combined discrete and continuous gravity observations at mount etna systematic investigation of discrete gravity measurements has continued at mount etna since 1986 the network now covers an area of 400 km2 with about 70 stations 0 5 3 km apart mass redistributions occurring at depths ranging between about 8 km below sea level and a few hundred metres below the surface magma level changes within the shallower parts of the feeding conduits have been identified from these data conventional discrete microgravity monitoring on a network of stations furnishes only instantaneous states of the mass distribution at continuously active systems in order to obtain information on the rate at which the volcanic processes and thus mass transfers occur three stations for continuously recording gravity where installed on mount etna in 1998 a 16 month long sequence from one of the continuously running stations pdn located 2 km from the active northeast crater at the summit of etna volcano is presented after removing the effects of earth tide and tilt the correlation of the residual gravity sequence with simultaneous recordings of meteorological parameters acquired at the same station was analysed once the meteorological effects have also been removed continuous gravity changes are within 10 gal of gravity changes measured using conventional microgravity observations at sites very close to the continuous station this example shows how discrete and continuous gravity observations can be used together at active volcanoes to get a fuller and more accurate picture of the spatial and temporal characteristics of volcanic processes

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

hydrologically induced slope deformations detected by gps and clinometric surveys in the cansiglio plateau southern alps abstract changes in groundwater or surface water level may cause observable deformation of the drainage basins in different ways we describe an active slope deformation monitored with gps and tiltmeter stations in a karstic limestone plateau in southeastern alps cansiglio plateau the observed transient gps deformation clearly correlates with the rainfall both gps and tiltmeter equipments react instantly to heavy rains displaying abrupt offsets but with different time constants demonstrating the response to different catchment volumes the gps movement is mostly confined in the horizontal plane ssw direction showing a systematic tendency to rebound in the weeks following the rain four gps stations concur to define a coherent deformation pattern of a wide area 12 5 km 2 concerning the whole southeastern slope of the plateau the plateau expands and rebounds radially after rain by an amount up to a few centimeters and causing only small vertical deformation the effect is largest where karstic features are mostly developed at the margin of the plateau where a thick succession of cretaceous peritidal carbonates faces the venetian lowland a couple of tiltmeters installed in a cave at the top of the plateau detect a much faster deformation that has the tendency to rebound in less than 6 h the correlation to rainfall is less straightforward and shows a more complex behavior during rainy weather the different responses demonstrate a fast hydrologic flow in the more permeable epikarst for the tiltmeters drained by open fractures and fissures in the neighborhood of the cave and a rapid tensile dislocation of the bedrock measured at the gps stations that affect the whole slope of the mountain in the days following the rain both tiltmeter and gps data show a tendency to retrieve the displacement which is consistent with the phreatic discharge curve we propose that hydrologically active fractures recharged by rainfall are the most likely features capable to induce the observed strain variations

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

infrasonic waves and volcanic tremor at stromboli the origin of the volcanic tremor is still under debate many theories have been proposed in the last years but none has yet been completely accepted in 1993 highly sensitive pressure sensors 2 175 pa volt used to monitor the explosive activity at stromboli have revealed unexpected correlation between small spike shaped pressure signals 1 2 pa and volcanic tremor these pressure pulses repeat regularly in time with a recurrent period of ca 1 s video camera images allowed us to correlate the pressure pulses with small gas bursts occurring at one of the active vents the striking correlation 0 971 between infrasonic and seismic energy fluctuations is particularly meaningful in the frequency domain infrasonic and seismic signal share the same spectral content 3 hz for every station within a range of 700 m around the craters correlations in time and frequency domain remained unaltered during the 1994 field experiments moreover during 1994 the increased degassing activity has been followed by an increase in pressure release 7 8 pa and by a shift towards higher frequencies 8 hz both in the infrasonic and seismic records infrasonic waves and volcanic tremor show similar energy fluctuations and frequency contents appearing therefore to be produced by the same dynamical process on this basis we claim that volcanic tremor at stromboli originates by continuous outbursting of small gas bubbles in the upper part of the magmatic column

north south variations of tropical storm genesis locations in the western hemisphere in the western hemisphere tropical storms or hurricanes form in the north atlantic and eastern north pacific previous studies have focused on storm variability in the frequency duration and intensity in each basin here we find that the tropical storm genesis location in one ocean basin ties to the other one on both interannual and multidecadal timescales a northward southward shift of the tropical storm genesis location is associated with a southward northward variation in the other ocean basin the change of cross central america wind in the upper troposphere which induces an out of phase relation of vertical wind shear bridges storm activity in the two ocean basins sea surface temperatures in both the tropical pacific and north atlantic can induce the zonal wind change across central america it implies that hurricane outlooks can be improved by considering the two ocean basins together and thus helping reduce the damage caused by hurricane landfall

a 15 year climatology of north atlantic tropical cyclones part i size parameters abstract the extended best track ebt dataset combines the information contained in the tropical cyclone best track dataset with measurements of tropical cyclone size parameters these parameters include the radii of the eye reye maximum winds rmw gale force winds or size 17 5 m s 1 r17 damaging force winds 25 7 m s 1 r26 hurricane force winds 32 9 m s 1 r33 and the outermost closed isobar roci the latest update of this dataset to be used in this study for a size parameter climatology contains the size parameters for north atlantic tropical cyclones from 1988 to 2002 such a climatology has not yet been established in this basin most of the results of this north atlantic study agree with documented tropical cyclone theory and results from similar studies of northwest pacific tropical cyclones this provides confidence that the observations of the size parameters in the dataset are reliable furthermore data west and east of 55 w the boundary beyond which no aircraft observati

nonlinear and minor ocean tides in the bay of biscay from the strain tides observed by two geodetic laser strainmeters at canfranc spain this work presents and discusses the tidal analysis of about 2 5 years of strain data recorded by two 70 m long high resolution laser strainmeters which are operating in the canfranc underground laboratory central pyrenees spain spectra show clear tidal peaks whose frequencies range from the diurnal band to at least 8 cycles per day strain amplitudes relative change in length for each strainmeter range from few 10 12 to 10 8 the reliability of observations and corrections for local distortions are testified by the excellent agreement between measurements and computations for all the diurnal and semidiurnal tides included in the tpxo8 and fes2012 tidal atlases with the exception of l2 observed higher frequency strain tides are mostly attributed to loading by nonlinear shallow water constituents in the bay of biscay more than 120 km from the measurement site the signals are quantitatively compared with computations using tpxo8 mn4 m4 and ms4 and fes2012 m3 n4 mn4 m4 ms4 and m6 computations fully agree with m4 observations for one strainmeter overestimate m4 by about 30 for the other strainmeter and m6 by about a factor of two and underestimate the other tides this work shows that data from high sensitivity strainmeters installed in high quality sites may provide valuable additional information for studying the nonlinear tidal dynamics and energetics of coastal waters and minor ocean tides at spatial resolutions of tens to thousands square kilometers depending on the strainmeter location with respect to the coastline

atlantic seasonal hurricane frequency part i el nino and 30 mb quasi biennial oscillation influences abstract this is the first of two papers on atlantic seasonal hurricane frequency in this paper seasonal hurricane frequency as related to e1 nino events during 1900 82 and to the equatorial quasi biennial oscillation qbo of stratospheric zonal wind from 1950 to 1982 is discussed it is shown that a substantial negative correlation is typically present between the seasonal number of hurricanes hurricane days and tropical storms and moderate or strong 15 cases el nin off the south american west coast a similar negative anomaly in hurricane activity occurs when equatorial winds at 30 mb are from an easterly direction and or are becoming more easterly with time during the hurricane season this association of atlantic hurricane activity with el nino can also be made with the southern oscillation index by contrast seasonal hurricane frequency is slightly above normal in non el nino years and substantially above normal when equatorial stratospheric winds blow from a westerly direction and or are bec

evidence for gas influence on volcanic seismic signals recorded at stromboli abstract the meaning of the large variety of seismic waveforms showing different frequencies associated with volcanic activity is still uncertain no definitive model for source dynamics has been proposed yet at present seismic models explaining the origin of the spectral content of the seismic signal are mainly linked to geometrical features of the volcanic conduit and to resonant effects induced by pressure fluctuations in a fluid filled conduit such models assume the physical system to be in a steady state over a long interval of time at stromboli the seismicity produced by each of the three active vents is not stable and can suddenly change in time therefore the application of stable resonator models appears to be unwarranted on the basis of infrared image analyses atmospheric pressure and seismic wavefield signals we show that different frequency contents and different explosive styles occur at stromboli at the same time at different vents moreover we give evidence to support the idea that seismicity and explosivity are both controlled by a variable gas flow regime released during explosions at the top of the magma column we have recognized two main pressure regimes controlling the explositivity at stromboli one is impulsive short and possibly produced by a gas accumulation beneath a cap rock the other has an intermittent regime feature and lasts longer we demonstrate how the first one generates a monochromatic low frequency wavefield while the second shows a high frequency spectrum where the frequency content depends on pressure fluctuations and on pressure gradient we suggest different pressure growth and gas flow in the magma as the common source for both explosive style and seismic wavefield

excavation induced microseismicity in the columnar jointed basalt of an underground hydropower station abstract large scale columnar jointed basalt cjb developments have had serious adverse effects on the stability of the project in progress to create the diversion tunnels at the baihetan hydropower station in china an in situ microseismic ms monitoring experiment was carried out to help understand the fracturing process in the cjb rock mass as a result of tunnel excavation ms monitoring performance accuracy of location estimation and system sensitivity is analyzed first then the spatiotemporal evolution of the ms activity associated with the baihetan cjb rock mass fractures along the tunnel axis and at the tunnel sidewalls during the entire excavation unloading process is obtained finally the forms and opportunities to deploy appropriate support are suggested according to the characteristics of the cjb microseismicity meanwhile the ms monitoring methods required for cjb or jointed hard rock engineering e g sensor types sensor spacing sensor array forms system protection and selection of analysis regions resulting from this exploration experiment are summarized

temporal and spatial characteristics of volcanic tremor wave fields abstract detailed volcanic tremor studies were carried out with portable seismic stations installed both in the near and distant zones at klyuchevskoy volcano in 1984 1986 and 1987 it has been determined that the coherence of wave field decreases with distance to 0 5 km and does not change at greater distances based on coherence and phase spectra the frequency dependence of the phase velocities has been determined the dispersion of phase velocity points to the surface character of the wave field the behaviour of volcanic tremor characteristics through time is stationary which implies stability of the parameters of the volcanic tremor source a detailed spectral study has demonstrated that when the intensity of volcanic tremor varies by a few orders of magnitude parts of the low frequency and high frequency spectra change which is likely due to the variations in source dimensions the detailed spectral characteristics of tremor may be used for both determining the source parameters and studying the structure of the medium

volcanic tremor related to the 1991 eruption of the hekla volcano iceland volcanic tremor at the hekla volcano is directly related to eruptive activity it starts simultaneously with the eruptions and dies down at the end of them no tremor at hekla has been observed during non eruptive times the 1991 hekla eruption began on 17 january after a short warning time local seismograph stations recorded small premonitory earthquakes from 16 30 gmt on at 17 02 gmt low frequency volcanic tremor became visible on the seismograph records marking the onset of the eruption the initial plinian phase of the eruption was short lived during the first day several fissures were active but by the second day the activity was already limited to a segment of one principal fissure the eruption lasted almost 53 days at the end of it during the early hours of 11 march volcanic tremor disappeared under the detection threshold and was followed by a swarm of small earthquakes at the start of the eruption the tremor amplitude rose rapidly and reached a maximum in only 10 min the tremor was most vigorous during the first hour and started to decline sharply during the next hour and later on more gently during the eruption as a whole the tremor had a continuous declining trend with occasional increases lasting up to about 2 days spectral analysis of the tremor during the first 7 h of the eruption shows that it settled quickly within a couple of minutes to its characteristic frequency band 0 5 1 5 hz the spectrum had typically one dominant peak at 0 7 0 9 hz and a few subdominant peaks hekla tremor likely has a shallow source particle motion plots suggest that it contains a significant component of surface waves the tremor started first when the connection of the magma conduit with the atmosphere was reached suggesting that degassing may contribute to its generation

a physical model for seismic noise generation by turbulent flow in rivers previous studies suggest that the seismic noise induced by rivers may be used to infer river transport properties and previous theoretical work showed that bedload sediment flux can be inverted from seismic data however the lack of a theoretical framework relating water flow to seismic noise prevents these studies from providing accurate bedload fluxes and quantitative information on flow processes here we propose a forward model of seismic noise caused by turbulent flow in agreement with previous observations modeled turbulent flow induced noise operates at lower frequencies than bedload induced noise moreover the differences in the spectral signatures of turbulent flow induced and bedload induced forces at the riverbed are significant enough that these two processes can be characterized independently using seismic records acquired at various distances from the river in cases with isolated turbulent flow noise we suggest that riverbed stress can be inverted finally we validate our model by comparing predictions to previously reported observations we show that our model captures the spectral peak located around 6 7 hz and previously attributed to water flow at hance rapids in the colorado river united states we also show that turbulent flow causes a significant part of the seismic noise recorded at the trisuli river in nepal which reveals that the hysteresis curve previously reported there does not solely include bedload but is also largely influenced by turbulent flow induced noise we expect the framework presented here to be useful to invert realistic bedload fluxes by enabling the removal of the turbulent flow contribution from seismic data

seismic monitoring of an alpine mountain river the canfranc underground laboratory lsc excavated under the central pyrenees is mainly devoted to the study of phenomena which needs cosmic silence it also hosts a geodynamical facility named geodyn which holds an accelerometer a broadband seismometer and two high resolution laser strainmeters during the routine processing of the seismic data we detected an unusual spectral signature in the 2 10 hz frequency band which does not correspond to the typical sources of seismic noise and which can also be recognized in the strain records after checking against meteorological and hydrological data we can relate those signals to variations in the discharge by the aragon river an alpine style river in the southern pyrenees located about 400 m from the lsc geodyn facility four main episodes have been identified since early 2011 each lasting 1 2 to 6 8 days additionally a limited number of shorter episodes have also been detected three types of river generated seismic events have been identified related respectively to moderate rainfall snowmelt and flooding events associated to severe storms each of those types has distinctive characteristics which allow monitoring the hydrological events from the analysis of seismic and deformation data a few previous studies have already described the seismic noise close to rivers with larger discharge or in small scale experimental settings and we are showing here that the so called fluvial seismology can be useful to study the hydrological evolution of alpine style streams and may have a potential interest for the civil authorities in charge of the management of hydrological basins

decadal and interannual sst variability in the tropical atlantic ocean abstract the mechanisms regulating interannual and decadal variations of sea surface temperature sst in the tropical atlantic are examined observed variations of sea surface temperature are typically in the range of 0 3 0 5 c and are linked to fluctuations in rainfall on both the african and south american continents the authors use a numerical model to simulate the observed time series of sea surface temperature for the period 1960 1989 based on the results experiments are conducted to determine the relative importance of heat flux and momentum forcing two dominant timescales for variability of sst are identified a decadal timescale that is controlled by latent heat flux anomalies and is primarily responsible for sst anomalies off the equator and an equatorial mode with a timescale of 2 5 years that is dominated by dynamical processes the interhemispheric gradient of anomalous sst the sst dipole is primarily linked to the former process and thus results from the gradual strengthening and weak

seismic activity related to the 2000 eruption of the hekla volcano iceland the 2000 hekla eruption took place from february 26 to march 8 its seismic expressions were a swarm of numerous small earthquakes related to its onset and low frequency volcanic tremor that continued throughout the eruption a swarm of small earthquakes was observed some 80 min before the onset of the eruption and the size of the events increased with time low frequency volcanic tremor with a characteristic frequency band of 0 5 1 5 hz and dominant spectral peak s at 0 7 0 9 hz became visible at 18 19 gmt on february 26 marking the onset of the eruption the tremor amplitude rose quickly and was very high in the beginning of the eruption however it soon began to decrease after about an hour in general the seismic activity related to the 2000 hekla eruption was very similar to what was observed in the previous eruption in 1991 based on knowledge gained from seismicity and strain observations from 1991 this was the first time that a hekla eruption was predicted

combining multi physical measurements to quantify bedload transport and morphodynamics interactions in an alpine braiding river reach abstract understanding the interactions between bedload transport and morpholdynamics in braided streams has important applications in river management and restoration direct field measurements addressing this question are however scarce as they are often challenging to perform here we report an extensive two month field campaign in an alpine braided reach la severaisse river french alps that experienced predictable daily peak discharge 48 events observed generating significant bedload transport and morphological changes during the melting season we monitored these processes using a wide range of direct and indirect techniques bedload sampling continuous seismic measurements pebbles tracking topographic surveys remote sensing using ground control cameras and drone flights doing so surrogate measurements allowed to extend temporally discrete manual bedload sampling and to extend spatially local riverbed cross section measurements these measurements provide unique complementary constraints on the targeted physics at various spatial and temporal scales which enabled us to draw robust conclusions data showed a progressive decrease in bedload transport for a given flow rate along the two months period simultaneously river morphology in the braided sections changed from an incised to a more distributed configuration which led to a decrease of local maxima in dimensionless shear stresses in the braided reach for similar flow conditions this control of bedload transport by maximum local shear stresses was in line with tracked pebble surveys indicating that coarse bedload particles were mostly transported in the main active channel at the reach scale this transport was found to be more efficient in laterally confined sections than in braided ones which has important implications in terms of bedload estimation in alternative confined and braided unconfined rivers finally this study highlight the interest to combine a large variety of traditional and innovative measurements techniques to better understand complex sediment transport processes in the field

climate modulation of north atlantic hurricane tracks the variability of north atlantic tropical storm and hurricane tracks and its relationship to climate variability is explored tracks from the north atlantic hurricane database for the period 1950 2007 are objectively separated into four groups using a cluster technique that has been previously applied to tropical cyclones in other ocean basins the four clusters form zonal and meridional separations of the tracks the meridional separation largely captures the separation between tropical and more baroclinic systems while the zonal separation segregates gulf of mexico and cape verde storms general climatologies of the seasonality intensity landfall probability and historical destructiveness of each cluster are documented and relationships between cluster membership and climate variability across a broad spectrum of time scales are identified composites with respect to cluster membership of sea surface temperature and other environmental fields show that regional and remote modes of climate variability modulate the cluster members in substantially

microseismicity stress and fracture in the coso geothermal field california abstract microseismicity stress and fracture in the coso geothermal field are investigated using seismicity focal mechanisms and stress analysis comparison of hypocenters of microearthquakes with locations of development wells indicates that microseismic activity has increased since the commencement of fluid injection and circulation microearthquakes in the geothermal field are proposed as indicators of shear fracturing associated with fluid injection and circulation along major pre existing fractures high seismicity zones are associated with the main fluid flow paths within the geothermal system calculated stress patterns from focal mechanisms provide direct evidence for the boundary between significantly different stress regimes within the coso geothermal field microseismicity in the coso geothermal field is spatially but not temporally related to regional seismicity extending southeast of the field the spatial distribution of these events defines a northwest trending seismic fracture zone consistent with a previously defined northwest striking zone the abrupt decrease of seismicity below this fracture zone may provide seismic evidence for the existence of a brittle and ductile transition zone at shallow depth beneath the coso geothermal field

hydrological changes and vertical crustal deformation in south india inference from grace gps and absolute gravity data abstract monsoon rainfall over indian subcontinent causes large hydrological changes that deform the earth on varied time scale the seasonal hydrological mass changes are in the range of 20 50 cm of equivalent water height over southern india which causes vertical deformation of 1 2 cm we compare the deformation computed from grace mass signal with that of height changes from continuous gps data from two locations in south india and find that the amplitude and phases of seasonal vertical deformation derived from both gps and grace are consistent indicating that hydrological effects are major cause of periodic deformation in the region this supports the earlier deduction that grace data can be utilized to remove hydrological effects from gps data high precision absolute gravity values measured near the gps location and groundwater levels measured in the boreholes corroborate the space based observations of hydrological changes and vertical deformation gps and grace data also indicate inter annual variation caused due to rainfall variability signifying that hydrological effects must be removed before deriving any long term vertical deformation trend

multiple fluvial processes detected by riverside seismic and infrasound monitoring of a controlled flood in the grand canyon as rivers transport water and sediment across earth s surface they radiate elastic and acoustic waves we use seismic and infrasound observations during a controlled flood experiment cfe in the grand canyon to show that three types of fluvial processes can be monitored from outside the channel first bed load transport under conditions of evolving bed mobility is identified as the dominant seismic source between 15 and 45 hz two lower frequency seismic bands also excited by the cfe exhibited greater power increases and are consistent with source processes related to fluid rather than sediment transport the second fluvial seismic source is inferred to be fluid tractions on the rough riverbed which drive the maximum seismic power increase at 0 73 hz but do not excite infrasound waves at the fluid air interface are suggested as a third source which generates a common 6 7 hz peak in seismic and infrasound responses to the cfe

seismic patterns and fluid dynamic features preceding and accompanying the january 15 1990 eruptive paroxysm on mt etna italy abstract on the basis of data collected during a seismological investigation carried out on mt etna italy during a phase of the volcanic activity marked by progressive transition from strombolian bursts to effusive paroxysms at the se crater january 1990 three types of seismic regime have been recognized they are interpreted to be linked to modifications in the regimes of volcanic gases and vapours within the upper levels of the magma column as suggested by recent studies on the dynamics of magmatic fluids our analysis also reveals that the use of usual seismic parameters such as the temporal patterns associated with the occurrence of discrete low frequency events spindles and the coefficient m of the ishimoto iida law can furnish information about variations in the behaviour of the system before the irreversible evolution of the volcanic activity toward eruptive paroxysms

ground vibrations produced by rock motions and debris flows 1 in this study we compare ground vibrations generated by various rocks and debris flows at the same channel to explore the origin of ground vibrations caused by debris flows in field experiments we identified the ground vibrations caused by motions of individual rocks ground vibrations were detected by geophones and analyzed in the time frequency domains we found that ground vibrations caused by individual rocks were 10 150 hz and that larger stones generate ground vibrations with lower peak frequencies a sphere packing model of granular rocks was used to estimate the propagation speed of ground vibrations this was found to be underestimated when compared with our experimental data the signal decay rate was obtained under the assumption that ground vibrations propagate as exponentially attenuating cylindrical waves ground vibrations produced by a debris flow at ai yu zi creek nan tou taiwan on 2 july 2004 revealed that the debris flow forefront produced vibrations lower than 50 hz and ranged between 50 and 100 hz after the front had passed when the main front was closest to the sensor the frequency spectrum covered a wide range from 10 to 250 hz the mean velocity of the debris flow front was 13 3 m s frequencies of ground vibrations caused by individual rocks are within the frequency range of ground vibrations captured during the debris flow confirming that one of the main sources of ground vibration caused by debris flows is the interaction of rocks or boulders with the channel bed

low frequency events at vulcano aeolian islands italy abstract data from a digital three component seismic array in operation during summer 1987 and 1988 at vulcano aeolian islands southern tyrrhenian sea italy allow us to put experimental constraints on the seismic source of the shallower events connected to volcanic activity in the region spectral and wave polarization analyses based on the properties of the covariance matrix of the three component signals emphasize sharp similarities between different stations evidence is provided of a possibly very complex source which cannot be explained by a simple model

passive acoustic monitoring of bed load discharge in a large gravel bed river surrogate technologies to monitor bed load discharge have been developed to supplement and ultimately take over traditional direct methods our research deals with passive acoustic monitoring of bed load flux using a hydrophone continuously deployed near a river bed this passive acoustic technology senses any acoustic waves propagated in the river environment and particularly the sound due to interparticle collisions emitted during bed load movement a data set has been acquired in the large alpine gravel bedded drau river analysis of the short term frequency response of acoustic signals allows us to determine the origin of recorded noises and to consider their frequency variations results are compared with ancillary field data of water depth and bed load transport inferred from the signals of a geophone array hydrophone and geophone signals are well correlated thanks to the large network of deployed geophones analysis of the spatial resolution of hydrophone measurements shows that the sensor is sensitive to bed load motion not only locally but over distances of 5 10 m 10 20 of river width our results are promising in terms of the potential use of hydrophones for monitoring bed load transport in large gravel bed rivers acoustic signals represent a large river bed area rather than being local hydrophones can be installed in large floods they can be deployed at a low cost and provide continuous monitoring at high temporal resolution

the 1995 and 1996 north atlantic hurricane seasons a return of the tropical only hurricane hurricane activity over the north atlantic basin during 1995 and 1996 is compared to the combined hurricane activity over the previous four years 1991 94 the earlier period produced a total of 15 hurricanes compared to a total of 20 hurricanes over the latter period despite this similarity in numbers the hurricanes of 1995 and 1996 were generally of the tropical only variety which marks a substantial departure from activity during the early 1990s the return of tropical only hurricanes to the atlantic basin is likely the result of several global and local factors including cool sst conditions in the equatorial central and eastern pacific and warm ssts in the tropical atlantic the hurricane activity of 1995 and 1996 is more reminiscent of activity of some seasons during the early and mid 1950s

modeling earth deformation from monsoonal flooding in bangladesh using hydrographic gps and gravity recovery and climate experiment grace data 1 the ganges brahmaputra and meghna rivers converge in bangladesh with an annual discharge second to the amazon most of the flow occurs during the summer monsoon causing widespread flooding the impounded water represents a large surface load whose effects can be observed in gravity recovery and climate experiment grace and gps data bangladesh is at the center of the second largest seasonal anomaly in the grace gravity field reflecting water storage in southeast asia eighteen continuous gps stations in bangladesh record seasonal vertical motions up to 6 cm that inversely correlate to river level we use 304 river gages to compute water height surfaces with a digital elevation model to separate surface water from groundwater porosity of 20 was used to estimate groundwater mass and calculate the water load results show 100 gt of water are stored in bangladesh 7 5 of annual discharge but can reach 150 gt during extreme events the calculated water mass agrees with monthly grace water mass equivalents from bangladesh within statistical limits we compute the deformation due to this water load on an elastic half space and we vary young s modulus to fit gps data from our two most continuous records the water loading can account for 50 of the variance in the gps data the best fitting young s modulus is 117 124 gpa for dhak and 133 135 gpa for sust although the upper bound is not well constrained these estimates lie between sediment 30 75 gpa and mantle 190 gpa values indicating that response to loading is sensitive to structure throughout the lithosphere and is not absorbed by the weak sediments

atlantic sea surface temperatures and tropical cyclone formation abstract it has long been accepted that interannual fluctuations in sea surface temperature sst in the atlantic are associated with fluctuations in seasonal atlantic basin tropical cyclone frequency to isolate the physical mechanism responsible for this relationship a singular value decomposition svd is used to establish the dominant covarying modes of tropospheric wind shear and sst as well as horizontal sst gradients the dominant svd mode of covarying vertical shear and sst gradients which comprises equatorially confined near zonal vertical wind shear fluctuations across the atlantic basin is highly correlated with both equatorial eastern pacific sst anomalies associated with el nino and west african sahel rainfall while this mode is strongly related to tropical storm hurricanes and major hurricane frequency in the atlantic it is not associated with any appreciable atlantic sst signal by contrast the second svd mode of covarying vertical shear and horizontal sst gradient variability wh

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

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

a spherical source model for low frequency volcanic earthquakes a resonant magma chamber is modeled by a spherically symmetric whole space consisting of a small gas filled chamber surrounded by magma which is encased in country rock source boundary conditions are specified on the cavity boundary simulating a possible sudden gas expansion in the magma the simplicity of this model leads to an analytical closed form solution for the fourier transform of radial displacement which predicts a peaked spectrum and an oscillating decaying seismogram for physically reasonable values of the rock and magma elastic properties and dimensions of the model the dominant frequency of the signal is in the range of 1 to 5 hz near the values observed for low frequency volcanic earthquakes and volcanic tremor furthermore the seismograms and spectra bear resemblance to those observed for low frequency earthquakes the fundamental mode of oscillation is a pure radial breathing mode which has markedly different properties from single cavity solutions the fundamental frequency is insensitive to the magma chamber boundary radius when both the inner and outer radii are greater than specified values this may help to explain the apparent similarity of the dominant frequency of volcanic earthquakes over a wide range of physical situations the presence of an inner effective bubble of a certain minimum size is necessary for the existence of the dominant low fundamental frequency spectral peak although highly idealized we believe that this fundamental fluid solid cavity mode may provide an explanation for the observations of tremor and low frequency volcanic earthquakes

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

concurrent changes to hadley circulation and the meridional distribution of tropical cyclones abstractpoleward trends in seasonal mean latitudes of tropical cyclones tcs have been identified in direct observations from 1980 to the present paleoclimate reconstructions also indicate poleward equatorward migrations over centennial millennial time scales hadley circulation hc is often both implicitly and explicitly invoked to provide dynamical linkages to these shifts although no direct analysis of concurrent changes in the recent period has been presented here the observational tc record 1981 2016 and era interim jra 55 and merra 2 are studied to examine potential relationships between the two a zonally asymmetric hc is defined by employing helmholtz theory for vector decomposition and this permits the derivation of novel hc diagnostics local to tc basins coherent variations in both long term linear trends and detrended interannual variability are found tc genesis and lifetime maximum intensity latitudes share trend sign and magnitude with shifts in local hc extent with rates being a

observations of seismic volcanic signals at stromboli volcano italy abstract digital recordings of ground motion during a seismic operation organized at stromboli volcano italy from may 31 1986 to june 26 1986 have been studied the amplitude of background seismic noise is greater at the summit than at the base of the volcano and the spectra calculated on different days are dominated by at least two frequencies 2 0 and 6 0 hz with subdominant frequencies at 4 1 4 8 and 8 hz according to their waveform and their spectral content three types of discrete volcanic signals are distinguishable the first type is characterized by a dominant frequency at 2 hz and a subdominant frequency at 4 1 hz the second type also has a dominant peak frequency at 2 hz with two important subdominant frequencies at 5 and 8 hz the type 3 has a sharp dominant frequency at 6 hz and subdominant frequency at 3 2 hz the frequencies observed for discrete signals and ground noise suggest that they are produced by the same repeated mechanism which probably has a volcanic origin the discrete signals are linked to explosions at the active vents within the craters

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

two high sensitivity laser strainmeters installed in the canfranc underground laboratory spain instrument features from 100 to 0 001 mhz two laser strainmeters are being operated in the canfranc underground laboratory lsc central pyrenees spain at about 350 m depth one of the two laser strainmeters gal16 striking 76 is located about 670 m from the spanish entrance of a decommissioned train tunnel along the side wall of one of the bypasses connecting a recent highway tunnel to the train tunnel the other strainmeter lab780 striking 32 is located about 780 m from the spanish entrance of the train tunnel inside two narrow side halls parallel to and built at the same time as the train tunnel their mechanical and optical setups derive from a previous installation at gran sasso italy with some changes and improvements here we show the main instrument features in the frequency range of 100 0 001 mhz at frequencies lower than 4 mhz strain noise compares well with the best laser strainmeters made till now while at higher frequencies strain noise is higher than at kamioka japan probably because of frequency instabilities of the laser source environmental air temperature and pressure effects on measured strain are quite small thus signal to noise ratio in the tidal bands is unusually high in particular diurnal 1 and 1 tides clearly emerge from noise even using a 2 year long strain record giving the opportunity to improve previous determinations of the free core nutation parameters from strain data as soon as more data are acquired the features of the lsc strainmeters allow investigating the earth in a very broad frequency range with a signal to noise ratio as good as or better than that of the best laser strainmeters in the world

long term strain oscillations related to the hydrological interaction between aquifers in intra mountain basins a case study from apennines chain italy abstract we analyze the multiyear strain cycle of a network of continuous gps stations in the l aquila intra mountain basin in central apennines italy the basin is bounded by two aquifers nuria velino and gran sasso hosted in two tectonically active mountain ranges all stations show coherent displacements mostly in the horizontal plane and orthogonal to the normal fault zones of the apennine mountain range the displacement repeats back and forth roughly every 4 5 years with elongation up to 6 mm the deformation occurs in the region bounded by the two aquifers and the displacement amplitude decreases with distance as predicted by two tensile sources acting in an elastic medium we interpret this type of deformation as induced by the opening of pre existing fractures related to two different fault systems as a response to hydrostatic pressure variations the strain cycle follows the average multiyear rainfall cycle and foresees a dilatation phase during high rainy seasons and a contraction during drier periods the estimated depth of the equivalent tensile sources ranges from 1 2 to 1 5 km affecting stations at distances up to 20 km away gps data show the cumulated movement induced by the two nearby aquifers and suggest a mutual interaction in the elastic space related to the different average annual rainfall and effective infiltration we fit two tensile sources located along the main faults affecting the aquifers the eastern source corresponds to the major active fault system affecting the gran sasso range while the western one includes the sub parallel active faults of the mt ocre in the nuria velino range where carbonate rocks show a higher structural permeability and effective infiltration these fault systems affect jurassic miocene limestones and dolomites inducing parallel fracturation style of the rock matrix and favoring a strong anisotropy allowing a prevalent lateral expansion as a reaction to pore pressure variations the recorded hydrological signal may hamper other geophysical signals in gps time series thus the measure of tectonic strains requires a careful mapping and modeling of major aquifers

bed load transport and boundary roughness changes as competing causes of hysteresis in the relationship between river discharge and seismic amplitude recorded near a steep mountain stream hysteresis in the relationship between bedload transport and river stage is a well documented phenomenon with multiple known causes consequently numerous studies have interpreted hysteresis in the relationship between seismic ground motion near rivers and some measure of flow strength i e discharge or stage as the signature of bedload transport here we test this hypothesis in the erlenbach stream swiss prealps using a metric to quantitatively compare hysteresis in seismic data with hysteresis recorded by geophones attached beneath steel plates within the streambed a well calibrated proxy for direct sediment transport measurements we find that while both the geophones and seismometers demonstrate hysteresis the magnitude and direction of hysteresis are not significantly correlated between these data indicating that the seismic signal at this site is primarily reflecting hysteresis in processes other than sediment transport seismic hysteresis also does not correlate significantly with the magnitude of sediment transport recorded by the geophones contrary to previous studies assumptions we suggest that hydrologic sources and changes in water turbulence for instance due to evolving boundary conditions at the bed rather than changes in sediment transport rates may sometimes contribute to or even dominate the hysteresis observed in seismic amplitudes near steep mountain rivers

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

fluctuations in north atlantic hurricane frequency the annual record of hurricane activity in the north atlantic basin for the period 1886 1996 is examined from the perspective of time series analysis singular spectrum analysis combined with the maximum entropy method is used on the time series of annual hurricane occurrences over the entire basin to extract the dominant modes of oscillation the annual frequency of hurricanes is modulated on the biennial semidecadal and neardecadal timescales the biennial and semidecadal oscillations correspond to two well known physical forcings in the local and global climate these include a shift in tropical stratospheric winds between an east and west phase quasi biennial oscillation qbo and a shift in equatorial pacific ocean temperatures between a warm

a physical model for seismic noise generation from sediment transport in rivers measuring sediment flux in rivers remains a significant problem in studies of landscape evolution recent studies suggest that observations of seismic noise near rivers can help provide such measurements but the lack of models linking observed seismic quantities to sediment flux has prevented the method from being used here we develop a forward model to describe the seismic noise induced by the transport of sediment in rivers the model provides an expression for the power spectral density psd of the rayleigh waves generated by impulsive impacts from saltating particles which scales linearly with the number of particles of a given size and the square of the linear momentum after incorporating expressions for the impact velocity and rate of impacts for fluvially transported sediment we observe that the seismic noise psd is strongly dependent on the sediment size such that good constraints on grain size distribution are needed for reliable estimates of sediment flux based on seismic noise observations the model predictions for the psd are consistent with recent measurements and based on these data a first attempt at inverting seismic noise for the sediment flux is provided

volcanic tremor at mt etna state of the art and perspectives volcanic tremor on etna seems to have its origin within the main magma feeding system on the basis of both spectral analyses at two permanent seismic stations and periodical measurements along the slopes of the volcano two distinct sources are proposed the former characterized by low frequency contents f 1 5 hz is located in a 2 km deep flat magma chamber whereas the latter source seems to be linked to the upper part of the active vents

seismic array constraints on reach scale bedload transport measurements and mechanical models of heterogeneous bedload transport in rivers remain basic challenges for studies of landscape evolution and watershed management a 700 m reach of the trinity river northern california usa a large gravel bed river was instrumented with an array of 76 seismographs during a dam controlled ood and gravel augmentation to investigate the potential for out of stream monitoring the temporal response to gravel augmentation during constant discharge provides strong evidence of seismic sensitivity to bedload transport and aids in identification of the seismic frequencies most sensitive to bedload in the study area following gravel augmentations the seismic array reveals a period of enhanced transport that spans most or all of the reach for 7 10 h neither the duration nor the downstream extent of enhanced transport would have been constrained without the seismic array sensitivity to along stream transport variations is further demonstrated by seismic amplitudes that decrease between the upper and lower halves of the reach consistent with decreased bedload ux constrained by time lapse bathymetry insight into the magnitude of impact energy that reaches the bed is also gained from the seismic array observed peak seismic power is 1 5 of that predicted by a model of saltation over exposed bedrock our results suggest that dissipation of impact energy due to cover effects needs to be considered to seismically constrain bedload transport rates and that noninvasive constraints from seismology can be used to test and refine mechanical models of bedload transport

intermittent behaviour of volcanic tremor at mt etna harmonic tremor is widely studied and modelled in a very narrow frequency band 1 5 hz which represents the eigenfrequencies of a resonator assumed as the source of the phenomenon minimal effort was dedicated towards understanding its behaviour in larger temporal scales here we characterise the dynamic behaviour of volcanic tremor while evaluating the complete spectrum of the generalised dimension of the phase space the starting time series constitutes the tremor amplitude picked every 10 minutes the choice of this lag time is made on the basis of a qualitative analysis of the properties of the tremor the results show intermittent behaviour of the dynamics which requires an 8 dimensional map to be completely described an interesting result is that the maximum clustering of point density in phase space occurs in a monodimensional space which implies a periodicity sometimes observed experimentally an appropriate predictive model needs more constraints on the nature of the eight variables involved in the process

bed load transport monitoring using seismic observations in a low gradient rural gravel bed stream the characterization of bed load transport in rivers is critical for the fundamental understanding and management of fluvial systems bed load monitoring based on seismological observations has recently emerged as a viable noninvasive measurement technique however applications of this new approach have been hitherto restricted to the case of sediment transport in steep mountain rivers here we further develop and evaluate the approach for a lower gradient gravel bed stream in a rural catchment using seismic observations in situ hydroacoustic measurements of bed load motion impact plate type device and 3 d hydromorphodynamic modeling the results of this joint analysis of seismic measurements hydroacoustic records and sediment transport simulations show that the seismic monitoring technique for bed load transport characterization is applicable for a broader range of river systems than previously investigated

towards the hydrologic and bed load monitoring from high frequency seismic noise in a braided river the torrent de st pierre french alps summary we explore the use of seismic noise produced by rivers to monitor the bed load transport in the case of a low discharge braided river in the french alps the torrent de st pierre for this purpose we deployed two dedicated seismic networks during summers 2007 and 2008 for which the characteristics of the recorded continuous signal are similar despite changes in the sensor locations for dry weather conditions only melting of nearby glaciers controls the supply of water to the stream in these conditions the river hydrology and the seismic energy in the 2 80 hz frequency band both follow a diurnal fluctuation similar to the thermal amplitude in contrast during rainfall episodes the temperature variation fails to explain the hydrodynamic changes dense cloud covers reduce glacier melting and the recorded seismic energy denotes bursts of high frequency seismic noise well correlated with water level data comparisons between the recorded seismic signals and the collected hydrological and sediment load data indicate that a frequency band of 3 9 hz best explains the water level changes and thus the seismic waves coming from the flow turbulence these analyses also reveal the presence of a seismic noise threshold that might be linked to the water shear stress exerted by the flowing water using the seismic energy in this frequency band as a proxy of the fluvial shear stress the seismic hydrologic relationship may be sensitive to variations in bed load transport the spectral content of the seismic energy shows patterns consistent with the mobilization of sediment particles from the interpretations of the seismic wave attenuation of river sources we finally propose that stations at a distance from the stream less than 50 m are able to record most sediment particles farther stations are still useful during extreme events when largest grain sizes are mobilized more generally this study demonstrates the feasibility of using the river seismic signal to survey bed load transport in various river types from small braided mountain rivers like the torrent de st pierre to the large entrenched himalayan rivers

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

spectral analysis of seismic noise induced by rivers a new tool to monitor spatiotemporal changes in stream hydrodynamics to 20 db relative to m s 2 hz for all the stations located along a steep 30 km long narrow and deeply incised channel of the trisuli river a major trans himalayan river the early summer increase in high frequency energy is modulated by a 24 h periodicity where the minimum of seismic noise level is reached around noon and the maximum is reached late in the evening a detailed study of seismic noise amplitude reveals a clear correlation with both regional meteorological and hydrological data along the trisuli river seasonal increase in ambient noise coincides with the strong monsoon rainfall and a period of rapid melting of snow and ice in the high elevations the observed 24 h cyclicity is consistent with the daily fluctuation of the precipitation and river discharge in the region river induced seismic noise is partly generated by stream turbulence but this mechanism fails to explain the observed clockwise hysteresis of seismic noise amplitude versus water level this pattern is better explained if a significant part of the observed seismic noise is caused by ground vibrations generated by bed load transport this points out the potential of using background seismic noise to quantify in continuous river bed load and monitor its spatial variations which remain difficult with classical approaches

the incidence and nature of bedload transport during flood flows in coarse grained alluvial channels a continuous record reveals that the incidence of bedload in a coarse grained river channel changes from flood to flood long periods of inactivity encourage the channel bed to consolidate sufficiently so that bedload is largely confined to the recession limb of the next flood wave but when floods follow each other closely the bed material is comparatively loose and offers less resistance to entrainment in this case substantial amounts of bedload are generated on the rising limb this is confirmed by values of bed shear stress or stream power at the threshold of initial motion which can be up to five times the overall mean in the case of isolated floods or those which are the first of the season this produces a complicated relationship between flow parameters and bedload and explains some of the difficulties in establishing bedload rating curves for coarse grained channels besides this the threshold of initial motion is shown to occur at levels of bed shear stress three times those at the thresholds of final motion this adds further confusion to attempts at developing predictive bedload equations and clearly indicates at least one reason why equations currently in use are unsatisfactory bedload is shown to be characterized by a series of pulses with a mean periodicity of 1 7 hours in the absence of migrating bedforms it is speculated that this well documented pattern reflects the passage of kinematic waves of particles in a slow moving traction carpet the general pattern of bedload including pulsations is shown to occur more or less synchronously at different points across the stream channel