statistical analyses and characteristics of volcanic tremor on stromboli volcano italy a study of volcanic tremor on stromboli is carried out on the basis of data recorded daily between 1993 and 1995 by a permanent seismic station str located 1 8 km away from the active craters we also consider the signal of a second station tf1 which operated for a shorter time span changes in the spectral tremor characteristics can be related to modifications in volcanic activity particularly to lava effusions and explosive sequences statistical analyses were carried out on a set of spectra calculated daily from seismic signals where explosion quakes were present or excluded principal component analysis and cluster analysis were applied to identify different classes of spectra three clusters of spectra are associated with two different states of volcanic activity one cluster corresponds to a state of low to moderate activity whereas the two other clusters are present during phases with a high magma column as inferred from the occurrence of lava fountains or effusions we therefore conclude that variations in volcanic activity at stromboli are usually linked to changes in the spectral characteristics of volcanic tremor site effects are evident when comparing the spectra calculated from signals synchronously recorded at str and tf1 however some major spectral peaks at both stations may reflect source properties statistical considerations and polarization analysis are in favor of a prevailing presence of p waves in the tremor signal along with a position of the source northwest of the craters and at shallow depth

volcanic tremor at mount etna january 1984 march 1985 its relationship to the eruptive activity and modelling of the summit feeding system spectral analyses of volcanic tremor at etna during january 1984 march 1985 have been performed and the relationship between tremor energy and observed volcanic phenomena have been examined the highest energy levels have been observed during the paroxysmal phases of eruptions whereas a gradual decrease was linked to the lowering of eruptive activity amplitude variations with time of some spectral frequency peaks 0 95 1 20 1 45 1 65 1 80 and 2 40 hz have been compared with volcanic activity at the summit craters and on the basis of these results a new schematic diagram for the feeding system of the summit vents is proposed

intertidal beach profile estimation using video images abstract in this paper we present a technique suitable for measurement of intertidal bathymetry over a broad range of length scales 10 1 to 10 3 m and time scales days to decades a series of time averaged images of the swash zone are used to map contour lines of the beach surface in each image contours are identified using bands of maximum brightness associated with breaking waves at the shoreline by mapping the location of these bands in a sequence of images collected over one tidal cycle contour maps of the intertidal bathymetry are generated we expect this technique to work best smallest absolute error under waves which are nearly reflective at the shoreline but break enough to be observed visually this is typical of a barred beach since the wave height at the shoreline is limited by wave breaking over the bar crest the ability of the measurements made with this technique to resolve actual beach elevation variation depends on the ratio of the measurement error variance to the true beach elevation variance thus large measurement errors may be compensated by either large tidal ranges or large temporal changes of the beach itself in a comparison to bathymetry surveyed using a differential global positioning system dgps during the duck94 experiment in duck n c the image based elevation estimates were well correlated with the actual bathymetry the deviations imagebased vs dgps measurements may be partially attributed to effects scaled by wave height at the shoreline wave induced setup and wave height saturation over the sand bar in particular setup was important during dissipative conditions the rms deviation vertical between the dgps and image based bathymetry was reduced from 0 24 m to 0 06 m by correcting for the systematic deviations due to variations in setup and wave height saturation further improvement of the elevation estimates resulted from parameterizing the actual bathymetry with a simple plane beach surface which reduced random or unresolvable measurement errors this led to estimates of the beach slope that were accurate to within 10 of the actual slope and estimates of the cross shore location of the mean sea level line accurate to about 0 50 m

observations of gravel beach dynamics during high energy wave conditions using a laser scanner the work described in this publication was supported by the epsrc project arcoes adaptation and resilience of the uk energy system to climate change epsrc reference ep 1035390 1 and by epsrc grant ep h040056 1 in partnership with the channel coastal observatory cco the full text is under embargo until 01 01 16

on the use of variance images for runup and shoreline detection abstract the use of variance images for runup and shoreline detection is analyzed in this work a methodology based on the variance images is first motivated with synthetic time stacks and then confirmed with real images a total of 55 time stack images from five different cameras at three video stations in spain and new zealand were digitized and used for the study these images include different tide and wave conditions from the time stack images we 1 obtained the mean shoreline position and maximum runup manually digitizing the water sand interface and 2 computed the variance function the variance function is shown to have a particular cross shore shape with two characteristic positions which allow us to satisfactorily recover the mean shoreline position and maximum runup obtained in the first step variance images were shown to be useful both for detecting mean shoreline and for evaluating runup providing a potential alternative for timex images the method did not work well when runup occurred within the groundwater seepage face

volcanic tremor at mt etna italy preceding and accompanying the eruption of july august 2001 the july 17 august 9 2001 flank eruption of mt etna was preceded and accompanied by remarkable changes in volcanic tremor based on the records of stations belonging to the permanent seismic network deployed on the volcano we analyze amplitude and frequency content of the seismic signal we find considerable changes in the volcanic tremor which mark the transition to different styles of eruptive activity e g lava fountains phreatomagmatic activity strombolian explosions in particular the frequency content of the signal decreases from 5 hz to 3 hz at our reference station etf during episodes of lava fountains and further decreases at about 2 hz throughout phases of intense lava emission the frequency content and the ratios of the signal amplitude allow us to distinguish three seismic sources i e the peripheral dike which fed the eruption the reservoir which fed the lava fountains and the central conduit based on the analysis of the amplitude decay of the signal we highlight the migration of the dike from a depth of ca 5 km to about 1 km between july 10 and 12 after the onset of the effusive phase the distribution of the amplitude decay at our stations can be interpreted as the overall result of sources located within the first half kilometer from the surface although on a qualitative basis our findings shed some light on the complex feeding system of mt etna and integrate other volcanological and geophysical studies which tackle the problem of magma replenishment for the july august 2001 flank eruption we conclude that volcanic tremor is fundamental in monitoring mt etna not only as a marker of the different sources which act within the volcano edifice but also of the diverse styles of eruptive activity

velocity and spectral characteristics of the volcanic tremor at etna deduced by a small seismometer array abstract a small l shaped short period seismic array was set up at etna volcano to measure the wave velocity and the incoming azimuth of the volcanic tremor generated by the volcanic activity at etna in non eruptive conditions cross correlation techniques were used to measure the phase shifts between the array stations an approximately n s direction of the propagation direction was estimated coincident with the azimuth of the crater area of etna an apparent velocity of less than 500 m s was estimated suggesting a surface propagation of the tremor waves spectral analysis confirming previous results shows velocity spectra peaked at approximately 2 hz a localized source coincident with the crater area agrees with our data and could generate the volcanic tremor at etna in non eruptive stages

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

runup kinematics on a natural beach runup kinematics on a gently sloping natural beach are examined with detailed measurements from video images resistance wires deployed at five elevations between 5 and 25 cm above and parallel to the beach face and pressure sensors located in the inner surf zone as suggested in a previous study comparing a single level resistance wire and manually digitized films runup measurements are sensitive to the sensor elevation above the bed owing to the elongated shape of the runup tongue the measured mean runup elevation setup and vertical excursion increase as the sensor elevation decreases with the video based runup estimates having the maximum means and variances for the six data runs the average ratios of the videobased setup and significant runup excursion to estimates based on wires elevated 15 cm above the bed are 2 7 and 1 5 respectively these trends combined with the high coherence and small phase difference between the video and the lowest wire demonstrate that the video based estimates correspond to a very near bed less than a few centimeters elevation wire measurement the measured increase in runup excursion with decreasing sensor elevation and the cross shore variation in the amplitudes of pressure fluctuations at infragravity frequencies are consistent with the theory for linear in viscid normally incident standing waves for example valleys in the pressure spectra occur at approximately the predicted standing wave nodal frequencies also in accord with small amplitude wave theory observed swash excursions are nearly identical to pressure fluctuations at the location of the measured runup mean for pressure sensors located seaward of the most offshore bed level rundown however at very low frequencies where reflection is typically assumed complete and dissipation negligible the observed near bed swash magnitudes are overamplified relative to a best fit of the linear standing wave model based on the amplitude and phase of the seaward observations

an iridium rich layer at the cretaceous tertiary boundary in the bidart section southern france we have measured an anomalous iridium concentration in the clays of the cretaceous tertiary boundary in the bidart section thus confirming the planetary character of this anomaly the iridium anomaly is synchronous with a very sharp minimum of the 13c 12c ratio and there is no evidence of any other iridium enrichment in marly concentrations away from the boundary the integrated iridium content is of the same order of magnitude as that calculated from deep sea cores in the pacific ocean in spite of a careful search we have found no evidence of any exotic material

the july august 2001 eruption of mt etna sicily the july august 2001 eruption of mt etna stimulated widespread public and media interest caused significant damage to tourist facilities and for several days threatened the town of nicolosi on the s flank of the volcano seven eruptive fissures were active five on the s flank between 3 050 and 2 100 m altitude and two on the ne flank between 3 080 and 2 600 m elevation all produced lava flows over various periods during the eruption the most voluminous of which reached a length of 6 9 km mineralogically the 2001 lavas fall into two distinct groups indicating that magma was supplied through two different and largely independent pathways one extending laterally from the central conduit system through radial fissures the other being a vertically ascending eccentric dike furthermore one of the eccentric vents at 2 570 m elevation was the site of vigorous phreatomagmatic activity as the dike cut through a shallow aquifer during both the initial and closing stages of the eruption for 6 days the magma column feeding this vent was more or less effectively sealed from the aquifer permitting powerful explosive and effusive magmatic activity while the eruption was characterized by a highly dynamic evolution complex interactions between some of the eruptive fissures and changing eruptive styles its total volume 25 106 m3 of lava and 5 10 106 m3 of pyroclastics was relatively small in comparison with other recent eruptions of etna effusion rates were calculated on a daily basis and reached peaks of 14 16 m3 s 1 while the average effusion rate at all fissures was about 11 m3 s 1 which is not exceptionally high the eruption showed a number of peculiar features but none of these except the contemporaneous lateral and eccentric activity represented a significant deviation from etna s eruptive behavior in the long term however the 2001 eruption could be but the first in a series of flank eruptions some of which might be more voluminous and hazardous placed in a long term context the eruption confirms a distinct trend initiated during the past 50 years toward higher production rates and more frequent eruptions which might bring etna back to similar levels of activity as during the early to mid seventeenth century

a video based technique for mapping intertidal beach bathymetry abstract measuring the location of the shoreline and monitoring foreshore changes through time are core tasks carried out by coastal engineers for a wide range of research monitoring and design applications with the advent of digital imaging technology shore based video systems provide continuous and automated data collection encompassing a much greater range of time and spatial scales than were previously possible using field survey methods a new video based technique is presented that utilises full colour image information which overcomes problems associated with previous grey scale methods which work well at steep reflective sites but are less successful at flatter dissipative sites identification of the shoreline feature is achieved by the automated clustering of sub aqueous and sub aerial pixels in hue saturation value hsv colour space and applying an objective discriminator function to define their boundary i e shoreline within a time series of consecutive geo referenced images the elevation corresponding to the detected shoreline features is calculated on the basis of concurrent tide and wave information which is incorporated in a model that combines the effects of wave set up and swash at both incident and infragravity frequencies validation of the technique is achieved by comparison with dgps survey results to assess the accuracy of the detection and elevation methods both separately and together the uncertainties associated with the two sub components of the model tend to compensate for each other the mean difference between image based and surveyed shoreline elevations was less than 15 cm along 85 of the 2 km study region which corresponded to an horizontal offset of 6 m the application of the intertidal bathymetry mapping technique in support of czm objectives is briefly illustrated at two sites in the netherlands and australia

the 1989 1990 activity of etna magma mingling and ascent of h2oclsrich basaltic magma evidence from melt inclusions abstract the melt inclusions in olivine phenocrysts from basaltic tephra erupted by etna volcano during the 1989 1990 eruptive period were investigated for major elements cl and s by electron microprobe fluorine by pigme particule induced gamma ray emission and h 2 o by sims the results indicate the ascent of basaltic magmas with different k 2 o concentrations possibly related to different feeding dykes lk basaltic melt inclusions rich in cl s and h 2 o are trapped in olivine fo 84 from the 1990 tephra and represent the early crystallization stage their composition in major elements is quite similar to those of most of the historic and even pre etnean alkali basalts but significantly lower in k 2 o compared with the 1989 1990 lavas only scarce hk basaltic melt inclusions were observed in the outer rim fo 79 6 of reversely zoned olivine phenocrysts and correspond to late crystallization stage at low pressure high sulfur concentration s 0 3 wt is a general characteristic of the etnean basaltic magmas with h 2 o s ratio as high as 7 the volatile abundances of the etna primitive basalts were computed at 1 45 wt for h 2 o 0 17 wt for cl and 0 047 wt for f with a high cl f ratio close to 3 6 the 1989 lava samples with cl at 660 90 ppm and f at 770 30 ppm have suffered a significant cl loss the possible behaviour of the volatile phase as co 2 h 2 o even cl is discussed with h 2 o and chlorine late degassing and an active role of h 2 o during the lava fountaining activity

analysis of simultaneous gravity and tremor anomalies observed during the 2002 2003 etna eruption abstract in this paper we discuss the data collected by a large aperture array of broadband seismometers and a continuously recording gravity station during the 2002 2003 eruption of etna volcano italy seismic signals recorded during the eruption are dominated by volcanic tremor whose energy spans the 0 5 5 hz frequency band on three different occasions 12 november 19 20 november and 8 9 december 2002 we observed marked increases of the tremor amplitude up to a factor of 4 which occurred simultaneously with gravity decreases up to 30 gal the three concurrent gravity tremor anomalies last 6 to 12 hours and terminate with rapid up to 2 hours changes after which the signals return back to their original levels based on volcanological observations encompassing the simultaneous anomalies we infer that the accumulation of a gas cloud at some level in the conduit plexus feeding a new eruptive vent could have acted as a joint source this study highlights the potential of joint gravity seismological analyses to both investigate the internal dynamic of a volcano and to improve the confidence of volcanic hazard assessment

modeling of volcanic tremor as explosive point sources in a single layered elastic half space i investigate path effects on the waveform of a volcanic tremor using a model that consist of an impulsive dilatational point source embedded in a single layered elastic half space such a source may arise during a variety of volcanic conditions such as a sequence of rapid explosions at a volcanic vent as well as gas piston activity observed in basaltic lava lakes using acoustic signals recorded during the 1975 tolbachik eruption the 1983 klyuchevskoy eruption and the 1989 tokachi dake eruption i propose a general impulsive time function for the tremor source consisting either of a single impulse or a sequence of identical impulses computed seismograms illustrate the influence of a low velocity surface layer on the shape and spectra of the waveforms for the same layered model a single impulse produces a dispersive wave while a sequence of identical impulses produces a wave of multiple harmonics for a single impulse the peak in the seismograms shifts to higher frequencies when the surface layer is very thin for multiple impulses spectral peaks shift to higher frequencies as the time between successive impulses increases indicating an increasing importance of higher order harmonics

coupling terrestrial lidar and video imagery to perform 3d intertidal beach topography abstract this study investigates the possibility of combining two shore based remote sensing techniques 2d lidar and video imagery to measure 3d intertidal beach topography the shoreline elevation measured on a single cross shore section of the beach by a 2d lidar was combined with the video derived shoreline contour to finally obtain intertidal beach topography vertical root mean square error between differential gps and remotely derived intertidal beach profiles had an average value of 0 12 m with maximum disparities of 0 14 m two 3d digital elevation models dems of the beach produced over two tidal cycles demonstrated the feasibility of shore based lidar video system of describing in detail the short term morphological evolution of the intertidal area results suggest that the lidar video system can improve the capability of remotely surveying intertidal beach topography providing high quality measurements

wave runup and overwash on a prototype scale sand barrier abstract accurate methods to predict wave runup are of critical importance to coastal engineers extreme runup during storm conditions can present a danger to coastal infrastructure and lead to dune overtopping and erosion overwash of barrier beaches and is an essential design parameter for certain coastal protection works this paper uses data obtained during the unique bardex ii prototype scale laboratory experiment on a reflective sand barrier to investigate wave runup and overwash runup measurements were acquired using ultrasonic altimeters 2d scanning lidar and camera systems under controlled wave and water level conditions it was found that extreme runup r 2 scaled well with the deepwater irribarren number where the beach slope was taken to be the beach face gradient the lower limit of the swash zone defined by the 2 wave rundown limit was also found to be a function of the irribarren number and was consistently below the swl in all tests the high resolution free surface measurements obtained using the ultrasonic altimeters and lidar enabled an analysis of the dynamics of individual swash events it was found that the vertical runup excursion of each swash correlated strongly with the height of the bore at collapse and could be predicted based on the assumption of a conversion of potential to kinetic energy at bore collapse

application of lidar technology for measurement of time varying free surface profiles in a laboratory wave flume abstract an experimental study was completed to investigate the ability of a fixed two dimensional lidar instrument to obtain detailed measurements of propagating waves within a laboratory wave flume the results show that this technology can be used to obtain synchronous free surface measurements at a horizontal spatial resolution o 10 mm with comparable vertical accuracy to that of more conventional high precision capacitance wave probes the principal advantage of using the lidar is that a single non intrusive instrument can be utilised to measure the entire wave field at high resolution allowing detailed evaluation of wave transformation throughout the experimental domain

measurements of the time varying free surface profile across the swash zone obtained using an industrial lidar the use of an industrial lidar instrument to measure time varying water surface elevations within the swash zone is investigated the propagation of the swash lens across the beach face was measured simultaneously by a lidar instrument and a network of precision ultrasonic altimeters at a sandy beach comparison of the two datasets indicates that the time varying swash free surface profile obtained using a lidar compare favourably with point measurements obtained using ultrasonic altimeters significantly the use of a continuously scanning laser beam enables a single lidar instrument to obtain measurements of free surface elevation near synchronously at several hundred points throughout the swash zone this high spatial resolution permits small scale flow features such as the swash front gradient and the presence of secondary bores to be detailed and negates the need for the deployment of a large multi sensor array

quantitative analysis of the tremor wavefield at etna volcano italy abstract the properties of volcanic tremor wavefield at mt etna volcano italy are investigated using data from two dense small aperture arrays of short period seismometers deployed on the north and south flank of the volcano spectral analysis shows that most of the seismic energy is associated to several narrow spectral peaks spanning the 1 5 hz frequency band analysis of simultaneous recordings evidences that most of these peaks are common to different sites thus suggesting a source effect as the origin of this energy frequency slowness analyses evidence a complex wavefield where body and surface waves alternatively dominate depending on the frequency band and component of motion taken into account surface waves are found to dominate at frequencies below 1 hz and above 3 hz conversely the 0 8 2 3 hz vertical and radial component wavefields at both arrays exhibit a nondispersive nature with apparent velocities spanning the 1 2 s km range particle motion analysis suggests these arrivals are associated to both p and sv waves inciding at shallow angles at the northern array back azimuths of these waves encompass the whole summit crater area at the southern array back azimuths are instead clustered around a direction pointing about 500 m east of the se crater at frequency around 4 hz the dominant direction of wave propagation at the southern site shifts about 30 w pointing to the bocca nuova voragine craters and concordance of location is found with the source imaged by the northern array the 0 8 2 3 hz transverse component of motion depicts velocities of about 0 5 km s a value which is about three times lower than those associated to the vertical and radial components results from polarization analyses at the two array sites depict the dominance of horizontal linear particle motion oriented transversally with respect to the source direction polarization ellipsoids at the stations of the sparse network all depict a quasi horizontal setting with two exceptions the direction of particle motion is always oriented tangentially to the summit volcanic edifice the origin of the large transverse motion observed at the two array sites is thus attributed to sh waves generated by free surface interaction of waves impinging the concave topography the correlation method is used to derive the dispersion properties of short period 0 5 5 hz rayleigh waves from which the shallow shear wave velocity structures are derived for beneath the two semicircular arrays using a probabilistic approach we invert slowness data measured at the two dense arrays for retrieving source location and extent the joint inversion of slowness data from the two arrays point to different sources this observation is interpreted in terms of ray bending associated to lateral heterogeneity and or strong topographic effects on wave propagation once the propagation effects are taken into account the most probable source locations are associated to a shallow region encompassing the summit craters and the eruptive fissures active at the time of the experiment september 1999

relationship between tremor and volcanic activity during the southeast crater eruption on mount etna in early 2000 1 the southeast crater of mount etna italy was characterized by a violent eruptive activity between 26 january and 24 june 2000 this activity produced 64 lava fountain episodes with repose periods from 3 hours to 10 days we estimated a volume of about 15 20 106 m3 lava and at least 2 3 106 m3 of tephra we compared the paroxysmal volcanic activity to its associated seismic signature the high number of events highlighted a strict correlation between tremor and volcanic activity seismic and volcanic characteristics such as the frequency of occurrence the duration of lava fountains and the associated tremor energy suggested the subdivision of the studied period into two stages separated by the 20 february event combining volcanic with seismic data we observed some useful relationships among lava fountain height sustained column height and reduced displacement in addition we found that the entire episode was well correlated with the duration of the amplitude increase computing the tremor energy linked to each event the total energy associated with lava fountains episodes results in 76 of the energy released during the whole period finally the different ratios among the overall spectral amplitude of the seismic signals of the stations located at different altitudes suggested to us the elaboration of a simple qualitative model to explain the dynamic behavior of the tremor source during the whole episode

estimating wave energy dissipation in the surf zone using thermal infrared imagery thermal infrared ir imagery is used to quantify the high spatial and temporal variability of dissipation due to wave breaking in the surf zone the foam produced in an actively breaking crest or wave roller has a distinct signature in ir imagery a retrieval algorithm is developed to detect breaking waves and extract wave roller length using measurements taken during the surf zone optics 2010 experiment at duck nc the remotely derived roller length and an in situ estimate of wave slope are used to estimate dissipation due to wave breaking by means of the wave resolving model by duncan 1981 the wave energy dissipation rate estimates show a pattern of increased breaking during low tide over a sand bar consistent with in situ turbulent kinetic energy dissipation rate estimates from fixed and drifting instruments over the bar when integrated over the surf zone width these dissipation rate estimates account for 40 69 of the incoming wave energy flux the duncan 1981 estimates agree with those from a dissipation parameterization by janssen and battjes 2007 a wave energy dissipation model commonly applied within nearshore circulation models

wavefield properties of a shallow long period event and tremor at kilauea volcano hawaii the wavefields of tremor and a long period lp event associated with the ongoing eruptive activity at kilauea volcano hawaii are investigated using a combination of dense small aperture 300 m and sparse large aperture 5 km arrays deployed in the vicinity of the summit caldera measurements of azimuth and slowness for tremor recorded on the small aperture array indicate a bimodal nature of the observed wavefield at frequencies below 2 hz the wavefield is dominated by body waves impinging the array with steep incidence these arrivals are attributed to the oceanic microseismic noise in the 2 6 hz band the wavefield is dominated by waves propagating from sources located at shallow depths 1 km beneath the eastern edge of the halemaumau pit crater the hypocenter of the lp event determined from frequency slowness analyses combined with phase picks appears to be located close to the source of tremor but at a shallower depth 0 1 km the wavefields of tremor and lp event are characterized by a complex composition of body and surface waves whose propagation and polarization properties are strongly affected by topographic and structural features in the summit caldera region analyses of the directional properties of the wavefield in the 2 6 hz band point to the directions of main scattering sources which are consistent with pronounced velocity contrasts imaged in a high resolution three dimensional velocity model of the caldera region the frequency and q of the dominant peak observed in the spectra of the lp event may be explained as the dominant oscillation mode of a crack with scale length 20 100 m and aperture of a few centimeters filled with bubbly water the mechanism driving the shallow tremor appears to he consistent with a sustained excitation originating in the oscillations of a bubble cloud resulting from vesiculation and degassing in the magma

seismic and infrasonic evidences for an impulsive source of the shallow volcanic tremor at mt etna italy during a seismo acoustic experiment we recorded volcanic tremor around the summit craters of mt etna volcano tremor shows amplitude modulation which disappear 900 m from the crater area the infrasonic wavefield is coherent even at distances of 750 m time delay between infrasonic transient is stable around 1 3 s and is consistent with the position of the source in the voragine crater amplitude modulation of tremor is well correlated 0 72 with infrasound amplitude with a time lag of 0 37 s coherent with a shallow position of the source amplitude of volcanic tremor decays over increasing distances according to geometrical spreading of body waves tremor wavefield shows a linear polarization following the same time occourrence as the infrasonic pulses polarization azimuth indicates that wavefield rectilinearity is mostly due to p waves we infer that most of the volcanic tremor we recorded at mt etna is generated by superimposition of small impulsive sources acting at 1 2 s rate caused by pressure instability during magma degassing

polarization analyses of broadband seismic data recorded on stromboli volcano italy from 1996 to 1999 1 we analyze broadband seismic data recorded at a single station deployed on stromboli island from 1996 to 1999 in order to determine basic parameters of the seismic wavefield and study their relationship with volcanic activity in addition to a characterization in the frequency domain we apply polarization analysis and study long term variations of these parameters possibly reflecting also changes in source properties our analysis is twofold first we focus on a meaningful reduction of the data to selected parameters i e azimuth and incidence angle which can be correlated with volcanic activity secondly we investigate if there is maintenance of the correlations over long time spans we observe statistically significant long term changes from several months to year in the wavefield parameters considered we interpret such changes as possibly being caused by the enhanced strength of a deep source potentially by supply of fluids from a low part of the magma feeder between the end of 1997 and the first months of 1998

array tracking of the volcanic tremor source at deception island antarctica we have found experimental evidence which shows that the volcanic tremor recorded at deception island south shetland islands antarctica is a superposition in time of overlapping hybrid events we studied data from a small aperture seismic array data analysis for tremor and hybrids included 1 spectral analysis 2 apparent slowness and back azimuth determination by using the zero lag cross correlation method and 3 polarization analysis both types of events share these common features a two dominant spectral bands at frequencies 1 3 hz the most energetic and 4 8 hz b several coherent phases with the same back azimuth to the source and apparent slowness along the whole signal c in the high frequency band the apparent slowness is very low around 0 17 s km indicating the propagation of body waves d in the low frequency band the apparent slowness is high around 1 6 s km consistent with the presence of surface waves and e clear p wave onset followed by a complex pattern of rayleigh waves therefore both types of events are strongly related because they share the same source region the same wave propagation properties and the same wave composition moreover several arrivals that resemble a single hybrid event have been found along the tremor signals due to these reasons we hypothesize that volcanic tremor of deception island is a superposition of hybrid type events the source of both types could be the interaction between thaw water and hot materials in a shallow aquifer

the role of combined laser scanning and video techniques in monitoring wave by wave swash zone processes abstract simulating swash zone morphodynamics remains one of the major weaknesses of beach evolution models one of the reasons is the limited availability of data on morphological changes at the temporal scales of individual swash events this paper sets out to present a new hybrid system consisting of 2d 3d laser scanners and several video cameras which was designed to monitor swash zone topographic change on a wave by wave basis a methodology is proposed consisting of sensor calibration and several data processing steps allowing a fusion of different sensors such an approach can improve the performance of several field laboratory optical technique applications for nearshore hydro and morpho dynamic measurements digital elevation models from a 3d scanner were used in the extrinsic camera calibration procedure and reduced the geo rectification errors from 0 035 m dz 10 cm the sediment transport direction and intensity of the monitored swash events was relatively balanced and sediment transport rates ranged between 3 5 kg m 1 s 1 q t 3 5 kg m 1 s 1 extreme transport swash events became rarer as the morphology was reaching equilibrium

approach to the volcanic tremor by covariance analysis application to the 1989 eruption of mt etna sicily polarization of the tremor wavefield recorded during three periods of the 1989 eruption of mt etna at a temporary array of three component stations is analyzed by use of a polarization filter the tremor shows steady horizontal near linear west east polarization at all stations such a behaviour which could be coherent with a p wavefield radiated by a vertical extended source with overall north south alignment excludes confinement of the source to the only active vent and is tentatively linked to activity of the main dyke system of mt etna

volcanic tremor location during the 2004 mount etna lava effusion 1 a lava emission started at mt etna italy on 7 september 2004 neither earthquake seismicity heralded or accompanied the opening of the fracture field from which the lava poured out nor volcanic tremor changed in amplitude and frequency content at the onset of the effusive activity to highlight long term changes we propose a method for the location of the tremor source based on a 3d grid search using the amplitude decay of the seismic signal from january to november 2004 we find the centroid of the tremor source within a zone close to and partially overlapped with the summit craters pre effusive phase which extended up to 2 km south of them effusive phase the depths are of between 1698 and 2387 m a s l we hypothesize the lava effusion stemmed from a degassed magma body although we find evidence of temporary magma overpressure conditions such as those documented on 25 september

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

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

volcanic tremor wave field during quiescent and eruptive activity at mt etna sicily abstract this paper reports the results of an analysis of volcanic tremor at etna in the years 1987 to 1992 the data utilized were obtained from the osservatorio vesuviano s serra la nave permanent station and several seismic surveys carried out by means of portable digital seismic stations equipped with three component geophones the spatial temporal patterns of main parameters such as intensity spectral content polarization and wave composition of volcanic tremor in different phases of etna s activity were studied eruptive activity appears to be significantly correlated with volcanic tremor in particular it is worth pointing out that the magma upwelling in the terminal part of the conduit is characterized by a marked increase in low frequency components 3 4 hz of the spectrum of volcanic tremor hence volcanic tremor at etna can be considered as a short period precursor of eruptions an analysis of polarization and propagation velocity of volcanic tremor shows the presence of love waves overlapping other seismic phases

wave runup video motion detection using the radon transform abstract a new method of runup detection from video imagery is introduced and validated at an energetic dissipative beach the instantaneous waterline is detected from uprush and backwash by using the radon transform rt the method is compared to conventional color contrast method from rgb images and lidar measurements in our observations the rt shows better detection skill even for adverse conditions such as those present on flat dissipative swash zones where contrast is reduced because the rt is a proxy of deeper waterline 0 1 m it is less sensitive to lack of contrast due to sand saturation moreover since it is based on motion detection it is less sensitive to changes in lighting conditions overall the rt offers an attractive alternative for long term automated detection of the runup

intertidal beach profile estimation from reflected wave measurements abstract the intertidal beach profile provides coastal engineers and managers with a good indication of the current state of a sandy coastline however regular beach profile measurements are time consuming and expensive to obtain using conventional surveying methods the potential to reconstruct the intertidal beach profile from measurements of reflected waves is tested here using three field datasets covering a different range of hydro morphological conditions from dissipative to reflective the swash is found to behave as a low pass filter on reflected waves with a cut off frequency that primarily depends on the swash slope an agreement is found between video derived swash spectrum saturation tail and the shortest reflected waves computed from deep water directional wave measurements by integrating this swash slope over a tidal cycle the shape of the intertidal beach profile can be reconstructed our results clearly show the potential of such method to estimate complex intertidal beach profile such as double slope beaches

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

setup and swash on a natural beach wave setup and swash statistics were calculated from 154 runup time series measured on a moderately steep beach under incident waves varying from 0 4 to 4 0 m significant wave height when scaled by the incident wave height setup swash height and total runup the sum of setup and half the swash height were found to vary linearly with the surf zone similarity parameter 0 h0 l0 1 2 the foreshore slope appeared the appropriate value for the calculation of 0 although the setup data showed some influence of an offshore bar at low tide for low irribaren numbers the swash height in the incident frequency band becomes saturated while for high irribaren numbers no such signs of saturations were seen thus the infragravity band appears to become dominant in the swash below some value of 0 for these data that value is approximately 1 75 although there is considerable scatter associated with that estimate

a new breaking wave height direct estimator from video imagery breaker height is a key parameter of nearshore processes and the demand for a continuous remote estimator is pressing in this paper we present a standalone remote video based method that estimates wave height at the breakpoint individual breaking events are first identified from changes in optical properties and wave height is further derived from the optical signature at the onset of breaking an extended validation is performed using a dense wave basin dataset the results show the ability of the method to measure individual breaker heights 9 of mean error 18 rms in addition the unique combination of in situ and remotely sensed data allows the estimation of two other breaking related parameters the height to depth ratio and wave front face slope which show a substantial amount of dispersion because nearshore video systems are rapidly spreading over world coasts this low cost remote breaker height estimator should encounter large interest in coastal engineering studies

intertidal beach slope predictions compared to field data this paper presents a test of a very simple model for predicting beach slope changes the model assumes that these changes are a function of both the incident wave conditions and the beach slope itself following other studies we hypothesized that the beach slope evolves towards an equilibrium value that depends nonlinearly on wave steepness h l the rate of beach slope response is assumed to depend on both the degree of slope disequilibrium and on the incident wave energy the model was tested against daily beach slope observations derived from digital images of the nearshore zone approximately 104 images were analyzed over eight mostly consecutive month long periods along a 2 km length of beach the slope change model was calibrated by fitting it to the daily differences in the alongshore averaged slopes which were obtained from a 500 m alongshore subset of the observations an equilibrium slope prediction proportional to the wave steepness h l raised to the 1st to 2nd power performed best compared to several alternative models the response rate of beach slope changes depended on the wave height raised to the 3rd or 4th power a characteristic response time for the system was found to be 1 2 days the calibrated i e hindcast model explained 30 40 of the observed slope change variance indicating that the model was consistent with the data however when the model was used to predict the evolution of the beach slope time series i e to forecast the prediction error variance was equal to or only slightly lower than the observed temporal variability in the slopes the present model is sufficiently accurate to characterize beach slope dynamics but its predictive capability would not outperform a model that predicts a constant mean slope

automated mapping of the intertidal beach bathymetry from video images this paper presents a fully automated procedure to derive the intertidal beach bathymetry on a daily basis from video images of low sloping beaches that are characterised by the intermittent emergence of intertidal bars bathymetry data are obtained by automated and repeated mapping of shorelines from video time exposure images for different tidal water levels aarninkhof s g j turner i l dronkers t d t caljouw m nipius l 2003 a video based technique for mapping intertidal beach bathymetry coastal engineering 49 275 289 plant n g and holman r a 1997 intertidal beach profile estimation using video images marine geology 140 1 24 the developed procedure handles intelligent selection of a shoreline search area and unsupervised quality control of the obtained bathymetry data the automatically retrieved beach bathymetries compare very well to bathymetries derived from the original manual mapping procedure and to ground truth data points dgps