mechanical interactions between rigid particles in a deforming ductile matrix analogue experiments in simple shear flow abstract the mechanical interaction between two or more particles is investigated in newtonian simple shear flow the experimental models allow observation of both the particle rotation and the deformation pattern around the particles the finite and instantaneous strain patterns around rigid particles are strongly heterogeneous and asymmetric with high finite strain zones aligned to the direction of maximum finite stretch these correspond to local flow with low vorticity number heterogeneous strain patterns around rigid particles spread over a distance of 1 2 times the particle length and this distance increases with increasing bulk strain where rigid particles are more concentrated these patterns coalesce and the overall pattern is then strongly controlled by the particles and cannot be simply related to the external boundary conditions in rocks the characteristic asymmetric strain pattern around rigid isolated particles is a reliable shear criterion which becomes unreliable with high concentrations of rigid particles particle rotation is significantly disturbed when the distance between adjacent particles of equal size is shorter than their length that is only in very concentrated suspensions of rigid particles in a composite shape fabric the development of the sub fabric corresponding to the smaller minerals will be more disturbed

geomorphometric analysis of the 2014 2015 barðarbunga volcanic eruption iceland abstract topographical information is of fundamental interest for a wide range of disciplines including glaciology agriculture communication network planning or hazard management in volcanology elevation data are of particular importance when assessing material flows throughout a volcanic system to obtain accurate estimates of time varying topography in volcanic active regions high resolution digital elevation models dems are required to monitor and evaluate topographical changes and especially volumetric gains and losses during the 2014 2015 bar arbunga eruption iceland multi temporal tandem x dem sequences were evaluated the 2014 2015 volcanic eruption was associated with the rare event of a caldera collapse visible on the surface of the vatnajokull glacier as well as major lava effusion in the holuhraun plain before investigating topographical change at the two study areas the tandem x dems were analysed for absolute and relative height errors resulting from the radar system parameters the sar processing or the local environment the uncertainty investigation determined that acquisitions over the snow covered bar arbunga caldera were primarily affected by microwave penetration into snow and dems over the holuhraun lava field exhibited increased height errors due to active lava flows and dynamic outwash plain the topographical analysis of the 2014 2015 bar arbunga eruption revealed a maximum vertical displacement of approximately 65 m and 43 m at the study area of the bar arbunga caldera and holuhraun lava field respectively with a total subsidence volume of 1 40 0 13 km3 and a dense rock equivalent dre lava volume of 1 36 0 07 km3 known uncertainties in volume were decreased by approximately 35 and 77 accordingly taking into account the calculation of rates the temporal development of caldera collapse and lava effusion was found to exhibit a near exponential decrease the ratio between subsidence and dre lava volume moreover indicated the coupling between piston collapse and magma drainage

basaltic calderas collapse dynamics edifice deformation and variations of magma withdrawal 1 the incremental caldera collapses of fernandina 1968 miyakejima 2000 and piton de la fournaise 2007 are analyzed in order to understand the collapse dynamics in basaltic setting and the associated edifice deformation for each caldera the collapse dynamics is assessed through the evolution of the 1 time interval t between two successive collapse increments 2 amount of vertical displacement during each collapse increment and 3 magma outflow rate during the whole collapse caldera process we show from the evolution of t that piton de la fournaise and fernandina were characterized by a similar collapse dynamics despite large differences in the caldera geometry and the duration of the whole collapse caldera process this evolution significantly differs from that of miyakejima where t strongly fluctuated throughout the whole collapse process quantification of the piston vertical displacements enables us to determine the magma outflow rates between each collapse increment displacement data tiltmeter and or gps for piton de la fournaise and miyakejima are used to constrain the edifice overall deformation and the edifice deformation rates these data reveal that both volcanoes experienced edifice inflation once the piston collapsed into the magma chamber such a deformation which lasts during the first collapse increments only is interpreted as the result of larger volume of piston intruded in the magma chamber than magma withdrawn before each collapse increment once the effect of the collapsing rock column vanishes edifice deflates we also determine for each caldera the critical amount of magma evacuated before collapse initiation and compare it to analog models the significant differences between models and nature are explained by the occurrence of preexisting weak zones in nature i e the ring faults that are not taken into account in analog models finally we show that t at piton de la fournaise and fernandina was equally controlled by the frictional resistance along the ring faults and the magma outflow rate in addition to these two parameters the collapse dynamics of miyakejima was also influenced by variations of the magma bulk modulus which changed after the influx of deep gas rich magma into the collapse related magma chamber altogether our results show that the dynamics of caldera collapse in basaltic volcanoes proceeds in two phases phase 1 starting with the first collapse is characterized by the largest collapse amplitude an incremental edifice inflation and a step by step increase of the rate of magma outflow phase 2 shows a rapid decrease of the magma discharge rate to a low level concomitant with the continuous edifice deflation if deep magma is injected into the magma chamber as at miyakejima an additional phase occurs phase 3

creep dike intrusion and magma chamber deflation model for the 2000 miyake eruption and the izu islands earthquakes 1 analysis of global positioning system data shows shrinkage of miyake island and the widening between nijima and kozu islands during the period of the miyake island volcanic activity and the ensuing izu islands earthquakes in 2000 the estimated time evolution of a model consisting of a dike creeping faults and a mogi source suggests that a crack opening on miyake island occurred immediately after the start of the seismic activities on 26 june and ended within several days at the west coast of miyake island after the seabed eruption on 27 june magma migrated from miyake island to kozu and nijima islands within several days the estimated volume of intruded magma totals around 1 2 109 m3 associated with the magma intrusion between miyake and kozu islands left lateral and right lateral creep motions occurred in regions off the west coast of miyake island and near kozu island the accumulated moment energy is equivalent to an earthquake of mw 6 6 and 6 6 for right lateral and left lateral creeping faults respectively the estimated magma chamber continued deflation beneath the southwestern part of miyake island from 26 june totaling around 0 12 109 m3 in volume change in addition to the collapse volume of 0 6 109 m3 at the summit of mount oyama on miyake island the volume change on miyake island can be compensated by the migrated magma toward kozu island from the deflation source beneath miyake island the deflation speed of the magma chamber beneath miyake island decreased and increased before and after the eruption of 14 15 july and 18 august suggesting a change in balance of mass influx and draining out rate of the magma chamber

seismomagnetic observation during the 8 july 1986 magnitude 5 9 north palm springs earthquake a differentially connected array of 24 proton magnetometers has operated along the san andreas fault since 1976 seismomagnetic offsets of 1 2 and 0 3 nanotesla were observed at epicentral distances of 3 and 9 kilometers respectively after the 8 july 1986 magnitude 5 9 north palm springs earthquake these seismomagnetic observation are the first obtained of this elusive but long anticipated effect the data are consistent with a seismomagnetic model of the earthquake for which right lateral rupture of 20 centimeters is assumed on a 16 kilometer segment of the banning fault between the depths of 3 and 10 kilometers in a region with average magnetization of 1 ampere per meter alternative explanations in terms of electrokinetic effects and earthquake generated electrostatic charge redistribution seem unlikely because the changes are permanent and complete within a 20 minute period

geomagnetic changes associated with the dike intrusion during the 2000 miyakejima eruptive activity japan abstract a marked magnetic field change exceeding 200 nt was detected by a three component magnetometer at the beginning of the 2000 miyakejima eruptive activity the change in the magnetic field is correlated with an earthquake activity and crustal deformation which indicate a dike intrusion very close to the observation site a dike model based on the crustal deformation data shows that the primary cause of the magnetic change was the piezomagnetic effect associated with the dike emplacement and that the other potential factors including thermal and electrokinetic effects were unlikely to be its principal cause we obtained a new dike model by combining both the crustal deformation and the magnetic field change which is sensitive to the strong stress changes near the edges of dike the new dike model shows lateral and upward propagation of the dike during its intrusion and suggests that shallow cracks induced by the dike intrusion near the ground surface contributed to the changes seen in the magnetic field

rising springs along the silk road despite its extreme aridity the hexi corridor in northwestern china part of the ancient silk road has recently been repeatedly flooded by rising springs forcing 1000 families to abandon homes here we use new isotopic and chemical data for waters collected from the corridor and the qilian mountains to investigate the cause of the rising springs the data show that the springs may have originated from the mountain slopes where glacier melt mixes with the precipitation from a local convective system between the extensively irrigated hexi corridor and the qilian mountains accelerated glacier melting may have increased recharge of groundwater in the qilian mountains that was subsequently released by recent earthquakes from the mountains to the valley to raise the local water table the result has potential implications for the impact of climate change on water resources and management in arid regions

spectrum response of lj well to various stresses during non seismic and seismic periods the well water level in a deep well has significant frequency dependence on various crustal stresses which can provide an effective pathway for determining the well aquifer properties and investigating the response mechanism of groundwater however due to the limitations and complexity of the field conditions there is a lack of on site stress strain data for rocks therefore it is difficult to directly and quantitatively interpret the transfer response between the strain stress and the well water level the observation item data for the lj well in china are relatively complete including rainfall barometric pressure volumetric strain and deep water level data by calculating the spectral period spectral density coherence function and transfer function of various physical variables the spectrum response characteristics of the well aquifer system to various stresses can be effectively obtained when the crust is in a relatively stable state the semidiurnal and diurnal waves are dominant moreover the transfer functions of the well water level s response to the theoretical semidiurnal and diurnal earth tides and the barometric pressure are basically consistent with the correlation analysis results in addition when earthquakes occur the signals of the volumetric strain and the well water level can more effectively highlight the relatively intermediate and high frequency information the transfer function between the well water level and the volumetric strain is nearly an order of magnitude smaller than that in the stable state indicating that the hydrogeological conditions of the lj well aquifer change instantaneously when subjected to seismic waves all the above conclusions show that the correlation and transfer function based on spectral analysis is a feasible and advantageous method of determining the correlation of various physical variables these results provide a foundation for further research on the hydrogeological characteristics of aquifers

back arc spreading of the northern izu ogasawara bonin islands arc clarified by gps data abstract we examined gps data in the northwestern pacific region which includes the izu ogasawara bonin mariana ibm arc and the japan arc gps velocity vectors on the izu islands including hachijo jima and aoga shima show systematic eastward movement deviating from that predicted by the rigid rotation of the philippine sea plate this deviation supports the active back arc spreading model suggested by previous geological studies the results of a statistical f test analysis with 99 confidence level showed that the forearc of the izu islands arc has an independent motion with respect to the rigid part of the philippine sea plate we developed a kinematic block fault model to estimate both rigid rotations of crustal blocks and elastic deformation due to locked faults on the block boundaries the model suggests that the back arc opening rate along the izu back arc rift zone ranges from 2 mm yr at its southern end to 9 mm yr near miyake jima its northern end it also predicts 23 28 mm yr of relative motion along the sagami trough in the direction of n25 w where the izu forearc subducts beneath central japan the orientation of this motion is supported by slip vectors of recent medium size earthquakes repeated slow slip events and the 1923 m 7 9 kanto earthquake

spatio temporal changes in seismic velocity associated with the 2000 activity of miyakejima volcano as inferred from cross correlation analyses of ambient noise abstract miyakejima volcano japan showed strong and interesting volcanic activities in 2000 with the occurrence of dike intrusions caldera formation and a large amount of gas emission to understand temporal changes of the volcanic structure associated with this activity we apply ambient noise correlation analyses to the seismic records of five seismic stations at miyakejima volcano from july 1999 to december 2002 we calculate cross correlation functions ccfs for eight available station pairs at frequency bands of 0 4 0 8 hz and 0 8 1 6 hz and retrieve the rayleigh waves propagating with a group velocity of about 1 0 km s comparing ccfs obtained for each day with the reference ccfs that are calculated from a few months of data we estimate seismic velocity changes before and after the 2000 activity results at the two frequency bands show seismic velocity increase and decrease shallow structure at the volcanic edifice on the flanks experienced a seismic velocity increase up to 3 3 on the other hand the regions located close to the collapsed caldera show a seismic velocity decrease down to 2 3 to understand the mechanisms that may introduce these seismic velocity increase and decrease we examine several possible mechanisms of the velocity changes stress changes due to volcanic pressure sources and caldera formation and topographic changes by using the deflation sources previously determined from gps data we calculate the stresses at depths of 0 km and 1 km at the volcano the results suggest that the seismic velocity increases observed at seismic paths on the volcanic flank are explained by the compression caused by the deflation sources associated with magma activity in 2000 stress sensitivities of the seismic velocity changes are estimated to be 1 5 10 2 to 2 2 10 2 mpa 1 and 4 6 10 3 to 2 4 10 2 mpa 1 at frequency bands of 0 4 0 8 hz and 0 8 1 6 hz respectively which are in the range of the previously reported results our three dimensional numerical calculations on seismic wave propagation show that the seismic velocity decreases observed at seismic paths crossing the collapsed caldera can be explained by topographic changes introduced by a caldera we further suggest that the seismic velocity decreases detected around the regions close to the caldera may originate from the dilated regions cause by formation of the caldera

crustal block kinematics and seismic potential of the northernmost philippine sea plate and izu microplate central japan inferred from gps and leveling data 1 we clarify the contemporary deformation observed by gps and leveling for the greater tokyo kanto eastern tokai and the izu islands region where the izu ogasawara bonin arc is subducting and colliding with the central part of the japan arc from these data we develop a kinematic model of fault sources with variable components of seismic and aseismic slip under the assumption that the contemporary deformation during 1995 2000 is representative of the long term interseismic strain field the geodetic data are inverted to estimate the rotation poles of the crustal blocks the degree of elastic strain accumulation on faults and the volumetric inflation sources beneath volcanoes the present crustal movements are explained by four crustal blocks the izu microplate the central japan block the pacific plate and the philippine sea plate along the suruga and sagami margins of the philippine sea plate lie strongly coupled faults which include sites of the 1854 m 8 4 tokai 1923 m 7 9 kanto and 1703 m 8 2 genroku kanto earthquakes in contrast the philippine sea plate boundary immediately north of the izu peninsula site of m 7 5 collisional earthquakes is only weakly coupled the boundary between the izu microplate and the philippine sea plate experiences left lateral motion with the rate of 30 mm yr most of this boundary is locked and thus has a large potential of future earthquakes the izu microplate is found to rotate rapidly clockwise at 10 myr with a rotation pole relative to the central japan block located just north of its northern boundary the pole and angular velocity of the izu microplate depends however on the assumed location of the boundary with the exception of the site of the 1938 m 7 earthquake swarm which we infer has the current potential to produce a m 8 1 earthquake the pacific megathrust has a very low seismic potential although the geodetic data have little resolving power for much of the pacific plate interface east of tokyo

relationship between volcanic activity and shallow hydrothermal system at meakandake volcano japan inferred from geomagnetic and audio frequency magnetotelluric measurements abstract hydrothermal activity at meakandake volcano japan from 2004 to 2014 was investigated by using long term geomagnetic field observations and audio frequency magnetotelluric amt surveys the total intensity of the geomagnetic field has been measured around the summit crater ponmachineshiri since 1992 by kakioka magnetic observatory we reanalyzed an 11 year dataset of the geomagnetic total intensity distribution and used it to estimate the thermomagnetic source models responsible for the surface geomagnetic changes during four time periods 2004 2006 2006 2008 2008 2009 and 2013 2014 the modeled sources suggest that the first two periods correspond to a cooling phase after a phreatic eruption in 1998 the third one to a heating phase associated with a phreatic eruption in 2008 and the last one to a heating phase accompanying minor internal activity in 2013 all of the thermomagnetic sources were beneath a location on the south side of ponmachineshiri crater in addition we conducted amt surveys in 2013 and 2014 at meakandake and constructed a two dimensional model of the electrical resistivity structure across the volcano combined the resistivity information and thermomagnetic models revealed that the demagnetization source associated with the 2008 eruptive activity causing a change in magnetic moment about 30 to 50 times greater than the other sources was located about 1000 m beneath ponmachineshiri crater within or below a zone of high conductivity a few ohm meters whereas the other three sources were near each other and above this zone we interpret the conductive zone as either a hydrothermal reservoir or an impermeable clay rich layer acting as a seal above the hydrothermal reservoir along with other geophysical observations our models suggest that the 2008 phreatic eruption was triggered by a rapid influx of heat into the hydrothermal reservoir through fluid rich fractures developed during recent seismic swarms the hydrothermal reservoir remained hot after the 2008 eruption and heat was sporadically transported upward through its low permeability ceiling

comment on numerical models of flow patterns around a rigid inclusion in a viscous matrix undergoing simple shear implications of model parameters and boundary conditions by n mandal s k samanta and c chakraborty journal of structural geology 27 2005 1599 1609

hydrological responses induced by the tokachi oki earthquake in 2003 at hot spring wells in hokkaido japan 1 thirty hydrological responses induced by the m8 0 tokachi oki earthquake in 2003 were observed at hot spring wells and an undersea coal mine in hokkaido japan most of the decreases and increases in groundwater levels or discharge rates can be explained as a poroelastic response to earthquake induced volumetric strain inferred from a fault model determined by dense static gps observation in five wells observed groundwater level changes and inferred volumetric strain steps induced by the tokachi oki earthquake are consistent with groundwater level changes that are proportional to the inferred volumetric strain steps induced by four large earthquakes in 1993 1994

sounding the plume of the 18 august 2000 eruption of miyakejima volcano japan using gps 1 we processed 79 days of gps data collected at four stations on miyakejima volcano japan before and during its eruption in 2000 this period includes a strong seismic swarm 27 june to 8 july followed by five eruptions 8 and 14 15 july 10 18 and 29 august surface motion is strong during the seismic swarm then remains almost steady during eruptions however during each eruption we found anomalous values of the lc ionosphere free double differences especially on 18 august with a peak of 0 6 cycles i e an apparent 290 mm increase of the satellite station range we cannot explain these anomalies by temporary ground displacements during the events instead we propose that they are due to path delay effects in the hot volcanic plume by adapting a seismic tomography algorithm the refractivity anomaly and the inferred temperature in the plume is mapped in time and space

detection and monitoring of ongoing aseismic slip in the tokai region central japan analysis of global positioning system data shows that the rate of crustal deformations in the tokai region of japan a seismic gap area changed over the past 18 months kalman filtering analysis shows aseismic slip on the plate boundary in the western tokai region centered on lake hamana adjacent to the anticipated tokai earthquake source area the cumulative moment magnitude reaches 6 7 in june 2002 with a relative slip increase northeast of lake haman from january 2002 an existence of aseismic slip in the western tokai supports the hypothesis of a silent event as the cause of uplifting several days before the 1944 tonankai earthquake

crustal deformation caused by magma migration in the northern izu islands japan intense crustal activity including earthquake swarms eruptions and a caldera formation in the northern izu islands started on june 26 2000 accompanied with large crustal deformation permanent gps data reveals the spatial pattern and time evolution of ground deformation the observations reveal shrinking and subsidence of miyakejima and extension between kouzushima and niijima we constructed a source model to explain the observed displacements during the period between june 26 and the end of august the model consists of a deflation source 0 12km beneath miyakejima tensile faults 1 04km located between miyakejima and kouzushima and several shear faults mass balance considerations suggest that a large amount of magma migrated 30km from miyakejima toward kouzushima

volcanic inflation of mount hokkaido komagatake japan determined from a dense gps array we installed and have been operating a dense gps array with low power consumption single frequency gps receivers around mount hokkaido komagatake volcano southwestern hokkaido japan since 2000 data were collected continuously and analyzed together with the geographical survey institute of japan s nationwide continuous gps network data the analysis of daily baseline length changes for two years indicate a steady inflation of the volcanic body with 10 7 yr extensional strain a pressure source was estimated at 2 4 km depth beneath the summit area with a volumetric increase rate of 4 86 10 5 m 3 yr the depth of the pressure source is in good agreement with the one expected from petrological study integrated magma volume has reached up to 2 6 x 10 7 m 3 if the inflation rate is possibly extrapolated back to the last magmatic eruption our results strongly suggest a steady magma accumulation at the reservoir beneath this volcano and an increasing potential to the next eruption near future

subsurface cyclic magma sill expansions in the 2000 miyakejima volcano eruption possibility of two phase flow oscillation 1 step like tilt changes were observed at intervals of dozens of hours during the caldera formation stage occurred during the 2000 miyakejima volcano eruption our analysis suggests that these tilt steps were caused by the cyclic expansion of a subsurface sill like magma plumbing system trending from se to nw of the volcano in the same period a caldera gradually grew at the summit area to a very large 1 6 km in diameter and 450 m in depth the source mechanism of these tilt steps is fairly well explained by a two phase flow instability called a pressure drop oscillation this model indicates that the gas phase capacity in the upper part of the conduit acts as a pump that controls the flux of two phase magma in the sill like reservoir caldera formation as well as magma uplift and descent in the conduit may reflect temporal changes in the intervals between tilt steps which are themselves proportional to the volume of this gas capacity

the plate coupling in the tokai district the central japan inferred from the different data using triangular dislocation elements abstract we estimate interseismic coupling on the subducting plate interface in the tokai area central japan by inverting two geodetic data sets the data record surface motion between march 1996 to may 2000 one represents vertical motion deduced from the leveling observations and the other is the horizontal velocity field deduced from gps observations in the inversion we employed the analytical solutions of surface displacement due to a triangular dislocation element embedded in a homogeneous elastic half space in order to represent the curved plate interface the vertical data show that the most strongly coupled portion of the subduction interface is concentrated beneath omaezaki cape while the horizontal data show strongest coupling in the shallower region of the subducting plate interface the estimated maximum value of coupling from the horizontal data is 40 mm year while that from vertical data is 25 mm year

reply to the comment by marques et al on numerical models of flow patterns around a rigid inclusion in a viscous matrix undergoing simple shear implications of model parameters and boundary conditions by n mandal s k samanta and c chakraborty

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

magnetic and electric field observations during the 2000 activity of miyake jima volcano central japan magnetic and electric field variations associated with the 2000 eruption of miyake jima volcano are summarized for about 1 week prior to the july 8 phreatic explosion significant changes in the total intensity were observed at a few stations which indicated uprising of a demagnetized area from a depth of 2 km towards the summit this nonmagnetic source can be regarded as a vacant space itself electric and magnetic field variations were observed simultaneously associated with the tilt step event which was the abrupt v50 s inflation at a few km depth within the volcano followed by gradual recovery vseveral hours the electric field is ascribed to the electrokinetic effect most probably due to forced injection of fluids from the source while the magnetic field to the piezomagnetic effect due to increased pressure large magnetic variations amounting to a few tens of nt were observed at several stations since july 8 and they turned almost flat after the august 18 largest eruption magnetic changes are explained mostly by the vanishing of magnetic mass in the summit and additionally by the thermal demagnetization at a rather shallow depth a large increase in the self potential by 130 mv was also observed near the summit caldera associated with the august 18 eruption which suggests that the hydrothermal circulation system sustained within the volcano for the past more than 10 years was destroyed by this eruption 9 2002 published by elsevier science b v

volcano geodesy recent developments and future challenges abstract ascent of magma through earth s crust is normally associated with among other effects ground deformation and gravity changes geodesy is thus a valuable tool for monitoring and hazards assessment during volcanic unrest and it provides valuable data for exploring the geometry and volume of magma plumbing systems recent decades have seen an explosion in the quality and quantity of volcano geodetic data new datasets some made possible by regional and global scientific initiatives as well as new analysis methods and modeling practices have resulted in important changes to our understanding of the geodetic characteristics of active volcanism and magmatic processes from the scale of individual eruptive vents to global compilations of volcano deformation here we describe some of the recent developments in volcano geodesy both in terms of data and interpretive tools and discuss the role of international initiatives in meeting future challenges for the field

detection of short term slow slip events along the nankai trough southwest japan using gnss data 1 we detected short term slow slip events sses previously observable only with tilt and strain data along the nankai trough southwest japan using gnss global navigation satellite system data offsets detected in gnss time series using akaike s information criterion helped automatically identify 207 episodes with a motion direction opposite to that of the relative plate motion from june 1996 to january 2012 by nonlinear inversion of the detected displacement we estimated rectangular fault models for 133 probable and 25 possible short term sses over 15 years the sse moment magnitudes range from 5 5 to 6 3 most sse fault models are located in a narrow band of non volcanic tremors on the interfaces of the subducting philippine sea plate large sses moment magnitude mw 6 often occur in western and central shikoku the cumulative slip is distributed heterogeneously along the strike generally decreasing eastward with the maximum slip 50 cm in western shikoku no definite short term sses were found in the kii channel but several short term sses occurred in ise bay both regions are known as tremor gaps the local maximum of the cumulative slip fills in the tremor gap located in ise bay the long term rate of short term sse cumulative moment increased by threefold around 2003 in eastern shikoku whereas it was almost constant in other regions comparison with short term sse catalogues using tilt data suggests that both this study and previous studies missed some sses along the nankai trough a combination of geodetic data is important in the monitoring of the spatiotemporal distribution of short term sses

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

vertical tectonics at an active continental margin direct observations of vertical movements of the earth s surface are now possible with space based gps networks and have applications to resources hazards and tectonics here we present data on vertical movements of the earth s surface in new zealand computed from the processing of gps data collected between 2000 and 2015 by 189 permanent gps stations we map the geographical variation in vertical rates and show how these variations are explicable within a tectonic framework of subduction volcanic activity and slow slip earthquakes subsidence of 3 mm yr is observed along southeastern north island and is interpreted to be due to the locked segment of the hikurangi subduction zone uplift of 1 3 mm yr further north along the margin of the eastern north island is interpreted as being due to the plate interface being unlocked and underplating of sediment on the subduction thrust the volcanic plateau of the central north island is being uplifted at about 1 mm yr which can be explained by basaltic melts being injected in the active mantle wedge at a rate of 6 mm yr within the central volcanic region there is a 250 km2 area that subsided between 2005 and 2012 at a rate of up to 14 mm yr time series from the stations located within and near the zone of subsidence show a strong link between subsidence adjacent uplift and local earthquake swarms

volcanomagnetic signals associated with the 2001 flank eruption of mt etna italy 1 geomagnetic changes were observed during the 2001 flank eruption at mt etna after differential magnetic fields were filtered from the seasonal thermic noise by using temperature data we recognized three stages in the total intensity changes related to different volcanic events a rapid variation of 4 nt associated with july 12 seismic swarm recorded beneath the summit craters b step like variation of 7 nt occurring during the quick propagation of fractures in the south flank which was followed by the off set of 2 nt before july 17 when the lava outpoured from fissures and c quick variation of 3 nt coincident with july 19 eruptive fissures opening up in the valle del leone these observations are consistent with those calculated from volcanomagnetic models in which the magnetic changes are generated by stress redistribution due to magmatic intrusions at different depth and by the thermal demagnetization at a rather shallow depth

accurate measurements of tropospheric effects in volcanic areas from sar interferometry data application to sakurajima volcano japan abstract the accuracy of surface deformation maps derived from dinsar differential interferomery synthetic aperture radar in volcanic areas is limited by temporal variations of the vertical refractivity profile in the troposphere between the radar data acquisitions due to their dependence on altitude such variations may produce topography related fringes in the computed interferograms the variations should be carefully estimated in a given area so that they can be discriminated with real ground deformation signals in this paper we present a clear example of tropospheric induced fringes reaching up to 2 9 fringes over 1200 m evidenced on sakurajima volcano japan from ers 1 and ers 2 data the analysis of phase altitude correlations based on network adjustments of the interferometric dataset leads to a simple linear model of the tropospheric excess path delay with an rms accuracy of 0 4 cm that might be used for further corrections a more detailed investigation of these phase variations providing accurate measurements of linear and non linear contributions of tropospheric effects is also presented and shows that tropospheric phase delays can be better modeled on sakurajima with a non linear model

seismicity and crustal structure related to the miyake jima volcanic activity in 2000 1 the largest earthquake swarm ever recorded in japan began off the islands of miyake jima kozu shima and nii jima and was linked to volcanic activity on miyake jima at the northern end of the volcanic front of the izu ogasawara bonin arc ocean bottom seismographic observations made directly above the swarm region gave clear indication of a magmatic intrusion the hypocenter distribution shows a vertical sheet 2 km wide and at a depth of 12 20 km that broadens markedly at depths up to 12 km the p wavespeed structure obtained from a seismic refraction survey shows no significant difference in the characteristics of the shallow crust between the strong swarm region and inactive region however a low wavespeed region was detected 10 15 km northwest of miyake jima

a constant influx model for dike propagation implications for magma reservoir dynamics 1 most observations of seismicity rate during dike propagation on basaltic volcanoes show 1 rate stationarity despite possible variations of the dike tip velocity 2 frequent lack of clear and monotonic hypocenter migration following dike propagation and 3 event occurrences located backward with respect to the dike tip position on these bases the origin of the seismicity contemporary to dike intrusion within basaltic volcanoes cannot be solely related to the crack tip propagation seismicity rather appears to be the response of the edifice itself to the volumetric deformation induced by the magma intruding the solid matrix the volume change induced into the volcano edifice over time by the intruding magma is equal to the magma flux injected into the dike from the reservoir the consequence of this is that the stationary seismicity rate observed during the intrusion is a proxy for the magma flux withdrawn from the reservoir we consider a two phase dike propagation model including a first vertical propagation followed by a lateral migration along a lithological discontinuity we explore 1 under which geophysical conditions the vertical dike is fed at constant flow rate of magma and 2 dike propagation patterns implications entailed by constant volumetric flux on the piton de la fournaise volcano case study suggest a minimum size for the magma reservoir of about 1 km3 and a maximum value for the initial magma reservoir overpressure of about 2 2 mpa considering similar magma inflow rates during vertical and lateral dike propagation phases we reproduce independent estimates of propagation velocities rise times and injected volumes when applying the model to the august 2003 piton de la fournaise eruption

time dependent model of magma intrusion in and around miyake and kozu islands central japan in june august 2000 abstract a time dependent model of magma intrusion is presented for the miyake kozu island area in central japan based on global positioning system gps measurements at 28 sites recorded between june 27 and august 27 2000 a model derived from a precise hypocenter distribution map indicates the presence of three dikes between miyake and kozu islands other dike intrusion models including a dike with aseismic creep and a dike associated with a deep deflation source are also discussed the optimal parameters for each model are estimated using a genetic algorithm ga approach using akaike s information criteria aic the three dike model is shown to provide the best solution for the observed deformation volume changes in spherical inflation and deflation sources as well as three dikes are calculated for seven discretized periods after ga optimization of the dike geometry the optimization suggests a concentration of dike expansion near miyake island in the period from june 27 to july 1 associated with large deflation at a depth of about 7 km below miyake volcano indicating magma supply from depth below miyake island in the period from july 9 to august 10 a huge dike intrusion near kozu island is inferred accompanied by expansion of the lower parts of a central dike suggesting magma supply from depth in the region between miyake and kozu islands

tsunami scenarios based on interseismic models along the nankai trough japan from seafloor and onshore geodesy the recent availability of global positioning system acoustic seafloor geodetic observations enables us to resolve the spatial distribution of the slip deficit rate near the nankai trough southwestern japan considering a tectonic block model and the transient deformation due to the major earthquakes in this area the slip deficit rate between the two relevant blocks can be estimated in this study we remove the time dependent postseismic deformation of the 2004 southeastern off the kii peninsula earthquakes mjma 7 1 7 4 which had led to the underestimation of the slip deficit rate in earlier studies we model the postearthquake viscoelastic relaxation using the 3d finite element model with bi viscous burgers rheology as well as the afterslip on the finite faults the corrected global positioning system acoustic and land based global navigation satellite systems data are aligned to the existing tectonic model and used to estimate the slip deficit rate on the plate boundary we then calculate the coseismic displacements and tsunami wave propagation with the simple assumption that a hundred years of constant slip deficit accumulation was released instantaneously to evaluate the influence of uncertainties in the plate interface geometry on a tsunami model for the nankai trough we investigated two different geometries and performed checkerboard inversion simulations although the two models indicate roughly similar results the peak height of the tsunami wave and its arrival time at several points are significantly different in terms of the expected hazard

direct magnetic signals from earthquake rupturing iwate miyagi earthquake of m 7 2 japan abstract the key point of this paper is that for the first time we successfully observed co rupturing earth s magnetic field changes due to the piezomagnetic effect caused by earthquake rupturing electromagnetic changes associated with earthquakes have been investigated previously most of them are coseismic step like offsets in the geomagnetic field which are regarded as the piezomagnetic effect caused by the total static stress changes resulting from an earthquake proton precession magnetometers have so far been mainly used to detect seismomagnetic effects for which the measurement interval was usually 1 or 10 min and the measurement accuracy was 0 1 nt for seismomagnetic observations we employed flux gate magnetometers whose specifications are the measurement with accuracy of 0 01 nt and with the sampling interval of 0 5 or 1 s by virtue of such highly sensitive magnetometers we show observations of magnetic signals accompanying fault movement our observation site happened to be situated at an epicentral distance of 26 km from the 2008 iwate miyagi nairiku earthquake of m 7 2 in ne japan magnetic field components began to change almost simultaneously with the onset of the earthquake rupture and grew non linearly until the first p wave arrival such magnetic signals are most probably generated by the changing stress field due to rupturing i e the piezomagnetic effect rather than the seismic dynamo effect or electromagnetic induction within the conducting crust because they lack oscillatory features like seismic waves we attempt to interpret the observations with the aid of quasi static piezomagnetic model calculation which strongly supported our observation results

depth extent of the long term slow slip event in the tokai district central japan a new insight 1 temporal changes to interplate coupling and long term aseismic slip in the tokai region of central japan from july 1996 to june 2009 are statically inverted using continuous global positioning system gps data and leveling observations and examined using a new interpretation of aseismic slip in this interpretation the interplate coupling and the aseismic slip should be inferred and compared with reference to a state of no coupling on the plate interface rather than assuming steady state interplate coupling before the occurrence of the aseismic event as previous works have done for this purpose we used original time series data without subtracting any linear trends the inferred distribution shows that the entire period can be divided into three subperiods based on the existence of the aseismic slip area from 2000 to 2005 the strength of the interplate coupling does not change throughout the observed period even though the distribution narrows along the dip direction after the aseismic slip terminates the aseismic slip area inferred in this study based on the no coupling reference was determined to be deeper than the area where the long term slow slip event sse defined as the slip corresponding to the residual displacement from the steady state was hypothesized to have occurred in numerous previous studies the total seismic moment released by the aseismic slip is equivalent to a mw 6 6 earthquake while the sse in previous works was considered to be equivalent to a mw 7 0 to 7 1 earthquake this difference can be attributed primarily to the effects on the interplate coupling which previous studies did not take into account when defining the sse the aseismic slip area coincides well with the distribution of other types of plate interactions such as short term slow slip events and low frequency earthquakes

the development of δ clasts in non linear viscous materials a numerical approach abstract winged porphyroclasts are often used as kinematic or strain indicators in shear zones in particular it has been suggested that the geometry of clasts in mylonites can give information about the rheological behaviour of the matrix around the clast passchier et al 1993 we tested this hypothesis with a numerical finite element simulation of the flow field of a viscous matrix around a relatively rigid clast power law viscous flow properties of the matrix with stress exponents of 1 linear viscous 3 and 5 were tested as well as three different sets of approximately simple shear boundary conditions which are relevant to experimental and or natural situations the simulations show that the flow field is primarily determined by the boundary conditions the stress exponent is of secondary importance in general the different boundary conditions produce two types of flow fields about the rigid clast an eye shaped flow field and a bow tie shaped flow field the former is produced by boundary conditions that approximate simple shear applied at an infinite distance from the rigid clast and the latter is produced by boundary conditions which are equivalent to a shear box or ring shear apparatus although both the shear box and ring shear boundary conditions produce bow tie flow patterns the wing geometries which result from the flow patterns for these two cases can be significantly different the geometry of the wings that develop on a clast is a direct function of the flow field around the clast for linear and non linear rheologies only the ring shear boundary conditions produce wings that show stair stepping i e wings that are parallel but not in the same plane in natural shear zones clasts both with and without stair stepping are observed in comparing geologic observations with experimental or numerical modelling it is essential to understand which boundary conditions are appropriate

simple shear of deformable square objects abstract finite element models of square objects in a contrasting matrix in simple shear show that the objects deform to a variety of shapes for a range of viscosity contrasts we catalogue the changing shapes and orientations of objects in progressive simple shear at moderate simple shear 1 5 the shapes are virtually indistinguishable from those in equivalent pure shear models with the same bulk strain r s 4 examined in a previous study in theory differences would be expected especially for very stiff objects or at very large strain in all our simple shear models relatively competent square objects become asymmetric barrel shapes with concave shortened edges similar to some types of boudin incompetent objects develop shapes surprisingly similar to mica fish described in mylonites

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

repeated magmatic intrusions at el hierro island following the 2011 2012 submarine eruption abstract after more than 200 years of quiescence in july 2011 an intense seismic swarm was detected beneath the center of el hierro island canary islands culminating on 10 october 2011 in a submarine eruption 2 km off the southern coast although the eruption officially ended on 5 march 2012 magmatic activity continued in the area from june 2012 to march 2014 six earthquake swarms indicative of magmatic intrusions were detected underneath the island we have studied these post eruption intrusive events using gps and insar techniques to characterize the ground surface deformation produced by each of these intrusions and to determine the optimal source parameters geometry location depth volume change source inversions provide insight into the depth of the intrusions 11 16 km and the volume change associated with each of them between 0 02 and 0 13 km 3 during this period 20 cm of uplift was detected in the central western part of the island corresponding to approximately 0 32 0 38 km 3 of magma intruded beneath the volcano we suggest that these intrusions result from deep magma migrating from the mantle trapped at the mantle lower crust discontinuity in the form of sill like bodies this study using joint inversion of gps and insar data in a post eruption period provides important insight into the characteristics of the magmatic plumbing system of el hierro an oceanic intraplate volcanic island

silicic magmas in the izu bonin oceanic arc and implications for crustal evolution abundant rhyolitehaseruptedfromthe izu bonin marianavolca nic arc ibm arc from its earliest stage eocene to the present geochemically three types of quaternary rhyolites exist in the izu bonin arcfront and theyare closely related tovolcanotypeand crus tal structure the dominantly basaltic islands of the volcanic frontproduce small volumes of rhyolites that we call r1 the submarinecalderas of the volcanic front erupt mostly rhyolite that we call r2 seamounts knolls and pillow ridges in thebackarcextensionalzoneare mostly basaltic but also contain rhyolites that we call r3 thethickest total crust and the thickest intermediate compositionmiddle crust occurs below the dominantly basaltic volcanoes whereas the intermediate composition middle crust tends to be thin nerbeneaththesubmarinecalderas r1rhyolitesmaybederivedfromquaternary andesitic sources whereas r2 and r3 rhyolites may bederivedfromoligoceneones thehighercao al

spatiotemporal characteristics of the displacement field revealed with principal component analysis and the mode rotation technique abstract principal component analysis pca was applied to the displacement field recorded at 147 gps stations in the kanto tokai district japan for the period from january 1999 to february 2003 some prominent geophysical events occurred during this period using pca we attempted to decompose the displacement field into some representative spatial modes and their corresponding temporal modes to quantitatively extract the primary geophysical events that have caused rapid crustal deformation in this region the displacement field was roughly decomposed into modes corresponding to the following three major events 1 the miyake kozu volcanic event which occurred in the region south of tokyo in 2000 it included large scale dyke intrusion and intensive earthquake swarm between the miyakejima and kozushima islands 2 the tokai slow slip event which is considered to have begun just after the miyake kozu volcanic event and is ongoing as of november 2005 it occurred on the boundary between the subducting philippine sea plate and the overriding eurasian amurian plate in the tokai district 3 the boso slow slip event which lasted for approximately 10 days in october 2002 it occurred on the boundary between the subducting pacific plate and the overriding north american plate near the boso peninsula in the decomposition process we combined the mode rotation technique with ordinary pca this is because pca causes contamination between modes i e a mode obtained with pca is contaminated by other modes for example the first principal mode corresponding to the miyake kozu volcanic event which is by far the largest in magnitude was clearly seen in many other modes in order to remove such contamination we applied the mode rotation technique in which the principal axes derived from pca are rotated so as to minimize the correlation coefficients between different temporal modes for a time period in which some prominent change occurs combining the mode rotation technique with pca exhibited a better performance in separating the displacement field

caldera collapse during the 2000 eruption of miyakejima volcano japan a collapsed caldera 1 6 km in diameter and 450 m in depth was formed at the summit of miyakejima volcano during the 2000 eruption the collapsed caldera appeared on 8 july with a minor phreatic eruption 12 days after seismic activity and magma intrusion occurred northwest of the volcano growth of the caldera took from 8 july to the middle of august with seismic swarms associated with the continuous intrusion of magma northwest of the volcano the growth rate of the caldera was about 1 4 107 m3 day and the final volume of the collapsed caldera was about 6 108 m3 major phreatomagmatic eruptions produced a total of about 1 6 1010 kg 1 1 107 m3 of volcanic ash after caldera growth the caldera structure and the nature of the eruptive materials of the first collapse on 8 july suggest that the surface subsidence was caused by the upward migration of a steam filled cavity with stoping of the roof rock above the magma reservoir the diameter of the stoping column was estimated to be 600 700 m from circumferential faults that developed in the caldera floor and the collapse of the caldera wall enlarged the diameter of the caldera to 1 6 km the total volume of the caldera and the horizontal diameter of the stoping column gave a subsidence of the caldera floor of 1 6 2 1 km

effect of regional tectonic setting on local fault response to episodes of volcanic activity 1 in this study we examine the interaction of tectonic and volcanically generated stress fields and their combined effect on patterns of volcanotectonic vt seismicity by calculating coulomb stress changes on local faults induced by a constant dike inflation event in a background stress field of systematically varying magnitude and orientation we find that patterns of vt seismicity earthquake locations and fault plane solutions resulting from dike inflation depend strongly on the relative strength and orientation of background tectonic stresses patterns of vt seismicity similar to those predicted by our coulomb stress models have been observed at several recently active volcanoes and appear to correspond to the relative strength of the regional stress field thus it is critical to consider the regional tectonic setting when interpreting patterns of vt seismicity in terms of magmatic processes

long term thermal activity revealed by magnetic measurements at kusatsu shirane volcano japan abstract repeated geomagnetic measurements commenced around the three summit crater lakes of kusatsu shirane volcano yugama mizugama and karegama lakes in 1976 and continuous measurements commenced in 1990 we reviewed and analyzed these geomagnetic data acquired over the 34 years starting in 1978 changes in the geomagnetic field related to eruptions during 1982 1983 were recorded in the repeated geomagnetic measurements from 1982 to 1985 a thermal demagnetization source was estimated to be 400 m below mizugama crater lake during this period although there were no eruptions from 1988 to 1991 there were numerous volcanic earthquakes thermomagnetic signals due to demagnetization of the material beneath the crater lakes were recorded by the repeated magnetic measurements during this period the demagnetized body was estimated to be 600 m below mizugama crater lake at this time previous seismological and geochemical studies attributed these demagnetization events to the ascent of hydrothermal water and volcanic gas the difference between the depths of demagnetized bodies during these two periods of demagnetization may provide important information about the mechanism of the 1982 1983 eruptions in contrast magnetization associated with cooling of rocks beneath the crater lakes was recorded from 1996 to 2012 according to our thermomagnetic modeling of this period the source of the magnetization was 400 to 700 m below an area immediately northeast of yugama crater lake and the cooling migrated gradually to shallower depths during this period based on our modeling seismological data and geochemical monitoring of yugama lake water we consider that the flux of hydrothermal fluid from depth decreased after 1992 and rock magnetization due to cooling began in 1996

tidal responses and earthquake related changes in the water level of deep wells monitoring of the water level has been continued in 100 m deep and 500 m deep wells in the southern kanto district japan to examine the relationship between changes in the well water level and earthquake occurrence by using a bayesian approach the observed data were decomposed into four components tidal response barometric response trend drift and irregular noise components loading effects of the ocean tide on aquifer dilatation were evaluated by using schwiderski s ocean tide models and the harmonic constants compiled by the international hydrographic bureau well aquifer properties were examined based on the tidal and barometric responses of the water level coseismic water level steps were detected in both wells for two earthquakes during the observation period from april 1985 to december 1989 by calibrating the strain sensitivity of the well water levels based on the tidal responses strain changes equivalent to the coseismic steps in the water levels were estimated the coseismic strain changes obtained for the deeper well can be explained reasonably by earthquake fault models in a viscoelastic half space however those observed in the shallower well were too large and in the wrong direction to be explained by the earthquake fault models

the magmatic plumbing of the submarine hachijo nw volcanic chain hachijojima japan long distance magma transport 1 recent geophysical observations on basaltic composite volcanoes in izu bonin arc reveal the process of long distance lateral magma transport within arc crust to clarify a long distance magma transport system of the basaltic arc volcano from geological and petrological aspects we investigated 20 km long submarine volcanic chains hachijo nw chain and hachijo kojima chain and cones on the northeastern slope ne edifices as well as subaerial satellite cones nested hachijo nishiyama volcano in the northern izu arc front basalts from hachijo nw chain have more primitive composition than those from other edifices the composition of the hachijo nw chain basalts is controlled by fractional crystallization while plagioclase accumulation occurred in ne edifices and subaerial satellite cones trace element and isotopic characteristics indicate that the same basaltic primary magma is involved in all sections of the volcano this leads us to consider that magma was transported long distances between the nishiyama volcano and the hachijo nw chain primitive magma was laterally transported nnw for at least 20 km in the middle to lower crust 10 20 km deep from nishiyama volcano with only minimal crustal level modifications and formed hachijo nw chain on the other hand magmas experienced crystal fractionation and accumulation at shallow magma chamber beneath nishiyama volcano seems to have been transported in a short distance 5 km and formed ne trending edifices and subaerial satellite cones the long distance magma transport seems to be controlled by a regional extensional stress regime while short distance transport may be controlled by local stress regime affected by load of main volcanic edifice

co seismic groundwater level changes induced by the may 12 2008 wenchuan earthquake in the near field the large scales of co seismic water level changes in mainland china were observed in response to the tragic 2008 ms 8 0 wenchuan earthquake to better understand the mechanism of these hydrogeological phenomena groundwater level data at 17 confined wells with an epicentral distance of 500 km were collected we compare the static strain predicted by dislocation theory with the volumetric strain calculated by the tide effect of the groundwater based on poroelastic theory the results show that the sign of the co seismic groundwater level change is consistent with the sign predicted by dislocation theory additionally the magnitude of the strain calculated by the two methods is also concordant in half of the wells in the rest of the wells the strains inversed from the groundwater level are one or two orders of magnitude larger than the fault dislocation model these wells mostly have an epicenter distance larger than 300 km therefore the dynamic stress induced by the seismic wave may be responsible for the co seismic water level changes in these wells according to these results we roughly estimate that the effect range of the static stress is approximately 300 km for the wenchuan earthquake and the dynamic stresses dominate beyond this epicenter distance in addition geological and hydrogeological conditions and other mechanisms may be responsible for these changes

aftershocks and pore fluid diffusion following the 1992 landers earthquake 1 we model the evolution of regional stress following the 1992 landers earthquake in order to test the importance of pore fluid flow in producing aftershocks rising fluid pressure due to pore fluid flow and the resulting coulomb stress changes were found to be strongly correlated with the time and location of aftershock events regional aftershock frequencies computed by integrating pore pressure decay rates also agreed quite well with aftershock data calculations show that regions of rising postseismic poroelastic coulomb stress overlap considerably with regions of positive coseismic coulomb stress thus pore fluid flow which affects pore pressure within faults and causes regional poroelastic stress evolution following earthquakes gradually evolves the initial coseismic stress changes together these changes provide a reasonable physical mechanism for aftershock triggering which agrees with data for the 1992 landers earthquake

boudinage and shearband boudins a meso to micro scale tool in structural analysis abstract a classification of boudinage and boudins is made presenting a simplified parametric description of boudin block geometry end members the most important shearband boudins parameters ratios microstructural domains and internal evolutions are described and interpreted shearband boudins are related to a large number of geological meso and microstructures e g pinch and swell drawn or torn boudins mica fish porphyroclasts foliation boudinage tectonic lozenges and c s c several factors can control the asymmetric boudinage process such as the obliquity of a competent layer the orientation of an initial fracture boudin axial ratio the viscosity ratio between matrix and layer flow type and shear strain this review highlights the correlation of shearband boudins with other asymmetrically deformed structures and shows their geological relevance finally this study presents a phenomenological framework for shearband boudins

magnetic signatures associated with magma ascent and stagnation at popocatepetl volcano mexico during 2006 monitoring of real time magnetic signals at popocatepetl during 2006 has allowed discrimination of magma injection and dome growth magnetic signals correlated with seismic volcanotectonic events and harmonic tremor as well as number of small emissions spring water ph ash components and dome evolution helped define upward magma transport and yield a better understanding of the volcanic plumbing system magma ascent occurs mostly in periods of 7 3 days associated with harmonic tremor and decreasing magnetic signals between 21 1 and 215 nt followed by increasing signals linked to cooling of the domes and increased seismicity over periods of 1 to more than 3 months the dome clogs the vent after the negative magnetic anomaly harmonic tremor period associated with magma ascent and forces an explosive crater reopening explosion larger negative changes in the magnetic signals occurred in april 26 nt august 23 to 26 nt and october to december 25 to 215 nt associated with dome formation and growth negative magnetic anomalies preceded eruptions