physical properties of tuffs from a scientific borehole at alban hills volcanic district central italy recent seismic swarms and hydrothermal activity suggest that the quaternary volcanic complex of the alban hills may pose a threat to the city of rome a 350 m scientific borehole was therefore drilled into this volcanic area to elucidate its inner structure for the first time wire line logs were run in the borehole in order to characterize the physical properties of the rocks and their variations with depth in particular a detailed sonic log was run to measure the p wave velocity from the well head down to 110 m to further investigate velocity changes we carried out laboratory measurements of p and s elastic wave velocities and fluid permeability at effective pressures up to 70 mpa during both increasing and decreasing pressure cycles on selected core samples representative of the main volcanic units specifically we studied samples from two pyroclastic units representative of two classes of volcanic deposits that are representative of the whole succession i a coarse grained well lithified facies pozzolane rosse unit containing abundant mm to cm lava clasts and crystals and ii a fine grained matrix supported pyroclastic deposit tufo pisolitico di trigoria unit with rare lithic lava clasts and sparse pumice elastic wave velocities reveal significant differences between units and indicate how within the same lithology the different degree of lithification and presence of clasts can affect significantly physical property values the mean laboratory value of the p wave velocity for pozzolane rosse and tufo pisolitico di trigoria units is respectively of 3 75 and 3 2 km s at an effective pressure equivalent to that at the depth at which the sonic velocity was measured under increasing effective pressure a profound influence on the transport properties is observed permeability ranges from the order of 10 18 m 2 for the pozzolane rosse unit to the order of 10 15 m 2 for the tufo pisolitico di trigoria unit in good agreement with the shallow aquifer circulating in the shallower units c 2008 elsevier b v all rights reserved

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

experimental study of acoustic anisotropy and birefringence in dry and saturated fontainebleau sandstone the velocities of ultrasonic p sh and sv waves have been measured in two perpendicular directions in samples of fontainebleau sandstone as received or thermally cracked dry or saturated under uniaxial stress we have investigated the effect of cracking saturation and uniaxial stress on the velocity of p and s waves in two orthogonal directions anisotropy and the velocity of s waves with two orthogonal polarizations in each direction of propagation birefringence the effect of cracking saturation and uniaxial stress on poisson s ratio has also been investigated the velocity anisotropy is larger for s waves than for p waves and practically disappears in saturated samples birefringence is attenuated in saturated samples inversion of the results using crampin s model gives values of the crack densities in three directions in qualitative agreement with the state of cracking observed by scanning electron microscopy in particular the crack density is found to be near zero in sandstones with r

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

laboratory studies of the acoustic properties of samples from salt on sea scientific drilling project and their relation to microstructure and field measurements compressional and shear wave velocities were measured at confining pressures up to 200 mpa for 12 core samples from the depth interval of 600 2600 m in the california state 2 14 borehole samples were selected to represent the various lithologies including clean heavily cemented sandstones altered impermeable claystones and several intermediate siltstones velocities measured at ultrasonic frequencies in the laboratory correspond closely with velocities determined from acoustic waveform logs and vertical seismic profiles the samples exhibit p wave velocities around 3 5 km s at depths above 1250 m but increase to nearly 5 0 km s at 1300 m in depth further increases with depth result in compressional wave velocity increasing to nearly 6 0 km s these increases in velocities are related to systematic variations in lithology microstructure and hydrothermal alteration of originally clay rich sediments scanning electron microscope observations of core samples confirm that local core velocities are determined by the combined effects of pore size distributions and the proportion of clays and alteration minerals such as epidote present in the form of pore fillings and veins

estimates of velocity dispersion between seismic and ultrasonic frequencies it is generally accepted that acoustic velocities in fluid saturated rocks vary with frequency evidence comes from experimental measurements and from theoretical causality arguments we have developed a simple analysis technique that gives estimates of total velocity dispersion between zero frequency and any measurement frequency the technique requires compressional p and shear s wave velocity measurements on dry and fully saturated rock assuming that the dry velocities are independent of frequency the biot gassmann equations are used to calculate the zero frequency velocities in the fully saturated rock any difference between the measured velocities and the calculated zero frequency velocities is interpreted as evidence of dispersion application of this analysis technique to a variety c ultrasonic data sets gives consistent results in many rocks dispersion between zero frequency and ultrasonic frequencies is on the order of 10 percent at low effective stress and it decreases to only a few pe

subsurface geophysics of the phlegrean fields new insights from downhole measurements 1 the volcanic complex of phlegrean fields located northwest of naples italy has been the site of deep geothermal exploration in the 1980s several wells were drilled by an agip enel joint venture with downhole continuous physical properties acquired in each well the main purpose of this study is to map and describe the spatial variations of the volcanic deposits in terms of their nature thickness and in situ physical properties we apply fuzzy k means classification of the well logging data available in the wells cored in the san vito area fuzzy set theory provides an approach that quantitatively assigns individuals to physically continuous classes the optimal number of classes is found by minimization of three mathematical functions thus reducing subjectivity the resulting classifications are found 1 to reflect the main lithologies in the san vito plain 2 to provide more detail on the geological stratigraphy allowing a more precise volcanic history and 3 to differentiate between transition zones and interbedded well defined deposits in addition to discriminating between lithologies that have different physical properties this study gives information on the degree of homogeneity of each lithologic unit and the range of variation for the measured properties finally using the physical classification of the deposits we are able to propose a detailed two dimensional compressional acoustic velocity structure of the studied area

reply to comment by jose pujol on laboratory measurements of ultrasonic wave velocities in rocks from the campi flegrei volcanic system and their relation to other field data

generic transformation models for some intact rock properties a global intact rock database of nine parameters including uniaxial compressive strength and young s modulus is compiled from 184 studies this database labeled as rock 9 4069 consists of 27

improving the simulation of landfast ice by combining tensile strength and a parameterization for grounded ridges in some coastal regions of the arctic ocean grounded ice ridges contribute to stabilizing and maintaining a landfast ice cover recently a grounding scheme representing this effect on sea ice dynamics was introduced and tested in a viscous plastic sea ice model this grounding scheme based on a basal stress parameterization improves the simulation of landfast ice in many regions such as in the east siberian sea the laptev sea and along the coast of alaska nevertheless in some regions such as the kara sea the area of landfast ice is systematically underestimated this indicates that another mechanism such as ice arching is at play for maintaining the ice cover fast to address this problem the combination of the basal stress parameterization and tensile strength is investigated using a 0 25 pan arctic cice nemo configuration both uniaxial and isotropic tensile strengths notably improve the simulation of landfast ice in the kara sea but also in the laptev sea however the simulated landfast ice season for the kara sea is too short compared to observations this is especially obvious for the onset of the landfast ice season which systematically occurs later in the model and with a slower build up this suggests that improvements to the sea ice thermodynamics could reduce these discrepancies with the data this article is protected by copyright all rights reserved

seismic to ultrasonic velocity drift intrinsic absorption and dispersion in crystalline rock an intrinsic velocity dispersion of 5 has been measured from 2 to 7 khz in a water saturated crystalline rock the porosity of the granite is 0 008 and consists of microcracks specific attenuation was observed to be weakly dependent on frequency over the same band we also measured longitudinal and shear specific attenuation as a continuous function of water saturation at 1 2 khz the constant q model inadequately describes the dispersion the dispersion mechanism is hydrodynamic relaxation of the microcracks an effective pressure of 10 mpa reduces the dispersion to less than 1 per decade or 4 from 1 hz to 1 mhz the intrinsic dispersion is insufficient to account for the discrepancies between seismic sonic and ultrasonic velocities which are observed in the field the in situ velocity drift is a factor of four greater than the maximum intrinsic dispersion we conclude that such a velocity drift in crystalline rocks is caused by sampling resolution of macroscopic fractures

understanding the seismic velocity structure of campi flegrei caldera italy from the laboratory to the field scale we report laboratory measurements of p and s wave velocities on samples of tuff from campi flegrei italy and a new tomographic velocity map of the campi flegrei caldera laboratory measurements were made in a hydrostatic pressure vessel during both increasing and decreasing effective pressure cycles selected samples were also thermally stressed at temperatures up to 600 c to induce thermal crack damage acoustic emission output was recorded throughout each thermal stressing experiment and velocities were measured after thermal stressing laboratory p and s wave velocities are initially low for the tuff which has an initial porosity of 45 but both increase by between 25 and 50 over the effective pressure range of 5 to 80 mpa corresponding to a decrease of porosity of 70 marked velocity hysteresis due to inelastic damage processes is also observed in samples subjected to a pressurization depressurization cycle tomographic seismic velocity distributions obtained from field recordings are in general agreement with the laboratory measurements integration of the laboratory ultrasonic and seismic tomography data indicates that the tuffs of the campi flegrei caldera can be water or gas saturated and shows that inelastic pore collapse and cracking produced by mechanical and thermal stress can significantly change the velocity properties of campi flegrei tuffs at depth these changes need to be taken into account in accurately interpreting the crustal structure from tomographic data

asymptotic waveform inversion for unbiased velocity and attenuation measurements numerical tests and application for vesuvius lava sample analysis summary recovering physical properties such as attenuation and velocity of the earth s heterogeneities is as important as recovering the shape and the surface reflectivity of the heterogeneities themselves a reliable estimate of attenuation in the earth is necessary to improve our knowledge of subsurface physical properties like the degree of fluid saturation moreover the attenuation may also be relevant to bright spot studies in reservoir characterization within this context this paper presents applications of asymptotic viscoacoustic waveform inversion to synthetic and ultrasonic laboratory data recorded to characterize the velocity and attenuation of a lava sample collected on the vesuvius volcano the waveform inversion method is based on a combination of ray theory and the born approximation to linearize the relation between the scattered wavefield and the velocity and attenuation perturbation models the iterative linearized inverse problem is solved using the classic least squares criterion asymptotic local analysis of the hessian operator published in a previous paper by ribodetti et al showed the theoretical uncoupling between the velocity and attenuation parameters the method is first applied to realistic and calibrated synthetic data computed using the discrete boundary integral wavenumber method the reliability of decoupling between the velocity and attenuation parameters during the inversion is confirmed through two case studies corresponding to a local velocity heterogeneity without any associated attenuation perturbation and a local attenuation heterogeneity without any associated velocity perturbation respectively second the method is applied to an ultrasonic laboratory data set that was recorded to determine the velocity and attenuation of a tephrite rock sample collected on the vesuvius volcano a velocity of 3200 m s 1 and an attenuation factor of 480 were found which are consistent with the geological nature of the analysed sample the numerical tests presented in this paper validate former theoretical development of asymptotic waveform inversion for characterization of viscoacoustic media application to ultrasonic data confirms that the proposed method can be used for reliable estimations of the velocity and attenuation properties of rock from laboratory experiments comparable methodology can be extended for use with data from multichannel seismic reflection surveys providing an opportunity to compare results of laboratory and field experiments

v s of the uppermost crust structure of the campi flegrei caldera southern italy from ambient noise rayleigh wave analysis abstract shear wave velocities v s are defined in the uppermost 1 2 km of the campi flegrei caldera through the non linear inversion of the group velocity dispersion curves of fundamental mode rayleigh waves extracted from ambient noise cross correlations between two receivers noise recordings three months long at 12 seismic stations are cross correlated between all couples of stations the experiment provided successful results along 54 paths inter stations distance of which 27 sampled a depth 1 km v s contour lines are drawn from 0 06 km b s l to 1 km depth b s l and show difference between the offshore gulf of pozzuoli and coastline and the onshore areas at 0 06 km b s l the gulf of pozzuoli and the coastline are characterized by v s of 0 3 0 5 km s and of 0 5 0 7 km s respectively such velocities are typical of neapolitan pyroclastic soils and fractured or altered tuffs the inland shows v s in the range 0 7 0 9 km s typical of neapolitan compact tuffs velocities increase with depth and at 1 km depth b s l velocities lower than 1 5 km s are still present in the gulf and along the coastline while velocities higher than 1 9 km s characterize the eastern sector grossly coincident with the neapolitan yellow tuff caldera rim the s vito plain and the area between solfatara and sw of astroni such features are much more evident along two cross sections drawn in the offshore and onshore sectors by integrating our v s models with literature data our models join previous noise cross correlation studies at greater scale at depths of 0 7 0 8 km hence the picture of the campi flegrei caldera is shown up to a depth of 15 km v s of about 1 7 km s corresponding to compression velocities v p of about 3 km s computed by using the v p v s ratio resulted in the inversion are found at depths of 1 1 km in the centre of the gulf of pozzuoli and at a depth of about 0 7 km b s l onshore an increment of v s velocity 1 9 2 0 km s is locally observed onshore which might be attributed to a layer of tuffs and tuffites interbedded with thin lava beds according to the correlation of v s with stratigraphies in the deep drillings of s vito

history of earthquakes and vertical ground movement in campi flegrei caldera southern italy comparison of precursory events to the a d 1538 eruption of monte nuovo and of activity since 1968 abstract the record of felt earthquakes around naples bay in southern italy is probably complete since the mid 15th century according to this record intense earthquake swarms originating beneath campi flegrei an explosive caldera located along the north coast of naples bay have occurred only twice 1 before the only historical eruption in campi flegrei in 1538 and 2 from mid 1983 to december 1984 earthquake activity during the earlier period which began at least a few years and possibly as many as 30 years before the 1538 eruption damaged many buildings in the city of pozzuoli located near the center of campi flegrei minor seismic activity which consisted of only a few felt earthquakes occurred from 1970 to 1971 the second period of intense earthquake swarms lasted from mid 1983 to 1984 again damaging many buildings in pozzuoli two periods of uplift along the shoreline within campi flegrei have also been noted since the mid 15th century 1 during the few decades before the 1538 eruption and 2 as two distinct episodes since 1968 uplift of a few meters probably occurred a few decades before the 1538 eruption uplift of as much as 3 0 m has occurred in pozzuoli since 1968 these similarities strongly suggest that for the first time in 440 years the same process that caused intense local earthquake swarms and uplift in the early 1500 s and led to an eruption in 1538 has again occurred beneath campi flegrei though no major seismicity or uplift has occurred since december 1984 because of the large amount of extensional strain accumulated during the past two decades if a third episode of seismicity and rapid uplift occurs it may lead to an eruption within several months after the resumption of activity

lithology discrimination from physical rock properties the estimation of lithology from multiple geophysical survey methods needs to be addressed to develop advanced tomographic methods an initial requirement for lithology discrimination is that lithology should be discriminable from the media properties physically related to the geophysical observations to test this condition for different combinations of the most common crustal rocks we performed several lithology discrimination exercises on rock samples under laboratory conditions the physical properties included mass density compressional velocity shear velocity electric conductivity thermal conductivity and magnetic susceptibility a categorical description of the sample lithology was followed hence the inference consisted of predicting the sample rock category lithotype membership the joint information provided by the physical properties of the rocks allowed us to discriminate the sample lithotype correctly with an overall success rate of 100 in the most favorable situation and over 85 in the least favorable situation we obtained successful classification results for a variety of common lithotypes granite gabbro limestone tuff marble basalt and gneiss using three common classification methods clustering analysis gaussian classification and discriminant analysis although discrimination was positive with each of these multivariate classification techniques discriminant analysis showed some advantages for the classification and graphic analysis of the data these results support our postulate that lithology can be estimated reliably if multiple geophysical observations are considered jointly

comment on laboratory measurements of ultrasonic wave velocities in rocks from the campi flegrei volcanic system and their relation to other field data by m zamora g sartoris and w chelini

a study of the correlation between electrical resistivity and matric suction for unsaturated ash fall pyroclastic soils in the campania region southern italy in the territory of the campania region southern italy critical rainfall events periodically trigger dangerous fast slope movements involving ashy and pyroclastic soils originated by the explosive phases of the mt somma vesuvius volcano and deposited along the surrounding mountain ranges in this paper an integration of engineering geological and geophysical measurements is presented to characterize unsaturated pyroclastic samples collected in a test area on the sarno mountains salerno and avellino provinces campania region the laboratory analyses were aimed at defining both soil water retention and electrical resistivity curves versus water content from the matching of the experimental data a direct relationship between electrical resistivity and matric suction is retrieved for the investigated soil horizons typical of an ash fall pyroclastic succession the obtained relation turns out to be helpful in characterizing soils up to close saturation which is a critical condition for the trigger of slope failure in such a regime the water content and the matric suction have small variations while electrical resistivity variations can be appreciated in a larger range of values for this reason besides suction measurements on very small soil volumes through classical tensiometers our analyses suggest the direct monitoring of in situ electrical resistivity values as an effective tool to recognise the hydrological state of larger and more representative soil volumes and to improve early warning of dangerous slope movements

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

multiscale geophysical characterization of an unstable rock mass abstract hazard mitigation from rockfalls and landslides is a priority in densely populated areas a proper characterization of the inner structure of the rock mass is key to the comprehension of the mechanisms enhancing the slope instabilities to this aim multi scale geophysical methods can provide a novel and valuable tool for a high resolution imaging of the internal structure of the rock mass and unique constraints on the physical state of the medium we present here a cross hole seismic tomography survey coupled with laboratory ultrasonic velocity measurements and physical properties determination on rock samples to characterize the damaged and potentially unstable granitic cliff of madonna del sasso nw italy results allowed to obtain i a lithological interpretation of the velocity field obtained at the site ii a systematic correlation of the measured velocities with physical properties density and porosity and macroscopic features of the granite weathering and anisotropy of the cliff the multi scale approach adopted within this study revealed to be crucial for the imaging at depth of the main fractures affecting the cliff site scale seismic tests and for the understanding of the variations in the seismic velocity between altered and intact rock laboratory scale tests similar approaches can be potentially used in further microseismic monitoring studies

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

shallow s wave velocity structure from ambient seismic noise at planchon peteroa volcanic complex argentina chileshallow s wave velocity structure from ambient seismic noise at planchon peteroa

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

an integrated 3d velocity inversion joint hypocentral determination relocation analysis of events in the northridge area abstract a subset of 3371 events recorded in the northridge area by the southern california seismic network during january to april 1994 was relocated with the joint hypocentral determination jhd technique this analysis showed two unexpected results a the jhd locations are shifted about 3 9 km on average in a northwest direction with respect to the locations determined using a single event location sel program and b the station corrections vary between 0 55 and 1 26 sec a rather large range in addition the jhd locations are less scattered than the sel locations for each station the weighted average of the arrival time residuals obtained when the events are located with the sel program which does not apply distance or error weighting are generally smaller than the corresponding jhd corrections the locations determined with sel and using the weighted average residuals as station corrections do not differ much from the sel locations but on average the rms residuals become as small as those corresponding to the jhd locations as the magnitude of the station corrections indicates the presence of large lateral velocity variations a 3d velocity model for the area was determined using the arrival times of 1012 events recorded by at least 17 stations the initial velocity model was that used routinely by the southern california earthquake center the first two layers 5 5 and 10 5 km thick were subdivided into 100 blocks each 12 12 km these layers show a pronounced low velocity anomaly 24 and 16 respectively immediately to the northwest of the epicentral area this low velocity zone coincides with the west ventura basin another pronounced low velocity zone to the southeast of the epicentral area reflects the presence of the los angeles basin the locations obtained with the 3d velocity model are consistently to the southeast of the jhd locations 2 4 km on average to establish the effect of these pronounced lateral velocity variations on the sel and jhd locations synthetic travel times were analyzed the synthetic times were generated for event locations determined by jhd shifted by various amounts and the 3d velocity model and were subsequently treated as the actual data the most important result of this analysis is that the jhd locations are affected by a quasi systematic shift in a northwest direction up to about 2 7 km on average depending on the initial shift but that the relative locations are well preserved therefore both the velocity inversion of the actual data and the analysis of the synthetic data indicate that the jhd locations determined for the actual data are quasi systematically mislocated to account for this mislocation an overall shift of 2 5 km to the southeast was applied to all the jhd locations one of the most important implications of the shifted locations is the possibility that the northeasterly dipping santa susana fault to the northwest of the epicentral area was seismically active during the aftershock sequence this feature is more diffuse in other published locations

australasian microtektites in the south china sea and the west philippine sea implications for age size and location of the impact crater abstract microtektites from two deep sea cores in the south china sea and the west philippine sea are identified as belonging to the australasian tektite strewn field based on the morphology chronostratigraphic occurrence and geographical location of these microtektites the higher concentrations of microtektites 1000 cm2 in the marginal seas of the western pacific with the peak concentration in the south china sea support the hypothesis of a large impact crater in indochina these two new occurrences lead to a more precise dating of the impact event at 793 ka whereas the size of the australasian source crater on the indochina peninsula is estimated to be 90 1 16 km introduction the australasian strewn field covering at least one tenth of the earth s surface is the largest and the youngest 0 77 0 02 ma izett and obradovich 1992 of the four known tektite strewn fields microtektites belonging to the australasian strewn field have been found in more than 40 deep sea cores throughout much of the indian ocean the western equatorial pacific ocean and the sulu celebes and philippine seas glass

experiments on vertical basement fault reactivation below volcanoes scaled modeling has been conducted to study the role played by the reactivation of vertical basement faults in the destabilization process of overlying volcanoes results show that basement fault reactivation induces the formation of faults within the volcanic edifice these faults delimite a central block which is extruded from between the two undeformed lateral parts of the edifice collapse of this central block can occur when heterogeneous cones are used in experiments revealing that mechanical interfaces are of paramount importance in triggering rockslide avalanches collapse structures may display horseshoe shapes in map view and are then surprisingly similar to avalanche scars resulting from failure created by magmatic intrusions in natural volcanoes large scale destabilisation of half the surface of the cone may also occur in a single event depending on the position of the reactivated basement fault below the edifice it is emphasized that the process under consideration may occur on a dormant volcano as well provided that a fault is reactivated below it

laboratory measurements of ultrasonic wave velocities in rocks from the campi flegrei volcanic system and their relation to other field data the campi flegrei caldera located near the city of naples italy has shown signs of unrest characterized by large ground deformation seismic activity and changes in the hydrothermal system since 1970 any attempt to model the processes giving rise to these phenomena requires some knowledge of the subsurface structure and of the physical properties of the rocks at depth in this study we report the results of laboratory measurements of ultrasonic compressional and shear wave velocities in rock samples cored in 4 different geothermal wells reaching a maximun depth of 3 km the wells are located in the san vito sv and mofete mf areas at about 3 km north and 4 km west respectively from the center of the caldera we selected 10 core samples 7 from the sv wells and 3 from the mf wells the attention being focused on the most important rock formations underneath campi flegrei and on the lower sections of the wells where data had been lacking the measurements involved the transmission of ultrasonic waves along three orthogonal directions through dry and water saturated rocks at room conditions the samples are only moderately anisotropic 13 for one sv sample and 8 for all the other samples wave velocities generally increase with the depth of the sample the range of velocities is 3 5 4 km s 1 for p waves and 1 5 2 9 km s 1 for s waves for the sv samples water saturation generally implies slightly larger 10 vp values and smaller 20 vs values as compared with dry velocities for the mf samples water saturation implies both higher vp and vs velocities up to 35 and 18 respectively these results may be explained by the different type of porosity of the sv samples vesicular and the mf samples fissurai the ultrasonic measurements on water saturated samples are slightly higher than the available in situ vp sonic measurements 25 for one sv sample and 15 for all the other samples these differences can be explained by velocity dispersion between ultrasonic and sonic frequencies and by the different pressure temperature conditions existing at depth

ultrasonic velocity measurements in volcanic rocks correlation with microtexture summary this paper summarizes results of a study of porosity permeability microstructure and acoustic properties of volcanic and pyroclastic rocks from campi flegrei cf and mt etna et italy we have measured the hydraulic transport and acoustics properties of 28 room dry samples at ambient conditions 25 room dry samples under confining pressure up to 60 mpa and 5 brine saturated samples under pressure up to 45 mpa effective pressure we established the following range of porosity permeability and vp and vs variations as functions of mineralogy and differential pressure in cf and et lithologies 1 porosity cf pyroclastic rocks 30 60 per cent cf and et lava rocks 2 20 per cent 2 permeability cf pyroclastic rocks 10 1000 md cf and et lava rocks 0 01 100 md 3 velocity and quality factor cf pyroclastic rocks vp 2 3 km s x1 vs 1 2 km s x1 qp 5 80 cf and et lava rocks vp 3 5 5 5 km s x1 vs 2 3 km s x1 qp 10 115 mineralogy and microstructure govern the acoustic and petrophysical properties of these rocks under pressure in pyroclastic rocks changes in acoustic response are directly related to presence of zeolites and pumice and their reactions with the pore fluid in dry conditions collapse of the internal texture of pumice leads to decreasing velocity with pressure in saturated conditions the water zeolite interactions compete with effects due to collapsing internal textures and so velocity change with pressure is not as pronounced the microstructural changes were confirmed by analyses of optical hydraulic and transport properties after pressure ct scans show a macroscopically more compact structure under optical microscopy pumice and zeolitized pumice appear shredded a significant reduction in porosity and permeability is measured after pressurization in lava rock samples acoustic velocities increase in function of pressure and the velocity pressure relationships are characteristic of samples with rounded pores our results emphasize the importance of conducting velocity measurements at simulated in situ conditions by constraining the computations using site and depth specific rock physics properties differences between ground deformation models in volcanic areas can be assessed and predicted more reliably thus reducing volcanic hazard