magnitude scale and quantification of earthquakes despite various shortcomings the earthquake magnitude scale is one of the most fundamental earthquake source parameters to be used for catalogs although use of a uniform scale is desirable it is not always possible because of changes in instrumentation the data reduction method and the magnitude formula the station distribution etc as a result various magnitude scales have been developed and are currently in use recent developments in seismometry and earthquake source theories provide more quantitative source parameters than the magnitude in order to maintain continuity and uniformity of the data it is important to relate these magnitude scales and the new parameters in view of this importance relations between different magnitude scales are examined with an emphasis on the difference in the period of the waves used for the magnitude determination use of several magnitude scales determined at different periods provides a convenient method for characterizing earthquakes the moment magnitude can be used to quantify both shallow and deep earthquakes on the basis of wave energy radiated and provides a uniform scheme

discrete element modelling of rock creep behaviour using rate process theory rock creep behavior is crucial in many rock engineering projects different approaches have been proposed to model rock creep behavior however many cannot reproduce tertiary creep i e accelera

source constraints of tungurahua volcano explosion events the most recent eruptive cycle of tungurahua volcano began in may 2004 and reached its highest level of activity in july 2004 this activity cycle is the last one of a series of four cycles that followed the reawakening and major eruption of tungurahua in 1999 between june 30 and august 12 2004 three temporary seismic and infrasonic stations were installed on the flanks of the volcano and recorded over 2 000 degassing events the events are classified by waveform character and include explosion events the vast majority spanning three orders of pressure amplitudes at 3 5 km from the vent 0 1 180 pa jetting events and sequences of repetitive infrasonic pulses called chugging events travel time analysis of seismic first arrivals and infrasonic waves indicates that explosions start with a seismic event at a shallow depth 200 m followed 1 s later by an out flux of gas ash and solid material through the vent cluster analysis of infrasonic signals from explosion events was used to isolate four groups of similar waveforms without apparent correlation to event size location or time the clustering is thus associated with source mechanism and probably spatial distribution explosion clusters do not exhibit temporal dependence

case study of slope deterioration characteristics simbal landslide salt range pakistan for a slope structure various deterioration phenomena progress in the slope over time and failure may occur which decreases the durability life and service life the approach to slope stability due to deterioration is a different concept from the existing limit equilibrium analysis which is limited to the physical characteristics and geometrical structure of the ground and groundwater in this study with a comparative review of various literatures related to the slope failure characteristics due to deterioration the optimal formulas for shear strength reduction such as the exponential function logarithmic function and inverse hyperbolic function are found to be the best fits for the variations in strength reduction in addition a case study was performed for the simbal landslide salt range pakistan where the slope failure of some carbonate rock formations vulnerable to deterioration occurred as a result it was confirmed that landslide occurred because of the reduction in shear strength by deterioration since the safety factor was approx 1 0 when the slope failure occurred finally as a quantitative approach to evaluate the slope stability due to deterioration a methodology to evaluate the slope stability using the limit equilibrium analysis of the slope with optimal strength reduction curves was proposed

triggering of the powerful 14 july 2013 vulcanian explosion at tungurahua volcano ecuador abstract the 14 july 2013 vulcanian explosion at tungurahua occurred after two months of quiescence and was extremely powerful generating some of the highest infrasound energies recorded worldwide here we report on how a combination of geophysical data textural measurements and physical and mechanical tests on eruptive products allowed us to determine the processes that led to the pressurization of the conduit and triggering of this large vulcanian event two weeks prior to the 14 july event daily seismic counts and radial tilt began to steadily increase indicating the probable intrusion of a new batch of magma into the edifice the 14 july explosion produced three different juvenile products that were each sampled for this study airfall juvenile vesicular pyroclastic density current material and dense plug rocks in the form of ballistic ejecta feldspar microlite textures and vesicle size distributions were measured and used jointly with a two step recompression model to characterize the spatial distribution of gas in the conduit and the decompression histories of the erupted samples model results reveal a vertically stratified conduit with regards to porosity crystallinity and volatile content prior to the explosion overall our data suggests a complex sequence of events that led eventually to this powerful explosion 1 remnants of magma from the previous eruptive phase in may stalled in the shallow conduit triggering crystallization which coupled with efficient outgassing formed a dense

acoustic source inversion to estimate volume flux from volcanic explosions we present an acoustic waveform inversion technique for infrasound data to estimate volume fluxes from volcanic eruptions previous inversion techniques have been limited by the use of a 1 d green s function in a free space or half space which depends only on the source receiver distance and neglects volcanic topography our method exploits full 3 d green s functions computed by a numerical method that takes into account realistic topographic scattering we apply this method to vulcanian eruptions at sakurajima volcano japan our inversion results produce excellent waveform fits to field observations and demonstrate that full 3 d green s functions are necessary for accurate volume flux inversion conventional inversions without consideration of topographic propagation effects may lead to large errors in the source parameter estimate the presented inversion technique will substantially improve the accuracy of eruption source parameter estimation cf mass eruption rate during volcanic eruptions and provide critical constraints for volcanic eruption dynamics and ash dispersal forecasting for aviation safety application of this approach to chemical and nuclear explosions will also provide valuable source information e g the amount of energy released previously unavailable

source characterization for an explosion during the 2009 eruption of redoubt volcano from very long period seismic waves abstract the 2009 eruption of redoubt produced several very long period vlp signals associated with explosions we invert for the source location and mechanism of an explosion at redoubt volcano using waveform methods applied to broadband recordings such characterization of the source carries information on the geometry of the conduit and the physics of the explosion process inversions are carried out assuming the volcanic source can be modeled as a point source with mechanisms described by a a set of 3 orthogonal forces b a moment tensor consisting of force couples and c both forces and moment tensor components we find that the source of the vlp seismic waves during the explosion is well described by either a combined moment force source located northeast of the crater and at an elevation of 1 6 km asl or a moment source at an elevation of 800 m to the southwest of the crater the moment tensors for the solutions with moment and force and moment only share similar characteristics the source time functions for both moment tensors begin with inflation pressurization and execute two cycles of deflation reinflation depressurization repressurization although the moment force source provides a better fit to the data we find that owing to the limited coverage of the broadband stations at redoubt the moment only source is the more robust and reliable solution based on the moment only solution we estimate a volume change of 19 000 m3 and a pressure change of 7 mpa in a dominant sill and an out of phase volume change of 5000 m3 and pressure change of 1 8 mpa in a subdominant dike at the source location these results shed new light on the magmatic plumbing system beneath redoubt and complement previous studies on vulcanian explosions at other volcanoes

sequential plug formation disintegration by vulcanian explosions and the generation of granular pyroclastic density currents at tungurahua volcano 2013 2014 ecuador following 84 years of repose tungurahua volcano ecuador initiated its present eruptive episode in october 1999 but its pdc activity only began in july 2006 a period of highly energetic vulcanian eruptions started in 2012 those of 14 july 2013 18 october 2013 and 1 february 2014 being the most important these eruptions were well monitored by a 5 station broadband seismic and acoustic array repeated repose intervals of 3 5 months between vulcanian events vei 2 suggest that gases in the ascending juvenile magma experienced sequential pressurization cycles as magma of preceding eruptive events solidified to form plugs that sealed the conduit every 34 months plug failure occurred abrupt decompression followed and the resulting vulcanian explosions are associated with the highest seismic and acoustic energies ever registered anywhere small to moderate sized pdc flows associated with the explosions and fountain collapses were generated and traveled 7 km down the steep n nw and w flanks of tungurahua s cone at velocities of 11 to 18 m s although a small lateral blast and its pdc were clocked at 33 m s descending the n flank the explosive fragmentation of the plugs a dense microcrystalline andesite and the juvenile magma a vesiculated glassy andesite comprise the principal rock fragments of the pdc deposits each deposit typically consisting of two layers a thin upper layer of large segregated and abraded clasts with few fines and a thicker lower layer that is fines rich with few large clasts many deposits were studied and photographed within a few days of their formation which are presented

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

locating tremor and shock sources recorded at bromo volcano abstract during a phase of high eruptive activity as well as high tremor activity seismic signals were recorded at bromo volcano east java for almost three months in 1995 the signals generated by the volcano cover a broad frequency range including long period signals with frequencies between 10 and 100 mhz tremor signals at about 5 hz and volcanic shocks with frequencies up to 25 hz seismic signals from volcanoes especially tremors have been classified and categorized in different ways but interpretation has always been limited by the difficulties in determining even approximate source locations volcanic tremor lacks an emergent first onset while the complex structure of the volcano makes it difficult to determine other phases from shock signals than first arrivals if the volcanic signal has been recorded in at least two stations the location of its seismic source can be estimated using a grid search method if we assume the source radiates isotropically in a homogeneous medium applying the grid method to data recorded at mt bromo we determine the locations of the sources of tremor and shock signals the sources for both types of signals are located in the northwestern part of the crater near the open vent and also near the source of long period signals gottschammer 1999 annal geofis 42 465 481

autopsy of an eruptive phase of tungurahua volcano ecuador through coupling of seismo acoustic and so2 recordings with ash characteristics abstract eruption style and dynamics are controlled by various parameters including magma supply rate magma viscosity volatile content and the permeability of the conduit rapid changes of these parameters can significantly modify the hazards associated to the eruption processes and understanding their relationship with multiparametric geophysical monitoring data can greatly improve our forecasting capacities from 2008 to 2016 volcanic activity at tungurahua was characterized by eruptive phases separated by episodes of quiescence these phases displayed great variability of eruptive patterns including vulcanian and strombolian explosions low pyroclastic fountaining continuous or sporadic ash emissions and passive degassing we use the comparison between geophysical data seismic acoustic and so2 emission recorded by permanent monitoring networks and the characteristics of the emitted ash to track changes in eruption dynamics during an eruptive phase that lasted from late december 2009 to march 2010 we show that the correlation between the analyzed parameters allows imaging and interpretation of the conditions at the vent at tungurahua these conditions can rapidly change at the time scale of a single eruptive phase corresponding to various degrees of opening plugging and permeability of the conduit two magma intrusions could be identified during a single eruptive phase showing transitions between violent strombolian and vulcanian activity changes in the componentry of the analyzed ash samples together with the geophysical data nicely highlight these evolutions studying these parameters simultaneously provides a unique insight into the physical processes controlling superficial volcanic activity and offers a potential tool for better understanding volcanoes and detecting changes in their activity the joint interpretation of multiparametric data which we propose is potentially applicable to multiple andesitic volcanoes

seismic source mechanism of degassing bursts at kilauea volcano hawaii results from waveform inversion in the 10 50 s band the current march 2008 to february 2009 summit eruptive activity at kilauea volcano is characterized by explosive degassing bursts accompanied by very long period vlp seismic signals we model the source mechanisms of vlp signals in the 10 50 s band using data recorded for 15 bursts with a 10 station broadband network deployed in the summit caldera 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 medium that takes topography into account the vlp signals associated with the bursts originate in a source region 1 km below the eastern perimeter of halemaumau pit crater the observed waveforms are well explained by the combination of a volumetric component and a vertical single force component for the volumetric component several source geometries are obtained which equally explain the observed waveforms these geometries include 1 a pipe dipping 64 to the northeast 2 two intersecting cracks including an east striking crack dike dipping 80 to the north intersecting a north striking crack another dike dipping 65 to the east 3 a pipe dipping 58 to the northeast intersecting a crack dipping 48 to the west southwest and 4 a pipe dipping 57 to the northeast intersecting a pipe dipping 58 to the west southwest using the dual crack model as reference the largest volume change obtained among the 15 bursts is 24 400 m3 and the maximum amplitude peak to peak of the force is 20 gn each burst is marked by a similar sequence of deflation and inflation trailed by decaying oscillations of the volumetric source the vertical force is initially upward synchronous with source deflation then downward synchronous with source reinflation followed by oscillations with polarity opposite to the volumetric oscillations this combination of force and volume change is attributed to pressure and momentum changes induced during a fluid dynamic source mechanism involving the ascent expansion and burst of a large slug of gas within the upper 150 m of the magma conduit as the slug expands upon approach to the surface and more liquid becomes wall supported by viscous shear forces the pressure below the slug decreases inducing conduit deflation and an upward force on the earth the final rapid slug expansion and burst stimulate vlp and lp oscillations of the conduit system which slowly decay due to viscous dissipation and elastic radiation consideration of the fluid dynamic arguments leads us to prefer the dual crack vlp source model as it is the only candidate model capable of producing plausible values of length scales and pressure changes the magnitudes of the vertical forces observed in the 15 bursts appear consistent with slug masses of 104 to 106 kg

tungurahua volcano ecuador structure eruptive history and hazards abstract tungurahua one of ecuador s most active volcanoes is made up of three volcanic edifices tungurahua i was a 14 km wide andesitic stratocone which experienced at least one sector collapse followed by the extrusion of a dacite lava series tungurahua ii mainly composed of acid andesite lava flows younger than 14 000 years bp was partly destroyed by the last collapse event 2955 90 years ago which left a large amphitheater and produced a 8 km3 debris deposit the avalanche collided with the high ridge immediately to the west of the cone and was diverted to the northwest and southwest for 15 km a large lahar formed during this event which was followed in turn by dacite extrusion southwestward the damming of the chambo valley by the avalanche deposit resulted in a 10 km long lake which was subsequently breached generating another catastrophic debris flow the eruptive activity of the present volcano tungurahua iii has rebuilt the cone to about 50 of its pre collapse size by the emission of 3 km3 of volcanic products two periods of construction are recognized in tungurahua s iii history from 2300 to 1400 years bp high rates of lava extrusion and pyroclastic flows occurred during this period the magma composition did not evolve significantly remaining essentially basic andesite during the last 1300 years eruptive episodes take place roughly once per century and generally begin with lapilli fall and pyroclastic flow activity of varied composition andesite dacite and end with more basic andesite lava flows or crater plugs this pattern is observed in the three historic eruptions of 1773 1886 and 1916 1918 given good age control and volumetric considerations tungurahua iii growth s rate is estimated at 1 5 106 m3 year over the last 2300 years although an infrequent event a sector collapse and associated lahars constitute a strong hazard of this volcano given the 3000 m relief and steep slopes of the present cone a future collapse even of small volume could cover an area similar to that affected by the 3000 year old avalanche the more frequent eruptive episodes of each century characterized by pyroclastic flows lavas lahars as well as tephra falls directly threaten 25 000 people and the agoyan hydroelectric dam located at the foot of the volcano

source mechanism of vulcanian degassing at popocatepetl volcano mexico determined from waveform inversions of very long period signals 1 the source mechanism of very long period vlp signals accompanying volcanic degassing bursts at popocatepetl is analyzed in the 15 70 s band by minimizing the residual error between data and synthetics calculated for a point source embedded in a homogeneous medium the waveforms of two eruptions 23 april and 23 may 2000 representative of mild vulcanian activity are well reproduced by our inversion which takes into account volcano topography the source centroid is positioned 1500 m below the western perimeter of the summit crater and the modeled source is composed of a shallow dipping crack sill with easterly dip of 10 intersecting a steeply dipping crack northeast striking dike dipping 83 northwest whose surface extension bisects the vent both cracks undergo a similar sequence of inflation deflation and reinflation reflecting a cycle of pressurization depressurization and repressurization within a time interval of 3 5 min the largest moment release occurs in the sill showing a maximum volume change of 500 1000 m3 pressure drop of 3 5 mpa and amplitude of recovered pressure equal to 1 2 times the amplitude of the pressure drop in contrast the maximum volume change in the dike is less 200 300 m3 with a corresponding pressure drop of 1 2 mpa and pressure recovery equal to the pressure drop accompanying these volumetric sources are single force components with magnitudes of 108 n consistent with melt advection in response to pressure transients the source time histories of the volumetric components of the source indicate that significant mass movement starts within the sill and triggers a mass movement response in the dike within a few seconds such source behavior is consistent with the opening of a pathway for escape of pent up gases from slow pressurization of the sill driven by magma crystallization the opening of this pathway and associated rapid evacuation of volcanic gases induces the pressure drop pressure recovery in the magma filling the sill is driven by diffusion of gases from the resulting supersaturated melt into bubbles assuming a penny shaped crack at ambient pressure of 40 mpa the observed pressure and volume variations can be modeled with the following attributes crack radius 100 m crack aperture 5 m bubble number density 1010 1012 m 3 initial bubble radius 10 6 m final bubble radius 10 5 m and net decrease of gas concentration in the melt 0 01 wt

shallow conduit system at kilauea volcano hawaii revealed by seismic signals associated with degassing bursts 1 eruptive activity at the summit of kilauea volcano hawaii beginning in march 2008 and continuing to the present time is characterized by episodic explosive bursts of gas and ash from a vent within halemaumau pit crater these bursts are accompanied by seismic signals that are well recorded by a broadband network deployed in the summit caldera we investigate in detail the dimensions and oscillation modes of the source of a representative burst in the 1 10 s band an extended source is realized by a set of point sources distributed on a grid surrounding the source centroid where the centroid position and source geometry are fixed from previous modeling of very long period vlp data in the 10 50 s band the source time histories of all point sources are obtained simultaneously through waveform inversion carried out in the frequency domain short scale noisy fluctuations of the source time histories between adjacent sources are suppressed with a smoothing constraint whose strength is determined through a minimization of the akaike bayesian information criterion abic waveform inversions carried out for homogeneous and heterogeneous velocity structures both image a dominant source component in the form of an east trending dike with dimensions of 2 9 2 9 km the dike extends 2 km west and 0 9 km east of the vlp centroid and spans the depth range 0 2 3 1 km the source model for a homogeneous velocity structure suggests the dike is hinged at the source centroid where it bends from a strike e 27 n with northern dip of 85 west of the centroid to a strike e 7 n with northern dip of 80 east of the centroid the oscillating behavior of the dike is dominated by simple harmonic modes with frequencies 0 2 hz and 0 5 hz representing the fundamental mode 11 and first degenerate mode 12 21 of the dike although not strongly supported by data in the 1 10 s band a north striking dike segment is required for enhanced compatibility with the model elaborated in the 10 50 s band this dike provides connectivity between the east trending dike and the new vent within halemaumau pit crater waveform inversions with a dual dike model suggest dimensions of 0 7 0 7 km to 2 6 2 6 km for this segment further elaboration of the complex dike system under halemaumau does not appear to be feasible with presently available data

determining the seismic source mechanism and location for an explosive eruption with limited observational data augustine volcano alaska 1 waveform inversions of the very long period components of the seismic wavefield produced by an explosive eruption that occurred on 11 january 2006 at augustine volcano alaska constrain the seismic source location to near sea level beneath the summit of the volcano the calculated moment tensors indicate the presence of a volumetric source mechanism systematic reconstruction of the source mechanism shows the source consists of a sill intersected by either a sub vertical east west trending dike or a sub vertical pipe and a weak single force the trend of the dike may be controlled by the east west trending augustine seldovia arch the data from the network of broadband sensors is limited to fourteen seismic traces and synthetic modeling confirms the ability of the network to recover the source mechanism the synthetic modeling also provides a guide to the expected capability of a broadband network to resolve very long period source mechanisms particularly when confronted with limited observational data

understanding cyclic seismicity and ground deformation patterns at volcanoes intriguing lessons from tungurahua volcano ecuador abstract cyclic seismicity and ground deformation patterns are observed on many volcanoes worldwide where seismic swarms and the tilt of the volcanic flanks provide sensitive tools to assess the state of volcanic activity ground deformation at active volcanoes is often interpreted as pressure changes in a magmatic reservoir and tilt is simply translated accordingly into inflation and deflation of such a reservoir tilt data recorded by an instrument in the summit area of tungurahua volcano in ecuador however show an intriguing and unexpected behaviour on several occasions prior to a vulcanian explosion when a pressurisation of the system would be expected the tilt signal declines significantly hence indicating depressurisation at the same time seismicity increases drastically envisaging that such a pattern could carry the potential to forecast vulcanian explosions on tungurahua we use numerical modelling and reproduce the observed tilt patterns in both space and time we demonstrate that the tilt signal can be more easily explained as caused by shear stress due to viscous flow resistance rather than by pressurisation of the magmatic plumbing system in general our numerical models prove that if magma shear viscosity and ascent rate are high enough the resulting shear stress is sufficient to generate a tilt signal as observed on tungurahua furthermore we address the interdependence of tilt and seismicity through shear stress partitioning and suggest that a joint interpretation of tilt and seismicity can shed new light on the eruption potential of silicic volcanoes

scale effect on the shear behaviour of rock joints based on a numerical study abstract a large number of studies have been carried out to investigate the effect of scale on the shear behaviour of rock joints however the nature of scale dependency of rock joints is still unknown and remains an ongoing debate this paper investigates the effect of joint length on the shear behaviour of rough rock joints using pfc2d in this numerical approach the intact material is simulated by a dense packing of bonded particles and the joint is represented by micro scale slip surfaces at contacts between particles the validity of this numerical approach in reproducing the shear behaviour of rock joints has been studied in previous studies of authors against the physical experiments analytical and empirical models in this study numerical direct shear tests on a natural tensile joint and subdivided joints were carried out and the shear behaviour of these joints at different scale was investigated results of this study show that as the joint length increases the peak shear strength peak dilation rate and shear stiffness decrease while the peak shear displacement increases in order to find out the reason of observed scale dependency the mechanism of asperity degradation at different scales was investigated and it was found that the mobilisation of different sized asperities at different scales resulted in the observed scale effect

size of popocatepetl volcano explosions 1997 2001 from waveform inversion several volcanic explosions have been recorded since april 1997 at broadband seismic stations located around the popocatepetl volcano mexico we have inverted waveforms of ten of these explosions to estimate the following source parameters depth duration magnitude and direction of the single force f the crustal structure used in generating green s function at nearest stations is derived from the inversion of teleseismic receiver functions at the broadband permanent station ppig located 5 km north of the volcano this inversion reveals a low velocity zone at 8 km beneath the summit with high poisson ratio possibly related to the magma chamber we find that f scales with the duration of the source time function as f tau based on this relationship we determine an impulse magnitude scale mk this magnitude is tied to the mount saint helens initial explosive phase of may 18 1980 whose magnitude is estimated as 4 6 mk of the ten popocatepetl explosions ranges between 1 8 and 3 2 finally we also propose an equivalent formula for rapid estimation of magnitude of future popocatepetl explosions which requires filtered amplitudes at ppig

the methodology of quantification of volcanic explosions from broad band seismic signals and its application to the 2004 2005 explosions at volcan de colima mexico summary a methodology is proposed for the quantification of volcanic explosions based on three parameters derived from broad band seismic signals the counter force of the eruption f the power of the explosion p and the duration of the upward movement of the gas slug in the conduit to the free surface of magma d this methodology was applied to the 2004 2005 sequence of

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

moment tensor inversion for the source location and mechanism of long period lp seismic events from 2009 at turrialba volcano costa rica abstract long period lp seismic events were recorded during the temporary installation of a broadband seismic network of 13 stations from march to september 2009 on turrialba volcano costa rica over 6000 lps were extracted using a modified sta lta method and a family consisting of 435 similar lp events has been identified for the first time at turrialba volcano full waveform moment tensor inversion is performed to jointly determine the location and source mechanism of the events the lps in the family are likely to be caused by crack mechanisms dipping towards the southwest at angles of approximately 10 to 20 located at shallow depths

a simplified analytical model for predicting the shear behaviour of regular triangular rock concrete joints under constant normal stiffness in developing a shear strength model for rock joints it is essential to understand the shear behaviour of idealised elastic asperities in this paper the shear behaviour of regular triangular elastic asperities subjected to constant normal stiffness cns boundary conditions is examined for a range of young s moduli of the rock the results show that dilation of the joint decreases with a decrease in rock young s modulus because of the increased elastic deformation of asperities finally a simplified analytical model for predicting the peak shear strength of regular triangular concrete rock joints is developed incorporating a non dimensional equation for joint normal stiffness

real time monitoring and massive inversion of source parameters of very long period seismic signals an application to stromboli volcano italy 1 we present a comprehensive processing tool for the real time analysis of the source mechanism of very long period vlp seismic data based on waveform inversions performed in the frequency domain for a point source a search for the source providing the best fitting solution is conducted over a three dimensional grid of assumed source locations in which the green s functions associated with each point source are calculated by finite differences using the reciprocal relation between source and receiver tests performed on 62 nodes of a linux cluster indicate that the waveform inversion and search for the best fitting signal over 100 000 point sources require roughly 30 s of processing time for a 2 min long record the procedure is applied to post processing of a data archive and to continuous automatic inversion of real time data at stromboli providing insights into different modes of degassing at this volcano

ascending seismic source during an explosive eruption at tungurahua volcano ecuador 1 application of seismic techniques to an explosion event at tungurahua volcano ecuador provided clear images to elucidate its source process a source location method using high frequency seismic amplitudes with an s wave velocity of 2000 m s indicates that the event was triggered at a depth of 6 km below the summit and the source ascended toward the summit at a speed of about 1600 m s waveform inversion of low frequency signals at the event onset points to an isotropic mechanism with initial deflation at a similar depth of 6 km the ascending source suggests that a pressure wave propagated along the magma conduit triggering fragmentation of magma at shallow depths rapid decompression of magma in a shock tube has been considered to be an important mechanism for explosive eruptions triggered by ruptures at the magma surface however our study suggests that explosive eruptions are triggered by pressure disturbances in magma at depth

distinct element method simulations of rock concrete interfaces under different boundary conditions abstract the shear behaviour of concrete rock interfaces has been the aim of extensive research in geotechnical engineering applications such as rock socketed piles rock bolts and concrete dam arch bridge foundations several experimental studies through direct shear tests have been conducted to evaluate the shear behaviour of rock concrete interfaces under cnl constant normal load and cns constant normal stiffness conditions in this paper pfc2d numerical simulations of unbonded rock concrete planar and saw tooth triangular joints under cnl and cns boundary conditions are conducted using the shear box genesis sbg approach proposed by bahaaddini et al 2013b the numerical simulation results are compared with experimental data published by gutierrez 2013 and gu et al 2003 results indicate that the sbg approach reproduces suitably the shear behaviour failure mode and asperity damage of unbonded planar and triangular rock concrete interfaces specially under cnl conditions

the source of explosive eruptions of sakurajima volcano japan to understand the nature of explosive eruptions in particular the role played by exsolution of magmatic gases we studied the seismic waveforms produced by two such eruptions of sakurajima volcano on october 30 and november 14 1986 an explosion begins when a mixture of magmatic gases and fragmented magma flows upward through a narrow vertical channel to the surface the source region is a reservoir of gas rich magma where the pressure drops as gases flow out the form of low frequency seismic waves can be explained by a source that consists of two components one component is a single force directed downward that represents the reaction to ejection of gas and magma the other more important component is a moment tensor that represents expansion or contraction of rock around a source the first motion of seismic waves produced by an explosion is directed away from the volcano tilt and strain measurements show that the initial motion directed outward is soon followed by subsidence around the volcano the eigenvectors of the seismic moment tensor are either nearly horizontal or vertical the ratio of horizontal to vertical eigenvalues was 1 8 1 for the october 30 explosion this suggests the geometry of the explosive source can be approximated as a buried vertical cylinder the volume of contraction 2 l03 m3 can be produced by a pressure change of 0 3 mpa over a cylinder with a radius of 160 m and a height of 300 m we propose that an explosive eruption occurs after a small shallow source of high pressure forms within a vertical conduit possibly exsolution of magmatic gases eventually the small source bursts and pushes open a pathway to the surface providing an upward escape for trapped gases it is this burst that causes the initial outwardly directed motion at the surface a deeper reservoir of gas rich magma is then subjected to a lower confining pressure and also bursts causing the explosion

experimental and numerical study of asperity degradation in the direct shear test abstract in this paper the shear behaviour and mechanisms of asperity degradation of rock joints under direct shear tests were studied using numerical and experimental approaches pfc2d was used for numerical simulations in which the intact material is simulated by a dense packing of circular particles bonded together at their contact points and by breakage of these bonds under loading regimes the damage process is simulated the joint interfaces were simulated by a newly developed modified smooth joint model in which micro scale slip surfaces are applied at contacts between particles of upper and lower blocks of the shear box in order to study the ability of this numerical approach in reproducing the shearing mechanisms and asperity degradation of rock joints in direct shear tests a comparative study was carried out against the physical experiments experimental and numerical direct shear tests were carried out on saw tooth triangular joints with the base angles of 20 and 30 under different normal stresses three shearing mechanisms of sliding surface wear and asperity shearing off were observed in these experiments the comparison of the shear behaviour and mechanisms of asperity degradation of physical and numerical experiments showed that the results of numerical models are in good agreement with physical experiments and this numerical approach can reproduce the shear behaviour of rock joints under different loading conditions

broadband seismic monitoring of active volcanoes using deterministic and stochastic approaches 1 we systematically used two approaches to analyze broadband seismic signals for monitoring active volcanoes one is waveform inversion of very long period vlp signals assuming possible source mechanisms the other is a source location method of long period lp events and tremor using their amplitudes the deterministic approach of the waveform inversion is useful to constrain the source mechanism and location but is basically only applicable to vlp signals with periods longer than a few seconds the source location method assumes isotropic radiation of s waves and uses seismic amplitudes corrected for site amplifications this simple approach provides reasonable source locations for various seismic signals such as a vlp event accompanying lp signals an explosion event and tremor associated with lahars and pyroclastic flows observed at five or fewer stations our results indicate that a frequency band of about 5 12 hz and a q factor of about 60 are appropriate for the determination of the source locations in this frequency band the assumption of isotropic radiation may become valid because of the path effect caused by the scattering of seismic waves the source location method may be categorized as a stochastic approach based on the nature of scattering waves systematic use of these two approaches provides a way to better utilize broadband seismic signals observed at a limited number of stations for improved monitoring of active volcanoes

moment tensor inversion of very long period seismic signals from strombolian eruptions of erebus volcano article i nfo strombolian eruptions from the long lived lava lake of erebus volcano ross island antarctica generate repeating very long period vlp signals containing energy between approximately 30 and 5 s that persist for several minutes and through the post eruptive refilling of the lava lake the initial approximately 10 s of this signal is moderately variable particularly with respect to its initial polarity while the following vlp coda has been observed to be stable since the earliest vlp observations were made 1996 to estimate forces and force couples consistent with the erebus vlp signature we perform moment tensor inversions for point sources using high signal to noise data stacks from the six station 18 component broadband seismographic network and green s function forward calculations that incorporate topography we infer a shallow approximate depth of less than 400 m below the lava lake surface source centroid that underlies the center to the northwestern rim of the main crater east and north of the lava lake integrated mii functions over the predominant 180 s signal duration of vlp events show that the net scalar moments for these events are on the order of 4 10 13 n m corresponding to a moment magnitude mw 3 for typical sized vlp events moment rate tensors which characterize force couple components are dominated 85 97 of variance by dilatational components approximately 25 of the data variance is attributable to single forces that are attributable to oscillatory reaction forces caused by fluid transport however the relative contributions of vertical forces and couples with this sparse network is poorly resolved for these shallow sources the generally high degree of repeatability in the vlp signal across thousands of eruptions over the past decade indicates that the response of the conduit system to gas slug ascent and subsequent gravitational disequilibrium is stable consistent with the generally unchanging surface manifestation of the convecting lava lake system and arguing for a thermally and dynamically stable conduit system beneath the lava lake

pressure recovery in magma due to bubble growth 1 pressure recovery in magma subject to sudden depressurization is investigated in terms of the growth of bubbles containing magmatic volatiles assuming conservation of volatile mass and pressure equilibration between the bubbles melt and a surrounding elastic medium the final magma pressure is completely determined by its initial pressure and the magnitude of the pressure drop simulations show that the initial magma pressure is easily recovered or even exceeded when magma containing tiny bubbles is surrounded by a relatively stiff elastic medium under low confining pressure this result suggests that when processes such as magma withdrawal dike intrusion and nearby seismicity decrease the pressure in a magma chamber magma re pressurization can occur without new injection of magma

characteristics and source modeling of broadband seismic signals associated with the hydrothermal system at satsuma iwojima volcano japan abstract the broadband seismic data observed at satsuma iwojima volcanic island in southwestern japan show a wide variety of interesting features one of them is the periodic and frequency dependent amplitude modulation of volcanic tremors another interesting feature is the occurrence of very long period vlp seismic pulses synchronized with the tremor amplitude modulation both the tremor amplitude modulation and the vlp pulses have fairly regular intervals of 46 50 min suggesting a spatially fixed non destructive repetitive source we performed waveform inversions to reveal the source mechanism of the vlp pulses assuming a point source embedded in a medium that realistically represented the topography of the island numerical tests showed that the green s functions used in the inversion were significantly affected by the topography the observed vlp pulses were well explained by the rapid expansion of an inclined crack 100 m beneath the floor of the summit crater which had a seismic moment of 3 10 10 nm both the characteristic amplitude modulation and the vlp pulses are explained systematically by a model consisting of a water filled crack and a network of gas paths the water filled crack was heated above the boiling temperature of the water in it a sudden break of the unstable superheated state caused sudden vaporization and a pressure increase which was observed as the vlp pulse the network of gas paths consisted of swollen portions and constricted portions which worked as tremor generators when vapor from the water filled crack passed through

eruption source parameters for forecasting ash dispersion and deposition from vulcanian eruptions at tungurahua volcano insights from field data from the july 2013 eruption tungurahua volcano located in the central area of the ecuadorian sierra is erupting intermittently since 1999 alternating between periods of quiescence and explosive activity volcanic ash has been the most frequent and widespread hazard provoking air contamination episodes and impacts on human health animals and crops in the surrounding area after two months of quiescence tungurahua erupted violently on 14th july 2013 generating short lived eruptive columns rising up to 9 km above the vent characterized as a vulcanian eruption the resulting fallout deposits were sampled daily during and after the eruptions to determine grain size distributions and perform morphological and componentry analyses dispersion and sedimentation of ash were simulated numerically coupling the meteorological weather research forecasting wrf with the volcanic ash dispersion fall3d models the combination of field and numerical studies allowed constraining the eruption source parameters esp for this event which could be used to forecast ash dispersion and deposition from future vulcanian eruptions at tungurahua this set of pre defined esp was further validated using two different eruptions as blind test occurring on 16th december 2012 and 1st february 2014

a theoretical model for rock joints subjected to constant normal stiffness direct shear abstract the authors have conducted an investigation into the behaviour of rock joints subjected to direct shear both concrete rock and rock rock joints were investigated the behaviour of rock rock joints is important for the assessment of stability issues involving rock masses e g rock slope stability concrete rock joints are vital to the assessment of performance of concrete piles socketed into rock rock anchors and concrete dam foundations this investigation included an extensive series of direct shear tests under a range of stress boundary conditions the rock used for the tests was a soft artificial siltstone called johnstone the results from the tests on concrete johnstone joints have been presented in seidel and haberfield geotech testing j 2002 accepted for publication and on johnstone johnstone joints in fleuter mengsc dissertation department of civil engineering monash university australia 1997 and pearce ph d dissertation department of civil engineering monash university australia 2001 in preparation this paper describes the theoretical models developed to simulate the observed behaviour including asperity sliding asperity shearing post peak behaviour asperity deformation and distribution of stresses on the interface these models have been combined into a micro mechanical simulation of joint shear comparisons between program predictions and measured performance are presented and discussed

three dimensional p wave velocity structure of tungurahua volcano ecuador abstract tungurahua volcano in the ecuadorian andes is a large andesitic stratovolcano 5023 m that has been erupting mildly since 1999 we studied the three dimensional 3 d p wave velocity vp structure beneath the volcano down to 5 km below the summit we inverted 1708 p wave first arrival times from 263 volcano tectonic vt earthquakes recorded by 5 to 10 short period vertical seismic stations on the volcano from august 1999 to may 2003 a tomographic inversion method was used to image the velocity structure in which first arrival times were calculated with a finite difference method the root mean square of the arrival time residuals rms was reduced by 43 after running 10 iterations from the initial rms of 0 15 s the relocated hypocenters in our model are tightly clustered along a vertical structure at depths between sea level and the summit crater a high velocity zone exists above the central base of the volcano under the vertically aligned hypocenters and may be interpreted as the source zone for recharge of the shallow magmatic system high velocity zones are also identified under the lower northeastern and southern flanks of the edifice the southern high velocity anomaly lies close to the surface and is connected to the high velocity zone in the central base of the volcano a feature suggesting an old lateral dike system except for these high velocity zones in the central northern and southern flanks the volcanic edifice is composed of low velocity materials down to a depth of 2 km above sea level these low velocity zones correlate with young unconsolidated deposits and older highly fractured and or altered volcanic materials

source mechanisms of volcanic explosion earthquakes single force and implosive sources abstract volcanic explosion earthquakes accompanying explosive eruptions are viewed as representing an abrupt release of pressurized magma beneath a volcano through a vent i examine the source mechanisms of explosion earthquakes assuming two extreme cases of magma property when magma is assumed to be a perfect gas which migrates upward isentropically through a vent acting as a nozzle the seismic source is expressed as a single force on the other hand when magma flow is assumed to be incompressible an implosive source is dominant both source models predict that the seismic magnitude is proportional to the cross sectional area of the vent i investigate observed seismic magnitudes for different volcanoes based on data in published papers and reports the results show that the seismic magnitude of the largest event for each volcano is essentially proportional to the cross sectional area of the vent for vent radii ranging from 10 to 600 m the consistency found between the theoretical prediction and the observed relation suggests that the vent area plays a substantial role in the magnitude of explosion earthquakes i further estimate that initial pressures in the reservoir are of the order of a few mpa with a one order of magnitude uncertainty based on the single force model i also apply the implosive source model to the observed seismic magnitudes and estimate the product of bulk modulus of magma and flow velocity to be 10 10 10 11 j m 2 s

non double couple earthquakes 1 theory historically most quantitative seismological analyses have been based on the assumption that earth quakes are caused by shear faulting for which the equiv alent force system in an isotropic medium is a pair of force couples with no net torque a double couple or dc observations of increasing quality and coverage however now resolve departures from the dc model for many earthquakes and find some earthquakes especially in volcanic and geothermal areas that have strongly non dc mechanisms understanding non dc earth quakes is important both for studying the process of faulting in detail and for identifying nonshear faulting processes that apparently occur in some earthquakes this paper summarizes the theory of moment tensor expansions of equivalent force systems and analyzes many possible physical non dc earthquake processes contrary to long standing assumption sources within the earth can sometimes have net force and torque components described by first rank and asymmetric sec ond rank moment tensors which must be included in analyses of landslides and some volcanic phenomena non dc processes that lead to conventional symmetric second rank moment tensors include geometrically complex shear faulting tensile faulting shear faulting in an anisotropic medium shear faulting in a heteroge neous region e g near an interface and polymorphic phase transformations undoubtedly many non dc earthquake processes remain to be discovered progress will be facilitated by experimental studies that use wave amplitudes amplitude ratios and complete waveforms in addition to wave polarities and thus avoid arbitrary assumptions such as the absence of volume changes or the temporal similarity of different moment tensor com ponents

long period and very long period events at mt etna volcano characteristics variability and causality and implications for their sources abstract almost 50 000 long period lp events were recorded at mt etna from november 2003 to may 2006 we analysed these events as well as very long period vlp events which were associated with some of them during some intervals the spectral and wavefield features of lp events remained steady with significant changes occurring between the intervals based on the times of the changes we distinguish five different sub periods in particular during sub period iii june november 2005 the wavefield at the stations nearest to the summit area was composed of p waves locations for 150 lp events occurring in sub period iii determined using radial semblance changed at the same time as the events spectral features changed it was during this sub period that many of the lp events were associated with vlp events based on similarity of the waveforms we distinguished two families of vlp events with gradually evolving waveforms the two families are located in slightly different places but near the sources of the lp events the change between the families occurred at the same time as the spectra of the lp events changed finally the source of the vlp events was investigated by performing complete waveform moment tensor inversion of stacks of the two families synthetic green s functions for the full moment tensor were calculated for a homogeneous half space for both families the source region with the highest variance reduction lies approximately beneath the active craters at 500 m below the altitudes of the stations the solutions for both families are very similar with sources that are between 60 and 70 isotropic attempts to determine deviatoric moment tensors produced consistently poorer fits the remaining energy is poorly constrained and is likely to be noise in conclusion these results highlight changes in the lp and vlp events at mt etna over time and the causal relationship between them

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

effects of volcano topography on seismic broad band waveforms volcano seismology often deals with rather shallow seismic sources and seismic stations deployed in their near field the complex stratigraphy on volcanoes and near field source effects have a strong impact on the seismic wavefield complicating the interpretation techniques that are usually employed in earthquake seismology in addition as most volcanoes have a pronounced topography the interference of the seismic wavefield with the stress free surface results in severe waveform perturbations that affect seismic interpretation methods in this study we deal predominantly with the surface effects but take into account the impact of a typical volcano stratigraphy as well as near field source effects we derive a correction term for plane seismic waves and a plane free surface such that for smooth topographies the effect of the free surface can be totally removed seismo volcanic sources radiate energy in a broad frequency range with a correspondingly wide range of different fresnel zones a 2 d boundary element method is employed to study how the size of the fresnel zone is dependent on source depth dominant wavelength and topography in order to estimate the limits of the plane wave approximation this approximation remains valid if the dominant wavelength does not exceed twice the source depth further aspects of this study concern particle motion analysis to locate point sources and the influence of the stratigraphy on particle motions furthermore the deployment strategy of seismic instruments on volcanoes as well as the direct interpretation of the broad band waveforms in terms of pressure fluctuations in the volcanic plumbing system are discussed

effect of inundation on shear strength characteristics of mudstone backfill a group of lithologies which includes claystone siltstone mudstone and shale also known as mudrocks are indurated sediments widely encountered throughout the world shear strength and deformation characteristics of mudstone were investigated using a fully automated hydraulic stress path testing system under three rock states dry short term inundated and long term it is observed that the maximum deviator stress q appeared to decrease meaning the strength deteriorated as the rock states changed from dry to wetted and to degraded conditions furthermore critical state interpretations of the mudstone under all three rock states have shown unique high curved mohr coulomb failure envelopes which are normally exhibited only by crushable soil nevertheless m which is the slope of stress path and angle shearing resistance values obtained from dry specimens were always higher than the partially saturated specimens however as dry mudstone sheared under higher mean effective stress 700 kpa the m value exhibited is similar to m value of wetted mudstone which is 1 20 and remained the same as mudstone degraded it is believed that the strength of mudstone decreasing as it begins to crush and gradually became constant