regimes of magma recharge and their control on the eruptive behaviour during the period 2001 2005 at mt etna volcano mount etna volcano italy during the period 2001 2005 has undergone a period of intense eruptive activity marked by three large eruptions 2001 2002 2003 and 2004 2005 these eruptions encompassed diverse eruptive styles and regimes from intensely explosive during 2001 and 2002 2003 eruptions to exclusively effusive in the 2004 2005 event in this work we put forward the idea that these three eruptions are the response of the progressive arrival into the uppermost segment of the open conduit system of a new magma which was geochemically distinct in terms of trace element and sr nd pb isotope signature from the products previously emitted by the etnean volcano the magma migrated upwards mainly through a peripheral tectonic system which can be considered as eccentric in spite of its relative proximity to the main system the ingress of the new magma and its gradual displacement from the eccentric system into the uppermost sector of the open conduit gave rise to different eruptive behaviours at the beginning the ascent of the undegassed magma able to exsolve a gas phase at depth and its interaction with closed system magma reservoirs less than 10 km deep gave rise to the explosive events of 2001 and 2002 2003 later when the same magma entered into the open conduit system it took part in the steady state degassing and partially lost its volatile load leading to a totally effusive eruption during the 2004 2005 event one further consideration highlighted here is that in 2001 2005 migration of the feeding axis from an eccentric and peripheral position towards the main open conduit has led to the development of a new vent south east crater 2 located at the eastern base of the south east crater through which most of the subsequent etnean activity occurred

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

high precision locations of the microseismicity preceding the 2002 2003 mt etna eruption 1 to recognize possible signals of intrusive processes leading to the last 2002 2003 flank eruption at mt etna we analyzed the spatial pattern of microseismicity between august 2001 and october 2002 and calculated 23 fault plane solutions fpss for shocks with magnitude greater than 2 5 by applying the double difference approach of waldhauser and ellsworth 2000 on 3d locations we found that most of the scattered epicentral locations further collapse in roughly linear features high precision locations evidenced a distribution of earthquakes along two main alignments oriented ne sw to ene wsw and nw se matching well both with the known tectonic and volcanic lineaments of etna and fpss results moreover microseismicity and swarms located along the nnw sse volcano genetic trend suggest together with geodetic data and volcanological evidence that progressive magma refilling has occurred since february 2002

shallow intrusive processes during 2002 2004 and current volcanic activity on mt etna 1 the understanding of shallow intrusive processes during 2002 2004 as well as the causes of the volcano tectonic seismicity has been improved at mt etna by comparing the inversion results from gps data with accurate 3d hypocentral locations our findings indicate that short periods of deflation about six months were followed by recharging phases after the end of both the 2001 and 2002 2003 flank eruptions during the last recharging phase june 2003 august 2004 modeling results and seismic observations suggest a composite mechanism of re injection of magma into the rift zones s and ne similar to that leading to the 2002 2003 flank eruption which could have triggered the summit eruption started on september 7 2004

the elastic properties of carbonates although carbonates contain about 60 of the world s oil reserves the characterization of carbonate reservoirs remains challenging because of their heterogeneity andcomplex microstructure central to the seismic characterization of carbonates is an understanding of the effect of porosity on the elastic moduli and seismic wave velocities figure 1 shows the compressional and shear wave velocities measured by rafavich et al 1984 for limestones and dolomites from the williston basin north dakota measured on air saturated samples it is seen that although the velocities decrease with increasing porosity there is considerable scatter of the data in this article the possible contribution of variations in pore shape to the elastic moduli of carbonates is discussed the role of microcracks and fractures is assessed and differences between the static and dynamic moduli are highlighted

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

review of microgravity observations at mt etna a powerful tool to monitor and study active volcanoes microgravity observations at mt etna have been routinely performed as both discrete since 1986 and continuous since 1998 measurements in addition to describing the methodology for acquiring and reducing gravity data from mt etna this paper provides a collection of case studies aimed at demonstrating the potential of microgravity to investigate the plumbing system of an active volcano and detect forerunners to paroxysmal volcanic events for discrete gravity measurements results from 1994 1996 and 2001 are reported during the first period the observed gravity changes are interpreted within the framework of the strombolian activity which occurred from the summit craters gravity changes observed during the first nine months of 2001 are directly related to subsurface mass redistributions which preceded accompanied and followed the july august 2001 flank eruption of mt etna two continuous gravity records are discussed a 16 month october 1998 to february 2000 sequence and a 48 hour 26 28 october 2002 sequence both from a station within a few kilometers of the volcano s summit the 16 month record may be the longest continuous gravity sequence ever acquired at a station very close to the summit zone of an active volcano by cross analyzing it with contemporaneous discrete observations along a summit profile of stations both the geometry of a buried source and its time evolution can be investigated the shorter continuous sequence encompasses the onset of an eruption from a location only 1 5 km from the gravity station this gravity record is useful for establishing constraints on the characteristics of the intrusive mechanism leading to the eruption in particular the observed gravity anomaly indicates that the magma intrusion occurred passively within a fracture system opened by external forces

past and future grounding line retreat of the west antarctic ice sheet the history of deglaciation of the west antarctic ice sheet wais gives clues about its future southward grounding line migration was dated past three locations in the ross sea embayment results indicate that most recession occurred during the middle to late holocene in the absence of substantial sea level or climate forcing current grounding line retreat may reflect ongoing ice recession that has been under way since the early holocene if so the wais could continue to retreat even in the absence of further external forcing

how is volcano seismicity different from tectonic seismicity we analyze the temporal patterns of volcano seismicity using the statis tics of waiting times between subsequent earthquakes we compare waiting time distributions of seismicity at mt etna and mt vesuvius volcanoes during 1 inter eruption phases and 2 dyke propagations with those of tectonic seismicity using the southern california catalog for inter eruption phases no matter their duration sta tistics of inter event times are well approximated by the gamma distribution this allows us to compute the proportion of background uncorrelated events molchan 2005 hainzl et al 2006 which is recovered in the range 20 40 for vesuvius three etna inter eruptive periods and the southern california catalog it argues for roughly 70 of earthquake activity to be cascades of aftershocks for both volcano inter eruptive and tectonic seismicity on the contrary statistics of inter event times recorded during both the 2001 and 2002 intrusive episodes at the etna volcano reject the gamma distribution to describe the observations these seismic crises are char acterized by an average seismicity rate about 2 orders of magnitude larger than that of inter eruptive periods it suggests that the origin of the specificity of waiting time patterns during dyke injections is driven by the external forcing rate using the epydemic type aftershock sequences model simulations we explore the effect of seis micity rate increases on inter event time distributions departures from the gamma law progressively emerges from both 1 an increase of the background seismicity rate and 2 a screening effect it prevents us from quantifying the portion of uncorrelated seis micity within the considered catalog and from clearly quantifying the forcing rate that characterizes the volcano dynamics during dyke intrusions

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

ring shear studies of till deformation coulomb plastic behavior and distributed strain in glacier beds a ring shear device was used to study the factors that control the ultimate steady strength of till at high shear strains tests at a steady strain rate and at different stresses normal to the shearing direction yielded ultimate friction angles of 26 3 and 18 6 for tills containing 4 and 30 clay sized particles respectively other tests at steady normal stresses and variable shear strain rates indicated a tendency for both tills to weaken slightly with increasing strain rate this weakening may be due to small increases in till porosity these results provide no evidence of viscous behavior and suggest that a coulomb plastic idealization is reasonable for till deformation however viscous behavior has often been suggested on the basis of distributed shear strain observed in subglacial till we hypothesize that deformation may become distributed in till that is deformed cyclically in response to fluctuations in basal water pressure during a deformation event transient dilation ofdiscrete shear zones should cause a reduction in internal pore water pressure that should strengthen these zones relative to the surrounding till a process called dilatant hardening consequent changes in shear zone position when integrated over time may yield the observed distributed strain

static grounding lines and dynamic ice streams evidence from the siple coast west antarctica 1 grounding line dynamics are key to our understanding of marine ice sheets such as the west antarctic ice sheet wais we present an accurate and rapid method for locating grounding lines using glas icesat laser altimetry data we then apply this technique to the siple coast region of the wais our technique exploits the high surface slope at the grounding line relative to the adjacent flat ice streams and ice shelf the technique is validated by ground based observations comparisons between the current grounding line and earlier measured locations demonstrate that the siple coast s grounding line has been largely static over the last two decades this is important as the ice streams have been undergoing considerable variations over this period we conclude that ice stream flow speeds can vary while the grounding line remains stable we suggest that grounding lines may migrate abruptly and then stabilize rather than undergoing continuous retreat

late pleistocene holocene retreat of the west antarctic ice sheet system in the ross sea part 1 geophysical results in the 1994 1995 and 1998 austral field seasons geophysical research efforts in the ross sea focused on acquiring a high resolution database designed to permit 1 reconstruction of the maximum extent and configuration of the ice sheet during the last glacial maximum i e oxygen isotope stage 2 2 reconstruction of conditions at the base of the ice sheet and 3 assessment of the relative retreat history of the ice sheet following the last glacial maximum five seismic facies are distinguished on the basis of external geometry relationships among features bounding surface amplitude intensity of internal acoustic signature and geometry of internal reflectors seismic facies 1 is a transparent draping unit correlated to diatomaceous mud interpreted as being deposited under open marine conditions seismic facies 2 and 3 are comprised of units displaying subdued massive internal signatures with smooth lower bounding surfaces and hummocky upper surfaces characterized by glacial lineations these units are interpreted to be grounding zone proximal deposits overridden by the expanded ice sheet seismic facies 2 may be a deforming till unit seismic facies 4a is characterized by an internally massive to chaotic signature an erosional often flat lower surface and a hummocky upper surface displaying glacial lineations this unit is interpreted to be till and is divided into deposits associated with the most recent glacial expansion 4a and with an earlier pre last glacial maximum expansion 4b seismic facies 5 is an acoustically laminated ponded and draping deposit interpreted to contain proglacial and sub ice shelf materials deposited continuously since the last interglacial period the associations of these units provide context for the interpretation of the ice edge maximum position conditions at the base of the ice sheet and the relative retreat history of the region there is compelling evidence for a much expanded ice sheet in the ross sea during the last glacial maximum in the western ross sea the maximum grounding position is marked by an isolated grounding zone wedge and placed in the vicinity of coulman island approximately 150 km from the continental shelf edge in the central ross sea the maximum grounding position is close to the continental shelf break based primarily on the presence of an extensive 60 m thick sheet like deposit with a fluted upper surface streaming ice may have occupied bathymetric lows on the continental shelf as suggested by 1 the configuration of bathymetry 2 the presence of glacially eroded troughs 3 the concentration of sediment interpreted to be deforming till within the middle to outer shelf reaches of the troughs and 4 the fluted nature of the upper surface absolute rates of streaming ice flow relative to inter ice stream areas are not implied the western ross sea continental shelf deposits record the retreat history of ice derived predominantly from the east antarctic ice sheet and glaciers of the transantarctic mountains ice flow on the continental shelf is interpreted to have remained fixed in position restricted by the walls of the troughs on the inner shelf of the western ross sea the ice flowed over and eroded lithified sedimentary strata slower moving ice occupied flat topped banks a single grounding zone wedge occurs on the western ross sea central shelf no substantial deposits are observed on the inner continental shelf this lack of grounding zone features reflects a restricted sediment supply and a relatively steady rapid retreat of the ice sheet during retreat ice flow acted independently in each major trough and on the bank tops ice retreated from victoria land basin drygalski trough before it retreated from joides basin ice remained on the bank tops shedding material into the abandoned troughs grounded ice in the central ross sea was derived predominantly from an expanded west antarctic ice sheet the ice sheet remained grounded on the continental shelf edge after retreat of ice from the western ross sea expanded ice eroded the inner shelf and deposited sheets of till on the central and outer shelf ice stream drainage shifted laterally as recorded by rounded laterally accreting ridges that separate bathymetric troughs the central ross sea is the repository for larger volumes of sediment derived from ice flow across basins of relatively thick unlithified sedimentary deposits two till sheets mark grounding zone positions in the central ross sea reflecting the higher sediment supply and a stepped deglaciation ice remained grounded on the pennell bank to the west a series of moraines marks the retreat of ice across the bank mega scale glacial lineations and other streamlined subglacial geomorphic features occur across the continental shelf primarily within the troughs the lineations substantiate the maximum reconstruction and support the interpretation of a deforming substrate beneath the outer reaches of the expanded ice sheet this deforming substrate may have contributed to the onset of deglaciation features associated with meltwater are rare or absent suggesting that basal meltwater played a minor role in retreat of the ice sheet

moment tensor inversion of lp events recorded on etna in 2004 using constraints obtained from wave simulation tests 1 the persistent occurrence of long period lp events at mt etna became apparent with the installation of the first fixed broad band seismic network in late 2003 repeating similar lp events from nov 03 to sept 04 indicate a non destructive source process we perform moment tensor mt inversions on a stacked high s n ratio representative lp signal conducting a grid search for the source geometry and l2 inversion for the source time function results indicate a nnw sse oriented resonating sub vertical crack as the most probable source this result is consistent with deformation and gps observations crucial to this result are constraints imposed by detailed 3d full waveform numerical simulations in a heterogeneous tomographic model with topography and in particular a detailed assessment of the influence of very near surface velocity structure on lp signals pulsating gas injection is hypothesised as the most likely lp trigger

composite ground deformation pattern forerunning the 2004 2005 mount etna eruption 1 after the end of the 2002 2003 eruption mount etna activity was characterized only by gentle degassing at the summit craters and some earthquake swarms suddenly an eruption started on 7 september 2004 in complete absence of summit crater volcanic activity seismicity or seismic tremor and ground deformation this is the first time that magma poured out passively without preeruptive and coeruptive volcanic and or geophysical phenomena the primary key to understanding this event is represented by the ground deformation pattern recorded through gps measurements during the year before the eruption the ground deformation shows inflation superimposed by a predominant eastward movement of the eastern sector at a rate never observed before in a noneruptive period the images from satellite radar interferometry confirmed this pattern the deformation field clearly shows that the maximum tension in the eastern sector of the volcano caused the opening of the eruptive fracture which favored the silent pouring out of already resident magma

west antarctic ice streams draining into the ross ice shelf configuration and mass balance extensive airborne radar soundings closely tied to accurately located ground stations made over a portion of the west antarctic inland ice sheet and the ross ice shelf have enabled us to map the boundaries of the ice streams and their flow bands on the ross ice shelf the surfaces of the active ice streams a and b are heavily crevassed but there are no visible crevasses on ice stream c however the existence of numerous crevasses at a depth of about 35 m implies that ice stream c ceased to be active about 250 years ago there is a complex zone at the head of ice stream b that suggests that ice stream b is currently widening and advancing toward the interior of the ice sheet the grounding lines between the inland ice and the ice shelf were mapped from the surface elevations using the requirement of hydrostatic balance and the character of the radar echoes the inland ice is more extensive than previously mapped and includes a large weakly grounded area downstream of ice streams a and b where the surface elevations are barely above hydrostatic equilibrium crary ice rise extends 70 km upstream of the previously mapped position to relate surface elevation data from satellite observations to sea level three geoidal models were tested we conclude that the gem 10c model is the best of the three for this section of antarctica a new map of surface elevation shows deep marginal troughs and longitudinal ridges along ice streams a and b but not on ice stream c whose surface contours show signs of stagnation ice stream c shows a strongly positive and ice stream b a significantly negative net balance rate ice streams a and d also show a significantly negative net flux whereas ice streams e and f do not the overall net balance of this part of the west antarctic inland ice is suggestively negative 23 15 km3 yr 1 from the measured flux into the ross ice shelf and previous measurements we calculate an average basal melt rate from beneath the ice shelf of 0 12 0 03 m yr 1

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

glacier surge propagation by thermal evolution at the bed bakaninbreen southern svalbard began a prolonged surge during 1985 in 1986 an internal reflecting horizon on radio echo sounding data was interpreted to show that the position of the surge front coincided with a transition between areas of warm unfrozen and cold frozen bed ground penetrating radar lines run in 1996 and 1998 during early quiescence show that the basal region of the glacier is characterized by a strong reflection interpreted as the top of a thick layer of sediment rich basal ice down glacier of the present surge front features imaged beneath the basal reflection are interpreted as the bottom of the basal ice layer the base of a permafrost layer and local ice lenses this indicates that this region of the bed is cold up glacier of the surge front a scattering zone above the basal reflection is interpreted as warm ice there is no evidence for this warm zone down glacier of the surge front nor do we see basal permafrost up glacier of it thus as in early surge phase the location of the surge front is now at the transition between warm and cold ice at the glacier bed we suggest that the propagation of the front is associated with this basal thermal transition throughout the surge because propagation of the front occurs rapidly and generates only limited heat basal motion during fast flow must have been restricted to a thin layer at the bed and occurred by sliding or deformation localized at the ice bed interface

improving seismic surveillance at mt etna volcano by probabilistic earthquake location in a 3d model the increasing accuracy of 3d velocity models developed recently for mt etna has enabled their use today in routine earthquake locations in this work we tested the potential and performance of a global search probabilistic earthquake lo cation method nonlinloc in a 3d velocity model to improve earthquake locations for seismic surveillance in addition nonlinloc hypocenter locations and those ob tained by standard iterative linear 3d locations simulps 14 have also been com pared to this end a dataset of 328 selected earthquakes occurring during the 2002 2003 etna flank eruption and the recent highest resolution 3d velocity model have been used the results revealed that the differences in hypocentral coordinates between the two methods are typically of the same order or smaller than the spatial location uncertainty to evaluate the consistency of results between the two 3d location algorithms synthetic datasets with real source receiver configuration are also considered furthermore by using nonlinloc we estimated the influence of the source receiver geometry on the quality of hypocenter locations if we vary the net work geometry in a dense and well distributed network like at etna reducing the number of stations by 20 and 50 it is significant that no large systematic hypo central shifts of the relocated earthquakes are observed if they occur within the net work nonlinloc is a fast and promising approach for automatic earthquake locations and surveillance purposes at mt etna because 1 it works well with a reduced num ber of seismic pickings which are usually available in the automatic locations 2 it is not particularly sensitive to tolerable levels of random noise in arrival times and 3 it produces full location uncertainty and resolution information with respect to standard iterative linear 3d locations

seismological features of the pernicana provenzana fault system mt etna italy and implications for the dynamics of northeastern flank of the volcano abstract the pernicana provenzana fault system is one of the most active tectonic systems of mt etna and it plays an important role in the dynamic of the eastern flank of the volcano earthquakes occurring close to this structural trend have reached magnitudes up to 4 2 sometimes with coseismic surface faulting and have caused severe damages to tourist resorts and villages in the vicinity of this structure in the last decade a large number of shocks sometimes in the form of swarms linked to pernicana provenzana fault system movements have been detected by the permanent local seismic network operating in eastern sicily in this paper we report on the detailed study of the seismic activity occurring during the 2000 2009 time span in the pernicana provenzana fault system area firstly we located 407 earthquakes using a standard location code and a 1d crustal velocity model we then applied two different approaches to calculate precise hypocenter locations of the events in particular a non linear code was adopted to obtain an estimate of the a posteriori probability density function in 3d space for the hypocenter location moreover a relative location of correlated event pairs was performed using the double difference method these two different location approaches allowed defining with good accuracy the most active and hazarding sectors of the structure the results of these precise locations showed a tighter clustering in the epicenters and in focal depths in comparison with standard locations earthquakes are located along the pernicana provenzana fault system and are mainly clustered in two zones separated by an area with very low rate of earthquakes occurrence but characterized by the highest energy release depths of the foci are very shallow ranging between the surface and about 3 km b s l kinematics of the pernicana provenzana fault system revealed by the fault plane solutions computed for the most energetic earthquakes highlights a predominant dip slip and left strike movements along e w oriented fault planes in agreement with field observations

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

changing in crust mechanical behaviour due to raising magma a fracturing model of se flank of mt etna sicily abstract associated with the remarkable flank eruption which started in late october 2002 a series of earthquakes occurred on the lower eastern flank of mt etna the m d 4 4 bongiardo s venerina earthquake at 10 02 am gmt 29th october affected a large nnw sse area severely damaging nearby villages the faulting model proposed in this paper seeks to justify the two causes of the fracturing process as well as its spatiotemporal development for this purpose a preliminary analysis of the morphotectonic framework and the detected fractures linked to october 2002 earthquakes has been carried out we will therefore consider the seismic activity which affected the volcano in 2001 and 2002 additionally we will review previous scientific studies of seismic tomography and macroseismic data in particular the fracturing mechanisms appear to be linked to the volcanic area uplift as a consequence of rising magma the consequent change in the rheology beneath this sector of the volcano explains the differing reaction of the crust at different levels

changes in heat released by hydrothermal circulation monitored during an eruptive cycle at mt etna italy the shallow vertical temperature profile has been measured in the proximity of an eruptive fissure far about 4 km north northeast from mt etna central craters the monitoring site was a steam heated soil lying between a group of flank fractures on the upper northeast flank of mt etna italy i e on the northeast rift we chose this area because it was close to an eruptive fissure that opened in 2002 and extended from about 2500 to about 1500 m a s l with our aim being to determine a connection between this fracture system and the ongoing volcanic activity heat flux anomalies from the ground from september 2009 to september 2012 were evaluated changes in the hydrothermal release which can be related to variations in volcanic activity are discussed and compared to the published geophysical data the heat flux ranges varied during the pre eruptive from about 7 to 38 w m 2 syn eruptive from about 3 to 49 w m 2 and post eruptive phases with the heat released being lowest at the latter phase from about 1 to 20 w m 2 moreover the heat flux time variation was strongly correlated with the eruption rate from the new southeast crater between january 2011 and april 2012 the migration of magma through active conduits acts as a changing heating source for steam heated soils located above the active fractures our findings suggest that tracking the heat flux above active fractures constitutes a useful investigation field for low cost thermal monitoring of volcanic activity time variations in their emissions could highlight the relationship between a hydrothermal circuit and the local network of fractures possibly indicating variation in the structural weakness of a volcanic edifice continuous monitoring of heat flux combined with a realistic model would contribute to multidisciplinary investigations aimed at evaluating changes in volcano dynamics

rock physics based relations for density and s velocity versus p velocity in deepwater subsalt gulf of mexico shales which is commonly used to estimate s wave velocity s from p wave velocity p where the units of velocity are km s and the empirical relations for estimating the shear wave velocity from the compressional wave velocity given by greenberg and castagna 1992 figure 1 compares the relationship between density and sonic velocity for two deepwater subsalt wells in the green canyon area of the gulf of mexico to gardner s predic tion assuming values for parameters a and b given by castagna et al 1993 for sands and shales while the gardner estimate is reasonable for the sands the shales at any given density indicate a significantly lower velocity than that predicted by gardner s relation similarly figure 2 compares p wave versus s wave ve locity data for the same two wells to the prediction of equation 2 and of the greenberg castagna relation for shales it is seen that these relations tend to overestimate s wave velocity for the shales at a given p wave velocity in this paper these discrepancies are investigated using a rock physics model this model not only gives a good descrip tion of the data but also allows the effective pore aspect ratio to be estimated rock physics model to model the elastic moduli of shales the shales were considered as a mixture of clay and quartz with properties taken as those given by carmichael 1989 for quartz and gulf clays han et al 1986 the properties used are listed in table 1 pore spaces were assumed filled by brine having a bulk mod ulus of 3 4 gpa appropriate for the pressure and temperature in the depth range of interest since quartz grains in shales are embedded within a softer continuous clay matrix the elastic moduli of the solid phase were estimated using the hashin sh trikman lower bound hashin and shtrikman 1963 the up per and lower hashin shtrikman bounds for the elastic moduli in table 1 are plotted in figure 3

etna 2002 eruption imaged from continuous tilt and gps data 1 on the night of october 26 2002 intense explosive activity and lava effusion began suddenly on the southern flank of mt etna at an altitude of 2750 m during the 27 and 28 october a long field of eruptive fractures propagated radially along the north eastern flank of the volcano ground deformation changes recorded between 26 and 27 october from gps and tilt data collected at the permanent geodetic network of mt etna were modeled to infer the positions and dimensions of the two dikes the observed deformation pattern was consistent with a response of the edifice to a composite mechanism consisting of a vertical uprising dike in the upper southern flank and a lateral intrusion propagating along the north eastern sector the first dike which triggered the eruption crossed the volcano edifice in a few hours and was located in the same area as the 2001 eruption while the second lateral dike which crossed the ne flank was the primary cause of the recorded deformation pattern

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

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

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

elemental and isotope covariation of noble gases in mineral phases from etnean volcanics erupted during 2001 2005 and genetic relation with peripheral gas discharges abstract during 2001 2005 mount etna was characterized by intense eruptive activity involving the emission of petrologically different products from several vents which involved at least two types of magma with different degrees of evolution we investigated the ratios and abundances for noble gas isotopes in fluid inclusions trapped in olivines and pyroxenes in the erupted products we confirm that olivine has the most efficient crystalline structure for preserving the pristine composition of entrapped gases while pyroxene can suffer diffusive he loss both the minerals also experience noble gas air contamination after eruption helium isotopes of the products genetically linked to the two different magmas fall in the isotopic range typical of the etnean volcanism this result is compatible with the metasomatic process that the etnean mantle is undergoing by fluids from the ionian slab during the last ten kyr as previously inferred by isotope and trace element geochemistry significant differences were also observed among olivines of the same parental magma that erupted throughout 2001 2005 with 3he 4he ratios moving from about 7 0 ra in 2001 volcanites to 6 6 ra in 2004 2005 products changes in he abundances and isotope ratios were attributed to variations in protracted degassing of the same magma bodies from the 2001 to the 2004 2005 events with the latter lacking any contribution of undegassed magma the decrease in 3he 4he is similar to that found from measurements carried out every fifteen days during the same period in gases discharged at the periphery of the volcano to our knowledge this is the first time that such a comparison has been performed so in detail and provides strong evidence of the real time feeding of peripheral emissions by magmatic degassing

faulting on the western flank of mt etna and magma intrusions in the shallow crust surface deformations on the western flank of mt etna volcano spanning 1980 2004 have been analysed as they pertain to stress interactions between magma intrusions within the shallow crust along the s se rift and faulting sensitivity during this period an accurate analysis of strain parameters computed by inversion of sw electro optical distance data suggested that the observed strong displacements on this flank of the edifice can also be related to dextral shear movements along a roughly ne sw buried fault crossing the area covered

magnetite dissolution in deep sediments and its hydrologic implication a detailed study of sediments from site 808 leg 131 our previous study of deep sea sediments from site 808 leg 131 of the ocean drilling program has demonstrated that the two anomalously low intensity zones of natural remanent magnetization nrm 675 to 925 and 1080 to 1243 m below seafloor were caused by unusually low magnetite content in the sediment sections and that this was not related to the variations in sediment sources calcite dilution or magnetite destruction occurring in the top sediment layer during early diagenesis for an explanation we now suggest that these low nrm intensity zones were produced by catagenesis at great depth by organic matter decomposition in sediments which in turn causes magnetite dissolution and hence a lower magnetite content a similar process also applies to manganese ions as a consequence iron and manganese concentration grain size and content of magnetite and nrm intensity all decrease whereas sulfur content increases in these sediments our interpretation is also supported by other studies of organic geochemistry and sedimentology of these same sediments we suggest therefore that detailed rock magnetic and geochemical tests should be carded out before geomagnetic field variations are studied using ocean sediments from such gmat depth additionally we suspect that catagenesis may have been retarded and magnetic degradation was prevented near a d6collement due to cold water percolation

source model for the 2001 flank eruption of mt etna volcano 1 using interferometric synthetic aperture radar insar we constrain the deformation sources for the july august 2001 flank eruption of mt etna volcano italy insar data from ascending and descending passes of the ers2 satellite reveal a pattern of deformation that cannot be explained by a dike intrusion alone in addition to a vertical dike beneath the south rift zone the spatially large 10 km scale 15 20 cm in range negative range displacement lobes across the western descending data and eastern ascending data flanks require a nearly symmetric set of shallowly dipping normal faults to each side of the central dike complexity in the observed insar surface displacements constrains an additional dike intrusion beneath its ne flank long term deformation of etna s eastern and southern flanks is well established through field and insar observations therefore the relative symmetry of motion beneath both the western and eastern flanks during the 2001 eruption is surprising our model of symmetric flank motion suggests that on the short time scales of a large dike intrusion volcanoes can deform differently from their long term deformation

comment on complex magma dynamics at mount etna revealed by seismic thermal and volcanological data by b behncke s falsaperla and e pecora

petrology of lavas from the 2004 2005 flank eruption of mt etna italy inferences on the dynamics of magma in the shallow plumbing system following the 2001 and 2002 2003 flank eruptions activity resumed at mt etna on 7 september 2004 and lasted for about 6 months this paper presents new petrographic major and trace element and sr nd isotope data from sequential samples collected during the entire 2004 2005 eruption the progressive change of lava composition allowed defining three phases that correspond to different processes controlling magma dynamics inside the central volcano conduits the compositional variability of products erupted up to 24 september is well reproduced by a fractional crystallization model that involves magma already stored at shallow depth since the 2002 2003 eruption the progressive mixing of this magma with a distinct new one rising within the central conduits is clearly revealed by the composition of the products erupted from 24 september to 15 october after 15 october the contribution from the new magma gradually becomes predominant and the efficiency of the mixing process ensures the emission of homogeneous products up to the end of the eruption our results give insights into the complex conditions of magma storage and evolution in the shallow plumbing system of mt etna during a flank eruption furthermore they confirm that the 2004 2005 activity at etna was triggered by regional movements of the eastern flank of the volcano they caused the opening of a complex fracture zone extending ese which drained a magma stored at shallow depth since the 2002 2003 eruption this process favored the ascent of a different magma in the central conduits which began to be erupted on 24 september without any significant change in eruptive style deformation and seismicity until the end of eruption

magma faults and gravitational loading at mount etna the 2002 2003 eruptive period 1 mount etna is characterized by a complex structural setting that influences its evolution in order to understand how the interaction between dike forming intrusions and faulting influences the kinematics of the volcanic edifice we developed a numerical model it takes account of the topography the medium heterogeneities the gravitational loading and the most active crustal discontinuities a parameterization of the apparent coefficient of friction as a function of the depth has been considered in the range from 0 01 to 0 5 the density values used young s modulus and poisson s ratio range from about 1700 to 3200 kg m3 8 5 to 140 gpa and 0 15 to 0 35 respectively the model was applied to the 2002 2003 etna eruption the resulting deformation pattern was in agreement with the data provided by the continuous gps stations and the seismological knowledge obtaining displacements up to 1 m some discrepancies between the recorded ground deformation field and the modeled displacements allowed us to make some hypotheses on the volcano tectonic e g for the pernicana fault or regional tectonic origin acireale s alfio fault system of the crustal discontinuities moreover our results suggested that the pernicana fault is characterized by a very low apparent coefficient of friction less than 0 1 furthermore we evaluated the contribution of the gravitational loading and found that it implies a variation of about 10 of the overall deformation pattern our results clearly showed that the weight of the volcanic edifice acts in opposition to the magmatic intrusions conversely we found that the presence of medium heterogeneities may favor the eastern flank movements toward the se and the spreading of the summit area playing a fundamental role in ascending magma finally we investigated the shallow sliding model and found that dike forming intrusions produce negligible displacements less than 1 mm along the subhorizontal detachment surface therefore the gravitational loading during dike forming intrusions is not able to trigger sliding processes along this plane

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

shear wave velocity estimation in porous rocks theoretical formulation preliminary verification and applications shear wave velocity logs are useful for various seismic interpretation applications including bright spot analyses amplitude versus offset analyses and multicomponent seismic interpretations measured shear wave velocity logs are however often unavailable we developed a general method to predict shear wave velocity in porous rocks if reliable compressional wave velocity lithology porosity and water saturation data are available the precision and accuracy of shear wave velocity prediction are 9 and 3 respectively the success of our method depends on 1 robust relationships between compressional and shear wave velocities for water saturated pure porous lithologies 2 nearly linear mixing laws for solid rock constituents 3 first order applicability of the biot gassmann theory to real rocks we verified these concepts with laboratory measurements and full waveform sonic logs shear wave velocities estimated by our method can improve formation evaluation our method has been successfully tested with data from several locations

basal sliding of ice stream b west antarctica a tethered stake apparatus is used to measure basal sliding in a borehole on ice stream b west antarctica about 300 km upstream east from its grounding line near the head of the ross ice shelf a metal stake emplaced at the top of a layer of unfrozen till underlying the ice is connected by a tether line to a metering unit that measures the tether line as it is pulled out from the borehole by the stake as a result of basal sliding the measured sliding motion includes any actual slip across the ice till interface and may include in addition a possible contribution from shear deformation of till within about 3 cm of the interface this 3 cm figure follows from a qualitative model of the movements of the stake in the course of the experiment based on features of the record of apparent sliding alternative but less likely models would increase the figure from 3 cm to 10 cm or 25 cm in any case it is small compared to the seismically inferred till thickness of 9 m measured apparent sliding averages 69 of the total motion of 1 2 m d 1 over 26 days of observation if a 3 5 day period of slow apparent sliding 8 of the total motion is included in the average the occurrence of the slow period raises the possibility that the sliding motion switches back and forth between c 80 and c 8 of the total motion on a time scale of a few days however it is likely that the period of slow apparent sliding represents instead a period when the stake got caught on the ice sole if the slow period is therefore omitted the indicated average basal sliding rate is 83 of the total motion in either case basal sliding predominates as the cause of the rapid ice stream motion in the last 2 days of observation the average apparent sliding rate reached 1 17 m d 1 essentially 100 of the motion of the ice stream if till deformation contributes significantly to the ice stream motion the contribution is concentrated in a shear zone 3 cm to possibly 25 cm thick at the top of the 9 m thick till layer these observations if applicable to the west antarctic ice sheet in general pose complications in modeling the rapid ice streaming motion

plio quaternary tectonic evolution and structure of the catania foredeep the northern hyblean plateau and the ionian shelf se sicily abstract available multi and single channel seismic reflection profiles calibrated by onshore borehole data have been used for defining the structural styles in the shelf and slope of the ionian sea between catania and augusta se sicily the geological and geophysical data suggest that this area represents a segment of the foredeep foreland system which collapsed after late pliocene times the foundering was controlled by normal faults trending ne sw which flank the southern margin of the catania foredeep onland in outcrop these faults appear largely to be post dated by lower pleistocene sediments nearshore carbonates passing laterally into basinal clays which lie unconformably upon older substrata offshore close to the southern edge of the foredeep seismic lines allow recognition of two distinct units a syn rift wedge upper pliocene submarine tholeiites and sediments and a post rift sequence which can be correlated with lower pleistocene carbonates sands and clays recognisable on land both in outcrop and by borehole data the true frontal part of the thrust belt as detected by the seismic lines occupies the inner part of the area investigated and is buried by upper pliocene and lower pleistocene sediments however the compressive deformation seems to propagate toward the south southeast by means of growing detachment levels developing at depth within pleistocene marine clays for a length of about 10 km ahead of the present day thrust front offshore the faults trending ne sw are dissected towards the east by faults trending nnw sse subparallel to the malta escarpment which flank the edge of the submerged messina rise these faults originating in a steep scarp which drops eastwards to the deep ionian basin have triggered submarine slides and affected the present day seafloor sediments as shown by seismic lines and as stressed by the modern seismicity of the area some of the faults along the malta escarpment could be still active

origin of the middle pleistocene transition by ice sheet erosion of regolith the transition in the middle pleistocene 0 9 ma seen in 18o deep sea core records from relatively low amplitude high frequency 41 kyr to high amplitude low frequency 100 kyr ice volume variations under essentially the same orbital forcing can be attributed to a change from an all soft bedded to a mixed hard soft bedded laurentide ice sheet through glacial erosion of a thick regolith and resulting exposure of unweathered crystalline bedrock a one dimensional ice sheet and bedrock model which includes transport of sediment and ice by subglacial sediment deformation demonstrates that a widespread deforming sediment layer maintains thin ice sheets before the transition which respond linearly to the dominant 23 and 41 kyr orbital forcing progressive removal of the sediment layer eventually causes a transition to thicker ice sheets whose dominant timescale of change 100 kyr reflects nonlinear deglaciation processes in model simulations over the last 3 ma initialized with no ice and a uniform 50 m sediment layer the time series of ice volume and extent agree in several important aspects with the observed records

expansion and rapid retreat of the west antarctic ice sheet in eastern ross sea possible consequence of over extended ice streams abstract marine geological data from the eastern ross sea provide compelling evidence that the west antarctic ice sheet extended to the continental shelf break during the last glacial maximum swath bathymetry records show mega scale glacial lineations within each of the four large glacial troughs on the shelf these features extend virtually uninterrupted across the shelf and have sharp lateral boundaries sediment cores that sampled the lineations recovered diamicton that is interpreted as deformation till the combined data indicate streaming ice the great extent of the paleo ice streams up to 1000 km in length is attributed to the fact that they flowed across unconsolidated sedimentary strata geomorphic features that are known to form at the retreating grounding line such as recessional moraines and ridges are restricted to the southeastern portion of the shelf iceberg furrows that occur at depths of up to 650 m overprint mega scale lineations these deep furrows are interpreted as having been formed by icebergs calved from the grounding line of the ice sheet which indicates the absence of a fringing ice shelf sediment cores sampled a thin layer of glaciomarine sediments resting sharply on till sub ice shelf deposits similar to those sampled in the western ross sea were not recovered in the eastern ross sea these combined results imply rapid retreat of the ice sheet from the shelf crosscutting lineations with different orientations indicate changes in flow direction that probably occurred as the ice profile was lowered and the physiography of the sea floor across which the ice sheet was retreating changed grounding zone wedges vary in number and location within individual troughs which indicates diachronous retreat of ice streams due to a lack of carbonate material for radiocarbon dating all radiocarbon ages were derived from acid insoluble organic aio fractions these dates indicate early retreat of the ice sheet relative to the western ross sea and other areas of west antarctica however the older dates must be viewed as suspect due to a paucity of diatomaceous material and contamination from old carbon while we were not successful at constraining the timing of ice sheet retreat from the continental shelf the data do indicate that the ice sheet was grounded on the shelf during the lgm

imaging composite dike propagation etna 2002 case 1 late on the night of 26 october 2002 a dike intrusion started suddenly at mount etna producing intense explosive activity and lava effusion on the southern flank five to six hours afterward a long field of eruptive fractures propagated radially along the northeastern flank of the volcano producing marked variations at the permanent tilt network the dike propagation velocity was inferred by the associated seismicity we modeled the temporal evolution of the continuously recorded tilt data both during the vertical dike propagation on the high south flank on 26 october and during the radial propagation along the northeast flank between 27 and 28 october the reproduction of the recorded tilt signal allowed us to describe the geometry and characteristics of the two dikes in greater detail than the previous static inversion we deduced that the eruption was characterized by an unusual composite mechanism clearly showing a transition from a nearly pure opening mode displacement to a mechanism characterized by an equally strong normal dip slip component and a smaller left lateral strike slip component in this study we demonstrate the interaction between the final segment of the dike and a preexisting structure that was reactivated in response to the intrusion we show that tilt and its modeling represent a powerful tool to verify and constrain dike intrusions in detail

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

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

a new approach to petroelastic modeling of carbonate rocks using an extended pore space stiffness method with application to a carbonate reservoir in central luconia sarawak malaysia

deglaciation of a major palaeo ice stream in disko trough west greenland recent work has confirmed that grounded ice reached the shelf break in central west greenland during the last glacial maximum lgm here we use a combination of marine sediment core data including glacimarine lithofacies and ird proxy records and geomorphological and acoustic facies evidence to examine the nature of and controls on the retreat of a major outlet of the western sector of the greenland ice sheet gris across the shelf retreat of this outlet which contained the ancestral jakobshavns isbrae ice stream from the outer shelf in disko trough was rapid and progressed predominantly through iceberg calving however minor pauses in retreat tens of years occurred on the middle shelf at a trough narrowing forming subtle grounding zone wedges by 12 1 cal kyr bp ice had retreated to a basalt escarpment and shallow banks on the inner continental shelf where it was pinned and stabilised for at least 100 years during this time the ice margin appears to have formed a calving bay over the trough and melting became an important mechanism of ice mass loss fine grained sediments muds were deposited alternately with ird rich sediments diamictons forming a characteristic deglacial lithofacies that may be related to seasonal climatic cycles high influxes of subglacial meltwater emanating from the nearby ice margins deposited muddy sediments during the warmer summer months whereas winters were dominated by iceberg calving leading to the deposition of the diamictons this is the first example of this glacimarine lithofacies from a continental shelf setting and we suggest that the calving bay configuration of the ice margin plus the switching between calving and melting as ablation mechanisms facilitated its deposition by channelling meltwater and icebergs through the inner trough the occurrence of a major stillstand on the inner shelf in disko trough demonstrates that the ice dynamical response to local topography was a crucial control on the behaviour of a major outlet in this sector of the gris during retreat

relationships between compressional wave and shear wave velocities in clastic silicate rocks new velocity data in addition to literature data derived from sonic log seismic and laboratory measurements are analyzed for clastic silicate rocks these data demonstrate simple systematic relationships between compressional and shear wave velocities for water saturated clastic silicate rocks shear wave veloci ty is approximately linearly related to compressional wave velocity and the compressional to shear velocity ratio decreases with increasing compressional velocity laboratory data for dry sandstones indicate a nearly constant compressional to shear velocity ratio with rigidity approximately equal to bulk modulus ideal models for regular packings of spheres and cracked solids exhibit behavior similar to the observed water saturated and dry trends for dry rigidity equal to dry bulk modulus gassmann s equations predict velocities in close agreement with data from the water saturated

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

time variant analysis of geomagnetic signals describes the volcanic activity of mt etna between early 2000 and late 2002 abstract volcanomagnetic anomalies have been mostly observed during strong eruptions our aim is to improve the geomagnetic data analysis to evidence the anomalies occurring in a larger time span especially in the phases preceding the eruptive events we developed a time variant statistical approach and applied it to the 2000 2002 etna geomagnetic temporal series it is based on an algorithm that statistically predicts the geomagnetic field at the station on the volcanic edifice by that recorded at the remote one in such a way a number of significant changes in the time series called statistical innovations marking the local magnetic field change were detected the distribution of such statistical innovations accurately describes the etna volcanic evolution we note a progressive increase of the innovation occurrence as the eruptive cycles were approaching and only few and weak innovations at times between the various eruptive cycles the significance of this analysis is further confirmed by the close agreement among the mean square prediction error strain release and the volcanic activity behavior on the contrary the geomagnetic field at a single station or its difference at two stations do not have any clear correlation with other measured physical quantities the complex pattern of the prediction error was also investigated by a multifractal analysis we found that the holder regularity increases with the intensification of the volcanic activity implying that innovations tend to be less sporadic and correlated during the major volcanic phases

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

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

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

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

piezomagnetic fields due to an inclined rectangular fault in a viscoelastic half space an application to the 2002 2003 etna eruption summary time dependent piezomagnetic fields due to inclined rectangular faults embedded in a viscoelastic homogeneous half space were investigated a viscoelastic rheology of the surrounding medium was assumed to relate piezomagnetic changes at the surface to the stress field at depth the viscosity of the medium strongly influences time dependent stress changes especially in volcanic areas rocks near magmatic sources are considerably heated the presence of higher temperatures produces a lower effective viscosity in the crust making it necessary to consider its inelastic properties rocks no longer behave in a purely elastic manner but permanently deform because the viscosity is significantly lowered to determine the time dependent piezomagnetic fields in a viscoelastic medium we applied the correspondence principle to the analytical elastic solutions for dislocation sources among all the possible rheological models we investigated three cases in which the bulk modulus is purely elastic and the shear modulus relaxes as for i a maxwell solid ii a standard linear solid sls and iii a kelvin solid the piezomagnetic field completely vanishes after the relaxation process for a maxwell rheology whereas it is found to decrease over time and reach some finite offset values for sls and kelvin rheologies a real case study concerning the magnetic anomalies observed during the 2002 2003 mt etna eruption is also investigated post eruptive magnetic variations were in general agreement with a viscoelastic relaxation process of a sls rheology undergoing in the volcano edifice

effect of sedimentation on ice sheet grounding line stability sedimentation filling space beneath ice shelves helps to stabilize ice sheets against grounding line retreat in response to a rise in relative sea level of at least several meters recent antarctic changes thus cannot be attributed to sea level rise strengthening earlier interpretations that warming has driven ice sheet mass loss large sea level rise such as the 100 meter rise at the end of the last ice age may overwhelm the stabilizing feedback from sedimentation but smaller sea level changes are unlikely to have synchronized the behavior of ice sheets in the past

late pleistocene holocene retreat of the west antarctic ice sheet system in the ross sea part 2 sedimentologic and stratigraphic signature sedimentologic geotechnical geochemical and accelerator mass spectrometer ams radiocarbon data from two marine geologic cruises in the ross sea have allowed us to constrain facies relationships and temporal changes in the west antarctic ice sheet the selection of core sites was facilitated by the use of multibeam bottom imagery and a good quality chirp subbottom reflection system a complex but consistent succession of facies documents a number of environments from subglacial to open marine massive mud rich diamictons have low water contents contain in places a calcareous microfossil assemblage show minimal textural variation and contain low and uniform total organic carbon values this reflects a subglacial setting this unit passes upward into a stratified thin granulated facies consisting of pelletized sandy muddy gravel that is loosely compacted and contains a variable water content and concentrated horizons of pebble sized clasts this facies reflects the lift off zone or thin water film between the basal debris and sea floor overlying this unit are silty clays that contain a well sorted very fine grained sand component there are no coarse grains within this unit this facies is in part laminated and reflects deposition beneath an ice shelf near and away from the grounding line zone the ice shelf facies passes upward into a siliceous mud and ooze unit that represents deposition in an open marine setting a sandy volcaniclastic rich subfacies marks the transition from ice shelf to open marine environments found at the calving line the 86 ams radiocarbon dates on organic matter provide an accurate chronology for 19 cores ice shelf conditions were established in the outer drygalski trough by 11 0 25 ka and perhaps earlier this transition took place in the joides basin by 10 8 ka the calving front of the ross ice shelf passed over the drygalski trough at 74 s by 9 5 0 25 ka the timing of deglaciation in the ross sea calls into question current models for the contribution of antarctic glacial ice to holocene sea level rise and suggests that recession was relatively gradual and more closely aligned with northern hemisphere deglaciation and its associated eustatic pulse

static stress changes induced by the magmatic intrusions during the 2002 2003 etna eruption 1 the shallow intrusive processes that occurred during 2002 2003 etna eruption as well as the complex interaction between the magma intrusive events and the tectonic response of the volcano s eastern flank are investigated with numerical deformation modeling and the estimation of changes in the static coulomb stress ground deformation and volcanologic evidence clearly indicate a composite mechanism of intrusion on both the southern and northeastern flanks of the volcano geodetic data inversions have been based on a homogeneous elastic half space model although geological data and seismic tomography indicate that mt etna is elastically inhomogeneous and that rigidity layering and heterogeneities are likely to affect the magnitude and pattern of the deformation field to account for topographic effects as well as a complicated distribution of material properties we use the finite element method fem to provide a more realistic model the presence of medium heterogeneity strongly affects the amplitudes of the static stress changes seismicity matches well the areas of positive increase in the static stress caused by the intrusive events along the southern and northeastern flanks the changes in the state of stress generated by the southern dike produce an extensional stress field that favors magma propagation along the north east rift the highest seismic releases were associated with the activation of two fault systems the timpe fault system and the pernicana fault the static stress changes resolved onto these faults indicate that the magma intrusions on the southern and northeastern flanks encouraged these seismogenic structures to slip

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

discovery of till deposition at the grounding line of whillans ice stream we report on the discovery of a grounding line sedimentary wedge till delta deposited by whillans ice stream west antarctica our observation is that grounding line deposition serves to thicken the ice and stabilize the position of the grounding line the ice thickness at the grounding line is greater than that of floating ice in hydrostatic equilibrium thus the grounding line will tend to remain in the same location despite changes in sea level until sea level rises enough to overcome the excess thickness that is due to the wedge further our observation demonstrates the occurrence of rapid subglacial erosion sediment transport by distributed subglacial till deformation and grounding line sedimentation which have important implications for ice dynamics numerical modeling of ice flow and interpretation of the sedimentation record