ground deformation patterns on mount etna 1992 to 1994 inferred from gps data in this paper ground deformation that occurred on mount etna from 1992 1994 is studied using gps data first problems relating to data processing of the 1993 and 1994 surveys carried out on the whole of the mount etna gps network are considered care has been paid to the network adjustment step particularly in evaluating effects of the reference frame stability in finding final solutions comparison between survey results allows us to invert the strain tensor and to compute displacement vectors the latter when fully constrained solutions are available the comparisons lead to the conclusion that during the 1992 1994 period at least two sources were active the first was related to a shallow dyke that produced the 1991 1993 eruptive fissures the second deeper source was depleted during the 1991 1993 eruption and recharged between 1993 and 1994 local ground movements correlate spatially and temporally with seismic phenomena

seismic activity accompanying the outbreak of the 1991 1993 eruption of mt etna italy abstract the character and location of seismic activity accompanying the onset of the 1991 1993 eruption at mt etna are compatible with the surface evidence of the volcanic pile rupture both the epicentral distribution and the focal mechanisms of a swarm that occurred on december 14 1991 agree with magma ascent occurring along the main nnw sse trending structure of the volcano and the consequent opening of a system of effusive fissures with the same trend a typical mainshock aftershock sequence recorded the day after and indicating transcurrent displacement occurring along the second principal structure of etna ne sw depicts the tectonic response of the volcanic pile and the underlying basement to major stresses applied by the magma push

new insights for the interpretation of ancient bog oak chronologies reactions of oak quercus robur l to a sudden peatland rewetting abstract subfossil bog oak material is an important palaeo climate and hydrology proxy for the holocene a correct interpretation of the subfossil material in terms of growth and population dynamics requires understanding of the underlying processes the catastrophic rewetting after dyke failure of a drained peatland forest in ne germany provides a unique natural laboratory to calibrate bog oak growth pattern with a known event growth differences among groups of currently vital damaged and dead oaks in the years before the flooding were used to estimate the adaptation potential in dependence on age tree size competition class and groundwater table dendrochronological analysis of growth patterns and wood anatomical parameters revealed changes in the wood in reaction to sharp hydrological shifts drainage and rewetting group specific chronologies were contrasted against instrumental data to evaluate the influence of climate and hydrology on radial growth of oak groundwater table proved to be the overriding factor influencing oak growth at our site already during times of intensive drainage results show an influence of micro site conditions elevation above soil water level along with a higher chance for slower growing and possibly former suppressed trees to survive the catastrophic rewetting these trees display a typical ring pattern with four to five years of depressed growth and a subsequent recovery characterised by a significant increase in ring width especially in the earlywood trees that died or were damaged following the rewetting typically show strongly reduced latewood width before they gradually die off our findings are discussed with regard to the interpretation of subfossil bog oak material and a modified version of release detection analysis is proposed as a tool to sharpen the identification of hydrological shifts in bog oak material the results of the study can contribute to a better understanding of ecophysiological mechanisms underlying growth reactions and adaptation potential of oaks to prevailing high water levels

late quaternary slip rates on the acireale piedimonte normal faults and tectonic origin of mt etna sicily abstract mt etna is located along the east coast of sicily near the boundary between the continental crust of the hyblean plateau and the mesozoic oceanic crust of the ionian basin the main active faults near mt etna cut the base of its eastern flank forming a 30 km long system of nne and nnw trending ene chelon fault segments the acireale piedimonte system showing dip slip and oblique right lateral motion most segments are associated with shallow depth seismicity and all have late pleistocene to holocene vertical slip rates ranging between 1 and 2 mm yr typical of major active normal faults worldwide eruptive fissures arranged in nne to ne trending zones cut the highest slopes of the volcano on the footwall of the normal fault system structural analysis suggests that current motions along both the active faults and eruptive fissures are kinematically compatible and simply linked with ongoing wnw ese directed regional extension such extension characterizes at a greater scale the active tectonics of southern italy where all large shallow historical earthquakes have remained confined within a narrow normal fault belt or rift zone stretching from the northern calabrian arc to southeastern sicily the southernmost west dipping faults of that rift zone in calabria aspromonte cut across the calabro peloritan thrust belt to join the mostly east dipping acireale piedimonte faults along the western boundary of ionian oceanic lithosphere which continues southwards as the malta escarpment we thus relate magmatism at etna to dilational strain on the footwall of an east facing crustal scale normal fault at the bend where the siculo calabrian rift zone veers 60 eastwards as it begins to cross the calabrian arc leaving the east facing margin of the ionian sea to catch up with the west facing margin of the tyrrhenian sea farther north

long period events the most characteristic seismicity accompanying the emplacement and extrusion of a lava dome in galeras volcano colombia in 1991 abstract since its reactivation in 1988 the principal eruptions of galeras volcano occurred on may 4 9 1989 july 16 1992 and january 14 march 23 april 3 april 14 and june 7 1993 the initial eruption was a phreatic event which clearly marked a new period of activity a lava dome was extruded within the main crater in october 1991 and subsequently destroyed in an explosive eruption on july 16 1992 the eruptions that followed were all vulcanian type explosions the seismicity accompanying the emplacement extrusion and destruction of the lava dome was dominated by a mix of long period lp events and tremor displaying a variety of waveforms repetitive lp events with dominant periods in the range 0 2 1 s were observed in october and november 1991 and visually correlated with short energetic pulses of gas venting through a crack bisecting the dome surface each lp event was characterized by a weak precursory signal with dominant periods in the range 0 05 0 1 s lasting roughly 7 s using the fluid driven crack model of chouet 1988 1992 we infer that two distinct cracks may have acted as sources for the lp and precursor signals spectral analyses of the data yield the following parameters for the lp source crack length 240 360 m crack width 130 150 m crack aperture 0 5 3 4 mm crack stiffness 100 500 sound speed of fluid 880 m s and excess pressure 0 01 0 19 mpa similar analyses yield the parameters of the precursor source crack length 20 30 m crack width 15 25 m crack aperture 2 3 8 7 mm crack stiffness 5 15 sound speed of fluid 140 m s and excess pressure 0 06 0 15 mpa combined with geologic and thermodynamic constraints obtained from field observations these seismic parameters suggest a gas release mechanism in which the episodic collapse of a foam layer trapped at the top of the magma column subjacent to the dome releases a slug of pressurized gas which escapes to the surface while dilating a preexisting system of cracks in the dome structure accordingly the fracture observed on the crystallized dome body is the surface extension of the lp source crack where lp activity is induced by the rapid emission and expansion of gas flowing through this conduit the width and aperture of the crack estimated in the model are in good agreement with the length and aperture of the fracture estimated from visual observations the source parameters of the precursor signal are suggestive of a nozzle like conduit connecting the lp source crack to the underlying magma reservoir excitation of this conduit segment is attributed to the rapid emission and acceleration of the frothy fluid resulting from the collapse of the foam layer at the top of the reservoir the calculated periodicity of foam collapse events is in agreement with the observed average rate of thirteen lp events per hour

statistical forecasting of repetitious dome failures during the waning eruption of redoubt volcano alaska february april 1990 abstract the waning phase of the 1989 1990 eruption of redoubt volcano in the cook inlet region of south central alaska comprised a quasi regular pattern of repetitious dome growth and destruction that lasted from february 15 to late april 1990 the dome failures produced ash plumes hazardous to airline traffic in response to this hazard the alaska volcano observatory sought to forecast these ash producing events using two approaches one approach built on early successes in issuing warnings before major eruptions on december 14 1989 and january 2 1990 these warnings were based largely on changes in seismic activity related to the occurrence of precursory swarms of long period seismic events the search for precursory swarms of long period seismicity was continued through the waning phase of the eruption and led to warnings before tephra eruptions on march 23 and april 6 the observed regularity of dome failures after february 15 suggested that a statistical forecasting method based on a constant rate failure model might also be successful the first statistical forecast was issued on march 16 after seven events had occurred at an average interval of 4 5 days at this time the interval between dome failures abruptly lengthened accordingly the forecast was unsuccessful and further forecasting was suspended until the regularity of subsequent failures could be confirmed statistical forecasting resumed on april 12 after four dome failure episodes separated by an average of 7 8 days one dome failure april 15 was successfully forecast using a 70 confidence window and a second event april 21 was narrowly missed before the end of the activity the cessation of dome failures after april 21 resulted in a concluding false alarm although forecasting success during the eruption was limited retrospective analysis shows that early and consistent application of the statistical method using a constant rate failure model and a 90 confidence window could have yielded five successful forecasts and two false alarms no events would have been missed on closer examination the intervals between successive dome failures are not uniform but tend to increase with time this increase attests to the continuous slowly decreasing supply of magma to the surface vent during the waning phase of the eruption the domes formed in a precarious position in a breach in the summit crater rim where they were susceptible to gravitational collapse the instability of the february 15 april 21 domes relative to the earlier domes is attributed to reaming the lip of the vent by a laterally directed explosion during the major dome destroying eruption of february 15 a process which would leave a less secure foundation for subsequent domes

operation of a digital seismic network on mount st helens volcano and observations of long period seismic events that originate under the volcano during 1981 we operated with the cooperation of the u s geological survey a 9 station digital seismic array on mount st helens volcano in washington state one of our stations was placed inside the crater of the volcano six were located on the flanks of the volcano within two km of the crater and two were approximately ten km from the crater four of the instruments recorded three components of motion and the remaining five recorded only the vertical component in addition to the monitoring and recording performed by the digital instruments we carried out a one day experiment during which we complimented our crater monitoring seismometer by the addition of two ink recording instruments during the one day experiment we had six observers including 4 usgs scientists who had significant experience working and making observations in the crater recording times of rockfall felt earthquake occurrences and changes in steam emissions from the dome in the crater using information obtained during the one day experiment we are able to classify seismic events recorded by our digital instruments as earthquakes rockfalls helicopter noise and a type of event that is unique to volcanoes which we call long period waveforms of these long period events have a duration of up to 30 seconds and a spectrum that is peaked at approximately 2 hz the frequency at which the peak in the spectrum occurs is nearly the same at all stations which means that the unique waveform of long period events is due to a source effect not a path effect the peak frequency is fairly insensitive to the amplitude of the signal which means that the size of the source region is constant independent of the signal amplitude long period events were not felt and were accompanied by no visible changes inside the crater which lead us to conclude that they are some sort of seismic disturbance generated inside the volcano

a geoarchaeological reassessment of the co occurrence of the oldest acheulean and oldowan in a fluvial ecotone from lower middle bed ii 1 7ma at olduvai gorge tanzania the coexistence of the oldest acheulean and oldowan industries means that the appearance of the former cannot be due to an anagenetic development from the latter at olduvai gorge tanzania both industries are found within the same chronostratigraphic unit the lower augitic sandstone las 1 7 ma at hwk hwk e hwk ee oldowan and flk w and flk n acheulean recently mchenry and stanistreet 2018 and stanistreet et al 2018 have argued that the acheulean site of flk west is actually located within a more recent stratigraphic unit the middle augitic sandstone mas if so the acheulean could potentially have evolved from the oldowan anagenetically we test this hypothesis by reviewing the stratigraphy of the las from the hwk area to the flk w site hay s 1976 previous work stresses the continuity of the las from hwk ee to flk nn and stratigraphic and sedimentological evidence indicates that while the mas has eroded away the las is continuous throughout the study area according to hay 1976 uribelarrea et al 2017 and this work the las is present at hwk ee hwk e hwk hwk w flk s flk w flk n and flk nn the emergence of the acheulean at olduvai gorge ca 1 7ma and its coexistence with the oldowan thus demonstrates a cladogenetic rather than an anagenetic origin for the acheulean this has implications for the behavioral and biological interpretations of the origin and co existence of both types of industries

analysis of long period events recorded at mount etna italy in 1992 and their relationship to eruptive activity seismic activity recorded at mount etna during 1992 was characterized by long period lp events and tremor with fluctuating amplitudes these signals were associated with the evolution of the eruptive activity that began on december 14 1991 following the occurrence of numerous volcano tectonic earthquakes at the onset of the eruption lp events dominated the overall seismicity starting in january 1992 the lp activity occurred primarily in swarms which were temporally correlated with episodic collapses of the crater floor in the northeast crater source depths determined for selected lp events suggest a source region located slightly east of northeast crater and extending from the surface to a depth of 2000 m based on the characteristic signatures of the time series four families of lp events are identified each family shares common spectral peaks independent of azimuth and distance to the source these spectral features are used to develop a fluid filled crack model of the source we hypothesize that the locus of the lp events represents a segment of the magma feeding system connecting a depressurizing magma body with a dike extending in the sse direction along the western wall of valle del bove toward the site of the mount etna eruption we surmise that magma withdrawal from the source volume beneath northeast crater may have caused repeated collapses of the crater floor some collapse events may have produced pressure transients in the subjacent dike which acted as seismic wave sources for lp events

geo archaeological and geometrically corrected reconstruction of the 1 84 ma flk zinj paleolandscape at olduvai gorge tanzania a geomorphological sedimentological stratigraphic and geometric study of 30 trenches excavated around flk zinj bed i olduvai gorge has enabled the partial reconstruction of the paleolandscape surrounding this site for a radius of 1000 m this is the largest sample of geological and archaeological information yet available to reconstruct the topography ecology and geomorphology of the zinj paleosurface and the hominin activities preserved within it contrary to previous interpretations which place flk zinj on an isolated and narrow peninsula it appears that the site was located on the edge of an elevated platform traceable for hundreds of meters hominins created flk zinj and other sites such as the recently discovered ptk and amk within the wooded habitats of this platform rather than the more open and grassy environments situated on lower portions of the lacustrine floodplain input areas probably in the form of alluvial fans existed to the south following a north south direction these input areas are partially responsible for changes in the type sequence restricted erosion documented on the wooded platform was mostly caused by runoff processes an archaeological study of the excavated trenches reveals a sharp contrast in fossil and stone tool density between flk zinj and the surrounding landscape further supporting the contention that the site may have acted as a central place where repeated carcass transport butchery and consumption took place taphonomic studies indicate that at this stage of human evolution hominins had primary access to carcasses and were not dependent on other carnivores for obtaining meat

deflation of mount etna monitored by spaceborne radar interferometry ground based measurements of volcano deformation can be used to assess eruptive hazard but require the costly and often hazardous installation and maintenance of an instrument network here we show that spaceborne radar interferometry which has already shown its utility in mapping earthquake related deformation1 can be used to monitor long term volcano deformation two families of synthetic aperture radar images acquired from ascending and descending orbits by the satellite ers 1 and looking at mount etna from opposite sides cover the time period from 17 may 1992 to 24 october 1993 and include the second half of etna s most recent eruption despite artefacts of the interferometric technique we can observe a volcano wide deflation which is an expected consequence of the eruption but which had not previously been appreciated we quantify it using a simple model based on the change of pressure in a sphere located in an elastic half space the modelled deformation increases linearly with time until the end of the eruption our results show that it will be possible to use this technique to detect the inflation of volcanic edifices that usually precedes eruptions

paleoecological reconstructions of the bed i and bed ii lacustrine basins of olduvai gorge tanzania and insights into early human behavior abstract the archaeological record of olduvai gorge has played a pivotal role in reconstructions of early human behavior classical oldowan sites from middle bed i and the extensive archaeological record from bed ii including the earliest acheulian at 1 7 ma enable the reconstruction of early human behavior throughout its evolution from almost 1 9 ma to 1 3 ma how such behavioral evolution was influenced by ecological factors is still an object of debate this special issue presents a detailed meso scale reconstruction of the paleoecology and paleogeography of the environments where some of these sites were formed including extensive reconstructions of the paleobotany of the sites and the areas surrounding them this provides for the first time a contextual ecological information framed in a scale large enough to understand human behavioral variability as determined by the exceptional ecological conditions of the olduvai paleo lake basin for almost one and a half million years this information is crucial to understand site functionality and the behaviors exhibited by hominins at each of the anthropogenic sites from olduvai gorge during the earliest stages of the evolution of the genus homo

mechanisms of magma eruption and emplacement at mt etna between 1989 and 1992 the present eruption sequence of mt etna began during september 1989 with extensive fracturing and culminated in 1991 93 with the largest lava eruption this century1 here we present measurements of gravity and ground deformation which in conjunction with seismic data provide a detailed record of the processes occurring before and during eruption these reflect a complex interplay between magma injection into the paths of lowest compressive stress through the volcano flanks forcing elastic deformation and fracture growth in response to gravitational stresses we find that after the end of the eruptive activity in 1989 fractures in the south southeast flank of the volcano remained unfilled until some months before the 1991 93 eruption these results indicate the utility of microgravity monitoring as the precursory processes that we identify were largely undetected by seismic and ground deformation monitoring

the global positioning system as a useful technique for measuring ground deformations in volcanic areas abstract in this paper the global positioning system technique for measuring ground deformations in volcanic areas is presented after an outline of the mathematical background the results of three years experience regarding the use of this technique on mt etna are reported the ground deformation patterns recorded between 1989 and 1991 are shown and discussed in the geodynamic framework which characterized mt etna in the time interval considered attention is focused on modeling a ground deformation episode which occurred on mt etna between 1990 and 1991 which contributed to characterizing the dynamic framework where the 1991 1992 eruptive event took place the deformation pattern mentioned has been interpreted by using a dislocation model the optimal solution for the inversion problem has been found by using an optimization approach based on the simplex method this solution agrees with the regional stress field whose compressive direction is nne ssw oriented

effects of magma storage and ascent on the kinetics of crystal growth the size distributions of crystals of olivine plagioclase and oxides of the 1991 93 eruption at mt etna italy are analyzed the simultaneous collection of this information for different minerals gives precious insight into the cooling history of lavas three distinct episodes are detectable a storage of the magma in a deep reservoir characterized by nearly constant and low nucleation and growth rates near to equilibrium an ascent phase with an ever increasing nucleation rate related to volatile exsolution and finally a quenching phase in addition to geochemical and geophysical evidence the similarity of the crystal size distributions of the present eruption with those of previous ones of this century makes it possible to exclude that crystal size distributions of etnean lavas are due to mixing of different populations this strongly suggests that the main features of the volcano feeding system have not changed despite observed variations in the magma output rates

a reconstruction of the paleolandscape during the earliest acheulian of flk west the co existence of oldowan and acheulian industries during lowermost bed ii olduvai gorge tanzania abstract based on detailed stratigraphic correlation and framework studies for flk w in lowermost bed ii and containing the oldest acheulian artifacts dated to 1 7 ma in olduvai gorge it is possible to document significant changes in the paleolandscape this study uses outcrops up to 1 6 km from the flk w locality to aid in the understanding of the environmental setting available to acheulian tool makers the reconstruction of the flk w isochronal paleosurface also provides a means to correlate flk w with other contemporary sites found at other lowermost bed ii localities these sites such as hwk hwk e and hwk ee are associated with oldowan artifact assemblages the reconstruction of the sedimentary environment and geomorphology of the paleosurface indicates these sites are all part of the same fluvial system although located at different sections along its course the oldowan levels are found in a set of small shallow braided channels the acheulian artifacts are associated with a deeper wider channel formed by the merging of several channels within the drainage network based on this analysis water may have been more readily available at flk w and there might have also been a thicker vegetation cover when compared to the oldowan localities the sedimentologic and geomorphic contexts appear to help explain the typological technological variability observed within this section of bed ii

characteristics of seismic waves composing hawaiian volcanic tremor and gas piston events observed by a near source array a correlation method specifically designed for describing the characteristics of a complex wave field is applied to volcanic tremor and gas piston events recorded by a semicircular array of geos instruments set at the foot of the puu oo crater on the east rift of kilauea volcano hawaii the spatial patterns of correlation coefficients obtained as functions of frequency for the three components of motion over the entire array are similar for gas piston events and tremor and clearly depict dispersive waves propagating across the array from the direction of puu oo the wave fields are composed of comparable amounts of rayleigh and love waves propagating with similar and extremely slow phase velocities ranging from 700 m s at 2 hz to 300 m s at 8 hz the highly cracked solidified lava flow on which the array was deployed and subjacent structure of alternating lava and ash layers formed during repeated eruptions of puu oo since 1983 appear to be responsible for the low velocities observed the results from puu oo stand in sharp contrast to those obtained in an experiment conducted in 1976 on the partially solidified lava lake of kilauea iki rayleigh waves were not observed in kilauea iki but well developed trains of love waves were seen to propagate there with velocities twice as high as those observed near puu oo these differences in the propagation characteristics of surface waves at the two sites may be attributed to the presence of a soft horizontal layer of molten rock in kilauea iki which may have lowered the phase velocity of rayleigh waves more drastically than that of love waves resulting in severe scattering of the rayleigh wave mode on the other hand the thin superficial pahoehoe flow under our array at puu oo may have favored the development of vertical columnar joints more extensively at this location than at kilauea iki which may have reduced the shear moduli controlling the love wave mode the average phase velocities in the frequency band from 2 to 5 hz found at puu oo are roughly similar to those determined for tremor at klyuchevskoy volcano kamchatka but the frequency dependence appears much stronger at puu oo

ignimbrite depositional facies the anatomy of a pyroclastic flow a model is presented for the depositional regimes in a pyroclastic flow to explain the origin of facies in the taupo ignimbrite and to compare these with other published examples in this model a pyroclastic flow consists of a head a body and a tail the head which is where fluidization caused by air ingestion occurs generates layer 1 deposits on lithological grounds these are divided into layers 1 p which is fines depleted and rich in pumice and 1 h which is fines depleted and rich in lithics and crystals layer 1 p represents material thrown forwards from the flow head and is termed the jetted deposits layer 1 h represents material sedimented from within the flow head and is termed the ground layer the body represents the bulk of the flow and the tail is its trailing part which is slowed by ground friction these parts generate the layer 2 deposits which include the valley pond ignimbrite and its associated ignimbrite veneer deposit localized depositional modes within the body and tail generate distinctive coarse pumice concentration zones and pumiceous lee side lenses behind obstacles at its outer limits all of the flow on interfluves is affected by air ingestion fluidization producing the distant facies which combines features of both layer 1 and 2 deposits one important conclusion of this work is that the thicknesses and compositions of the various facies are not related in any simple way to the thickness and composition of the parent flow

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

geochemical fingerprints for olduvai gorge bed ii tuffs and implications for the oldowan acheulean transition bed ii is a critical part of early pleistocene olduvai gorge tanzania its deposits include transitions from humid to more arid conditions with associated faunal changes from homo habilis to erectus and from oldowan to acheulean technology bed ii 1 8 1 2 ma is stratigraphically and environmentally complex with facies changes faulting and unconformities making site to site correlation over the 20 km of exposure difficult bed ii tuffs are thinner less evenly preserved and more reworked than those of bed i five marker tuffs tuffs iia iid bird print tuff bpt plus local tephra were collected from multiple sites and characterized using stratigraphic position mineral assemblage and electron probe microanalysis of phenocryst feldspar hornblende augite titanomagnetite and glass where available composition lowermost bed ii tuffs are dominantly nephelinitic middle bed ii tuffs bpt tuff iic have basaltic components and upper bed ii tuff iid is trachytic the bpt and tuff iid are identified widely using phenocryst compositions high ca plagioclase and high ti hornblende respectively though iid was originally hay 1976 misidentified as tuff iic at loc 91 shk annexe in the side gorge this work helps establish a high resolution basin wide paleolandscape context for the oldowan acheulean transition and helps link hominin faunal and archaeological records

high precision relative locations of earthquakes at mount st helens washington several earthquake sequences have occurred at mount st helens as clusters of shallow events with nearly identical waveforms multiplets we present a technique that allows the relative relocation of events within a multiplet to at least an order of magnitude higher precision than is typically possible with traditional techniques a multiplet is studied in pairs of events called doublets each doublet is made up of a reference event and one other event from the multiplet the cross spectrum of a short window beginning just before the p arrival is used to compute differences in arrival times between seismograms from the same station for each doublet these time differences computed with a precision of 1 2 ms are then used to locate each earthquake relative to the reference event engineering explosions with well known locations are used to test the relocation technique explosions can be relocated with accuracy better than 20 m for events within 250 m of the reference explosion the relocation technique is applied to earthquakes preceding the september 10 1984 and the may june 1985 dome building eruptions of mount st helens forty events that occurred during a 12 hour period in september 1984 are located in a volume approximately 30 m in diameter beneath the lava dome the earthquakes following the extrusion do not occur in multiplets and appear to be distributed over a much larger volume in the may june 1985 eruption we recognize three multiplet sets that took place successively in time the multiplets are interpreted as repeated failure or slip within a relatively small volume due to high strain rates around the magma supply conduit

seismological significance of the 1977 1978 eruptions and the magma intrusion process of usu volcano hokkaido abstract an earthquake swarm and the major pumice eruptions in august 1977 which followed marked the start of the dacitic doming activity of usu volcano in southwestern hokkaido japan the sequence of magma intrusion processes was investigated in detail by means of seismological and other geophysical data the distribution of the abundant hypocenters shows clearly an earthquake free zone beneath the summit crater the hypocenters migrated in a manner consistent with the development of the observed asymmetrical surface deformations considered due to magma intrusion into this earthquake free zone the earthquake mechanism solutions are mostly of dip slip type and are interpreted in terms of the doming deformations the existence of earthquake families earthquakes with similar waveforms is the main cause of the peculiar occurrence of earthquakes in space time and magnitude the concept of scattered barriers of different sizes and strengths can explain well the distinct characteristics of the occurrence of the swarm and the observed episodic deformations

paleoenvironments of the earliest stone toolmakers gona ethiopia fluvio lacustrine sediments of the hadar and busidima formations along the northern awash river ethiopia archive almost three million years 3 4 to 0 6 ma of human evolution including the earliest documented record of stone toolmaking at 2 5 2 6 ma this paper brings together sedimentologic and isotopic evidence for the paleoenvironmental context of early hominids from both formations but with particular emphasis on the setting for the early toolmakers the pre 2 92 ma record hadar formation is characterized by low gradient fl uvial paludal and lacustrine deposition in an undissected topography most analogous to reaches of the modern middle awash river near gewane the gona area experienced repeated deep dissection and aggradation by the awash river starting between 2 92 and ca 2 7 ma and continuing through the top of the record at 0 6 ma busidima formation each aggradational succession is 10 20 m in thickness and fi nes upward from wellrounded conglomerates at the base to capping paleosols at the top during this period the ancestral awash represented by these fi ning upward sequences was dominantly meandering and fl owed northeast as it does today smaller channels tributary to the axial awash system are also extensively exposed in the busidima formation compared to the axial system conglomerates the tributary channels transported fi ner less mature volcanic clasts mixed with abundant carbonate nodules reworked from adjacent badlands stone artifacts oldowan 2 6 2 0 ma at the oldest archaeological sites are only associated with the axial awash system in the bedded silts or capping paleosols of the fi ning upward sequences the implements were made from rounded cobbles from the channels but manufacture and use of the tools was always away from the channel bars on the nearby sandy banks and silt dominated fl oodplains archaeological sites higher in the record acheulian 1 7 ma occur in similar axial river contexts as well as along tributary channels further removed from artifact raw material sources mature paleosols in the hadar and busidima formations are mostly pale to darkbrown vertisols typifi ed by abundant clay slickensides pseudo anticlinal and vertical fracturing and carbonate nodules such calcic vertisols are common in the region today demonstrating that the paleoclimate over the past 3 4 m y has been semi arid and strongly seasonal carbon isotopic results from pedogenic carbonates in the vertisols allow reconstruction of the proportion of c 3 plants trees and shrubs to c 4 plants grasses through time the 13

melt inclusion investigation of the volatile behaviour in historic alkali basaltic magmas of etna crystallization paths of basaltic 1763 eruption and hawaiitic 1865 and 1329 eruptions scoria from etna were deduced from mineralogy and melt inclusion chemistry the volatile behaviour was investigated through the study of melt inclusions trapped in the phenocrysts and those of the whole rocks and the matrix glasses the results from the 1763 eruption point to the early crystallization of olivine fo 81 7 from a water rich alkaline basalt with high cl 1750 2000 ppm and s 2100 2400 ppm concentrations the hawaiitic melt inclusions trapped in olivine fo 74 salite and plagioclase are characterized by a decrease in cl k2o and s k2o ratios in each investigated system there is good correlation between k2o and p2o5 in the whole rocks cl ranges from 980 to 1680 ppm from basaltic to hawaiitic lavas whereas s 110 136 ppm remains low cl and s behaviour in the 1763 magma suggests an early degassing stage of cl and s with co2 and a water rich gaseous phase for a pressure close to 100 mpa consistent with a permanent outgassing at the summit craters of etna during the eruption the sulphur remaining in the hawaiitic liquid is lost and the degassing of chlorine is limited such a degassing model can be extended to the 1865 and 1329a d eruptions

petrology and sr nd isotope geochemistry of recent lavas from mt etna bearing on the volcano feeding system abstract the volcanic activity of mt etna during the period 1971 1987 has been investigated based on new volcanological petrographic geochemical and isotopic data the magma output rate since 1971 is much higher than that of the last 200 years marking a significant change in the feeding regime of mt etna the highest output rate has been observed for the 1981 eruption sub aphyric lavas emitted during the excentric activity of 1974 are the most primitive of those studied mg 57 55 the major and trace element chemistry of the lavas indicates limited differentiation by crystal fractionation mainly involving mafic phases nevertheless the observed variability of some ratios between highly incompatible elements suggests possible source heterogeneities the sr nd isotopic compositions range between 0 70362 0 70377 and 0 512829 0 512892 respectively with the lowest and highest 87sr 86sr ratios measured in the 1981 and 1974 lavas the observed isotopic variability is not due to late contamination processes but probably to the mantle source variations in sr and nd isotopic composition could indicate the lack of large magma chambers at any level in mt etna feeding system suggesting a model in which magma reaches the surface through a network of dikes where complete homogenization of different batches cannot be attained

dynamic deformation of etna volcano observed by satellite radar interferometry satellite radar interferometry of mt etna volcano sicily italy reveals a sequence of deformation characterized by deflation during the end of the 1993 eruption inflation from 1993 1995 with an increase in the inflation rate immediately before its resumed eruptive activity in late 1995 this was followed by very low deformation levels during the following year the source of the deformation changed from a depth of 9 km during deflation to more than 11 14 km during the subsequent inflation consistent with a model in which deflation at shallower levels is followed by inflation at greater depth as the volcano system recharges from below before its next eruption this study demonstrates that radar interferometry provides an important contribution towards understanding the dynamic deformation of volcanoes by revealing large scale changes in their pre eruption deformation rates radar interferometry could play an important role in volcano eruption monitoring

a model of vulcanian eruptions at galeras volcano colombia abstract a series of six vulcanian eruptions at galeras volcano colombia occurred during 1992 1993 these eruptions followed the emplacement of a lava dome in late 1991 which was accompanied by cooling crystallizing and partial solidification of the column of magma plugging the conduit five of the eruptions were preceded by episodes of monochromatic long period seismicity suggesting cyclic pressurization of the magma the quiescent intervals between eruptions generally decreased with each successive eruption we propose a model of gas release from magma into confined stationary pore spaces by 5 10 crystallization of anhydrous minerals causing repeated overpressurization of the magmatic system using initial lithostatic pressures of 20 100 mpa 800 3900 m depth gas buildup by crystallization indicates overpressures of 3 17 mpa which is the approximate fracture criterion for a magma chamber our galeras data suggest two models of pressurization 1 gas exsolution may have occurred at similar depths but with progressively smaller overpressures being developed before each successive eruption according to this model the comparatively long quiescent periods between the first eruptions resulted in relatively large amounts of gas exsolution from the magma and accumulation in pore spaces whereas the shorter quiescent periods for the later eruptions exsolved less gas the decrease in overpressure with time may have resulted from progressive fracturing of partly solidified magma during the eruptions which progressively decreased the tensile strength and increased the permeability of the magma 2 since overpressures are smaller at shallower depths for a given amount of crystallization the first eruptions of 1992 1993 were caused by gas exsolution at shallow depths while the last eruptions having shorter quiescent intervals resulted from a greater amount of gas exsolution at greater depths in this case the rate of gas exsolution varied as a function of depth the two scenarios for pressurization may be combined into a more general model involving edifice weakening and the development of a shallow hydrothermal system from continued degassing of the magma plug as weakening of the edifice formed an extensive system of fractures the shallow hydrothermal system deepened due to meteoric water input and magmatic degassing with time a greater number of fractures were filled and partly sealed by hydrothermal minerals at progressively deeper levels as a result the source of the overpressure also deepened with time

precursory swarms of long period events at redoubt volcano 1989 1990 alaska their origin and use as a forecasting tool abstract during the eruption of redoubt volcano from december 1989 through april 1990 the alaska volcano observatory issued advance warnings of several tephra eruptions based on changes in seismic activity related to the occurrence of precursory swarms of long period lp seismic events dominant period of about 0 5 s the initial eruption on december 14 occurred after 23 years of quiescence and was heralded by a 23 hour swarm of lp events that ended abruptly with the eruption after a series of vent clearing explosions over the next few days dome growth began on december 21 another swarm with lp events similar to those of the first began on the 26th and ended in a major tephra eruption on january 2 eruptions continued over the next two weeks and then ceased until february 15 when a large eruption initiated a long phase of repetitive dome building and dome destroying episodes that continued into april warnings were issued before the major events on december 14 and january 2 but as the eruptive sequence continued after january 2 the energy of the swarms decreased and forecasting became more difficult a significant but less intense swarm preceded the february 15 eruption which was not forecast this eruption destroyed the only seismograph on the volcanic edifice and stymied forecasting until march 4 when the first of three new stations was installed within 3 km of the active vent from march 4 to the end of the sequence on april 21 there were eight eruptions six of which were preceded by detectable swarms of lp events although weak these swarms provided the basis for warnings issued before the eruptions on march 23 and april 6 the initial swarm on december 13 had the following features 1 short duration 23 hours 2 a rapidly accelerating rate of seismic energy release over the first 18 hours of the swarm followed by a decline of activity during the 5 hours preceding the eruption 3 a magnitude range from 0 4 to 1 6 4 nearly identical lp signatures with a dominant period near 0 5 s 5 dilatational first motions everywhere and 6 a stationary source location at a depth of 1 4 km beneath the crater this occurrence of long period events suggests a model involving the interaction of magma with groundwater in which magmatic gases steam and water drive a fixed conduit at a stationary point throughout the swarm the initiation of that sequence of events is analogous to the failure of a pressure relief valve connecting a lower supercharged magma dominated reservoir to a shallow hydrothermal system a three dimensional model of a vibrating fluid filled crack recently developed by chouet is found to be compatible with the seismic data and yields the following parameters for the lp source crack length 280 380 m crack width 140 190 m crack thickness 0 05 0 20 m crack stiffness 100 200 sound speed of fluid 0 8 1 3 km s compressional wave speed of rock 5 1 km s density ratio of fluid to rock 0 4 and ratio of bulk modulus of fluid to rigidity of rock 0 03 0 07 the fluid filled crack is excited intermittently by an impulsive pressure drop that varies in magnitude within the range of 0 4 to 40 bar such disturbance appears to be consistent with a triggering mechanism associated with choked flow conditions in the crack

elephants and subsistence evidence of the human exploitation of extremely large mammal bones from the middle palaeolithic site of preresa madrid spain the archaeological site at preresa madrid spain has been dated to 84 5 6 ka by optically stimulated luminescence osl mis 5a an area 255 m2 was excavated and 754 lithic pieces were recovered as well as a large amount of micro and macro vertebrate remains including proboscidean bones the aim of this paper is to outline the results of the taphonomic study of these remains the identification of cut marks on a number of the bones recovered strengthens the theory that the exploitation of extremely large mammals was more than just a marginal practice before the upper palaeolithic additionally the identification of green bone fractures and percussion marks confirm for the first time that the bone marrow of these taxa was also consumed few other cases of this practice have been identified firstly because obtaining this substance would not be an easy matter and secondly because similar nutritional needs can also be met by the consumption of brain matter which is easier to acquire

seismological aspects of the 1989 1990 eruptions at redoubt volcano alaska the ssam perspective abstract ssam is a simple and inexpensive tool for continuous monitoring of average seismic amplitudes within selected frequency bands in near real time on a pc based data acquisition system during the 1989 1990 eruption sequence at redoubt volcano the potential of ssam to aid in rapid identification of precursory long period lp event swarms was realized and since this time ssam has been incorporated in routine monitoring efforts of the alaska volcano observatory in particular an eruption that occurred on april 6 was successfully forecast primarily on the basis of recognizing the precursory lp activity on ssam of twenty two significant eruptions that occurred between december 14 and april 21 eleven had precursory swarms longer than one hour in duration that could be detected on ssam for individual swarms the patterns of relative spectral amplitudes are distinct at each station and remain largely stationary through time thus indicating that one source may have been preferentially and repeatedly activated throughout the swarm typically a single spectral band dominates the signal at each seismic station for the vigorous one day swarm that preceded the first eruption on december 14 signals were sharply peaked in the 1 9 2 7 hz band at the closest station located 4 km from the vent but were dominated by 1 3 1 9 hz energy at three more distant stations located 7 5 22 km from the vent the tendency for the signals from different swarms recorded at the same station to be peaked in the same frequency band suggests that all of the sources are characterized by a predominant length scale signals from the precursory lp swarms became weaker as the eruption sequence progressed and swarms that occurred in march and april could only be detected at seismographs on the volcanic edifice onset times of precursory lp swarms prior to eruptions ranged from a few hours to about one week but after the initial vent clearing phase that ended december 19 these intervals tended to become progressively shorter for successive swarms these trends in the relative onset times and intensities of successive precursory lp swarms are consistent with an overall depressurization of the magmatic system through time in general each of the swarms had an emergent onset but the intensities did not always increase steadily until the eruptions instead as the time of an eruption approached the intensity usually increased more rapidly before peaking and then declining prior to the eruption for three of the swarms two distinct peaks in intensity were apparent the time intervals between final peaks in swarm intensity and ensuing eruptions ranged from about 2 hours to almost 2 days but the peaks always occurred closer to the eruptions than to the swarm onsets both the onset of lp swarm activity and a decline in intensity prior to an eruption may represent critical points in the process of pressurization that drives the flow of fluids and gas in a sealed magmatic system a notable exception to this pattern is the eruption of march 9 which lacked a detectable precursory lp swarm but was followed by an unusually long period of strong lp seismicity that may have been stimulated by a depressurization of the magmatic system resulting from dome failure on both december 14 and january 2 the spectra of early syn eruptive signals have peaked signatures much like those of the spectra of precursory lp activity from shortly before the eruptions these similarities may indicate that the source of precursory seismicity continued to be active during at least the early part of each eruption in syn eruptive signals from march and april recorded at stations on the volcanic edifice the dominant spectral energy progressively shifts with time during the eruption to lower frequencies at least part of the energy in these signals may have been generated by the debris flows associated with dome failures

application of gravity and deep dipole geoelectrics in the volcanic area of mt etna sicily abstract the structural pattern of the basement of the mt etna volcano is studied by combining results from new gravity and deep dipole geoelectric field data at first the bouguer map was separated into regional and residual contour maps by a 50 km cut off wavelength then by the geoelectric interpretation n s and e w resistivity cross sections were elaborated which were used as guidelines for modelling gravity residuals after observing a close correspondence between bouguer anomalies and resistivity classes by a trial and error adjustment to the relationship between resistivity and density a 3 d block model of the basement was finally constructed which consistently matched with both gravity and geoelectric information content two main conclusions emerged from the combined interpretation the first is the presence of diffuse inhomogeneities in the upper portion of the basement down to an average depth of 2 km below sea level in contrast with the regularity of the explored underlying portion the second is the absence of geophysical markers suggesting the existence of a large magmatic chamber down to about 3 km below sea level

volcanic tremors at etna a model for hydraulic origin spectral analysis of volcanic tremors at etna reveals 2 characteristic features 1 the escaping vapor and gas streams drive the magma in random turbulent motion generating a seismic wave emission according toa f n exp m f k wherea amplitude f frequency n m k parameters 2 sudden transients in the boundary conditions of the piping system generate hydraulic pressure pulses which in the seismogram appear as wave packages their monochromatic frequency content suggests that their origin is associated with strong resonance phenomena it is conclusive that volcanic eruptions may be distinguished and classified according to different eigenfrequencies of the fissure and pipe network involved in the volcanic activity furthermore positions of active dykes may be traced following the amplitude distributions associated with pronounced spectral lines in the tremor spectra

recent deformations and the seismogenic source in the messina strait southern italy abstract the relationships between mechanisms and mode of faulting in pliocene and pleistocene times and seismic release are the basis for an interpretation of the growth of deformation energy in the messina strait the major fault systems trending in ne sw nw se and e w directions divide blocks subjected to high mobility in concurrence with greater uplifting of the calabrian side with respect to sicily across the two sides of the strait as revealed by structural analyses the tectonic features of the area are dominated by normal faulting many synsedimentary features seem to indicate repeated and intermittent pulses of high velocity fault slippage possibly related to seismic shaking when considering the seismic record it seems that the strongest shocks are generated by preferential strain accumulations along the nne ssw fault systems from a geological standpoint it seems clear that the largest events may be alternately related to either the nne ssw e w or nw se fault systems which dissect an extremely cataclastic upper crust the recent deformations of the messina strait can be related to the large scale processes induced by the overthrusting of the thinned tyrrhenian crust over the thickened african crust as suggested by seismic refraction profiles along the inner margin of the calabrian arc the deep deformation mechanisms are reflected by contrasting vertical movements between a stretched and downfaulted tyrrhenian domain and an uplifted chain with resulting large strain accumulations and seismic failure in the brittle upper crust

the feeding of the eruptive activity of etna volcano the regional stress field as a constraint to magma uprising and eruption an analysis of the structural lineaments as observed on the middle and upper slopes of etna volcano was made with the aim of checking stress distribution within the volcanic structure

volcano wide fringes in ers synthetic aperture radar interferograms of etna 1992 1998 deformation or tropospheric effect mount etna 3300 m is the volcano that has been first and most studied by differential synthetic aperture radar previous papers gave evidence for a large scale deformation of the entire edifice consistent with unrest episodes but with a poor fit with classical elastic models also atmospheric effects on mountainous areas are known to be very significant accordingly interferograms may reflect both deformation and tropospheric effects we investigate here the possibility of evaluating and correcting tropospheric effects directly from the interferograms from 38 ers synthetic aperture radar ascending scenes taken from 1992 to 1999 we have computed 238 interferograms the amount of data allows us to analyze how the coherence is maintained over long periods of time and thus how it reveals the location of permanent scatters from a simple analysis of phase elevation relation we give evidence for the clear difference in pattern between stratified tropospheric effects and large scale deformation produced by a source in a three dimensional elastic body with topography using combination of inversion processes we analyze both deformation source and tropospheric effects for the complete set of 238 interferograms finally time evolution of the parameters and modeling probability estimation are retrieved for each sar image estimated relative change in tropospheric delay varies in time from 2 7 to 3 0 1 2 fringes they are consistent with other tropospheric estimations at etna based on ground met and global positioning system observations on the same period of time magmatic volume variations remain below error bars and thus cannot be estimated properly finally some of the interferograms may be entirely explained by the difference in tropospheric conditions between the two acquisition periods without the need to invoking a deformation of the volcano