t waves from the 1998 papua new guinea earthquake and its aftershocks timing the tsunamigenic slump t waves recorded at hydrophone and seismic stations following the papua new guinea earthquake of 17 july 1998 and its aftershocks show that a small event at 09 02 gmt featured source properties incompatible with an elastic dislocation of appropriate body wave magnitude m b 4 4 these include an exceptional duration 47 s at the wake island hydrophone station wk31 a spectrum rich in high frequencies 7 to 12 hz and a generally low spectral amplitude these characteristics can be explained by the model of an underwater slump accelerating from a standstill and eventually slowing down the relocation of the 09 02 event is compatible with its location within an amphitheater inside which shipboard cruises in 1998 and 1999 documented the presence of a 4 c km3 geologically fresh slump we propose that the slump took place at 09 02 on 17 july 1998 i e 13 minutes after the mainshock and that it generated the locally catastrophic tsunami whose properties amplitude and distribution of runup timing could not be explained by a dislocation model

source mechanisms of explosions at stromboli volcano italy determined from moment tensor inversions of very long period data 1 seismic data recorded in the 2 30 s band at stromboli volcano italy are analyzed to quantify the source mechanisms of strombolian explosions during september 1997 to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous elastic medium that takes topography into account two source centroids are identified each representative of the distinct event types associated with explosive eruptions from two different vents the observed waveforms are well reproduced by our inversion and the two source centroids that best fit the data are offset 220 and 260 m beneath and 160 m northwest of the active vents the source mechanisms include both moment tensor and single force components the principal axes of the moment tensor have amplitude ratios 1 1 2 which can be interpreted as representative of a crack if one assumes the rock matrix at the source to have a poisson ratio n 1 3 a value appropriate for hot rock both imaged cracks dip 60 to the northwest and strike northeast southwest along a direction parallel to the elongation of the volcanic edifice and a prominent zone of structural weakness as expressed by lineaments dikes and brittle structures for our data set the volume changes estimated from the moments are 200 m 3 for the largest explosion from each vent together with the volumetric source is a dominantly vertical force with a magnitude of 10 8 n consistent with the inferred movement of the magma column perched above the source centroid in response to the piston like rise of a slug of gas in the conduit index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms keywords very long period seismicity moment tensor inversions eruption mehanics

researching the earth and a few of its neighbors during my career our knowledge of erupting geysers and volcanoes in the solar system has exploded in this prefatory i tell how i became fascinated with high speed processes through studying meteorite impact dynamics and then how my initial idea of studying old faithful geyser as a volcanic analog led me to work not only on the dynamics of eruption of mount st helens in 1980 but also on geysers erupting on io a fiery satellite of jupiter triton a frigid satellite of neptune and enceladus an active satellite of saturn unforeseeably the study of these events also led to work on mineral thermodynamics and the hydraulics and geomorphic evolution of rapids in the grand canyon this is a narrative not a formal review article but the reader can find references in the related resources section to explore topics in more detail

mesozoic paleomagnetic results of the tarim craton tertiary relative motion between china and siberia paleomagnetic poles from two late jurassic to late cretaceous stratigraphic sections on the northern boundary of the tarim craton in western china are concordant with poles of similar age from eastern china when combined with previously published data these new results suggest that the major tectonic blocks which comprise china the tarim yangtze and sino korean cratons have been arranged in approximately their present relative configuration since cretaceous times the averaged cretaceous paleomagnetic pole for china is significantly different from the averaged cretaceous pole for siberia the difference may reflect significant relative post cretaceous motion between the composite china terrane and the siberian craton alternatively the cretaceous pole for siberia may not be reliable

centroid single force inversion of seismic waves generated by landslides the centroid moment tensor cmt waveform inversion method of dziewonski et al 1981 is modified to analyze long period seismic waves generated by single force events such as the gigantic landslides associated with the 1980 eruption of mount st helens we refer to the method as centroid single force csf inversion as the result of the inversion we obtain the spatio temporal centroid and three components of a vector we call the csf vector which is the seismic point source representation of a landslide and whose direction is the opposite of the direction of sliding the sealer magnitude of the csf vector measures the overall size of the landslide and is given by mcsf md where m is the mass of the sliding object and d is the sliding distance we apply csf inversion to the long period surface waves generated by the 1980 mount st helens event the 1975 kalapana earthquake and the 1974 mantaro landslide using seismograms from the gdsn ida and hglp networks the csf solution for the st helens event is remarkably consistent with the actual geological observations and proves the efficacy of csf inversion the csf solution for the kalapana event does not fit the overall waveforms better than the cmt solution does however because the cmt solution does not explain the observed love wave radiation pattern it may be necessary to invoke a combination of both types of mechanism for this event although the geometry of the csf solution the direction of the force for the mantaro event is consistent with the actual landslide mcsf is about 5 times smaller than that expected from the mass and travel distance of the landslide estimated by geological observations this discrepancy may suggest either the relatively aseismic nature of this landslide or that the total volume of the slide was overestimated by analogy to single station cmt inversion single station csf inversion also appears to be stable and useful

experimental constraints on shock induced microstructures in naturally deformed silicates abstract planar deformation features pdfs in various minerals have long been accepted as evidence of impact induced deformation the uniqueness of this association was challenged in the context of the k t boundary extinction debate after mosaicism and microstructures similar to pdfs were reported from the products of explosive volcanism as a result of this debate a significant volume of new experimental and observational data on the development of shock induced microstructures has become available over the last ten years the results reveal that factors such as pre shock temperature pulse duration and crystallographic orientation of target minerals to the shock wave have a primary influence on how these microstructures develop data from diamond anvil cell and high pressure friction experiments reveal that the same solid state amorphization process that produces shock induced pdfs at low temperatures also occurs at much lower strain rates in static experiments the experimental data indicate that the amorphization process is thermally activated and that the character of the resulting pdfs is a function of the applied strain rate shock induced amorphization occurs along those crystallographic planes that are most readily transformed to the high pressure phase during very short pulse durations and produces pdfs that are visible at the optical scale lower strain rate deformation produces tem scale amorphization with orientations that are more homogeneously distributed throughout the target mineral and produces no optically visible pdfs the data confirm the uniqueness of multiple intersecting sets of optically visible pdfs as a diagnostic indicator of hypervelocity impact the data also support the hypothesis that the amorphization process can occur at a wide range of strain rates and that the limiting pressure for the process is controlled by the phase stability of the target mineral under the applied loading conditions not by the hel the data also suggest that the onset pressure the maximum pressure and the pressure range for producing optically visible pdfs decrease with increasing temperature and decreasing strain rate as the pressure range for optically visible pdf formation decreases it is replaced by homogeneous amorphization as observed in the anvil cell experiments thus the uniqueness of multiple intersecting sets of optically visible pdfs to hypervelocity impact is not due to a unique process but rather to a specific set of loading conditions that produce an optically visible microstructure likewise single sets of microdeformations observed in volcanic rocks are produced by the same process but at different loading conditions that preclude the development of multiple intersecting sets of pdfs the data also indicate that shock mosaicism which occurs above the hel represents a plastic response of the target mineral to loading rates that are too large to be accommodated by crystal plastic mechanisms observational data for some naturally deformed samples from the k t boundary the vredefort dome and volcanic rocks along with the experimental observations are used to constrain the range of conditions under which the natural microstructures form and to understand the differences between microstructures produced by impact volcanic and other natural processes finally some possible mechanisms for producing the microstructures observed in volcanic rocks are proposed

analysis of long period seismic waves excited by the may 18 1980 eruption of mount st helens a terrestrial monopole long period 100 to 260 s love and rayleigh waves excited by the eruption of mount st helens on may 18 1980 and recorded by ida sro and asro stations were analyzed to determine the mechanism of the eruption the amplitude radiation patterns of both rayleigh and love waves are two lobed with a nodal direction in e5 s for rayleigh waves and in n5 e for love waves these radiation patterns preclude any double couple mechanism the radiation pattern the initial phase the relatively large amplitude ratio of love to rayleigh waves and the existence of clear nodes in the radiation patterns of fundamental mode and higher mode rayleigh waves suggest that the source is represented by an almost horizontal less than 15 from the horizontal single force pointed toward s5 w the surface wave spectra fall off very rapidly at periods shorter than 75 s suggesting a very slow source process although the details of the source time history could not be determined a smooth bell shaped time function f o s t 1 2 f o l cos t for 0 t 2 and f o s t 0 for t 2 with 75 s is considered appropriate on the basis of comparison between synthetic and observed seismograms and of the shape of the source spectrum the peak value of the force f 0 is about 10 18 dynes the tailing end of the source time function could not be resolved and some overshoot may be added the magnitude and the time history of the force can be explained by a northward landslide followed by a lateral blast observed at the time of the eruption two distinct events about 110 s apart can be identified on body wave and short period surface wave records the first event may correspond to the earthquake which triggered the landslide and the lateral blast the second event appears to correspond to a second large earthquake and explosion which took place about 2 minutes after the first earthquake

seismic signals associated with landslides and with a tsunami at stromboli volcano italy in this article we analyze the seismic signals produced by two landslides that occurred at the stromboli volcano on 30 december 2002 recorded by both broadband and short period seismic stations located in the 2 5 22 km distance range from the source for both landslides the characteristics of the low frequency seismograms indicate a complex time history in the release of seismic energy the first landslide occurred over the submerged part of the northwest sector of the volcano and had associated a large amplitude low frequency pulse representative of the abrupt detachment of a large mass lower amplitude phases in the following 3 minutes possibly indicate minor detachment events the highest amplitude low frequency signals are well described by a single force source model the second mass failure episode is also characterized by a complex source and can be interpreted as a multiple event with a less abrupt onset and at least four detachments occurring during 4 5 minutes and producing low frequency signals synthetic seismograms generated by a shallow single force located in the submerged area of sciara del fuoco and directed upslope fit well the first low frequency seismic pulse recorded at stromboli and panarea by three component stations from this simulation we estimated the force exerted by the first mass failure the estimate of the volume through two different procedures gives values in the range of 1 0 1 5 million m3 and about 14 million m3 respectively the landslides which involved both the submarine and the subaerial northwest flank of the volcano produced a tsunami that struck the coast of stromboli island and in a few minutes reached the other islands of the aeolian archipelago three broadband seismic stations installed on land about 100 m from the coastline at panarea island located 20 km southwest of stromboli recorded very long period seismic signals produced by the tsunami waves analysis of these signals gives invaluable information on the spectral content and propagation properties of tsunami waves and on their interaction with the ground at a short distance from the coast synthetic tsunami waves obtained by a landslide source model and taking into account the bathymetry of the sea surrounding stromboli and panarea islands fit the observed phenomena and the experimental data very well manuscript received 19 november 2003

process of the 1977 nyiragongo eruption inferred from the analysis of long period earthquakes and volcanic tremors abstract the lava lake present in the summit crater of nyiragongo from 1928 to 1977 completely disappeared after the short lived eruption of january 10th 1977 the sequence of events during this eruption was elucidated by analysis of seven long period earthquakes lp events and volcanic tremors recorded at stations lwi nai and bul the seven lp events observed were composed mainly of rayleigh waves with large amplitudes and were classified into two groups one containing three and the other containing four events based on waveform similarities it was determined that the former events were excited by the vertical downward single forces and the latter events by the vertical upward ones the short period seismograms recorded at lwi and nai showed that continuous volcanic tremors began roughly 6 min before the occurrence of the first lp event after the appearance of seven burst type tremor activities tremor amplitudes suddenly increased and then gradually decreased taking the analytical results of seismic events and observed surface activities into consideration we inferred the process of the 1977 nyiragongo eruption to be as follows 1 1 quick draining of the liquid lava through the fissures and disappearance of the long lived lava lake less than 6 min 2 2 large terraces collapsing onto the bottom of crater causing the first three lp events during the next 8 min 3 3 intermittent vesiculation of lava at the top of magma chamber exciting the last four lp events during the next 8 min 4 4 magma flowing in deeper parts of the conduit generating the intense tremors measurable at nai and lasting for roughly 30 min

was the 18 may 1980 lateral blast at mt st helens the product of two explosions the 18 may 1980 lateral blast at mt st helens has been interpreted as the product of a single explosion by some stratigraphers and as two closely spaced explosions by others the stratigraphic evidence that bears on this question is inconclusive strata change dramatically over short distances and this complexity provides wide latitude for interpretation some independent non stratigraphic evidence however suggests that the blast was the product of two explosions or clusters of explosions the independent evidence comes from eyewitness accounts and photographs from satellite sensors and from seismic records this paper reviews the pertinent evidence offers a new interpretation and concludes that the blast was indeed the product of two explosions or clusters of explosions

microevents produced by gas migration and expulsion at the seabed a study based on sea bottom recordings from the sea of marmara summary different types of 4 component ocean bottom seismometers obs were deployed for variable durations ranging from 1 week to about 4 months in 2007 over soft sediments covering the seafloor of the tekirdag basin western part of the sea of marmara turkey non seismic microevents were recorded by the geophones but generally not by the hydrophones except when the hydrophone is located less than a few tens of centimetres above the seafloor the microevents are characterized by short durations of less than 0 8 s by frequencies ranging between 4 and 30 hz and by highly variable amplitudes in addition no correlation between obss was observed except for two obss located 10 m apart interestingly a swarm of 400 very similar microevents based on principal component analysis was recorded in less than one day by an obs located in the close vicinity of an active gas prone fault cutting through the upper sedimentary layers the presence of gas in superficial sediments together with analogies with laboratory experiments suggest that gas migration followed by the collapse of fluid filled cavities or conduits could be the source of the observed microevents this work shows that obss may provide valuable information to improve our understanding of natural degassing processes from the seafloor

source mechanism of vulcanian eruption at tungurahua volcano ecuador derived from seismic moment tensor inversions source mechanisms of explosive volcanic eruptions are critical for understanding magmatic plumbing systems and magma transport tungurahua is a large andesitic stratovolcano where seismoacoustic data has been recorded over several years in may 2010 an energetic eruption cycle began with a midsize vulcanian explosion followed by swarms of explosive eruptions the five station seismoacoustic network recorded significant seismic and infrasonic signals from the explosions source mechanisms of 50 explosion earthquakes associated with vulcanian explosions during this eruptive period are investigated here the source centroid locations and geometries of explosive signals in the 10 2 s band were determined by full waveform moment tensor inversion the observed waveforms are well explained by a combination of volumetric moment tensor components and a single vertical downward force component the source centroids are positioned about 1 5 km below and about 320 m north of the active crater eigenvalue and eigenvector analysis indicates that the source geometries can be described by a subhorizontal thin ellipsoid representing a sill like magma accumulation resultant source time histories show a repetitive sequence of inflation and deflation from event to event indicating identical source processes frequently occurred over the period the inflation deflation in the deep source region may be the result of crack opening volatile bubble growth at depth opens a pathway for gases to escape and triggers shallow explosions at the summit crater the associated downward single force is interpreted as an exchange of linear momentum between the source and the surrounding region during the escaping gas flow

blast dynamics at mount st helens on 18 may 1980 at 8 32 a m on 18 may 1980 failure of the upper part of the north slope of mount st helens triggered a lateral eruption the blast that devastated the conifer forests in a sector covering 500 km2 north of the volcano i present here a steady flow model for the blast dynamics and propose that through much of the devastated area the blast was a supersonic flow of a complex multiphase solid liquid vapour mixture the shape of the blast zone pressure temperature velocity mach number and density distributions within the flow positions of weak and strong internal shocks and mass flux energy flux and total energy are calculated the shape of blast zone was determined by the initial areal expansion from the reservoir by internal expansion and compression waves including shocks and by the density of the expanding mixture the pressure within the flow dropped rapidly away from the source of the blast until at a distance of 11 km the flow became underpressured relative to the surrounding atmosphere weak shocks within the flow subparallel to the east and west margins coalesced at about this distance into a strong mach disk shock across which the flow velocities would have dropped from supersonic to subsonic as the pressure rose back towards ambient the positions of the shocks may be reflected in differences in the patterns of felled trees at the limits of the devastated area the temperature had dropped only 20 from the reservoir temperature because the entrained solids thermally buffered the flow the dynamic and thermodynamic effects of the admixture of the surrounding atmosphere and the uprooted forest and soils into the flow are not considered the density of the flow decreased with distance until at the limits of the blast zone 20 25 km from the volcano the density became comparable with that of the surrounding dirty atmosphere and the flow became buoyant and ramped up into the atmosphere according to the model the mass flux per unit area at the source was 0 6 104 g s 1 cm 2 and the energy flux per unit area was 2 5 mw cm 2 from the measured total ejected mass 0 25 1015 g the total energy released during the eruption was 1024 erg or 24 megatons the model triggering of the eruption and the transition from unsteady to steady flow and applications to eyewitness observations and atmospheric effects are discussed in ref 1

spatio temporal evolution of rockfall activity from 2007 to 2011 at the piton de la fournaise volcano inferred from seismic data abstract seismic data have been used to catalog the location and volume of most of the rockfalls that occurred at the piton de la fournaise volcano from may 2007 just after the major collapse of the dolomieu summit crater floor to may 2011 this catalog made it possible to compare the evolution of the number and volume of rockfalls at a high temporal resolution and to investigate their links with eruptions seismicity deformations and rainfalls affecting the piton de la fournaise volcano results show that the purge of unstable areas created by the dolomieu crater floor collapse occurred in two phases a first phase lasting three months during which the intense rockfall activity immediately following the collapse decreased abruptly and a second phase lasting more than two years during which the daily volume of the rockfalls slowly decreased before reaching a steady state a detailed study of 4 time periods including 3 eruptive cycles indicates that strong seismicity can increase the number of rockfalls furthermore when a dike reaches the surface at the summit of the central cone giving birth to an eruption the associated local forcing can in some cases increase the volume of rockfalls possibly by creating or expanding weak zones in most cases this is not observed for dike intrusions that do not reach the surface the newly created weak zones are most often far from the eruptive fissures of the ongoing eruption but close to the location of the next eruption this suggests that these distant zones are also weakened at depth thus creating preferred paths for future dikes propagating toward the surface the impact of rainfall on rockfall activity was also studied given that la reunion island is subject to very intense rainfall events our results show that rainfall can in some cases trigger rockfalls rapidly with response times of less than a day but not systematically and no triggering rainfall threshold was found

analysis of source characteristics of experimental gas burst and fragmentation explosions generated by rapid decompression of volcanic rocks gas burst and fragmentation explosions induced by rapid decompression of volcanic rocks in a high pressure autoclave have been analyzed we performed experiments from 4 to 20 mpa on 1 loose pyroclasts and 2 pumice from recent eruptions of popocatepetl volcano our aim is to characterize the source mechanism distinguishing the physical processes that operate in the conduit which determine the dynamics of explosive volcanoes for this aim we have analyzed experimentally the parameters that indicate the state and behavior of the conduit i e decompression time fragmentation threshold and speed forces and the partitioning of energy using microseismic monitoring the decompression time curves and the sample rheological properties the initial available potential energy in the system and its partitioning into different types of energies are correlated in space and time with specific stages of the explosive phenomenon such correlations taken together with the energy distribution enable the distinction of the individual physical processes involved and their causal sequence and relationships our observations suggest that in volcanic conduits with regular explosive activity a source mechanism may operate whereby a causal sequence of processes results in a system that undergoes both rapid and stable transitions such behavior may persist over long periods of time

tsunami simulations for regional sources in the south china and adjoining seas we present 14 scenarios of potential tsunamis in the south china sea and its adjoining basins the sulu and sulawezi seas the sources consist of earthquake dislocations inspired by the the study of historical events either recorded since 1900 or described in historical documents going back to 1604 we consider worst case scenarios where the size of the earthquake is not limited by the largest known event but merely by the dimension of the basin over which a coherent fault may propagate while such scenarios are arguably improbable they may not be impossible and as such must be examined for each scenario we present a simulation of the tsunami s propagation in the marine basin exclusive of its interaction with the coastline our results show that the south china sulu and sulawezi seas make up three largely independent basins where tsunamis generated in one basin do not leak into another similarly the sunda arc provides an efficient barrier to tsunamis originating in the indian ocean furthermore the shallow continental shelves in the java sea the gulf of thailand and the western part of the south china sea significantly dampen the amplitude of the waves the eastern shores of the malay peninsula are threatened only by the greatest and most improbable of our sources a mega earthquake rupturing all of the luzon trench we also consider two models of underwater landslides which can be triggered by smaller events even in an intraplate setting these sources for which there is both historical and geological evidence could pose a significant threat to all shorelines in the region including the malay peninsula

seismological analysis of conduit dynamics in fragmentation experiments we simulate gas burst and volcanic explosions under controlled laboratory conditions inducing fragmentation of volcanic rocks by rapid depressurization a series of experiments were performed in a shock tube apparatus at room temperature and a pressure range of 4 to 20 mpa using argon ar gas and particles or pumice samples of different porosities the instrumentation of this system with high precision piezoelectric sensors enabled us to capture elastic waves and to recognize their characteristic signatures by relating these signals to physical processes in the wave field we have been able to characterize the conduit mechanism and the source dynamics we compare and discuss conspicuous features of the waveforms and frequency spectra of these experimental signals with those of volcanic origin despite the fact that these signals are different in amplitude resulting from different scale conditions our observations indicate that the physical processes that occur during simulated explosions and those that occur during volcanic eruptions yield comparable signatures in their respective records the effects of the source receiver configuration and resonance also have significant implications all this suggests that the physical processes e g pressurization and depressurization of a system involve a system response that causes similar distinctive effects independent of the system size reflecting its intrinsic dynamics these similarities imply that powerful constraints on the source mechanisms of volcanic seismicity can emerge from seismic investigations of experimental simulations of volumetric sources such constraints may yield significant advances in the understanding of volcanic conduit dynamics and in the interpretation of seismic unrest at volcanic centers

model space exploration for determining landslide source history from long period seismic data the seismic signals generated by two large volcanic debris avalanches montserrat lesser antilles 1997 and mount st helens usa 1980 and a large rock ice avalanche mount steller usa 2005 have been analyzed for the two debris avalanches given the times and locations of such landslides their signals were recorded by only a few seismic stations moreover these signals cover only a very narrow frequency band and include considerable noise the mount steller on the contrary was precisely recorded for each event the source mechanism i e point force has been determined by waveform inversion using at most two broadband seismic stations the resulting force is very difficult to interpret in terms of landslide characteristics a monte carlo inversion was therefore performed by imposing a simple force model associated with the landslide based on the schematic view of an accelerating decelerating mass traveling down the slope the best parameter set of the force model was then found by minimizing misfits and maximizing correlations between data and synthetic signals this model appears to contain the minimum degree of complexity required to well reproduce the seismic data we detail here the method for the montserrat debris avalanche and then present it s validation on the well studied mount st helens debris avalanche and the well recorded mount steller rock ice avalanche the horizontal and vertical components of the resulting force have different source time functions the best force model compares well with the force obtained by waveform inversion finally this simple force model was interpreted using analytical and empirical relations derived from the sliding block model granular flow model and landslide studies this made it possible to estimate the order of magnitude of the mass flow duration and direction initial topography slope mean velocity and travel distance of the avalanches for these three avalanches the calculated characteristics are consistent with former studies

a theoretical comparison of tsunamis from dislocations and landslides we use simple physical models to evaluate and compare the orders of magnitude of the energy generated into a tsunami wave by seismic dislocations and underwater slumps we conclude that the two sources can generate tsunamis of comparable total energy however the slumping source is shown to be fundamentally dipolar in nature which results in a low frequency deficiency in the far field these simple conclusions corroborate the interpretation of the 1998 papua new guinea tsunami as being generated by an underwater slump

a single force model for the 1975 kalapana hawaii earthquake a single force mechanism is investigated as the source of long period seismic radiation from the 1975 kalapana hawaii earthquake m s 7 1 the observed love wave radiation pattern determined from the spectra of world wide standard seismograph network and high gain long period records at 100 s is two lobed with azimuth consistent with a near horizontal single force acting opposite strike 330 to the observed displacement direction of the earthquake this pattern is inconsistent with the expected double couple pattern assuming a form of the force time history of a one cycle sinusoid the total duration of the event estimated from rayleigh waves at two international deployment of accelerometers stations is approximately 180 s the peak amplitude f o of the time function is 1 10 15 n from amplitudes of love and rayleigh waves the interpretation is that the bulk of the seismic radiation was produced by large scale slumping of a large area of the south flank of kilauea volcano the single force is a crude representation of the effect on the earth of the motion of a partially decoupled large slide mass using the mass estimated from the tsunami generation area 10 15 10 16 kg the peak acceleration of the slide block 0 1 1 m s 2 inferred from the seismic force is comparable with the acceleration due to gravity on a gently inclined plane the slump model for the kalapana earthquake is also more qualitatively consistent with the large horizontal deformation 8 m on land and tsunami associated with the earthquake which are difficult to explain with the conventional double couple source model the single force source has been used previously to model the long period seismic waves from the landslide accompanying the eruption of mount st helens volcano and may explain other anomalous seismic events as being due to massive slumping of sediments or unconsolidated material and not to elastic dislocation

analysis of broadband seismic recordings of landslide using empirical green s function the 2010 mount meager landslide generated strong seismic waves we used seismic signals generated by a smaller landslide that occurred within 2 min of the end of the main landslide as the empirical green s function egf with which to obtain landslide dynamics from high frequency signals we then obtained the apparent force time function of the landslide based on the egf by inverting the higher frequency seismic signals the apparent force time function shows that the source material of the main landslide came from four collapses and that the second collapse involved multiple small collapses we also used the egf to simulate the vertical seismogram recorded at one station and found that the synthesized seismogram fits the response of the bulk mobilization of the sliding materials remarkably well our study demonstrates that the use of the egf can significantly broaden quantitative insights into landslide dynamics plain language summary seismic records reflect the effects of landslide dynamics and the path of seismic waves through the earth because the calculation of the high frequency component of the effect of a wave s path through the earth requires a detailed characterization of the velocity and attenuation structure the effects of landslide dynamics can only be estimated by inverting the long period seismic signals to study the high frequency seismic signals generated from the mount meager landslide we considered the seismic signals generated by a smaller landslide as the effects of the path of seismic waves we used the seismic signals generated by the smaller landslide to simulate the signal generated by the main landslide to overcome the effects of a potential overlap in the frequency domain between signals from the bulk and those from smaller particles our results show that the seismic signals generated by a small landslide can be used to improve our understanding of those generated by the main landslide

seismic detection of underwater volcanism the example of french polynesia we present a review of the principal methods used for the seismic detection and identification of active underwater volcanism based on our experience in french polynesia in particular we descrobe the 5 year activity in the tahiti mehetia area during which more than 32000 earthquakes were detected by the polynesian network we discuss the use of the following three types of seismic waves conventional mostly body waves seismic tremor andt waves propagated in the low velocity acoustic channel of the ocean for each of these waves we discuss the principal characteristics of the signals their spectral content the type of information they provide on the activity of the volcano and the various limitations faced by their use in detection or monitoring of underwater volcanic edifices we present a review of the principal swarms monitored by the polynesian network and discuss their characterization as either volcanic or tectonic

volcanic plume height measured by seismic waves based on a mechanical model journal of geophysical research vol 116 b01306 doi 10 1029 2010jb007620 2011 volcanic plume height measured by seismic waves based on a mechanical model stephanie g prejean 1 and emily e brodsky 2 received 4 april 2010 revised 3 november 2010 accepted 23 november 2010 published 26 january 2011 1 in august 2008 an unmonitored largely unstudied aleutian volcano kasatochi erupted catastrophically here we use seismic data to infer the height of large eruptive columns such as those of kasatochi based on a combination of existing fluid and solid mechanical models in so doing we propose a connection between a common observable short period seismic wave amplitude to the physics of an eruptive column to construct a combined model we estimate the mass ejection rate of material from the vent on the basis of the plume height assuming that the height is controlled by thermal buoyancy for a continuous plume using the estimated mass ejection rate we then derive the equivalent vertical force on the earth through a momentum balance finally we calculate the far field surface waves resulting from the vertical force the model performs well for recent eruptions of kasatochi and augustine volcanoes if v the velocity of material exiting the vent is 120 230 m s 1 the consistency between the seismically inferred and measured plume heights indicates that in these cases the far field 1 s seismic energy radiated by fluctuating flow in the volcanic jet during the eruption is a useful indicator of overall mass ejection rates thus use of the model holds promise for characterizing eruptions and evaluating ash hazards to aircraft in real time on the basis of far field short period seismic data this study emphasizes the need for better measurements of eruptive plume heights and a more detailed understanding of the full spectrum of seismic energy radiated coeruptively citation prejean s g and e e brodsky 2011 volcanic plume height measured by seismic waves based on a mechanical model j geophys res 116 b01306 doi 10 1029 2010jb007620 1 introduction and motivation 2 empirical studies have suggested that the amplitude of high frequency or broadband seismic waves radiated during large volcanic eruptions generally scales with the height of an eruption column mcnutt 1994a however a direct calculation of the expected seismic wave amplitude based on physical models has not yet been successful connecting commonly observable data such as seismic wave amplitudes to a model of the flow in the eruptive jet would provide a new tool to test and improve our understanding of eruptive physics for instance small scale turbulence is thought to play a major role in the entrainment of hot particles and gases and hence the buoyancy of eruptive columns yet there are few measurements of the strength or distribution of small scale features in real eruptive columns andrews and gardner 2009 using seismic data to provide observational constraints on eruption column flow processes is particularly attractive as seismic data are often available even in remote u s geological survey alaska volcano observatory anchorage alaska usa department of earth and planetary sciences university of california santa cruz california usa copyright 2011 by the american geophysical union 0148 0227 11 2010jb007620 settings thus use of the seismic database would greatly increase the number and type of eruptions amenable to study 3 pragmatically a physical model connecting plume height and seismic data would allow the use of seismology as a remote sensing technology to infer volcanic plume height it would be a particularly useful tool for exploring eruption dynamics in remote environments where direct observation is not possible such as the volcanoes of the northern pacific ocean although many volcano observa tories worldwide are gradually replacing short period seismometers with broadband seismometers we still largely rely on short period instruments for forecasting monitoring and analyzing eruptions these realities motivate the development of the model described below 4 in this study we build on previous work to develop a physical model for the expected amplitude of seismic waves from an eruption that generates a plume of a given height as a cautionary note we explore the potential errors in this formulation and describe situations where the model is not applicable such as small eruptions or eruptions where most mass ejected is not entrained in the plume after reviewing previous work on coeruptive seismology and the char acteristics of the 2008 kasatochi and 2006 augustine eruptions we use the connection between plume height and b01306 1 of 13

pressure changes associated with the ascent and bursting of gas slugs in liquid filled vertical and inclined conduits at basaltic volcanoes the sources of long period and very long period seismicity and acoustic signals are frequently described in terms of fluid dynamic processes in particular the formation and ascent of gas slugs within the magma column and their bursting at the surface to investigate pressure changes associated with these processes two phase flow experiments have been carried out in vertical and inclined pipes with both single gas slugs and a continuously supplied gas phase the ascent of individual gas slugs is accompanied by strong dynamic pressure variations resulting from the flow of liquid around the slug these dynamic transients generate sub static pressures below the ascending slug in viscosity controlled systems and produce super static pressures when the slug reaches the surface and motion ceases in inertia dominated systems conduit inclination promotes a change of regime from bubbly to slug flow and favours an increase in size and velocity of the slugs at the expense of their frequency of occurrence during continuously supplied two phase flow the experimental pressure data support previous theoretical analyses of oscillatory sources in ascending slugs as the slugs approach the surface and burst pressure oscillations are also observed during the release of gas slugs and in their wake region

long period seismicity and very long period infrasound driven by shallow magmatic degassing at mount pagan mariana islands long period lp seismicity and very long period infrasound ivlp were recorded during continuous degassing from mount pagan mariana islands in july 2013 to january 2014 the frequency content of the lp and ivlp events and delay times between the two arrivals were remarkably stable and indicate nearly co located sources using phase weighted stacking over similar events to dampen noise we find that the lp source centroid is located 60 m below and 180 m west of the summit vent the moment tensor reveals a volumetric source modeled as resonance of a subhorizontal sill intersecting a dike we model the seismoacoustic wavefields with a coupled earth air 3 d finite difference code the ratios of pressure to velocity measured at the infrasound arrays are an order of magnitude larger than the synthetic ratios so the ivlp is not the result of lp energy transmitting into the atmosphere at its epicenter based on crater shape and dimensions determined by structure from motion we model the ivlp as acoustic resonance of an exponential horn the source of the continuous plume from gas analysis is shallow magmatic degassing which repeatedly pressurized the dike sill portion of the conduit over the 7 months of observation periodic gas release caused the geologically controlled sill to partially collapse and resonate while venting of gas at the surface triggered resonance in the crater lp degassing only accounts for 12 of total degassing indicating that most degassing is relatively aseismic and that multiple active pathways exist beneath the vent

particulate kinematic simulations of debris avalanches interpretation of deposits and landslide seismic signals of mount saint helens 1980 may 18 summary we construct a new class of granular landslide models in which avalanches are simulated with large numbers of independent particles moving under the influence of topographically derived gravitational and centripetal acceleration concurrently the particles suffer deceleration due to basal and dynamic friction the novel aspect of the calculation is that complex particle toparticle interactions fluctuating basal contacts and unresolved topographic roughness within and below the deforming flow are mimicked by random perturbations in along track and cross slope acceleration we apply the method to the 1980 may 18 mount saint helens debris avalanche by constraining the initial geometry and structure of the slide mass from geological data and the initial failure sequence from eyewitness accounts after tuning coefficients of mechanical friction and random accelerations the landslide simulation generates a final deposit whose extent thickness morphological structure and lithological variation closely replicate those observed moreover the model avalanche is consistent kinematically with mapped patterns of bedrock scouring deposit superelevation and net force history implied from seismic records to be successful the slide mass must be divided into upper high friction and lower low friction members this division corresponds to fresh water unsaturated and hydrothermally altered water saturated rock units and points to a mechanical explanation of the kinematics of the debris avalanche success in reproducing many features of the mount saint helens avalanche indicates that debris deposit data may be used to determine the kinematic histories of less well observed landslides

ground coupled acoustic airwaves from mount st helens provide constraints on the may 18 1980 eruption abstract the may 18 1980 mount st helens eruption perturbed the atmosphere and generated atmosphere to ground coupled airwaves which were recorded on at least 35 seismometers operated by the pacific northwest seismograph network pnsn from 102 distinct travel time picks we identify coherent airwaves crossing washington state primarily to the north and east of the volcano the travel time curves provide evidence for both stratospheric refractions at 200 to 300 km from the volcano as well as probable thermospheric refractions at 100 to 350 km the very few first hand reports of audible volcano sounds within about 80 km of the volcano coincide with a general absence of ground coupled acoustic arrivals registered within about 100 km and are attributed to upward refraction of sound waves from the coherent refracted airwave arrivals we identify at least four distinct sources which we infer to originate 10 s 114 s 180 s and 319 s after the onset of an 8 32 11 pdt landslide the first of these sources is attributed to resultant depressurization and explosion of the cryptodome most of the subsequent arrivals also appear to be coincident with a source located at or near the presumed volcanic conduit but at least one of the later arrivals suggests an epicenter displaced about 9 km to the northwest of the vent this dislocation is compatible with the direction of the sector collapse and lateral blast we speculate that this concussion corresponds to a northern explosion event associated with hot cryptodome entering the toutle river valley

analysis of seismic body waves excited by the mount st helens eruption of may 18 1980 seismic body waves which were excited by the may 18 1980 eruption of mount st helens and recorded by the global digital seismographic network stations are analyzed to determine the nature and the time sequence of the events associated with the eruption the polarity of teleseismic p waves period 20s is identical at six stations which are distributed over a wide azimuthal range this observation together with a very small s to p amplitude ratio at 20 s suggests that the source is a nearly vertical single force a simple model shows that for seismic radiation a volcanic eruption can be represented by a single force applied in the direction opposite to the blast direction the time history of the vertical force suggests two distinct groups of events about 2 min apart each consisting of several subevents with a duration of about 25 s the magnitude of the force is approximately 2 6 10 12 n this vertical force is in contrast with the long period 150 s southward horizontal single force which has been determined by a previous study and interpreted to be due to the massive landslide an m s 5 2 earthquake initiated the eruption sequence the direction of the p wave first motion of this event observed at two nearby stations is consistent with the radiation pattern expected for the landslide and suggests that it represents the onset of the landslide the ground motions observed at station lon 67 km are dominated by rayleigh waves i e lamb pulse and provide tight constraints on the time sequence of the events