shallow seismicity beneath ruapehu crater lake results of a 1994 seismometer deployment virtually all the seismicity within ruapehu volcano recorded during a 2 month deployment in early 1994 with 14 broadband seismographs around the tongariro national park volcanoes in the north island of new zealand was associated with the active vent and occurred within approximately 1 km of ruapehu crater lake high frequency volcano tectonic earthquakes and low frequency events similar to bursts of 2 hz volcanic tremor were both found to have sources in this region the high frequency events which often consisted of a smaller precursor event followed approximately 2 s later by the main event had sharp onsets and were locatable using standard techniques the depth of these events ranged from the surface down to approximately 1500 m below crater lake the low frequency events did not have sharp onsets and were located by phase correlation methods nearly all occurred under a small region on the east side of crater lake at depths from 200 to 1000 m below the surface this low frequency earthquake source region in which no high frequency events occurred may be the steam zone within the actual vent of ruapehu volcano

formation of coastline features by large scale instabilities induced by high angle waves along shore sediment transport that is driven by waves is generally assumed to smooth a coastline this assumption is valid for small angles between the wave crest lines and the shore as has been demonstrated in shoreline models but when the angle between the waves and the shoreline is sufficiently large small perturbations to a straight shoreline will grow here we use a numerical model to investigate the implications of this instability mechanism for large scale morphology over long timescales our simulations show growth of coastline perturbations that interact with each other to produce large scale features that resemble various kinds of natural landforms including the capes and cuspate forelands observed along the carolina coast of southeastern north america wind and wave data from this area support our hypothesis that such an instability mechanism could be responsible for the formation of shoreline features at spatial scales up to hundreds of kilometres and temporal scales up to millennia

transport of gravel and cobble on a mixed sediment inner bank shoreline of a large inlet grays harbor washington gravel and cobble transport measurements were obtained by particle tracing experiments from a mixed sand gravel and cobble beach at the head of a crenulate shaped shoreline half moon bay in grays harbor washington the direct measurements and results provide insight regarding the differential transport of gravel and cobble sized material on mixed sediment beaches the results are of relevance to the development of both predictive formulae for coarse grained sediment transport and guidance for practical gravel and cobble beach design net alongshore transport of gravel and cobble is generally several times greater than the net cross shore transport at half moon bay larger and smaller particles both move preferentially alongshore however smaller particles tend to move across shore more than larger particles particle transport distance during a tidal cycle increases with particle size or mass up to a point beyond which the particle transport rate begins to decrease with increasing size the direct relationship between transport rate and particle size may reflect the selective entrainment and the rejection or overpassing of larger particles which are more exposed to fluid forces on the beach surface than smaller particles which are sheltered within the matrix of larger particles as well as the higher susceptibility to burial of smaller particles the decrease in transport rate for the largest sizes may reflect the limited competency of the fluid forces to transport larger and heavier particles under the observed conditions the direct transport measurements are consistent with the overall particle size and shape distributions observed on this crenulate shaped inner bank beach whereby the larger and flatter particles have tended to outrun the smaller and more spherical particles in the downdrift direction

a field based classification scheme for gravel beaches a tripartite classification of gravel beaches based upon morphodynamic properties is proposed and demonstrated for 42 new zealand beaches the main advantage of this scheme is that it is based on simple visual classification that can be applied globally in the field and is underpinned by morphodynamic differences between the beach types the three types identified from the results are 1 pure gravel beach 2 mixed sand and gravel beach 3 composite gravel beach pure gravel beaches have steep slopes tan 0 08 0 24 and gravels extending from the storm berm to below mean low water spring tide level mixed sand and gravel beaches have moderate slopes tan 0 04 0 13 with sand and gravel entirely mixed both cross shore and at depth composite gravel beaches have a steep gravel berm fronted by a low angle intertidal terrace with overall beach slopes of tan 0 05 0 14 on composite beaches there is distinct hydrodynamic cross shore sorting of the sand and gravel component these broad types are tested using discriminant analysis and the three classes are shown to be highly significant f 16 24 df 8 p 0 00005 the key discriminating variables are iribarren number beach width average grain size and storm berm height

empirical ground motion relations for subduction zone earthquakes and their application to cascadia and other regions ground motion relations for earthquakes that occur in subduction zones are an important input to seismic hazard analyses in many parts of the world in the cascadia region washington oregon northern california and british columbia for example there is a significant hazard from megathrust earthquakes along the subduction interface and from large events within the subducting slab these hazards are in addition to the hazard from shallow earthquakes in the overlying crust we have compiled a response spectra database from thousands of strong motion record ings from events of moment magnitude m 5 8 3 occurring in subduction zones around the world including both interface and in slab events the 2001 m 6 8 nis qually and 1999 m 5 9 satsop earthquakes are included in the database as are many records from subduction zones in japan kyoshin net data mexico guerrero data and central america the size of the database is four times larger than that available for previous empirical regressions to determine ground motion relations for subduc tion zone earthquakes the large dataset enables improved determination of attenu ation parameters and magnitude scaling for both interface and in slab events soil response parameters are also better determined by the data we use the database to develop global ground motion relations for interface and in slab earthquakes using a maximum likelihood regression method we analyze regional variability of ground motion amplitudes across the global database and find that there are significant regional differences in particular amplitudes in cascadia differ by more than a factor of 2 from those in japan for the same magnitude distance event type and national earthquake hazards reduction program nehrp soil class this is believed to be due to regional differences in the depth of the soil profile which are not captured by the nehrp site classification scheme regional correction factors to account for these differences are proposed for cascadia and japan the results of this study differ significantly from previous analyses based on more limited data and have important implications for seismic hazard analysis the ground motion relations predict that a great megathrust earthquake m 8 at a fault distance of about 100 km would produce pseudoacceleration psa 5 damped horizontal component on soil sites of about 110 cm sec 2 at 0 5 hz 660 cm sec 2 at 2 5 hz and 410 cm sec 2 at 5 hz with a peak ground acceleration of about 180 cm sec 2 these damaging levels of motion would be experienced over a very large area corresponding to a rectangular area about 300 km wide by 500 km long large in slab events m 7 5 would produce even higher psa values within 100 km of the fault but the in slab motions attenuate much more rapidly with distance thus the hazard posed by moderate to large in slab events such as the 2001 nisqually earth quake is modest compared to that of a cascadia megathrust earthquake of m 8 in terms of the area that would experience damaging levels of ground motion

interseismic coupling and seismic potential along the central andes subduction zone we use about two decades of geodetic measurements to characterize interseismic strain build up along the central andes subduction zone from lima peru to antofagasta chile these measurements are modeled assuming a 3 plate model nazca andean sliver and south america craton and spatially varying interseismic coupling isc on the nazca megathrust interface we also determine slip models of the 1996 m w 7 7 nazca the 2001 m w 8 4 arequipa the 2007 m w 8 0 pisco and the m w 7 7 tocopilla earthquakes we find that the data require a highly heterogeneous isc pattern and that overall areas with large seismic slip coincide with areas which remain locked in the interseismic period with high isc offshore lima where the isc is high a m w 8 6 8 8 earthquake occurred in 1746 this area ruptured again in a sequence of four m w 8 0 earthquakes in 1940 1966 1974 and 2007 but these events released only a small fraction of the elastic strain which has built up since 1746 so that enough elastic strain might be available there to generate a m w 8 5 earthquake the region where the nazca ridge subducts appears to be mostly creeping aseismically in the interseismic period low isc and seems to act as a permanent barrier as no large earthquake ruptured through it in the last 500 years in southern peru isc is relatively high and the deficit of moment accumulated since the m w 8 8 earthquake of 1868 is equivalent to a magnitude m w 8 4 earthquake two asperities separated by a subtle aseismic creeping patch are revealed there this aseismic patch may arrest some rupture as happened during the 2001 arequipa earthquake but the larger earthquakes of 1604 and 1868 were able to rupture through it in northern chile isc is very high and the rupture of the 2007 tocopilla earthquake has released only 4 of the elastic strain that has accumulated since 1877 the deficit of moment which has accumulated there is equivalent to a magnitude m w 8 7 earthquake this study thus provides elements to assess the location size and magnitude of future large megathurst earthquakes in the central andes subduction zone caveats of this study are that interseismic strain of the forearc is assumed time invariant and entirely elastic also a major source of uncertainty is due to fact that the available data place very little constraints on interseismic coupling at shallow depth near the trench except offshore lima where sea bottom geodetic measurements have been collected suggesting strong coupling

experimental study of the transport of mixed sand and gravel we measured a wide range of transport rates for five different sand gravel mixtures in a laboratory flume each mixture used the same gravel and sand was added to produce mixtures containing 6 15 21 27 and 34 sand control of other variables allows us to isolate the effect of bed sand content on transport as sand content increases gravel transport rates increase by orders of magnitude even though the proportion of gravel in the bed decreases the increase in gravel transport rate is most rapid over the range of bed sand content between 15 and 27 the increase in transport rate is larger than predicted using standard scaling relations between transport rate and grain size indicating that models of transport and sorting and predictions of stream channel response to sand inputs need to be revised to account for the influence of sand content bed surface grain size was measured at the end of each run surface grain size varied with sand content but showed little or no coarsening with flow strength and transport rate this casts doubt on the idea that armor layers form at small flows and weaken or vanish with increasing flow and transport rate

changes in attenuation related to eruptions of mt ruapehu volcano new zealand abstract temporal variations of seismic attenuation have been observed at different volcanoes around the world and are often claimed to correlate with volcanic activity seismic attenuation and its variation in time at mt ruapehu volcano new zealand was measured for the period october 1990 to may 2005 using local earthquakes originating from a nearby cluster of earthquakes called the waiouru swarm as recorded on 5 permanent seismometer stations cross correlation of p and s waves reveals a similarity of events from this ongoing seismic source which suggests that alterations due to source and path effects are minimized therefore the swarm is suitable for the study of temporal changes in seismic attenuation the attenuation q c 1 of coda waves following the direct p and s waves are calculated for five frequency bands centred at 1 5 3 0 6 0 9 0 and 12 0 hz using the single scattering model a best fit equation of q c q 0 f with q 0 54 7 and 1 02 0 06 shows an overall high frequency dependence of coda attenuation which is characteristic for tectonically active regions small fluctuations of q c 1 are observed at all stations over the entire time period and do not act as an apparent indicator of volcanic activity relative changes in integrated direct wave attenuation t along the whole path are obtained using a spectral ratio method in which spectra of individual 1 second p wave windows are compared to a reference spectrum during the time of volcanic activity the following changes were significant at the 95 confidence level in the low frequency band 1 5 6 hz a high attenuation anomaly with an abrupt increase of t by 0 23 s was detected in waveforms that have travelled through the volcano and a shift from negative to positive t by 0 25 s was observed at a station next to the volcano we suggest that these observations are related to variations detected in seismic anisotropy studies which propose a model of a change in stress caused by pressurisation of magma dykes under the volcano

real time seismic amplitude measurement rsam a volcano monitoring and prediction tool seismicity is one of the most commonly monitored phenomena used to determine the state of a volcano and for the prediction of volcanic eruptions although several real time earthquake detection and data acquisition systems exist few continuously measure seismic amplitude in circumstances where individual events are difficult to recognize or where volcanic tremor is prevalent analog seismic records provide a quick visual overview of activity however continuous rapid quantitative analysis to define the intensity of seismic activity for the purpose of predicing volcanic eruptions is not always possible because of clipping that results from the limited dynamic range of analog recorders at the cascades volcano observatory an inexpensive 8 bit analog to digital system controlled by a laptop computer is used to provide 1 min average amplitude information from eight telemetered seismic stations the absolute voltage level for each station is digitized averaged and appended in near real time to a data file on a multiuser computer system raw realtime seismic amplitude measurement rsam data or transformed rsam data are then plotted on a common time base with other available volcano monitoring information such as tilt changes in earthquake activity associated with dome building episodes weather and instrumental difficulties are recognized as distinct patterns in the rsam data set rsam data for domebuilding episodes gradually develop into exponential increases that terminate just before the time of magma extrusion mount st helens crater earthquakes show up as isolated spikes on amplitude plots for crater seismic stations but seldom for more distant stations weather related noise shows up as low level long term disturbances on all seismic stations regardless of distance from the volcano implemented in mid 1985 the rsam system has proved valuable in providing up to date information on seismic activity for three mount st helens eruptive episodes from 1985 to 1986 may 1985 may 1986 and october 1986 tiltmeter data the only other telemetered geophysical information that was available for the three dome building episodes is compared to rsam data to show that the increase in rsam data was related to the transport of magma to the surface thus if tiltmeter data is not available rsam data can be used to predict future magmatic eruptions at mount st helens we also recognize the limitations of rsam data two examples of rsam data associated with phreatic or shallow phreatomagmatic explosions were not preceded by the same increases in rsam data or changes in tilt associated with the three dome building eruptions

geochemistry of fluids associated with the 1995 1996 eruption of mt ruapehu new zealand signatures and processes in the magmatic hydrothermal system abstract the 1995 1996 eruption of mt ruapehu has provided a number of insights into the geochemical processes operating within the magmatic hydrothermal system of this volcano both pre eruption degassing of the rising magma and its eventual intrusion into the convective zone of the hydrothermal system beneath the lake were clearly reflected in lake water compositions the eruptions of september october 1995 expelled the lake and provided the first ever opportunity to characterise gas discharges from this volcano the fumarolic discharges revealed compositions typical of andesite volcanoes and strong interaction with the enclosing meteoric and hydrothermal system fluids some 1 1 mt of so 2 gas was released from the volcano between september 1995 and december 1996 whereas ca twice this amount 2 2 mt equivalent so 2 was erupted as soluble i e leachable oxyanions of sulphur significantly more sulphur was released from the volcano over this period than can be accounted for from the magma volume actually erupted the evidence suggests that a sizable component of the evolved sulphur was remobilised from the long lived hydrothermal system within the volcano during the 1995 1996 activity

seismicity associated with the reactivation of nevado del ruiz colombia july 1985 december 1986 abstract renewed activity of nevado del ruiz was first evidenced in november 1984 by increased fumarolic activity and felt earthquakes this increased activity prompted an installation of seismometers on the volcano in july 1985 earthquakes recorded in 1985 indicate that most of the seismic activity prior to the eruption on november 13 1985 was confined to an l shaped epicentral zone beneath the summit of the volcano a swarm prior to the november eruption originated west of the summit telemetered stations installed after the eruption enabled better locations of post eruptive activity majority of located post eruptive earthquakes originate within 5 km of the summit at a depth less than 7 km and only few exceeded magnitude 3

monitoring of phreatic eruptions using interferometry on retrieved cross correlation function from ambient seismic noise results from mt ruapehu new zealand abstract since the last major eruption in 1995 96 mt ruapehu has erupted twice on 4 october 2006 and on 25 september 2007 these events occurred without any clear precursors and were mostly phreatic explosions the technique of interferometry on retrieved cross correlation function from ambient seismic noise irccasn is used to monitor subtle temporal changes of mt ruapehu s elastic properties the computation of cross correlation functions of seismic noise recorded at several stations around the volcano allowed us to observe variations during the 2006 eruption period the comparison between a reference cross correlation function and a current cross correlation function allows us to infer relative seismic velocity variations a 0 8 decrease of relative seismic velocity in the edifice starting two days before the 2006 eruption was observed this drop is due to a reversible and ephemeral effect which can be attributed to a pressurization of a magma pocket beneath the east flank of ruapehu due to new magma entering a small reservoir this pressure increase produced an inflation of the east flank of ruapehu and opened fractures in this area leading to a localised drop of seismic velocity we conducted the same analysis for the 2007 eruption but no significant seismic velocity variation was observed this difference is possibly due to the varying time scales of pressurization for the two events and also the irccasn time resolution an analysis of the seismicity before these two eruptions allows us to propose a conceptual model which explains the velocity drop for the 2006 eruption and the lack of velocity variations for the 2007 eruption since there was no surface deformation recorded by the geonet gps network we modelled the maximum radius and pressure change for a simple mogi point source at 5 km depth that produced no deformation we inferred the maximum fresh magma volume of 0 0017 km 3 entering the reservoir as a detectability threshold for gps ground deformation measurements

the andean subduction zone between 22 and 25 s northern chile precise geometry and state of stress abstract one year of seismicity recorded by a local network is used to obtain more precision about the geometry and the stress regime of the andean subduction between 22 and 25 s in the northern chile seismic gap a sharp image of the wadati benioff zone wbz is obtained down to 270 km in depth a seismically quasi quiescent zone is observed in the wbz below the volcanic arc between 150 and 210 km in depth hypocentres of distant intermediate depth earthquakes located with the local network are compared with worldwide seismic network hypocentres in order to evaluate the accuracy of the wbz image at depth greater than 100 150 km in depth no shallow microearthquakes have been observed in the continental crust but some seismic activity is likely to occur locally at the deep root of the atacama fault the stress field and the characteristics of faulting along the subducted slab are investigated underthrusting and localized reverse faulting earthquakes define the seismically coupled plate interface from 20 to 50 km in depth locked zone downdip intra slab normal faulting prevails tensile zone but some strike slip faulting is observed a transition between normal faulting with variable fault azimuth and normal faulting with nearly homogeneous nnw to nw oriented fault plane is found at about 80 km in depth it is found that the stress axes 1 and 3 in the locked zone are oriented in the convergence direction 75 80 e downdip in the tensile zone 3 has a mean azimuth 60 65 e there the slab is hence submitted to a tensional force slab pull oblique relatively to the convergence the transition between seismic underthrusting and intraplate normal faulting downdip occurs at the depth where the continental moho encounters the wadati benioff zone suggesting that a relationship exists between seismic coupling and the presence of continental crust at the plate interface the pre seismic state of this segment of the andean subduction zone is confirmed by the occurrence of strong earthquakes located by the global network around the presumed rupture area and by the stress regime found along the wadati benioff zone

hydrodynamics and morphological adjustment of a mixed sand and gravel beach torere bay of plenty new zealand detailed measurements of cross shore wave energy transformation swash sediment transport and beach profile change under low energy conditions are reported from a mixed sand and gravel beach at torere bay bay of plenty new zealand measurements were undertaken during a 10 day period following a storm event and document post storm recovery of the beach nearshore wave spectra identify periods in which incident wave energy is dominated by swell and wind wave energy results show that wind wave energy observed in the nearshore is effectively removed from beachface spectra at the break point step under lower tidal stages swash is driven by longer period swell energy although dissipation of short period wave energy is critical in entraining sediments on the lower beach at higher tidal stages wind wave energy is able to propagate across the break point step shoal and break on the lower beachface tidal modulation of wave processes across the lower beachface under low incident wave conditions is found to stimulate active sediment reworking migration of the break point step and shoreward sediment flux to promote beach accretion

variability of volcanic gas emissions during a crater lake heating cycle at ruapehu volcano new zealand abstract we present the first routine measurements of emissions co 2 so 2 and h 2 s from ruapehu volcano new zealand during a crater lake heating cycle emissions were generally at a low level consistent with quiescent degassing of the volcano and the presence of a crater lake maximum concentrations 3 4 km downwind during the highest measurement in may 2004 were 14 ppm 0 37 ppm and 7 ppb for co 2 so 2 and h 2 s respectively co 2 emissions varied between not detectable to 900 t d 1 over periods of months so 2 was not detectable until february but gradually increased to 35 t d 1 emissions of h 2 s were detected in april and may although were 1 the co 2 so 2 ratio in the plume was 37 by weight for each measurement during the peak of the cycle suggesting that significant scrubbing of so 2 occurs through the crater lake and that a common source exists for both gases magma volumes estimated from co 2 emissions 0 001 0 004 km 3 are consistent with eruptive volumes given repose periods of 20 30 years delays between peaks in crater lake heating and degassing suggests that volcanic emissions do not primarily reside in the shallow hydrothermal system directly beneath the crater further data is needed to adequately model the system but first indications of the travel time associated with the degassing cycle suggests that the gas resides at minimally 300 m depth beneath the crater lake depths greater than 300 m are consistent with the top of the single phase steam zone in heat pipe models 200 700 m depth or perhaps even below the plastic brittle transition zone above the cooling magmas 1 km deep

a preliminary seismic study of taal volcano luzon island philippines abstract the very active taal volcano lies in the southern part of luzon island only 60 km from manila the capital of the philippines in march 2008 we deployed a temporary seismic network around taal that consisted of 8 three component short period seismometers this network recorded during the period from march to november 2008 about 1050 local events in the early data processing stages unexpected linear drifting of clock time was clearly identified for a number of stations the drifting rates of each problematic station were determined and the errors were corrected before further processing initial location of each event was derived by manually picked p s phases arrival times using hypo71 and a general velocity model based on ak135 since the velocity structure beneath taal is essentially unknown we used travel times of 338 well located events in order to derive a minimum 1d velocity model using velest the resulting locations show that most events occurred at the shallow depth beneath the taal volcano and two major earthquake groups were noticed with one lying underneath the western shore of taal lake and the other one spread around the eastern flank of the taal volcano since there is no reported volcano activities during the operation period of our seismic array we are still not confident to interpret these findings in terms of other natures of volcano at the current stage however our work represents an important pioneer step towards other more advanced seismic studies in taal volcano

stress and strain from earthquakes at the southern termination of the taupo volcanic zone new zealand abstract we use first motion polarity data from small earthquakes recorded by a recent dense seismograph deployment to determine 16 new focal mechanisms at the southern termination of the taupo volcanic zone tvz these crustal earthquakes are between 11 km and 41 km deep and have focal mechanisms which range from normal to strike slip we then combine these focal mechanism data with previously determined focal mechanisms to investigate earthquake strain directions a prominent feature of the combined data is the consistency of the t axes which indicates that subhorizontal nnw extensional strain predominates at all depths in the crust at the southern termination of the tvz we then use all currently available first motion data to invert for the stress tensor orientation first motion data from earthquakes throughout the crust show a consistent minimum principal stress 3 orientation which is subhorizontal and oriented nw the 3 azimuth that we observe 316 is perpendicular to the strike of recent aligned vents in the southern tvz very similar to the extension direction in the ruapehu segment of the tvz determined from structural data and consistent with the 3 direction determined from a stress inversion using crustal earthquakes in the central tvz north of lake taupo this suggests that the stresses driving the opening of the tvz continue to be active at its southern termination the stress and strain results combined with the earthquake distribution are consistent with a model where the tvz is only the present day surface expression of an extensive region of active mantle corner flow that is progressively eroding thicker crust to the south we also investigate the temporal evolution of stress around mt ruapehu the southernmost large andesitic volcano in the tvz given previous suggestions that this may change during the eruption cycle we find no major change in the stress tensor orientation at the time of the 1995 eruption using first motion data from earthquakes 15 20 km from the volcano

seismo acoustic evidence for an avalanche driven phreatic eruption through a beheaded hydrothermal system an example from the 2012 tongariro eruption abstract the 6 august 2012 te maari eruption comprises a complex eruption sequence including multiple eruption pulses a debris avalanche that propagated 2 km from the vent and the formation of a 500 m long arcuate chasm located 300 m from the main eruption vent the eruption included 6 distinct impulses that were coherent across a local infrasound network marking the eruption onset at 11 52 18 all times utc an eruption energy release of 3 1012 j was calculated using a body wave equation for radiated seismic energy a similar calculation based on the infrasound record shows that 90 of the acoustic energy was released from three impulses at onset times 11 52 20 20 of total eruption energy 11 52 27 50 and 11 52 31 20 these energy impulses may coincide with eyewitness accounts describing an initial eastward directed blast followed by a westward directed blast and a final vertical blast pre eruption seismic activity includes numerous small unlocatable micro earthquakes that began at 11 46 50 two larger high frequency earthquakes were recorded at 11 49 06 and 11 49 21 followed directly by a third earthquake at 11 50 17 the first event was located within the scarp based on an arrival time location from good first p arrival times and probably represents the onset of the debris avalanche the third event was a tornillo characterised by a 0 8 hz single frequency resonance and has a resonator attenuation factor of q 40 consistent with a bubbly fluid filled resonator this contrasts with a similar tornillo event occurring 2 5 weeks earlier having q 250 1000 consistent with a dusty gas charged resonator we surmise from pre eruption seismicity and the observed attenuation change that the debris avalanche resulted from the influx of fluids into the hydrothermal system causing destabilisation and failure the beheaded hydrothermal system may have then caused depressurisation frothing of the remaining gas charged system leading to the onset of explosive activity

volcanic hazard assessment for ruapehu composite volcano taupo volcanic zone new zealand ruapehu is a very active andesitic composite volcano which has erupted five times in the past 10 years historical events have included phreatomagmatic eruptions through a hot crater lake and two dome building episodes ski field facilities road and rail bridges alpine huts and portions of a major hydroelectrical power scheme have been damaged or destroyed by these eruptions destruction of a rail bridge by a lahar in 1953 caused the loss of 151 lives other potential hazards with holocene analogues include strombolian and sub plinian explosive eruptions lava extrusion from summit or flank vents and collapse of portions of the volcano the greatest hazards would result from renewed phreatomagmatic activity in crater lake or collapse of its weak southeastern wall three types of hazard zones can be defined for the phreatomagmatic events inner zones of extreme risk from ballistic blocks and surges outer zones of disruption to services from fall deposits and zones of risk from lahars which consist of tongues down major river valleys ruapehu is prone to destructive lahars because of the presence of 107 m3 of hot acid water in crater lake and because of the surrounding summit glaciers and ice fields the greatest risks at ruapehu are to thousands of skiers on the ski field which crosses a northern lahar path three early warning schemes have been established to deal with the lahar problems collapse of the southeastern confining wall would release much of the lake into an eastern lahar path causing widespread damage this is a long term risk which could only be mitigated by drainage of the lake

retrieval of microphysical and morphological properties of volcanic ash plumes from satellite data application to mt ruapehu new zealand a quantitative analysis of the properties of several mt ruapehu new zealand ash plumes has been performed using multispectral satellite data from the avhrr 2 and atsr 2 instruments the analysis includes identification of the plume from background clouds using the reverse absorption effect in the thermal channels modelling and retrieval of particle sizes determination of the plume height from cloud shadows stereoscopy and meteorological data and estimates of the mass of fine particles radii less than 10 m a new spectral technique for identifying opaque silica rich ash clouds is demonstrated by utilizing the near infrared 1 6 m and visible 0 67 m channels of the atsr 2 and the optical properties of a simple volcanic cloud are presented for use in radiative transfer studies it is found that the ruapehu eruption cloud contained silica rich ash particles with radii generally less than a few micrometres the distribution of fine particles is monomodal with a dominant mode peak of about 3 m radius mass loadings of fine particles are found to be in the range 1 to 7 mg m 3 and are consistent with estimates of mass loadings of volcanic clouds from eruptions of other volcanoes the height of the plume top derived from radiosonde data and plume top temperatures in the opaque regions was found to be between 7 5 and 8 5 km while the plume thickness was estimated to be between 1 5 and 3 km cloud height derived from atsr 2 stereoscopy on a different plume gave heights in the range 5 to 8 km the results of this study provide important information on the optical properties of nascent volcanic eruption plumes this information may prove useful in determining the potential effects of volcanic clouds on local climate and in assessing any hazard to aviation

influence of alteration on the mechanical behaviour and failure mode of andesite implications for shallow seismicity and volcano monitoring volcanoes often host hydrothermal systems that alter the host rock to understand the influence of alteration on mechanical behaviour of edifice forming rock we performed a series of triaxial deformation experiments on variably altered andesite from mt ruapehu new zealand under constant effective pressure under the imposed conditions andesite with intermediate argillic alteration deforms in a brittle manner forming fractures by contrast andesite with advanced argillic alteration deforms in a ductile manner with sample failure driven by distributed cataclastic pore collapse we consider this the result of an increase in porosity and clay content with increasing alteration ancillary experiments highlight that the brittle ductile transition occurs at lower effective pressure i e at shallower depths in andesites with advanced argillic alteration relative to unaltered andesites of comparable porosity we conclude that advanced argillic alteration can create an anomalous shallow ductile zone which has important implications for fluid flow and pre eruptive seismicity

environmental hazards of fluoride in volcanic ash a case study from ruapehu volcano new zealand abstract the vent hosted hydrothermal system of ruapehu volcano is normally covered by a c 10 million m3 acidic crater lake where volcanic gases accumulate through analysis of eruption observations granulometry mineralogy and chemistry of volcanic ash from the 1995 1996 ruapehu eruptions we report on the varying influences on environmental hazards associated with the deposits all measured parameters are more dependent on the eruptive style than on distance from the vent early phreatic and phreatomagmatic eruption phases from crater lakes similar to that on ruapehu are likely to contain the greatest concentrations of environmentally significant elements especially sulphur and fluoride these elements are contained within altered xenolithic material extracted from the hydrothermal system by steam explosions as well as in residue hydrothermal fluids adsorbed on to particle surfaces in particular total f in the ash may be enriched by a factor of 6 relative to original magmatic contents although immediately soluble f does not show such dramatic increases highly soluble naf and casif6 phases demonstrated to be the carriers of available f in purely magmatic eruptive systems are probably not dominant in the products of phreatomagmatic eruptions through hydrothermal systems instead slowly soluble compounds such as caf2 alf3 and ca5 po4 3f dominate fluoride in these phases is released over longer periods where only one third is leached in a single 24 h water extraction this implies that estimation of soluble f in such ashes based on a single leach leads to underestimation of the f impact especially of a potential longer term environmental hazard in addition a large proportion of the total f in the ash is apparently soluble in the digestive system of grazing animals in the ruapehu case this led to several thousand sheep deaths from fluorosis

timescales of magmatic processes at ruapehu volcano from diffusion chronometry and their comparison to monitoring data abstract recent eruptions from mt ruapehu have been difficult to predict despite the presence of a multi parametric monitoring network as a result it is necessary to assess precursory signals prior to an eruption and align those to magmatic processes at depth fortuitously scoria from all historical ruapehu eruptions contains pyroxene crystals that are strongly reversely zoned in the form of a thin 2 to 3 m outermost rim these crystals therefore preserved changes in the magmatic system soon before their eruption we used experimentally determined diffusion coefficients to assess the timescales of magma magma interaction and compared those to the monitoring record four of the five eruptions analysed 1969 1971 1977 1995 gave diffusion timescales 3 to 5 months before their eruption with an increased number of crystals recording timescales within 1 month of eruption pyroxene crystals from the 1996 eruption record events that occurred prior to and during the 1995 eruption suggesting that the bulk of the 1996 crystals was derived from the 1995 magma these diffusion timescales do not compare well to a change in any monitoring signal before historical eruptions however an examination of recent seismicity 2005 2013 since a significant upgrade both in number of stations and type of seismometers showed that two phreatic eruptions in 2006 and 2007 were preceded by a seismic swarm from 5 to 15 km depth 3 to 5 months before each eruption consistent with the diffusion timescales based on this correlation deep seismic swarms likely indicate a period of pressurisation in the magmatic system which may lead to gas rich phreatic eruptions

distinguishing between stress induced and structural anisotropy at mount ruapehu volcano new zealand 1 we have created a benchmark of spatial variations in shear wave anisotropy around mount ruapehu new zealand against which to measure future temporal changes anisotropy in the crust is often assumed to be caused by stress aligned microcracks and the polarization of the fast quasi shear wave is thus interpreted to indicate the direction of maximum horizontal stress but can also be due to aligned minerals or macroscopic fractures changes in seismic anisotropy have been observed following a major eruption in 1995 96 and were attributed to changes in stress from the depressurization of the magmatic system three component broadband seismometers have been deployed to complement the permanent stations that surround ruapehu creating a combined network of 34 three component seismometers this denser observational network improves the resolution with which spatial variations in seismic anisotropy can be examined using an automated shear wave splitting analysis we examine local earthquakes in 2008 we observe a strong azimuthal dependence of and so introduce a spatial averaging technique and two dimensional tomography of recorded delay times the anisotropy can be divided into regions in which agrees with stress estimations from focal mechanism inversions suggesting stress induced anisotropy and those in which is aligned with structural features such as faults suggesting structural anisotropy the pattern of anisotropy that is inferred to be stress related cannot be modeled adequately using coulomb modeling with a dike like inflation source we suggest that the stress induced anisotropy is affected by loading of the volcano and a lithospheric discontinuity

earthquake swarms to the west of mt ruapehu preceding its 1995 eruption abstract some months prior to the 1995 eruption of mt ruapehu new zealand a series of shallow earthquake swarms occurred about 15 20 km west of the summit of ruapehu several earthquakes in these swarms were felt and the largest event was m l 4 8 crustal earthquakes of m l 3 0 within 20 km of the summit of ruapehu have been rather uncommon in recent years furthermore the two periods of strongest activity were both just before times when the temperature of crater lake showed rapid increases the second of these rapid heating phases was immediately followed by increases in the mg 2 ion concentration in crater lake indicating that chemical interactions were occurring between fresh magmatic material and the lake water the coincidence between seismicity and lake changes suggested a link with the following eruption a 1 d simultaneous inversion to locate the earthquakes more accurately showed that most of the earthquakes fell into three spatial clusters each cluster having a small horizontal cross section the predominant depth was about 10 16 km the b value of this swarm was 0 74 quite compatible with ordinary tectonic earthquakes each cluster of earthquakes lies close to the normal raurimu fault which runs predominantly north south to the west of ruapehu with an east trending branch splaying off near its northern end see fig 1 b composite focal mechanisms of events in the two more southern clusters are oblique normal while the other cluster to the north has an oblique reverse mechanism the two oblique normal mechanisms suggest that extension has occurred on part of the fault this stress pattern was also observed in the focal mechanism solutions of events that occurred after the eruption when a denser network of portable seismographs covered the region although we cannot definitely connect the occurrence of these swarms to the eruptions later in 1995 there is a strong suggestion that the seismicity was connected to the process of magma movement which temperature and chemical changes in crater lake suggest was occurring during the first half of 1995

ndsha a new paradigm for reliable seismic hazard assessment abstract a new paradigm is needed for reliable seismic hazard assessment rsha not only from consideration of a the huge human losses experienced in the many recently destructive earthquakes worldwide but also from b theoretical considerations of seismic wave generation and propagation phenomena through often non homogeneous media within the earth s crust particularly when large and more complex fault ruptures occur the neo deterministic seismic hazard assessment ndsha method proposed some twenty years ago is found to reliably and realistically simulate the wide suite of earthquake ground motions that may impact civil populations as well as their heritage buildings the scenario based ndsha modeling technique is developed from comprehensive physical knowledge of i the seismic source process ii the propagation of earthquake waves and iii their combined interactions with site effects thus ndsha effectively accounts for the tensor nature of earthquake ground motions a formally described as the tensor product of the earthquake source functions and the green s functions of the transmitting pathway medium and b more informally described as mathematical arrays of numbers or functions indices that transform according to certain rules under a change of coordinates importantly ndsha therefore uses all available information about the spacial distribution of large magnitude earthquake phenomena including a maximum credible earthquake mce which is based on seismic history and seismotectonics and b geological and geophysical data thus it does not rely on scalar empirical ground motion attenuation models gmpes as these are often both a weakly constrained by available observations and b fundamentally unable to account for the tensor nature of earthquake ground motions

a magnetotelluric study of mount ruapehu volcano new zealand summary mt ruapehu is an active andesite cone volcano which marks the southern termination of the kermadec volcanic arc results from 40 broad band magnetotelluric soundings have been analysed using the phase tensor this approach provides a way of determining dimensionality allowing for distortion removal and visualizing data in a 3 d situation the phase tensor analysis suggests that the shallow resistivity structure is largely 1 d in character but that the deeper structure requires a 3 d interpretation 1 d inversions show that at sites on ruapehu a shallow conductive layer lies between a high resistivity layer of a few hundred metres thickness and higher resistivity layer corresponding to basement greywacke the low resistivity layer is contiguous with the waters of the highly acidic crater lake and thus is believed to be the hydraulically controlled upper limit of a zone of acid alteration overlain by dry volcanic rock and ash to the southwest of the volcano the conductive layer merges with a surface conductor associated with tertiary sediments following initial 2 d inversions the deep resistivity structure has been derived through 3 d inversion of data from 38 sites this indicates the existence of a dyke like low resistivity zone that persists to at least 10 km depth and extends from beneath the summit of ruapehu to the northeast where it appears to connect to a poorly constrained region of high conductivity which lies outside the network of measurement sites the low resistivity dyke like feature may be identified with a volcanic feeder system which also supplies the other volcanoes of the tongariro volcanic centre and marks the conduit by which hot gases and occasionally magma reach the surface

the hydrothermal vent system of mount ruapehu new zealand a high frequency mt survey of the summit plateau high frequency magnetotelluric mt measurements made on the summit plateau of mount ruapehu some 1 km to the north of the presently active vent beneath crater lake have been used to derive the electrical resistivity structure associated with the volcanic hydrothermal vent system the entire summit plateau area is underlain at shallow depth by low resistivity which is inferred to be the result of hydrothermal alteration caused by rising volcanic gases mixing with local groundwater two areas of localised higher resistivity one between 200 and 500 m depth beneath the central part of the plateau and one at a depth of 1000 m below the northern part of the plateau are interpreted as being the result of hydrothermal alteration at higher temperature forming chlorite dominated alteration products these regions are believed to represent the locations of further heat pipes within the volcanic system both correlate with the locations of eruption centres on ruapehu active within the last 10 ka

a probabilistic seismic hazard assessment of southern peru and northern chile abstract southern peru and northern chile 17 30 s 67 74 w make up a seismically active region due to the convergence of the nazca plate and the south american plate the region has experienced a number of destructive earthquakes and tsunamis over the past few centuries which have caused loss of human life and significant damage to infrastructure highlighting the importance of seismic hazard assessment in the region in fact a reliable seismic hazard assessment is critical for developing policies for seismic hazard mitigation and risk reduction in this study we performed a probabilistic seismic hazard assessment psha of the study area based on an earthquake catalog that was very carefully analyzed in earlier studies we demonstrated that inappropriate treatment of the earthquake catalog can result in a serious bias in evaluations of seismicity parameters e g a bias of up to 42 in the b parameter of the gutenberg richter law to address this issue we compiled a homogenous earthquake catalog consisting of 39 977 events during the 1513 2016 period and accounted for site specific local effects by developing site specific scaling relationships between different measures of magnitude e g mb ms md and moment magnitude mw the study area was subdivided into 15 seismogenic zones accounting for site specific seismicity patterns the parameters a and b of the gutenberg richter law were estimated for each zone based on independent earthquake events the psha was performed using a standard logic tree approach which allowed us to systematically take into account the model based uncertainty and its influence on the estimated ground motion parameters uniform hazard spectra for return periods of 475 and 2475 years were estimated for peak ground accelerations and spectral accelerations at 0 2 s and 1 0 s to meet the definitions of seismic hazards provided by the international building code ibc international code council icc 2009 this study is expected to provide a basis for design maps for building codes and emergency planning

a fifty year perspective of magmatic evolution on ruapehu volcano new zealand verification of open system behaviour in an arc volcano geochemical and petrological data for samples from well documented eruptions that occurred at ruapehu volcano over the period 1945 1996 can be used to illustrate the complexity of short term geochemical variation in an arc type volcano collectively data from ruapehu volcano show trends with time of increasing sio2 abundance and rising 87sr 86sr ratios consistent with broad control by assimilation and crystal fractionation processes afc however the magmas emplaced during the past fifty years show geochemical variability that spans most of the range shown by lavas erupted over the entire history of the volcano magma compositions fluctuate through wide ranges over relatively short time intervals reflecting the effects of processes associated with magma recharge events within the volcano these complex trends are also manifested when the geochemistry and petrography of sequences of prehistoric lavas are examined in detail and they arise from short term effects that are imposed during recharge on the overall afc trend we show that the temporal geochemical and petrographic variations among erupted magmas are modulated by processes of mixing and mingling between fresh magma from below and stagnant melt and entrained crystals from earlier events remaining in the volcanic edifice probably in dikes and sills these processes are probably replicated over longer time periods hundreds to thousands of years as melts arrested at different levels in the near surface conduit system are progressively displaced by new magma batches arc type volcanoes such as ruapehu are characterised by pulsatory growth in which bursts of high magma production are superimposed on a background of subdued but more or less continuous activity this style of activity is difficult to predict through the usual seismicity ground deformation lake water geochemistry volcano monitoring techniques and petrology and geochemistry may provide the basis for an alternative strategy

interseismic coupling segmentation and mechanical behavior of the central chile subduction zone global positioning system gps measurements carried out in chile over the last two decades showed that an entire portion of the nazca south america subduction zone 38 s 24 s was locked over this period of time the induced accumulation of elastic deformation in the upper plate was not released until the recent maule earthquake of 27 february 2010 mw 8 8 that ruptured the southern part of this section locking or coupling between the two plates varies both with depth and along strike here we use our own gps data an updated solution of our extended network in central chile combined with other published data sets to quantify the spatial variations of the coupling that prevailed before the maule earthquake using a simple elastic model based on the back slip assumption we show that coupling variations on the subduction plane are sufficient to explain the observed surface deformation with no need of a sliver in central chile we identify four segments characterized by higher coupling and separated by narrow areas of lower coupling this segmentation is in good agreement with historical and recent seismicity in chile in particular the narrow zones of lower coupling seem to have stopped most large seismic ruptures including maule s these zones are often associated with irregular bathymetric or coastal features fracture zones or peninsulas finally coseismic and early post seismic slip distribution of the maule earthquake occurring either in previously highly or weakly coupled zones map a complex distribution of velocity weakening and velocity strengthening patches on the subduction interface

swash zone sediment transport step dynamics and morphological response on a gravel beach abstract state of the art morphodynamic field data were collected from slapton sands uk a fine gravel beach d50 2 10 mm over a 10 day period under a range of wave tide conditions comprising a mixture of southerly swell and easterly wind waves hs 0 5 1 m ts 4 8 s tide range 3 4 m over the field period the upper beach experienced accretion and berm formation during tides with low steepness swell dominated wave conditions h l 0 01 surprisingly the intertidal beach showed an opposite trend with sediment losses under swell conditions and an increase in sediment volume due to wind waves and suggests that upper beach morphological change can be decoupled from the overall sediment budget a submerged accretionary feature the beach step grew and migrated onshore on the rising tide typically reaching a maximum relief of around 0 5 m then gradually decreased in prominence while migrating offshore as the tide fell resulting in little net morphological change the step was better developed during the falling tide than the rising tide and through its control on the swash hydro and sediment dynamics the step had a significant effect on the development of the berm swash flow velocities under the conditions measured were often in excess of 2 m s 1 for both the uprush and the backwash onshore mean flows occurred in the upper swash region 40 inundation was characterised by offshore mean flows swash infiltration losses in the swash zone increased from 40 in the lower swash region to 100 in the upper swash region the most energetic swash flows and the strongest offshore mean flows occurred at the transition between swash zone and surf zone 90 100 inundation

the hekla eruption 1980 1981 the sixteenth eruption of hekla since 1104 began on august 17th 1980 after the shortest repose period on record only ten years the eruption started with a plinian phase and simultaneously lava issued at high rate from a fissure that runs along the hekla volcanic ridge the production rate declined rapidly after the first day and the eruption stopped on august 20th a total of 120 million m3 of lava and about 60 million m3 of airborne tephra were produced during this phase of the activity in the following seven months steam emissions were observed on the volcano activity was renewed on april 9th 1981 and during the following week additional 30 million m3 of lava flowed from a summit crater and crater rows on the north slope

continuing megathrust earthquake potential in chile after the 2014 iquique earthquake the 2014 iquique event was not the earthquake that had been expected to fill the regional seismic gap given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence two groups publishing in this issue of nature analyse the seismic context of the iquique earthquake that occurred off the coast of northern chile on 1 april 2014 in a seismic zone that had been quiescent since a significant event in 1877 gavin hayes et al identify areas of remaining or elevated earthquake hazard along the megathrust fault in the region and conclude that the 2014 iquique event was not the earthquake that had been anticipated given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years they suggest that it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence bernd schurr et al show that the april 2014 earthquake broke a central fraction of the northern chile seismic gap the last major segment of the south american plate boundary that had yet to rupture in the past century from july 2013 up to the april earthquake they identify three seismic clusters along this part of the plate boundary each lasting a few weeks with earthquakes of increasing peak magnitudes they conclude that these seismic clusters and their slip transients reflect a gradual weakening of the central part of the seismic gap that was instrumental in initiating the final failure the seismic gap theory1 identifies regions of elevated hazard based on a lack of recent seismicity in comparison with other portions of a fault it has successfully explained past earthquakes see for example ref 2 and is useful for qualitatively describing where large earthquakes might occur a large earthquake had been expected in the subduction zone adjacent to northern chile3 4 5 6 which had not ruptured in a megathrust earthquake since a m 8 8 event in 1877 on 1 april 2014 a m 8 2 earthquake occurred within this seismic gap here we present an assessment of the seismotectonics of the march april 2014 iquique sequence including analyses of earthquake relocations moment tensors finite fault models moment deficit calculations and cumulative coulomb stress transfer this ensemble of information allows us to place the sequence within the context of regional seismicity and to identify areas of remaining and or elevated hazard our results constrain the size and spatial extent of rupture and indicate that this was not the earthquake that had been anticipated significant sections of the northern chile subduction zone have not ruptured in almost 150 years so it is likely that future megathrust earthquakes will occur to the south and potentially to the north of the 2014 iquique sequence

breaker turbulence and sediment suspension in the surf zone field measurements of fluid velocities and suspended sediment concentrations were used to investigate the relative role of coherent vortices related to wave breaking in suspended sediment dynamics the measurements were obtained from a barred intermediate type beach and the instrument rig was exposed to a range of wave types during the experiment including shoaling waves and both spilling and plunging breakers the time scale of the observed breaker vortices was 5 hz and thus in the frequency range of wave orbital motion coherent breaker vortices were separated from wave orbital motions and incoherent higher frequency turbulence using a threshold magnitude for the vertical velocity component plunging breakers displayed the largest root mean square rms and maximum vertical velocities the latter reaching approximately 1 m s 1 these measurements were made at an elevation of 0 15 m above the bed given the observed scale of the breaker vortices and the phase match between suspended sediment concentrations and fluid velocities the turbulence injected into the water column by the plunging breakers played a significant role in suspending bed sediment on the other hand the role of coherent vortex structures in suspending sediment under spilling breakers and shoaling waves is more limited rms vertical velocities under the spilling breakers and shoaling waves in this experiment were respectively a factor 2 and 4 smaller than for plunging breakers different phase relationships were observed between the horizontal fluid velocity and vortex induced sediment suspension for each of the wave types which may contribute to an explanation of net offshore and onshore sediment transport observed during episodes of beach erosion and recovery respectively

evolution of a vent hosted hydrothermal system beneath ruapehu crater lake new zealand a two year chemical monitoring program of ruapehu crater lake shows that it has evolved considerably since the volcano s more active eruptive periods in the early 1970s the present ph 20 c of 0 6 is about one half unit more acid than the baseline values in the 1970s whereas s cl ratios have increased markedly owing in part to declining hcl inputs into the lake but also to absolute increases in so4 levels which now stand at the highest values ever recorded increases in k mg and na mg ratios over the 20 year period are attributed to hydrothermal reaction processes in the vent which are presently causing dissolution of previously formed alteration phases such as natroalunite these observations combined with results of a recent heat budget analysis of the lake have led to the development of hydrothermal convection model for the upper portion of the vent possible vent lake chemical reaction processes between end member reactants have been modelled with the computer code chiller the results are consistent with the view that variations in lake chemistry which are initiated by the introduction of fresh magmatic material into the vent reflect the extent of dissolution reaction progress on the magmatic material and or its alteration products the results also provide insights into the role of such vent processes in the formation of high sulfidation type ore deposits

modeling of seismic hazard for turkey using the recent neotectonic data abstract recent developments in the neotectonic framework of turkey introduced new tectonic elements necessitating the reconstruction of turkey s seismic hazard map in this regard 14 seismic source zones were delineated maximum earthquake magnitudes for each seismic zones were determined using the fault rupture length approximation regression coefficients of the earthquake magnitude frequency relationships for the seismic zones were compiled mostly from earlier works along with these data a strong ground motion attenuation relationship developed by joyner and boore joyner w b boore d m 1988 measurement characterization and prediction of strong ground motion earthquake engineering and soil dynamics 2 recent advances ground motion evaluation pp 43 102 was utilized to model the seismic hazard for turkey using the probabilistic approach for the modeling the earthquake location uncertainty concept was employed a grid of 5106 points with 0 2 intervals was constituted for the area encompassed by the 25 46 e longitudes and 35 43 n latitudes for the return periods of 100 and 475 years the peak horizontal ground acceleration pga in bedrock was computed for each grid point isoacceleration maps for the return periods of 100 and 475 years were constructed by contouring the pga values at each node

rheological controls on the eruption potential and style of an andesite volcano a case study from mt ruapehu new zealand abstract the evolving magma rheology of three recent ruapehu eruptions 1969 1977 and 1995 is estimated using a combination of thermodynamic models and rheological calculations supported by textural observations of the erupted scoria we use a well established thermodynamic model to determine the composition of these representative ruapehu magmas from 300mpa to 30mpa the outputs of the model provide the changing crystal and bubble content in a closed system assuming no gas loss as well as the fractionating melt compositions we calculate the melt viscosity and the effect of bubbles and crystals to quantify the rheology of the magma during ascent under assumed equilibrium conditions the moderately high phenocryst content of ruapehu scoria 30 means that only a small amount of additional microlite crystallisation 5 would result in a yield strength which may lead the magma to stall however if the strain rates are high enough more crystallisation would be possible without developing a yield stress this suggests that microlite rich magmas are almost certain to stall unless they encounter significant fluid addition from a source such as a hydrothermal system groundwater or surface water i e ruapehu s crater lake ruapehu magmas are initially h 2 o undersaturated and as a consequence crystallisation and bubble growth were suppressed until the magma achieved saturation at 100 to 50 mpa from this analysis we suggest that ruapehu magmas are more likely to erupt compared to magmas of a similar composition that are h 2 o saturated this partly explains the regular albeit small volume eruptions at ruapehu and the propensity for phreatomagmatic eruptions when the magma water ratio is low

volcano tectonic earthquakes a new tool for estimating intrusive volumes and forecasting eruptions abstract we present data on 136 high frequency earthquakes and swarms termed volcano tectonic vt seismicity which preceded 111 eruptions at 83 volcanoes plus data on vt swarms that preceded intrusions at 21 other volcanoes we find that vt seismicity is usually the earliest reported seismic precursor for eruptions at volcanoes that have been dormant for decades or more and precedes eruptions of all magma types from basaltic to rhyolitic and all explosivities from vei 0 to ultraplinian vei 6 at such previously long dormant volcanoes because large eruptions occur most commonly during resumption of activity at long dormant volcanoes vt seismicity is an important precursor for the earth s most dangerous eruptions vt seismicity precedes all explosive eruptions of vei 5 and most if not all vei 4 eruptions in our data set surprisingly we find that the vt seismicity originates at distal locations on tectonic fault structures at distances of one or two to tens of kilometers laterally from the site of the eventual eruption and rarely if ever starts beneath the eruption site itself the distal vt swarms generally occur at depths almost equal to the horizontal distance of the swarm from the summit out to about 15 km distance beyond which hypocenter depths level out we summarize several important characteristics of this distal vt seismicity including swarm like nature onset days to years prior to the beginning of magmatic eruptions peaking of activity at the time of the initial eruption whether phreatic or magmatic and large non double couple component to focal mechanisms most importantly we show that the intruded magma volume can be simply estimated from the cumulative seismic moment of the vt seismicity from log10 v 0 77 log moment 5 32 with volume v in cubic meters and seismic moment in newton meters because the cumulative seismic moment can be approximated from the size of just the few largest events and is quite insensitive to precise locations the intruded magma volume can be quickly and easily estimated with few short period seismic stations notable cases in which distal vt events preceded eruptions at long dormant volcanoes include nevado del ruiz 1984 1985 pinatubo 1991 unzen 1989 1995 soufriere hills 1995 shishaldin 1989 1999 tacana 1985 1986 pacaya 1980 1984 rabaul 1994 and cotopaxi 2001 additional cases are recognized at frequently active volcanoes including popocateptl 2001 2003 and mauna loa 1984 we present four case studies pinatubo soufriere hills unzen and tacana in which we demonstrate the above mentioned vt characteristics prior to eruptions using regional data recorded by neic we recognized in near real time that a huge distal vt swarm was occurring deduced that a proportionately huge magmatic intrusion was taking place beneath the long dormant sulu range new britain island papua new guinea that it was likely to lead to eruptive activity and warned rabaul volcano observatory days before a phreatic eruption occurred this confirms the value of this technique for eruption forecasting we also present a counter example where we deduced that a vt swarm at volcan cosiguina nicaragua indicated a small intrusion insufficient to reach the surface and erupt finally we discuss limitations of the method and propose a mechanism by which this distal vt seismicity is triggered by magmatic intrusion

a 20th century acceleration in global sea level rise 1 multi century sea level records and climate models indicate an acceleration of sea level rise but no 20th century acceleration has previously been detected a reconstruction of global sea level using tide gauge data from 1950 to 2000 indicates a larger rate of rise after 1993 and other periods of rapid sea level rise but no significant acceleration over this period here we extend the reconstruction of global mean sea level back to 1870 and find a sea level rise from january 1870 to december 2004 of 195 mm a 20th century rate of sea level rise of 1 7 0 3 mm yr 1 and a significant acceleration of sea level rise of 0 013 0 006 mm yr 2 this acceleration is an important confirmation of climate change simulations which show an acceleration not previously observed if this acceleration remained constant then the 1990 to 2100 rise would range from 280 to 340 mm consistent with projections in the ipcc tar

a simple autocorrelation algorithm for determining grain size from digital images of sediment abstract autocorrelation between pixels in digital images of sediment can be used to measure average grain size of sediment on the bed grain size distribution of bed sediment and vertical profiles in grain size in a cross sectional image through a bed the technique is less sensitive than traditional laboratory analyses to tails of a grain size distribution but it offers substantial other advantages it is 100 times as fast it is ideal for sampling surficial sediment the part that interacts with a flow it can determine vertical profiles in grain size on a scale finer than can be sampled physically and it can be used in the field to provide almost real time grain size analysis the technique can be applied to digital images obtained using any source with sufficient resolution including digital cameras digital video or underwater digital microscopes for real time grain size mapping of the bed

ground motion prediction equation for the chilean subduction zone abstract a ground motion prediction equation for the horizontal component of the response spectral values from the chilean subduction zone is developed the dataset contains 3774 recordings from 473 earthquakes including the latest megathrust events that occurred in the country i e 2010 m w 8 8 maule 2014 m w 8 1 iquique and 2015 m w 8 3 illapel the functional form for the median model follows the proposal by abrahamson et al 2016 site effects are estimated based on v s 30 an additional model is built using only ground motions associated with measured values of v s 30 and reliable m w estimates termed the high quality hq model the standard deviation of the hq model is much lower than the main model particularly the component of the standard deviation that corresponds to site to site variability indicating that better site characterization can significantly reduce the overall uncertainty in ground motion estimation electronic supplement tables of regression coefficients for the high quality hq model and 95 confidence intervals for model s coefficients and matlab implementation of the ground motion prediction equation gmpe

concepts in gravel beach dynamics abstract the dominant processes in gravel beach dynamics are reviewed highlighting some common themes which unify the various components of the gravel beach system the repercussions of which impart on how gravel beach dynamics might be understood conceptually in particular gravel beach dynamics are thought to be highly dependent on the temporal and spatial variation in grain size and the continual adjustments made by an active beach step both of which act not only as the expression of changing morphodynamic conditions but also as a controlling influence morphodynamics the notion that the exchanges on beaches between the hydrodynamics sediment transport and morphological change takes the form of reciprocal relationships which are mediated through feedback mechanisms in such a way that they cannot be thought of or studied independently is not a new one yet it appears that for the gravel beach morphodynamics must be re defined to describe conditions where variations in sediment size are thought to deserve parity rather than as merely a sequent entity or boundary condition morpho sedimentary dynamics is a phrase coined to intuit such cause and effect detailing the co evolution of morphology hydro hydraulics and sediment properties whilst acknowledging causative pluralism feedbacks and multiplier effects this is the recommended conceptual framework within which to crystallise thought and organise further research for the gravel beach essentially it increases the minimum number of parameters needed to describe the state of the gravel beach as a physical system therefore it is advised that simplicity will be most expedient in our future modelling efforts if complexity is to be adequately encapsulated

beach morphology and change along the mixed grain size delta of the dammed elwha river washington abstract sediment supply provides a fundamental control on the morphology of river deltas and humans have significantly modified these supplies for centuries here we examine the effects of almost a century of sediment supply reduction from the damming of the elwha river in washington on shoreline position and beach morphology of its wave dominated delta the mean rate of shoreline erosion during 1939 2006 is 0 6 m yr which is equivalent to 24 000 m3 yr of sediment divergence in the littoral cell a rate approximately equal to 25 50 of the littoral grade sediment trapped by the dams semi annual surveys between 2004 and 2007 show that most erosion occurs during the winter with lower rates of change in the summer shoreline change and morphology also differ spatially negligible shoreline change has occurred updrift west of the river mouth where the beach is mixed sand to cobble cuspate and reflective the beach downdrift east of the river mouth has had significant and persistent erosion but this beach differs in that it has a reflective foreshore with a dissipative low tide terrace downdrift beach erosion results from foreshore retreat which broadens the low tide terrace with time and the rate of this kind of erosion has increased significantly from 0 8 m yr during 1939 1990 to 1 4 m yr during 1990 2006 erosion rates for the downdrift beach derived from the 2004 2007 topographic surveys vary between 0 and 13 m yr with an average of 3 8 m yr we note that the low tide terrace is significantly coarser mean grain size 100 mm than the foreshore mean grain size 30 mm a pattern contrary to the typical observation of fining low tide terraces in the region and worldwide because this cobble low tide terrace is created by foreshore erosion has been steady over intervals of at least years is predicted to have negligible longshore transport compared to the foreshore portion of the beach and is inconsistent with oral history of abundant shellfish collections from the low tide beach we suggest that it is an armored layer of cobble clasts that are not generally competent in the physical setting of the delta thus the cobble low tide terrace is very likely a geomorphological feature caused by coastal erosion of a coastal plain and delta which in turn is related to the impacts of the dams on the elwha river to sediment fluxes to the coast

observations of coarse sediment movements on the mixed beach of the elwha delta washington abstract mixed beaches with poorly sorted grains of multiple sizes are a common and globally distributed shoreline type despite this rates and mechanisms of sediment transport on mixed beaches are poorly understood a series of tracer deployments using native clasts implanted with radio frequency identifier rfid tags was used to develop a better understanding of sediment transport directions and magnitudes on the mixed grain size beach of the elwha river delta using tracer samples selected to match the distribution of the coarse fraction on the beach we find that all grain sizes up to large cobbles 128 256 mm were mobile under most measured wave conditions and move in relationship to the direction of the alongshore component of wave energy as estimated by incident breaking wave angles in locations where the breaking wave is normal to the shoreline we find that tracers move in both alongshore directions with approximately equal frequency in locations where breaking waves are oblique to the shoreline we find that alongshore transport is more unidirectional and tracers can approach average velocities of 100 m day under winter wave conditions we use the tracer cloud to estimate the beach active width the mobile layer depth and sediment velocity our results suggest that while sediment velocity increases under increased incident wave angles the active layer depth and width decrease reducing sediment flux at the site with the more oblique breaking waves this result is contrary to what is suggested by traditional wave energy transport models of alongshore sediment transport

the 1991 eruption of hekla iceland the eruption that started in the hekla volcano in south iceland on 17 january 1991 and came to an end on 11 march produced mainly andesitic lava this lava covers 23 km2 and has an estimated volume of 0 15 km3 this is the third eruption in only 20 years whereas the average repose period since 1104 is 55 years earthquakes as well as a strain pulse recorded by borehole strainmeters occurred less than half an hour before the start of the eruption the initial plinian phase was very short lived producing a total of only 0 02 km3 of tephra the eruption cloud attained 11 5 km in height in only 10 min but it became detached from the volcano a few hours later several fissures were active during the first day of the eruption including a part of the summit fissure by the second day however the activity was already essentially limited to that segment of the principal fissure where the main crater subsequently formed the average effusion rate during the first two days of the eruption was about 800 m3 s 1 after this peak the effusion rate declined rapidly to 10 20 m3 s 1 then more slowly to 1 m3 s 1 and remained at 1 12 m3 s 1 until the end of the eruption site observations near the main crater suggest that the intensity of the volcanic tremor varied directly with the force of the eruption a notable rise in the fluorine concentration of riverwater in the vicinity of the eruptive fissures occurred on the 5th day of the eruption but it levelled off on the 6th day and then remained essentially constant the volume and initial silica content of the lava and tephra the explosivity and effusion rate during the earliest stage of the eruption as well as the magnitude attained by the associated earthquakes support earlier suggestions that these parameters are positively related to the length of the preceeding repose period the chemical difference between the eruptive material of hekla itself and the lavas erupted in its vicinity can be explained in terms of a density stratified magma reservoir located at the bottom of the crust we propose that the shape of this reservoir its location at the west margin of a propagating rift and its association with a crustal weakness all contribute to the high eruption frequency of hekla

attenuation relations of strong ground motion in japan using site classification based on predominant period a spectral acceleration attenuation model for japan is presented in the present study the data set includes a very large number of strong ground motion records up to the 2003 off tokach main and aftershocks site class terms instead of individual site correction terms are used the site classes of recording stations are from a recent study on site classification for strong motion recording stations in japan according to a classification scheme that has been used in japanese engineering design the use of site class terms enables tectonic source type effects to be identified and accounted for in the present model the effects of a faulting mechanism for crustal earthquakes also are accounted for for crustal and interface earthquakes a simple form of an attenuation model with respect to distance is able to capture the main strong motion characteristics and achieves unbiased estimates for subduction slab events a simple distance modification factor is employed to achieve plausible and unbiased predictions the effects of source depth tectonic source type and faulting mechanism of crustal earthquakes are significant the need for magnitude squared terms is evaluated and the use of magnitude squared terms reduces the interevent error further

a numerical empirical approach for evaluating morphodynamic processes on gravel and mixed sand gravel beaches abstract pedrozo acuna et al pedrozo acuna a simmonds d j otta a k and chadwick a j 2006 on the cross shore profile change of gravel beaches coastal engineering 53 4 335 347 presented a numerical empirical investigation of the processes that control sediment transport in the swash zone on steep gravel beaches this was based on a sensitivity analysis of a sediment transport profile model driven by a highly non linear boussinesq model lynett p j wu t r and liu l f p 2002 modelling wave run up with depth integrated equations coastal engineering 46 89 107 which was compared to near full scale measurements performed in the gwk flume in hanover in this paper we have extended our analysis to compare these earlier results with those relating to a mixed sediment gravel and sand beach the parametric sensitivity analysis also incorporates a discussion of the effects of acceleration about which there is much debate the sensitivity analysis suggests that fluid acceleration can contribute to the onshore movement of sediment that causes steepening of initially flat beach faces composed of coarse sediment however acceleration alone cannot be the cause of the observed berm growth during the gwk tests instead a complex balance of processes is responsible for the profile evolution of coarse grained beaches with no single dominant process

seismicity associated with the 1995 1996 eruptions of ruapehu volcano new zealand narrative and insights into physical processes abstract seismicity associated with the 1995 1996 eruptions of ruapehu reflects processes associated with the intrusion of magma to shallow depth in the volcanic edifice its subsequent eruption and changes in the volcanic plumbing system resulting from the eruptions the sequence consisted of two distinct periods of eruptive activity the first lasting from september 17 1995 until late october or early november 1995 and the second from june 16 1996 until late july 1996 immediately prior to and during the early stages of the 1995 eruptions seismicity was similar to that recorded at ruapehu during the previous 25 years with the exception of the occurrence between september 17 and 25 1995 of sub 1 hz tremor which is thought to represent magmatic intrusion in early october a new pattern of seismicity was established with the disappearance of the 2 hz tremor resonator source and a change to wideband 2 10 hz tremor and wideband volcanic earthquakes this change coincided with the ejection of the last vestiges of crater lake and the change in eruptive style from phreatomagmatic to magmatic seismicity associated with the 1996 eruptions was very similar to that which accompanied the later part of the 1995 activity implying the same eruption processes and that no significant changes had occurred in the volcanic plumbing system during the intervening period geochemical geodetic and seismic precursors to the 1995 eruptions were both minor and inconsistent highlighting the difficulty in forecasting these eruptions furthermore deep volcano tectonic earthquakes were extremely rare throughout the 1995 and 1996 eruptive sequences suggesting that stresses associated with magmatic intrusion were minor this most likely resulted from the existence of either an open or a ductile pathway from the deep magma source to the surface prior to the eruptions and because the volume of magma intruded and subsequently erupted was relatively small 3

passive seismic monitoring of mine scale geothermal activity a trial at lihir open pit mine the lihir open pit mine in papua new guinea is located inside an old volcano where geothermal activity is strongly present outbursts of hot water and steam into the mining areas were a major safety concern passive seismic monitoring was carried out at the mine to investigate whether the geothermal activities could be detected and located using microseismic techniques in a mining environment in this trial sixteen triaxial geophones which can withstand temperature up to 200 c were used and installed in four deep boreholes inside the pit the microseismic events were discriminated using the sta lta triggering criterion during 6 weeks of monitoring more than 17 000 events were recorded approximately 12 of the events showed harmonic vibration characteristics similar to those observed in other geothermal and volcanic areas suggesting that the geothermal activity inside the pit was captured by the microseismic monitoring system more than 75 of the events present both p and s waves and they were interpreted to be associated with rock fracturing due to stress release near the bottom of the pit many geothermal type events were located in areas where shear events occurred implying that the detected geothermal events were not far from the mining area below the pit and they may also be associated with mining the borehole installation of the geophones significantly reduced the interference of mining noise and achieved good observation of the seismic events however equipment installation requires great attention as the geophones may be destroyed due to unexpected rising temperature within the boreholes

time variation of spectral and wavefield features of volcanic tremor at mt etna january june 1999 abstract we have studied the volcanic tremor recorded at mt etna during january june 1999 by using three component seismic stations this time period was characterised by both explosive and effusive eruptions occurring at the summit craters we found significant time variations in the trend of the overall spectral amplitude of tremor as well as in the dominant spectral peaks moreover the tremor wavefield features polarization particle motion and ratios between the amplitude of the three components of the ground velocity have been studied too confirming significant time variations this leads us to suggest the existence of at least two tremor sources a shallow one mainly characterised by relatively high frequencies 3 5 7 hz is linked to the upper portions of the active conduits and directly related to the observed eruptive activity the latter deeper source was active for only a few weeks and characterised by frequencies lower than about 2 5 hz it had no relationship with the observed eruptive activity and was speculatively related to the gas exsolution from fresh magma refilling a small batch

nasa eos terra aster volcanic topographic mapping and capability up to date accurate topographic data are a crucial resource for volcanic research and risk mitigation efforts in particular for modeling volcanic flow processes at a detailed spatial resolution in this paper we examine the utility of the advanced spaceborne thermal emission and reflection radiometer aster instrument currently operating on the nasa terra satellite which provides near infrared vnir stereo imaging from which topography can be derived we wrote software to generate digital elevation models dems from the aster level 1a product which employs an automated stereo matching technique to calculate the parallax offsets between the images acquired by the nadir and aft looking sensors comparison of aster dems with dems derived from other sources digitized 1 50 k topographic maps and aerial interferometric radar at ruapehu volcano reveal an rms error of about 10 m for the aster dem in the absence of significant atmospheric water vapor a qualitative assessment of surface features showed that the aster dem is superior to the interpolated 1 50 k map product but falls short of the detail provided by aerial interferometric radar especially in terms of stream channel preservation a second aster dem was generated for taranaki volcano where previously only 1 50 k topographic map data were available although the 2000 space shuttle radar topography mission srtm will largely remedy the previous global paucity of adequate topographic data at volcanoes such as taranaki we anticipate the problem that at active volcanoes the topography may change significantly following activity rendering the srtm data inaccurate with the high temporal coverage of the dataset aster not only provides a means to update significant 10 m topographic measurements at active volcanoes via a time series of dems but also provides a simultaneous means to map surface cover and localized land use via the near infrared sensors thus we demonstrate the potential for up to date volcanic economic risk assessment using geographic information systems gis analysis

radio frequency identification rfid technology applied to the definition of underwater and subaerial coarse sediment movement abstract in this paper radio frequency identification technology has been applied to track both underwater and subaerial displacement of pebbles along an artificial coarse beach at marina di pisa italy several preliminary laboratory tests have been performed to adapt the rfid technique for underwater use which has been the primary impediment to this promising approach to the study of coarse sediment transport and movement tests showed the reliability of low frequencies for this kind of work since they enable good signal transmission and reception through water passive abs plastic transponders were inserted into about 100 pebbles and released onto the beach in march 2009 a core 125 reader was chosen as the operating antenna to continuously transmit low frequency 125 khz signals an acoustic signal toned whenever a pebble was detected while the unambiguous identification code of the pebble is shown immediately on the screen of a laptop connected to the reader the positions of the pebbles were recorded with a total station after two months may 2009 74 marked pebbles were retrieved 77 of the total the positions of the retrieved pebbles were also recorded with the total station thus allowing calculation of the coarse sediment transport tendency about 60 of the recovered pebbles 44 out of 74 were found on the upper shoreface the analysis of the marked pebble trajectories revealed a divergent transport movement in the northernmost sector of the beach this movement was probably triggered by an irregularity of the submerged breakwater fronting the shoreline the southern sector is characterised by chaotic pathways related to the formation and evolution of beach cusps this outcome highlights and confirms the importance of a complete definition of the beach system with no separation between the underwater and the subaerial portion of the shore when it comes to sediment transport and movement this successful application of rfid technology to the underwater environment provides a chance to broaden understanding of a topic in need of further study

the heat source of ruapehu crater lake deductions from the energy and mass balances abstract regular observations of temperature outflow rates and water chemistry of crater lake mt ruapehu new zealand have been made for the last 25 years these data have been used to derive a model of the dynamics of the lake and determine the input of energy mass and chloride from the volcano to the crater lake the recent relatively quiescent state of the volcano when virtually no heat has been input to the lake has also enabled an assessment to be made of the surface heat loss characteristics which play an important role in the model of the lake the modelling suggests that since about 1982 the ratio of the volcanic heat to mass added to the base of the lake is about 6 mj kg which is not compatible with heating of the lake by magmatic steam alone thus only about 50 of the heating has been by magmatic steam it is suggested that heat could be transferred from a magmatic source to the region below the lake by a heat pipe mechanism commonly associated with geothermal systems the simultaneous upward movement of vapour phase and downward movement of liquid phase from condensed vapour allows efficient heat transfer without overall mass transfer the permeability necessary to supply the required heat is of the order of 10 darcy and is consistent with a rubble filled vent for at least the last five years there has been a characteristic pattern in the crater lake temperature record with alternate heating and cooling phases the heating phase generally lasts for one or two months while the cooling phase lasts for six months to a year a possible explanation for this cyclic behaviour is the presence of a layer of liquid sulphur under crater lake acting as a partial barrier between the heat pipe and the lake the unusual variations of the viscosity of liquid sulphur with temperature will mean that at temperatures greater than 160 c the layer of sulphur becomes highly viscous and would block any upwards steam flow and hence stop the heat input to crater lake so producing a cooling phase this blockage would last until the heating from below raised the temperature of the sulphur beyond the high viscosity region so gases could again pass through the sulphur

historical and recent large megathrust earthquakes in chile abstract recent earthquakes in chile 2014 mw 8 2 iquique 2015 mw 8 3 illapel and 2016 mw 7 6 chiloe have put in evidence some problems with the straightforward application of ideas about seismic gaps earthquake periodicity and the general forecast of large megathrust earthquakes in northern chile before the 2014 iquique earthquake 4 large earthquakes were reported in written chronicles 1877 1786 1615 and 1543 in north central chile before the 2015 illapel event 3 large earthquakes 1943 1880 1730 were reported and the 2016 chiloe earthquake occurred in the southern zone of the 1960 valdivia megathrust rupture where other large earthquakes occurred in 1575 1737 and 1837 the periodicity of these events has been proposed as a good long term forecasting however the seismological aspects of historical chilean earthquakes were inferred mainly from old chronicles written before subduction in chile was discovered here we use the original description of earthquakes to re analyze the historical archives our interpretation shows that a priori ideas like seismic gaps and characteristic earthquakes influenced the estimation of magnitude location and rupture area of the older chilean events on the other hand the advance in the characterization of the rheological aspects that controlled the contact between nazca and south american plate and the study of tsunami effects provide better estimations of the location of historical earthquakes along the seismogenic plate interface our re interpretation of historical earthquakes shows a large diversity of earthquakes types there is a major difference between giant earthquakes that break the entire plate interface and those of mw 8 0 that only break a portion of it

seismic evolution of the 1989 1990 eruption sequence of redoubt volcano alaska abstract redoubt volcano in south central alaska erupted between december 1989 and june 1990 in a sequence of events characterized by large tephra eruptions pyroclastic flows lahars and debris flows and episodes of dome growth the eruption was monitored by a network of five to nine seismic stations located 1 to 22 km from the summit crater notable features of the eruption seismicity include 1 small long period events beginning in september 1989 which increased slowly in number during november and early december 2 an intense swarm of long period events which preceded the initial eruptions on december 14 by 23 hours 3 shallow swarms 0 to 3 km of volcano tectonic events following each eruption on december 15 4 a persistent cluster of deep 6 to 10 km volcano tectonic earthquakes initiated by the eruptions on december 15 which continued throughout and beyond the eruption 5 an intense swarm of long period events which preceded the eruptions on january 2 and 6 nine additional intervals of increased long period seismicity each of which preceded a tephra eruption hypocenters of volcano tectonic earthquakes suggest the presence of a magma source region at 6 10 km depth earthquakes at these depths were initiated by the tephra eruptions on december 15 and likely represent the readjustment of stresses in the country rock associated with the removal of magma from these depths the locations and time history of these earthquakes coupled with the eruptive behavior of the volcano suggest this region was the source of most of the erupted material during the 1989 1990 eruption this source region appears to be connected to the surface by a narrow pipe like conduit as inferred from the hypocenters of volcano tectonic earthquakes concentrations of shallow volcano tectonic earthquakes followed each of the tephra eruptions on december 15 these shocks may represent stress readjustment in the wall rock related to the removal of magma and volatiles at these depths this shallow zone was the source area of the majority of long period seismicity through the remainder of the eruption the long period seismicity likely reflects the pressurization of the shallow portions of the magmatic system

spectral characteristics of volcano tectonic earthquake swarms in nevado del ruiz volcano colombia abstract spectral analyses for volcano tectonic earthquakes were carried out at nevado del ruiz volcano nrv for the period 1985 1996 for several earthquake swarms around the volcano named north east west south and crater swarm zones important spectral peaks for each earthquake swarm zone were found by counting the number of spectra that had the same spectral peaks each swarm zone showed some characteristic peaks which could help to differentiate between them however the most important peaks were similar for all the zones these results suggest that the earthquake swarms at nrv were influenced directly by the source activity of the volcano and could also be influenced by the site effect some temporal changes were observed in spectral parameters such as a change in the frequency contents in almost all the swarm zones and the frequency of the p waves in the west earthquake swarm zone before the eruptions on november 13 1985 and september 1 1989 p waves showed low frequencies 1 2 hz at the west earthquake swarm after the eruptions the frequencies of p increased 2 4 hz this fact showed that changes decreasing of frequencies in the spectra of p waves at the west earthquake swarm could help in the monitoring of volcanic activity at nrv this swarm zone seems to be related directly with the most important volcanic crises that have occurred this suggests that the west swarm zone should be monitored in more detail in the future

probabilistic seismic hazard assessment for northeast india region northeast india bounded by latitudes 20 30 n and longitudes 87 98 e is one of the most seismically active areas in the world this region has experienced several moderate to large sized earthquakes including the 12 june 1897 shillong earthquake mw 8 1 and the 15 august 1950 assam earthquake mw 8 7 which caused loss of human lives and significant damages to buildings highlighting the importance of seismic hazard assessment for the region probabilistic seismic hazard assessment of the region has been carried out using a unified moment magnitude catalog prepared by an improved general orthogonal regression methodology geophys j int 190 1091 1096 2012 probabilistic seismic hazard assessment of northeast india region ph d thesis department of earthquake engineering iit roorkee roorkee 2013 with events compiled from various databases isc neic gcmt imd and other available catalogs the study area has been subdivided into nine seismogenic source zones to account for local variation in tectonics and seismicity characteristics the seismicity parameters are estimated for each of these source zones which are input variables into seismic hazard estimation of a region the seismic hazard analysis of the study region has been performed by dividing the area into grids of size 0 1 0 1 peak ground acceleration pga and spectral acceleration sa values for periods of 0 2 and 1 s have been evaluated at bedrock level corresponding to probability of exceedance pe of 50 20 10 2 and 0 5 in 50 years these exceedance values correspond to return periods of 100 225 475 2475 and 10 000 years respectively the seismic hazard maps have been prepared at the bedrock level and it is observed that the seismic hazard estimates show a significant local variation in contrast to the uniform hazard value suggested by the indian standard seismic code indian standard criteria for earthquake resistant design of structures fifth edition part i bureau of indian standards new delhi 2002 not only holistic treatment of earthquake catalog and seismogenic zones has been performed but also higher resolution in spatial distribution could be achieved the cov maps have been provided with the strong ground motion maps under various conditions to show the confidence in the results obtained results obtained in the present study would be helpful for risk assessment and other disaster mitigation related studies

intertidal sand body migration along a megatidal coast kachemak bay alaska 1 using a digital video based argus beach monitoring system abms on the north shore of kachemak bay in south central alaska we document the timing and magnitude of alongshore migration of intertidal sand bed forms over a cobble substrate during a 22 month observation period two separate sediment packages sand bodies of 1 2 m amplitude and 200 m wavelength consisting of well sorted sand were observed to travel along shore at annually averaged rates of 278 m yr 0 76 m d and 250 m yr 0 68 m d respectively strong seasonality in migration rates was shown by the contrast of rapid winter and slow summer transport though set in a megatidal environment data indicate that sand body migration is driven by eastward propagating wind waves as opposed to net westward directed tidal currents greatest weekly averaged rates of movement exceeding 6 m d coincided with wave heights exceeding 2 m suggesting a correlation of wave height and sand body migration because kachemak bay is partially enclosed waves responsible for sediment entrainment and transport are locally generated by winds that blow across lower cook inlet from the southwest the direction of greatest fetch our estimates of sand body migration translate to a littoral transport rate between 4 400 6 300 m3 yr assuming an enclosed littoral cell minimal riverine sediment contributions and a sea cliff sedimentary fraction of 0 05 we estimate long term local sea cliff retreat rates of 9 14 cm yr applying a numerical model of wave energy dissipation to the temporally variable beach morphology suggests that sand bodies are responsible for enhancing wave energy dissipation by 13 offering protection from sea cliff retreat

the use of passive integrated transponder pit tags to trace cobble transport in a mixed sand and gravel beach on the high energy oregon coast usa abstract cobble transport is investigated on a mixed sand and gravel beach on the high energy oregon coast using radio frequency identification technology rfid to detect passive integrated transponder pit tags inserted in the gravels pit tags are glass encapsulated transponders that are activated when an antenna passes near them with each tag characterized by its own unique identification number the tags are sealed within the cobbles minimizing any effect on the hydrodynamic character of the particles the tags draw power from the antenna itself and have a potential lifespan of up to 50 years pit tags are simple to use and inexpensive permitting the release and tracking of large numbers of gravel particles as a result pit tags have tremendous potential for examining the complexities of particle movement and the parameters that control their distribution on the beach our experiments have been conducted at cape lookout state park on the northern oregon coast on a composite beach where a seasonally variable sand beach fronts a mixed sand and gravel beach with the latter impacted by waves only during the winter when the sand beach is cut back a total of 400 cobble tracers have been released at five different locations subsequent monitoring of the gravel tracers revealed that they can be detected up to 1 m below the surface of the beach using a 1 0 m diameter antenna and up to 0 5 m below the surface using a smaller 0 3 m diameter antenna while their positions were determined using a trimble 5700 5800 rtk dgps survey system gravel tracer recovery rates were found to vary significantly between the different release points from as high as 90 recovery after 8 months to a low of 18 after 17 months the lowest recovery rates are thought to be due to the extent of aggradation of the sandy beach during the summer partially covering the gravel berm and burying the tracer particles to depths where they could not be detected by the antennas used with our rfid system relocation of the gravel tracers has revealed a predominant northward migration of the cobbles and locally demonstrate a strong cross shore transport both upslope and downslope movements initial attempts to examine the relationship between the transport distances and particle sizes and shapes have thus far revealed that the larger gravels are tending to outrun the smaller particles this is despite the fact that both small and large particles were found to be capable of being transported both short and long distances in contrast our results revealed no relationships between particle shape and distance moved in time it is expected that the pit tag tracers may begin to yield more definitive patterns of sorting the results did highlight that the gravel movement occurs predominantly near the sand gravel beach junction on the profiles a region dominated by a higher incidence of wave breaking and strong swash activity finally our analyses revealed the potential for using pit tags to provide field assessments of the abrasion rates of gravel particles having already found measurable degrees of weight loss to abrasion in our experiments

earthquake classification location and error analysis in a volcanic environment implications for the magmatic system of the 1989 1990 eruptions at redoubt volcano alaska abstract determination of the precise locations of seismic events associated with the 1989 1990 eruptions of redoubt volcano posed a number of problems including poorly known crustal velocities a sparse station distribution and an abundance of events with emergent phase onsets in addition the high relief of the volcano could not be incorporated into the hypoellipse earthquake location algorithm this algorithm was modified to allow hypocenters to be located above the elevation of the seismic stations the velocity model was calibrated on the basis of a posteruptive seismic survey in which four chemical explosions were recorded by eight stations of the permanent network supplemented with 20 temporary seismographs deployed on and around the volcanic edifice the model consists of a stack of homogeneous horizontal layers setting the top of the model at the summit allows events to be located anywhere within the volcanic edifice detailed analysis of hypocentral errors shows that the long period lp events constituting the vigorous 23 hour swarm that preceded the initial eruption on december 14 could have originated from a point 1 4 km below the crater floor a similar analysis of lp events in the swarm preceding the major eruption on january 2 shows they also could have originated from a point the location of which is shifted 0 8 km northwest and 0 7 km deeper than the source of the initial swarm we suggest this shift in lp activity reflects a northward jump in the pathway for magmatic gases caused by the sealing of the initial pathway by magma extrusion during the last half of december volcano tectonic vt earthquakes did not occur until after the initial 23 hour long swarm they began slowly just below the lp source and their rate of occurrence increased after the eruption of 01 52 ast on december 15 when they shifted to depths of 6 to 10 km after january 2 the vt activity migrated gradually northward this migration suggests northward propagating withdrawal of magma from a plexus of dikes and or sills located in the 6 to 10 km depth range precise relocations of selected events prior to january 2 clearly resolve a narrow steeply dipping pencil shaped concentration of activity in the depth range of 1 7 km which illuminates the conduit along which magma was transported to the surface a third event type named hybrid which blends the characteristics of both vt and lp events originates just below the lp source and may reflect brittle failure along a zone intersecting a fluid filled crack the distribution of hybrid events is elongated 0 2 0 4 km in an east west direction this distribution may offer constraints on the orientation and size of the fluid filled crack inferred to be the source of the lp events

seismic hazard map of turkey using the deterministic approach abstract because the instrumental records of turkey are far from being satisfactory for modeling the seismic hazard using the probabilistic approach an attempt was made in this study to accomplish it through the deterministic way in this regard all active faults of turkey small and large were evaluated together to obtain major fault systems then the procedure suggested by wells and coppersmith bull seismol soc am 4 1994 975 applied to those faults to obtain the maximum magnitude earthquake that they can generate to do this it was assumed that 1 3 of the total fault length would rupture to yield the maximum earthquake following that seven different attenuation relationships of the strong ground motion were utilized to calculate the maximum horizontal ground accelerations for the whole turkey at 0 2 intervals using the computer model tumdes written in basic programming language the computed peak ground acceleration pga values were contoured and the iso acceleration map based on sadigh et al seismol res lett 1 1997 180 relationship was selected as the new seismic hazard map of turkey on which the seismic zonations were determined as following pga 0 3 g zone 1 0 3 g

a volcanic tremor monitoring system abstract the digitising system installed at the chateau observatory in the north island of new zealand to monitor ruapehu and ngauruhoe volcanoes is used to digitise the seismic records from three seismometers and to calculate the power spectra of volcanic tremor in real time with the smoothed power spectra being recorded every 5 minutes on magnetic disk the 5 minute averages are later processed to remove the effects of earthquakes and interference before hourly averages are calculated this system has a better dynamic range than visual chart records and analysis of the data requires much less labour

tracking volcanic and geothermal activity in the tongariro volcanic centre new zealand with shear wave splitting tomography abstract we apply a simplified two dimensional tomographic inversion of recorded delay times of shear wave splitting and a spatial averaging of fast direction of anisotropy to data from temporary seismic deployments in the tongariro volcanic centre in order to identify regions of changing seismic anisotropy we observe a region of strong anisotropy 0 025 s km greater than the surrounding area centered on mt ruapehu in 1995 the time of a major magmatic eruption this is interpreted to be due to an increase in fluid filled fractures during the eruption we also observe strong anisotropy 0 018 s km greater than the surrounding area and a change in fast direction 80 at mt tongariro in 2008 and examine the temporal evolution of this anomaly using clusters of earthquakes and permanent seismic stations in operation since 2004 this anomaly is attributed to a change in the geothermal system a pronounced and unchanging feature is observed at waiouru even when the source and receiver locations differ we therefore conclude that the transient features of strong anisotropy associated with volcanic and geothermal activity detected with this method are also robust