time resolved seismic tomography detects magma intrusions at mount etna the continuous volcanic and seismic activity at mount etna makes this volcano an important laboratory for seismological and geophysical studies we used repeated three dimensional tomography to detect variations in elastic parameters during different volcanic cycles before and during the october 2002 january 2003 flank eruption well defined anomalous low p to s wave velocity ratio volumes were revealed absent during the pre eruptive period the anomalies trace the intrusion of volatile rich 4 weight percent basaltic magma most of which rose up only a few months before the onset of eruption the observed time changes of velocity anomalies suggest that four dimensional tomography provides a basis for more efficient volcano monitoring and short and midterm eruption forecasting of explosive activity

crustal seismic velocity structure near faial and pico islands azores from local earthquake tomography the azores archipelago portugal is located on an oceanic plateau in a geodynamic environment prone to intense seismic and volcanic activity in order to investigate the crustal structure in this region we have conducted a local earthquake tomography study in the area of the islands of faial pico and s jorge using data recorded in july 1998 the july 9th 1998 earthquake near faial island triggered an aftershock sequence of thousands of events that lasted for several months and were recorded by a total of 14 stations located on the three islands surrounding the epicentral area in the upper crustal layers consistency is seen between the tomographic results and the islands surface volcanic units beneath the faial central volcano a low vp b6 0 km s anomaly roughly located at 3 7 km depth suggests a connection to the plumbing system possibly the presence of a magma chamber in ne faial a high vp n6 3 km s body was found located at mid lower crust most likely an intrusion of gabbroic composition that is bordered by the registered seismic activity its shape suggesting a tectonic controlled mechanism the relocated hypocenters together with the overall analysis of the tomographic model suggest a tectonic segmentation of faial island the crustal thickness under the islands volcanic buildings of the faial pico area was estimated at around 14 km 2007 elsevier b v all rights reserved

vp vs ratios in the yellowstone national park region wyoming abstract in this paper we study the variation of v p v s and poisson s ratio in the yellowstone national park region using earthquakes which were well recorded by a local seismic network we find that the average v p v s value within the geothermally active yellowstone caldera is about 7 lower than in the area outside the caldera within the caldera itself there may be a further 2 7 reduction of v p v s in the hydrothermally active norris geyser basin the upper and lower geyser basins and the yellowstone lake and mud volcano regions after considering various possible causes for v p v s changes such as geologic and structural differences thermal effects partial melting and hydrothermal activity we conclude that the most plausible explanation for the observed v p v s reduction is the presence of hot water at temperatures and pore pressures near the water steam transition in the caldera geothermal reservoirs

three dimensional seismic tomography from p wave and s wave microearthquake travel times and rock physics characterization of the campi flegrei caldera 1 the campi flegrei cf caldera experiences dramatic ground deformations unsurpassed anywhere in the world the source responsible for this phenomenon is still debated with the aim of exploring the structure of the caldera as well as the role of hydrothermal fluids on velocity changes a multidisciplinary approach dealing with three dimensional delay time tomography and rock physics characterization has been followed selected seismic data were modeled by using a tomographic method based on an accurate finite difference travel time computation which simultaneously inverts p wave and s wave first arrival times for both velocity model parameters and hypocenter locations the retrieved p wave and s wave velocity images as well as the deduced v p v s images were interpreted by using experimental measurements of rock physical properties on cf samples to take into account steam water phase transition mechanisms affecting p wave and s wave velocities also modeling of petrophysical properties for site relevant rocks constrains the role of overpressured fluids on velocity a flat and low v p v s anomaly lies at 4 km depth under the city of pozzuoli earthquakes are located at the top of this anomaly this anomaly implies the presence of fractured overpressured gas bearing formations and excludes the presence of melted rocks at shallow depth a high v p v s anomaly located at 1 km suggests the presence of rocks containing fluids in the liquid phase finally maps of the v p v s product show a high v p v s horseshoe shaped anomaly located at 2 km depth it is consistent with gravity data and well data and might constitute the on land remainder of the caldera rim detected below sea level by tomography using active source seismic data

high resolution velocity structure beneath mount vesuvius from seismic array data 1 a high resolution p wave image of mt vesuvius edifice has been derived from simultaneous inversion of travel times and hypocentral parameters of local earthquakes land based shots and small aperture array data the results give details down to 300 500 m the relocated local seismicity appears to extend down to 5 km below the central crater distributed in a major cluster centered at 3 km below the central crater and in a minor group with diffuse hypocenters inside the volcanic edifice the two clusters are separated by an anomalously high vp region at around 1 km depth a zone with high vp vs in the upper layers is interpreted as produced by the presence of intense fluid circulation the highest energy quakes up to m 3 6 are located in the deeper cluster in a high p wave velocity zone our results favor an interpretation in terms of absence of shallow magma reservoirs

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

effect of pore geometry on vp vs from equilibrium geometry to crack seismic wave velocities of melt or aqueous fluid containing systems are studied over a wide range of pore shapes including oblate spheroids tubes cracks and an equilibrium geometry controlled by a dihedral angle the relative role of liquid compressibility and pore geometry on the v p v s velocity ratio is clarified the result clearly indicates that p and s velocity structures determined by seismic tomography can be used to verify whether interfacial energy controlled melt or fluid geometry equilibrium geometry is achieved relationships between the diverse models are clearly established by relating each model to the oblate spheroid model in terms of the equivalent aspect ratio as a function of the aspect ratio a significant effect of pore geometry on d in v s d in v p the ratio of the fractional changes in v s and v p is shown equilibrium geometry of the partially molten rocks characterized by a dihedral angle of 20 40 corresponds to an aspect ratio of 0 1 0 15 the value of d in v s d in v p expected for the texturally equilibrated partially molten rocks is shown to be 1 1 5 which is much smaller than that expected for cracks and dikes with an aspect ratio of 10 2 10 3 in the upper mantle low velocity regions the seismologically obtained value of d in v s d in v p is within this range beneath the bolivian andes 1 1 1 4 but is as high as 2 beneath iceland 1 7 2 3 and beneath northeastern japan 2 0 the former region can be regarded as a region where equilibrium geometry is achieved and the latter regions can be regarded as regions where dikes and veins typical of a system far from the textural equilibrium dominate

the active portion of the campi flegrei caldera structure imaged by 3 d inversion of gravity data 1 we present an improved density model and a new structural map of the neapolitan yellow tuff caldera the active portion of the nested campi flegrei caldera the model was built using a new 3 d inversion of the available high precision gravity data and a new digital terrain and marine model the inversion procedure based on a variable depth lumped assembling of the subsurface gravity distribution via cell aggregation gives better defined insights into the internal caldera architecture that well agree with the available geological geophysical and geochemical data the adopted 3 d gravity method is highly efficient for characterizing the shallow caldera structure down to 3 km depth and defining features related to regional or volcano tectonic lineaments and dynamics in particular the resulting density distribution highlights a pronounced density low in correspondence of the central portion of the caldera with a detail not available till now the joint interpretation of the available data suggests a subsurface structural setting that supports a piecemeal collapse of the caldera and allows the identification of its headwall positive gravity anomalies localize dense intrusions presently covered by late volcanic deposits along the caldera marginal faults and the main structural lineaments both bordering the resurgent block and cutting the caldera floor these results allow us to both refine the current geological structural framework and propose a new structural map that highlights the caldera boundary and its internal setting this map is useful to interpret the phenomena occurring during unrest and to improve both short term and long term volcanic hazards assessment

vertical profile of effective turbidity reconstructed from broadening of incoherent body wave pulses ii application to kamchatka data summary the vertical profile of evective turbidity under kamchatka is reconstructed from observations of distance dependent broadening of the inchoherent pulse of highfrequency body waves from small earthquakes by means of a new approach and data processing scheme developed in paper i the key evective turbidity parameter g e u sed is an immediate generalization of the common isotropic turbidity scattering coeycient g measurements of 200 600 onset to peak delays for p and s waves for five kamchatka stations are used for interpretation the estimates based on these data correspond to the 2 4 hz frequency band the inversion of data is performed in terms of the parameters of two generic vertical evective turbidity structures a piecewise constant profile pcp and truncated inverse power law profile tplp both used in several variants the variants of the inversions give consistent results but also reveal rather limited resolution not permitting the recovery of detailed profiles or a comparison of results among individual stations the inversions indicate that the values of evective turbidity decay from the surface down within the depth interval h 0 50 km the decay is gradual at greater depths it is much steeper roughly following the inverse cube law the estimates of average evective mean free path l e 1 g e are very close for p and s waves 50 60 km 20 per cent for the 0 20 km layer 250 300 km 30 per cent for the 20 80 km layer and at h 60 80 km l e 100 h 40 2 4 for both p and s waves the value of both the p and the s wave optical thickness total scattering loss of the upper 200 km is about 0 75 25 per cent and the lithosphericscattering contribution to t p is estimated as 0 2 s at 1 hz the expected s wave scattering loss agrees reasonably with the standard regional amplitude attenuation curve probably reflecting the secondary role of intrinsic loss at 3 hz the s wave scattering q in the lithosphere of kamchatka is estimated for f 1 hz as 125 205 and 255 for hypocentral distances of shallow events of 30 100 and 300 km respectively

tomographic imaging of seismic velocity structure in and around the onikobe volcanic area northeastern japan implications for fluid distribution abstract we estimated three dimensional p vp and s wave velocity vs and vp vs structures in and around the onikobe volcanic area northeastern japan by local travel time tomography we used travel time data from source and receiver pairs located within and outside the study area which plays an important role in obtaining the optimum ray coverage and in elucidating the deeper structure more accurately detailed information on deeper structures is essential for imaging the complete volcanic system from the magmatic source zone through areas of shallow hydrothermal circulation more than 50 000 travel time data for the p waves and 35 000 for the s waves were used to image the velocity structure our results show the following dominant features 1 two conduits in the upper crust with low vp and low vs indicative of h2o rich fluid pathways one lying beneath naruko volcano the other beneath the focal area of the 1962 northern miyagi earthquake m6 5 2 an underlying broad region in the lower crust with low vp low vs and high vp vs suggestive of a zone of partial melt from which the fluids in 1 are derived and 3 low vp vs areas near the surface of the sanzugawa and onikobe calderas suggesting a diffuse vapor saturated cap

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

merging active and passive data sets in traveltime tomography the case study of campi flegrei caldera southern italy we propose a strategy for merging both active and passive data sets in linearized tomographic inversion we illustrate this in the reconstruction of 3d images of a complex volcanic structure the campi flegrei caldera located in the vicinity of the city of naples southern italy the caldera is occasionally the site of significant unrests characterized by large ground uplifts and seismicity the p and s velocity models of the caldera structure are obtained by a tomographic inversion based on travel times recorded during two distinct experiments the first data set is composed of 606 earthquakes recorded in 1984 and the second set is composed of recordings for 1528 shots produced during the serapis experiment in 2001 the tomographic inversion is performed using an improved method based on an accurate finite difference traveltime computation and a simultaneous inversion of both velocity models and earthquake locations in order to determine the adequate inversion parameters and relative data weighting factors we perform massive synthetic simulations allowing one to merge the two types of data optimally the proper merging provides high resolution velocity models which allow one to reliably retrieve velocity anomalies over a large part of the tomography area the obtained images confirm the presence of a high p velocity ring in the southern part of the bay of pozzuoli and extends its trace inland as compared to previous results this annular anomaly represents the buried trace of the rim of the campi flegrei caldera its shape at 1 5 km depth is in good agreement with the location of hydrothermalized lava inferred by gravimetric data modelling the vp vs model confirms the presence of two characteristic features at about 1 km depth a very high vp vs anomaly is observed below the town of pozzuoli and is interpreted as due to the presence of rocks that contain fluids in the liquid phase a low vp vs body extending at about 3 4 km depth below a large part of the caldera is interpreted as the top of formations that are enriched in gas under supercritical conditions

crustal heterogeneity and subduction processes 3 d vp vp vs and q in the southern north island new zealand summary along the southern hikurangi subduction zone in the southern north island new zealand the subduction zone changes from volcanic with moderately weak interseismic coupling to non volcanic with strong coupling in wellington to investigate how material heterogeneity relates to subduction processes we compute 3 d seismic properties using 342 earthquakes and 2 shots recorded by a 165 station seismic array the time base for some telemetered temporary stations was not stable which required revising the inversion code to allow an additional origin time related to the telemetered stations progressive inversions from 2 d to fine 3 d were carried out for vp vp vs and qp combined interpretation of these three seismic properties highlights features of the subduction zone the subducted slab is imaged as a high velocity high q feature in the overlying crust from southeast to northwest there is low velocity in the accretionary wedge high velocity in the axial ranges and low velocity in the wanganui basin high vp vs and low qp characterize the crust east of the north island dextral fault belt high vp vs is imaged above the subducted slab to 40 km depth in the northern half of the study area low qp is also prominent above the slab particularly trenchwards of the volcanic region in marked contrast to the high vp vs the low qp above the slab extends as a continuous feature up to the low qp in the shallow crust underlying the volcanic region the low qp and high vp vs are correlated with the region of weaker coupling and are consistent with significant subducted sediments with associated fluid release vp vs is particularly sensitive to overpressured fluid in the compressional forearc whereas qp also images the hydrostatically pressured fluid transport in the more permeable extensional volcanic region the rheology of the lower crust of the overlying plate is a factor in large scale subduction coupling as evidenced by the terrane boundaries and haast schist in the section near wellington the changing rheology of the lower crust of the overlying plate in the southern north island also provides a possible explanation for the southward cessation of volcanism

earthquake source scaling relationships from 1 to 5 ml using seismograms recorded at 2 5 km depth the scaling relationships of earthquake sources less than about magnitude 3 have been the subject of considerable controversy over the last two decades studies of such events have shown a tendency for the constant stress drop self similarity of larger earthquakes to breakdown at small magnitudes and an apparent minimum source dimension of about 100 m has been observed other studies showed that this apparent breakdown in scaling could be an artifact of severe near surface attenuation limiting the spatial resolution of surface data in this study source parameters are determined for over 100 nearby tectonic earthquakes from recordings at a depth of 2 5 km in granite in the cajon pass scientific drill hole southern california comparison of the seismograms recorded at this depth with those at the wellhead clearly demonstrates the effect of the severe attenuation in the upper kilometers of the earth s crust source parameters are calculated by spectral modeling of three component p and s waves assuming four source models based on the brune 2 n 2 model in model l n 2 is fixed and q of p and s waves is determined to be 912 581 1433 and 1078 879 1323 respectively the numbers in parentheses are 1 standard deviation in model 2 qp qs 1000 is assumed and n is allowed to vary the 2 model is a good average for the data set but there is some real scatter supported by the data in model 3 qp qs 1000 is also assumed and 2 is constrained and in model 4 attenuation is ignored and n is allowed to vary source dimensions of less than 10m are observed for all four models 10 times smaller than the proposed minimum no breakdown in constant stress drop scaling is seen in the downhole data approximately ml 1 to 5 5 m0 109 1016 nm the ratio between radiated seismic energy estimated by integrating the velocity squared spectra with adequate signal bandwidth and seismic moment appears to decrease gradually with decreasing moment in the magnitude range 1 to 7 this is not incompatible with a constant stress drop but could result from errors in calculating energy the ratio of the s wave energy to that radiated by the p waves is about 14 after correction for attenuation this low value is consistent with the corner frequency shift of about 1 3 this corner frequency shift is observed for all four source models and therefore is interpreted as being source controlled

three dimensional p and s wave velocity structure of redoubt volcano alaska the three dimensional p and s wave structure of redoubt volcano alaska and the underlying crust to depths of 7 8 km is determined from 6219 p wave and 4008 s wave first arrival times recorded by a 30 station seismograph network deployed on and around the volcano first arrival times are calculated using a finite difference technique which allows for flexible parameterization of the slowness model and easy inclusion of topography and source receiver geometry the three dimensional p wave velocity structure and hypocenters are determined simultaneously while the three dimensional s wave velocity model is determined using the relocated seismicity and an initial s wave velocity model derived from the p wave velocity model assuming an average vp vs ratio of 1 78 convergence is steady with approximately 73 and 52 reduction in p and s wave arrival time rms respectively after 10 iterations the most prominent feature observed in the three dimensional velocity models derived for both p and s waves is a relative low velocity near vertical pipelike structure approximately 1 km in diameter that extends from 1 to 6 km beneath sea level this feature aligns axially with the bulk of seismicity and is interpreted as a highly fractured and altered zone encompassing a magma conduit the velocity structure beneath the north flank of the volcano between depths of 1 and 6 km is characterized by large lateral velocity variations high velocities within this region are interpreted as remnant dikes and sills and low velocities as regions along which magma migrates no large low velocity body suggestive of a magma chamber is resolved in the upper 7 8 km of the crust

detection of synoptic scale vertical velocities using an mst radar comparisons of the time averaged vertical velocity observations from the platteville co mst radar with synoptic scale vertical velocities computed by the adiabatic and quasi geostrophic omega equation methods are made for several case studies these first results show that an mst radar can detect synoptic scale vertical velocities and that at platteville the most favorable comparison occurs when the synoptic scale vertical velocity is large and the temporal variance of the mst radar data is small

3d multi step travel time tomography imaging the local deep velocity structure of rabaul volcano papua new guinea abstract in this paper we put forward an alternative approach to combine the travel times from regional events with local earthquakes including explosions to reconstruct the deep velocity structure but still on a local crustal scale a synthetic example is first used to explain the multi step seismic tomographic procedure before progressing to recover the 3d velocity structure beneath rabaul volcano papua new guinea down to a depth 20 km the main velocity structures at shallow depth range are similar to those reported previously finlayson d m gudmunsson o itikarai i nishimura s shimamura h 2003 rabaul volcano papua new guinea seismic tomographic imaging of an active caldera j volc geotherm res 124 153 171 based on both wide angle seismic profiling using explosion data and 3d tomography using only local earthquake information including the explosions but we have found the bottom boundary of the interpreted shallow magma chamber under rabaul caldera complex to be 4 km depth and not 6 km depth as previously reported the other difference in this shallow depth range is that an additional low velocity zone was delineated beneath tavui another caldera near rabaul volcano in the medium depth range we obtained a similar v shaped low velocity zone under rabaul volcano to that found by finlayson et al finlayson d m gudmunsson o itikarai i nishimura s shimamura h 2003 rabaul volcano papua new guinea seismic tomographic imaging of an active caldera j volc geotherm res 124 153 171 but this extends to 12 km depth in our study compared to the previous determination of 9 km depth in the deeper range below 10 km the dominant seismic structure is a cylindrical shaped low velocity zone in the depth range from 12 to18 km beneath rabaul volcano this deep low velocity zone appears to be linked to the shallow interpreted magma chamber by a low velocity funnel feature which suggests the possible existence of deep magma storage

three dimensional p wave velocity structure of mt etna italy the three dimensional p wave velocity structure of mt etna is determined to depths of 15 km by tomographic inversion of first arrival times from local earthquakes recorded by a network of 29 permanent and temporary seismographs results show a near vertical low velocity zone that extends from beneath the central craters to a depth of 10 km this low velocity region is coincident with a band of steeply dipping seismicity suggesting a magmatic conduit that feeds the summit eruptions the most prominent structure is an approximately 8 km diameter high velocity body located between 2 and 12 km depth below the southeast flank of the volcano this high velocity body is interpreted as a remnant mafic intrusion that is an important structural feature influencing both volcanism and east flank slope stability and faulting

pyroclastic density currents resulting from the interaction of basaltic magma with hydrothermally altered rock an example from the 2006 summit eruptions of mount etna italy after 16 months of quiescence mount etna began to erupt again in mid july 2006 the activity was concentrated at and around the southeast crater sec one of the four craters on the summit of etna and eruptive activity continued intermittently for 5 months during this period numerous vents displayed a wide range of eruptive styles at different times virtually all explosive activities took place at vents at the summit of the sec and on its flanks eruptive episodes which lasted from 1 day to 2 weeks became shorter and more violent with time volcanic activity at these vents was often accompanied by dramatic mass wasting processes such as collapse of parts of the cone highly unusual flowage processes involving both old rocks and fresh magmatic material and magma water interaction the most dramatic events took place on 16 november when numerous rockfalls and pyroclastic density currents pdcs were generated during the opening of a large fracture on the se flank of the sec cone the largest pdcs were clearly triggered explosively and there is evidence that much of the energy was generated during the interaction of intruding magma with wet rocks on the cone s flanks the most mobile pdcs traveled up to 1 km from their source this previously unknown process on etna may not be unique on this volcano and is likely to have taken place on other volcanoes it represents a newly recognized hazard to those who visit and work in the vicinity of the summit of etna

seismicity associated with the 2004 2006 renewed ground uplift at campi flegrei caldera italy abstract following the significant ground uplift 1 8 m of the 1982 1984 bradyseismic crisis the recent history of campi flegrei volcanic complex italy has been dominated by a subsidence phase recent geodetic data demonstrate that the subsidence has terminated and that positive ground deformation renewed in november 2004 at a low but accelerating rate leading to about 4 cm of uplift by the end of october 2006 as in previous episodes ground uplift has been accompanied by swarms of micro earthquakes m 1 4 in three distinct episodes october 2005 october 2006 and december 2006 hypocenters of these earthquakes are mainly located beneath the solfatara volcano at depths ranging between 0 5 and 4 km inversion of s wave spectra indicates source radius and stress drop on the order of 30 60 m and 104 9 105 pa respectively fault plane solutions indicate predominantly normal mechanisms accompanying the october 2006 swarm we detected intense long period lp activity for about 1 week these signals consist of weak monochromatic oscillations whose spectra exhibit a main peak at frequency 0 8 hz this peak is common to all the stations of the network and not present in the noise spectra suggesting that it is a source effect about 75 of the detected lps cluster into three groups of mutually similar events adjustment of waveforms using cross correlation allows for precise alignment and stacking which enhances signal onsets and permits accurate absolute arrival picks and thus better absolute as well as relative locations locations associated with the three different clusters are very similar and appear to delineate the se rim of the solfatara volcano at a depth of about 500 m the most likely source process for the lp events involves the resonance of a fluid filled buried cavity quality factors of the resonator cluster in a narrow interval around 4 which is consistent with the vibration of a buried cavity filled with a water vapour mixture at poor gas volume fractions we propose a conceptual model to interpret the temporal and spatial patterns of the observed seismicity

three dimensional seismic image of a geothermal reservoir the geysers california three dimensional seismic travel time tomography of the geysers geothermal area in the coast ranges of northern california shows a strong 9 anomaly in vp vs the ratio of the compressional and shear wave speeds that is not evident in vp alone and corresponds closely to the most intensively exploited part of the geothermal reservoir this anomaly probably indicates low pore pressure and relatively dry conditions caused partly by boiling of pore water as steam is extracted steam pressure decreases over the last decade have probably caused seismologically measurable changes in wave speeds tomographic measurement of vp vs is a promising technique both for identifying geothermal resources and for monitoring them during exploitation

determination of δσ and κ0 from response spectra of large earthquakes in greece we fit an 09 2 model to response spectra from eight recent greek earth quakes ranging in size from m 5 8 to m 6 9 the diminution parameter k o was determined for each site with a value near 0 06 for a typical soil site the stress parameter aa showed little variation from earthquake to earthquake and had a mean value of 56 bars over all earthquakes predictions of peak velocity peak acceleration rupture duration and fault length using the derived stress parameters are consistent with observations frequency dependent site amplifications were included in all es timates the combined effect of amplification and attenuation had a maximum value close to a factor of 2 5 for a typical soil site relative to the motions at the surface of a perfectly elastic uniform half space composed of materials near the source the results form the foundation for predictions of strong motions in greece for distances and magnitudes other than those for which data are available

seismic site amplification factors in campi flegrei southern italy the method of spectral ratios of s waves from local small earthquakes recorded at various sites in the campi flegrei volcanic area southern italy has been used to evaluate the seismic site response in the frequency range 1 15 hz the spectra of the s wave trains recorded at the short period seismic stations are corrected for attenuation using attenuation parameters quality factor q previously determined for the area using the coda method a reference station has been used selected on the basis of the highest number of recorded earthquakes and not on geological considerations the relative uniformity of the geological conditions and the absence of hard rock sites conditioned such choice the method has been checked using the coda wave method to estimate the spectral site response and similar results were obtained the results show a relative peak of the spectral ratio pattern centred at low frequency 2 3 hz and a minimum of 0 2 at 8 hz for two stations located on yellow tuff such results are interpreted as being caused by a filtering effect produced by selective attenuation such a pattern could be of interest for seismic engineering purposes in view of the abundance of tuff over a wide area in this densely inhabited region

monitoring and modelling hydrothermal fluid emission at la solfatara phlegrean fields italy an interdisciplinary approach to the study of diffuse degassing discharge of hydrothermal fluids at la solfatara is one of the many pieces of evidence testifying to the level of activity and the potential danger characterizing the volcanic complex of the phlegrean fields recent measurements of diffuse degassing shed light on the unexpected magnitude of this process and prompted further research to improve our understanding of the hydrothermal system feeding the surface phenomenon at la solfatara in this work we first present new data on co2 diffuse degassing that were collected during a campaign in july 2000 and confirm previous measurements of the degassing rate these data together with other information on subsurface structures and conditions provided the necessary constraints to perform physical modelling of the hydrothermal fluid circulation at la solfatara numerical simulations describe the ascent and evolution of a hot multi phase and multi component fluid composed of water and carbon dioxide through a homogeneous porous medium when certain system properties and conditions are used this model reproduces some of the main features which characterize the natural system including the energy budget associated with the ascent and condensation of hot fluids and the development of a single phase gas region whose existence was inferred from independent chemical data further simulations investigated the effects associated with changes in rock properties and fluid injection rates results showed that an increase in the permeability at shallow depth may have an important influence on the system conditions and fluid discharge they imply that surface phenomena accompanied by very high temperatures at shallow depths may survive long after deep feeding has ceased

three dimensional vp vs variations for the coso region california recent seismological studies of the coso region of southeastern california document both low p wave velocities and abnormal sv attenuation in indian wells valley south of the pleistocene volcanics of the coso range in order to learn more about the physical nature of these colocated anomalies a tomographic inversion for the three dimensional variations of vp vs the ratio of compressional to shear velocity was performed iterative back projection of 2966 shear and compressional wave travel time residuals from local earthquakes recorded on vertical instruments reveals that vp vs is generally high at the surface and decreases systematically to 10 km depth superimposed on this trend are several large anomalies near devil s kitchen in the coso geothermal area vp vs values are very low near the surface consistent with measured values for steam dominated geothermal systems abnormally high values of vp vs are observed in portions of indian wells valley and also below the cactus peak rhyolite dome from 2 to 5 km in depth in indian wells valley the co occurrence of low p velocities low s velocities high vp vs and anomalous sv attenuation are indicative of subsurface partial melt because the inversion is based on vertical data only however the results cannot be considered conclusive only suggestive

fast wavefield decomposition of volcano tectonic earthquakes into polarized p and s waves by independent component analysis abstract in the present work a new approach for the analysis of polarization of seismic signals is proposed the method is based on independent component analysis and allows the identification and separation of the basic sources which are naturally polarized into the vertical and horizontal planes the results from the case study of a swarm of volcano tectonic earthquakes occurred at campi flegrei in october 2015 are impressive a clear separation of the p and s wave seismic phases in the time domain is obtained in addition the efficiency of the method in retrieving the polarization parameters is demonstrated by the comparison with other standard techniques the presented approach provides wavefield decomposition and polarization analysis in a single step thus avoiding a priori cumbersome filtering procedures and segmentation of the signals it is useful for discriminating and analysing different seismic phases and can be applied to a variety of volcanic and tectonic signals therefore it can strongly support all the studies on propagation and source mechanism moreover due to its fastness and robustness this stand alone tool can be routinely used in the volcano monitoring practice

three dimensional seismic velocity structure beneath aso volcano kyushu japan tomographic results for p and s wave velocity structure beneath the active aso volcano kyushu japan using 800 well recorded earthquakes and ten shots recorded by an eight station seismic network are presented a 68 variance reduction was achieved upon simultaneous inversion for hypocenter and velocity structure well resolved velocity anomalies associated with the active crater reveal heterogeneity up to 26 slower and 18 faster in p velocity and up to 31 slower and 22 faster in s velocity than the one dimensional model the largest anomaly is seen over the upper 11 km in the central and northern parts beneath the central cones two low velocity regions are imaged the first region a 10 15 km region encompassing the upper 3 km centered near the caldera wall at tateno valley is characterized by p velocities up to 19 slower 20 for s the second low velocity region is associated with the central cones and active magma conduit system at 6 km depth velocities as low as 4 3 km s up to 26 in p and 2 km s 31 slower in s characterize the 7 km wide volume the magma chamber is roughly spherical in shape centered at 6 km depth flattens at 10 km depth and is located between mt kishima mt eboshi and mt naka the present focus of magmatism a sharp velocity contrast at the depth of 3 km with high velocities to the southwest and lower velocities to the northeast characterizes different abutting structures associated with the oita kumamoto tectonic line

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

electromagnetic outline of the solfatara pisciarelli hydrothermal system campi flegrei southern italy abstract we describe the results from a combined controlled source audio magnetotelluric csamt and natural source magnetotelluric mt survey carried out in the solfatara pisciarelli s p area located in the central part of the campi flegrei cf composite caldera west of naples southern italy the s p area represents the most active zone within the cf caldera in terms of hydrothermal manifestations and local seismicity since 1969 the cf caldera is experiencing ground deformation seismicity and geochemical fluid changes which are particularly evident in the s p area a 1 km long nearly w e directed csamt mt profile crossing the fumarole field was carried out in the s p area with the aim of deducting a resistivity model of the structural setting of the hydrothermal system in the first 3 km depth an interpretation of the modelled section across the profile is given in this paper taking advantage from already existing seismic gravity and geochemical data in the same area three well distinct zones have been outlined the first zone is a very shallow electrically conductive body localized beneath the westernmost segment of the profile which within a short distance of about 100 m dips westwards from near surface down to some hundred metres in depth mostly accounting for the very low resistivity 1 10 m and the exceedingly high values of v p v s 4 this shallow zone has been ascribed to a water saturated high pressurized geothermal reservoir the second zone which has been localized below the west central portion of the csamt mt transect appears as a composite body made up of a nearly vertical plumelike structure that escapes at about 2 25 km depth from the top edge of the east side of a presumably horizontal platelike body the plumelike structure rises up to the free surface in correspondence of the fumarole field whereas the platelike structure deepens at least down to the 3 km of maximum exploration depth the combined interpretation of resistivity 50 100 m body wave velocity ratio v p v s 3 and geochemical data indicates that the plumelike portion can likely be associated with a steam gas saturated column and the platelike portion with a high temperature 300 c over pressurized gas saturated reservoir finally the third zone which has been localized beneath the eastern half of the transect from about 1 2 km down to about 3 km of depth is also characterized by very low resistivity values 1 10 m jointly interpreted with seismic v p v s 0 g cm 3 data this last electrically conductive structure appears to be associated with a hydrothermally mineralized clay rich body

seismic velocity and attenuation structure of the east rift zone and south flank of kilauea volcano hawaii it has been proposed that a deep magma body beneath the east rift zone erz of kilauea volcano hawaii must be present in order to explain the observed deformation of the south flank from november 1999 to june 2000 29 iris passcal three component seismographs were operated across kilauea9s erz and south flank using local earthquakes recorded by these stations supplemented with data from the hawaiian volcano observatory stations we investigated the deep structure of the erz and south flank through two approaches seismic velocity tomography and seismic attenuation tomography results along two north northwest south southeast profiles are examined the western profile shows a low velocity region beneath and south of the hilina pali and earthquakes at depth are sandwiched between a high v p v s high q zone and a low v p v s low q zone the velocity and attenuation differences are interpreted to reflect the contrast in material properties between the overlying volcanic pile and the underlying fluid rich ocean sediments and fractured altered ocean crust beneath the south flank thrust fault the eastern profile shows an anomalous feature with low v p low v p v s high q p and low q s at about 7 km depth beneath the erz the low v p v s ratio is inconsistent with the presence of partial melt instead this anomaly is attributed to a trapped reservoir of co 2 our results do not support the existence of a sizable molten or partially molten body at depth beneath the erz if the deep magma body exists it must be relatively small based on synthetic resolution tests an estimated limit on the maximum allowable cross sectional size of the deep magma body is about 2 by 4 km

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

signature of magmatic processes in strainmeter records at campi flegrei italy volcanic unrest at campi flegrei caldera southern italy is characterized by episodes of ground deformation seismicity and enhanced fumarolic activity whether its origin is purely hydrothermal or magmatic is highly debated we have identified ground deformation patterns in strainmeter records from a heightened unrest period in late 2006 closely resembling synthetic signals from numerical simulations of shallow magma chamber replenishment and mixing together with other recent findings our results depict a situation whereby periodic arrivals of deep magma feed a shallow intrusion at 3 4 km depth these results suggest that the analysis of strainmeter records coupled with advanced numerical simulations of magma dynamics could lead to new approaches in imaging subsurface dynamic processes in volcanic areas

the origin of the fumaroles of la solfatara campi flegrei south italy abstract the analysis of gaseous compositions from solfatara campi flegrei south italy fumaroles since the early 1980s clearly reveals a double thermobarometric signature a first signature at temperatures of about 360 c was inferred by methane based chemical isotopic geoindicators and by the h2 ar geothermometer these high temperatures close to the critical point of water are representative of a deep zone where magmatic gases flash the hydrothermal liquid forming a gas plume a second signature was found to be at around 200 240 c at these temperatures the kinetically fast reactive species h2 and co re equilibrate in a pure vapor phase during the rise of the plume a combination of these observations with an original interpretation of the oxygen isotopic composition of the two dominant species i e h2o and co2 shed light on the origin of fumarolic fluids by showing that effluents are mixture between fluids degassed from a magma body and the vapor generated at about 360 c by the vaporization of hydrothermal liquids a typical andesitic water type d 20 18o 10 and a co2 rich composition x co 2 0 4 has been inferred for the magmatic fluids while for the hydrothermal component a meteoric origin and a co2 fugacity fixed by fluid rock reaction at high temperatures have been estimated in the time the fraction of magmatic fluids in the fumaroles increased up to 0 5 at each seismic and ground uplift crisis bradyseism which occurred at campi flegrei suggesting that bradyseismic crises are triggered by periodic injections of co2 rich magmatic fluids at the bottom of the hydrothermal system

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

modelling gravity variations consistent with ground deformation in the campi flegrei caldera italy abstract in recent years 1970 72 and 1982 84 two inflation episodes took place in the campi flegrei caldera italy characterized by significant ground uplift and gravity variations an elastic half space model with vertical density stratification is employed to compute the displacement field and the gravity variations produced by the deformation of buried layers following the inflation of a spherically symmetric deformation source contributions to gravity variations are produced by dilation contraction of the medium by the displacements of density interfaces the free surface and subsurface layers and of source boundaries and possibly by new mass input from remote distances into the source volume three cases were examined in detail in case i the magma chamber is identified as the deformation source and volume and pressure increase in the magma chamber is due to input of new magma from remote distances in case ii deformation is due to magma differentiation within the magma chamber deformation source with constant mass in case iii the geothermal system is identified as the deformation source and a pressure increase possibly driven by the exsolution of high temperature and high pressure volatiles in the magma chamber is assumed to play a dominant role from the comparison between measured and computed gravity residuals free air corrected gravity variations we can assess that in case i an inflation source with constant density would predict gravity residuals compatible with observations whereas an expansion at constant mass case ii would predict gravity residuals much lower than observed the resolving power of gravity data however prevents accurate assessment of the density of the emplaced material in case iii the pervasive density increase of the geothermal fluids induced by pressure increase is assumed to be the main source of gravity variations the average porosity value required for this model to match both the ground deformation and the gravity residuals is found to be 10 a value which is compatible with measured porosity values at campi flegrei in deep wells the subsidence phases following both inflation episodes and the gravity residuals during subsidence lead us to consider case iii as more plausible even if a suitable combination of cases i and iii cannot be discarded

joint hypocentral determination and the detection of low velocity anomalies an example from the phlegraean fields earthquakes abstract arrival time data from the phlegraean fields italy earthquake swarm recorded by the university of wisconsin array in 1983 to 1984 were reanalyzed using a joint hypocentral determination jhd technique the p and s wave station corrections computed as part of the jhd analysis show a circular pattern of central positive values surrounded by negative values whose magnitudes increase with distance from the center of the pattern this center roughly coincides with the point of the maximum uplift almost 2 m associated with the swarm corrections range from 0 85 to 0 10 sec for p wave arrivals and from 1 09 to 0 70 sec for s wave arrivals we interpret these patterns of corrections as caused by a localized low velocity anomaly in the epicentral area which agrees with the results of a previous 3 d velocity inversion of the same data set the relocated jhd epicenters show less scatter than the epicenters obtained in the velocity inversion and move more of the seismic activity to the vicinity of the only presently active fumarolic feature the capability of the jhd technique to detect low velocity anomalies and at the same time to give reliable locations particularly epicenters was verified using synthetic data generated for a 3 d velocity model roughly resembling the model obtained by velocity inversion

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

determination of shear and compressional wave velocity variations and hypocenter locations in a rapidly inflating caldera the campi flegrei during 1982 1985 the campi flegrei caldera underwent a large h 1 7 m rapid hmax 2 mm day 1 and localized radius 6 km uplift p and s arrival times from three component digital seismograms recorded during this period have been used to invert for hypocenter locations and for three dimensional shear and compressional velocity to 3 km first order residual based tomography shows a significant and well resolved high p s ratio anomaly for the volume encompassing the central caldera and the active solfatara crater three dimensional tomographic inversion resolves this central anomaly as a zone of depressed p and s with a high 2 1 p s ratio the three dimensional velocity model and hypocenter distribution are consistent with modeling the central caldera as a zone of nearly water saturated cracks presumably a result of recurrent inflation and deflation in a zone with a shallow water table although the presence of small shallow magma bodies is not precluded

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

the present state of the magmatic system of the campi flegrei caldera based on a reconstruction of its behavior in the past 12 ka abstract new geochemical and sr isotope data have been acquired on samples representative of volcanic units erupted inside the resurgent campi flegrei caldera cfc over the past 12 ka these data integrated with previous published petrological and with newly acquired geochronological volcanological and geothermal data shed light on the nature and timing of the processes that controlled the evolution of the phlegraean magmatic system in the past 12 ka three isotopically and geochemically distinct magmatic components were erupted at the cfc as either homogeneous or mixed magma batches one component campanian ignimbrite component cic 87 sr 86 sr 0 70735 0 70740 is similar to the trachytic magma extruded during the first phase of the campanian ignimbrite ci eruption 37 ka a second component neapolitan yellow tuff component nytc 87 sr 86 sr 0 70750 0 70757 is similar to the latitic alkali trachytic magma batches extruded during the course of the neapolitan yellow tuff nyt eruption 12 ka a third component minopoli component mic 87 sr 86 sr 0 7086 is similar to the trachybasaltic magma of the minopoli 2 mi eruption 9 7 ka these components were erupted as either single batches of magma or mixed ci nyt or mi nyt batches of magma through vents located either along the structural boundary of the nyt caldera or inside the nyt caldera mainly on portions of the resurgent block under extensional stress the ci and nyt components represent residual portions of older large volume magma reservoirs which have fed eruptions since about 60 and 15 ka respectively the least evolved mi component was erupted only during the 12 9 5 ka and 8 6 8 2 ka epochs of activity through vents located on a ne sw regional fault system this component could represent a deeper reservoir tapped by the ne sw regional fault system reactivated after the nyt caldera collapse deeper mi and shallower ci and nyt magmatic systems interacted by mixing among batches of magma during their rise to surface overall the data suggest that the cfc magmatic system today is characterized by the presence of two larger independent reservoirs filled by residual portions of the ci and nyt magmas these generated many smaller shallower pockets of evolved magma that fed most of the eruptions that occurred in the cfc over the past 12 ka moreover a deeper reservoir mi tapped by the ne sw regional fault system provided batches of less evolved magma that mixed with magma present in the shallower pockets

complex patterns of fluid and melt transport in the central andean subduction zone revealed by attenuation tomography abstract we present a high resolution 3 d model of p wave attenuation q p 1 for the central andean subduction zone data from 1500 mostly intermediate depth 60 250 km earthquakes recorded at three temporary seismic networks covering the forearc arc and backarc around 23 s were used for tomographic inversion the forearc is characterised by uniformly high q p values indicating low temperature rocks in accordance with low surface heat flow values prominent low q p anomalies are found beneath the magmatic arc and the backarc in the crust and mantle continuous regions of low q p connect earthquake clusters at 100 km and 200 km depth with zones of active volcanism in the arc and backarc fluids fluxed from the subducted oceanic lithosphere into the overlying mantle wedge where they induce melting explain our observations we propose that low q p regions indicate source and ascent pathways of metamorphic fluids and partial melts ascent of fluids and melts as imaged by seismic q p are not vertical as is often implicitely assumed instead sources of fluids are located at different depth levels and ascent paths are complex and exhibit significant variation within the study area the largest quaternary backarc volcano cerro tuzgle is fed by mantle melts which are imaged as a plume of low q p material that reaches to the strong earthquake cluster at 200 km depth

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

multiple resolution seismic attenuation imaging at mt vesuvius abstract a three dimensional s wave attenuation tomography of mt vesuvius has been obtained with multiple measurements of coda normalized s wave spectra of local small magnitude earthquakes we used 6609 waveforms relative to 826 volcano tectonic earthquakes located close to the crater axis in a depth range between 1 and 4 km below the sea level recorded at seven 3 component digital seismic stations we adopted a two point ray tracing rays were traced in an high resolution 3 d velocity model the spatial resolution achieved in the attenuation tomography is comparable with that of the velocity tomography we resolve 300 m side cubic cells we statistically tested that the results are almost independent from the radiation pattern we also applied an improvement of the ordinary spectral slope method to both p and s waves assuming that the differences between the theoretical and the experimental high frequency spectral slope are only due to the attenuation effects consequently we could check the coda normalization method also comparing the s attenuation image with the p attenuation image the images were obtained inverting the spectral data with a multiple resolution approach results have shown the general coincidence of low attenuation with high velocity zones the joint interpretation of velocity and attenuation images allows us to interpret the low attenuation zone intruding toward the surface until a depth of 500 m below the sea level as related to the residual part of solidified magma from the last eruption in the depth range between 700 and 2300 images are consistent with the presence of multiple acquifer layers no evidence of magma patches greater than the minimum cell dimension 300 m has been found a shallow p wave attenuation anomaly beneath the southern flank of the volcano is consitent with the presence of gas saturated rocks the zone characterized by the maximum seismic energy release cohincides with a high attenuation and low velocity volume interpreted as a cracked medium