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

modelling glacier advances and related climate conditions during the last glaciation cycle in the kuzigun valley tashkurgan catchment on the north west tibetan plateau understanding regional climate during the last glaciation cycle lgc is far from complete for the north western tibetan plateau recent improvements in understanding glacial extents and chronologies in the tashkurgan catchment north west tibetan plateau present an opportunity to estimate the glacial climatic conditions of the lgc here we use a coupled mass balance and ice flow model to reconstruct glacier advances in the kuzigun valley during the lgc and quantify the related climate conditions in the tashkurgan hangdi and kuzigun glacial stages for the region the model results show that the kuzigun valley contained ice volumes of 5 713 0 005 4 874 0 005 and 3 631 0 004 km3 with equilibrium line altitude lowering values of 500 560 and 610 m in the three successive glacial stages respectively by referencing the climatic 18o proxy records we conclude that temperature decreased by 5 8 4 and 140 modern values in the kuzigun hangdi and tashkurgan glacial stages respectively our climatic estimates for the kuzigun stage are generally consistent with previous studies that showed the last glacial maximum climate was 4 9 c colder than today on the tibetan plateau more accurate climate proxies are needed for evaluating our modelled tashkurgan climatic conditions

well documented travel history of mesozoic pelagic chert in japan from remote ocean to subduction zone the mino tanba belt in southwest japan a segment of the cordilleran type orogenic chain of jurassic east asia is composed mainly of a middle upper jurassic subduction accretion complex in which triassic and lower jurassic bedded radiolarian cherts occur as large allochthonous units structurally interlayered with middle upper jurassic clastic rocks high resolution microfossil conodont and radiolaria research has identified very low average sedimentation rates of about 0 5 g cm 1000 yr in the chert units similar to those of modern pelagic sediments accumulated in open ocean environments judging from the low average sedimentation rate high purity of biogenic silica long duration of continuous deposition 50 m y and wide along strike extent 1000 km the bedded radiolarian cherts in the mino tanba belt are best understood as ancient pelagic sediments that accumulated in open ocean environments accordingly the alleged origin in smaller marginal basins is untenable upward lithologic change from bedded chert to overlying siliceous mudstone in the uppermost portion of chert sequences suggests the gradual landward approach of the oceanic plate toward a trench the tectonic interlayering of these cherts and coarse grained terrigenous elastics is a secondary feature that was added through duplexing underplating in the subduction zone on the basis of the primary stratigraphy and field occurrence of triassic bedded chert in the mino tanba belt newly proposed are an idealized oceanic plate stratigraphy and a generalized travel history of a cordilleran type bedded chert from its birth at a mid oceanic ridge to its demise at a subduction zone

recent seismicity and tomographic modeling of the mount etna plumbing system the monitoring of seismic activity in eastern sicily southern italy has been recently improved in the framework of the poseidon project to investigate both tectonics and volcanic processes of mount etna this effort has produced a homogeneous and complete data set which we use to image the deep structure of the volcano and to define the space and time distribution of the recent seismicity encompassing the 1995 eruption diffuse eruptions between 1995 and 1997 a further magma intrusion started in 1997 and an increase of volcanic activity in july 1998 we inverted p wave arrival times from 307 selected local earthquakes to obtain a three dimensional velocity model of the volcano with a simultaneous inversion for hypocenters and velocity parameters the new tomographic images permit us to define the structure beneath the volcano from the surface down to 18 km depth the main structural feature revealed by our inversion is a high velocity body located beneath the central craters whose lateral extent increases from 6 km between 18 and 9 km depth to 12 km between 9 and 3 km depth near the surface the fast anomaly branches in two separate high vp regions which are located below the summit craters and the eastern flank valle del bove respectively the high velocity features are interpreted as high density cumulates of solidified magma that intruded the shallow crust we hypothesize that magma ascends the crust within the relatively small high velocity conduit below 9 km depth and is stored at depth shallower than 9 km within the broad high velocity region as also suggested by petrological data a sharp increase of seismicity in 1997 with earthquakes occurring at the border of the high velocity body suggests that mount etna sustained recent episodes of intrusions which possibly herald future eruptions no large low velocity anomaly interpretable as a melted magma chamber is imaged in the upper 18 km of the crust while a broad low velocity anomaly in the uppermost mantle revealed by regional seismic data possibly indicates the magma source region at depth earthquake occurrence from the deep source to the shallow intrusive area helps to trace the magma migration and the feeding of the volcanic system

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

evidence of multiple strain fields beneath the eastern flank of mt etna volcano sicily italy deduced from seismic and geodetic data during 2003 2004 we carried out a study of the seismicity and ground deformation occurring on mt etna volcano after the end of the 2002 2003 eruption and before the onset of the 2004 2005 eruption data were recorded by the permanent local seismic network run by istituto nazionale di geofisica e vulcanologia sezione di catania and by geodetic surveys carried out in july 2003 and july 2004 on the gps network most earthquakes were grouped in two main clusters located in the northeastern and southeastern sectors of the volcano the areal distribution of seismic energy associated with the recorded earthquakes allowed us to highlight the main seismogenic areas of mt etna in order to better understand the kinematic processes of the volcano 3d seismic locations were used to compute fault plane solutions and a selected dataset was inverted to determine stress and strain tensors the focal mechanisms in the northeastern sector show clear left lateral kinematics along an e w fault plane consistent with events occurring along the pernicana fault system the fault plane solutions in the southeastern sector show mainly right lateral kinematics along a nne and ene fault plane and left lateral kinematics along nw fault planes that together suggest roughly e w oriented compression surface ground deformation affecting mt etna measured by gps surveys highlighted a marked inflation during the same period and exceptionally strong seawards motion of its eastern flank the 2d geodetic strain tensor distribution was calculated and the results show mainly ene wsw extension coupled with wnw ese contraction indicating right lateral shear along a nw se oriented fault plane the different deformation of the eastern sector of the volcano as measured by seismicity and ground deformation must be interpreted by considering the different depths of the two signals seismic activity in the southeastern sector of volcano is located between 3 and 8 km b s l and can be associated with a very strong additional e w compression induced by a pressurizing source just westwards and at the same depth located by inverting gps data ground deformation in contrast is mainly affected by the shallower dynamics of the fast moving eastern flank which produces a shallower opposing e w extension the entire dataset shows that two different processes affect the eastern flank at the same time but at different depths the boundary is clearly located at a depth of 3 km b s l and could represent the decollement surface for the mobile flank

the 2004 2005 etna eruption implications for flank deformation and structural behaviour of the volcano the development of the 2004 2005 eruption at etna italy is investigated by means of field surveys to define the current structural state of the volcano in 2004 2005 a fracture swarm associated with three effusive vents propagated downslope from the se summit crater towards the se such a scenario is commonly observed at etna as a pressure increase within the central conduits induces the lateral propagation of most of the dikes downslope nevertheless some unusual features of this eruption slower propagation of fractures lack of explosive activity and seismicity oblique shear along the fractures suggest a more complex triggering mechanism a detailed review of the recent activity at etna enables us to better define this possible mechanism in fact the nw se trending fractures formed in 2004 2005 constitute the southeastern continuation of a n s trending fracture system which started to develop in early 1998 to the east of the summit craters the overall 1998 2005 deformation pattern therefore forms an arcuate feature whose geometry and kinematics are consistent with the head of a shallow flank deformation on the e summit of etna similar deformation patterns have also been observed in analogue models of deforming volcanic cones in this framework the 2004 2005 eruption was possibly induced by a dike resulting from the intersection of this incipient fracture system with the se crater a significant acceleration of this flank deformation may be induced by any magmatic involvement the central conduit of the volcano is presently open constantly buffering any increase in magmatic pressure and any hazardous consequence can be expected to be limited a more hazardous scenario may be considered with a partial or total closing of the central conduit in this case magmatic overpressure within the central conduit may enhance the collapse of the upper eastern flank triggering an explosive eruption associated with a landslide reaching the eastern lower slope of the volcano

stress and the direction of slip on fault planes the shear stress direction on a fault plane depends only on four of the six components of the stress tensor assuming only that the slip direction marks the shear stress direction on any fault plane and that stress is homogeneous it is possible to estimate these four stress parameters from populations of fault planes with known slip directions as several workers have observed different formulations of the problem may yield varying best fitting stresses and estimates of uncertainty in the simplest case no assumptions are made regarding the orientations of fault planes relative to the stress tensor thus the technique allows for the possibility that the fault planes may be very weak here we present simple analytical and graphical descriptions of the field of admissible fault geometries relative to any four parameter stress model which can be used to illustrate the significance of various inverse strategies in particular this paper explores the effects of using two alternative measures of misfit between an observed fault datum and stress model 1 the pole rotation the angle between the observed and predicted slip direction on the observed fault plane and 2 the minimum rotation the smallest angle between the observed fault geometry and any fault geometry which is consistent with the model by allowing for variation of the fault plane as well as the slip vector the minimum rotation procedure generally achieves a more stable and presumably realistic estimate of the actual discrepancy between a fault observation and stress model than the pole rotation procedure in a test case using 17 earthquake focal mechanisms from the yuii region of eastern taiwan separate inversions based on the two misfit criteria yield different optimum stress models and uncertainty estimates additional constraints on the stress tensor such as the effect of friction can be superimposed on the ones used here

contrasting triggering mechanisms of the 2001 and 2002 2003 eruptions of mount etna italy abstract mount etna produced two significant eruptions in 2001 and 2002 2003 which we have analysed using geological seismic and deformation data these eruptions showed some similarities such as the activating of two magmatic plumbing systems central lateral and eccentric but they differed in their triggering mechanisms while the 2001 eruption was largely the result of the emplacement of a n s eccentric dike independent from the central conduits consistent with e w regional extension the 2002 2003 eruption occurred in response to a major flank slip on the eastern and southeastern sides of the volcano this is demonstrated by the spatial and temporal distribution of seismicity and deformation preceding and accompanying the two eruptions during the months prior to the 2001 eruption most epicenters were concentrated on the southern flank at depths of 5 15 km below sea level during the 4 days before the eruption earthquake hypocenters migrated to shallower levels from 5 km bsl upward indicating the emplacement of the eccentric dike this is confirmed by the patterns of ground fracturing observed in the field and deformation documented by electronic distance measurements edm in contrast the months before the 2002 2003 eruption were characterised by shallower seismicity mainly concentrated along the active faults bordering the slipping flank sector flank slip accelerated in september 2002 and a second more vigorous acceleration of flank slip occurred on 26 27 october 2002 accompanying the opening of eruptive vents the very short 2 h seismic crisis preceding the onset of eruptive activity stands in neat contrast with the 4 days of intense seismicity before the 2001 eruption subsequently flank slip deformation extended all over the eastern and southeastern flanks of the volcano causing serious damage in this sector the events of 2001 2003 can be seen as a continuous chain of intimately interacting processes including regional tectonics magma accumulation and eruption and flank instability in this scenario the 2001 eruption led to increased flank instability that subsequently accelerated and culminated with the massive flank slip which in turn facilitated the 2002 2003 eruption this sequence of events points to a long term feedback mechanism between magmatism and flank instability at etna

comparison of orientations of stress and strain tensors based on fault plane solutions in kaoiki hawaii the stress tensor orientation was estimated based on inversion from 238 first motion fault plane solutions of earthquakes with mostly m 3 5 0 6 located in the 10 km radius kaoiki crustal volume separate inversions for subvolumes containing 20 50 events yielded the same results in several adjacent volumes suggesting that the stress tensor is homogeneous in those parts of the kaoiki area and that the inversion results are stable and meaningful five spatial subsets of the data were found for which the orientation of at least one of the principal axes was different from that in the other sets by 20 80 and at confidence levels exceeding 95 the volcano summits of kilauea and mauna loa and their rift systems are identified as the source of stress in the kaoiki crust because the greatest principal stress points to kilauea and mauna loa in addition the strain tensor due to energy released by these 238 earthquakes was computed for the kaoiki area and several subvolumes of it by summing the moment tensors the moment tensor of each earthquake was constructed from the individual fault plane solutions and from an estimate of the scalar moment derived from the moment magnitude relationship a comparison of the directions of strain and stress tensors showed close agreement for subvolumes with predominantly strike slip faulting in these volumes the inversion process for stress directions led to misfits of approximately equal size for the conjugate near vertical nodal planes these observations are interpreted to show that in the strike slip regime of the upper part of the crust neither of the nodal planes is preferred for faulting rupture probably occurs along the nw and along the nh striking nodal planes in separate earthquakes subvolumes with more decollement faulting showed significant differences of 30 40 between the principal strain and stress directions in these volumes the near horizontal nodal planes showed noticeably smaller misfits in the inversion for the stress directions these facts are interpreted to indicate that the decollement plane is weak allowing slip on it even if the principal stresses are inclined at a large angle to it it is proposed that comparison of strain and stress tensor calculations may be able to differentiate between tectonic regimes uniform in strength no well developed fault plane and regimes in which a fault with low frictional strength dominates as a function of time significant rotations of the strain tensor by approximately 45 can be observed which seem to be related to the occurrences of kaoiki mainshocks during three background periods of about 7 years each the average strain tensor showed an orientation typical for predominant decollement faulting while two premainshock periods of 2 5 years each showed an orientation closer to strike slip faulting it is proposed that this pattern may be repeated before the next kaoiki mainshock the strain released seismically is less than the geodetically observed strain by approximately an order of magnitude stress strain fault plane solutions hawaii

volcano tectonic activity along structures of the unstable ne flank of mt etna italy and their possible origin abstract we describe the prehistoric historic activity of the main and minor volcano tectonic structures of the northeastern flank of mt etna giving new data which provide a clearer view of how destabilized volcanoes react to magma pressure and gravity forces data are mostly based on new lithostratigraphic surveys and on offset measurements of late pleistocene holocene deposits and historic man made features the north east rift ne rift is a volcanic rift that has guided mostly explosive but also secondary effusive activity since the end of the pleistocene monogenetic cones and explosive craters are strongly elongated and aligned along 66 main surface fractures and several others hidden but inferred from sinkhole alignments the opening direction is locally oblique with a left lateral component in the north eastern segment of the rift at the ne tip of the rift the movements are relieved by the normal left lateral pernicana fault pf an 11 km long structure comprising e w fault segments connected by right stepping en echelon faults our study demonstrates that the very high slip rates at a centennial scale of these structures are well constrained and similar ne rift 0 6 1 8 cm a pf 0 5 2 2 cm a and have been also recognized in the latest pleistocene holocene 2 7 cm a the e w fiumefreddo fault ff has normal left lateral kinematics and a historic slip rate of 0 1 cm a ripa della naca faults strike ne and are covered by unfaulted

new integrated geodetic monitoring system at stromboli volcano italy stromboli is a composite volcano forming the northernmost island of the aeolian archipelago volcanic arc tyrrhenian sea on december 28th 2002 lava flows outpoured from the northern wall of the ne crater and descended into the sciara del fuoco sdf a deep depression marking the nw flank of the volcano edifice on december 30th 2002 two landslides occurred on the northern part of the sdf they moved a mass in the order of tens of millions of cubic meters both above and below sea level the landslide produced a tsunami causing significant damage to the eastern coast of the island reaching the other aeolian islands and the sicilian and southern italian coasts this event led to the upgrading of the ground deformation monitoring system already existing on the island the new requirement was the real time detection of the deformations related to potential slope failures of the sdf to this end a remotely controlled monitoring system based both on gps and geodetic techniques was planned and set up in a few months the new monitoring system allowed to continuously measure the ground deformations occurring on the sdf by integrating both terrestrial and satellite geodetic techniques although this system was severely damaged during the 7 month long eruption it allowed to monitor important eruptive phases for the first time an accurate data set on the actual mass movements of the sdf and the crater area was available it provided data that significantly supported the civil protection authorities in making decisions and constrains theories related to landslide movements and volcanic activity after the end of the eruption the system was overhauled in order to optimize the instruments and set up a monitoring system aimed at measuring deformations forecasting other flank collapses

reconstructed oceanic plate stratigraphy of the ino formation in the ino district kochi prefecture central shikoku japan abstract the ino formation which has been regarded as a member of the kurosegawa terrane is distributed in the ino district central shikoku japan it is composed of metamorphosed and unmetamorphosed rocks radiolarians in the late triassic to early jurassic strata are found in the unmetamorphosed components the late triassic radiolarians were collected from chert and siliceous mudstone the early jurassic radiolarians are discriminated from the siliceous mudstone and mudstone samples based on chronological data and findings from previous studies the oceanic plate stratigraphy ops of the unmetamorphosed part of the ino formation is reconstructed as follows late carboniferous to late triassic or earliest jurassic bedded chert late triassic late carnian to early jurassic siliceous mudstone and early jurassic mudstone in ascending order based on this observation it is confirmed that the unmetamorphosed part of the ino formation is an early jurassic accretionary complex its origin can be attributed to the chichibu terrane the reconstructed ops of the unmetamorphosed part of the ino formation is possibly correlated to the yusugawa sumaizuku and kamiyoshida units of the northern chichibu terrane or the unknown oldest unit of the southern chichibu terrane

deformation and eruptions at mt etna italy a lesson from 15 years of observations this work was partly funded by ingv and the italian dpc and was supported by asi the preview project and crdc amra dpc ingv flank project providing the funds for the publication fees

insight into mt etna italy kinematics during the 2002 2003 eruption as inferred from seismic stress and strain tensors 1 seismic activity linked to the 2002 03 mt etna eruption was investigated by analyzing the md 2 3 earthquakes the results of 3d relocation were used to compute fault plane solutions and a selected dataset was inverted to determine stress and strain tensors the analysis revealed a complex kinematic response of the eastern flank dominated by fast stress propagation and reorientation we hypothesize that a vertical dike intruded the southern flank generating an extensional regime that triggered a radial intrusion in the northeast sector of the volcano the combined effects gave rise to a rotation of the stress tensor that controlled the activation of the pernicana fault system the volcanic and tectonic interactions produced a second reorientation of the stress tensor causing a structural response in the southeast lower flank the overall result of the deformation processes observed during the eruption was an e w extension on the eastern flank of the volcano

structural features of the july august 2001 mount etna eruption evidence for a complex magma supply system we describe the evolution of the volcanic activity and deformation patterns observed at mount etna during the july august 2001 eruption seismicity started at 3000 m below sea level on 13 july accompanied by moderate ground swelling ground deformation culminated on 16 july with the development of a ne sw graben c 500 m wide and c 1 m deep in the cisternazza area at 2600 2500 m above sea level on the southern slope of the volcano on 17 july the eruption started at the summit of mount etna from the se crater central lateral eruptive system from which two radial c 30 m wide c 3000 m long fracture zones associated with eruptive fissures propagated both southward 17 july and northeastward 20 july on 18 july a new vent formed at 2100 m elevation at the southern base of the montagnola followed on the next day by the opening of a vent further upslope at 2550 m eccentric eruptive system the eruption lasted for 3 weeks approximately 80 of the total lava volume was erupted from the 2100 m and the 2550 m vents the collected structural data suggest that the cisternazza graben developed as a passive local response of the volcanic edifice to the ascent of a north south eccentric dyke which eventually reached the ground surface in the montagnola area 18 19 july in contrast the two narrow fracture zones radiating from the summit are interpreted as the lateral propagation from the conduit of the se crater of north south and ne sw oriented shallow dykes 2 3 m wide the evolution of the fracture pattern together with other volcanological data magma ascent and effusion rate eruptive style petrochemical characteristics of the erupted products and petrology of xenoliths within magma suggest that the eccentric and central lateral eruptions were fed by two distinct magmatic systems examples of eccentric activity accompanied by central lateral events have never been described before at etna

a past giant lateral collapse and present day flank instability of fogo cape verde islands fogo island is a large and extremely steepsided oceanic island volcano in the cape verde archipelago it has a large ca 9 km across east facing summit collapse structure the monte amarelo collapse with a probable volume of at least 150 200 km3 for most of its history the monte amarelo volcano had a small but productive central vent complex and radial rift zones fed by laterally propagating dykes shortly before the collapse the latter were replaced by north south trending arrays of en echelon vertically propagating dykes since the monte amarelo collapse the scar has partly filled with a new volcano the cha das caldeiras volcano the summit cone of this volcano the pico do fogo is a very young feature but has been abandoned in the most recent phase of activity from the 18th century onwards the same period has also seen the abandonment of earlier radial rift zones with laterally propagating dykes and their replacement with en echelon arrays of vents fed by vertically propagating dykes these form an n s trending array within the older collapse structure and are associated with seaward displacement of the eastern flank of the volcano within the old collapse structure the most recent eruptions those of 1951 and 1995 appear to be associated with episodes of flank instability manifested in n s surface fissuring and east facing normal faults these recent structural changes in the volcano parallel those which took place in the monte amarelo volcano prior to its collapse

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

structural features of an active strike slip fault on the sliding flank of mt etna italy abstract the strike slip pernicana fault system pfs was activated along the eastern flank of mt etna during an earthquake in september 2002 and one month later during the eruption of the ne rift structural and volcanological data suggest that the pfs was activated as a result of the slide of the ne flank of etna this activation produced surface fracturing on walls and on paved and unpaved roads the segments of the pfs arranged in a right stepping en echelon configuration show a an inverse proportion between length and frequency b fractal behavior over scales of 10 2 10 1 m between their length overstep and overlap c consistent strike with regard to their fault array and d a progressive eastward decrease in the displacement along the smallest faults the consistent geometric and kinematic features of the pfs related to the sector collapse of etna are similar to those of faults in strike slip settings

seismogenic stress field beneath mt etna south italy and possible relationships with volcano tectonic features abstract shallow shear type seismic activity occurring beneath the etna volcano during 1990 1995 has been analysed for hypocenter locations focal mechanisms and stress tensor inversion the results have been examined jointly with electronic distance measurements and tiltmeter data collected in the same period and reported in the literature significant seismicity located in the upper 10 km was found to be confined to the time intervals in which ground deformation data indicated inflation of the volcano edifice e g the periods preceding the december 1991 march 1993 and august 1995 march 1996 eruptive phases the shocks mostly occurred in a sector approximately centered on the crater area and elongated in the east west direction the causative seismogenic stress shows a low dip east west orientation of 1 in agreement with existing knowledge on relationships between local fault systems and magma uprise processes the shallow seismicity in question is tentatively explained as being due to lateral compression by magma inside a nearly north south system the volcano deflation phase revealed by electronic distance measurements and tilt data during the 1991 1993 major eruption was not accompanied by any significant shear type shallow event below the depth of 10 km the north south prevailing orientation of 1 reflects the dominant role of the regional stress

volcanological inferences from seismic strain tensor computations at mt etna volcano sicily kostrov s 1974 algorithm for seismic strain tensor computations in the version implemented by wyss et al 1992a for error estimates has been applied to shear type earthquakes occurring beneath the etna volcano during 1990 1996 space time variations of strain orientations and amplitudes have been examined jointly with ground deformation and gravimetric data collected in the same period and reported in the literature taking also into account the information available from volcanological observations and structural geology we propose a model assuming that hydraulic pressure by magma emplaced in nearly north south vertical structures produces the e w orientation of the maximum compressive strain found in the upper 10 km beneath the crater area in contrast regional tectonics deriving from the slow north south convergence between the african and european plates appear to play a dominant role in the generation of stress and strain fields at crustal depths deeper than 10 km below the volcano according to our interpretation the progressive ascent of magma through the upper crust prior to eruption produces the observed gravity changes cone inflation and unusual seismic strain rate in the upper 10 km associated with a more sharply defined seismic deformation regime i e very small confidence limits of the e1 orientation in agreement with this model deflation revealed by ground deformation data during the course of the major 1991 1993 eruption was accompanied by a practically nil level of shallow seismicity

the role of the pernicana fault system in the spreading of mt etna italy during the 2002 2003 eruption flank instability and collapse are observed at many volcanoes among these mt etna is characterized by the spreading of its eastern and southern flanks the eastern spreading area is bordered to the north by the e w trending pernicana fault system pfs during the 2002 2003 etna eruption ground fracturing along the pfs migrated eastward from the ne rift to as far as the 18 km distant coastline the deformation consisted of dextral en echelon segments with sinistral and normal kinematics both of these components of displacement were one order of magnitude larger 1 m in the western previously known portion of the pfs with respect to the newly surveyed 9 km long eastern section 0 1 m this eastern section is located along a pre existing but previously unknown fault where displaced man made structures give overall slip rates 1 1 9 cm year only slightly lower than those calculated for the western portion 1 4 2 3 cm year after an initial rapid motion during the first days of the 2002 2003 eruption movement of the western portion of the pfs decreased dramatically while parts of the eastern portion continued to move these data suggest a model of spreading of the eastern flank of etna along the pfs characterized by eruptions along the ne rift instantaneous short lived meter scale displacements along the western pfs and more long lived centimeter scale displacements along the eastern pfs the surface deformation then migrated southwards reactivating one after the other the nnw sse trending timpe and trecastagni faults with displacements of 0 1 and 0 04 m respectively these structures along with the pfs mark the boundaries of two adjacent blocks moving at different times and rates the new extent of the pfs and previous activity over its full length indicate that the sliding eastern flank extends well below the ionian sea the clustering of seismic activity above 4 km b s l during the eruption suggests a deep decollement for the moving mass the collected data thus suggests a significant movement volume 1 100 km3 of the eastern flank of etna both on shore and off shore

tectonic control on the eruptive dynamics at mt etna volcano sicily during the 2001 and 2002 2003 eruptions abstract the eruptive events of the july august 2001 and october 2002 january 2003 at mt etna provide new insights for reconstructing the complex geometry of the feeding system and their relationship to regional tectonics the 2001 eruption took place mainly on the upper southern sector of the volcano the eruption was preceded by a large earthquake swarm for a few days before its onset and accompanied by ground deformation and fracturing the development of surface cracking along with the seismic pattern has allowed us to recognize three distinct eruptive systems the sw ne nnw sse and n s systems which have been simultaneously active such eruptive systems are only the upper portions of a complex feeding system that was fed at the same time by two distinct magmas the sw ne and nnw sse systems connected with the se crater conduit were fed by magma coming from depth whereas the n s system served instead as an ascending pathway for an amphibole bearing magma residing in a shallow reservoir the eruptive activity started again on october 2002 on the ne rift zone where about 20 eruptive vents were aligned between 2500 and 1900 m a s l and on the southern flank from the central crater to the montagnola the onset of eruptive activity was accompanied by a seismic swarm as in the 2001 eruptive event two independent feeding systems formed characterized by distinct magmas the sw ne system controlled the feeding of the northeast rift and was accommodated by left lateral displacement along the wnw ese trending pernicana fault the n s system fed the eruptions on the southern flank moreover the associated crustal deformation triggered seismic reactivation of tectonic structures in the eastern flank of the volcano and offshore these two last eruptions indicate that at mt etna the ascent of magma as well as the accommodation of deformation is strongly dominated by local extensional structures that are connected to a regional tectonic regime

catastrophic collapse of the volcanic island of hierro 15 ka ago and the history of landslides in the canary islands landslides play an important role in the evolution of many volcanic islands producing huge fields of blocky volcanic debris on their submarine slopes sidescan sonar images presented in this paper provide evidence for a large debris avalanche el golfo on the northern flank of hierro island in the canary islands angular blocks as much as 1 2 km across and 200 m high cover the debris avalanche surface el golfo avalanche is related to both the canary debris flow and a volcaniclastic turbidite found in the madeira abyssal plain 600 km west of the canaries dating of the turbidite and the failure scarp onshore indicates that the failure probably occurred between 13 and 17 ka there appears to be a general correlation between volcaniclastic turbidites in the abyssal plain sequence and landslides in the canaries during the past 750 ka tentatively this correlation suggests that seven major landslides have affected the canaries in that time

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

recognizing oib and morb in accretionary complexes a new approach based on ocean plate stratigraphy petrology and geochemistry abstract we present a new approach for recognizing the origin of accreted basaltic rocks based on ocean plate stratigraphy ops and on the petrology and geochemistry of basalts from mid oceanic ridges morb and oceanic islands oib using examples from four accretionary complexes ac in sw japan akiyoshi mino tamba chichibu and shimanto the key to the problem is the model of ops which includes an association of igneous and sedimentary rocks that form on an oceanic plate during its travel from a mid oceanic ridge to a subduction zone we propose the reconstruction of the tectonic settings of basalts according to their relationships with associated ops sediments their petrogenesis and their geochemical features five types of ops are recognized in the accretionary complexes of sw japan 1 sandstone shale 2 sandstone shale and chert 3 sandstone shale chert and morb 4 sandstone shale chert morb and gabbro peridotite 5 seamount ops including oib cap carbonates slope clastics and basal shale chert the alkaline tholeiitic or calc alkaline composition of basaltic melts which are typical of oceanic islands mid oceanic ridges and island arcs respectively can be identified by the sequence in crystallization of their major phenocrysts i e olivine ol clinopyroxene cpx and plagioclase pl and by their compositions alkaline and calc alkaline mafic lavas are characterized by an ol cpx pl succession whereas tholeiitic melts by their ol pl cpx succession titanium rich minerals e g ti augite kaersutite ti biotite are typical of alkaline lavas the application of geochemistry based tectonic discrimination diagrams is also a powerful tool if not supported by geological and petrological data may result in confusion due to magma contamination post magmatic alteration and secular change of mantle thermal conditions we propose that a direct comparison of normalized multi element patterns and key binary plots from older volcanic rocks with their modern analogues provides a more viable and reliable method of basalt discrimination our ops petrology geochemistry method allows us to confirm the above conclusions that the lavas of the akiyoshi mino tamba and southern chichibu ac formed in oceanic islands because they are associated with seamount ops sediments crystallized from ol to cpx and pl contain ti augite and kaersutite and are enriched in tio2 lree and nb in this paper we present geochemical data from the inuyama basalts of the mino tamba ac and from the toba complex in the huge mikabu greenstone belt of the chichibu ac the inuyama basalts are in contact with jurassic pelagic cherts but their geochemical features are confusing they contain phenocrysts of ol ti augite and kaersutite and therefore probably formed in seamounts the toba volcanic rocks are a part of the huge ophiolite belt they have flat to slightly lree enriched ree patterns are characterized by an ol cpx succession of phenocrysts and they plot in the oib field in binary plots suggesting they formed in an oceanic plateau

tectono stratigraphy and low grade metamorphism of late permian and early jurassic accretionary complexes within the kurosegawa belt southwest japan implications for mechanisms of crustal displacement within active continental margin abstract we characterize the tectono stratigraphic architecture and low grade metamorphism of the accretionary complex preserved in the kurosegawa belt of the kitagawa district in eastern shikoku southwest japan in order to understand its internal structure tectono metamorphic evolution and assessments of displacement of continental fragments within the complex we report the first ever documented occurrence of an early jurassic radiolarian assemblage within the accretionary complex of the kurosegawa belt that has been previously classified as the late permian accretionary complex thus providing a revised age interpretation for these rocks the accretionary complex is subdivided into four distinct tectono stratigraphic units late permian melange and phyllite units and early jurassic melange and sandstone units the stratigraphy of these four units is structurally repeated due to an e w striking steeply dipping regional fault we characterized low grade metamorphism of the accretionary complex via illite crystallinity and raman spectroscopy of carbonaceous material the estimated pattern of low grade metamorphism showed pronounced variability within the complex and revealed no discernible spatial trends the primary thermal structure in these rocks was overprinted by later tectonic events based on geological and thermal structure we conclude that continental fragments within the kurosegawa belt were structurally translated into both the late permian and early jurassic accretionary complexes which comprise a highly deformed zone affected by strike slip tectonics during the early cretaceous different models have been proposed to explain the initial structural evolution of the kurosegawa belt i e micro continent collision and klippe tectonic models even if we presuppose either model the available geological evidence requires a new interpretation whereby primary geological structures are overprinted and reconfigured by later tectonic events

type of faulting and orientation of stress and strain as a function of space and time in kilauea s south flank hawaii earthquake focal mechanisms of events occurring between 1972 and 1992 in the south flank of kilauea volcano hawaii are used to infer the state of stress and strain as a function of time and space we have determined 870 fault plane solutions from p wave first motion polarities for events with magnitudes m l 2 5 and depth ranging between 6 and 12 km faulting is characterized by a mixture of decollement reverse and normal faults most large earthquakes with magnitude m 7 rupture the decollement plane since it is the only surface large enough to generate magnitude 7 or larger earthquakes the percentage of reverse faulting events is high compared to the decollement and normal faulting mechanisms for the period 1972 1983 the percentage of decollement type focal mechanisms becomes dominant after 1983 this pattern of faulting activity suggests that pressure was building up within kilauea s rift zone prior to the 1983 puu oo eruption overall a single stress orientation with the maximum compressive stress oriented se perpendicular to the rift and dipping at 45 is compatible with the coeval existence of decollement reverse and normal faults however in a crustal volume east of longitude 155 10 w we find a change of the orientation of 1 from nearly horizontal to plunging 45 se occurring in 1979 this stress rotation suggests magma movements within the aseismic part of kilauea s east rift zone the strain and stress orientations are coaxial in the south flank except within the volume where the stress rotation is observed we observe a change in the relationship between stress and strain directions caused either by the shifting of seismic activity from reverse faults to decollements while stress stays constant or by a rotation of stress while strain remains constant assuming that the model of a noncohesive coulomb wedge is appropriate for kilauea s south flank we find that high pore pressures are prevalent along the decollement and within the wedge for a coefficient of friction equal to 0 85

a syn eruptive ground deformation episode measured by gps during the 2001 eruption on the upper southern flank of mt etna ground deformation occurring on the southern flank of mt etna volcano during the july august 2001 eruption was monitored by gps measurements along an e w profile crossing the fissure system this profile was measured eight times during the eruption using the stop and go semi kinematic technique horizontal and vertical displacements between gps surveys are reported for each station the most significant event is a deformation episode occurring during the first week of the eruption between 25 27 july displacements were measured on benchmarks close to the eruptive fissure and the tensile 1989 fracture data inversions for measured displacements were performed using the okada model the model shows the narrowing of the 2001 dyke accompanied by a dextral dislocation along an east dipping fault parallel to the 1989 fracture