noble gases and nitrogen mixing and temporal evolution in the fumarolic fluids of vulcano italy abstract since 1979 noble gases he ne ar and n 2 in the medium temperature fumaroles of vulcano crater have been analyzed repeatedly during these 10 years of surveillance variations have been noticed in fluid composition until 1986 40 ar 36 ar ratios up to 2000 were found n 2 ar was 1600 and he ar was 1 9 indicating the presence of a deep component as the result of a mixing between mantle and crustal fluids since 1987 the atmospheric component has increased and the fluid composition has evolved towards an air saturated groundwater asw this change is considered to be the result of mixing between magmatic fluids and meteoric waters that release their atmospheric gases on entering the volcanic system these gases thus mask the magmatic component which has remained more or less constant in the last decade

18o exchange between steam and carbon dioxide in volcanic and hydrothermal gases implications for the source of water abstract the oxygen isotopic compositions of h 2 o and co 2 from 31 fumaroles from different volcanoes vesuvio campi flegrei vulcano and etna in italy soufriere of guadeloupe in lesser antilles prove that 18 o exchange between co 2 and steam is fast enough in natural gas phases to allow rapid isotopic reequilibration within a wide temperature range 100 1000 c the isotopic composition of h 2 o discharged by volcanic hydrothermal fumaroles is affected by isotopic reequilibration along with cooling of the gas phase and this secondary process must be taken into account when interpreting the origin of the water from isotopic data the use of corrected 18 o values computed considering the overall oxygen isotopic composition of the h 2 o co 2 system is therefore compulsory to overcome interpretative biases as an example we apply this method to 100 600 c fumaroles at vulcano crater whose isotopic composition is reinterpreted considering the effects of 18 o exchange between co 2 and h 2 o in contrast to most previous interpretations the corrected isotopic values for h 2 o clearly show that the vulcano system is fed by a two component mixture of magmatic water with a typical andesitic composition and either 18 o shifted seawater or magmatic steam partly condensed within the volcanic ground with minor contribution of local meteoric water the possible additional effects of isotopic reequilibration involving other o and h bearing gas species in volcanic fluids such as so 2 h 2 s hcl hf and h 2 have been also considered the influence of so 2 upon the isotopic composition of h 2 o is subordinate with respect to that of co 2 whereas significant shifts in deuterium composition are expected from hydrogen isotopic exchanges in the h 2 o h 2 s hcl hf h 2 gas system

stuck in the mud earthquake nucleation and propagation through accretionary forearcs 1 subduction zone earthquakes can propagate to the surface causing large seafloor displacements resulting in tsunamis this requires the earthquake to rupture through clay rich sediments of the accretionary wedge which are largely aseismic as found previously the frictional properties of a range of wet clays at low slip velocity are velocity strengthening thus inhibiting earthquake nucleation however at high slip velocity the same materials weaken almost immediately resulting in a negligible critical slip weakening distance and fracture energy we interpret this behaviour as rapid thermal pressurization of the pore fluid within the clay gouge the lack of fracture energy can explain how a large rupture propagating from depth might not be arrested by clay rich velocity strengthening sediments as is commonly seen the results suggest that generally earthquakes may be difficult to nucleate on mature faults dominated by clay but the propagation of earthquakes through these zones is energetically very favourable

genesis of fumarolic emissions as inferred by isotope mass balances co2 and water at vulcano island italy we have developed a quantitative model of co2 and h2o isotopic mixing between magmatic and hydrothermal gases for the fumarolic emissions of the la fossa crater vulcano island italy on the basis of isotope balance equations the model takes into account the isotope equilibrium between h2o and co2 and extends the recent model of chemical and energy two end member mixing by nuccio et al 1999 as a result the h2o and co2 content and the d 18o and 13c isotope compositions for both magmatic and hydrothermal end members have been assessed low contributions of meteoric steam added at a shallow depth have been also recognized and quantified in the fumaroles throughout the period from 1988 to 1998 nonequilibrium oxygen isotope exchange also seems to be occurring between ascending gases and wall rocks along some fumarolic conduits the 13cco2 of the magmatic gases varies around 3 to 1 vs peedee belemnite pdb following a perfect synchronism with the variations of the co2 concentration in the magmatic gases this suggests a process of isotope fractionation because of vapor exsolution caused by magma depressurization the hydrogen isotopes in the magmatic gases 1 to vs standard mean ocean water smow as well as the above 13cco2 value are coherent with a convergent tectonic setting of magma generation where the local mantle is widely contaminated by fluids released from the subducted slab magma contamination in the crust probably amplifies this effect the computed isotope composition of carbon and hydrogen in the hydrothermal vapors has been used to calculate the d and 13c of the entire hydrothermal system including mixed h2o co2 vapor liquid water and dissolved carbon we have computed values of about 10 vs smow for water and 2 to 6 5 vs pdb for co2 on these grounds we think that mediterranean marine water dh2o 10 feeds the hydrothermal system it infiltrates at depth throughout the local rocks reaching oxygen isotope equilibrium at high temperatures interaction processes between magmatic gases and the evolving seawater also seem to occur causing the dissolution of isotopically fractionated aqueous co2 and providing the source for hydrothermal carbon these results have important implications concerning fluid circulation beneath vulcano and address the more convenient routine of geochemical surveillance

interaction between the deep fluids and the shallow groundwaters on vulcano island italy the aim of this work is to study the interactions processes between the fluids of deep origin and the shallow groundwaters of the vulcano porto area during 1995 13 well waters were sampled three times may july and november and analysed for major and some minor elements b br and nh4 and for dissolved gases the close relationship of these waters with the deep magmatic source is highlighted by the composition of the dissolved gases furthermore the areal distribution of dissolved species is controlled mainly by the gas fluxes from depth and by the presence of a deeper thermal aquifer the distribution of major anomalies in the parameters measured in the groundwaters in fact overlaps the soil gas fluxes distribution that are related to the existence of preferential upflow routes of fumarolic fluids through weak structural lines in the volcanic edifice

genesis and evolution of the fumaroles of vulcano aeolian islands italy a geochemical model a geochemical model explaining the presence of fumaroles having different gas composition and temperature at the top of the crater and along the northeastern coast of vulcano island is proposed a pressurized biphase liquid vapor reservoir at the depth of about 2 km is hypothesized energy and mass balance sheets controlp t conditions in the system p t must vary along a boiling curve of brine as liquid is present the co2 content in the steam is governed by the thermodynamic properties of the fluids in the h2 nacl co2 system on the assumption that oxygen fugacity in the system is between the hm fmq oxygen buffers observed so2 h2s co2 co co ch4 ratios in the fumarolic gases at the fossa crater appear in equilibrium with a temperature higher than that observed such as may exist at depth the more reduced gas phases present on the sea side may result from re equilibrium processes in shallower aquifers the suggested model would help in monitoring changes in volcanic activity by analyzing fumarolic gases

thermal characterization of the vulcano fumarole field ground based thermal infrared surveys can contribute to complete heat budget inventories for fumarole fields however variations in atmospheric conditions plume condensation and mixed pixel effects can complicate vent area and temperature measurements analysis of vent temperature frequency distributions can be used however to characterise and quantify thermal regions within a field we examine this using four thermal infrared thermometer and thermal image surveys of the vulcano fossa fumarole field italy during june 2004 and july 2005 these surveys show that regions occupied by low temperature vents are characterised by distributions that are tightly clustered around the mean i e the standard deviation is low highly peaked positive kurtosis and skewed in the low temperature direction negative skewness this population is associated with wet fumaroles where boiling controls maximum temperature to cause a narrow distribution with a mode at 90 100 c in contrast high temperature vent regions have distributions that are widely spread about the mean i e the standard deviation is high relatively flat negative kurtosis and skewed in the high temperature direction positive skewness in this dry case fumaroles are water free so that maximum temperatures are not fixed by boiling as a result greater temperature variation is possible we use these results to define two vent types at vulcano on the basis of their thermal characteristics 1 concentrated localized regions of high temperature vents and 2 dispersed low temperature vents these occur within a much larger region of diffuse heat emission across which surfaces are heated by steam condensation the heat from which causes elevated surface temperatures for vulcano s lower fumarole zone high and low temperature vents occupied total areas of 3 and 6 m2 respectively and occurred within a larger 430 m2 vent free zone of diffuse heat emission for this lower zone we estimate that 21 43 103 w of heat was lost by diffuse heat emission a further 4 5 103 w was lost by radiation from high temperature vents and 6 5 103 w from low temperature vents thus radiative heat losses from high and low temperature vents within vulcano s lower fumarole zone respectively account for 10 and 15 of the total heat lost from this zone this shows that radiation from open vents can account for a non trivial portion of the total fumarole field heat budget

trace elements in the thermal groundwaters of vulcano island sicily abstract the chemical concentrations of many trace elements that have never before been examined in vulcano island groundwaters are reported chemical data indicate that rock composition is not the only factor determining the metal content in the aqueous system the observed concentrations depend mainly on 1 the chemical composition of the host rocks 2 the chemical physical conditions of the weathering solution temperature acidity redox conditions 3 input of magmatic gases 4 adsorption of metal ions on oxide particles formation of soluble complexes and or precipitation of solid phases chloride complexes in solution are of minimal significance for all elements with the exception of cd whereas carbonate complexes are important for pb uo 2 zn and ni temperature and trace element distribution maps are also presented

nmo velocity surfaces and dix type formulas in anisotropic heterogeneous media reflection moveout of pure modes recorded on conventional length spreads is described by a normal moveout nmo velocity that depends on the orientation of the common midpoint cmp line here we introduce the concept of nmo velocity surfaces which are obtained by plotting the nmo velocity as the radius vector along all possible directions in 3 d space and use it to develop dix type averaging and differentiation algorithms in anisotropic heterogeneous media the intersection of the nmo velocity surface with the horizontal plane represents the nmo ellipse that can be estimated from wide azimuth reflection data we demonstrate that the nmo ellipse and conventional spread moveout as a whole can be modeled by dix type averaging of specifically oriented cross sections of the nmo velocity surfaces along the zero offset reflection raypath this formalism is particularly simple to implement for a stack of homogeneous anisotropic layers separated by plane dipping boundaries since our method involves computing j

an example of slip instability resulting from displacement varying strength a rock cylinder containing a clay filled sawcut making an angle of 30 to the sample axis was deformed at constant confining and pore pressures and constant remote shortening rate the sawcut surfaces contained a series of regularly spaced ridges and grooves oriented perpendicular to the direction of shear the interaction of these grooved surfaces resulted in a sliding strength which varied periodically with displacement by varying the effective machine stiffness through the use of an electronic feedback circuit a range of stable and unstable slip behavior was achieved in this way we examined fault slip behavior which was dominated by displacement dependent strength

under the hood of the earthquake machine toward predictive modeling of the seismic cycle advances in observational laboratory and modeling techniques open the way to the development of physical models of the seismic cycle with potentially predictive power to explore that possibility we developed an integrative and fully dynamic model of the parkfield segment of the san andreas fault the model succeeds in reproducing a realistic earthquake sequence of irregular moment magnitude m w 6 0 main shocks including events similar to the ones in 1966 and 2004 and provides an excellent match for the detailed interseismic coseismic and postseismic observations collected along this fault during the most recent earthquake cycle such calibrated physical models provide new ways to assess seismic hazards and forecast seismicity response to perturbations of natural or anthropogenic origins

signs of potential renewal of eruptive activity at la fossa vulcano aeolian islands since the end of the last magmatic eruption 1890 activity of la fossa southern tyrrhenian sea italy has consisted of fumarolic emissions of fluctuating intensity fluids are discharged principally at two fumarolic fields located in the northern rim of the active crater and at the beach sited at its northern foot increased thermal seismic and geochemical activity has been recorded since 1978 when an earthquake of m 5 5 occurred in the region this paper combines available geophysical and geochemical information in order to develop a tentative interpretation of two episodes of apparent unrest which occurred in 1985 and 1987 1988 enhancing the risk of renewal of the eruptive activity the 1985 unrest consisted essentially of a sharp build up of the internal pressure in the shallow hydrothermal system which was induced by the injection of hot gases of magmatic origin the crater fumaroles displayed significant increases in co2 and other acid species but their outlet temperature did not change conversely the 1987 1988 episode was characterized by appreciable modifications at the crater fumaroles with only secondary effects at the fumarole system of the beach the sliding of part of the eastern flank of the la fossa cone into the sea occurred on 20 april 1988 when the region was affected by crustal dilatation producing a seismic sequence of relatively high intensity both episodes of unrest were accompanied by increases of local microseismic activity which affected the nothern sector of the island in 1985 and the southern one in 1988 finally a phase of appreciable areal contraction was detected in 1990 probably due to the effect of the cooling and crystallization of magma at relatively shallow depths accompanying the increased thermal activity at the crater fumaroles regional tectonic stress seems to play an important role in the transition of the volcanic system from a phase of relative stability to a phase of apparent unrest inducing the heating and the expansion of shallow hydrothermal fluids available information is insufficient to indicate whether or not the volcano is building towards the renewal of a magmatic eruption and there is no evidence to hypothesize episodes of significant magma migration the frequency of measurements of many parameters needs to be increased in order to learn more about the temporal relationships between geochemical and geophysical variations preceding and accompanying periods of increased thermal activity this will probably be a valid tool for recognizing short term precursors of a future eruption reducing the risk of false alarms

aftershock slip behavior of the 1989 loma prieta california earthquake an analysis of 745 aftershocks of the m7 1 loma prieta earthquake of 17 october 1989 reveals a wide variety of focal mechanisms at the northwestern end of the aftershock zone earthquakes that apparently occurred off the main rupture plane exhibit mechanisms with predominantly reverse slip on planes nearly parallel to the san andreas fault at the southeastern end the mechanisms exhibit right lateral motion on near vertical planes suggesting that these aftershocks involve slip on the san andreas fault few of the aftershock mechanisms in the central zone resemble the main shock mechanism strike n130 degree e dip 70 degree sw rake 104 degree but instead exhibit reverse right lateral left lateral and normal motion on planes subparallel to the main shock rupture plane the dip of the aftershock zone is parallel to the main shock slip plane and includes the main shock hypocenter however the lack of agreement between the main shock and the aftershock mechanisms suggests that few of the aftershocks occurred on the main shock slip plane this behavior is consistent with observations of aftershock sequences for other dip slip events and also with studies indicating that main shock rupture zones are at all other times mostly aseismic if the stress drop for the main shock relievedmore most of the tectonic stress the mechanisms could reflect the heterogeneity of the near field stress redistribution alternatively the variety of the aftershock mechanisms may reflect deformation by block motion within a narrow zone adjacent to the main shock rupture plane less

physical chemical conditions of the teide volcanic system tenerife canary islands the teide volcano 3717 m is the central structure of the island of tenerife and at present its morphology is that of a stratovolcano which has grown on a large caldera with a collapse 17 km in diameter which was generated some 0 6 million years ago the different studies that have been carried out seem to indicate that in a oversimplified model there is an intermediate magma chamber with an approximate volume of 30 km3 and located 2 3 km below the actual base of the caldera i e almost at sea level with a temperature of 430 50 c and a pressure of 400 100 bar the summit fumarole emissions are 85 c and are formed mainly of co2 with small amounts of sulphur species h2 ch4 and he the water vapor 68 82 emitted with the gases comes from the vaporization of a perched aquifer in the upper cone as shown by the isotopic analyses

chemical features and isotopic composition of gaseous manifestations on vulcano island aeolian islands italy an interpretative model of fluid circulation abstract between 1987 and 1995 gases were sampled from various manifestations on vulcano island including various fumaroles at la fossa crater and baia di levante and diffuse soil gas emissions in several areas which are characterized by high c02 fluxes since the end of 1987 volcanic activity has increased considerably showing a marked rise in temperature 300 c in 1987 to 670 c in december 1992 and in output of steam from crater fumaroles in addition variations have been observed in the chemical and isotopic compositions of gases and thermal waters which can be attributed to an increased inflow of deeper fluids the isotopic composition of fumarolec steam seems to be the result of mixing processes between a positive endmember of deep origin d 10 15 18o 6 8 and two endmembers of meteoric origin with different oxygen shifts variations observed in the c02 isotopic composition suggest that all sampled manifestations are fed by a single deep source which may be magmatic such a source would be characterized by the 613cco2 values of high temperature fumaroles 13cco2 0 these values are noticeably more positive than those generally attributed to magmatic gases 13cco2 5 8 implying crustal contamination processes of the magma the observed decrease in 18oco2 values of the crater fumaroles from 20 in 1978 to between 12 and 15 in 1993 1994 was probably caused by two different processes the first is a reduction of the enrichment factor between c02 and h2o which is related to the increased temperature of the gases and the second is a mixing with more negative waters of meteoric origin finally c02 addition or removal processes caused by interactions between deep gases and shallow hydrothermal waters are likely to be responsible for the different chemical and isotopic compositions of gaseous emissions in the vulcano porto area and the crater fumaroles

genesis of chlorine and sulphur in fumarolic emissions at vulcano island italy assessment of ph and redox conditions in the hydrothermal system chlorine and sulphur bearing compounds in fumarole discharges of the la fossa crater at vulcano island italy can be modelled by a mixing process between magmatic gases and vapour from a boiling hydrothermal system this allows estimating the compounds in both endmembers magma degassing cannot explain the time variation of sulphur and hcl concentrations in the deep endmember which are more probably linked to reactions of solid phases at depth before mixing with the hydrothermal vapours based on the p t conditions and speciation of the boiling hydrothermal system below la fossa the hcl and stot contents in the hydrothermal vapours were used to compute the redox conditions and ph of the aqueous solution the results suggest that the haematite magnetite buffer controls the hydrothermal fo2 values while the ph has increased since the end of the 1970s the main processes affecting ph values may be linked to na ca exchanges between evolved seawater feeding the boiling hydrothermal system and local rocks while na is removed from water calcium enters the solution undergoes hydrolysis and produces hcl lowering the ph of the water the increasing water rock ratio within the hydrothermal system lowers the ca availability so the aqueous solution becomes less acidic seawater flowing towards the boiling hydrothermal brine dissolves a large quantity of pyrite along its path in the boiling hydrothermal system dissolved sulphur precipitates as pyrite and anhydrite and becomes partitioned in vapour phase as h2s and so2 these results are in agreement with the paragenesis of hydrothermal alteration minerals recovered in drilled wells at vulcano and are also in agreement with the isotopic composition of sulphur emitted by the crater fumaroles

identifying fault heterogeneity through mapping spatial anomalies in acoustic emission statistics 1 seismicity clusters within fault zones can be connected to the structure geometric complexity and size of asperities which perturb and intensify the stress field in their periphery to gain further insight into fault mechanical processes we study stick slip sequences in an analog laboratory setting analysis of small scale fracture processes expressed by acoustic emissions aes provide the possibility to investigate how microseismicity is linked to fault heterogeneities and the occurrence of dynamic slip events the present work connects x ray computer tomography ct scans of faulted rock samples with spatial maps of b values slope of the frequency magnitude distribution seismic moments and event densities our current experimental setup facilitates the creation of a series of stick slips on one fault plane thus allowing us to document how individual stick slips can change the characteristics of ae event populations in connection to the evolution of the fault structure we found that geometric asperities identified in ct scan images were connected to regions of low b values increased event densities and moment release over multiple stick slip cycles our experiments underline several parallels between laboratory findings and studies of crustal seismicity for example that asperity regions in lab and field are connected to spatial b value anomalies these regions appear to play an important role in controlling the nucleation spots of dynamic slip events and crustal earthquakes

imaging structures below dipping ti media seismic anisotropy in dipping shales causes imaging and positioning problems for underlying structures we developed an anisotropic depth migration approach for p wave seismic data in transversely isotropic ti media with a tilted axis of symmetry normal to bedding we added anisotropic and dip parameters to the depth imaging velocity model and used prestack depth migrated image gathers in a diagnostic manner to refine the anisotropic velocity model the apparent position of structures below dipping anisotropic overburden changes considerably between isotropic and anisotropic migrations the ray tracing algorithm used in a 2 d prestack kirchhoff depth migration was modified to calculate traveltimes in the presence of ti media with a tilted symmetry axis the resulting anisotropic depth migration algorithm was applied to physical model seismic data and field seismic data from the canadian rocky mountain thrust and fold belt the anisotropic depth migrations offer significant improvements in positioning and reflector continuity over those obtained using isotropic algorithms

75 plus years of anisotropy in exploration and reservoir seismics a historical review of concepts and methods the idea that the propagation of elastic waves can be anisotropic i e that the velocity may depend on the direction is about 175 years old the first steps are connected with the top scientists of that time people such as cauchy fresnel green and kelvin for most of the 19th century anisotropic wave propagation was studied mainly by mathematical physicists and the only applications were in crystal optics and crystal elasticity during these years important steps in the formal description of the subject were made at the turn of the 20th century rudzki stressed the significance of seismic anisotropy he studied many of its aspects but his ideas were not applied research in seismic anisotropy became stagnant after his death in 1916 beginning about 1950 the significance of seismic anisotropy for exploration seismics was studied mainly in connection with thinly layered media and the resulting transverse isotropy very soon it became clear that the effect of layer induced anisotropy on data ac

depth domain velocity analysis in vti media using surface p wave data is it feasible the main difficulties in anisotropic velocity analysis and inversion using surface seismic data are associated with the multiparameter nature of the problem and inherent trade offs between the model parameters for the most common anisotropic model transverse isotropy with a vertical symmetry axis vti media p wave kinematic signatures are controlled by the vertical velocity v0 and the anisotropic parameters e and however only two combinations of these parameters nmo velocity from a horizontal reflector vnmo 0 and the anellipticity coefficient can be determined from p wave reflection traveltimes if the medium above the reflector is laterally homogeneous while vnmo 0 and are sufficient for time domain imaging in vti media they cannot be used to resolve the vertical velocity and build velocity models needed for depth migration here we demonstrate that p wave reflection data can be inverted for all three relevant vti parameters v0 e and if the model contains nonhorizontal intermediate i

the evolution of a dynamic geological system the support of a gis for geochemical measurements at the fumarole field of vulcano italy abstract the island of vulcano aeolian arc southern italy has displayed several periods of volcanic unrest since the end of the last eruption 1890 we report here results obtained from a long term survey concerning variations of both the steam output and the exhaling surface area at the summit crater fumarolic field of la fossa the field measurements analysed in a geographical information system gis show a highly dynamic volcanic system in which deep variations in the geochemistry and the temperature of the released fluids were accompanied by fluctuations in the mass output of steam and the topography of the crater field the use of a gis facilitated digitized reconstructions of maps of the crater field in addition to analysis of the steam flux data the fumarolic field expanded its surface area from 50 m 2 in 1983 to more than 2400 m 2 in 1995 accompanied by an increase in steam output from 152 to about 1400 tonnes per day the possibility that the observed phenomena are related to volcano tectonic activity and to magma uprising is taken into consideration

volcanic hazards at fossa of vulcano data from the last 6 000 years stratigraphic reconstruction of the complete sequence of deposits that formed the fossa cone of vulcano has distinguished four principal eruptive cycles punte nere palizzi commenda and pietre cotte at least three additional eruptive cycles one of which ends with the campo sportivo lava occur between deposits of the punte nere and palizzi cycles however exposure is inadequate for their characterization the assignment of the modern deposits that follow the pietre cotte lava is uncertain

isotopic composition of natural thermal discharges on vulcano island southern italy this paper reviews the isotopic 18o16o and d h ratios reported in the literature for phreatic waters in the plain of vulcano island off sicily and condensates from high temperature fumaroles at the top of the summit crater the vulcano phreatic waters have a rather high average annual temperature greater than 30 dgc but do not seem to be heated directly by mixture with condensates of fumarolic steam they seem to originate from rainwater and to undergo high evaporation particularly in summer owing to high conductive heat flow in the island by comparing the 18o16o and d h ratios with cl as hcl content it is estimated that 75 of the steam from the high temperature fumaroles comes from seawater and 25 from low salinity waters the latter however do not seem to come directly from the shallow aquifer of vulcano because the steam from the fumaroles does not contain radiogenic tritium this mixing model and the lack of steam condensation in the vulcano aquifer implies indirectly that there are no steam losses during the rise of deep fluids and that some observed variations in the outlet temperatures without accompanying variations in the composition of the associated gas phase may be due to increased or decreased extent of fracturation in the volcanic edifice as a result for instance of tectonic movements which cause more or less vaporization of low salinity fresh water into the volcanic ducts as well as faster or slower outflow of deep gases

the episodic and abrupt geochemical changes at la fossa fumaroles vulcano island italy and related constraints on the dynamics structure and compositions of the magmatic system abstract herein we report on the chemical and isotopic c h o and he compositions of the fluids from la fossa crater fumaroles of vulcano from 1999 to 2010 consistent with records obtained since the end of the 1980s our data show that the geochemical features of the fumarole system have experienced several episodes of remarkable change each lasting no more than a few months typical signatures of these short term anomalies are large increments in co 2 n 2 and he concentrations coupled to increased 13 c 12 c isotopic ratios but their meaning remains widely debated within a model of fumarolic fluids based on mixing between hydrothermal and magmatic endmembers we have developed a novel approach to constrain chemical he co 2 and n 2 he and isotopic 13 c 12 c d h and 3 he 4 he ratios of the magmatic endmember during the short term anomalies although much of the geochemical variability in fumaroles results from changes in mixing proportions the magmatic fluid unquestionably shows significant variations in time the magmatic he co 2 n 2 he 13 c 12 c and 3 he 4 he values throughout 1988 1996 differed from those feeding the anomaly at the end of 2004 early clues of the new magmatic fluid appeared in 1998 1999 far from any short term anomaly whereas new and old magmatic fluids coexisted after 2004 we quantitatively prove that the detected geochemical changes are consistent with the degassing path of a magma having a latitic composition and suggest the presence of two magma ponding levels at slightly different pressures where bubble melt decoupling can occur the different he isotope compositions at these levels suggest low hydraulic connectivity typical of a complex reservoir with dike and sill structures in this framework the short term geochemical anomalies are probably due to gas accumulation at the top of magma bodies followed by massive escape or activation of new degassing levels in the reservoir for which the stress field almost certainly plays a key role such a scenario explains the observed increases in both fumarole output and shallow high frequency seismicity due to increased pore pressure during the anomalies while being consistent with the concomitant absence of any deep seismicity or ground deformation eventually related to magma movement

review of the evolution of geochemical monitoring networks and methodologies applied to the volcanoes of the aeolian arc italy abstract fluids discharged from volcanic systems are the direct surface manifestation of magma degassing at depth and provide primary insights for evaluating the state of volcanic activity we review the geochemical best practice in volcanic surveillance based to a huge amount of monitoring data collected at different active volcanoes using both continuous and discontinuous approaches the targeted volcanoes belong to the aeolian arc located in the tyrrhenian sea italy and they have exhibited different activity states during the monitoring activities reported here la fossa cone on vulcano island has been in an uninterrupted quiescent stage characterized by variable solfataric activity in contrast stromboli island has shown a persistent mild explosive activity episodically interrupted by effusive eruptions in 1985 2002 2007 and 2014 panarea island which is the summit of a seamount rising from the seafloor of the southern tyrrhenian sea showed only undersea fluid release the only observable clues of active volcanism at panarea island have been impulsive changes in the undersea fluid release with the last submarine gas burst event being observed in november 2002 the geochemical monitoring and observations at each of these volcanoes has directly involved the volcanic plume and or the fumarole vents thermal waters and diffuse soil degassing depending on the type of manifestations and the level of activity encountered through direct access to the magmatic samples when possible and the collection of as much observable data related to the fluid release as possible the aim has been i to verify the thermodynamic equilibrium condition ii to discern among the possible hydrothermal magmatic marine and meteoric sources in the fluid mixtures iii to develop models of the fluid circulation supported by data iv to follow the evolution of these natural systems by long term monitoring and v to support surveillance actions related to defining the volcanic risk and the evaluation and possible mitigation of related hazards the examples provided in this review article show the close relationships among data analysis interpretation and modeling we particularly focus on describing the fieldwork procedures since any theoretical approach must always be verified and supported by field data rather than just by experiments controlled in laboratory indeed the natural systems involve many variables producing effects that cannot be neglected the monitored volcanic systems have been regarded as natural laboratories and all of the activities have focused on both volcanological research and surveillance purposes in order to ensure that these two goals have overlapped an appendix is also included that explains the scientific approach to the systematic activities regarding geochemical monitoring of volcanic activity

premonitory acoustic emissions and stick slip in natural and smooth faulted westerly granite 1 a stick slip event was induced in a cylindrical sample of westerly granite containing a preexisting natural fault by loading at constant confining pressure of 150 mpa continuously recorded acoustic emission ae data and computer tomography ct generated images of the fault plane were combined to provide a detailed examination of microscale processes operating on the fault the dynamic stick slip event considered to be a laboratory analog of an earthquake generated an ultrasonic signal that was recorded as a large amplitude ae event first arrivals of this event were inverted to determine the nucleation site of slip which is associated with a geometric asperity on the fault surface ct images and ae locations suggest that a variety of asperities existed in the sample because of the intersection of branch or splay faults with the main fault this experiment is compared with a stick slip experiment on a sample prepared with a smooth artificial saw cut fault surface nearly a thousand times more ae were observed for the natural fault which has a higher friction coefficient 0 78 compared to 0 53 and larger shear stress drop 140 compared to 68 mpa however at the measured resolution the ultrasonic signal emitted during slip initiation does not vary significantly between the two experiments suggesting a similar dynamic rupture process we propose that the natural faulted sample under triaxial compression provides a good laboratory analogue for a field scale fault system in terms of the presence of asperities fault surface heterogeneity and interaction of branching faults

isotopic variation of the hydrothermal system on vulcano island italy the isotopic and chemical composition of thermal waters and the isotopic composition of high temperature fumarolic steam at vulcano island indicate an evolution of the hydrothermal system from its magmatic origin through interaction with rocks and mixing with meteoric water seawater is not a component in this system the isotopic values of the fumaroles indicate a local magmatic composition of 7 to 8 18o and 5 to 15 d the high d values of this vapor may reflect contamination of the magma by connate water the isotopic and chemical composition of water from well w2 indicates the existence of geothermal fluid formed by mixing of hcl and so2 bearing condensates of volcanic origin with groundwater with subsequent evolution via water rock interaction the estimated isotopic composition of the geothermal water is 18o 1 and d 5 local shallow seismic events result in a temporary increase in fracture permeability enabling the mixing of magmatic vapor with groundwater or geothermal water tectonic activity associated with deep structures appears to increase the contribution of magmatic vapor to the fumaroles

geochemical surveillance of the solfatara of pozzuoli phlegraean fields during 1983 geochemical surveillance of the phlegraean fields area has been intensified since 1983 in response to the increased uplift rate brady seismic activity fumarolic gases from solfatara pozzuoli were sampled and analyzed monthly a reducing capacity rc monitoring unit was installed at soffione the most active fumarole in the solfatara system the preliminary analysis of the rc temporal variations suggest they are consistent with the rate of the seismic energy release the composition of fumarolic gases indicates that the equilibrium temperature and pressure are higher than those of sampling the observed variations in ch4 content are explained as an increase of pressure from 1982 to the end of 1983 of about 70 at an extimated depth of 3 3 5 km finally during 1983 there were no geochemical indications of both rising magma and significant accumulation of energy at shallow depth

modeling and inversion of ps wave moveout asymmetry for tilted ti media part 2 dipping tti layer dipping transversely isotropic layers with a tilted symmetry axis tti media cause serious imaging problems in fold andthrust belts and near salt domes here we apply the modified pp ps ss method introduced in part 1 to the inversion of longoffset ppand ps reflection data for the parameters of atti layer withthesymmetryaxisorthogonaltothebedding theinversion algorithmcombinesthetime andoffset asymmetryattributesof the psv wave with the hyperbolic pp and ss wave moveout in thesymmetry axisplanei e theverticalplanethatcontainsthe symmetryaxis the weak anisotropy approximations for the moveout asymmetry attributes verified by numerical analysis indicate that small offsetleadingtermsdonotcontainindependentinformation for the inversion therefore the parameter estimation algorithm relies on ps data recorded at large offsets the offset todepth ratio has to reach at least two which makes the results generally less stable than those for a horizontal tti layer in part1 the least resolved parameter is thomsen s coefficient thatdoesnotdirectlyinfluencethemoveoutofeitherpureorconvertedmodes still the contribution of the ps wave asymmetry attributes helps to constrain thetti model for large tilts of the symmetry axis 40 the accuracy of the inversion for large tilts can be improved further by using wide azimuth pp and ps reflections with high quality ps data the inversion remains feasible formoderatetilts25 40 butitbreaksdownformodels with smaller values of in which the moveout asymmetry is too weak the tilt itself and several combinations of the medium parameters e g the ratio of the p and s wave velocities in the symmetry direction however are well constrained for all symmetry axisorientations the results of parts 1 and 2 show that 2d measurements of the ps wave asymmetry attributes can be used effectively in anisotropic velocity analysis for tti media in addition to providing an improved velocity model for imaging beneath tti beds our algorithms yield information for lithology discrimination and structuralinterpretation

steam output from fumaroles of an active volcano tectonic and magmatic hydrothermal controls on the degassing system at vulcano aeolian arc the results from measurements of extensive parameters steam output and exhaling surface area taken at the crater fumarolic field of vulcano island aeolian arc southern italy are reported along with a detailed description of the measuring method the steam emission rate increased by 1 order of magnitude during the observation time 1983 1995 while its concentration in the released gases was only slightly changed during the same period the total exhaling surface expanded from 50 m2 to more than 2400 m2 and evolved following preferential trends that coincide with the main tectonic structures of the island the observed peaks in steam output show a positive correlation with episodes of volcanic activity unrest the temporal increase of steam output and the observed development in the exhaling surface areas are consistent with a volcano tectonic triggering of the exhaling activity particularly the peaks in the steam output are interpreted as a consequence of degassing from an active magma slowly moving toward the surface

spatial variability of seismicity parameters in aftershock zones the spatial variability of the b value of the frequency magnitude relationship and the decay rate of aftershocks as described by the p value of the modified omori law is investigated by using dense spatial grids we map out the distribution of b and p values within the landers northridge morgan hill and kobe aftershock sequences considerable spatial variability is found with b values of independent subvolumes ranging from 0 6 to 1 4 and p values ranging from 0 6 to 1 8 these systematic and statistically highly significant differences argue that it is an oversimplification to assign one single p and b value to an aftershock sequence that extends up to 100 km the spatial distribution of these two parameters is compared with the slip distribution during the mainshock suggesting that the areas of largest slip release correlate with high b value regions we hypothesize that the frictional heat created during the event may influence the p value distribution within an aftershock zone while applied shear stress crack density and pore pressure govern the frequency magnitude distribution by investigating the frequency magnitude distribution separately for preseismic and postseismic periods for the morgan hill mainshock we find that only the volume in the vicinity of the highest slip release shows a significant increase in the b value which decays to premainshock values within a year surrounding areas of the aftershock zone show an approximately constant b value with time because the aftershock hazard after a mainshock depends strongly on both the b and p value we propose that aftershock hazard assessment can be improved by taking into account the spatial distribution of the parameters

velocity analysis for tilted transversely isotropic media a physical modeling example transverse isotropy with a tilted symmetry axis tti media has been recognized as a common feature of shale formations in overthrust areas such as the canadian foothills since tti layers cause serious problems in conventional imaging it is important to be able to reconstruct the velocity model suitable for anisotropic depth migration here we discuss the results of anisotropic parameter estimation on a physical modeling data set the model represents a simplified version of a typical overthrust section from the alberta foothills with a horizontal reflector overlaid by a bending transversely isotropic layer assuming that the tti layer is homogeneous and the symmetry axis stays perpendicular to its boundaries we invert p wave normal moveout nmo velocities and zero offset traveltimes for the symmetry direction velocity v0 and the anisotropic parameters e and the coefficient e is obtained using the traveltimes of a wave that crosses a dipping tti block and reflects from the bottom of the model t

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

a practical method for estimating effective parameters of anisotropy from reflection seismic data the location of any event imaged by p wave reflection seismic data beneath a tilted transversely isotropic tti overburden is shifted laterally if isotropic velocities are used during data processing the magnitude of the shift depends on five independent parameters overburden thickness angle of tilt symmetry axis velocity and the thomsen anisotropy parameters and the shift also varies with source receiver offset we have developed a procedure to estimate these five parameters when the tilt of the symmetry axis from the vertical is equal to the dip of the tti layer except in the special cases transverse isotropy with vertical or horizontal axis of symmetry we observe three attributes of seismic data processed using isotropic velocities the zero offset arrival time of a selected reflection the difference in arrival time between a near offset and a far offset arrival and the difference in imaged location smear of this target event between the same offsets we then perform a cascaded scan of t

asperity generating upper crustal sources revealed by b value and isostatic residual anomaly grids in the area of antofagasta chile in our study we show that the locations of largest coseismic slip asperities on the fault plane of the m w 8 0 1995 antofagasta earthquake in northern chile can be mapped by the spatial distribution of the seismic b value obtained from the aftershock sequence of the megathrust earthquake these areas of high seismic moment release and concurrent high b values are congruent with anomalies of the gravity isostatic residual ir field in the antofagasta region they are superimposed on the seismogenic part of the north chilean subduction zone where the strongest coupling of the upper and lower plate is expected the ir anomalies are interpreted to be caused by large jurassic early cretaceous batholiths which intruded into the upper crust the observed positive correlations between high seismic b values ir anomalies and geologic structures enable us to propose a mechanical model for the generation of the asperities in the antofagasta region we suggest that the batholiths in conjunction with buoyant forces acting on the subducted slab of the nazca plate are responsible for locking the interface where the asperities are located this implies long term conditions for the existence of the asperity generating tectonic situation concequently the asperities around antofagasta could be stationary features at least for several seismic cycles hence we propose that the ir anomalies along the north chilean convergent margin can be used as an indicator for high moment release and slip in future large earthquakes

geogenic and atmospheric sources for volatile organic compounds in fumarolic emissions from mt etna and vulcano island sicily italy 1 in this paper fluid source s and processes controlling the chemical composition of volatile organic compounds vocs in gas discharges from mt etna and vulcano island sicily italy were investigated the main composition of the etnean and volcano gas emissions is produced by mixing to various degrees of magmatic and hydrothermal components vocs are dominated by alkanes alkenes and aromatics with minor though significant concentrations of o s and cl f substituted compounds the main mechanism for the production of alkanes is likely related to pyrolysis of organic matter bearing sediments that interact with the ascending magmatic fluids alkanes are then converted to alkene and aromatic compounds via catalytic reactions dehydrogenation and dehydroaromatization respectively nevertheless an abiogenic origin for the light hydrocarbons cannot be ruled out oxidative processes of hydrocarbons at relatively high temperatures and oxidizing conditions typical of these volcanic hydrothermal fluids may explain the production of alcohols esters aldehydes as well as o and s bearing heterocycles by comparing the concentrations of hydrochlorofluorocarbons hcfcs in the fumarolic discharges with respect to those of background air it is possible to highlight that they have a geogenic origin likely due to halogenation of both methane and alkenes finally chlorofluorocarbon cfc abundances appear to be consistent with background air although the strong air contamination that affects the mt etna fumaroles may mask a possible geogenic contribution for these compounds on the other hand no cfcs were detected in the vulcano gases which are characterized by low air contribution nevertheless a geogenic source for these compounds cannot be excluded on the basis of the present data

image mispositioning due to dipping ti media a physical seismic modeling study a scaled physical model was constructed to investigate the magnitudes of imaging errors incurred by the use of isotropic processing code when there is seismic velocity anisotropy present in the dipping overburden the model consists of a block of transversely isotropic ti phenolic material with the ti axis of symmetry dipping at an angle of 45 its scaled thickness is 1500 m and it is intended to simulate the dipping clastic sequences found in many fold thrust belts a piece of isotropic plexiglas affixed to the underside of the anisotropic block has a step function in it to simulate a target reef edge or fault the anisotropy parameters of the material are 0 1 and e 0 24 on zero offset data the imaged position of the target is shifted laterally 320 m in the updip direction of the beds whereas on time and depth migrated multichannel sections the shift is 300 m the lateral shift is offset dependent with the amount of shift in any common midpoint gather decreasing from 320 m on the near off

multiparametric approach in investigating volcano hydrothermal systems the case study of vulcano aeolian islands italy seismic activity ground deformation and soil and fumarole temperatures acquired during 2004 2007 at vulcano aeolian islands are analysed and the time relations among the different time series are discussed changes in temperature of fumarolic gases took place during four anomalous periods november 2004 march 2005 october 2005 february 2006 august october 2006 july december 2007 at the same time as an increasing number of volcano seismic events in particular the temperatures at high temperature vents and at steam heated soil ranged in time from 180 to 440 c and from 20 to 90 c respectively the maximum daily number of volcano seismic events was 57 reached during the second anomalous period this seismicity characterised by focal depth generally lower than 1 km below sea level b s l and composed of different kinds of events associated to both resonance and shear failure processes is related to the shallow dynamics of the hydrothermal system during the analysed period very few volcano tectonic earthquakes took place and tilt recordings showed no sharp or important changes in light of such observations the increases in both temperature and volcano seismic events number were associated to increases in the release of gas from a deep and stable magma body without magma intrusions within the shallow hydrothermal system indeed a greater release of gas from depth leads to increased fluid circulation that can promote increases in volcano seismic events number by both fracturing processes and resonance and vibration in cracks and conduits the different trends observed in the measured geochemical and geophysical series during the anomalous periods can be due to either time changes in the medium permeability or a changing speed of gas release from a deep magma body finally all the observed variations together with the changing temporal distribution of the different seismic event kinds suggest that the hydrothermal system at vulcano can be considered unsteady and dynamic

distribution of seismicity across strike slip faults in california 1 the distribution of seismicity about strike slip faults provides measurements of fault roughness and damage zone width in california seismicity decays with distance from strike slip faults according to a power law 1 x2 d2 2 this scaling relation holds out to a fault normal distance x of 3 6 km and is compatible with a rough fault loading model in which the inner scale d measures the half width of a volumetric damage zone and the roll off rate is governed by stress variations due to fault roughness according to dieterich and smith s 2 d simulations approximates the fractal dimension of along strike roughness near fault seismicity is more localized on faults in northern california nocal d 60 20 m 1 65 05 than in southern california socal d 220 40 m 1 16 05 the parkfield region has a damage zone half width d 120 30 m consistent with the safod drilling estimate its high roll off rate 2 30 25 indicates a relatively flat roughness spectrum k 1 versus k 2 for nocal k 3 for socal our damage zone widths the first direct estimates averaged over the seismogenic layer can be interpreted in terms of an across strike fault core multiplicity that is 1 in nocal 2 at parkfield and 3 in socal the localization of seismicity near individual faults correlates with cumulative offset seismic productivity and aseismic slip consistent with a model in which faults originate as branched networks with broad multicore damage zones and evolve toward more localized lineated features with low fault core multiplicity thinner damage zones and less seismic coupling our results suggest how earthquake triggering statistics might be modified by the presence of faults

stacking velocity inversion with borehole constraints for tilted ti media transversely isotropic models with a tilted symmetry axis ttiplayanincreasinglyimportantroleinseismicimaging especially near salt bodies and in active tectonic areas here we present a 2d parameter estimation methodology for tti media based on combining p wave normal moveoutnmo velocities zero offset traveltimes and reflection time slopes with borehole data that include check shot traveltimes as well as the reflector depths and dips for a dipping tti layer withthesymmetryaxisconfinedtothedipplaneofthereflector simultaneous estimation of the symmetry direction velocityvp0 theanisotropyparameters and andthetilt of the symmetry axis proves to be ambiguous despite the borehole constraints if the symmetry axis is orthogonal to the reflector vp0 and can be recovered with high accuracy even when the symmetry axis deviates by 5 from the reflector normal theparameter however cannotbeconstrainedfor dips smaller than 60 without using nonhyperbolic moveout toinvertfortheintervalparametersoflayeredttimedia we apply 2d stacking velocity inversion supplemented with the sameboreholeconstraints thedipplanesinalllayersareassumed to be aligned and the symmetry axis is set orthogonal to the reflector in each layer information about reflector dips can be replaced with near offset walkaway vertical seismic profiling vsp traveltimes tests on noise contaminated data demonstrate that the algorithm produces stable estimatesoftheintervalparametersvp0and iftherangeofdips does not exceed 30 our method can be used to build an accurate initialtti model for post migration reflection tomography and other techniques that employ migration velocity analysis

chemical variations in fumarolic gases at vulcano island southern italy seasonal and volcanic effects abstract because of increasing in fumarolic activity at vulcano since september 1987 regular sampling and analysis is conducted on the well known f5 crater fumarole t 330 5 c significant chemical variations have been recorded over the period 1987 1989 variations of water vapour in the fumarolic fluid follow seasonal pattern and can be related to both external seasonal and internal volcanic influences suggesting a control by a shallow water aquifer significant variations of h 2 o and of some species in the anhydrous gas phase h 2 so 2 hcl hf n 2 he probably result from chemical or dynamic changes in the feeding system at depth several mechanism are considered for explaining the chemical trends results in relationship to the recent increase in activity a growing input of deep magmatic fluids is not supported by the low co content and the apparent constancy of the 3 he 4 he ratio apparent equilibrium temperatures close to the fumarolic outlet temperature 350 400 c were calculated suggesting isothermal expansion of the gas from a shallow equilibration zone comparison with the fumaroles at sea level porto di levante suggests that these latter may be fed a different hydrothermal systems variable interaction between both systems may account for some of the chemical variations observed at f5 fumarole

fluid geochemistry at vulcano island a change in the volcanic regime or continuous fluctuations in the mixing of different systems increasing fumarolic activity and the rise of outlet fumarole temperatures has occurred at vulcano island southern italy since september 1987 regular sampling and analysis have been conducted on the well known f5 fumarolic and later on f5ht and fa f umaroles on the fossa crater plus other gas emanations from different sites on the island significant chemical and isotopical oscillations have been recorded over the period 1987 1991 variations of water vapor in the fumarolic fluid follow a seasonal pattern and can be related to both external seasonal and magmatic influences but they suggest a control by a source other than magmatic significant variations of h2o and of some species in the anhydrous gas phase h2 co2 so2 n2 and he have been related in the past to chemical or dynamic changes in the feeding system at depth oscillations of the isotopic composition of helium and carbon suggest possible mixing with a nonsurficial source possibly crustal in origin argon and neon isotopic data support this hypothesis several mechanisms are considered for explaining the chemical and isotopic data in relation to the recent increase in activity not all of the chemical and isotopic variations recorded are related to geophysical parameters such as seismicity and deformation the low co content of the f5 fumarolic and the apparent constancy of the 3he 4he ratio do not suggest an increase in the input of deep magmatic fluids the high co content of the high temperature 650 c fa fumarole located at the interior of the crater along with helium and carbon isotopic ratios similar to other fumarolics is probably due to an easier ascent of these fluids to the surface apparent equilibrium temperatures close to the fumarolic outlet temperature indicate isothermal expansion of the gas from a shallow equilibration zone for both high and lower temperature gases in particular the chemical and isotopic features of fluids belonging to both crater and beach fumarole fields are consistent with the existence of two intermediate system independently feeding the two fields high 3he 4he ratios for the beach fluids similar to those of the crater fluids suggest a large magmatic reservoir at depth feeding both the crater and the beach intermediate reservoirs

stable creeping fault segments can become destructive as a result of dynamic weakening faults in earth s crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast seismic wave producing rupture events perceived as earthquakes these types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment one with stable rate strengthening friction and the other with rate weakening friction that leads to stick slip the 2011 tohoku oki earthquake with moment magnitude m w 9 0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping here we propose a model in which stable rate strengthening behaviour at low slip rates is combined with coseismic weakening due to rapid shear heating of pore fluids allowing unstable slip to occur in segments that can creep between events the model parameters are based on laboratory measurements on samples from the fault of the m w 7 6 1999 chi chi earthquake the long term slip behaviour of the model which we examine using a unique numerical approach that includes all wave effects reproduces and explains a number of both long term and coseismic observations some of them seemingly contradictory about the faults at which the tohoku oki and chi chi earthquakes occurred including there being more high frequency radiation from areas of lower slip the largest seismic slip in the tohoku oki earthquake having occurred in a potentially creeping segment the overall pattern of previous events in the area and the complexity of the tohoku oki rupture the implication that earthquake rupture may break through large portions of creeping segments which are at present considered to be barriers requires a re evaluation of seismic hazard in many areas

multiple hazards and paths to eruptions a review of the volcanic system of vulcano aeolian islands italy abstract vulcano is one of the 7 volcanic islands and 6 seamounts forming the aeolian volcanic district italy vulcano has a long eruptive record and its last eruption 1888 90 originated the definition of the vulcanian eruptive style like most volcanic islands vulcano generates many potentially interconnected hazards determining a potentially high risk here we review the state of knowledge on its geology eruptive activity historical accounts structural setting geophysical and geochemical surveillance and available hazard quantifications in order to have an updated picture of the state knowledge on volcanic hazard we follow a prototypal reviewing scheme based on three standardized steps i review of the volcanic system ii review of available eruptive and non eruptive hazard quantifications iii development of a conceptual interpretative model we find that while a rather vast literature is dedicated to the volcanic system of vulcano and the reconstruction of past events few quantitative hazard assessments exist in addition the range of natural variability considered for each hazard is potentially underestimated e g limited range of considered eruption magnitude and style and of vent position as it is the potential effect of multi hazard impact the developed conceptual model for the feeding system provides a synthetic picture of the present knowledge about the system as emerged from the review in addition it allows for the identification of potential paths to eruption and provides a first order link among the main hazards this review provides an up to date snapshot of existing knowledge on volcanic hazard at vulcano on which to build future hazard quantifications as well as to support present and future decision making

source analysis of acoustic emissions in aue granite cores under symmetric and asymmetric compressive loads the effect of stress anisotropy on the brittle failure of granite is investigated under uniaxial compression non standard asymmetric compression tests are performed on cores of aue granite diameter 52 mm length 100 mm in which 20 per cent of the core top surface remains unloaded the edge of the asymmetric steel loading plate acts as a stress concentrator from where a shear rupture is initiated the propagation of the fracture related process zone from top to bottom of the core is mapped by microcrack induced acoustic emissions compared to standard uniaxial tests with symmetric loading in the asymmetric tests both a greater quantity and more localized distributions of emission event hypocentres are observed the maximum event density doubles for asymmetric 20 events per 10 6 m3 compared to symmetric tests the cluster correlation coefficient a measure of strain localization in the faulting process reaches 0 15 for symmetric and 0 30 for asymmetric tests the clustering of events however is found post failure only three different amplitudes are used to determine b values discussed as a possible failure precursor focal amplitudes determined at a 10 mm source distance and maximum amplitudes measured at eight piezoceramic sensors lead to b values that drop before rock failure first pulse amplitudes automatically picked from emission wavelets show no anomaly first motion polarity statistics of amplitudes indicate that a shear crack type radiation pattern is responsible for 70 per cent of the failure of granite irrespective of stress boundary conditions for type s events with an equal percentage of dilatational and compressional first motions focal mechanisms are determined by fitting measured first pulse amplitudes to an assumed double couple radiation pattern while hypocentres of large type s events align parallel to the later fracture plane their fault plane solutions show no coherent pattern spatial views of fracture planes reconstructed from x ray computed tomograms reveal local small scale changes in fracture plane orientation nodal planes from average fault plane solutions of the microscopic acoustic emission events coincide with the overall orientation of the macroscopic fracture plane azimuth strike angle determined from thin sections and tomograms

generalized dix equation and analytic treatment of normal moveout velocity for anisotropic media despite the complexity of wave propagation in anisotropic media reflection moveout on conventional common midpoint cmp spreads is usually well described by the normal moveout nmo velocity defined in the zero offset limit in their recent work grechka and tsvankin showed that the azimuthal variation of nmo velocity around a fixed cmp location generally has an elliptical form i e plotting the nmo velocity in each azimuthal direction produces an ellipse and is determined by the spatial derivatives of the slowness vector evaluated at the cmp location this formalism is used here to develop exact solutions for the nmo velocity in anisotropic media of arbitrary symmetry for the model of a single homogeneous layer above a dipping reflector we obtain an explicit nmo expression valid for all pure modes and any orientation of the cmp line with respect to the reflector strike the contribution of anisotropy to nmo velocity is contained in the slowness components of the zero offset ray along with the derivatives of the vertical slowness with respect to the horizontal slownesses quantities that can be found in a straightforward way from the christoffel equation if the medium above a dipping reflector is horizontally stratified the effective nmo velocity is determined through a dix type average of the matrices responsible for the interval nmo ellipses in the individual layers this generalized dix equation provides an analytic basis for moveout inversion in vertically inhomogeneous arbitrarily anisotropic media for models with a throughgoing vertical symmetry plane i e if the dip plane of the reflector coincides with a symmetry plane of the overburden the semi axes of the nmo ellipse are found by the more conventional rms averaging of the interval nmo velocities in the dip and strike directions modelling of normal moveout in general heterogeneous anisotropic media requires dynamic ray tracing of only one zero offset ray remarkably the expressions for geometrical spreading along the zero offset ray contain all the components necessary to build the nmo ellipse this method is orders of magnitude faster than multi azimuth multi offset ray tracing and therefore can be used efficiently in traveltime inversion and in devising fast dip moveout dmo processing algorithms for anisotropic media this technique becomes especially efficient if the model consists of homogeneous layers or blocks separated by smooth interfaces the high accuracy of our nmo expressions is illustrated by comparison with ray traced reflection traveltimes in piecewise homogeneous azimuthally anisotropic models we also apply the generalized dix equation to field data collected over a fractured reservoir and show that p wave moveout can be used to find the depth dependent fracture orientation and to evaluate the magnitude of azimuthal anisotropy

observations of premonitory acoustic emission and slip nucleation during a stick slip experiment in smooth faulted westerly granite 1 to investigate laboratory earthquakes stick slip events were induced on a saw cut westerly granite sample by triaxial loading at 150 mpa confining pressure acoustic emissions ae were monitored using an innovative continuous waveform recorder the first motion of each stick slip was recorded as a large amplitude ae signal these events source locate onto the saw cut fault plane implying that they represent the nucleation sites of the dynamic failure stick slip events the precise location of nucleation varied between events and was probably controlled by heterogeneity of stress or surface conditions on the fault the initial nucleation diameter of each dynamic instability was inferred to be less than 3 mm a small number of ae were recorded prior to each macro slip event for the second and third slip events premonitory ae source mechanisms mimic the large scale fault plane geometry

a comparison of seismicity characteristics and fault structure between stick slip experiments and nature fault zones contain structural complexity on all scales this complexity influences fault mechanics including the dynamics of large earthquakes as well as the spatial and temporal distribution of small seismic events incomplete earthquake records unknown stresses and unresolved fault structures within the crust complicate a quantitative assessment of the parameters that control factors affecting seismicity to better understand the relationship between fault structure and seismicity we examined dynamic faulting under controlled conditions in the laboratory by creating saw cut guided natural fractures in cylindrical granite samples the resulting rough surfaces were triaxially loaded to produce a sequence of stick slip events during these experiments we monitored stress strain and seismic activity after the experiments fault structures were imaged in thin sections and using computer tomography the laboratory fault zones showed many structural characteristics observed in upper crustal faults including zones of localized slip embedded in a layer of fault gouge laboratory faults also exhibited a several millimeter wide damage zone with decreasing micro crack density at larger distances from the fault axis in addition to the structural similarities we also observed many similarities between our observed distribution of acoustic emissions aes and natural seismicity the aes followed the gutenberg richter and omori utsu relationships commonly used to describe natural seismicity moreover we observed a connection between along strike fault heterogeneity and variations of the gutenberg richter b value as suggested by natural seismicity studies areas of low b value marked the nucleation points of large slip events and were located at large asperities within the fault zone that were revealed by post experimental tomography scans our results emphasize the importance of stick slip experiments for the study of fault mechanics the direct correlation of acoustic activity with fault zone structure is a unique characteristic of our laboratory studies that has been impossible to observe in nature

nanometre scale spheroids on sands vulcano sicily possible nannobacterial alteration spheroids in the size range of 30 200 nm coat sand grains on sediments around the island of vulcano they occur as single individuals as ball shaped clumps resembling biological colonies with radiating chains of bodies and eventually merge into sheets in which the individual nannobacteria are no longer evident rarely they appear to bore into the glass grains older rocks are composed mainly of closely packed nanospheroids these spheroids are believed to be nannobacterial cells based on their resemblance to nannobacteria found in other surficial environments and their occurrence in colony like groups if so nannobacteria play a very important role in the destruction of volcanic materials on vulcano

mechanism diversity of the loma prieta aftershocks and the mechanics of mainshock aftershock interaction the diverse aftershock sequence of the 1989 loma prieta earthquake is inconsistent with conventional models of mainshock aftershock interaction because the aftershocks do not accommodate mainshock induced stress changes instead the sense of slip of the aftershocks is consistent with failure in response to a nearly uniaxial stress field in which the maximum principal stress acts almost normal to the mainshock fault plane this orientation implies that i stress drop in the mainshock was nearly complete ii mainshock induced decreases of fault strength helped were important in controlling the occurrence of after shocks and iii mainshock rupture was limited to those sections of the fault with preexisting shear stress available to drive fault slip

helium isotopic ratio in vulcano island fumaroles temporal variations in shallow level mixing and deep magmatic supply intensive gas emanations occur throughout the island of vulcano italy sharp fluctuations recorded in the crater gas composition suggest the presence of two separate volcanic reservoirs and continuous mixing with another source crustal waters this mixing differs between the beach and crater fumaroles gas samples from three crater fumaroles with temperatures ranging from 200 to 550 c were sampled repeatedly over a one year period during the same interval of time six samples from submarine and subaerial beach fumaroles and water well gases were also sampled gases from one crater fumarole f5 showed variations of 3he4he fumarole to 3he4he air between 5 and 6 correlated with variations of several chemical species high 3he4he ratios for the beach fluids similar to those of crater fluids suggest the existence of a unique large magmatic reservoir at depth feeding both the crater and beach intermediate reservoirs however temporal changes clearly indicate variable degrees of fluids mixing and the geographic distribution of the 3he4he ratios as well as the chemical composition of the fluids suggest the existence between the magma reservoir and the surface of two intermediate different reservoirs independently related to crater and to beach fumaroles

mapping fumarolic fields in volcanic areas a methodological approach based on the case study of la fossa cone vulcano island italy abstract changes in the activity state of a volcano can be inferred by monitoring the steam flux from fumarolic fields in terms of 4d x y z time variations in temperature and extension of the zone during the last decades several studies in this field have been conducted worldwide and at vulcano island italy in particular both direct and remotely sensed measurements have been used for identifying thermally anomalous areas but the possible role of the hydrothermal alteration of volcanic products producing a sealing effect that obscures the surface thermal evidence of fumarolic activity have never been explored the novelty of the present study carried out at la fossa cone vulcano island was the integration of direct and remotely sensed temperature measurements with the evaluation of soil permeability for the precise mapping of areas where shallow hydrothermal circulation could occur even in the absence of surface evidence the main results of this study concern the role of a coating found on rock surfaces and regolith in introducing mapping errors especially during diachronic temperature surveys based on remotely sensed measurements

thermal surveys of the vulcano fossa fumarole field 1994 1999 evidence for fumarole migration and sealing abstract between 1994 and 1999 we carried out five thermal surveys of the vulcano fossa fumarole field each consisted of 485 1213 vent temperature measurements distributed across the field these show that the field has been cooling and expanding where mean and maximum vent temperatures decreased from 216 to180 c and 541 to 428 c respectively between 1994 and 1997 however expansion of the field resulted in increased heat loss from 45 to 67 mw we suggest that cooling and expansion has been caused by increased gas flux and or permeability where increased flow of fluids of magmatic origin during 1996 is implied by chemical and isotopic data capasso g favara r francofonte s inguaggiato s 1999 chemical and isotopic variations in fumarolic discharge and thermal waters at vulcano island aeolian islands italy during 1996 evidence of resumed volcanic activity j volcanol geotherm res 88 1999 167 175 we propose that the size of the conduit has increased causing the fumarole field to expand and vent temperatures to generally decline as gas and heat losses become distributed over a wider area the increase in exhaling area has outweighed the modulating effect of cooling on total heat losses so that heat loss has increased due to an increased input from the magmatic source and or an increase in system permeability within these field wide trends the rim and then the middle zones have been cooling conversely the lower zone showed evidence of warming during 1994 98 before cooling in 1999 throughout the measurement period a se s thermal migration has been apparent and a new hot zone has developed on the field s southern edge we suggest that sealing of fumaroles by complete boiling of marine fluids on the northern edge of the system and higher permeability on the southern edge may have influenced this expansion direction if vent temperatures drop below 100 c then shallow sulfur sealing will quickly diminish fumarole life expectancy and contribute to the abandonment of vents in cooling zones in our model increased gas flux and or permeability e g due to increased magmatic degassing and or fracturing is the primary mechanism driving observed changes in the field temperature size and location deep and shallow conduit sealing are secondary mechanisms influencing the location of new zones once increased gas and heat fluxes have been triggered

moveout inversion of wide azimuth p wave data for tilted ti media currently tti transversely isotropic with a tilted symmetry axis models are widely used for velocity analysis and imaging in many exploration areas we develop a 3d parameter estimation algorithm for tti media composed of homogeneous layers separated by plane dipping interfaces the input data include p wave nmo ellipses and time slopes horizontal slownesses of the zero offset rays combined with borehole information if the symmetry axis is perpendicular to the bottom of each layer it is possible to estimate the interval symmetry direction velocity vp0 anisotropy parameter d and the reflector orientation using a single constraint the reflector depth the algorithm can tolerate small 5 deviation of the symmetry axis from the reflector normal however as is the case for the 2d problem the parameter e can seldom be obtained without nonhyperbolic moveout inversion if the symmetry axis deviates from the reflector normal but is confined to the dip plane stable parameter estimation requires specifying a relationship between the tilt and dip in each layer when the tilt represents a free parameter the input data have to be supplemented by wide azimuth vsp traveltimes with the offset reaching at least 1 4 of the maximum reflector depth moreover the additional angle coverage provided by vsp data may help resolve the parameter e in the upper part of the model the developed methodology can be used to build an accurate initial anisotropic velocity model for processing of wide azimuth surveys

seismic signals in geothermal areas of active volcanism a case study from la fossa vulcano italy since the last eruption 1888 1890 volcanism at vulcano aeolian archipelago southern tyrrhenian sea has taken the form of persistent fumarolic activity the gas vapour phases of the geothermal systems are mainly discharged within two restricted areas about 1 km apart from each other in the northern part of the island these areas are la fossa crater and the beach fumaroles of the baia di levante fluids released at the two main fumarolic fields display quite different chemical and temperature characteristics implying different origins the local seismicity essentially takes the form of discrete shocks of shallow origin depth 1 km at la fossa usually with energy 1013ergs they are thought to be related to the uprise of pressurized hot gases and vapours discharged at the crater fumaroles the present investigation points to the existence of two principal categories of seismic events called m shocks and n shocks these are short events normally 10 s m type shocks are thought to be due to resonance vibrations within the interior of the volcano probably driven by the excitation of shock waves within cavities deeply affected by deposition and alteration of self sealant hydrothermal minerals n type events display features that resemble those of volcano tectonic earthquakes but have no recognizable s phases here they are tentatively attributed to microfracturing of rocks which have been extensively hydrothermally altered results of the present study permit a preliminary conceptual model of the local shallow seismic processes in the framework of geochemical modelling of fumarolic activity and geological inferences from geothermal drilling

physical models of fumarolic flow abstract transport of gas from subsurface magma to the atmosphere is modelled as flow through a narrow rough pipe and through a wider conduit filled with spheres representing flow in a porous pipe macroscopic mass momentum and energy balances are written for a control volume representing a short vertical section of the pipe the balances are solved for a perfect gas with the approximate thermodynamic properties of steam losing heat by steady state radial conduction through the pipe walls with boundary conditions of magmatic temperature at the base of the pipe atmospheric pressure at the surface and an ambient geotherm at a specified distance from the conduit results yield the variation of exit temperature with magmatic source depth conduit radius mass flow rate per unit area distance to ambient temperatures vent porosity and porous particle size two ambient geotherms are used 1 a linear gradient from atmospheric to magmatic temperatures and 2 a hydrothermal geotherm based on water saturation temperatures assuming a hydrostatic pressure gradient because individual vents commonly cluster the porous pipe model is considered to be more realistic than the rough pipe model mainly because the conductive cooling approximation is more likely to remain valid exit temperatures fall as conductive losses increase i e as the source depth increases the conduit narrows the mass flow decreases the distance to ambient temperatures reduces or the ambient geotherm cools the porous pipe model is applied to data from two fumarole fields and indicates magmatic source depths of

origin of fumarolic fluids at vulcano italy insights from isotope data and numerical modeling of hydrothermal circulation abstract hydrothermal activity is often associated with active volcanic systems during quiescent times geochemical monitoring of discharged fluids commonly is carried out to gain insights on the state of evolution of the whole volcanic system the interest in geochemical monitoring derives from the observation that compositional variations of discharged fluids are commonly observed as a new eruptive phase is approaching in particular an increase in the gas components of direct magmatic origin may indicate a higher magma degassing rate at depth potentially related to a renewal of explosive activity surveillance programs devoted to hazard mitigation in active volcanic areas generally include periodic analyses of discharged fluids at various locations on the volcanic edifice unfortunately when significant changes are observed in gas composition their correct interpretation in terms of system evolution is not always clear and straightforward several mechanisms may in fact be responsible for differences in the proportion of magmatic gases and shallower fluid components and it is not always possible to recognize the magmatic gas fraction discrimination among fluids of different origin ideally is accomplished based on the isotope composition that each fluid acquires at the time of its generation however this isotope signature can be altered before the fluids reach the surface because of mixing between fluids of different origin or due to reactions that modify the original isotope composition thus the interpretation of isotope data sometimes is quite complex and it can be highly misleading in this work the origin of the steam discharged at the hydrothermal system of vulcano italy was investigated by the means of a dual approach first the available isotope data on the discharged steam were analyzed on the basis of on these and other data a conceptual model of the hydrothermal system was developed and numerical simulations of a multiphase multicomponent flow through a heterogeneous porous medium were carried out to evaluate the effects of various parameters on the system evolution results suggest that the hydrothermal system of vulcano is controlled by the entrance of large quantities of seawater whose original isotope composition has been altered by water rock interaction rock permeability and its distribution at depth were shown to be a primary parameter controlling the overall system evolution the fluid composition and fluid discharge rate at the surface

spatial domain analysis of carbon dioxide from soils on vulcano island implications for co2 output evaluation abstract the carbon dioxide emissions of volcanoes have been targeted as effective contributors of co 2 to the atmosphere however different sources can be effective and active at the same time in the generation and release of co 2 in volcanic zones since isotopic fingerprinting of co 2 allows the precise identification of different sources coupling carbon isotope and co 2 flux measurements enables the evaluation of the mass contribution of each source to the carbon dioxide emissions this paper accounts for the first extensive spatial analysis of coupled measurements of carbon isotopologues of co 2 in the soil gases and co 2 fluxes discharged by soils on vulcano island an innovative method has been designed tested and fine tuned in the laboratory to measure 13 c co 2 values directly in field using a new type of laser based isotopologues analyzer namely a deltaray thermo fisher scientific the method can be used to determine the carbon isotope composition across the full range of co 2 concentrations in the soil gases 0 100 vol these data have been combined with measurements of the co 2 contents in the soil gases to distinguish co 2 from deep origins from co 2 of biogenic origin in the inhabited area of vulcano porto the method of evaluating the amount of deep origin co 2 in the soil gases is widely applicable in volcanic and geothermal zones for evaluation and monitoring purposes for both gas and volcanic hazards

vertical ground deformation on vulcano aeolian islands southern italy observations and interpretations 1976 1986 abstract vertical ground deformation studies have continued on vulcano southern italy since 1976 as part of a broader geophysical and geochemical program to monitor activity on the island following a magnitude 5 5 earthquake on 15th april 1978 located a few kilometers south of vulcano the northern part of the island was found to have subsided relative to its southern part two further episodes of displacement the first of inflation and the second of deflation were recorded before september 1981 these displacements have been interpreted using a model that considers the effect of pressure change at the point source located at a depth centered at 6 5 km in the northern part of the island such pressure change according to other geophysical and geochemical data is due to increasing and subsequent decreasing pressure connected with the migration of high temperature fluids through fractures and channels beneath the fossa area opened as a result of the april 15 earthquake subsequent measurements until november 1986 detected only one additional significant movement a small inflation between may 1984 and may 1985 this uplift appears to be related to the shallow seismicity recorded beneath the fossa in this period

isotope composition of rain water well water and fumarole steam on the island of vulcano and their implications for volcanic surveillance abstract water samples from eight wells in the vulcano porto area and fumarole steam from the crater of vulcano southern italy were collected at monthly intervals over a two year period from february 1987 to january 1989 samples of bulk precipitation were also collected in three points at vulcano porto and vulcano piano island of vulcano and castroreale tyrrhenian coast of sicily again at monthly intervals the weighted mean isotopic composition of rain water on vulcano is d 32 and d 18 o 6 4 results for well waters tend to support the existence of at least two water bodies one of purely meteoric water and the other of brackish thermal water an intermediate water body probably the result of mixing of the other two was also recognized the isotope composition of fumarolic steam from the crater suggests the mixed contribution of both sea and rain waters although mixing is not the only process occurring the existence of a deep marine brine body is inferred characterized by d and 18o values more positive than those of mediterranean sea water a close relationship indicating common source effects is shown by temporal isotopic variations at some wells and the fumarolic steam wich may be used for volcano survey at distance from the active crater

fault slip rates at depth from recurrence intervals of repeating microearthquakes unique attributes in sequences of recurring similar microearthquakes at parkfield california provide a means for inferring slip rate at depth throughout the active fault surface from the time intervals between sequence events application of the method using an 11 year microseismicity record revealed systematic spatial and temporal changes in the slip rate that were synchronous with earthquake activity and other independent measures of fault zone slip if this phenomenon is found to be generally common behavior in active faults it forms the basis for a method to monitor the changing strain field throughout a seismogenic fault zone

vent temperature trends at the vulcano fossa fumarole field the role of permeability between 1994 and 2010 we completed 16 thermal surveys of vulcano s fossa fumarole field aeolian islands italy in each survey between 400 and 1 200 vent temperatures were collected using a thermal infrared thermometer from distances of 1 m the results show a general decrease in average vent temperature during 1994 2003 with the average for the entire field falling from 220 c in 1994 to 150 c by 2003 however between 2004 and 2010 we witnessed heating with the average increasing to 190 c by 2010 alongside these annual scale field wide trends we record a spatial re organisation of the fumarole field characterised by shut down of vent zones towards the crater floor matched by rejuvenation of zones located towards the crater rim heating may be expected to be associated with deflation because increased amounts of vaporisation will remove volume from the hydrothermal system gambino and guglielmino j geophys res 113 b07402 2008 however over the 2004 2010 heating period no ground deformation was observed instead the number of seismic events increased from a typical rate of 37 events per month during 1994 2000 to 195 events per month during 2004 2010 as part of this increase we noticed a much greater number of high frequency events associated with rock fracturing we thus suggest that the heating event of 2004 2010 was the result of changed permeability conditions rather than change in the heat supply from the deeper magmatic source within this scenario cooling causes shut down of lower sectors and re establishment of pathways located towards the crater rim causing fracturing increased seismicity and heat flow in these regions this is consistent with the zone of rejuvenation which lies towards and at the rim being the most favourable location for fracturing given the stress field of the fossa cone schopa et al j volcanol geotherm res 203 133 145 2011 it is also the most established zone having been active at least since the early twentieth century our data show the value of deploying multi disciplinary geophysical campaigns at degassing fumarolic hydrothermal systems this allows more complete and constrained understanding of the true heat loss dynamics of the system in the case study presented here it allows us to distinguish true heating from apparent heating phases while the former are triggered from the bottom up i e they are driven by increases in heat supply from the magmatic source the latter are triggered from the top down i e by changing permeability conditions in the uppermost portion of the system to allow more efficient heat flow over zones predisposed to fracturing

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

light hydrocarbons in hydrothermal and magmatic fumaroles hints of catalytic and thermal reactions volcanic gaseous mixtures emitted from active volcanoes frequently show variable amounts of saturated alkanes unsaturated alkenes and aromatic volatile hydrocarbons three major patterns of distributions can be recognized apparently related to the chemical physical environment of formation of the gas exhalations alkane rich low temperature gas emissions from recently active volcanic areas aromatic rich hydrothermal manifestations and alkene rich magmatic fumaroles on active volcanoes thermodynamic data together with theoretical and practical findings from the petroleum industry point to two main types of reactions occurring in these volcanic environments cracking and reforming cracking processes mainly caused by thermal effects occur when hydrocarbon bearing hydrothermal fluids enter and mix with a hot and dry rapidly rising magmatic gas phase the most probable products are light alkenes with carbon numbers decreasing with increasing reaction temperatures the presence of aromatic species in hydrothermal fluids can be linked to reforming processes catalysed by several possible agents such as smectites and zeolites generally present in the hydrothermally altered volcanic terranes and facilitated by long residence times in a hydrothermal envelope

boron isotopic variations in fumarolic condensates and thermal waters from vulcano island italy implications for evolution of volcanic fluids abstract temporal variation in the isotopic composition of boron has been monitored in fumarolic condensates collected over an extended time period 1970 1996 from la fossa crater volcano island we also report comparative boron isotopic data for representative vulcano lavas and for shallow hydrologic samples seawater wells thermal springs from the north flank of la fossa combined with concurrent chemical and isotopic 18o d data for the fumaroles these results indicate that the fumarolic fluids record mixing relations between three distinct fluid end members 1 a dominantly magmatic fluid em1 2 a mixture of modified seawater with magmatic fluid em2 and 3 an aqueous fluid produced from seawater by extensive wall rock reaction evaporation and boiling af differences between the latter two end members are most clearly accentuated on the basis of the boron isotopic data long term compositional variations for crater fumaroles were dominated by em1 af mixing between 1979 88 with progressive decrease in em1 contribution with time and by em2 af mixing between 1988 96 the exact spatial distribution of these fluid reservoirs remains unclear but all must have been present throughout the monitoring period to account for the observed variations moreover the combined b o h data seem to preclude important contributions from shallow meteoric reservoirs marked short term variations in 11b closely coincide with episodes of local seismicity which presumably triggered reorganization of hydrothermal circulation patterns gradual variations over periods up to 3 4 years are associated with relatively low seismicity during which fluid circulation was likely influenced by effects of mineral precipitation on permeability of the hydrologic system

temporal variations in seismicity during quasi static and dynamic rock failure abstract a comprehensive model is presented which can explain temporal fluctuations in seismic b values in the period leading to mechanical failure in terms of the underlying physical processes of time varying applied stress and stress corrosion enhanced crack growth under conditions of constant strain rate the form of the b value anomaly in the period leading to failure depends on the form of the stress time relationship for the case where dynamic failure occurs at peak stress after a period of strain hardening the model predicts a single cusp like b value anomaly reaching a critically low value of 0 5 at failure for the physically most realistic case where dynamic failure is preceded by a period of precursory strain energy release during strain softening the model predicts two minima in the b value separated by a temporary maximum or inflection point these fluctuations in the b value are consistent with reported intermediate term and short term earthquake precursors separated by a period of seismic quiescence for the case of quasi static cataclastic flow the b value mirrors the stress and never falls to the critical value because there is no critical rupture new results from a series of controlled laboratory experiments are presented in which microseismic event rates and b value were monitored contemporaneously with stress time data for all variants of the stress time relationship recent field observations of temporal changes in seismicity rates and b value preceding major earthquakes are also reported both data sets exhibit b value anomalies which are consistent with the model predictions

implications for mechanical properties of brittle faults from observations of the punchbowl fault zone california field observations of the punchbowl fault zone an inactive trace of the san andreas are integrated with results from experimental deformation of naturally deformed punchbowl fault rocks for a qualitative description of the mechanical properties of the fault and additional information for conceptual models of crustal faulting the punchbowl fault zone consists of a single continuous gouge layer bounded by zones of extensively damaged host rock fault displacements were not only localized to the gouge layer but also to discrete shear surfaces within the gouge deformation in the exposure studied probably occurred at depths of 2 to 4 km and was dominated by cataclastic mechanisms textural data also suggest that significant amounts of pore fluids were present during faulting and that fluid assisted mechanisms such as dissolution diffusion and precipitation were operative the experimental data on specimens collected from the fault zone suggest that there is a gradual decrease in strength and elastic modulus and an increase in relative ductility and permeability toward the main gouge zone the gouge layer has fairly uniform mechanical properites and it has significantly lower strength elastic modulus and permeability than both the damaged and the undeformed host rock for the punchbowl fault and possibly other brittle faults the variations in loading of the gouge zone with time are primarily governed by the morphology of the fault and the mechanical properties of the damaged host rock in addition the damaged zone acts as the permeable unit of the fault zone and surrounding rock it appears that the gouge primarily governs whether displacements are localized and it therefore may have a significant influence on the mode of slip

inversion of azimuthally dependent nmo velocity in transversely isotropic media with a tilted axis of symmetry just as the transversely isotropic model with a vertical symmetry axis vti media is typical for describing horizontally layered sediments transverse isotropy with a tilted symmetry axis tti describes dipping ti layers such as tilted shale beds near salt domes or crack systems p wave kinematic signatures in tti media are controlled by the velocity vp0 in the symmetry direction thomsen s anisotropic coefficients e and and the orientation tilt and azimuth of the symmetry axis here we show that all five parameters can be obtained from azimuthally varying p wave nmo velocities measured for two reflectors with different dips and or azimuths one of the reflectors can be horizontal the shear wave velocity vs0 in the symmetry direction which has negligible influence on p wave kinematic signatures can be found only from the moveout of shear waves using the exact nmo equation we examine the propagation of errors in observed moveout velocities into estimated values of the anisotropic parame

earthquake induced variations in the composition of the water in the geothermal reservoir at vulcano island italy abstract during 1979 1989 variations were observed in the oxygen composition of the water contained in the geothermal reservoir at vulcano island italy the reservoir water that has a magmatic origin showed an oxygen composition of 1 0 0 5 18o during periods without local tectonic earthquakes and an oxygen composition of 3 4 0 5 18o after the highest energy seismic activity that occurred recently near the island a slight increase of the 18o value in the reservoir water was also observed after a low energy sequence of tectonic earthquakes that occurred at very shallow depth just beneath vulcano island these 18o variations in the reservoir water are consistent with earthquake induced increases in the contribution from high temperature 18o rich magmatic condensate to the geothermal reservoir and with subsequent decreases in the 18o value due to 18o exchanges at the temporarily increased reservoir temperature during reactions between the highly reactive magmatic condensate and the local rocks only minor changes in the deuterium composition of the reservoir water occurred with time as the d value in the magmatic condensate released from the magma after major local earthquakes quickly approached the d value of the water contained in the geothermal reservoir also the chloride concentration in the reservoir water appears to be linked to the contribution from the magmatic fluid this chloride content seems not to have undergone major changes with time as it may be buffered by temporary increases in the reservoir temperature up to values 300 c induced by major local earthquakes this mechanism may possibly occur also in other magmatic hydrothermal systems

evolution of br cl ratios in fumarolic salammoniac from vulcano aeolian islands italy bromine chlorine ratios in salammoniac samples collected from 1983 to 1994 at the fossa crater fumaroles of vulcano aeolian islands were determined the data obtained in this work have been compared to those obtained by coradossi et al 1985 in order to carry out a systematic study of the br cl ratio variations since 1977 br cl ratios range from 0 04 to 0 29 the br cl ratio variations observed have been interpreted as the result of different contributions among deep and shallow components feeding the fumarolic fluids of vulcano the br cl increases which occurred from 1977 to 1979 in 1983 1984 and in 1992 1993 have been connected to an increased input of magmatic gases

most likely locations of large earthquakes in the kanto and tokai areas japan based on the local recurrence times abstract we examined the hypothesis that minima in local recurrence time tl or equivalently maxima in local probability pl may map asperities in the kanto and tokai areas of japan where the earthquake catalog of the national research institute for earth science and disaster prevention nied is complete at the m 1 5 m1 5 level we mapped tl pl based on the a and b values of the nearest earthquakes within 20 km of every node of a grid spaced 0 01 for m7 target events only earthquakes within the top 33 km were used the b values increase strongly with depth in several areas therefore some of the tl pl anomalies are not revealed if data from the entire crustal seismogenic zone are mixed thus we mapped tl pl separately for the top 15 km and the rest of the depth range as well as for the entire seismogenic crust the resulting tl and pl maps show that approximately 12 of the total area shows anomalously short recurrence times out of six shallow target events with m 6 5 and which occurred since 1890 five are located within the anomalous areas with tl

organic and inorganic geochemistry of low temperature gas discharges at the baia di levante beach vulcano island italy abstract discharge from subaereal and submarine gas vents of the baia di levante beach gases from the vulcano island were sampled for major and trace gas components in may and november 1995 chemical compositions and equilibrium calculations suggest three different groups of co 2 rich gas emissions depending on their distance from the la fossa crater 1 gas vents close to the faraglione area are characterised by high h 2 s contents high calculated equilibrium temperatures based on inorganic species and relatively high proportion of alkene compounds 2 gas vents close to vulcanello are characterised by low calculated equilibrium temperatures and low amounts of alkenes and 3 pontile sample has the highest equilibrium co 2 pressure up to 68 bars which may account for the observed absence of benzene the relative large variability of h 2 s in the baia di levante beach gas discharge may be attributed to either different interactions between iron sulphides and weakly acid waters or catalytic effect of elemental sulphur on the de hydrogenation of cyclo hexane thermodynamic calculations suggest that the main inorganic species and ch 4 may have re equilibrated at relatively shallow depth 10 200 m b s l and 30 600 m b s l for a lithostatic and hydrostatic pressure respectively the slow kinetics of reactions in the c n h 2 n c n h 2 n 2 systems with respect to that of ch 4 co co 2 may explain the observed propene propane ratios which can only be reached at reaction temperatures of 300 350 c this low speed of reactions can also explain the observed disequilibrium of c1 c4 alkanes

u series disequilibrium radionuclides in sulphur incrustations from the fumarolic field of vulcano island abstract u series disequilibrium radionuclides 238 u 234 u 210 pb 210 po in sulphur incrustations deposited at la fossa cone vulcano island italy were measured over the period 1990 1995 to collect information about changes in the feeding system of the fumarolic field the 210 po 210 pb and 210 pb pb ratios of the sulphur incrustations allowed the identification of a fumarolic vent which is free from magmatic contribution and remobilized sublimate contamination in spite of the low temperature of the selected fumarole 280 350 c kinetic data show that 210 po is almost fully volatilized due to the relatively high velocity of the gas as a result the 210 po 222 rn activity ratio of the gas can be used to estimate fluid rising times about 100 days 234 u 238 u activity ratios of sulphur incrustations deposited in 1991 1993 showed a shift toward high values typical of nonmagmatic fluids both short lived and long lived u series disequilibrium radionuclides contribute to volcanic forecasting and give information on fluid sources and rising times as well as the residence times of the aquifers involved in the degassing process of the fumarolic field

geochemical modeling of mixing between magmatic and hydrothermal gases the case of vulcano island italy abstract in this study we present a geochemical approach to model the mixing of magmatic and hydrothermal gases our model is based on a rigorous formulation of a perfectly dimensioned system of mass and energy balance equations inputs of the equation set are the h2o and co2 content and gas emission temperature at the surface together with some constraints gained from the chemical physical features of the hydrothermal system the output data give the composition of magmatic gas mixing fractions and temperatures of gas mixtures in the mixing zone the comparison of the emission temperature of fumarolic gases with their calculated mixing temperatures provides valuable indications on the expansion process that gases undergo during their ascent towards the surface our mixing model is exemplified by the fumarolic system of vulcano island italy we calculate the thermodynamic parameters of the hydrothermal system by means of an h2o co2 nacl equation of state while the thermo baric conditions of the magma have been assessed by previous geophysical and petrologic investigations the obtained results show that during volcanic crises at vulcano island and in agreement with magma degassing processes both the co2 and the he contents of magmatic gas display peaks with a progressively declining amplitude suggesting a progressive magmatic impoverishment of volatiles strongly partitioned in the gas phase mixing fractions of various fumaroles are normally variable while they display almost homogeneous values during periods of increased volcanic activity on the basis of results gained some implications regarding the hazard of phreato magmatic explosions are also discussed the high temperature reached by fumarolic gases strongly constrains their probable expansion process during the ascent towards the surface a comparison between the temperature of the fumarolic gas and the calculated mixing temperature at depth indicates that the expansion process can be reasonably described as almost iso enthalpic although field evidences suggest that the fumarolic emission temperature could be affected by the sharp permeability changes in the last few hundred meters therefore our results and field evidences clearly indicate that variations in gas emission temperature cannot be considered a good indicator of volcanic activity as it is strongly dependent on expansion process and ultimately on rock permeability changes the model greatly improves the knowledge of the volcanic system of vulcano island and provides an important tool for the interpretation and evaluation of volcanic activity moreover a similar approach can be considered for other volcanic systems having analogous characteristics