a continuum of stress strength and slip in the cascadia subduction zone movement of the down going oceanic plate in subduction zones is accommodated by earthquakes slow slip and free slip with increasing depth analysis of accompanying tremor reveals a continuum of slow slip events in the cascadia subduction zone which suggests that deep free slip of the subducted plate may cause stress to be gradually transferred up the plate interface towards the seismogenic zone

constraints on the nature and evolution of the magma plumbing system of mt etna volcano 1991 2008 from a combined thermodynamic and kinetic modelling of the compositional record of minerals maren kahl sumit chakraborty massimo pompilio and fidel costa school of earth and environment university of leeds leeds ls2 9jt uk institut fur geologie mineralogie und geophysik ruhr universit at bochum bochum 44780 germany istituto nazionale di geofisica e vulcanologia sezione di pisa pisa 56126 italy and earth observatory of singapore nanyang technological university singapore 639798 singapore

empirical relationships among seismic velocity effective pressure porosity and clay content in sandstone we use a multivariate analysis to investigate the influence of effective pressure pe porosity and clay content c on the compressional velocity vp and shear velocity vs of sandstones laboratory measurements on water saturated samples of 64 different sandstones provide a large data set that was analyzed statistically for each sample relationships between effective pressure and vp and vs have been determined all samples were well fit by relationships that have an exponential increase in velocity at low pe tapering to a linear increase with pe for pe greater than 0 2 kbar there are differences in the pressure dependences of velocity for different rocks particularly at very low pressures however the differences cannot be attributed to or c for the combined set of measurements from all samples the best fitting formulations are vp 5 77 6 94 1 73c 0 446 pe e 16 7pe and vs 3 70 4 94 1 57c 0 361 pe e 16 7pe while this is admittedly a very simplified parameterization it is remarkable how well

imaging subduction from the trench to 300 km depth beneath the central north island new zealand with vp and vp vs summary recent dense deployments of portable digital seismographs have provided excellent control on earthquakes beneath the central north island of new zealand here we use a subset of the best recorded earthquakes in an inversion for the 3 d vp and vp vs structure the data set includes 39 123 p observations and 18 331 s observations from 1239 earthquakes and nine explosions the subducted plate is imaged as a high vp low vp vs feature vp within the mantle of the subducted slab is almost always 8 5 km s 1 which requires the ca 120 myr slab to be unusually cold the low vp vs within the subducted plate closely parallels the lower plane of the dipping seismic zone it most likely indicates fluid resulting from dehydration of serpentine in the slab mantle and the earthquakes themselves are likely to be promoted by dehydration embrittlement we identify a region with vp 8 0 km s 1 directly above the dipping seismic zone can be interpreted as sinking entrained with the motion of the subducted slab and forming a viscous blanket that insulates the slab from the high temperature mantle wedge material in the overlying low vp region can be interpreted as rising within a return flow within the wedge the volcanic front appears to be controlled by where this dipping low vp region meets the base of the crust the thickness of the backarc crust also shows significant variation along strike in the central taupo volcanic zone tvz the crust is ca 35 km thick while southwest of mt ruapehu the crust thickens by ca 10 km there is no significant low vp zone in the mantle wedge in this southwestern region suggesting that this thicker crust has choked off mantle return flow the seismic tomography results when combined with constraints on mantle flow from previous shear wave splitting results provide a plausible model for both the distribution of volcanism in the central north island and the exceptional magmatic productivity of the central tvz

a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

accuracy of timescales retrieved from diffusion modeling in olivine a 3d perspective diffusion modeling in olivine is a useful tool to resolve the timescales of various magmatic processes practical olivine geospeedometry applications employ 1d chemical transects across sections that are randomly sampled from a given 3d crystal population but the accuracy and precision with which timescales can be retrieved from this procedure are not well constrained here we use numerical 3d diffusion models of fe mg to evaluate and quantify the uncertainties associated with their 1d counterparts the 3d diffusion models were built using both simple and realistic olivine morphologies and incorporate diffusion anisotropy as well as different zoning styles the 3d model crystals were sectioned along ideal or random planes which were used to perform 1d models and timescale comparisons results show that the timescales retrieved from 1d profiles are highly inaccurate and can vary by factors of 0 1 25 if diffusion anisotropy is not taken into account even when anisotropy is corrected for timescales can still vary between 0 2 10 times the true 3d diffusion time due to crystal shape and sectioning effects simple grain selection procedures are described to reduce the misfit between calculated and actual diffusion times and achieve an accuracy and precision of 5 and 15 25 relative respectively provided that the grains are carefully selected about 20 concentration profiles and associated 1d models suffice to achieve this accuracy

a branched magma feeder system during the 1669 eruption of mt etna evidence from a time integrated study of zoned olivine phenocryst populations the 1669 eruption of mt etna was one of the most voluminous and devastating of its flank eruptions in historical times despite a large body of relevant research knowledge of the timing and duration of magma transfer and magma recharge through the internal plumbing system preceding and during the eruption is still limited to address that lack of knowledge we apply a three way integrated method linking systems analysis of crystals a time integrated study of zoned olivine populations and a forward modelling approach using thermodynamic calculations analysis of 202 olivine crystals erupted during the initial pre march 20 i e set1 and the final post march 20 i e set2 and mtrs stages of the eruption reveals the existence of three magmatic environments mes in which the majority of the olivine cores m 1 fo 75 78 and rims i e m 5 fo 51 59 and m 3 fo 65 69 formed application of the rhyolite melts software allowed us to constrain the key intensive variables associated with these mes we find that temperature water content and oxidation state vary between these mes application of diffusion modelling to the zoned olivine crystals allowed us to reconstruct the timing and chronology of melt and crystal transfer prior to and during the 1669 flank eruption we find that following the formation of the olivine cores m 1 fo 75 78 the reservoir m 1 was intruded by batches of more evolved degassed and possibly aphyric m 5 type magma commencing 1 center dot 5 years prior to eruptive activity this is the origin of the set1 olivine rims i e fo 51 59 in the months prior to eruption timescale data show that recharge activity along the newly established pathway m 1 m 5 increased notably starting in november 1668 only a few weeks after the first intrusive episode into the m 1 reservoir a second pulse of magma injections m 3 type magma occurred and a new pathway m 1 m 3 opened this is how the set2 olivine rims i e fo 65 69 formed for several weeks a bifurcated transport system with two dominant magma pathways developed along m 1 m 5 and m 1 m 3 dyke injections accompanied by vigorous seismicity in the days immediately before eruption the local magma transfer dynamics changed and the m 1 m 5 recharge activity slowed down as shown by a relative lack of crystals recording shorter timescales m 1 m 3 recharge however remained high and persisted following the eruption onset on march 11 during which the set1 lavas were drained we propose that the change of the local magma transfer dynamics might be linked to changes in the local stress field brought on during eruption this may potentially have been due to repeated dyke injections into etna s shallow plumbing system disrupting the early m 1 m 5 pathway and at the same time stabilizing the m 1 m 3 route as a dominant feeder this transfer of system feeding would reproduce the observed syn eruptive recharge and mixing in the weeks following eruption onset culminating in the eruption of the later set2 lavas

the 1891 submarine eruption offshore pantelleria island sicily channel italy identification of the vent and characterization of products and eruptive style high resolution bathymetry and seafloor sampling have been used to characterize the 1891 submarine eruption of the pantelleria volcanic complex this submarine eruption has been documented mainly by historical reports describing basaltic scoria bombs floating on the sea surface i e lava balloons in this study the 1891 eruptive vent has been identified as a small cone volume of 700 000 m3 rising 90 m from 350 m w d and located within a newly discovered submarine volcanic field covering a wide area offshore from the nw coast of pantelleria recently kelly et al 2012 confirmed this location by a multibeam and rov survey pyroclasts from the 1891 eruption crop out directly on the seafloor and are fresh scoria clasts i e small bombs bomb fragments and lapilli and glass ash sized grains both have been characterized in their morphology textures and geochemistry the distinctive vesicularity and crystallization characteristics displayed by the scoriaceous pyroclasts reflect modes of degassing in both syn and posteruptive regimes these characteristics along with the distribution of deposits suggest for the strongest eruptive phase of the 1891 eruption a style analogous to hawaiian fountaining glass grains from a buoyant plume were dispersed northward from the vent up to distances of 1 5 km redirected by the levantine intermediate water the identification of the 1891 submarine eruptive vent offshore pantelleria as well as the features of erupted pyroclasts improve our knowledge of submarine explosive eruptions that occur at shallow intermediate depths and among these of the rare eruptions producing lava balloons

variety and spatial heterogeneity of tectonic tremor worldwide 1 deep tectonic tremor occurs at various sites worldwide and the source characteristics are heterogeneous even at small scales in this study tremor sources were determined using data sets of seismic waveforms from various locations some of which are not well recognized as being a site of tremor activity the regions of interest are subduction zones at nankai and kyushu japan cascadia in western north america mexico southern chile and new zealand tremor locations are consistent with the geometry of subducting plates and tremor depth tends to be shallower where younger plate is subducting tremor duration shows a negative correlation with tidal sensitivity as reported previously in western shikoku in the nankai subduction zone the duration is also related to the width of the tremor zone in the dip direction of the subducting plate linear structures resembling striations are observed in hypocenter distributions in western shikoku and in the probability of short term migration direction these spatial heterogeneities in tremor activity may be controlled by the heterogeneous frictional properties of the downgoing slab due to long term plate subduction thereby providing information on the maturity of the plate interface

a tremor and slip event on the cocos caribbean subduction zone as measured by a global positioning system gps and seismic network on the nicoya peninsula costa rica in may 2007 a network of global positioning systems gps and seismic stations on the nicoya peninsula of northern costa rica recorded a slow slip event accompanied by seismic tremor the close proximity of the nicoya peninsula to the seismogenic part of the cocos caribbean subduction plate boundary makes it a good location to study such events several centimeters of southwest motion were recorded by the gps stations over a period of several days to several weeks and the seismic stations recorded three distinct episodes of tremor during the same time span inversion of the surface displacement data for the depth and pattern of slip on the plate interface shows peak slip at a depth of 25 30 km downdip of the main seismogenic zone estimated temperatures here are 250 300 c lower than in other subduction zones where events of this nature have been previously identified there may also be a shallower patch of slip at 6 km depth these results are significant in that they are the first to suggest that slow slip can occur at the updip transition from stick slip to stable sliding and that a critical temperature threshold is not required for slow slip tremor and low frequency earthquake locations are more difficult to determine our results suggest they occur on or near the plate interface at the same depth range as the deep slow slip but not spatially colocated

millennial scale phase relationships between ice core and mediterranean marine records insights from high precision 40ar 39ar dating of the green tuff of pantelleria sicily strait abstract with the advent of annually resolved polar ice records extending back to 70 ka marine and continental paleoclimate studies have now matured into a discipline where high quality age control is essential for putting on an equal pace layer counted timescale models and late quaternary sedimentary records high resolution u th dating of speleothem records and 40ar 39ar dating of globally recorded geomagnetic excursions have recently improved the time calibration of quaternary archives reflecting the cross disciplinary effort made to synchronize the geologic record at the millennial scale yet tie points with such an absolute age control remain scarce for paleoclimatic time series extending beyond the radiocarbon timescale most notably in the marine record far travelled tephra layers recorded both onland and offshore provide an alternative in such instance to synchronize continental and marine archives via high resolution 40ar 39ar dating of the parent volcanic eruption high resolution 40ar 39ar data are reported herein for one such volcanic marker the green tuff of pantelleria and its y 6 tephra equivalent recorded throughout the central and eastern mediterranean published radiochronometric and 18o orbitally tied ages for this marker horizon scatter widely from about 41 ka up to 56 ka our new 40ar 39ar age at 45 7 1 0 ka 2 reveals that previous estimates are biased by more than their reported errors would suggest including recent orbital tuning of marine records hosting the tephra bed that are reevaluated in the context of this study this improved estimate enables potential phase lags and leads to be studied between deep sea and terrestrial archives with unrivaled near millennial 40ar 39ar precision in the marine record

timescales of magma storage and migration recorded by olivine crystals in basalts of the march april 2010 eruption at eyjafjallajokull volcano iceland the early eruptive phase of the 2010 eruption at the fimmvor uhals pass east of eyjafjallajokull volcano produced poorly evolved basalts with mildly alkaline affinity and benmoreitic tephra were emitted during the second explosive phase from the summit vent of the volcano in this study textural features and chemical zoning preserved in olivine crystals of the early erupted basalts have been used to define the timescales of differentiation processes and magma ascent before the eruption these lavas contain a mineral assemblage constituted by olivine fo70 88 and plagioclase an57 83 in similar proportions with scarce clinopyroxene and opaque oxides olivine occurs as euhedral or embayed crystals characterized by different core compositions and zoning patterns three main olivine populations have been found namely crystals with 1 wide fo88 cores with normal zoning toward narrow rims p1 2 fo81 cores with either no zoning or slight reverse zoning patterns toward the rims p2 3 fo77 cores with reverse zoning at the rims p3 the olivine reverse zoning indicates that these poorly evolved magmas experienced mixing processes in addition to limited fractional crystallization at different levels of the plumbing system timescales of transfer dynamics before the eruption have been estimated through fe mg diffusion modeling on these olivine populations the olivine melt equilibration through diffusion was triggered by interaction of magmas differing in their evolutionary degree p1 and p2 crystals recorded a first event of interaction in a 22 km deep reservoir that took place about one month before the emission of the analyzed products only part of p2 crystals records reverse zoning due to interaction with more basic magma bearing p1 crystals which consequently develop normal zoning suggesting fast timescales of magma mixing that prevented the complete homogenization a second mixing event which is evident in the p3 olivines occurred at shallower levels 5 6 km of depth 15 days before the emplacement and can be considered the triggering mechanism leading to the eruption at the fimmvor uhals pass integration of our timescales with seismic data relative to the hypocenter migration indicate rates of magma ascent throughout the deep plumbing system of 0 01 m s this study provides evidence that magmas emitted at eyjafjallajokull volcano and more in general at similar other volcanic systems in ocean ridge settings can undergo complex processes during their storage and transport in the crust chiefly due to the presence of a multilevel plumbing system

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

the pre eruptive volatile contents of recent basaltic and pantelleritic magmas at pantelleria italy abstract pantelleria island located in the sicily channel rift zone italy is the type locality for the peralkaline rhyolitic rocks called pantellerites in the last 50 ka after the large green tuff caldera forming eruption volcanic activity at pantelleria has consisted of effusive and explosive eruptions mostly vented inside and along the rim of the caldera and producing silicic lava flows lava domes and poorly dispersed pantelleritic pumice fall deposits basaltic cinder cones and lava flows are only present outside the caldera in the nw sector of the island the most recent basaltic cuddie rosse 20 ka and pantelleritic cuddia randazzo and cuddia del gallo 6 ka pyroclastic products were sampled to investigate magmatic volatile contents through the study of melt inclusions the melt inclusions in pyroxene and olivine phenocrysts of cuddie rosse scoriae have an alkali basalt composition the dissolved volatiles comprise 0 9 1 6 wt h2o several hundred ppm of co2 1600 2000 ppm of sulphur and 500 900 ppm of chlorine the water carbon dioxide couple gives a confining pressure 2 kbar prior to the eruption this result indicates that episodes of magma ponding and crystallization occurred in the upper crust prior to eruption the melt inclusions in feldspar fayalite and aenigmatite phenocrysts of cuddia del gallo and cuddia randazzo pumice have a pantelleritic composition agpaitic indices 1 3 2 1 up to 4 4 wt h2o 8700 ppm cl 6000 ppm f and co2 below the detection limit sulphur averaging 420 ppm has been measured in cuddia randazzo melt inclusions these data indicate relatively high volatile contents for these low energy strombolian type eruptions melt inclusions in cuddia del gallo pumice show the most evolved composition agpaitic indices 2 2 1 and the highest volatile content in agreement with fluid saturation conditions in the magma chamber prior to the eruption this implies a confining pressure of 1 kbar for the top of the pantelleritic reservoir the composition of melt inclusions and mineralogical assemblage of cuddia randazzo pumice indicate that it has a lower evolutionary degree agpaitic indices 1 3 1 8 and lower pre eruptive cl and h2o contents than cuddia del gallo pumice an increase in pressure due to the exsolution of volatiles in the upper part of the pantelleritic reservoir may have triggered the cuddia del gallo explosive eruption evidence of widespread pre eruptive mingling between trachytes and pantellerites suggests that the intrusion of trachytic magma into the pantelleritic reservoir likely played a major role in destabilizing the magma system just prior to the cuddia randazzo event

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

subducting slab ultra slow velocity layer coincident with silent earthquakes in southern mexico great earthquakes have repeatedly occurred on the plate interface in a few shallow dipping subduction zones where the subducting and overriding plates are strongly locked silent earthquakes or slow slip events were recently discovered at the down dip extension of the locked zone and interact with the earthquake cycle here we show that locally observed converted sp arrivals and teleseismic underside reflections that sample the top of the subducting plate in southern mexico reveal that the ultra slow velocity layer usl varies spatially 3 to 5 kilometers with an s wave velocity of 2 0 to 2 7 kilometers per second most slow slip patches coincide with the presence of the usl and they are bounded by the absence of the usl the extent of the usl delineates the zone of transitional frictional behavior

geology of the peralkaline volcano at pantelleria strait of sicily situated in a submerged continental rift pantelleria is a volcanic island with a subaerial eruptive history longer than 300 ka its eruptive behavior edifice morphologies and complex multiunit geologic history are representative of strongly peralkaline centers it is dominated by the 6 km wide cinque denti caldera which formed ca 45 ka ago during eruption of the green tuff a strongly rheomorphic unit zoned from pantellerite to trachyte and consisting of falls surges and pyroclastic flows soon after collapse trachyte lava flows from an intracaldera central vent built a broad cone that compensated isostatically for the volume of the caldera and nearly filled it progressive chemical evolution of the chamber between 45 and 18 ka ago is recorded in the increasing peralkalinity of the youngest lava of the intracaldera trachyte cone and the few lavas erupted northwest of the caldera beginning about 18 ka ago inflation of the chamber opened old ring fractures and new radial fractures along which recently differentiated pantellerite constructed more than 25 pumice cones and shields continued uplift raised the northwest half of the intracaldera trachyte cone 275 m creating the island s present summit montagna grande by trapdoor uplift pantellerite erupted along the trapdoor faults and their hingeline forming numerous pumice cones and agglutinate sheets as well as five lava domes degassing and drawdown of the upper pantelleritic part of a compositionally and thermally stratified magma chamber during this 18 3 ka episode led to entrainment of subjacent crystal rich pantelleritic trachyte magma as crenulate inclusions progressive mixing between host and inclusions resulted in a secular decrease in the degree of evolution of the 0 82 km3 of magma erupted during the episode

simple shearing block resurgence in caldera depressions a model from pantelleria and ischia abstract similar resurgent blocks occur in caldera depressions at the islands of pantelleria and ischia the two blocks which are tilted show similar deformation patterns and similar distributions of volcanic vents related to resurgence the remaining parts of the floors of the two calderas are not deformed similarities between the two features are so striking that the resurgence mechanism must have been alike a dynamic model for resurgence is presented and called simple shearing block resurgence the triggering mechanism is an increase of the magmatic pressure in the upper part of a shallow magma chamber which results in a vertical direction of the maximum stress applied on the roof rocks the block is first defined by high angle inland dipping marginal detachments and then deformed through a simple shearing mechanism reverse faults on its mostly uplifted side determine an horizontal shortening of the block which is balanced on the opposite side by normal faults oblique movements take place along the other two sides due to this distribution of the stress around the block magmas can reach the surface only through the extensional faults on the less uplifted side

petrology and geochemistry of submarine volcanism in the sicily channel rift abstract submarine magmatism in the sicily channel rift began in the early pliocene and lasted until almost 200 yr ago we present here petrological and geochemical data on volcanic rocks dredged from graham and nameless banks and pantelleria seamounts in the pelagian sector of the sicily channel rift petrological evidence suggests that the ascent of magmas to the surface was relatively rapid probably through channels superimposed over the major tectonic discontinuities of the rift major and trace element data indicate an ocean island basalt affinity for graham and nameless bank alkaline lavas and a depleted tholeiitic signature for one pantelleria seamount which had a shallower mantle source sr nd pb isotopic compositions suggest a heterogeneous mantle source involving both focus zone fozo and high himu components lead isotopic compositions are slightly less radiogenic in the tholeiitic basalt and more radiogenic closer to himu in the alkaline lavas we hypothesize that a decompressional me

phenomenology of deep slow earthquake family in southwest japan spatiotemporal characteristics and segmentation 1 the phenomenology of deep slow earthquakes including low frequency tremors very low frequency earthquakes and short term slow slip events on the subducting plate interface in southwest japan is investigated on the basis of their spatiotemporal characteristics the belt like distribution of tremors is divided into segments bounded by gaps the repetition of tremor episode depends on the magnitude of the episode which is defined by the number of detected tremors within each episode major tremor episodes with a large number of detected tremors recur at an interval of approximately 6 months accompanying the short term slow slip events in large segments in small segments tremor episodes with small numbers of tremors have recurrence intervals of a few months some of them occasionally accompany the slight ground tilting caused by a small size slow slip event even in the same segment there exist different recurrence intervals according to the magnitude of the tremor episode the migration pattern varies greatly in initiation termination direction and speed however the migration direction has a general tendency for each segment on both sides of the gap the tremor starts next to the gap and propagates to the other side assuming all tremor episodes are caused by slow slip events the equivalent moment and slip are estimated from the number of detected tremor counts and the area of each tremor episode the equivalent slip history estimated from all tremor episodes is almost constant in each segment this indicates that tremor activity is a good proxy for slow slips

modeling short and long term slow slip events in the seismic cycles of large subduction earthquakes 1 slow slip events sses occur in the deeper extents of areas where large interplate earthquakes are expected in subduction zones such as the nankai region of japan and the cascadia region of north america in the nankai region sses are divided into long and short term sses depending on their duration and recurrence interval we modeled and examined the occurrence of long and short term sses and changes in their behavior during the seismic cycles of large interplate earthquakes in these numerical simulations we adopted a rate and state dependent friction law with cutoff velocities and assumed that the distribution of pore fluid controls the recurrence interval of both long and short term sses the recurrence intervals of reproduced short term sses decrease during a long term sse as observed in western shikoku in the nankai region the recurrence intervals of both types of sses become shorter in the later stages of interseismic periods large interplate earthquakes nucleate between the region where sses occur and the locked region of the large earthquakes as suggested from observations of the 1944 tonankai earthquake our numerical results suggest that the stress buildup process in a seismic cycle affects the recurrence behavior of sses

the origin of trachyte and pantellerite from pantelleria italy insights from major element trace element and thermodynamic modelling abstract trachyte and peralkaline rhyolite pantellerite and comendite frequently comprise the felsic end member in bimodal suites in continental rift and oceanic island settings in these settings the relationship between the mafic mildly alkaline or transitional basalt and felsic lavas is ambiguous major and trace element models and isotopic data are often consistent with an origin for felsic lavas from either fractional crystallization of transitional basalt or partial melting of alkali gabbro followed by fractional crystallization in this paper we present representative mineral analyses and whole rock analyses from forty samples of a basalt trachyte pantellerite suite collected at pantelleria italy in the strait of sicily rift zone and compare the results of major and trace element modelling with the results of thermodynamic melts modelling from these results we conclude that metaluminous trachyte formed as a result of 70 to 75 low pressure 0 1 gpa fractional crystallization of an assemblage of plagioclase clinopyroxene olivine magnetite and apatite from a hydrous 1 0 1 5 wt h2o transitional basalt magma at relative oxygen fugacities approximately one log unit below the fayalite magnetite quartz buffer fmq 1 the daly gap a lack of intermediate 49 62 wt sio2 volcanic rocks at pantelleria is concluded to be primarily the result of rapid differentiation through that interval relatively rapid crystallization at low pressure may have effected the partial degassing of water saturated 4 wt h2o metaluminous trachyte magma some metaluminous trachyte lavas have positive eu anomalies high k rb ratios high concentrations of ba and low concentrations of incompatible trace elements these are interpreted to be the result of up to 40 accumulation of alkali feldspar comenditic trachyte pantelleritic trachyte and pantellerite formed after an additional 20 to 80 fractional crystallization of an assemblage dominated by alkali feldspar from metaluminous trachyte magma the most evolved pantellerite lavas and tuffs are the result of a total of 95 fractional crystallization of transitional basalt with phenocrysts that equilibrated at low temperatures 4 wt water contents

the recent explosive volcanism at pantelleria many of the least eighty eruptions of the six silicic eruptive cycles in the last 50 ka at pantelleria started out with explosive phases and ended with lava effusion the pyroclastic rocks are rhyolitic in composition while the later erupted lavas are less evolved up to trachyte probably due to the presence of a shallow and compositionally zoned magma chamber tapped at increasing depth during the eruptions the products of twenty explosive eruptions have been recognized most of them are represented by fallout deposits the only exceptions being the green tuff and the fossa carbonara tuff hydromagmatism is very rare though the magmas interacted with sea water it is supposed that interaction was not efficient because the magmas were not vesiculated and disrupted horizons showing variable degrees of welding up to vitrophyres have often been identified in the air fall tuffs most of the eruptions were characterized by low eruptive columns and were likely to have involved a strombolian type mechanism

the 2006 slow slip event and nonvolcanic tremor in the mexican subduction zone the last decade featured an explosive sequence of discoveries of slow slip events sse and nonvolcanic tremor nvt in different subduction zones and continental faults many observations show that sse is usually associated with an increased nvt activity but it is not clear yet if those events are the result of the same process or are independent expressions of a common underlying seismotectonic source a large sse in central mexico occurred in 2006 during the meso american subduction experiment mase which provided continuous observations of the nvt for the years 2005 2007 gps and abundant seismic data show that although the nvt energy increased notably during the 2006 sse the two phenomena were separated spatially and not completely synchronized in time significant nvt episodes occur during the period between sses suggesting again that large slow slip events and nvt observed in the mexican subduction zone are of different origins the results presented here contribute to uncovering the nature of these two separate phenomena that have been indistinguishable in some other regions

high pore fluid pressure may cause silent slip in the nankai trough silent slip events have been detected at several subduction zones but the cause of these events is unknown using seismic imaging we detected a cause of the tokai silent slip which occurred at a presumed fault zone of a great earthquake the seismic image that we obtained shows a zone of high pore fluid pressure in the subducted oceanic crust located down dip of a subducted ridge we propose that these structures effectively extend a region of conditionally stable slips and consequently generate the silent slip

relationships between magmatism and tectonics in a continental rift the pantelleria island region sicily channel italy abstract field geological data of the pantelleria island a large late quaternary volcano located in the sicily channel rift zone integrated with offshore geophysical information are used to derive the structural setting of the island and the surrounding region and to analyse the relationships between tectonics and magmatism field work shows that the principal faults exposed on the island fall into two systems trending nne ssw and nw se mapped faults from offshore multichannel seismic profiles show similar trends and some of them represent the offshore extension of the pantelleria island structures the nw se faults bound the pantelleria graben one of the three main depressions formed since the late miocene early pliocene within the african continental platform which compose the sicily channel rift zone a 3 d moho depth geometry derived from inversion of bouguer gravity data shows a significant uplift of the discontinuity up to 16 17 km beneath the westernmost part of the pantelleria graben and beneath the pantelleria island it lows rapidly to 24 25 km away from the graben north eastward and south westward the moho uplift could explain the presence of a shallow magma chamber in the southern part of the island where processes of magmatic differentiation are documented geological and geophysical data suggest that the northwestern part of the sicily channel is presently dominated by a roughly e w directed extensional regime crustal cracking feeding the quaternary volcanism could be also related to this extensional field that would be further responsible for the development of the n s trending volcanic belt that extends in the sicily channel from lampedusa island to the graham bank this mode of deformation is confirmed also by geodetic data this implies that in the northwestern part of the sicily channel the e w extension replaced the ne sw crustal stretching that originated the nw trending tectonic depressions constituting the rift zone

the pantelleria caldera geothermal system data from the hydrothermal minerals abstract this paper proposes on the basis of petrographic and mineralogic data on cutting and cores from two deep wells pantelleria 1 and pantelleria 2 the first model of the active hydrothermal system of the island of pantelleria phyllosilicates were studied in detail because they are considered key minerals in the identification of hydrothermal processes the results of these studies emphasize differences between the intracaldera and pericaldera areas of the island within the 45 ka caldera there is a high temperature 240 260 c at 600 800 m depth active hydrothermal system with five zones of characteristic alteration minerals with increasing depth rocks are unaltered to a depth of 200 m contain smectite and mixed layer chlorite smectite c s between 200 and 380 m chlorite illite chalcedony and quartz from 380 to 500 m albite adularia and saponite from 500 to 680 m mixed layer biotite vermiculite from 680 m to the depth drilled 1100 outside the caldera but near the rim a low temperature and low permeability

slow earthquakes linked along dip in the nankai subduction zone we identified a strong temporal correlation between three distinct types of slow earthquakes distributed over 100 kilometers along the dip of the subducting oceanic plate at the western margin of the nankai megathrust rupture zone southwest japan in 2003 and 2010 shallow very low frequency earthquakes near the nankai trough as well as nonvolcanic tremor at depths of 30 to 40 kilometers were triggered by the acceleration of a long term slow slip event in between this correlation suggests that the slow slip might extend along dip between the source areas of deeper and shallower slow earthquakes and thus could modulate the stress buildup on the adjacent megathrust rupture zone

hikurangi plateau a cretaceous large igneous province in the southwest pacific ocean the first dredge haul of basement rocks obtained from the hikurangi plateau in the southwest pacific ocean consists dominantly of volcanic and volcaniclastic rocks of probable pre late cretaceous age all samples have undergone extensive seafloor weathering to phyllosilicate and zeolite bearing assemblages petrography mineral chemistry and whole rock element concentrations and ratios of the least altered lavas e g tio2 1 3 1 6 wt cr 132 224 ppm zr y 2 9 3 6 zr nb 19 29 ti v 22 29 suggest a restricted igneous compositional range broadly comparable with normal to enriched mid ocean ridge basalt however isotopic compositions of leached samples 87sr 86sri 0 70361 0 70374 endi 5 7 6 2 are comparable with oceanic island basalt suites collectively these petrological characteristics are similar to rocks from large igneous provinces of cretaceous age in the western pacific ocean e g manihiki and ontong java plateaus consequently we interpret the hikurangi plateau as another of these early cretaceous basaltic oceanic plateaus speculatively parts of the obducted tangihua and matakaoa igneous complexes of the north island may have been derived from the hikurangi plateau as the plateau collided with the new zealand continent in the early miocene

aseismic slip transients emerge spontaneously in three dimensional rate and state modeling of subduction earthquake sequences 1 to investigate the possible physical mechanisms of recently observed aseismic slip events in the cascadia japan and mexico subduction zones we apply a dieterich ruina rate and state friction law to a three dimensional model of a shallow subduction fault that is loaded by imposed steady plate slip rate far downdip along the thrust interface friction properties are temperature and hence depth dependent such that sliding is stable at depths below about 30 km the system is perturbed into a significantly nonuniform slip mode along strike by introducing small along strike variations in the constitutive parameters a and a b in addition to large heterogeneous earthquake slip at seismogenic depths and associated postseismic transients we found that slip events which have clearly aseismic slip rates emerge spontaneously around the downdip end of the seismogenic zone both transients which start well after a seismic event and those which are triggered by other transients are observed from the simulations the slip velocity depth range and sometimes along strike migration speed of simulated transients are similar to the observations from natural subduction zones unstable stable transitional friction properties near the downdip end of the seismogenic zone are suggested to be an ingredient allowing such transients simulated transients can weaken the locking intensity of the updip seismogenic zone while enhancing that of the transition zone spatial temporal correlation of aseismic transients and nearby seismicity in the guerrero mexico area suggests that transients may signal a period of increased probability for nucleating their high frequency counterparts as damaging subduction thrust events

changing modes and rates of mafic magma supply at pantelleria sicily channel southern italy new perspectives on the volcano factory drawn upon olivine records

dynamic plumbing system beneath volcanoes revealed by kinetic modeling and the connection to monitoring data an example from mt etna abstract our ability to monitor volcanoes using seismic signals ground deformation gas fluxes or other ground and satellite based observations as well as our understanding of melt reservoirs that feed eruptions have evolved tremendously in recent years the complex plumbing systems that are thought to feed eruptions are however difficult to relate to the monitoring signals here we show that the record preserved in compositional zoning of erupted minerals may be used to reconstruct sections of the plumbing system kinetic modeling of such zoning can yield information on the residence time of magma in different segments of the plumbing systems this allows a more nuanced evaluation of the link between observed monitoring signals or eruption styles and the magmatic processes and movement of batches of melts at depth the approach is illustrated through a study of the compositional zoning recorded in olivine crystals from the 1991 1993 se flank eruption products of mt etna sicily the zoning patterns in crystals reveal that the plumbing system of the volcano consisted of at least three different magmatic environments between which magma was transported and mixed in the year or two preceding the start of eruption quantification of this history indicates that two main pathways of melt migration and three timescales dominated the dynamics of the system combination of this information with the timing of observation of various monitoring signals allows a reconstruction of the dynamic evolution of this section of the plumbing system during the early stages of the 1991 1993 eruption it is seen for example how the migration of melt through the same sections of the plumbing system can cause pre eruptive triggering enhance strombolian activity and through the ensuing eruption cleanse and flush the plumbing system different kinds of mixing occur simultaneously at different sections of the plumbing system on different timescales a few days up to two years

the eruptive history of pantelleria sicily channel in the last 50 ka six silicic eruptive cycles have been recognized in the last 50 ka at pantelleria the products of each cycle exhibit a compositional variation from pantellerite to less peralkaline rhyolite or to trachyte the relationships between the range of chemical variation the erupted volume and the time of eruptions allow us to estimate an average differentiation rate of 5 crystal fractionation per 1000 years and a constant long term rate of magma discharge of 0 1 km3 per 1000 years pressure increase in the magma chamber caused by the addition of new magma accumulation of highly differentiated volatile rich magma in the roof zone and a concomitant build up of a vapour phase is postulated as a possible triggering mechanism for eruptions

decadal time gaps between mafic intrusion and silicic eruption obtained from chemical zoning patterns in olivine abstract intrusion of mafic magma in a silicic crustal reservoir has been reported in numerous studies of subduction related volcanoes and is considered a main process for triggering explosive eruptions and for transferring geochemical signatures from the mantle to the crust here we determine the timescales between mafic silicic encounters and eruption by exploiting the fact that during such interactions magmas exchange crystals and their mineral compositions will strive to equilibrate to the new environmental conditions specifically we model the fe mg zoning patterns of olivine found in the dacites andesite and quenched mafic inclusions of the holocene zoned eruption of volcan san pedro 36 s chilean andes the san pedro eruption is an example where mixing between silicic and mafic magmas produced intermediate compositions e g andesite at depth in the magma reservoir for modeling the compositional profiles we took into account the anisotropy of fe mg diffusion in olivine and also the effects of diffusion in multiple dimensions aspects that have been largely neglected in previous works the retrieved timescales for olivine melt equilibration by diffusion display an array ranging from 1 year for the most silica rich dacite to 50 years for the andesite this array of timescales rather than a single value provides new insight into the details of mafic silicic mixing at depth they reveal processes that occur on a longer timescale than the days to weeks time gap for cases where the mafic intrusion triggered the eruption and they might be associated with the instances where seismic activity or significant inflation of the volcanic edifice was not immediately followed by eruption on the other hand the year to decade timescales that we report for producing magmas of intermediate composition e g andesites are much shorter than the 10 3 10 5 years inferred from u series disequilibria data for igneous differentiation by closed system fractionation to produce similar magma compositions at subduction zones

three years 2011 2013 of eruptive activity at mt etna working modes and timescales of the modern volcano plumbing system from micro analytical studies of crystals abstract tracking magma dynamics at active volcanoes by using the compositional and textural records of minerals is becoming an important aspect of modern volcanology to solve key issues such as temporal relationships between magma recharge and eruption duration of magma storage and final ascent upward to the surface these issues are relevant at mt etna where the style of volcanic activity during the last years showed drastic variations in duration and intensity the paroxysmal activity between 2011 and 2013 at the volcano summit has given the opportunity to investigate the chemical physical processes driving the activity and to fix their spatial temporal relationships into the plumbing system an extensive compositional dataset of plagioclase and olivine crystals from lavas emitted between the 2011 and 2013 at mt etna has been used to constrain modes and timescales of magma storage and transfer to the surface plagioclase crystals display either near equilibrium or disequilibrium textures at the core and rim that indicate complex histories of magma crystallization under variable chemical and physical conditions crystals with different textures have been characterized for major an minor fe and mg and trace elements sr ba textural relationships at the plagioclase cores support the idea that crystals undergo variable decompression rates in the deep parts of the plumbing system fe and mg zoning vs anorthite in correspondence of plagioclase sieve textures at the rim suggest that processes of gas flushing have a dominant role in triggering paroxysmal eruptions determining a sudden intensification of the eruptive activity up to the fountaining phase the sr ba ratio in oscillatory zoned plagioclase revealed the dominant presence into the plumbing system of high sr magma volumes coexisting with low sr magma batches that preserve a geochemical signature similar to that of magmas feeding the pre 1971 activity through sr diffusion modeling in plagioclase the maximum time of magma storage during the considered eruptive period has been evaluated timescales of crystal residence in the plumbing system are short five years to three decades suggesting limited magma storage and faster transfer dynamics to the surface chemical zoning of olivine crystals highlights processes of multi step magma transfer and residence at different levels of the plumbing system the upward migration of magmas occurred primarily through multiple episodes of injection and mixing between five compositionally distinct magmatic environments m i whose p t o 2 characteristics and concentrations in dissolved volatiles were constrained by thermodynamic modeling on the basis of the forsterite contents found at the olivine cores from a deepest reservoir located at depth of 600 mpa the most primitive magma m00 fo 84 moved along dominant pathways intercepting the m0 fo 80 82 at 390 mpa and or m1a fo 78 250 mpa m1b fo 75 140 mpa and finally the shallow m2 fo 70 73 40 mpa storage zones for some eruptive episodes olivine zoning highlights a preferential route of transfer connecting the m00 and m2 storage zones that facilitated the fast migration of primitive magma at shallow depth fe mg diffusion modeling on olivine normal and reverse zoning defines the timescales of magma transfer and storage across these magmatic environments which vary from 1 to 18 months whereas intrusion and mixing by more basic magma into the shallowest reservoir occurred always within 5 months before the eruption relevance of this study mainly relies on the quantification of volcanic processes at depth that may have considerable consequences in development of unusual high energy eruptions at basaltic volcanoes generally acknowledged for their weak to mild explosive activity

recent volcanic history of pantelleria a new interpretation abstract the island of pantelleria is located in the pantelleria rift between sicily and africa this rift is floored by a 20 km thick continental type crust that is characterized by horsts and grabens formed by nw se tensional faults and ne sw shear faults several faults and fractures that intersect the island follow these regional trends prominent volcano tectonic features on the island include two calderas the younger being related to the eruption of the green ignimbrite and the uplifted montagna grande block pantelleria mostly consists of peralkaline silicic rocks with minor trachytes and basalts volcanism on the island is characterized by both explosive and effusive activity reconstruction of the volcanic history of the island since the eruption of the green ignimbrite is based on geological and geochronological data the eruption of the green ignimbrite 50 000 y b p was followed by collapse of the monastero caldera that has been the site of most of the subsequent acid volcanism the montagna grande volcanic complex 35 000 y b p fills the central part while the lower pantelleritic lava flows 16 000 y b p erupted along its rim very probably the young mt gelfiser and khaggiar domes are also located on the caldera rim the montagna grande block rose within the caldera at an estimated average rate between 1 0 and 1 5 cm y for about 20 000 y subsequent pumice cones 9 000 y b p endogenous domes and lava flows also erupted inside this caldera among the main acid volcanic units younger than the green ignimbrite only the mt gelkhamar endogenous dome is not linked to this caldera in the last 50 000 years basaltic activity only occurred in the northern part of the island the basaltic vents are aligned parallel with the main tensional trends of the rift at least two phases have been recognized the older is about 29 000 y b p and the younger is a few thousands of years old a change occurred in the eruptive style after the eruption of the green ignimbrite and collapse of the monastero caldera explosive activity diminished and extrusion of lava became dominant

the green tuff of pantelleria rheoignimbrite or rheomorphic fall detailed stratigraphic analysis of the green tuff of pantelleria shows that this formation can be divided into several members designateda throughh from base to top these members have a coherent pattern when traced from outcrop to outcrop throughout the island shedding light on their origin only memberg completely mantles the entire island the distribution of the other members is controlled by prevailing wind direction or by topography membera is entirely of fall origin membersc ande are of fall and or surge type membersb d andh have the characteristics of thin welded ash flow tuffs membersf andg are ash flow tuffs with textural characteristics of compound cooling units most of the ash flow tuffs exhibit characteristics of ignimbrites vertical fluidization pipes local concentrations of lithic lapilli imbrication of clasts and valley ponding memberg is unusual in that it is highly welded exhibits large scale rheomorphic structures contains huge lithic clasts and has near vertical foliation where it adheres to cliffs and caldera walls

onset of caldera collapse during ignimbrite eruptions the rapid depressurisation and discharge of volatile rich silicic magma chamber and the onset of caldera collapse associated with ignimbrite eruption is investigated using combined theoretical and experimental approaches we first present a scaling analysis of the force balance on the roof of a depressurising magma chamber this provides a failure criterion for the chamber roof and shows that the chamber underpressure required to trigger coherent piston collapse along a vertical or steeply outward dipping reverse ring fault increases with the roof aspect ratio r thickness width the failure criterion is validated by a series of experiments that reveal a transition with increasing roof aspect ratio from piston collapse to either 1 no collapse low reservoir underpressure or 2 non coherent collapse high reservoir underpressure then taking into account the failure criterion obtained with the scaling analysis a theoretical model allows calculation of the erupted chamber volume fraction required to trigger caldera collapse we consider a two stage model with an initially overpressured chamber that becomes progressively underpressured as the eruption proceeds the main input parameters are the chamber depth vertical extent and ellipticity in plan view the magma water content the cohesion and coefficient of internal friction of the roof and the ring fault dip in the case of a mechanically homogeneous roof and a single large and rapid eruption the erupted volume fraction required to trigger piston collapse increases with the roof aspect ratio until the chamber is totally emptied before initiation of any collapse at r 1 1 4 the exact value depending mainly on the ring fault dip and to a lesser extent on the coefficient of internal friction of the roof as shown by experiments collapse into reservoirs with r 1 1 4 probably cannot collapse as a piston and if a surface caldera forms at all collapse is more likely to occur non coherently data for the onset of caldera collapse during seven well documented major ignimbrite eruptions are in broad agreement with the model

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

a revision of the structure and stratigraphy of pre green tuff ignimbrites at pantelleria strait of sicily abstract at pantelleria peralkaline silicic magmas were erupted across a range of eruptive typologies and magnitudes pyroclastic flows plinian to strombolian pumice fallout and lava flows in this paper we focus on the intermediate cycle of eruptive activity which is bracketed by ignimbrite units slightly older than the two caldera collapses which marked the volcanological activity of the island this age interval 180 85 ka was punctuated by six ignimbrite forming eruptions silicic and variably peralkaline for a cumulative erupted magma volume of approximately 6 km 3 dense rock equivalent based on new 40 ar 39 ar na k feldspar ages and petrographic data we propose an updated volcanostratigraphic scheme for these welded and rheomorphic ignimbrites that can be summarised as follows i the age of the old la vecchia caldera collapse is now tightly constrained between 140 and 146 ka and the caldera forming eruption can be traced to a lithic rich welded tuff breccia that outcrops in two opposite sectors of the island south west and north east ii four ignimbrite units previously considered unrelated are now merged in two distinct eruptive paroxysmal events at 107 and 85 ka in particular the 85 ka eruptive event is comparable in magnitude to the younger caldera forming green tuff plinian eruption iii the recurrence patterns of the 107 and 85 ka eruptions compared to the green tuff allow us to qualitatively assess that the climax in production of low temperature silicic and peralkaline melt was focused in the age interval 85 45 ka

deep tremor in new zealand triggered by the 2010 mw8 8 chile earthquake 1 deep non volcanic tremor nvt is usually associated with episodic slow slip events new zealand is one notable exception where numerous slow slip events have been identified yet nvt has remained undetected here we present the first known case of triggered nvt at new zealand s hikurangi subduction margin following the mw8 8 chilean earthquake of february 27 2010 we identify coherent high frequency tremor signals that are in phase with and modulated by the passing rayleigh waves this is consistent with the surface wave triggering potential for strike normal incidence on a low angle thrust fault after constraining the tremor depth on the plate interface we locate the tremor source within 20 km of the source area of episodic slow slip the tremor location is also near the edge of a region with high seismic attenuation that marks the boundary between dehydrated subducted slab and inferred hydrated underplated sediment we speculate that reduced interface friction and high fluid pressures provided by fluid rich underplated sediment facilitates the tremor generation

newly observed deep slow slip events at the central hikurangi margin new zealand implications for downdip variability of slow slip and tremor and relationship to seismic structure 1 we present previously undocumented deep 25 45 km depth moderate duration 2 3 months slow slip events sses directly downdip of known shallow 15 km depth short term 2 3 weeks sses at the central hikurangi margin new zealand the moderate duration sses produce 2 6 mm of horizontal displacement at continuous global positioning system stations in 2006 and 2008 similar to cascadia sses they involve 2 5 cm of slip over 5000 km2 of the subduction interface tremor occurs just downdip of the deep sse source area we also present results from a large shallow 12 km sse in 2013 just updip of the 2006 2008 sses the location of deep sses between shallow short term sses and tremor indicates strong downdip variation of subduction interface slip behavior at central hikurangi the deep sses occur where qp and vp vs data suggest an accumulation of fluid rich underplated sediment at the interface consistent with the idea that sses occur under high fluid pressure

simultaneous long term and short term slow slip events at the hikurangi subduction margin new zealand implications for processes that control slow slip event occurrence duration and migration 1 we document a sequence of simultaneous short term and long term slow slip events sses at the hikurangi subduction zone during the 2010 2011 period the sequence of short term events each 2 3 weeks in duration ruptured much of the shallow plate interface 15 km at central and northern hikurangi over a 6 month period was accompanied by microseismicity and involved patchy irregular migration of sse slip we suggest that the patchy migration of the short term sse is due to large scale 100 3500 km heterogeneities on the plate interface related to seamount subduction and sediment subduction and or underplating this is in contrast to a 2010 2011 long term sse at the central hikurangi margin which evolved steadily over 1 5 years and ruptured much of the plate interface between 20 and 70 km depth we suggest that the occurrence of long term versus short term sses at hikurangi is related to differences in effective normal stresses and relative heterogeneity of the subduction interface the long term sse sequence began 1 year before the short term sequence coulomb stress change models suggest that the long term sse may have triggered initiation of the subsequent short term sse sequence initiation of the short term sequence occurred in a region just updip of or within an interseismically locked portion of the plate interface and may be located within the updip transition from seismic to aseismic behavior alternatively it could be characteristic of a region undergoing partial interseismic coupling this is in contrast to sses observed elsewhere in the world that typically occur within the downdip transition from seismic to aseismic behavior

modeling of gas driven magmatic overturn tracking of phenocryst dispersal and gathering during magma mixing 1 we present a combined multiphase numerical and crystal tracking approach that provides a framework to investigate the transport and zoning of crystals associated with a gas driven mixing event mixing in compositionally intermediate to silicic magmatic systems is often initiated by gas exsolution in the recharging magma causing a density inversion and subsequent overturn the overturn is simulated for a range of bubble volume fractions bubbles and therefore indirectly for a range of reynolds numbers re all simulations show chaotic flow dynamics with fast overturn timescales of minutes to hours the large scale mixing is inefficient during a single overturn resulting in a continuously stratified system with respect to bubble volume fraction the crystal tracking algorithm provides us with information on the small scales i e 10 cm on this length scale we observe gathering of different crystals during the overturn that typically ranges on the order of tens of meters thus a complex crystal population may arise within a single overturn this gathering and dispersal of crystals is strongest and most uniform for high re for low re crystal populations are characterized by less gathering of crystals that originated from distal portions of the magma body during the overturn the crystals pass through environments of changing chemical potential we apply the damkohler number da which compares the crystallization or dissolution to the advection timescale results show an asymmetry between crystallization and dissolution crystallization times are too slow during gas driven overturn to record transient changes in chemical potential crystals most likely only record their initial as well as their final chemical environment in contrast dissolution and advection rates are of similar order suggesting potential dissolution during the overturn on the basis of the results for gas driven overturn we expect that slower physical mixing processes may be continuously recorded in the zonation pattern of the crystal phases as long as the changes in chemical potential produce crystal growth

time scales of magmatic processes from modeling the zoning patterns of crystals the advent of polarized light microscopy in the middle of the 19th century allowed mineralogists and petrologists interested in igneous rocks to recognize the widespread occurrence of fine scale heterogeneities in the optical properties of minerals e g see young 2003 for details the interpretation of mineral zoning patterns as archives of magmatic processes has been with us for some time e g larsen et al 1938 tomkeieff 1939 the development of the electron microprobe in the 1960 s allowed mineral zoning profiles to be quantitatively analyzed and modeled e g bottinga et al 1966 moore and evans 1967 enhanced textural observations permitted recognition of many kinds of detailed structures during the growth and dissolution of magmatic minerals fig 1 e g anderson 1983 pearce and kolisnik 1990 and these processes were also explored using experimental and numerical models e g albarede and bottinga 1972 lofgren 1972 kirkpatrick et al 1976 loomis 1982 major element zoning patterns are routinely measured and with the arrival of the ion microprobe the identification of heterogeneous distribution of trace elements opened the window for more realistic and sophisticated scenarios and models fig 1 e g kohn et al 1989 blundy and shimizu 1991 singer et al 1995 we now measure abundances of naturally occurring isotopes at the scale of tens of micrometers e g davidson et al 2007a ramos and tepley 2008 and this allows in situ dating of crystals e g cooper and reid 2008 figure 1 a nomarski dic image of a plagioclase crystal from a gabbroic xenolith of volcan san pedro costa et al 2002 the crystal shows a well defined core and a rim separated by an oscillatory zoned interval ion microprobe analysis pits and the trace of the electron microprobe traverse between the pits are evident b major

influence of basement faults on the development of salt structures in the danish basin scaled centrifuged models based on interpreted seismic profiles were used to simulate the salt structures in the danish basin the models consisted of a viscous layer simulating rock salt overlain by layers of cohesive sand that mimic brittle failure in natural overburdens model results support the hypothesis that basement faults trigger the growth of many salt diapirs in the danish basin in plan view model diapirs are localized as buoyant walls along faults in the overburden which collapsed due to basement fault movement with further burial single diapirs rose from these buoyant walls some of the diapirs surfaced through the faulted overburden a few were trapped beneath the competent cretaceous units and others were starved due to lack of supply from below in section model diapirs were asymmetric and were rooted on the tip of the faults or located on the rotated footwall blocks model diapirs not located over faults were triggered by differential loading and collapsing of overburden layers due to basement block rotation models show that the presence of fewer salt structures in the northern than the southern part of the basin is due to differential subsidence and flow of buoyant material from north to south where they rise diapirically in the model the pressure due to loading by overburden layers changed from 1 3 102 pa in the south to 2 3 102 pa in the northern part of the basin in general the model results illustrate that basement faults influence diapirs by accumulating buoyant material in half grabens and introducing a slope and steps at the base of the buoyant layer weakening its overburden and causing differential loading and compaction the spreading overhangs of salt diapirs beneath the cretaceous chalk in the danish basin would seal any potential pre cretaceous reservoir rocks

evidence of magma mixing in the daly gap of alkaline suites a case study from the enclaves of pantelleria italy the island of pantelleria consists of trachytes pantellerites and minor mildly alkaline basalts rocks of intermediate composition falling in the so called daly gap such as mugearites benmoreites and mafic trachytes occur only in the form of enclaves in trachytes and pantellerites inside the main caldera of the island caldera cinque denti which collapsed during the green tuff ignimbrite eruption at 50 ka the enclaves include volcanic subvolcanic and intrusive rock types the enclaves in host trachyte contain traces of glass devitrified glass occurs within enclaves in host pantellerites minerals in the enclaves show regular compositional variations with whole rock silica content glass present in the medium grained samples is interpreted to be the result of incipient melting the major and trace element compositions of the enclaves show regular and linear variations between an evolved mafic magma hawaiite and a felsic end member similar to the green tuff trachyte fractional crystallization modelling of compatible and incompatible trace elements v ni zr la sm lu nb y th does not reproduce the observed trends rocks of intermediate composition within the daly gap can be explained only by magma mixing between an already differentiated mafic magma hawaiite and an anorthoclase rich trachytic melt in the lower and higher parts respectively of a stratified magmatic chamber medium grained enclaves are interpreted as the result of fragmentation of solidified mixing layers in the roof of the magma chamber during the eruption of the green tuff when the collapse of the caldera took place diffusion calculations suggest a residence time of 5 days for the enclaves in their host magmas

cracking the olivine zoning code distinguishing between crystal growth and diffusion olivine composition and zoning patterns are widely used to reconstruct the evolution of mafic magmas from source to surface and to extract time scales of magmatic processes deciphering the olivine zoning code is challenging because the contributions of growth and diffusion may overlap a detailed multielement fe mg p al and ni examination of zoning in an exceptional olivine with skeletal morphology allows unequivocal discrimination between these two processes using simple but powerful geometrical arguments olivine crystals initially grow rapidly and diagonally from corner locations whereas diffusion effectively tracks mutually perpendicular crystal lattice orientations generating the zoning patterns for our case study olivine required at least 4 5 months of diffusive reequilibration of fe mg further demonstrating that crystal morphologies produced by rapid growth can survive at magmatic temperatures for extended periods no significant major element zoning is preserved after rapid growth lending further credibility to time scales retrieved via diffusion modeling extending multielement approaches to decoding olivine zoning patterns can help determine whether the kinetic relationship between growth and diffusion induced zoning recognized herein is widely applicable such studies will improve our understanding of time scales of magma storage solidification mixing and or transit toward the surface

correlation of welded ignimbrites on pantelleria strait of sicily using paleomagnetism although the oldest volcanic rocks exposed at pantelleria strait of sicily are older than 300 ka most of the island is covered by the 45 50 ka green tuff ignimbrite thought to be related to the cinque denti caldera and younger lavas and scoria cones pre 50 ka rocks predominantly rheomorphic ignimbrites are exposed at isolated sea cliffs and their stratigraphy and chronology are not completely resolved based on volcanic stratigraphy and k ar dating it has been proposed that the older la vecchia caldera is related to ignimbrite q 114 ka and that ignimbrites f d and z 106 94 and 79 ka respectively were erupted after caldera formation we report here the paleomagnetic directions obtained from 23 sites in ignimbrite p 133 ka and four younger ignimbrites and from an uncorrelated and loosely dated welded lithic breccia thought to record a caldera forming eruption the paleosecular variation of the geomagnetic field recorded by ignimbrites is used as correlative tool with an estimated time resolution in the order of 100 years we find that ignimbrites d and z correspond in good agreement with recent ar ar ages constraining the d z eruption to 87 ka the welded lithic breccia correlates with a thinner breccia lying just below ignimbrite p at another locality implying that collapse of the la vecchia caldera took place at 130 160 ka this caldera was subsequently buried by ignimbrites p q f and d z paleomagnetic data also show that the northern caldera margin underwent a 10 west northwest outwards tilting after emplacement of ignimbrite p possibly recording magma resurgence in the crust

compositional and thermodynamic variability in a stratified magma chamber evidence from the green tuff ignimbrite pantelleria italy the green tuff ignimbrite pantelleria is compositionally zoned from pantellerite at the base to comenditic trachyte at the top the variation apparently representing an inverted vertical zonation in the pre eruptive reservoir the main phenocryst assemblages are alkali feldspar olivine clinopyroxene ilmenite apatite in the trachytes and alkali feldspar aenigmatite clinopyroxene quartz in the rhyolites thermodynamic modelling indicates that the temperature range was 900 700 c fo2 fmq 1 5 to fmq 0 5 where fmq is fayalite magnetite quartz buffer and asio2 relative to quartz saturation 0 74 1 00 melt water contents ranged from 1 wt in the trachytes to 4 wt in the pantellerites matrix glass analyses in the more evolved rocks are highly variable showing that compositional layers in the upper parts of the reservoir formed by fractional crystallization were mixed during eruption the proportion of rhyolitic to trachytic melts increasing towards the top of the reservoir some areas of glass have low al2o3 contents 5 16 5 46 wt and high feo contents 9 66 10 02 wt making them the most evolved melts yet reported from pantelleria the new glass data reveal how whole rock analyses do not truly reflect the complete range of melt compositions in the pre eruptive reservoir the trachytes contain 40 modal phenocrysts which with relatively high ba contents and positive eu anomalies are considered to have originated in a feldspar accumulitic layer phenocrysts in the trachytes are commonly heavily resorbed inferred to be a result of heating by influxes of intermediate composition magma which however were not erupted it is argued that magmas of intermediate composition were present in the green tuff reservoir but were efficiently trapped in a crystal rich layer below the green tuff magmas which was eventually erupted during a resurgent phase as the montagna grande trachyte

the kinematics of a transition from subduction to strike slip an example from the central new zealand plate boundary 1 we develop a kinematic model for the transition from subduction beneath the north island new zealand to strike slip in the south island constrained by gps velocities and active fault slip data to interpret these data we use an approach that inverts the kinematic data for poles of rotation of tectonic blocks and the degree of interseismic coupling on faults in the region convergence related to the hikurangi subduction margin becomes very low offshore of the northern south island indicating that in this region the majority of the relative plate motion has been transferred onto faults within the upper plate as suggested by previous studies this result has implications for understanding the likely extent of subduction interface earthquake rupture in central new zealand easterly trending strike slip faults such as the boo boo fault are the key features that facilitate the transfer of strike slip motion from the northern south island faults further north into the southern north island and onto the hikurangi subduction thrust our results also indicate that the transition from rapid forearc rotation adjacent to the hikurangi subduction margin to a strike slip dominated plate boundary with negligible vertical axis rotation in the south island occurs via a crustal scale hinge or kink in the upper plate compatible with paleomagnetic and structural geological data despite the ongoing tectonic evolution of the central new zealand region our study highlights a remarkable consistency between data sets spanning decades gps thousands of years active faulting data and millions of years paleomagnetic data and bedrock structure

an integrated perspective of the continuum between earthquakes and slow slip phenomena slow slip a mechanism by which faults can relieve stress was thought to be distinct from earthquakes however a global review of slow slip phenomena suggests that instead there is a continuum between the two types of event

transtensional tectonics in the sicily channel abstract structural geophysical and volcanological data available for the sicily channel demonstrate that the whole area is characterized by the occurrence of transtensional structures activated in a dextral shear zone trending roughly wnw ese these data allowed us to put forward a kinematic model of the area which accounts for both the existence of discrete tectonic depressions and for the localized volcanic activity of this sector of the pelagian sea the proposed model is somewhat different from other rifting mechanisms available for the sicily channel in that it may explain the occurrence of extensional features and the associated volcanism in a zone of continental collision through the development of large scale pull apart basins involving deep crustal levels