obtained v p and v p v s space distributions allow us to detail the already known structural features and to find new velocity anomalies a major aseismic high velocity body is recognized in the upper 10 km beneath the central crater area and the southeastern flank of the volcano interpreted as high strength magmatic rocks such as cumulites dike structures etc a high level of seismic activity and low v p values are found immediately to the west and the east of the high velocity body suggesting the presence of highly fractured weakness zones which also taking into account the local distribution of seismogenic stress can be supposed to include paths for magma rising and stationing clear evidence is also found of a shallow aseismic low velocity zone beneath the volcano s southwestern flank corresponding to the volume where previous investigators hypothesized the presence of a magma chamber on the grounds of geodetic data and seismic b value mapping

qp melting temperature relation in peridotite at high pressure and temperature attenuation mechanism and implications for the mechanical properties of the upper mantle the anelastic properties of compressional waves in a peridotite have been determined in the laboratory at sufficiently high temperatures to 1280 c and pressures to 0 73 gpa to warrant comparison with seismic measurements of the earth a substantial decrease of qp is observed at temperatures well below the onset of partial melting qp systematically increases with increasing pressure over the entire temperature range of major significance is the finding that qp is dependent on the ratio of the temperatures to the melting solidus temperature i e qp depends on the homologous temperature the pressure dependence of qp appears through the pressure dependence of the solidus of the peridotite within the uncertainties of measurement of both qp and the phase diagram it appears that melting and high temperature anelastic properties have a common origin in peridotite the homologous temperature dependence of qp suggests that we may estimate the temperature and pressure dependence of qp for peridotites of different compositions and possibly even for hydrous peridotites if solidus temperatures are known as a function of pressure a far easier measurement than elastic and anelastic properties the activation volume of qp is greatly reduced at high pressure since the slope of solidus versus pressure rapidly decreases with increasing pressure pressure dependence of seismic velocity and melt fraction in peridotite also appears to be related to the homologous temperature the qp homologous temperature relation suggests a connection between qp and the properties of the grain boundaries that is the major loss of seismic energy occurs at the grain boundaries grain boundary relaxation or high temperature background attenuation is a possible mechanism for the grain boundary damping no frequency dependence of qp is resolved 0 0 2 in qp f over the pressure temperature and frequency ranges of the measurement the present results and the model of grain boundary relaxation suggest that an appropriate choice of grain size may give an ultrasonic q that is applicable to the earth experimentally determined anelastic properties of a peridotite are critical for modeling mechanical properties of the upper mantle implications of the results are as follows 1 seismic data commonly interpreted as indicating a partially molten asthenosphere may instead reflect a hot solid asthenosphere at 90 100 of the solidus temperature 2 partial melting may not produce any abrupt change of seismic velocity and q rather elastic and anelastic properties of the upper mantle will change gradually at the boundary where the geotherm crosses the solidus 3 there may be no sharp mechanical boundary between the lithosphere and the asthenosphere

volcanic deformation and flank instability due to magmatic sources and frictional rheology the case of mount etna summary the overall picture of mount etna deformation emerging since a couple of decades of geodetic surveys shows effects of magma accumulation characterized by inflation deflation cycle accompanied by a sliding instability of the southeast flank whose manifestation is an increase in the horizontal deformation away from the volcano summit this is a very interesting case to test whether advanced models taking into account topography internal structure and frictional rheology may contribute to a better understanding of the complex interplay among mechanical response magmatic activity and gravitational load occurring in a volcanic system using finite element numerical models we make predictions of surface displacements associated with a simple expansion source and with a dike like vertical discontinuity a new methodology is developed to initialize the lithostatic stress field according to the material and geometrical complexities of the models considered our results show that while an amplification of the horizontal displacement can be easily obtained up to a maximum distance of 10 km from the source we have not been able to find any configuration to extend further this signal for the case of mount etna this suggests that the large horizontal displacements observed in the east flank along the coast cannot be directly related to magma accumulation below the volcano s summit

decadal evolution of a degassing magma reservoir unravelled from fire fountains produced at etna volcano italy between 1989 and 2001 between 1989 and 2001 five eruptions at etna displayed a regular alternation between repose periods and episodes rich in gas termed quasi fire fountains and consisting of a series of strombolian explosions sometimes leading to a fire fountain this behaviour results from the coalescence of a foam layer trapped at the top of the reservoir which was periodically rebuilt prior to each episode vergniolle and jaupart j geophys res 95 2793 2809 1990 visual observations of fire fountains are combined with the foam dynamics to estimate the five degassing parameters characteristic of the degassing reservoir i e the number of bubbles gas volume fraction bubble diameter reservoir thickness and reservoir volume the study of decadal cycles of eruptive patterns allard et al earth sci rev 78 85 114 2006 suggests that the first eruption with fire fountains occurred in 1995 while the last one happened in 2001 the number of bubbles and the gas volume fraction increase smoothly from the beginning of the cycle 1995 to its end 2001 the increasing number of bubbles per cubic metre from 0 61 20 105 to 0 1 3 4 109 results from cooling of the magma within the reservoir the simultaneously decreasing bubble diameter from 0 67 0 43 to 0 30 0 19 mm is related to the decreasing amount of dissolved volatiles meanwhile the thickness and the volume of the degassing reservoir diminish from values typical of the magma reservoir to values characteristic of a very thin bubbly layer marking the quasi exhaustion of volatiles the magma reservoir has a slender vertical shape with a maximum thickness of 3 300 8 200 m and a radius of 240 m vergniolle 2008 making its detection from seismic studies difficult its volume at most 0 58 1 4 km3 is in agreement with geochemical studies 0 5 km3 le cloarec and pennisi j volcanol geotherm res 108 141 155 2001 the time evolution of both the total gas volume expelled per eruption and the inter eruptive gas flux results from the competition between the increasing number of bubbles and the decreasing bubble diameter the smooth temporal evolution of the five degassing parameters also points towards bubbles being produced by a self induced mechanism within the magma reservoir rather than by a magmatic reinjection prior to each eruption the decadal cycles are therefore initiated by a magmatic reinjection in agreement with a typical return time of 14 80 years albarede 1993 hence the 1995 eruption results from a fresh magma being newly emplaced while the magma from the following eruptions is progressively depleted in volatiles species until reaching a state of quasi exhaustion in 2001 a magmatic reinjection of 0 13 0 6 km3 every few decades is sufficient to explain the expelled gas volume including so2 a scenario is also proposed for the alternation between gas rich summit eruptions and gas poor flank eruptions which are observed during decadal cycles the scenario proposed for etna could also be at work at piton de la fournaise and erta ale volcanoes

shallow magma pathway geometry at mt etna volcano 1 a fundamental goal of volcano seismology is to understand the dynamics of active magmatic systems in order to assess eruptive behavior and the associated hazard imaging of magma conduits quantification of magma transport and investigation of long period seismic sources together with their temporal variations are crucial for the comprehension of eruption triggering mechanisms at mt etna volcano several intense episodes of tremor activity were recorded during 2007 in association with strombolian activity and or intense fire fountaining episodes occurring from the south east crater sec the locations of the tremor sources and of the long period seismic events are used here to constrain both the area and the depth range of magma degassing highlighting the geometry of the shallow conduits feeding sec the imaged conduits consist of two connected resonating dike like bodies nnw sse and nw se oriented extending from sea level to the surface in addition we show how tremor long period lp and very long period vlp event locations and signatures reflect pressure fluctuations in the plumbing system associated with the ascent discharge of gas rich magma linked to the lava fountains the evidence here reported also corroborated by ground deformation variations can help develop a better prediction and early warning system for those eruptions effusive or explosive that apparently manifest no clear precursors

magma ascent and the pressurization of mount etna s volcanic system after a period of deflation during the 1991 1993 flank eruption mount etna underwent a rapid inflation seismicity and ground deformation show that since 1994 a huge volume of magma intruded beneath the volcano producing from 1998 onward a series of eruptions at the summit and on the flank of the volcano the last of these started on 27 october 2002 is still in progress and can be considered one of the most explosive eruptions of the volcano in recent times here we show how geodetic data and seismic deformation between 1994 and 2001 indicate a radial compression around an axial intrusion consistent with a repressurization of mount etna s plumbing system at a depth of 6 to 15 kilometers which triggered most of the seismicity and provoked the dilatation of the volcano and the recent explosive eruptive activity

evidence for the contemporary magmatic system beneath long valley caldera from local earthquake tomography and receiver function analysis 1 we present a new p wave and s wave velocity model for the upper crust beneath long valley caldera obtained using local earthquake tomography and receiver function analysis we computed the tomographic model using both a graded inversion scheme and a traditional approach we complement the tomographic vp model with a teleseismic receiver function model based on data from broadband seismic stations mlac and mkv located on the se and sw margins of the resurgent dome inside the caldera the inversions resolve 1 a shallow high velocity p wave anomaly associated with the structural uplift of a resurgent dome 2 an elongated wnw striking low velocity anomaly 8 10 reduction in vp at a depth of 6 km 4 km below mean sea level beneath the southern section of the resurgent dome and 3 a broad low velocity volume 5 reduction in vp and as much as 40 reduction in vs in the depth interval 8 14 km 6 12 km below mean sea level beneath the central section of the caldera the two low velocity volumes partially overlap the geodetically inferred inflation sources that drove uplift of the resurgent dome associated with caldera unrest between 1980 and 2000 and they likely reflect the ascent path for magma or magmatic fluids into the upper crust beneath the caldera

the failed eruption of mt etna in december 2005 evidence from volcanic tremor analyses 1 strong changes in seismic radiation comparable to those preceding and or accompanying eruptive activity in recent years were recorded at mt etna volcano italy from november 2005 to january 2006 the amplitude of volcanic tremor peaked in mid december 2005 after a continuous slow increase from august 2005 onward during which neither effusive nor paroxysmal activity was observed by volcanologists and alpine guides during this time span the centroid locations of volcanic tremor moved toward the surface more and more clustered below the summit craters the application of pattern classification analysis based on self organizing maps and fuzzy clustering to volcanic tremor data highlighted variations in the frequency domain as well these changes were temporally associated with ground deformation variations as indicative of a mild inflation of the summit of the volcano and with a conspicuous increase in the so2 plume flux emission overall we interpret this evidence as the result of recharging of the volcanic feeder at depth 3 km below sea level during which magma did not reach the shallow plumbing system

an experiment of muon radiography at mt etna italy interactions of conduit geometry with gas liquid flows control volcanic activity implying that the evaluation of volcanic hazards requires quantitative understanding of the inner structure of the volcano the more established geophysical imaging techniques suffer from inherent ambiguity may require spatially dense measurements in active areas and may not provide sufficient spatial resolution in the uppermost part of the conduit system it is thus desirable to develop new imaging techniques allowing a better spatial resolution of a volcano s upper feeding system with reduced ambiguity and a low level of risk for operators muon particles can be utilized to image the internal density distribution of volcanic structures the principle of muon radiography is essentially the same as x ray radiography except for substituting penetrating particles in place of photons muons are more attenuated by higher density parts inside the target and thus information about its inner structure are obtained from the differential muon absorption we report on a muon imaging experiment that was conducted at mt etna in 2010 the target structure was one of the summit craters of the volcano this experiment was performed using a muon telescope suitably designed to withstand the harsh conditions in the summit zone of a high volcano we found a marked difference between synthetic and observed attenuation of muons through the target this discrepancy is likely due to the bias on the observed flux arising from false muon tracks they are caused by low energy particles that by chance hit simultaneously the two matrixes of the telescope leading to detection of a false positive we separated the useful from the unwanted signal through a first order model of the background noise the resulting signal is compared with the corresponding synthetic flux eventually we found regions of higher and lower than expected muon flux that are possibly related to inner features of the target crater

reservoir depletion at the geysers geothermal area california shown by four dimensional seismic tomography intensive geothermal exploitation at the geysers geothermal area california induces myriads of small magnitude earthquakes that are monitored by a dense permanent local seismometer network using this network tomographic inversions were performed for the three dimensional vp and vp vs structure of the reservoir for april 1991 february 1993 december 1994 october 1996 and august 1998 the extensive low vp vs anomaly that occupies the reservoir grew in strength from a maximum of 9 to a maximum of 13 4 during the 7 year study period this is attributed to depletion of pore liquid water in the reservoir and replacement with steam this decreases vp by increasing compressibility and increases vs because of reduction in pore pressure and the drying of argillaceous minerals e g illite which increase the shear modulus these effects serendipitously combine to lower vp vs resulting in a strong overall effect that provides a convenient tool for monitoring reservoir depletion variations in the vp and vs fields indicate that water depletion is the dominant process in the central part of the exploited reservoir and pressure reduction and mineral drying in the northwest and southeast parts of the reservoir the rate at which the vp vs anomaly grew in strength in the period 1991 1998 suggests most of the original anomaly was caused by exploitation continuous monitoring of vp vs and vp vs is an effective geothermal reservoir depletion monitoring tool and can potentially provide information about depletion in parts of the reservoir that have not been drilled

isotope study of moisture sources recharge areas and groundwater flow paths within the eastern batinah coastal plain sultanate of oman oxygen and hydrogen isotope analyses of rainfall samples collected on the eastern batinah coastal plain of northern oman between 1995 and 1998 indicate two different principal water vapor sources for precipitation in the area a northern mediterranean source and a southern indian ocean source as a result two new local meteoric water lines were defined for the study area isotopic analyses of groundwater samples from over 200 springs and wells indicate that the main source of water to the batinah coastal alluvial aquifer is high altitude rainfall from the adjacent jabal akhdar mountains originating from a combination of northern and southern moisture sources the groundwater recharged at high altitude forms two plumes of water which is depleted in the heavy isotopes 18o and 2h and stretches from the mountains across the coastal plain to the sea thereby retaining a chemical homogeneity horizontally and vertically down to a depth exceeding 300 m in contrast in areas adjacent to these two plumes the alluvial aquifer is geochemically stratified near the coast saline intrusion results in abrupt changes in chloride concentrations and isotope values

body wave attenuation heralds incoming eruptions at mount etna how fast and how foreseeable is magma ascent is one of the most compelling and unanswered issues of volcanology the velocity of the magma upwelling depends on the local conditions of the volcanic conduit and rheology of the magma during magma emplacement in the shallow crust transient variations of physical properties underneath active volcanoes are expected and in a few cases observed the predictability of such changes strongly depends on how fast this process is compared to our ability to handle geophysical data and consistently resolve transient anomalies in the physical properties of the medium mount etna italy is a perfect natural laboratory to investigate such issues due to the almost continuous magmatic activity and the high quality of seismologic and geodetic data here we show for the first time that seismic attenuation of local earthquakes strongly increases due to the emplacement of magma within the crust forecasting an incipient eruption at mount etna

velocity and attenuation tomography of the umbria marche 1997 fault system evidence of a fluid governed seismic sequence abstract the 1997 umbria marche is probably the best ever monitored normal faulting seismic sequence seismicity migration and multiple main shocks characterize the activation of a 40 km long system of contiguous fault segments as documented by seismological data many authors as indicative of fault weakening by fluids migration have interpreted this behaviour in this study we create a new catalogue of high quality p and s wave arrival times merging data recorded by permanent and temporary stations to improve the resolution of velocity and attenuation models and earthquake locations we show that the relocated earthquakes and the joint interpretation of p and s wave velocity and attenuation models help in understanding the faulting processes revealing new details of the geometry of the main faults and physical state of fluids within the crustal volume we observe that large aftershocks occur on the top and within the triassic evaporitic layer a rock volume locally characterised by fluid over pressured as evidenced by high vp vs and low qp qs anomalies velocity and attenuation heterogeneities are evidence that the migration of fluid pressure along the fault system is the driving mechanism of the prolonged earthquake sequence

seismological studies at parkfield i simultaneous inversion for velocity structure and hypocenters using cubic b splines parameterization a model for the 3d p and s wave velocity structure at parkfield has been developed by the systematic inversion of arrival times for microearthquakes and surface vibroseis sources recorded by nearby calnet stations and by the local borehole installed 10 station high resolution seismic network there a modification of the linear b splines model parameterization method of thurber 1983 to a cubic b splines formulation through tests inverting synthetic data sets for the parkfield configuration is found to produce smooth velocity distributions that still retain some small scale features application of the method to 953 p wave and 288 s wave arrivals from 111 microearthquakes and 8 vibroseis locations throughout the study area yields a velocity structure having variable resolution a low velocity zone appears to coincide with the creeping segment of the san andreas fault zone northwest of the 1966 parkfield earthquake epicenter an increase of about 15 per cent in seismic velocities is seen from the northeast to southwest across this segment of the fault zone the higher velocities to the southwest apparently correspond to the granitic basement the contrast across the fault is subdued to the southeast along the 1966 rupture zone a high vp vs ratio of 1 9 is seen in a 2 km wide volume near the location of the 1966 main shock hypocenter presumably the nucleation zone for the expected m 6 parkfield earthquake