a mechanism for magmatic accretion under spreading centres the most active volcanic zone on earth occurs along the global mid ocean ridge system where the lithosphere is pulled apart and new oceanic crust is created at rates between 10 and 200 km myr 1 this volcanism is segmented and is concentrated along the axial valleys and highs of slow and fast spreading ridges respectively with transform fault zones separating and generally offsetting each active ridge segment volcanic activity may be nearly absent at the ridge transform intersection where a slow spreading ridge is offset and greatly reduced where a fast spreading ridge is offset implying thinner crust in these regions1 the source of magmas erupted along ocean ridges is the underlying mantle which undergoes decompression melting when rising to fill the gap between the spreading plates the resulting magma aggregates in the upper mantle and ascends to the crust due to its low density compared with the parent mantle rock the melt is believed to pool in crustal magma chambers whence it periodically erupts to the surface typically the formation ascent and aggregation of magmas along the mid ocean ridges is regarded two dimensionally and modelled in a section through the crust and mantle across the strike of the ridges see ref 2 here however we consider the problem with a three dimensional model for which we provide supporting geological evidence in which the magmas rise as a result of a gravitational instability modified rayleigh taylor in the underlying partial melt zone

microstructure and fabric development in ice lessons learned from in situ experiments and implications for understanding rock evolution abstract in this contribution we present a review of the evolution of microstructures and fabric in ice based on the review we show the potential use of ice as an analogue for rocks by considering selected examples that can be related to quartz rich rocks advances in our understanding of the plasticity of ice have come from experimental investigations that clearly show that plastic deformation of polycrystalline ice is initially produced by basal slip interaction of dislocations play an essential role for dynamic recrystallization processes involving grain nucleation and grain boundary migration during the steady state flow of ice to support this review we describe deformation in polycrystalline standard water ice and natural ice samples summarize other experiments involving bulk samples and use in situ plane strain deformation experiments to illustrate the link between microstructure and fabric evolution rheological response and dominant processes most terrestrial ice masses deform at low shear stresses by grain size insensitive creep with a stress exponent n 3 however from experimental observations it is shown that the distribution of plastic activity producing the microstructure and fabric is initially dominated by grain boundary migration during hardening primary creep followed by dynamic recrystallization during transient creep secondary creep involving new grain nucleation with further cycles of grain growth and nucleation resulting in near steady state creep tertiary creep the microstructural transitions and inferred mechanism changes are a function of local and bulk variations in strain energy i e dislocation densities with surface grain boundary energy being secondary except in the case of static annealing as there is a clear correspondence between the rheology of ice and the high temperature deformation dislocation creep regime of polycrystalline quartz we suggest that lessons learnt from ice deformation can be used to interpret polycrystalline quartz deformation different to quartz ice allows experimental investigations at close to natural strain rate and through in situ experiments offers the opportunity to study the dynamic link between microstructural development rheology and the identification of the dominant processes

magma intrusion and effusion at sinabung volcano indonesia from 2013 to 2016 as revealed by continuous gps observation abstract we analyzed continuous global positioning system gps data from sinabung to capture and model the migration of magma from the pre eruptive and syn eruptive time period between june 2013 and january 2016 we divided this time into four periods of significant deformation two extensional stages followed by two contractional stages using a grid search method we determined the location and volume change of a mogi source for each deformation stage cumulative volume changes during the contraction periods were approximated by an exponentially decaying function with time period 1 began in june 2013 with slight extension for which an inflation source was modeled at a depth of 3 8 km below sea level bsl and a volume change of 0 3 1 8 mm3 seismicity in period 1 was marked by a notable increase in deep high frequency volcano tectonic earthquakes vts beginning in july 2013 and shallow vts in september 2013 period 2 began in late october 2013 with accelerated extension with at least 1 cm extension in the baseline length during period 2 the modeled inflation source ascended to a shallower depth of 0 9 0 4 2 1 km below sea level bsl beneath sinabung with a change in volume of 0 39 0 18 0 60 mm3 and with accelerated rates of volume increase during the time period when the magma migrated to the surface seismicity during period 2 was marked first by an increase in the incidence of shallow volcano tectonic vt earthquakes and later by repetitive self similar hybrid events as the magma migrated to the surface period 3 began in january 2014 after the appearance of the lava dome and was marked by rapid steady contraction of 3 cm through march 2014 the modeled source located at 8 4 7 4 9 9 km bsl beneath the eastern flank of sinabung with a volume change of 20 51 26 89 to 14 12 mm3 period 4 began in april 2014 with decelerating contraction and the modeled deformation center shifted to the northeast reaching a depth of 12 2 10 1 14 8 km bsl between sinabung and sibayak volcanoes and a change in volume of 88 26 123 87 to 52 66 mm3 approximately 2 3 of the total volume change related to contraction occurred between january 2014 and may 2016 and the current activity of sinabung is expected to decrease gradually and almost terminate in the early 2020s assuming no new intrusion or deformation rate changes both of the eruptions at sinabung in 2010 and unzen in 1991 1995 show characteristics of ground inflation and subsequent deflation indicating magma migration and effusion processes similar to the current sinabung activity the inflation before the 2010 sinabung eruptions likely started before 2007 and is an indication of magma intrusion before the 2010 and 2013 eruptions

seismic energy releases from volcanoes seismic energy release during the precursory eruptive and declining stages of volcanic activities provides various information about the mechanisms of volcanic eruptions and the temporary developments of their activities hitherto the energy release patterns from precursory earthquake swarms were used to predict the eruption times especially of andesitic or dacitic volcanoes in this paper the discussion is expanded to quantify the total amount of seismic energy released at the threshold of volcanic eruptions with reference to the results observed at several volcanoes the results generally indicate that the cumulative seismic energy release from the precursory earthquake swarms exceed 1017 18ergs before eruptions at any andesitic or dacitic volvanoes this allows the seismic efficiency or the ratio of energy radiated seismically and the energy required for the volumetric expansion to be estimated by incorporating available deformation data with the seismic data the dependency of seismic efficiency on the type of volcanic activity i e non explosive outbreaks phreatic and magmatic eruptions dome formation etc was evaluated from observations at a few volcanoes that provided a variety of examples

repeated fracture and healing of silicic magma generate flow banding and earthquakes textures in an exceptionally preserved effusive rhyolite conduit at torfajokull iceland indicate that rising magma repeatedly fractured and healed at shallow levels in the conduit rfh process anastomosing tuffisite veins filled by fine grained juvenile clasts were generated by shear fracture of highly viscous magma in the glass transition interval welding of the particulate material during subsequent deformation led to thorough healing of veins allowing repeated fracture of the same body of magma we propose that the rfh process is a rechargeable trigger mechanism for hybrid seismicity and show that the time scale of the process and the fractures formed by it are consistent with the repeat time and magnitude of hybrid earthquakes during silicic eruptions the rfh process may also form the flow banding that is nearly ubiquitous in obsidian

rheological properties of water ice applications to satellites of the outer planets 1 abstract the icy moons of the outer solar system have not been quiescent bodies in part because many have a substantial water component and have experienced significant internal heating we can begin to understand the thermal evolution of the moons and the rate of viscous relaxation of surface topography because we now have good constraints on how ice in several of its polymorphic forms flows under deviatoric stress at planetary conditions details of laboratory derived flow laws for pure polycrystalline ice are reviewed in detail one of the more important questions at hand is the role of ice grain size grain size may be a dynamic quantity within the icy moons and it may or may not significantly affect rheology one recent beneficiary of revelations about grain size sensitive flow is the calculation of the rheological structure of europa s outer ice shell which may be no thicker than 20 km

rheology of ices a key to the tectonics of the ice moons of jupiter and saturn the polymorphic varieties of water ice are important rock forming minerals in the outer solar system the voyager 1 and 2 missions have shown that most of the ice moons of jupiter and saturn have had some form of tectonic or internal activity understanding of the tectonics and building reasonable models of the interior of these planets depend on our knowledge of the theological properties and viscosity of high pressure and low temperature forms of ice

a multichannel seismic study of lithospheric flexure across the hawaiian emperor seamount chain existing models assume that the thickened crust beneath seamounts is the result of a surface volcanic load flexing an elastic plate new results suggest that flexed oceanic crust beneath the hawaiian emperor seamount chain is underlain by a 4 km thick deep crustal body we intepret the body as a deep crustal sill complex associated with the tholeiitic stage of volcano building along the chain

east pacific rise from siqueiros to orozco fracture zones along strike continuity of axial neovolcanic zone and structure and evolution of overlapping spreading centers we have used the sea beam multibeam echo sounding system to survey the east pacific rise epr from 8 20 n to 18 30 n obtaining complete coverage of the epr axial neovolcanic zone and all intervening transform faults here we focus on the epr neovolcanic zone and the definition of overlapping spreading centers ocs s between the orozco and siqueiros transform faults the neovolcanic zone is narrow 0 5 2 0 km and continuous along strike and occurs within and near a strike continuous axial summit graben the neovolcanic zone and summit graben reside along the crest of a volcanic axial high which is 2 10 km wide and which continues uninterrupted along strike for 40 140 km within 20 50 km of an intersection with a transform fault the axial neovolcanic zone narrows and deepens and within only 3 6 km of the intersection the neovolcanic zone turns sharply into the transform valley at seven locations between the siqueiros and orozco transform faults the axial neovolcanic zone is discontinuous and is laterally offset a short distance 1 15 km in contrast with a classic ridge transform ridge plate boundary however offset rise terminations overlap each other by a distance approximately 3 times greater than their offset they curve toward each other and often one merges into the other along strike separating the osc s is an elliptical overlap basin up to 600 m deep whose long axis is subparallel to the adjacent spreading centers the overlap basin is characterized by volcanic constructional edifices a key difference between these offsets and small transform faults in the atlantic is that there are no transform fault structures in the overlap basin which link the offset rise axes a continuous axial depth profile reveals a long wavelength 20 60 km undulation of the rise axis which may be associated with variations in the magmatic budget along strike the lowest points in the axial depth profile occur near transform faults and at osc s suggesting that these features are associated with along strike minima in the magmatic budget we suggest that major phases of volcanic activity propagate episodically along the axis away from centers of magmatic inflation and that osc s develop where magmatic pulses fail to meet due to misalignment of fracture systems sinuous bends in the rise axis or other heterogeneities transform faults fail to develop on fast spreading centers where the lateral offsets are small 15 km because the lithosphere is too thin and weak to maintain a classic rigid plate ridge transform fault pattern the osc geometry is unstable and evolves rapidly and the overlapping rises may propagate at rates faster than the local spreading rate one of the two osc s prevails while the other is abandoned while the locations of osc s may not be fixed relative to the rise axis they may tend to recur near the same place creating scars in older lithosphere which resemble fracture zones but whose fine scale structure is quite different there is excellent agreement between the observed structure of osc s and laboratory studies of osc s using wax models photoelastic studies of overlapping cracks and boundary element modeling of overlapping cracks seismic refraction and reflection near two osc s suggests that large offset osc s have separate magma chambers beneath the offset rise axes while small offset osc s may share a single axial magma chamber three dimensional inversion of magnetic anomalies suggests that significant petrologic anomalies may occur near some osc tips waxing and waning of overlapping magma chambers may give rise to the eruption of highly fractionated feti basalts and associated magnetic anomalies

the ml scale in southern california measurements 9 941 of peak amplitudes on wood anderson instruments or simulated wood anderson instruments in the southern california seismographic network for 972 earthquakes primarily located in southern california were studied with the aim of determining a new distance correction curve for use in determining the local magnitude m l events in the mammoth lakes area were found to give an unusual attenuation pattern and were excluded from the analysis as were readings from any one earthquake at distances beyond the first occurrence of amplitudes less than 0 3 mm the remaining 7 355 amplitudes from 814 earthquakes yielded the following equation for m l distance correction log a 0 log a 0 1 110log r 100 0 00189 r 100 3 0 where r is hypocentral distance in kilometers a new set of station corrections was also determined from the analysis the standard deviation of the m l residuals obtained by using this curve and the station corrections was 0 21 the data used to derive the equation came from earthquakes with hypocentral distances ranging from about 10 to 700 km and focal depths down to 20 km with most depths less than 10 km the log a 0 values from this equation are similar to the standard values listed in richter 1958 for 50 200 km the effect at close distances is consistent with that found in several other studies and is simply due to a difference in the observed 1 r geometrical spreading for body waves and the 1 r 2 spreading assumed by gutenberg and richter in the construction of the log a 0 table m l s computed from our curve and those reported in the caltech catalog show a systematic dependence on magnitude small earthquakes have larger magnitudes than in the catalog and large earthquakes have smaller magnitudes by as much as 0 6 units to a large extent these systematic differences are due to the nonuniform distribution of data in magnitude distance space small earthquakes are preferentially recorded at close distances relative to large earthquakes for large earthquakes however the difference in the two magnitudes is not solely due to the new correction for attenuation magnitudes computed using richter s log a 0 curve are also low relative to the catalog values the differences in that case may be due to subjective judgment on the part of those determining the catalog magnitudes the use of data other than the caltech wood anderson seismographs the use of different station corrections or the use of teleseismic magnitude determinations whatever their cause the departures at large magnitude may explain a 1 0 0 7 proportionality found by luco 1982 between m l s determined from real wood anderson records and those from records synthesized from strong motion instruments if it were not for the biases in reported magnitudes luco s finding would imply a magnitude dependent shape in the attenuation curves we studied residuals in three magnitude classes 2 0 m l 3 5 3 5 m l 5 5 and 5 5 m l 7 0 and found no support for such a magnitude dependence based on our results we propose that local magnitude scales be defined such that m l 3 correspond to 10 mm of motion on a wood anderson instrument at 17 km hypocentral distance rather than 1 mm of motion at 100 km this is consistent with the original definition of magnitude in southern california and will allow more meaningful comparison of earthquakes in regions having very different attenuation of waves within the first 100 km

reconstructed seismic velocity structure of the lewis hills massif and implications for oceanic fracture zones the lewis hills massif of the bay of islands ophiolite complex provides a lower crustal to upper mantle cross section of an oceanic fracture zone segment and adjacent oceanic lithosphere the structural and petrologic character of the fracture zone region is distinctly different from the comparatively simple layered structure of the rest of the bay of islands complex results of detailed field mapping petrography and laboratory seismic velocity measurements have been combined in order to reconstruct the seismic velocity structure of this slice of oceanic lithosphere velocities and velocity anisotropies of each of the major rock units in the massif are restored to their preobduction geometries relative to different stratigraphic levels in the complex and proximity to the fracture zone region although all oceanic fracture zones probably have unique structural and petrologic characteristics in detail from the perspective of the present study it is suggested that in general seismic properties differing from that of normal oceanic crust and upper mantle may be expected within approximately 10 km of the axis of fracture zones in these regions lower crustal as well as upper mantle anisotropy is expected the moho might be expected to shallow due to the presence of abundant ultramafic cumulates resulting in crustal thinning and significant velocity inversions may occur with depth where large cyclic mafic layers occur within cumulate ultramafics in oceanic lithosphere which has passed or is passing through a transform fault domain enhanced mantle anisotropy might occur the middle to lower crust in these regions should be composed of highly anisotropic metamorphic rocks which grade upward into serpentinites and highly fractured gabbros diabases and basalts with relatively low velocities it is suggested that velocities as well as velocity anisotropies produced by these types of structures might be determined in situ by seismic refraction experiments and may be used to map the extent of deformation in the oceanic lithosphere near fracture zones

the regional geology and evolution of the toba volcano tectonic depression indonesia the late quaternary toba volcano tectonic depression in the sunda arc is the largest resurgent cauldron in the world and lies in one of the largest ignimbrite fields the toba tuffs although composed of at least 3000 km 3 of acid tuffs spread over 20000 km 2 of mainland sumatra the greater part of the toba tuffs is believed to be a single ignimbrite cooling unit formed about 100 000 years ago the toba tuffs also include a 30000 year old airfall tuff which was erupted from a centre just n of the toba depression the toba depression developed through the same stages as other resurgent cauldrons it formed after lithification of the toba tuffs by collapse along regional faults crossing an eastwards bulge in the sumatran geanticline resurgent uplift raised lake sediments within the depression by about 500 m the uplift which was not confined to the depression was probably caused by continuing influx of magma and it is possible that the toba depression is still in the stage of post resurgence volcanism the eruption of the toba tuffs and of all post ignimbrite volcanism took place on the line of the western marginal fault of the depression this marginal fault once extended northwards offshore into a zone of miocene back arc rifting

friction of ice on ice 1 new measurements have been made of the friction coefficient of freshwater polycrystalline ice sliding slowly 5 10 8 to 1 10 3 m s 1 upon itself at temperatures from 98 to 263 k under low normal stresses 98 kpa sliding obeys coulomb s law the shear stress is directly proportional to the normal stress across the interface while cohesion offers little contribution to frictional resistance the coefficient of kinetic friction of smooth surfaces varies from k 0 15 to 0 76 and at elevated temperatures 223 k exhibits both velocity strengthening at lower velocities 10 5 to 10 4 m s 1 and velocity weakening at higher velocities strengthening and weakening are attributed to creep deformation of asperities and localized melting respectively at intermediate temperatures of 173 and 133 k the kinetic coefficient appears to not exhibit significant dependence upon velocity however at the low temperature of 98 k the coefficient of kinetic friction exhibits moderate velocity strengthening at both the lowest and the highest velocities but velocity independence over the range of intermediate velocities no effect was detected of either grain size or texture over the range of roughness 0 4 10 6 m ra 12 10 6 m a moderate effect was detected where k ra0 08 slide hold slide experiments revealed that the coefficient of static friction increases by an amount that scales logarithmically with holding time implications of the results are discussed in relation to shearing across tiger stripe faults within the icy crust of saturn s enceladus sliding of the arctic sea ice cover and brittle compressive failure of cold ice

local earthquake magnitude scale and seismicity rate for the ethiopian rift a calibrated local earthquake magnitude scale is essential for quantitative analyses of seismicity in ethiopia effective monitoring of earthquakes and resulting assessment of seismic hazard are especially important as regions with seismic and volcanic activity coincide with regions of economic significance and population growth we have developed a local magnitude m l scale for the northern main ethiopian rift mer using earthquake data collected during 2001 2003 on 122 three component broadband seismic stations waveform data from 2139 local earthquakes were corrected for instrument response and convolved with the nominal wood anderson torsion seismograph response appropriate for the original definition of local magnitude the hypocentral distances considered are 5 to 800 km with the best represented range from 5 to 150 km a total of 30 908 maximum zero to peak amplitudes awa were incorporated into a direct linear inversion for individual earthquake local magnitudes m l 244 station factors c and 2 linear distance dependent factors n k in the distance correction term log a o of the equation for local magnitude m l log awa log a o c the resulting distance correction is given by log a o 1 196997log r 17 0 001066 r 17 2 which implies that ground motion attenuation is relatively high consistent with ongoing magma intrusion and the presence of shallow magma reservoirs beneath the mer station corrections significantly reduce m l residuals and range between 0 42 m l units the catalog of earthquakes is complete above m l 2 1 and the annual cumulative seismicity rate follows the relation log n 4 5 1 13 m l our results are critical for accurate routine quantitative analysis of past current and future seismicity in ethiopia

transient and steady state creep response of ice i and magnesium sulfate hydrate eutectic aggregates 1 using uniaxial compression creep experiments we characterized the transient and steady state deformation behaviors of eutectic aggregates of system ice i and mgso4 11h2o ms11 meridianiite which has significance because of its likely presence on moons of the outer solar system synthetic samples of eutectic liquid bulk composition which produce eutectic colonies containing 0 35 0 50 volume fraction ms11 were tested as functions of colony size and lamellar spacing temperature 230 250 k and confining pressure 0 1 and 50 mpa to strains 0 2 up to a differential stress of 6 mpa the ice i ms11 aggregates display an order of magnitude higher effective viscosity and higher stress sensitivity than do aggregates of pure polycrystalline ice at the same conditions the creep data and associated microstructural observations demonstrate however that the aggregates are additionally more brittle than pure ice approaching rate independent plasticity that includes rupture of the hydrate phase at 6 8 mpa depending on the scale of the microstructure microstructures of deformed samples reveal forms of semibrittle flow in which the hydrate phase fractures while the ice phase deforms plastically semibrittle flow in the icy shell of a planetary body would truncate the lithospheric strength envelope and thereby decrease the depth to the brittle ductile transition by 55 and reduce the failure limit for compressional surface features from 10 to 6 mpa a constitutive equation that includes eutectic colony boundary sliding and intracolony flow is used to describe the steady state rheology of the eutectic aggregates

joint 3 d tomographic imaging of vp vs and vp vs and hypocenter relocation at sinabung volcano indonesia from november to december 2013 abstract we conducted travel time tomography using p and s wave arrival times of volcanic tectonic vt events that occurred between november and december 2013 to determine the three dimensional 3d seismic velocity structure vp vs and vp vs beneath sinabung volcano indonesia in order to delineate geological subsurface structure and to enhance our understanding of the volcanism itself this was a time period when phreatic explosions became phreatomagmatic and then magma migrated to the surface forming a summit lava dome we used 4846 vt events with 16 138 p and 16 138 s wave arrival time phases recorded by 6 stations for the tomographic inversion the relocated vts collapse into three clusters at depths from the surface to sea level from 2 to 4 km below sea level and from 5 to 8 5 km below sea level the tomographic inversion results show three prominent regions of high vp vs 1 8 beneath sinabung volcano at depths consistent with the relocated earthquake clusters we interpret these anomalies as intrusives associated with previous eruptions and possibly surrounding the magma conduit which we cannot resolve with this study one anomalous region might contain partial melt at sea level and below the eventual eruption site at the summit our results are important for the interpretation of a conceptual model of the plumbing system of this hazardous volcano

rheology of ice ii and ice iii from high pressure extrusion rheological parameters for ice ii and ice iii needed in tectonic models of the icy satellites of the major planets are obtained from extrusion experiments and compared with the rheology of ice i at pressures 2 kbar and temperatures 240k ice ii has a higher effective viscosity by a factor 10 than ice i at similar stress levels whereas ice iii has a lower viscosity by a factor 0 01 the rheological contrasts among the ice phases are related to differences in the dielectric relaxation behavior and state of proton order disorder in the structures in a way that sheds light on the nature of dislocation motion in ice a striking transformation plasticity accompanies the ice i iii transition and could have large tectonic effects

a process based model of pre eruption seismicity patterns and its use for eruption forecasting at dormant stratovolcanoes abstract using long term data sets the eruptive size timing and style can typically be successfully forecast for dormant volcanoes using current monitoring data and knowledge of precursory eruptive patterns the usaid usgs volcano disaster assistance program vdap utilizes seismic data over multiple eruption cycles and across volcano types to successfully forecast eruption size style and onset times as well as changes within ongoing eruptions from millions of seismic event observations we show that seismic data a proxy for rate dependent strain changes in the magmatic system combined with a process based conceptual geologic model enables eruption forecasting especially for stratovolcanoes dormant 20 years we show that this model often works for some open systems ones that sufficiently reseal to plug the conduit and also where a deep intrusion occurs after phreatic or phreatomagmatic explosions have begun this model is divided into four seismicity and geologic stages we describe each of the four stages of seismicity in detail and how they relate to the ongoing geologic process of that stage stage 1 deep intrusion and seismicity occurring at 10 to 40 km depth below the volcanic edifice stage 2 distal vt seismicity induced at distances from 2 to 30 km laterally from the summit by magma intruding into and inflating the upper crustal magma storage region stage 3 vent clearing seismicity associated with the initial vent creation and clearing phase of eruptive activity stage 4 repetitive event seismicity associated with the final ascent of magma from 2 km to the surface we present 36 examples of this seismic progression from 26 volcanoes we believe that this progression generally correlates with the magma flux and the eventual explosivity and is invaluable for forecasting eruptions

local and duration magnitudes in northwestern italy and seismic moment versus magnitude relationships in the present work we develop some local magnitude scales for northwestern italy based on vertical short period records this study is motivated by the possibility of applying the computed scales to an instrumental catalog of more than 25 000 local earthquakes as this region has been continuously monitored by 12 short period vertical component 1c stations since the mid 1980s furthermore a digital network of three component 3c broadband or 5 second sensors has monitored northwestern italy since 1996 today a significant number of earthquakes have been simultaneously recorded by both networks allowing the calibration of the 1c local scale by using magnitudes computed according to a scale derived for the 3c digital network moreover because station sant anna di valdieri houses both a 3c code stv2 and 1c code stv sensors the magnitude scales for the two networks can be developed using the same reference station the magnitude scale m l log a log r 100 0 0054 r 100 3 s is derived for the 3c digital network with the requirement that the correction s of station stv2 is zero this scale is based on 10 057 maximum amplitudes 2822 earthquakes computed from horizontal synthesized wood anderson seismograms in the hypocentral distance 10 to 310 km and in the range 0 m l 5 with respect to an carlier magnitude scale derived for the 3c network constraining the sum of all the station corrections to zero the magnitudes predicted by the previous equations show an average bias of 0 2 0 1 which can be ascribed to the different constraint applied to the station corrections the magnitudes predicted by the scale for the 3c network are used to calibrate magnitude scales based on either total duration or maximum amplitude from synthesized wood anderson seismograms computed for each short period vertical recording the magnitude scale obtained considering maximum amplitudes from vertical short period recordings is m l log a log r 100 0 0041 r 100 3 s the reliability of the obtained magnitude scales is assessed using 827 earthquakes different from those we considered in the regression analysis finally the following seismic moment versus local magnitude relations are valid in the western alps in the range 0 where m l3c is the local magnitude computed starting from the horizontal component of broadband flat frequency response from 0 033 to 50 hz or semibroadband flat frequency response from 0 2 to 40 hz sensors and m l1c is the magnitude computed starting from the vertical short period recordings 1 embed graphic 1 gif

lateral variation in slab orientation beneath toba caldera northern sumatra the investigator fracture zone ifz subducts beneath toba caldera the earth s largest quaternary caldera in northern sumatra suggesting a possible relationship between them locations of sub crustal earthquakes based on arrival times of p and s waves at a seismograph network surrounding toba reveal the geometry of the subducted slab and the ifz beneath toba a vertical tear of less than 20 km in the slab across the ifz as previously suggested cannot be ruled out but the large scale geometry of the slab is dominated by a broad bend of slab contours parallel to the concaveseaward indentation of the trench the slab shape is probably a response to the trench curvature can explain the change in trend of the volcanic arc near toba and may cause shallowing of the forearc basin near nias island the decrease in radius of curvature of the slab contours is not accompanied by an observable decrease in dip angle possibly resulting in lateral compressive stress in the slab the high rate of seismicity along the subducted investigator fracture zone that intersects the slab obliquely to its plunge direction is uncommon at subducted fracture zones and is likely caused by such lateral stress in the slab

differences in the seismicity preceding the 2007 and 2014 eruptions of kelud volcano indonesia abstract a significant increase in the number of volcano tectonic vt and vb earthquakes preceded the 2007 and 2014 eruptions of kelud volcano indonesia the background seismicity rates at the volcano is generally

southern california hypocenter relocation with waveform cross correlation part 1 results using the double difference method we present the results of relocating 327 000 southern california earthquakes that occurred between 1984 and 2002 we apply time domain waveform cross correlation for p and s waves between each event and 100 neighboring events identified from the catalog based on a 3d velocity model to simplify the computation we first divide southern california into five polygons such that there are 100 000 events or less in each region the polygon boundaries are chosen to lie in regions of sparse seismicity we calculate and save differential times from the peaks in the cross correlation functions and use a spline interpolation method to achieve a nominal timing precision of 0 001 sec these differential times together with existing p and s phase picks are input to the double difference program of waldhauser and ellsworth 2000 2002 to calculate refined hypocenters we divide the southern california region into grid cells and successively relocate hypocenters within each grid cell the overall resulting pattern of seismicity is more focused than the previously determined pattern from 1d or 3d models the new improved locations are more clustered in many cases by a factor of two or three and often show clear linear alignments in particular the depth distribution is improved and less affected by layer boundaries in velocity models or other similar artifacts

crustal seismicity associated to rpid surface uplift at laguna del maule volcanic complex southern volcanic zone of the andes abstract laguna del maule volcanic complex lmvc southern andes of chile has been experiencing large rates ca 30 cm yr of surface uplift as detected since 2008 by satellite geodetic measurements previous works have modeled the source of this deformation as an inflating rectangular sub horizontal sill underlying lmvc at 5 km depth which is supposedly related to an active process of magmatic replenishment of a shallow silicic reservoir however little is known about the tectonic context on which this activity is taking place particularly its relation with crustal seismicity that could help understanding and monitoring the current deformation process here we present the first detailed characterization of the seismic activity taking place at lmvc and integrate it with structural data acquired in the field in order to illuminate the possible connection between the ongoing process of surface uplift and the activation of crustal faults our main finding is the recognition of repetitive volcano tectonic vt seismic swarms that occur periodically between 2011 and 2014 near the sw corner of the sill modeled by insar studies a cross correlation analysis of the waveforms recorded for these vt events allows identifying three different seismic families families f1 and f3 share some common features in the stacked waveform and its locations which markedly differ from those of family f2 swarms belonging to this later family are more energetic and its energy was increasing since 2011 to a peak in january 2013 which coincide with maximum vertical velocities detected by local gps stations this points to a common process relating both phenomena the location of vt seismic swarms roughly coincides with the intersection of a ne sw lineament with a wnw ese lineament the former shows clear field evidences of dextral strike slip that are fully consistent with one nodal plane of focal mechanism for well recorded f2 events the conjugate nodal plane of these focal mechanisms could coincide with the wnw ese lineament for which our field reconnaissance suggests a dominant normal motion events belonging to families f1 and f3 are also dominantly strike slip but with some mixture with thrust and normal components our results in conjunction with results of previous authors suggest a complex mechanical interaction between the arrangement of crustal faults forming the structural framework on which the magmatic plumbing system of lmvc is emplaced and the inflating source at depth

water ice phases ii iii and v plastic deformation and phase relationships several of the high pressure crystalline forms of ice exist in the interiors of the larger icy moons of the outer planets guided by the phase relations established by bridgman 75 years ago we have transformed ordinary water ice i to ices ii iii v and perhaps vi we subsequently deformed those phases in a gas deformation apparatus designed for these experiments we found ice ii to be the strongest of the high pressure phases having a strength roughly comparable to that of ice i ice ii is very weak at fixed levels of stress ice iii flows 10 sup 2 10 sup 3 times faster than ice ii we confirm bridgman s 1912 findings that ices iii and v can exist metastably within the ice ii field and in addition find that these phases may be deformed plastically within much of the metastable region without reverting to ice ii the most persistent metastable existence of ice iii occurs in the warmer portions of the ice ii field through which historical and present day temperature pressure profiles in the icy moons pass thus although the stability field of ice iii is small the weakness of this phase may have profoundly influenced the evolution and present day behavior of themore icy moons less

surface displacements on faults triggered by slow magma transfers between dyke injections in the 2005 2010 rifting episode at dabbahu manda hararo rift afar ethiopia the rifting episode that occurred in dabbahu manda hararo ethiopia between 2005 and 2010 during which 14 dyke intrusions were emitted was a unique opportunity to study interactions between tectonic deformation and magmatic processes while magmatism has been shown to control primarily the spatial and temporal distribution of dyke intrusions during this accretion sequence the role of faults in accommodating plate spreading in rift segments is poorly understood during interdyking periods transient ground deformation due to magma movement is generally observed investigating such a small scale deformation and in particular the movement along faults during these periods will help understanding the factors that trigger fault movement in magmatic rifts we analyse fault activity during three interdyking periods 2006 december june d0 d1 2007 january july d5 d6 and 2009 november january d10 d11 the time space evolution of surface displacements along 700 faults is derived from pairs of ascending and descending sar interferograms surface slip distributions are then compared with codyking ground deformation fields the results show that faults are mainly activated above the areas affected by magma emplacement during interdyking periods a detailed analysis of brittle deformation during the six months following the 2005 september intrusion shows asymmetric deformation on the rift shoulders with significant opening on faults located to the west of the dyke we explain this feature by the activation of westward dipping pre existing faults with block rotations in between in addition we observe that the strip encompassing the activated faults narrows by 30 per cent from co to interdyking period this suggests that magma keeps migrating to shallower depths after the dyke intrusion during a rifting episode activation of faults in a pre existing fracture network therefore seems to be mainly controlled by deep magma processes

local magnitude discrepancies for near event receivers implications for the u k traffic light scheme local seismic magnitudes provide a practical and efficient scale for the implementation of regulation designed to manage the risk of induced seismicity such as traffic light schemes tls we demonstrate that significant magnitude discrepancies up to a unit higher occur between seismic events recorded on nearby stations 5 km compared with those at greater distances this is due to the influence of sedimentary layers which are generally lower in velocity and more attenuating than the underlying crystalline basement rocks and requires a change in the attenuation term of the m l scale this has a significant impact on the united kingdom s u k hydraulic fracturing tls whose red light is set at m l 0 5 because the nominal detectability of the u k network is m l 2 this scheme will require the deployment of monitoring stations in close proximity to well sites using data collected from mining events near new ollerton nottinghamshire we illustrate the effects that proximity has on travel path velocities and attenuation then perform a damped least squares inversion to determine appropriate constants within the m l scale we show that the attenuation term needs to increase from 0 00183 to 0 0514 and demonstrate that this higher value is representative of a ray path within a slower more attenuating sedimentary layer compared with the continental crust we therefore recommend that the magnitude scale m l log a 1 17log r 0 0514 r 3 0 should be used when local monitoring networks are within 5 km of the event epicenters

volcano tectonic earthquakes a new tool for estimating intrusive volumes and forecasting eruptions abstract we present data on 136 high frequency earthquakes and swarms termed volcano tectonic vt seismicity which preceded 111 eruptions at 83 volcanoes plus data on vt swarms that preceded intrusions at 21 other volcanoes we find that vt seismicity is usually the earliest reported seismic precursor for eruptions at volcanoes that have been dormant for decades or more and precedes eruptions of all magma types from basaltic to rhyolitic and all explosivities from vei 0 to ultraplinian vei 6 at such previously long dormant volcanoes because large eruptions occur most commonly during resumption of activity at long dormant volcanoes vt seismicity is an important precursor for the earth s most dangerous eruptions vt seismicity precedes all explosive eruptions of vei 5 and most if not all vei 4 eruptions in our data set surprisingly we find that the vt seismicity originates at distal locations on tectonic fault structures at distances of one or two to tens of kilometers laterally from the site of the eventual eruption and rarely if ever starts beneath the eruption site itself the distal vt swarms generally occur at depths almost equal to the horizontal distance of the swarm from the summit out to about 15 km distance beyond which hypocenter depths level out we summarize several important characteristics of this distal vt seismicity including swarm like nature onset days to years prior to the beginning of magmatic eruptions peaking of activity at the time of the initial eruption whether phreatic or magmatic and large non double couple component to focal mechanisms most importantly we show that the intruded magma volume can be simply estimated from the cumulative seismic moment of the vt seismicity from log10 v 0 77 log moment 5 32 with volume v in cubic meters and seismic moment in newton meters because the cumulative seismic moment can be approximated from the size of just the few largest events and is quite insensitive to precise locations the intruded magma volume can be quickly and easily estimated with few short period seismic stations notable cases in which distal vt events preceded eruptions at long dormant volcanoes include nevado del ruiz 1984 1985 pinatubo 1991 unzen 1989 1995 soufriere hills 1995 shishaldin 1989 1999 tacana 1985 1986 pacaya 1980 1984 rabaul 1994 and cotopaxi 2001 additional cases are recognized at frequently active volcanoes including popocateptl 2001 2003 and mauna loa 1984 we present four case studies pinatubo soufriere hills unzen and tacana in which we demonstrate the above mentioned vt characteristics prior to eruptions using regional data recorded by neic we recognized in near real time that a huge distal vt swarm was occurring deduced that a proportionately huge magmatic intrusion was taking place beneath the long dormant sulu range new britain island papua new guinea that it was likely to lead to eruptive activity and warned rabaul volcano observatory days before a phreatic eruption occurred this confirms the value of this technique for eruption forecasting we also present a counter example where we deduced that a vt swarm at volcan cosiguina nicaragua indicated a small intrusion insufficient to reach the surface and erupt finally we discuss limitations of the method and propose a mechanism by which this distal vt seismicity is triggered by magmatic intrusion

analysis of the seismic activity associated with the 2010 eruption of merapi volcano java abstract the 2010 eruption of merapi is the first large explosive eruption of the volcano that has been instrumentally observed the main characteristics of the seismic activity during the pre eruptive period and the crisis are presented and interpreted in this paper the first seismic precursors were a series of four shallow swarms during the period between 12 and 4 months before the eruption these swarms are interpreted as the result of perturbations of the hydrothermal system by increasing heat flow shorter term and more continuous precursory seismic activity started about 6 weeks before the initial explosion on 26 october 2010 during this period the rate of seismicity increased almost constantly yielding a cumulative seismic energy release for volcano tectonic vt and multiphase events mp of 7 5 10 10 j this value is 3 times the maximum energy release preceding previous effusive eruptions of merapi the high level reached and the accelerated behavior of both the deformation of the summit and the seismic activity are distinct features of the 2010 eruption the hypocenters of vt events in 2010 occur in two clusters at of 2 5 to 5 km and less than 1 5 km depths below the summit an aseismic zone was detected at 1 5 2 5 km depth consistent with studies of previous eruptions and indicating that this is a robust feature of merapi s subsurface structure our analysis suggests that the aseismic zone is a poorly consolidated layer of altered material within the volcano deep vt events occurred mainly before 17 october 2010 subsequent to that time shallow activity strongly increased the deep seismic activity is interpreted as associated with the enlargement of a narrow conduit by an unusually large volume of rapidly ascending magma the shallow seismicity is interpreted as recording the final magma ascent and the rupture of a summit dome plug which triggered the eruption on 26 october 2010 hindsight forecasting of the occurrence time of the eruption is performed by applying the material failure forecast method ffm using cumulative real time seismic amplitude rsam calculated both from raw records and on signals classified according to their dominant frequency stable estimates of eruption time with errors as small as 4 h are obtained within a 6 day lapse time before the eruption this approach could therefore be useful to support decision making in the case of future large explosive episodes at merapi

seismic energy release in mexican subduction zone earthquakes we estimated radiated seismic energy es from 18 shallow thrust mexican subduction zone earthquakes 4 1022 m 1 1 1028 dyne cm 11 h 37 km using digital accelerograms from the guerrero accelerograph array and neglecting stations with large site effects es is computed by integrating squared velocity spectra after applying geometrical spreading and q corrections we discarded epicentral recordings for the largest michoacan event we find that log es m 4 152 0 275 which gives a median value of es m and apparent stress a of 7 1 10 5 and 24 bars respectively the median es m value is in accordance with gutenberg and richter s g r 1956 formula for es in which es m 5 10 5 is implicit worldwide es m data where es is computed from local records mostly fall between 5 10 5 and 5 10 4 for events with m 1022 dyne cm on the other hand es m values generally lie between 5 10 6 and 5 10 5 if es is estimated from teleseismic records especially anomalous are the es m data from kikuchi and fukao 1988 for large and great earthquakes which fall near 5 10 6 thus while es from local data suggests that the g r relation seldom overestimates seismic energy release the teleseismic data point to the contrary the cause of this discrepancy may lie in the difficulty of resolving incoherent radiation from the fault and inappropriate choice of t in the analysis of teleseismic data

small scale models of multiring basins small scale sand silicone simulations of multiring impact structures have been undertaken in order to understand the effects of the rheology of the lithosphere on the variability of natural multiring structures for low sand silicone thickness ratio 1 3 brittle strain is accommodated by spiral strike slip faults for higher sand silicone ratios 1 1 or 2 1 an inner concentric ring affected by strike slip faults is relayed by an external ring affected by concentric normal faults the diameter of the inner ring decreases with the increase of the sand silicone thickness ratio it is suggested that the flexure of the brittle layer due to the silicone flow is responsible for the brittle strain field which is enhanced by the channel flow of the lower crust the characteristic geometry of the intersection of conjugated strike slip faults can be observed around large multiring basins on silicate crust such as orientale on the moon and on icy crust such as valhalla on callisto and gilgamesh on ganymede the strain field around these large craters is discussed in terms of mechanical properties of the lithospheres on the moon large craters without relaxation faults such as imbrium are located on thin crust regions the crust was too thin to have a ductile lower layer at the time of impact gilgamesh on ganymede is surrounded mainly by strike slip faults asgard on callisto has the same diameter as gilgamesh but is surrounded by concentric normal faults the brittle ductile thickness ratio is thus higher on callisto than on ganymede

two dimensional seismic reflection modeling of the inferred fossil oceanic crust mantle transition in the bay of islands ophiolite we investigate the origin and character of oceanic moho reflections by computing two dimensional synthetic seismogram profiles of the inferred fossil oceanic crust mantle transition observed in the bay of islands ophiolite to simulate a seismic reflection experiment we calculated near vertical incidence seismograms at a horizontal spacing of 500 m for three separate sections of the ophiolite totaling 64 km in length in the synthetic profiles the moho reflection event varies from a single phase to two or more phases of up to 1 s two way travel time total duration individual phases show lateral variation in amplitude and their two way travel times vary by as much as 0 25 s over horizontal distances as short as 10 km lateral discontinuity of phases results in abrupt variations in the travel times of first arriving high amplitude moho phases the geological structures generating the highest amplitude moho reflections vary from high and low velocity lenses of mafic and ultramafic material in the lower crust and upper mantle to interlayered mafic and ultramafic lithologies in the moho transition zone reflection amplitudes from the residual upper mantle are insignificant and our modeling suggests that using the first arriving high amplitude moho phase to estimate thickness of magmatic material might result in errors of up to 1 s two way travel time 3 4 km multichannel seismic data from both the western pacific and western north atlantic show moho travel time variations similar to those observed in the synthetic profiles the western north atlantic data also show multiphase moho reflection events that are laterally discontinuous on a scale similar to that observed in the synthetic data suggesting that the structures observed in the inferred fossil crust mantle transition of the ophiolite are characteristic of oceanic lithosphere

3 d seismic tomographic study of sinabung volcano northern sumatra indonesia during the inter eruptive period october 2010 july 2013 abstract we estimated 3d p wave velocity vp s wave velocity vs and vp vs tomographic structures in and around the sinabung volcano area northern sumatra indonesia during the intereruptive period between october 2010 and july 2013 using high quality p and s wave phases from 600 local volcano tectonic vt earthquakes and 5000 phase picks we used the iterative damped least squares method of simulps12 to simultaneously invert for the velocity structure and hypocenter relocations we find that the majority of the vt earthquakes locate beneath sinabung volcano to depths of about 8 km with distal hypocenters dominantly to the north and northwest of the summit we find six anomalous regions with the most notable including an area of low seismicity high vp vs and low vp at depths of around 5 km slightly south of the summit we believe this anomaly most likely represents hot material with some partial melt that may be the source for the 2010 phreatic eruptions and continued unrest throughout the study period we also find a region below the summit with high seismicity high vp high vs and low vp vs that we believe likely represents old intrusive material that has been fractured by the processes of the 2010 phreatic eruptions other shallow anomalous values of vp vs and vp vs are consistent with the known geology of sinabung anomalies of high vp and vs likely represent old well consolidated rock and are observed to the sw and ne of sinabung while low vp low vs and high vp vs likely represent increased fracture densities temperatures or gas contents in geothermal features to the west of the summit finally we compare our results to those of the tomographic study of the october to november 2013 eruptive period in nugraha et al 2019 and find evidence that suggests magma rose from the lower region imaged in our study to within a few kilometers of the surface

creep of water ices at planetary conditions a compilation many constitutive laws for the flow of ice have been published since the advent of the voyager explorations of the outer solar system conflicting data have occasionally come from different laboratories and refinement of experimental techniques has led to the publication of laws that supersede earlier ones in addition there are unpublished data from ongoing research that also amend the constitutive laws here we compile the most current laboratory derived flow laws for water ice phases i ii iii v and vi and ice i mixtures with hard particulates the rheology of interest is mainly that of steady state and the conditions reviewed are the pressures and temperatures applicable to the surfaces and interiors of icy moons of the outer solar system advances in grain size dependent creep in ices i and ii as well as in phase transformations and metastability under differential stress are also included in this compilation at laboratory strain rates the several ice polymorphs are rheologically distinct in terms of their stress temperature and pressure dependencies but with the exception of ice iii have fairly similar strengths hard particulates strengthen ice i significantly only at high particulate volume fractions ice iii has the potential for significantly affecting mantle dynamics because it is much weaker than the other polymorphs and its region of stability which may extend metastably well into what is nominally the ice ii field is located near likely geotherms of large icy moons

the origin of volcano tectonic earthquake swarms volcano tectonic vt seismicity is commonly recorded prior to and during eruptions vt seismicity may reflect stresses induced by dike propagation as indicated by propagating hypocenters and fault plane solutions fps reflecting regional stresses or stresses induced by dike inflation indicated by randomly distributed hypocenters and fps with pressure axes rotated 90 to regional maximum compression although numerical models of dike induced stresses indicate that both regimes should occur during dike emplacement this has not yet been observed according to published seismic data instead 90 rotated fps are observed in some cases while propagating hypocenters mark dike formation in other cases we suggest that differences in the seismic expression of upper crustal magma migration may result from differences in the regional tectonic setting and in the nature of magma wall rock interactions ultimately it may be possible to use information contained in vt seismicity to forecast changes in a volcano s behavior by establishing the characteristic stress field response for a given volcano or through a deeper understanding of the complex relationships between vt seismicity local crustal stresses and the physical mechanisms of magma migration

differences of precursory seismic energy release for the 2007 effusive dome forming and 2014 plinian eruptions at kelud volcano indonesia abstract early warnings of the timing style and size of volcanic eruptions made on the basis of seismic monitoring are important for mitigation of the hazards associated with volcanic eruptions we calculated the rates of seismic energy release at kelud volcano indonesia preceding both the 2007 effusive lava dome eruption and the 2014 plinian eruption for the 2007 eruption there was first a step wise increase in the rate of release of seismic energy followed by a gradual decrease until the eruption for the 2014 eruption the rate of energy release was almost constant until 10 days before the eruption then gradually increased until there was a dramatic acceleration during the last day before the eruption the total seismic energy released by the 2007 and 2014 eruptions were 3 10 8 j and 2 2 10 9 j respectively the relative difference between the ejected volumes of the 2007 and 2014 eruptions is roughly equivalent to that of the total seismic energy released preceding the eruptions we conducted several trials of the material failure forecast method ffm applying it to the square root of the rate of seismic energy released to assess its usefulness for predicting the timing of eruptions the predicted onset of the 2007 eruption was one day earlier than the actual eruption and the seismic energy release preceding the actual eruption did not increase dramatically as suggested by the ffm model several trials of ffm for the 2014 eruption predicted the onset of the eruption to be three days to two weeks later than the actual eruption even as the end time of the ffm time window approaches several hours to 10 min before the actual eruption onset the predicted eruption onset is still 3 h later than the actual onset thus the results of our ffm modeling did not show the method to be useful for predicting eruption times for kelud volcano the differences of the ffm modeling results for the 2007 and 2014 eruptions likely reflect the differences in the rate of energy release immediately before the two eruptions a deceleration before the 2007 eruption and an acceleration before the 2014 eruption these differences may reflect differences in precursory processes for effusive lava dome and plinian eruptions

local magnitude coda magnitude and radiated energy of volcanic tectonic earthquakes from october 2010 to december 2011 at sinabung volcano indonesia in august 2010 sinabung volcano began erupting after more than a thousand years of dormancy following several weeks of phreatic eruptions the eruptions ceased and sinabung entered what became an inter eruptive period of dominantly seismic unrest while standard equations for understanding the size of an earthquake local magnitude ml coda magnitude mc and seismic energy release er have long been developed it is best practice to fine tune these relations for a given region and period of study to more accurately describe seismicity and to directly compare it with other volcanic systems more accurate descriptions of magnitudes and energy release are vital to accurate volcanic eruption forecasting and evaluation of seismic and volcanic risk in this study we use high frequency volcano tectonic vt earthquakes recorded on a temporary three component network installed between october 2010 and december 2011 in the region around sinabung volcano to better constrain the seismic parameters of and better understand this previously unstudied volcano we determine region specific formulas for ml mc and er as follows mathrm m mathrm l log 10 a 1 1252 log 10 r 0 0280 r 2 5427 kern0 5em mathrm m mathrm c 0 7764 log 10 t coda 0 0676 r 0 7185 kern0 5em mathrm and kern0 5em log 10 left mathrm e mathrm r right 1 5720 mathrm m mathrm l 11 5258 where a r and tcoda are maximum amplitude on a wood anderson seismogram hypocentral distance km and the coda duration s respectively constants in the ml equation have physically interpretable meanings the constant for the geometrical spreading term log10r term equals one for perfect spherical spreading of the waveform our value is greater than one and thus suggests that wavefronts spread at a slightly different rate than for simple spherical spreading the constant for the attenuation term r term is consistent with locally mapped attenuative deposits limestones and tuffs and previous 3d tomographic results our mc equation differs from a previous study likely because different data in a different time period were used earthquake hypocenters are consistent with those located in previous tomographic studies and we interpret the earthquakes in this study as distal vt earthquakes induced by continued magmatic intrusion at sinabung over the period of october 2010 december 2011

site effect evaluation using spectral ratios with only one station the spectral ratio technique is a common useful way to estimate empirical transfer function to evaluate site effects in regions of moderate to high seismicity the purpose of this paper is to show that it is possible to estimate empirical transfer function using spectral ratios between horizontal and vertical components of motion without a reference station the technique originally proposed by nakamura to analyze rayleigh waves in the microtremor records is presented briefly and it is discussed why it may be applicable to study the intense s wave part in earthquake records results are presented for three different cities in mexico oaxaca oax acapulco gro and mexico city these cities are very different by their geological and tectonic contexts and also by the very different epicentral distances to the main seismogenic zones affecting each city each time we compare the results of nakamura s technique with standard spectral ratios in all three cases the results are very encouraging we conclude that if site effects are caused by simple geology a first estimate of dominant period and local amplification level can be obtained using records of only one station

overview of the eruptions of sinabung volcano 2010 and 2013 present and details of the 2013 phreatomagmatic phase abstract a small phreatic eruption of sinabung volcano north sumatra on 28 august 2010 at 18 30 local time marked the first eruption in the past 1200 years the eruption took place from two small vents in the south crater area explosions and ash emissions from these vents generated multiple ash plumes that reached altitudes of up to 5 km during early to mid september by the end of september 2010 only low level steam plumes were visible and the alert level was reduced from level 4 highest to level 3 the 2010 eruption effectively ended at this time beginning two days after the initial 2010 eruption activity of the eruption has been monitored continuously by a telemetered seismic network surrounding the volcano and by remotely sensed observations this monitoring system was supplemented with a near field continuous gps network beginning in february 2011 persistent fumarolic emissions continued for almost 3 years following the 2010 eruption before a new eruption began on 15 september 2013 this eruption continues to the present the ongoing eruption is divided into 5 major phases 1 phreatomagmatic phase july 2013 18 december 2013 2 first dome and collapse phase with pyroclastic density currents pdcs block and ash flows and related surges to south 18 december 2013 10 january 2014 3 lava flow and collapse phase 10 january 2014 mid september 2014 4 second lava dome and collapse phase with pdcs to south mid september 2014 july 2015 5 lava dome collapse and ash explosion phase with pdcs to southeast and east august 2015 present the volcano erupted intermittently during the early phreatomagmatic phase with small vertical ash explosions then the eruption became increasingly vigorous with more repetitive and intense vertical ash explosions during late october through november the first small pyroclastic density currents pdcs began on november 1 these pyroclastic flows descended the southeastern flank to a distance of 2 km swarms of volcano tectonic vt earthquakes and volcanic tremor lasting hours occurred repeatedly during the phreatomagmatic phase and some of these vt swarms were followed by explosions in early december 2013 during the transition between phreatomagmatic and dome collapse phases swarms of hybrid earthquakes took place preceding and accompanying dome growth the first lava dome was observed in satellite images on 18 december near the main crater rim partial collapses of the dome produced pdcs beginning on 30 december growth of this first lava dome continued into january and was accompanied by additional collapses and pdcs by about 10 january the lava had transitioned from a summit dome morphology into a lava flow morphology the resulting lava flow descended the southeast flank of the volcano producing flow front and marginal collapses with associated pcds one such flow flank collapse on 2 february 2014 resulted in a pcd that killed 16 the lava flow phase continued through mid september 2014 when a second summit lava dome began to grow and collapse producing pdcs initially to the south and southeast and then beginning in july 2015 to the east and southeast the eruption of sinabung resulted in major impacts on the population of the resort and farming area near the volcano and in the ginting and karo regencies of north sumatra local residents having not experienced eruptions in their lifetimes were initially curious and eager to receive any information about the eruption regardless of its source various institutions provided information with little coordination resulting in confusion with time communications have improved and communities and the responsible governments have become better prepared in dealing with the persistent eruption the government of indonesia has provided funding to support villagers who lived within a 5 km radius danger zone to stay in relocation camps as a permanent relocation area is being identified unfortunately on 21 may 2016 9 additional fatalities took place in the village of gamber within the danger zone when a dome collapse sent a pyroclastic density current into the area throughout the eruption the volcano has been monitored by the indonesian center for volcanology and geologic hazard mitigation cvghm in partnership with the usgs usaid volcano disaster assistance program and the disaster prevention research institute of kyoto university monitoring techniques have included seismic geodetic gas satellite and field observations as well as occasional sampling of ash and lava for geochemical analyses in this paper we summarize key aspects of the monitoring data their interpretations and their use in forecasting eruptive behavior and in issuance of alerts and warnings more detailed interpretations of the monitoring data and their use are found in other papers of this special issue

relocation and focal mechanisms of earthquakes in the south central sector of the aeolian archipelago new structural and volcanological insights abstract to recognize possible spatial clusters and identify active seismogenic zones and structures in the aeolian archipelago in the south of italy we analyzed the spatial pattern of seismicity between 1993 and 2010 in a selected area comprising vulcano lipari salina and filicudi and calculated 22 fault plane solutions fpss for shocks with magnitude greater than 2 7 first we computed a 1 d velocity model for this area including information from recorded earthquakes by a joint hypocenter velocity inversion kissling et al 1994 successively we applied the double difference approach of waldhauser and ellsworth 2000 finding that a certain part of the scattered epicenter locations collapse in roughly linear features relocated seismicity evidenced three main alignments oriented nnw sse and ne sw at different depths that concur well with the known tectonic lineaments and focal mechanisms a detailed discussion is focused on a seismogenetic structure ne sw oriented 3 8 km deep located in the northern area of vulcano island this recognized element could represent a link between magma accumulation zones thus representing a possible preferential pathway along which magma may intrude two earthquake clusters located south west and east of vulcano with their focal mechanisms highlight the aeolian tindari letojanni fault system seismic activity and the existence of a transitional zone going from the n s compressive domain that dominates the aeolian islands to the nw se extensional domain characterizing the south eastern tyrrhenian

seismicity of the bora tullu moye volcanic field 2016 2017 the bora tullu moye tm volcanic field is a geothermal energy prospect in the central main ethiopian rift but little is known about the seismicity of the region here we document seismic activity between february 2016 and october 2017 locating more than a 1 000 seismic events of local magnitude 0 to 2 7 this provides new insights into fluid movement and deformation beneath what we only now realize is a complicated volcanic system a discrete cluster of events lies beneath tm but surprisingly most of the seismicity lies in two clusters that are beneath neither the bora or tm edifices in these regions we use earthquake cluster orientations fault plane solutions and fast seismic shear wave orientations to show that seismicity is triggered by hydrothermal circulation of fluids along preexisting fractures the fractures trend in multiple directions and are in general not parallel to rifting related structures instead the fractures are parallel to structures created during previous caldera forming eruptions at both bora and tm highly fractured regions such as this could be attractive targets for geothermal power generation we estimate a minimum depth for a magmatic body beneath tm to be 6 5 km using the mapped brittle ductile transition frequency analysis of the earthquake waveforms reveal the bulk of the events to be volcano tectonic but some low frequency seismicity is present at a depth of 5 km beneath the tm edifice triggered by high pore fluid pressures

seismic evidence for hydrothermally altered mantle beneath old crust in the tydeman fracture zone abstract to study the structure of old atlantic fracture zones seismic refraction profiles were obtained using ocean bottom seismometers and two ship multichannel expanding spread experiments on two inactive sections of the tydeman fracture zone the results indicate that a crustal seismic velocities are low compared with normal oceanic crust b there is a marked absence of an identifiable layer 3 c the depth to the moho is shallow though not exceptionally so and d anomalously low seismic velocities of 7 2 7 5 km s 1 are observed over ranges at which upper mantle velocities are normally detected s wave arrivals corresponding to both crustal and mantle refractions are also observed which enable the first estimates of poisson s ratio within a fracture zone to be made using these results and those from other surveys we show that the seismic velocity in the upper mantle beneath fracture zones decreases systematically with increasing age these findings suggest that hydrothermal circulation which can lower the upper mantle velocity by serpentinization persists under fracture zones for at least 70 ma and occurs at greater depths than for normal oceanic crust the serpentinization process is not sufficiently rapid to obscure the location of the original crust mantle boundary

the tectonic framework of the sumatran subduction zone the great aceh andaman earthquake of december 26 2004 and its tragic consequences brought the sumatran region and its active tectonics into the world s focus the plate tectonic setting of sumatra has been as it is today for tens of millions of years and catastrophic geologic events have likely been plentiful the immaturity of our understanding of great earthquakes and other types of geologic hazards contributed to the surprise regarding the location of the 2004 earthquake the timing however is probably best understood simply in terms of the inevitability of the infrequent events that shape the course of geologic progress our best hope is to improve understanding of the processes involved and decrease our vulnerability to them

ground motion amplification at rock sites across canada as determined from the horizontal to vertical component ratio we determine the frequency dependent amplification inherent in hard rock sites across canada under the assumption that it can be estimated from the ratio of the horizontal to vertical h v components of ground motion the use of h v as an estimate of amplification was originally proposed by nakamura 1989 for microtremors and then generalized to earthquake ground motions by lermo and chavez garcia 1993 the h v method was applied to a fourier spectra database compiled from 424 earthquakes of magnitude greater than or equal to 2 recorded on 32 three component stations of the canadian national seismograph network cnsn all sited on rock shear wave velocity 1500 m sec in each case we analyzed the s wave portion of the seismograms including the direct s and other strong s phases such as lg the average amplification h v for rock sites does not vary significantly across the country it is weakly frequency dependent increasing from a factor near unity at 0 5 hz to a maximum in the range from 1 2 to 1 6 at 10 hz this amplification is consistent with what would be expected from a gradual decrease in shear wave velocity as the seismic waves approach the surface due to factors such as near surface weathering the interpretation of the h v ratio as a measure of site response is consistent with the general geological conditions of the recording sites in particular the 5 hz h v ratio can be correlated with local geological conditions the central canada sites have the lowest estimated site amplification this is consistent with competent hard rock site conditions with high near surface shear wave velocities there are two stations that show anomalous h v ratios that suggest significant local site effects these are edm near edmonton which may be influenced by topographic amplification and a61 a station in the charlevoix seismic zone

effect of strain rate cycling on microstructures and crystallographic preferred orientation during high temperature creep strain rate histories and strain magnitude are two crucial factors governing the evolution of dynamic recrystallized grain size and crystallographic preferred orientation cpo in rocks and ice masses to understand the effect of cyclic variations in strain rate or non steady state deformation we conducted two dimensional coaxial plane strain experiments with time lapse observations from a fabric analyzer there is a continuous reequilibration of microstructure and cpo development associated with constant and oscillating strain rate cycles these can be correlated with c axis small circle distributions diagnostic of dynamic recrystallization involving new grain nucleation and grain boundary migration gbm as observed in the high temperature deformation of ice and quartz inhomogeneous stress distribution can lead to grain size reduction for relatively slower strain rates and gbm for relatively faster rates within a long interval cycling event a behavior that contradicts the classic view for dynamic recrystallization processes where there is a rapid short term cycling of strain rate gbm is hampered and nucleation dominates accompanied by a marked reduction of grain size and no new cpo development during such short term cycling gbm and crystallographic change is impeded not by impurities but by an inability of newly nucleated grains to grow