applications of autoregressive models and time frequency analysis to the study of volcanic tremor and long period events volcanic tremor and long period lp events are characterized by sharp spectral peaks that generally result from resonance effects at the source and which concentrate most of the radiated energy the understanding of these seismovolcanic phenomena requires good descriptions of the distribution in time and frequency of the different spectral components included in the signals as well as a separation of the resonance effects from less energetic effects such as excitation and propagation we address the issue of extracting from individual records information as detailed as possible on the physical processes involved at the source we introduce and compare several time frequency analysis methods and we describe the application of autoregressive modeling and deconvolution methods to the characterization and separation of the main spectral components we propose a signal analysis approach based on the joint use of a set of complementary methods and we present applications to several examples of volcanic tremor and lp events the time frequency analysis of some of the lp events taken as examples reveals short duration components at the seismogram onsets with energy concentrated at frequencies either higher or lower than the main resonance frequencies these seismic phases are probably related to the excitation processes of the volcanic resonators in several cases the arrival of the main spectral peak has a delay of a few tenths of a second with respect to the first arrival the residual signals obtained by deconvolving and eliminating the main spectral components contain information about the excitation such as duration delay or frequency band the residual signals are short for lp events and continuous for volcanic tremor the autoregressive modeling of the sample records gives precise estimations of the frequency and quality factor of the main spectral peaks the measured parameters cover a wide range of values which is consistent with the great variety of fluids filling resonating cavities in volcanoes

applicability of insar to tropical volcanoes insights from central america measuring volcano deformation is key to understanding the behaviour of erupting vol canoes and detecting those in periods of unrest satellite techniques provide the opportunity to do so on a global scale but with some notable exceptions the deformation of volcanoes in the tropics has been understudied relative to those at higher latitudes largely due to technical difficulties in applying interferometric synthetic aperture radar insar we perform a systematic survey of the central american volcanic arc to investigate the appli cability of interferometric synthetic aperture radar insar to volcanoes in the tropics volcano characteristics that may prevent insar measurement include 1 dense vegetation cover 2 per sistent activity and 3 steep slopes measurements of deformation are further inhibited by atmos pheric artefacts associated with 4 large changes in topographical relief we present a systematic method for distinguishing between water vapour artefacts and true deformation our data show a linear relationship c 2 cm km between the magnitudes of water vapour artefacts and volcano edifice height for high relief volcanoes e g fuego guatemala 3763 m a s l above sea level errors are of the order of 4 5 cm across the volcano s edifice but are less than 2 cm for lower relief e g masaya nicaragua 635 m a s l examples such as arenal atitlan and fuego illustrate that satellite acquisition strategies incorporating ascending and descending tracks are particularly important for studying steep sided volcanoes poor coherence is primarily associated with temporal decorrelation which is typically more rapid in southern central america where evergreen broadleaf vegetation dominates land use classification is a better predictorof decorrelation rate thanvegetationindex comparisonof coher ence for different radar wavelengths match expectations high resolution x band radar is best suited to local studies where high resolution digital elevation models dems exist while l bandwavelengths are necessary for regional surveys however this is the first time that relation ships between phase coherence and time perpendicular baseline radar wavelength and land use have been quantified on the scale of a whole volcanic arc

shortening of an overriding plate and its implications for slip on a subduction thrust central hikurangi margin new zealand 1 at subduction plate boundaries strains accumulate within the overriding plate in response to motion of the down going plate to a first approximation margin normal interplate slip and shortening in the overriding plate sum to the total plate convergence therefore margin normal interplate slip can be estimated by measuring shortening in the overriding plate and total plate convergence here we quantify margin normal interplate slip by measuring shortening of the upper plate along a profile which extends up to 480 km across and approximately normal to the central hikurangi margin new zealand long term deformation is estimated for periods of millions of years using data from seismic reflection lines and cross sections while contemporary strain rates are derived from global positioning system gps geodetic velocities these data permit comparison of plate convergence rates determined by seafloor spreading data with the rates of contraction over short 7 years and long 2 5 and 5 myr periods of time on this part of the plate boundary total margin normal shortening in the overriding plate over the last 5 myr was 9 28 km and accounts for 6 19 of the total convergence 145 160 km at rates of 2 6 mm yr the remaining 80 or more of plate convergence has been accommodated by slip on the subduction thrust gps contraction along approximately the same profile indicates 14 16 mm yr of contemporary shortening across the terrestrial part of the upper plate which is approximately modeled by 80 interplate coupling on the subduction interface down to depths of 30 km the contrasting proportions of inferred interplate coupling for contemporary and geological data sets are consistent with stick slip behavior on the plate interface and with slip being principally achieved during intermittent large earthquakes the general shapes of short and long term shortening profiles are similar and suggest that the highest strains occur at or immediately east of the mohaka fault these strain profiles are consistent with a model where high strains in the upper plate are concentrated near the down dip end of the contemporary locked zone on the plate interface this model requires that the down dip end of the interseismic locked zone has on average been approximately stable over a period of at least 2 5 5 myr

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

evolution of fluid geochemistry at the turrialba volcano costa rica from 1998 to 2008 turrialba 10 02 n 83 45 w is a 3 349 m high stratovolcano belonging to the holocene cordillera central volcanic belt of costa rica the summit consists of three ew oriented craters east central and west since its last eruptive phase 1864 1866 the central and west craters have displayed modest fumarolic activity with outlet temperatures clustering around 90 c in 2001 seismic swarms ground deformation and increasing fumarolic activity occurred from 2005 to 2008 new fumarolic vents opened between and within the central and west craters and along the western and southwestern outer flanks of the volcanic edifice these physical changes were accompanied by a drastic modification in the gas chemistry that can be divided in three stages 1 hydrothermal from 1998 to autumn 2001 characterized by the presence of h2o co2 h2s and to a very minor extent hcl and hf 2 hydrothermal magmatic autumn 2001 2007 with the appearance of so2 and a significant increase of hcl and hf and 3 magmatic dominated 2007 2008 characterized by increased so2 content so2 h2s 100 and temperatures up to 282 c accordingly gas equilibrium in the co2 ch4 h2 system suggests a progressive evolution of the deep fluid reservoir toward higher temperatures and more oxidizing conditions the chemical physical modifications of turrialba in the last decade can be interpreted as part of a cyclic mechanism controlling the balance between the hydrothermal and the magmatic systems nevertheless the risk of rejuvenation of the volcanic activity cannot be excluded and an appropriate seismic ground deformation and geochemical monitoring program is highly recommended turrialba lies at a distance of 35 and 15 km from san jose and cartago respectively the two largest cities in costa rica

how a complex basaltic volcanic system works constraints from integrating seismic geodetic and petrological data at mount etna volcano during the july august 2014 eruption the petrological part of this study was supported by the fir 2014 research grant to marco viccaro from the university of catania italy grant number 2f119b title of the project dynamics of evolution ascent and emplacement of basic magmas case studies from eruptive manifestations of eastern sicily

interplate coupling in the kanto district central japan and the boso peninsula silent earthquake in may 1996 i studied crustal deformation in the kanto district central japan based on continuous gps data horizontal as well as vertical displacement rate demonstrate significant interaction between the landward kanto block and the philippine sea plate although the subduction effect of the pacific plate is not apparent it is reasonable to consider the entire kanto district is displaced westward due to the interaction with the pacific plate the gps velocity data were inverted to estimate the slip deficit distribution on the sagami trough subduction zone the result delineates a strongly coupled region on the plate interface part of which corresponds to the 1923 kanto earthquake the strongly coupled region is located shallower than 20 km in addition the plate interaction is laterally heterogeneous even in the same depth range implying thermal structure is not the only factor controlling interplate coupling the gps data also detected a silent earthquake event on the interface of the philippine sea slab east of the boso peninsula in the middle of may 1996 the silent rupture propagated over a 50 km 50 km wide area during about a week the maximum slip was approximately 50 mm and the released seismic moment was 4 7 1018nm mw 6 4 there was a small seismicity triggered by this silent event the silent slip was located in the peripheral of the strongly coupled area suggesting that frictional properties and or stress conditions are inhomogeneous on the plate boundary interface

eruptive activity at turrialba volcano costa rica inferences from 3he 4he in fumarole gases and chemistry of the products ejected during 2014 and 2015 a new period of eruptive activity started at turrialba volcano costa rica in 2010 after almost 150 years of quiescence this activity has been characterized by sporadic explosions whose frequency clearly increased since october 2014 this study aimed to identify the mechanisms that triggered the resumption of this eruptive activity and characterize the evolution of the phenomena over the past 2 years we integrate 3he 4he data available on fumarole gases collected in the summit area of turrialba between 1999 and 2011 with new measurements made on samples collected between september 2014 and february 2016 the results of a petrological investigation of the products that erupted between october 2014 and may 2015 are also presented we infer that the resumption of eruptive activity in 2010 was triggered by a replenishment of the plumbing system of turrialba by a new batch of magma this is supported by the increase in 3he 4he values observed since 2005 at the crater fumaroles and by comparable high values in september 2014 just before the onset of the new eruptive phase the presence of a number of fresh and juvenile glassy shards in the erupted products increased between october 2014 and may 2015 suggesting the involvement of new magma with a composition similar to that erupted in 1864 1866 we conclude that the increase in 3he 4he at the summit fumaroles since october 2015 represents strong evidence of a new phase of magma replenishment which implies that the level of activity remains high at the volcano this article is protected by copyright all rights reserved

turmoil at turrialba volcano costa rica degassing and eruptive processes inferred from high frequency gas monitoring eruptive activity at turrialba volcano costa rica has escalated significantly since 2014 causing airport and school closures in the capital city of san jose whether or not new magma is involved in the current unrest seems probable but remains a matter of debate as ash deposits are dominated by hydrothermal material here we use high frequency gas monitoring to track the behavior of the volcano between 2014 and 2015 and to decipher magmatic versus hydrothermal contributions to the eruptions pulses of deeply derived co2 rich gas co2 s total 4 5 precede explosive activity providing a clear precursor to eruptive periods that occurs up to 2weeks before eruptions which are accompanied by shallowly derived sulfur rich magmatic gas emissions degassing modeling suggests that the deep magmatic reservoir is similar to 8 10km deep whereas the shallow magmatic gas source is at similar to 3 5km two cycles of degassing and eruption are observed each attributed to pulses of magma ascending through the deep reservoir to shallow crustal levels the magmatic degassing signals were overprinted by a fluid contribution from the shallow hydrothermal system modifying the gas compositions contributing volatiles to the emissions and reflecting complex processes of scrubbing displacement and volatilization h2s so2 varies over 2 orders of magnitude through the monitoring period and demonstrates that the first eruptive episode involved hydrothermal gases whereas the second did not massive degassing 3000t d so2 and h2s so2 1 followed suggesting boiling off of the hydrothermal system the gas emissions show a remarkable shift to purely magmatic composition h2s so2 0 05 during the second eruptive period reflecting the depletion of the hydrothermal system or the establishment of high temperature conduits bypassing remnant hydrothermal reservoirs and the transition from phreatic to phreatomagmatic eruptive activity

crustal deformation measurements in guerrero mexico 1 gps measurements of crustal deformation in guerrero southern mexico include surveys collected between 1992 and 2001 as well as continuous gps measurements at a few sites these geodetic observations are used to calculate interseismic deformation rates and assess the presence and possible location of transient deformation during the period encompassing 1992 25 to 2001 75 the data are used to examine transient deformation in 1998 previously described from data at a single site by lowry et al 2001 survey measurements and continuous data from a site near popocatepetl volcano confirm the 1998 transient and survey data also suggest another transient occurred following the 14 september 1995 mw 7 3 copala earthquake all of the available gps position estimates have been inverted for a combined model of slip during each event plus the steady state slip on the plate interface modeling of the steady state deformation rates confirms that the guerrero seismic gap is partially frictionally locked at depths shallower than about 25 km and accumulating strain that may eventually be released in a great earthquake the data also suggest that there is frictional coupling to much greater 40 km depths which releases more frequently in aseismic slip events the locations and sizes of the transient events are only partially constrained by the available data however the transient models which best fit the gps coordinate time series suggest that aseismic slip was centered downdip of the seismogenic portion of the plate bounding thrust in both events and the moment release had equivalent magnitudes mw 7 1 1 3 1 0 in 1995 1996 and 7 1 0 4 0 1 in 1998

aseismic slow slip on an inland active fault triggered by a nearby shallow event the 2008 iwate miyagi nairiku earthquake mw6 8 1 using gps observations we have detected an aseismic slip event on the intraplate dedana fault that was triggered by the iwate miyagi nairiku earthquake mw6 8 13 jun 2008 utc on a nearby but separate fault the observations cannot be satisfactorily explained in terms of either viscoelastic relaxation or poroelastic rebound and we cannot explain the observed displacement time series without presuming that aseismic slip occurred on the dedana fault this slip was likely triggered by the mainshock stress change the detection of future such aseismic slip events on intraplate faults is likely to require denser geodetic networks than are currently in operation but is important for fully characterizing the seismic hazard associated with intraplate earthquakes

thermal constraints on the seismogenic portion of the southwestern japan subduction thrust for coastal cities an important factor in earthquake hazard from subduction zone earthquakes is the landward extent of the seismogenic portion of the subduction thrust fault in this study we test the hypothesis that the maximum downdip extent is defined by a critical temperature we have developed a transient thermal model for the nankai subduction zone of southwest japan to allow comparison of the thermally estimated downdip extent of the seismogenic zone with that from 1 seismicity and tsunami data for two great subduction earthquakes 2 the coseismic faulting extent of these events estimated from geodetic deformation data and 3 the interseismic locked zone determined from interseismic geodetic data the nankai margin has extensive heat flow and heat production data to control thermal models and thus crustal temperatures it has earthquake tsunami and geodetic data that constrain the coseismic rupture portion of the subduction thrust fault for past great earthquakes and the portion of the thrust fault that is locked and storing interseismic elastic strain on the nankaido margin off shikoku island the thermal model indicates that a temperature of 350 c taken to be the limit for seismic initiation from laboratory and field data is reached on the subduction thrust fault 150 km from the trench a transition zone into which rupture may extend with decreasing offset taken to be 450 c extends an additional 45 km downdip the thermal model results are in excellent agreement with the maximum downdip extent of coseismic displacement for the 1946 nankaido ms 8 2 earthquake off shikoku island and with the downdip extent of the present locked zone in the region of the 1944 tonankai ms 8 2 earthquake to the northeast the subduction angle is much steeper and the thermal models indicate a narrower downdip seismogenic extent the seismogenic locked zone from earthquake and geodetic data is also narrower thus our analysis of the southwest japan margin indicates that all three constraints on the downdip extent of the seismogenic zone thermal coseismic and interseismic geodetic data are in general agreement the study also supports the hypothesis that the seismogenic portion of subduction thrust faults is limited primarily by temperature the thermal control implies that subduction thrust faults with shallow dip have wider seismogenic zones compared to those with steep dip the subducting plate age and thus heat flow and the thickness of the insulating sediments on the incoming plate are also very important to the thermal regime and thus to the seismogenic width the relation of the maximum seismic rupture area to the interseismic locked zone is particularly important for earthquake hazard estimation on subduction margins such as cascadia where there have been no great historical events

a model with rigid rotations and slip deficits for the gps derived velocity field in southwest japan abstract we interpret the gps derived velocity field in southwest japan by a superposition of the elastic deformation caused by fault interactions slips or slip deficits on the rigid motion of tectonic blocks or plates based on the strain rate field and crustal seismicity we apply a model with three blocks inner arc outer arc and the northern ryukyu block and slip deficits along the block boundaries several characteristics of the synthesized contributions are found 1 westward motion of the outer arc relative to the amurian plate and the inner arc 2 southeastward motion of the northern ryukyu block relative to the amurian plate 3 2 4 mm yr deficits of left lateral slip rates along the boundary at 32 n in southern kyushu 4 0 8 mm yr deficits of right lateral slip rates along the median tectonic line and the beppu shimabara graben 5 slip deficit rates on the plate interface smaller than those in the case without any consideration for rigid block motions 6 clockwise deflection of slip deficit rate vector on the plate interface from that estimated when not taking rigid block motions into consideration

slow slip on the northern hikurangi subduction interface new zealand 1 in october 2002 a surface displacement episode of 20 30 mm magnitude was observed over a 10 day period on two continuous global positioning system gps instruments near gisborne north island new zealand we interpret this to result from slow slip on the northern hikurangi subduction interface using ten years of regional campaign gps 1995 2004 and recent continuous gps data we estimate the recurrence interval for similar events to be 2 3 yrs in november 2004 a similar slow slip event occurred within this recurrence period the 2002 event can be modeled by 18 cm of slow slip near the down dip end of the seismogenic zone on the subduction interface offshore of gisborne the campaign gps data show that the 2002 slow slip event had little effect on regional strain patterns

noise properties of continuous gps data from concrete pillar geodetic monuments in new zealand and comparison with data from u s deep drilled braced monuments 1 reducing noise levels in geodetic data is critical for the interpretation and modeling of geophysically interesting signals in this paper i estimate noise properties of continuous gps time series collected on concrete pillar monuments and compare them with similar data from deep drilled braced monuments that are considered the most stable three dimensional monuments available i show that the time series noise properties are very similar between the monument types at least for time series up to 4 5 years duration differences between the monument types are therefore not a dominant influence on these time series implying that the less expensive concrete pillar monuments are a valid choice for recording many signals of geophysical interest

the 2006 aseismic slow slip event in guerrero mexico new results from gps 1 crustal deformation measurements from guerrero mexico were made with continuous gps instrumentation this network spans 75 km along the coast and a 275 km transect from the coast to mexico city which is perpendicular to the middle america trench a large aseismic slip transient occurred from april to december 2006 yielding horizontal displacements of nearly 6 cm in the direction opposite to that recorded interseismically this transient slip episode closely follows a series of m5 deep intraplate events that occurred in the northwestern portion of the guerrero region both horizontal and vertical displacements are inverted for the guerrero gps network to determine slip along the subduction interface using a simple fault model that accommodates changes in the subduction zone geometry it is found that slip is concentrated on interior fault patches and propagated to the southeast this slip event has a minimum equivalent mw of 7 5

so2 degassing from turrialba volcano linked to seismic signatures during the period 2008 2012 in 1996 after 150 years of relative calm turrialba volcano was reawakening a visible plume and serious damage to surrounding vegetation due to acid rain are the most obvious signals as part of the network for observation of volcanic and atmospheric change project four gas monitoring stations were initially installed on the west flank of the volcano with the purpose of measuring sulphur dioxide emissions during this period of increased activity using the scanning differential optical absorption spectroscopy technique we present here the results of semicontinuous gas flux measurements over a period of 5 years from 2008 to 2012 providing a novel data set that documents a relatively rapid increase in so2 fluxes from around 350 t day 1 to around 4 000 t day 1 leading up to an eruptive period followed by a gradual return to the former baseline values gas flux data were also compared with seismic data for selected periods of interest providing insights into the link between degassing and seismicity the most important result from this comparison is the identification of an inflexion point in the gas emissions followed by a clearly increasing trend in seismic activity distinguishable 6 months prior to a phreatic eruptive event that occurred on 5 january 2010 this signal can be interpreted as a possible indicator of future eruptive events monitoring of so2 thus complements seismic monitoring as a forecasting tool for eruptive events such monitoring is critical considering the proximity of turrialba to the central valley an area inhabited by more than 50 of costa rica s population

diverse slow slip behavior at the hikurangi subduction margin new zealand 1 the installation of a continuous gps cgps network in new zealand since 2002 has enabled the discovery of 15 slow slip events at the hikurangi subduction margin our analysis and interpretation of the cgps data reveal a marked diversity in characteristics of slow slip events sses in the north island with durations varying from 6 days to 1 5 years equivalent moment release between mw 6 3 7 2 and recurrence intervals of repeating sses on the order of 2 years to more than 5 years the duration and magnitude characteristics of hikurangi sses appear to be related to the depth where they occur the deepest longest duration and largest sses occur at the southern hikurangi margin near the downdip limit of deep down to 40 km depth strong interseismic coupling the shallowest shortest duration smallest and most frequent sses occur at the northern and central hikurangi margin near the downdip limit of unusually shallow 10 15 km depth interseismic coupling the direction of slip on the interface in the hikurangi sses is consistent with slip partitioning at the hikurangi subduction margin we also show that moment accumulation rates on the interface for the time periods between sses are 40 higher than for the period of more than a decade averaging through the sses indicating that sses compose a major portion of the overall moment release budget of the hikurangi subduction interface

carbon isotope systematics of turrialba volcano costa rica using a portable cavity ring down spectrometer over the past two decades activity at turrialba volcano costa rica has shifted from hydrothermal to increasingly magmatic in character with enhanced degassing and eruption potential we have conducted a survey of the 13c signatures of gases at turrialba using a portable field based crds with comparison to standard irms techniques our 13c results of the volcanic plume high temperature vents and soil gases reveal isotopic heterogeneity in the co2 gas composition at turrialba prior to its recent phase of eruptive activity the isotopic value of the regional fault system falla ariete 3 4 0 1 is in distinct contrast with the central crater gases 3 9 0 1 and the 2012 high temperature vent 4 4 0 2 an indication that spatial variability in 13c may be linked to hydrothermal transport of volcanic gases heterogeneities in the source composition or magmatic degassing isotopic values of co2 samples collected in the plume vary from 13c of 5 2 to 10 0 indicative of mixing between atmospheric co2 9 2 0 1 and a volcanic source we compare the keeling method to a traditional mixing model hyperbolic mixing curve to estimate the volcanic source composition at turrialba from the plume measurements the predicted source compositions from the keeling and hyperbolic methods 3 0 0 5 and 3 9 0 4 respectively illustrate two potential interpretations of the volcanic source at turrialba as of the 29 october 2014 turrialba has entered a new eruptive period and continued monitoring of the summit gases for 13c should be conducted to better understand the dominant processes controlling 13c fractionation at turrialba

the march 25 1990 mw 7 0 ml 6 8 earthquake at the entrance of the nicoya gulf costa rica its prior activity foreshocks aftershocks and triggered seismicity on march 25 1990 a large earthquake mw 7 0 ml 6 8 occurred at the entrance of the nicoya gulf costa rica at 1322 55 6 utc producing considerable damage in central costa rica and generating much interest about whether or not the nicoya seismic gap nishenko 1989 had broken the local country wide seismographic network recorded 6 years of activity prior to this large earthquake 16 hours of foreshocks the mainshock and its aftershocks this network is operated jointly by the costa rica volcanological and seismological observatory at the national university ovsicori una and the charles f richter seismological laboratory at the university of california santa cruz cfrsl ucsc we obtained high resolution locations from this network and located the mainshock at 9 38 5 n 84 55 6 w depth is 20 0 km and the largest foreshock mw 6 0 march 25 1990 at 1316 05 8 utc at 9 36 4 n 84 57 1 w depth is 22 4 km we find that the aftershock zone abuts the southeast boundary of the nicoya seismic gap suggesting that the seismic gap did not rupture since the installation of the local network in april 1984 to march 24 1990 nearly 1900 earthquakes with magnitudes from 1 7 to 4 8 318 with magnitude 3 0 or larger have been located at the entrance of the nicoya gulf one of the most active regions in costa rica the march 25 earthquake occurred at the northwest edge of this region where a sequence of foreshocks began 16 hours prior to the mainshock the spatial temporal distribution of aftershocks and directivity analysis of the mainshock rupture process using teleseismic records both indicate a southeast propagating rupture the mainshock ruptured an asperity of approximately 600 km2 of area with this area expanding to 4000 km2 after 7 days we present evidence that suggests that the ruptured asperity is produced by the subduction of a seamount inversion of teleseismic broadband and long period p and sh waves yields a thrust faulting mechanism with the shallow plane striking 292 dipping 26 and with a rake of 88 in agreement with the subduction of the cocos plate under the caribbean plate local first motions for the largest foreshock and the mainshock agree with this solution we also present evidence suggesting that the march 25 1990 earthquake triggered and reactivated several seismic swarms in central costa rica and temporally decreased the activity in the epicentral area of the july 3 1983 ms 6 2 perez zeledon earthquake

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

are the ashes from the latest eruptions 2010 2016 at turrialba volcano costa rica related to phreatic or phreatomagmatic events abstract the initial eruptive episodes of explosive eruptions are classified as phreatic if the amount of juvenile material scoria glass pumice is null and the amount of fresh accidental lithics and hydrothermally altered lithics is substantial phreatic eruptions have been in some cases recognized as precursory events preceding phreatomagmatic and magmatic eruptive phases usually the lithological features of tephra deposits are investigated and sampled in the field investigation of ash samples under binocular microscope or by back scattered electron bse microscope images of polished sections is usually considered sufficient to typify the fragmentation mechanism of the eruption the opening eruptive phases at turrialba volcano together with the formation of new intracraters i e 2010 2012 2014 and the enlargement of the western crater 29 october 2014 to present were classified in previous papers and internal reports as phreatic we studied a series of ash samples erupted from 2010 to 2016 with the aim of understanding the fragmentation processes characterizing the vent opening phases we used sem eds analyses in addition to field and microscopic investigation results showed a composition of accidental lithics of fresh to hydrothermally altered clasts and secondary minerals 82 98 besides juvenile andesite fragments 2 18 which leads us to revisit the classification of the initial eruptive phases of turrialba as phreatomagmatic our method allowed the detection of a juvenile component directly involved in an effective magma water interaction which was possible only by a scrutinous examination of the glass surface textures by sem in the range size between 3 and 3 5 phi we recommend such a type of investigation when the identification of fresh magma in a new eruption is crucial for the preparedness and hazard evaluation at active volcanoes

scattering behaviour at merapi volcano java revealed from an active seismic experiment summary the seismic structure of the stratovolcano merapi java indonesia was studied using an active seismic experiment three 3 km long seismic profiles each consisting of up to 30 three component seismometers with an interstation distance of 100 m were built up in an altitude range between 1000 and 2000 m above sea level the detailed study of the seismic properties of the propagation media in active volcanic regions is important to understand the natural seismic signals used for eruption forecasting the seismic experiment at merapi therefore concentrates on the heterogeneous structure within a radius of 5 km from the active dome where the sources of most of the natural volcanic seismic events are located the cone of merapi volcano consists of different materials changing on a small scale due to the layering of eruptive material additionally the topography of the erosion valleys leads to an irregular deposition which cannot be described by a simple 1 d layering these inhomogeneities have a strong influence on seismic signals the direct p and s waves are attenuated quickly and show only small amplitudes on seismograms the energy lost from the direct waves however is not changed into heat but scattered and can be observed as seismic coda following the direct waves the observed seismograms show a spindle like amplitude increase after the direct p phase this shape of the envelope can be explained by the diffusion model according to this model there are so many strong inhomogeneities that the direct wave can be neglected and all energy is concentrated in multiple scattered waves besides the envelope the coherence and polarization properties of the wavefield also indicate strong scattering only the first onset shows coherence over a station spacing of 100 m whereas the late phases carrying the major part of the energy are mainly incoherent the horizontal components of the seismograms have larger amplitudes than the vertical component but within the horizontal plane the polarization is almost arbitrary corresponding to waves arriving from scatterers located arbitrarily in space as a result of the inversion using the diffusion model we obtain values of the s wave scattering attenuation coefficient gs and the s wave intrinsic absorption coefficient gi in the frequency range of 4 20 hz used in this study the scattering attenuation is at least one order of magnitude larger than the intrinsic absorption gs gi the mean free path of s waves is as low as 100 m gs1 100 m the scattering coefficient is independent of frequency gsyf 0 0 whereas the coefficient of intrinsic attenuation increases with increasing frequency giyf 1 6 the natural seismic signals at merapi volcano show similar characteristics to the artificial shots the first onsets have only small amplitudes and the energy maximum arrives delayed compared to the direct waves therefore these signals appear to be strongly affected by multiple scattering also

multi stage chaotic magma mixing at turrialba volcano abstract after a century of quiescence turrialba a quaternary stratovolcano in the costa rican volcanic front started a new eruptive cycle in 2010 that is ongoing to this date july 3rd 2019 violent eruptions began in 2014 producing columns of ash that reached 4 km above the summit of the volcano here we provide new major and trace element data from fresh glassy fragments basaltic to rhyolitic and mineralogical data for feldspars olivines and pyroxenes from ash fallout collected from 2016 and 2017 eruptions we investigate the composition of the magma replenishing the system as well as the different juvenile components involved in the latter phase of this renewed eruption cycle we find a range of mafic to felsic compositions in every eruptive event sampled our new geochemical data coupled with monte carlo binary mixing simulations indicate that magmas at turrialba volcano are influenced by the input of a back arc type strongly high field strength element enriched 20 60 ppm component generated by decompression melting from subduction driven corner flow thermodynamic modeling using melts software suggests that fractional crystallization alone fails to explain the compositional range of turrialba s eruptive products we instead propose that a complex multi stage magma mixing process produced renewed activity at turrialba based on the trace element variability the dominant intermediate magmatic compositions observed and the results of our multi element mixing simulations this mixing process occurs upon injection of new mantle derived melts into turrialba s fractionated magmatic reservoirs and is governed by chaotic dynamics induced by gradients in temperature and viscosity

space and ground based measurements of sulphur dioxide emissions from turrialba volcano costa rica remotely sensed measurements of sulphur dioxide so2 emitted by turrialba volcano costa rica are reported for the period september 2009 january 2011 these measurements were obtained using images from advanced spaceborne thermal emission and reflexion radiometer ozone monitoring instrument and a ground based uv camera these three very different instruments provide flux measurements in good agreement with each other which demonstrate that they can be integrated for monitoring so2 fluxes fluxes from turrialba increased fourfold in january 2010 following a phreatic explosion that formed a degassing vent in the w crater of turrialba since then the so2 flux has remained high 30 50 kg s but seems to be showing a slowly decreasing trend we interpret this evolution as the start of open vent degassing from a recently intruded magma body the opening of the degassing vent decreased the confining pressure of the magma body and allowed the gases to bypass the hydrothermal system

provenance of obsidian artifacts from the natural protected area laguna del diamante mendoza province argentina and upper maipo valley chile by la icp ms method abstract by means of inductively coupled plasma mass spectrometry associated with laser ablation la icp ms we analyzed several obsidian artifacts from the natural protected area laguna del diamante mendoza argentina and upper maipo valley chile this analytical method almost non destructive is a powerful tool for the determination of trace elements and is very useful in characterizing and determining the provenance of obsidian fragments of archeological interest although care must be taken to avoid or account for heterogeneities within obsidian such as microcrysts in the macro region of study two types of sources can be differentiated on the basis of their primary location high altitude sources emplaced in the andes range 2500 m a s l including laguna del diamante laguna del maule and las cargas sources and low altitude 1500 m a s l extra andean sources situated on the eastern plains cerro huenul and el peceno in addition while the primary location of arroyo paramillos source is currently unknown we consider it as a sub source of laguna del diamante since its wide archaeological distribution has a main core within laguna del diamante area and in the upper maipo river basin considering this pattern the assignation of provenances presented here improves the basis for assessing the use of high andean environments from both sides of the mountain range in addition we will also improve the geochemical discrimination between the two sources arroyo paramillos and las cargas that based on only previous xrf analysis are chemically overlapping leading to an incorrect interpretation of their pattern of archaeological distribution the better characterization of the obsidian sources of the laguna del diamante and neighboring regions allows discussions of mobility exchange and human use of this lithic resource in the highland of central western argentina central chile

measurements of volcanic so2 and co2 fluxes by combined doas multi gas and ftir observations a case study from turrialba and telica volcanoes over the past few decades substantial progress has been made to overcome the technical difficulties of continuously measuring volcanic so2 emissions however measurements of co2 emissions still present many difficulties partly due to the lack of instruments that can directly measure co2 emissions and partly due to its strong atmospheric background in order to overcome these difficulties a commonly taken approach is to combine differential optical absorption spectroscopy doas by using novac scan doas instruments for continuous measurements of crateric so2 emissions and electrochemical ndir multi component gas analyser system multi gas instruments for measuring co2 so2 ratios of excerpts of the volcanic plume this study aims to quantify the representativeness of excerpts of co2 so2 ratios measured by multi gas as a fraction of the whole plume composition by comparison with simultaneously measured co2 so2 ratios using cross crater fourier transform infrared spectroscopy ftir two study cases are presented telica volcano nicaragua with a homogenous plume quiescent degassing from a deep source and ambient temperature and turrialba volcano costa rica which has a non homogeneous plume from three main sources with different compositions and temperatures our comparison shows that in our easier case telica ftir and multi gas co2 so2 ratios agree within a factor about 3 in our complicated case turrialba multi gas and ftir yield co2 so2 ratios differing by approximately 13 25 at most these results suggest that a fair estimation of volcanic co2 emissions can be provided by the combination of doas and multi gas instruments for volcanoes with similar degassing conditions as telica or turrialba based on the results of this comparison we report that by the time our measurements were made telica and turrialba were emitting approximately 100 and 1 000 t day 1 of co2 respectively

subduction zone structure and magmatic processes beneath costa rica constrained by local earthquake tomography and petrological modelling summary a high quality data set of 3790 earthquakes were simultaneously inverted for hypocentre locations and 3 d p wave velocities in costa rica tests with synthetic data and resolution estimates derived from the resolution matrix indicate that the velocity model is well constrained in central costa rica to a depth of 70 km northwestern and southeastern costa rica are less well resolved owing to a lack of seismic stations and seismicity maximum h2o content and seismic wave speeds of mid ocean ridge basalt and harzburgite were calculated for metamorphic phase transformations relevant to subduction both the 3 d p wave velocity structure and petrological modelling indicate the existence of low velocity hydrous oceanic crust in the subducting cocos plate beneath central costa rica intermediate depth seismicity correlates well with the predicted locations of hydrous metamorphic rocks suggesting that dehydration plays a key role in generating intermediate depth earthquakes beneath costa rica wadati benioff zone seismicity beneath central costa rica shows a remarkable decrease in maximum depth toward southeastern costa rica the presence of asthenosphere beneath southeastern costa rica which entered through a proposed slab window may explain the shallowing of seismicity due to increased temperatures and associated shallowing of dehydration of the slab tomographic images further constrain the existence of deeply subducted seamounts beneath central costa rica large low p wave velocity areas within the lower crust are imaged beneath the southeasternmost volcanoes in central costa rica these low velocities may represent anomalously hot material or even melt associated with active volcanism in central costa rica tomographic images and petrological modelling indicate the existence of a shallow possibly hydrated mantle wedge beneath central costa rica

a large slow slip event on the central hikurangi subduction interface beneath the manawatu region north island new zealand 1 we present continuous gps observations of a surface deformation episode in the manawatu region of the north island new zealand lasting 18 months from january 2004 to june 2005 we invert vertical and horizontal displacements of gps sites during the event for slow slip on the hikurangi subduction thrust we find that up to 350 mm of slip occurred on the thrust in the transition zone between strong interseismic coupling and aseismic creep if the entire slip in the manawatu slow slip event had occurred instantaneously it would have resulted in an mw 7 0 earthquake given the large amount of slip we expect that the recurrence interval for similar slow slip events may be ten years or more

constraining the sulfur dioxide degassing flux from turrialba volcano costa rica using unmanned aerial system measurements abstract observed sulfur dioxide so 2 mixing ratios onboard unmanned aerial systems uas during march 11 13 2013 are used to constrain the three day averaged so 2 degassing flux from turrialba volcano within a bayesian inverse modeling framework a mesoscale model coupled with lagrangian stochastic particle backward trajectories is used to quantify the source receptor relationships at very high spatial resolutions i e 2 variations when using a first order closure non local planetary boundary layer pbl scheme the optimized so 2 degassing fluxes vary from 0 59 0 37 to 0 83 0 33 kt d 1 depending on the pbl scheme used these fluxes are in good agreement with ground based gas flux measurements and correspond to corrective scale factors of 8 12 to the posteruptive so 2 degassing rate in the aerocom emission inventory the maximum a posteriori solution for the so 2 flux is highly sensitive to the specification of prior and observational errors and relatively insensitive to the so 2 loss term and temporal averaging of observations our results indicate relatively low degassing activity but sustained sulfur emissions from turrialba volcano to the troposphere during march 2013 this study demonstrates the utility of low cost small uas platforms for volcanic gas composition and flux analysis

evidence from gps measurements for contemporary interplate coupling on the southern hikurangi subduction thrust and for partitioning of strain in the upper plate the spatial extent and strength of contemporary coupling between the pacific and australian plates on the hikurangi subduction interface beneath the wellington region of new zealand are not well known consequently the potential for the plate interface to produce great thrust earthquakes or to load the major wellington and wairarapa faults in the overlying plate is also unknown to address these issues a gps network across the southern north island has been partially or wholly surveyed six times between 1992 and 1999 and yields well determined relative velocities between 82 points the relative velocity of the east coast with respect to the west coast across the 80 km width of the southern end of the north island is 14 mm yr 1 at an azimuth of 258 this is about one third of and closely parallel to the nuvel 1a relative velocity of the pacific with respect to the australian plate 39 4 mm yr 1 at 261 strain rate solutions indicate partitioning of contemporary strain with a 35 change in principal axis orientations across the network using elastic dislocation theory an inversion of the observed point velocities and their full variance covariance matrix determines the variation with depth of contemporary coupling at the subduction interface if uniform coupling is assumed then 100 coupling occurs from very shallow depths down to 29 1 km however if variable coupling is assumed it reaches 100 at depths between 16 and 24 km at greater depths there is a transition zone at least 20 km wide down to a depth of at least 40 km over which contemporary coupling diminishes to zero these depth ranges correlate moderately well with low angle thrust focal mechanisms recently obtained by other workers and indicate that the downdip width of the interface over which a great thrust earthquake could occur exceeds 100 km elastic dislocation models also explain the observed partitioning of strain with coulomb stress calculations indicating that the wairarapa fault is being loaded at seismogenic depths

the updip and downdip limits to great subduction earthquakes thermal and structural models of cascadia south alaska sw japan and chile this study examines thermal and structural controls of the updip and downdip rupture limits of great subduction thrust earthquakes data on past great earthquake seismic limits have been compiled for four continental subduction zones cascadia sw japan south alaska and chile these limits have then been compared to the predictions of several models for what constrains great earthquake rupture temperatures on the subduction thrusts have been estimated by finite element numerical models the landward limits of the observed updip aseismic zones correspond to the position where the thrust temperature reaches about 100 c that is depths of about 2 to 10 km for the subduction zones studied this temperature agrees with the dehydration of stable sliding smectite clays to illite chlorite the temperatures in this region are controlled mainly by the thickness of sediment on the incoming crust and by the crustal age and thus heat flow the downdip limits correspond to the depth on the thrust where either 1 the temperature reaches about 350 c which corresponds to thermally activated stable sliding behavior for crustal rocks with a transition to 450 c or 2 about 40 km depth if 350 c is reached at greater depth depths of about 40 km approximately correspond to the intersection of the thrust with the continental forearc moho and this downdip limit may be a consequence of stable sliding serpentinite or talc and other hydrated forearc mantle rocks the primary temperature controls on the downdip region are the age of the subducting oceanic plate and the thrust dip profile secondary control comes from the thickness of incoming sediment the convergence rate and the radioactive heat generation in the overlying forearc the 100 c updip limit occurs near the trench for young subducting plates with a thick sediment section such as cascadia 6 8 ma and up to 80 km landward for older oceanic crust such as south alaska 50 ma the 350 c downdip thermal limit is applicable for young oceanic plates e g cascadia and nankai whereas the forearc mantle limit applies for older plates e g south alaska and chile except near the chile rise for the margins studied that have experienced great earthquakes there is generally good agreement between the postulated thermal and moho limits and the rupture or seismogenic zone as defined by the distribution of aftershocks and by waveform tsunami and dislocation modeling the downdip limit of the interseismic locked zone from dislocation modeling is also in agreement with these limits

geophysical geochemical and geodetical signals of reawakening at turrialba volcano costa rica after almost 150 years of quiescence article i nfo turrialba is a basaltic andesitic stratovolcano 3340 masl in the cordillera volcanica central in costa rica after the last eruption 1864 1866 volcanic manifestations were limited to weak fumarolic discharge continuous since 1980 from the summit from 1996 onward the degassing activity has progressively been increasing reaching its climax after 2005 new fumaroles have appeared in the central and west summit craters the latter now being the most active and in the fracture system in between showing sulphur deposits and progressively increasing degassing rate in 2004 fumaroles and new fissures have appeared on the sw outer and ssw distal flanks the latter being located along a major ne oriented tectonic lineament fumarolic temperatures at the bottom of the west crater have increased from 88 to 282 c in early 2008 changes in chemical and isotopic compositions of discharged fluids have shown a progressive enhancing of the magmatic signature since 2001 since late 2007 so2 flux measured with mini doas has increased two orders of magnitude 1 t day in 2002 to 740 t day in january 2008 the enhanced gas discharge at turrialba volcano has caused significant interference on tropospheric o3 measurements at 2 3 km altitude 50 km w from the volcano seismic swarms followed an increasing trend consistent with that of the fumaroles the maximum seismic activity to date up to thousands of events day was recorded in mid 2007 an inflationary trend was observed in the crater area in this paper we present for the first time all the available data on the activity of turrialba volcano new geophysical geodetical and geochemical data and published geophysical and geochemical data are presented and discussed as a whole the multidisciplinary approach indicated that from 1996 to 2009 three stages deriving by the delicate equilibrium between the hydrothermal and the magmatic reservoirs were recognized the magmatic dominated phase is still prevailing as evidenced by the fact that while completing the present paper on the 4th of january 2010 at 16 57 gmt a loud explosion occurred at the west crater and was followed by three others spaced out every 10 min these events were interpreted as associated with phreatic eruptions

crustal structure across the costa rican volcanic arc 1 island arcs are proposed to be essential building blocks for the crustal growth of continents however island arcs and continents are fundamentally different in bulk composition mafic and felsic respectively the substrate upon which arcs are built oceanic crust versus large igneous province may have a strong influence on crustal genesis we present results from an across arc wide angle seismic survey of the costa rican volcanic front which test the hypothesis that juvenile continental crust is actively forming at this location travel time tomography constrains velocities in the upper arc to a depth of 15 km where average velocities are 6 5 km s the upper 5 km of crust is constrained by velocities between 4 0 and 5 5 km s which likely represent sediments volcaniclastics flows and small intrusions between 5 and 15 km depth velocities increase slowly from 5 5 to 6 5 km s crustal thickness and lower crustal velocities are roughly constrained by reflections from an inferred crust mantle transition zone crustal thickness beneath the volcanic front in costa rica is 40 km with best fit average lower crustal velocities between 6 8 and 7 1 km s overall velocities across the arc in central costa rica are at the high velocity extreme of bulk continental crust velocities and are lower than modern island arc velocities suggesting that continental compositions are created at this location these data suggest that preexisting thick crust of the caribbean large igneous province has a measurable effect on bulk composition this thickened arc crust may be a density filter for mafic material and thereby support differentiation toward continental compositions

mass and heat flux balance of la soufriere volcano guadeloupe from aerial infrared thermal imaging abstract la soufriere of guadeloupe is an active volcano of lesser antilles that is closely monitored due to a high eruptive hazard potential since 1992 it exhibits a medium level but sustained background hydrothermal activity with low energy and shallow seismicity hot springs temperature increase and high flux acidic gas fumaroles at the summit the problem of estimating the heat balance and quantifying the evolution of hydrothermal activity has become a key challenge for surveillance this work is the first attempt of a global mapping and quantification of la soufriere thermal activity performed in february 2010 using aerial thermal infrared imagery after instrument calibration and data processing we present a global map of thermal anomalies allowing to spot the main active sites the summit area including the fumaroles of tarissan pit and south crater the ty fault fumarolic zone and the hot springs located at the vicinity of the dome in a second step we deduce the mass and the energy fluxes released by the volcano in particular we propose a simple model of energy balance to estimate the mass flux of the summit fumaroles from their brightness temperature and size in february 2010 tarissan pit had a 22 8 8 1 kg s 1 flux 1970 704 tons day 1 while south crater vents had a total of 19 5 4 0 kg s 1 1687 348 tons day 1 once converted into energy flux summit fumaroles represent 98 of the 106 30 mw released by the volcano the 2 remaining being split between the hot springs and the thermal anomalies at the summit and at the ty fault fumarolic zone these values are in the high range of the previous estimations highlighting the short term variability of the expelled fluxes such a heat flux requires the cooling of 1500 m 3 of magma per day in good agreement with previous geochemical studies

degassing of halogens from basaltic volcanism insights from volcanic gas observations abstract the currently available data set of s cl f abundances in volcanic gas plumes and high temperature fumarolic gas samples from basaltic volcanism is reviewed here in the attempt to derive constraints on the modes of halogen degassing from mafic silicate melts apart from large volcano to volcano variations reflecting remarkable differences in volatile abundances in the source magmas each of the explored volcanoes displays large changes of so2 hcl and so2 hf ratios with the style of volcanic activity with hcl hf staying fairly constant halogen abundances are low and so2 hcl and so2 hf are high when fresh volatile rich magmas sustain degassing as during explosive eruptions at the onset of eruptive cycles or shortly before paroxysmal events low so2 hcl and so2 hf ratios are instead characteristic of late stages of volcanic degassing typically being observed in the concluding stages of basaltic eruptions or during periods of reduced magma supply at persistently degassing volcanoes these observations are taken as evidence of halogens being less keen to enter the gas phase relative to s during degassing of basaltic magmas and quantitatively interpreted in light of a rayleigh type open system degassing model the model though simple quantitatively reproduces the range of volcanic gas compositions observed at basaltic volcanoes worldwide and allows prediction of vapour melt partitioning contrasts of factors 9 and 36 for the volatile couples s cl and s f respectively these predictions require validation from appropriately designed experiments of halogen partitioning between magmatic vapours and silicate melts over a range of p t x conditions

slow slip and frictional transition at low temperature at the hikurangi subduction zone temperature changes with depth do not appear to be a primary control for either slow slip or fault locking processes at the hikurangi margin north island new zealand both slow slip events and the geodetically observed transition from fault locking to free slip at depth occur at temperatures as low as 100 c shallow portions of faults exhibit brittle stick slip behaviour that gives way to more stable sliding with increasing depth limiting the depths to which earthquake inducing slip can occur the increase of temperature with depth is often assumed to transform friction in the fault from velocity weakening unstable to velocity strengthening stable and to change conditions from brittle to ductile1 2 3 4 5 a temperature of 350 c has been suggested to mark the base of the frictionally unstable portion of the fault which becomes free slipping at depth where temperatures rise above 450 c refs 2 4 6 here we show that both slow slip events and the geodetically observed transition from fault locking to free slip at the hikurangi subduction zone east of the north island new zealand occur at temperatures as low as 100 c suggesting that temperature is not a primary control on either slow slip or fault locking processes at the hikurangi margin although globally shallow slow slip events are rare five out of seven events observed so far at the hikurangi margin are less than 15 km deep

a brittle failure model for long period seismic events recorded at turrialba volcano costa rica a temporary seismic network consisting of 23 broadband and six short period stations was installed in a dense network at turrialba volcano costa rica between 8 march and 4 may 2011 during this time 513 long period lp events were observed due to their pulse like waveforms the hypothesis that the events are generated by a slow failure mechanism based on a recent new model by bean et al 2014 is tested a significant number 107 of the lps are jointly inverted for their source locations and mechanisms using full waveform moment tensor inversion the locations are mostly shallow with depths 800 m below the active southwest crater the results of the decompositions of the obtained moment tensor solutions show complex source mechanisms composed of high proportions of isotropic and low but seemingly significant proportions of compensated linear vector dipole and double couple components it is demonstrated that this can be explained as mode i tensile fracturing with a strong shear component the source mechanism is further investigated by exploring scaling laws within the data the lps recorded follow relationships very similar to those of conventional earthquakes exhibiting frequency magnitude and corner frequency versus magnitude relationships that can be explained by brittle failure all of these observations indicate that a slow failure source model can successfully describe the generation of short duration lp events at turrialba volcano

relocation of long period lp seismic events reveals en echelon fractures in the upper edifice of turrialba volcano costa rica swarms of long period lp events were recorded on turrialba volcano costa rica during a seismic field experiment in 2009 families of lp events were previously identified and located using a joint inversion for source location and mechanism however the spatial resolution of the obtained locations was not sufficient for imaging the structures on which they occur using a waveform similarity based location method we take advantage of the joint location mechanism inversion by relocating events around the obtained familial location the location method is successfully tested on a synthetic data set and is then applied to the turrialba lp data set the relocated events are jointly interpreted with their source mechanisms and reveal an en echelon structure within the upper edifice of the volcano this can be interpreted as a response of a shearing band with high fluid pressure inducing tensile fractures at unconsolidated rock layer interfaces within the upper edifice of the volcano

weak interplate coupling by seamounts and repeating m 7 earthquakes subducting seamounts are thought to increase the normal stress between subducting and overriding plates however recent seismic surveys and laboratory experiments suggest that interplate coupling is weak a seismic survey in the japan trench shows that a large seamount is being subducted near a region of repeating earthquakes of magnitude m 7 both observed seismicity and the pattern of rupture propagation during the 1982 m 7 0 event imply that interplate coupling was weak over the seamount a large rupture area with small slip occurred in front of the seamount its northern bound could be determined by a trace of multiple subducted seamounts whereas a subducted seamount itself may not define the rupture area its width may be influenced by that of the seamount

spatiotemporal evolution of aseismic interplate slip between 1996 and 1998 and between 2002 and 2004 in bungo channel southwest japan 1 interplate aseismic slip in the bungo channel area southwest japan occurred during 1996 1998 and 2002 2004 we employed a square root information filter following the time dependent inversion technique to time series of daily coordinates of global positioning system gps sites the results show that aseismic interplate slip occurred beneath the southwestern part of shikoku island from late 1996 then shifted southwestward to the bungo channel area from may 1997 to february 1998 and subsided over time with a moment magnitude mw of 7 1 in contrast the 2002 2004 event shows slip in the area beneath the bungo channel in an early stage from march 2003 to august 2003 from august 2003 to january 2004 the slip area expanded by around 30 km northeastward to the southwestern part of shikoku island and the northern part of the bungo channel and then decayed over time with mw reaching 7 1 in the 2002 2004 event the start of the northeastward expansion and acceleration of the aseismic slip coincided with the occurrence of a short term slow slip event and low frequency earthquakes in a deep area this is a different spatiotemporal evolution from that of the 1996 1998 event despite having occurred in almost the same area with similar moment magnitudes a balance of slip deficit and forward aseismic slip on the plate boundary suggests that part of the bungo channel area releases strain energy mainly by episodic long term slow slip events

temporal stability of deformation rates comparison of geological and geodetic observations hikurangi subduction margin new zealand abstract we examine how well contemporary horizontal velocity fields from global positioning system gps geodetic measurements describe long term deformation rates million year rates of extension shortening strike slip and vertical axis rotations are compared with modelling of gps velocities from the last 10 15 years in the hikurangi subduction margin new zealand within measurement uncertainties of mainly 50 the rates of deformation and vertical axis rotations for each time interval are usually indistinguishable the comparable deformation rates are consistent with the notion of near constant rates since 1 5 ma during this time oblique relative plate motion was partitioned with the majority 85 of margin normal motion accommodated on the plate interface and most 60 margin parallel motion by strike slip faulting and vertical axis rotations in the upper plate prior to 1 5 ma gps velocities cannot be reliably used to describe deformation and rotations of the hikurangi margin because at this time the taupo rift commenced opening the boundary between raukumara and wairoa rotational domains was abandoned and the rates of upper plate shortening increased the broad compatibility of gps and geological deformation and rotation rates since 1 5 ma suggests that the build up of contemporary elastic strains in the north island measured by gps is largely uniform for much of the duration of each seismic cycle the good agreement between the gps and geological deformation rates in the north island is consistent with the view that contemporary elastic strains will mainly be converted to permanent dip slip on the subduction thrust and to displacement on upper plate faults during future large magnitude earthquakes

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses

magma transport and storage at mt etna italy a review of geodetic and petrological data for the 2002 03 2004 and 2006 eruptions abstract a detailed reconstruction of magma movements within the plumbing system of mt etna volcano has been made by reviewing the eruptions occurring during the october 2002 december 2006 period the availability of continuous gps data allowed detecting at least ten different ground deformation stages highlighting deflationary and inflationary episodes as well as the occurrence of a shallow dike intrusion these data have been coupled with the available petrological datasets including major trace elements and sr nd pb isotope compositions for the volcanic rocks erupted in the 2002 2006 period we identified two main magmatic reservoirs located at different depths along the plumbing system of the volcano the former is located at a depth of 7 km bsl and fed the 2001 and 2002 03 eruptions while the latter located from 3 5 to 5 5 km bsl fed the 2004 05 and 2006 eruptions petrological characteristics of emitted products have been correlated with the inflation vs deflation cycles related to the identified sources providing evidence for changes through time of the evolutionary degree of the erupted magmas along with variations in their geochemical feature finally we suggest that a modification of the deep plumbing system of the volcano might have occurred during the 2002 03 eruption as a consequence of the major seaward motion of the eastern flank of the volcano