source parameters and time dependent slip distributions of slow slip events on the cascadia subduction zone from 1998 to 2008 1 we invert for the time dependent slip history of slow slip events on the cascadia subduction zone using gps data from 1998 to 2008 the 16 slip transients have sufficient station coverage to solve for the slip distribution on the plate interface gps time series are inverted for fault slip using the extended network inversion filter limited station coverage south of portland 45 5 n latitude restricts our analysis to events on the northern half of the subduction zone slip is resolved at the base of the seismogenic zone and the slip distributions suggest a potential segment boundary near seattle 47 6 n that correlates roughly with geologic and tectonic boundaries events that initiate to the north and south tend to overlap at about this latitude we compile statistics on source parameters such as propagation rate recurrence interval and stress drop which can be used to constrain proposed models of the source mechanics over a 10 year period total strain release from slow slip events is nonuniform along strike with the greatest cumulative slip 27 cm centered beneath port angeles 48 1 n this slip patch also exhibits the most regular recurrence of mw 6 events relative to other locations along strike the spatial extent of the slip patch beneath port angeles correlates with the along strike bend of the cascadia subduction zone in northwestern washington suggesting that plate geometry plays an important role in controlling the along strike characteristics of slow slip

geochemistry of rainfall at stromboli volcano aeolian islands isotopic composition and plume rain interaction the chemical and isotopic compositions of the precipitation at stromboli island italy were investigated between october 2003 and october 2005 we employed a rain gauge network designed to cover the range in exposures and elevations of the volcanic edifice the hydrogen and oxygen isotopic ratios vary greatly on a seasonal basis and correlate with air temperature deuterium excess values show a positive correlation with altitude no direct contribution of volcanogenic h or o is evident in the isotopic composition of the rainwater the chemical composition of the rainwater is principally controlled by the sea aerosol contribution at the coastal sites whereas it is significantly influenced by volcanic activity near the summit vents interaction with volcanic acid gases is indicated by the ph which is usually 1 2 units lower near the craters than at the coastal sites the s cl cl f and s f molar ratios in rainwater 1 5 km from the craters are consistent with those measured in the volcanic plume using other methods diffusive tubes and fourier transform infrared spectroscopy rising of undegassed magmas changes these molar ratios because of the differential degassing of sulphur chlorine and fluorine from the magma we therefore propose that the chemical composition of precipitation within 1 5 km of the craters provides additional information that is useful for monitoring volcanic activity at stromboli island moreover this paper presents estimates of the fluxes of f cl s na k ca and mg to the soil that could be useful for geochemical studies on groundwater

correlated increase in co2 fumarolic content and diffuse emission from la fossa crater vulcano italy evidence of volcanic unrest or increasing gas release from a stationary deep magma body 1 the peculiarity of the quiescent la fossa volcano is the occurrence of crises characterized by strong increases of fumarole t and output and by chemical changes indicative of an increasing input of magmatic fluids several surveys carried out during a new crisis began in november 2004 indicate that the total diffuse co2 emission for the crater area increases by one order of magnitude during crises up to 1600 ton d 1 in december 2005 concern exists on the possibility that these crises be related to an unrest process leading to eruption the repetition along decades of the same gas compositional variations during crises their temporal coincidence with increases of the local shallow seismicity and the lack of any significant ground motion rather suggest that they correspond to moments of increasing volatile release from a stationary magma system

time dependent inversion of three component continuous gps for steady and transient sources in northern cascadia 1 an approach to invert gps time series to estimate crustal block rotations fault locking and strain rates while simultaneously solving for transient slow slip events is described and applied to the northern cascadia subduction zone the method can use continuous or survey mode gps time series or both i invert 5 6 years of 3 component continuous gps time series at 53 sites from cascadia to estimate simultaneously the block motions and strains locking on the subduction zone and source parameters of the four most recent slow slip events over the time period and section of the cascadia margin sampled the strain released in slow slip was 7 to 10 of the accumulated subduction strain but at the base of and immediately downdip of the locked zone beneath the olympic peninsula

rainwater and ash leachate analysis as proxies for plume chemistry at soufriere hills volcano montserrat chloride and sulphate concentrations in rainwater and water soluble leachates from volcanic ash samples track the compositions of gas emissions at the soufriere hills volcano montserrat from 1996 to 2001 there are both systematic spatial and temporal variations in the chloride sulphate ratio expressed as the equivalent hcl so2 mass ratio in rainwater and ash leachates temporal variations reflect changes in eruption rate and eruptive style mass ratios of hcl so2 in ash leachates correspond closely with those obtained by open path fourier transform infrared op ftir spectroscopy and reflect changes in volatile emissions throughout the eruption both leachate and op ftir spectroscopic analyses show mass ratios of hcl so2 1 during dome growth and hcl so2 1 during non eruptive periods the hcl so2 mass ratios in rainwater samples from 1996 and 1997 show temporal variations that correlate with changes in extrusion rate the hcl so2 ratios in plume affected rainwater and ash leachates from june and july 2001 correlate positively with increasing rockfall energy and with increasing eruption rate prior to a dome collapse event the hcl so2 mass ratios in water soluble ash leachates and rainwater samples collected at the same time and from the same sites are linearly correlated with rainwater hcl so2 ratios systematically two to three times higher than ash leachate ratios spatial patterns of rainwater ph and hcl so2 in rainwater and ash leachates are principally influenced by the proximity of the sampling sites to the active dome and to the typical pattern of dispersion of the plume by tropospheric winds these results demonstrate that rainwater chemistry and ash leachate analysis provides a useful indicator of volcanic activity and represents a valuable supplement to volcano surveillance efforts

intense foreshocks and a slow slip event preceded the 2014 iquique mw 8 1 earthquake the subduction zone in northern chile is a well identified seismic gap that last ruptured in 1877 the moment magnitude mw 8 1 iquique earthquake of 1 april 2014 broke a highly coupled portion of this gap to understand the seismicity preceding this event we studied the location and mechanisms of the foreshocks and computed global positioning system gps time series at stations located on shore seismicity off the coast of iquique started to increase in january 2014 after 16 march several mw 6 events occurred near the low coupled zone these events migrated northward for 50 kilometers until the 1 april earthquake occurred on 16 march on shore continuous gps stations detected a westward motion that we model as a slow slip event situated in the same area where the mainshock occurred

carbonate oxygen isotope paleoaltimetry evaluating the effect of diagenesis on paleoelevation estimates for the tibetan plateau carbonate oxygen isotope paleoaltimetry is based on analysis of the d 18 o value of carbonate precipitated from surface water deciphering the diagenetic history is important for establishing whether particular carbonates are accurate recorders of paleosurface waters which reflect paleoelevation this study provides examples from southern east central and northeastern tibet of approaches aimed at evaluating the diagenetic history of lacustrine micrites and pedogenic carbonates the most desirable technique for avoiding erroneous interpretations related to diagenetic overprinting is to analyze carbonates that are known to be primary such as aragonitic shell material in rocks that do not contain shell material we have compared lacustrine micrites and pedogenic carbonates to diagenetic carbonate phases to determine the effects of diagenesis on the isotopic composition of primary carbonates where the potential effects of diagenesis are subtle or ambiguous we have evaluated the fidelity of the carbonate record from systematic trends in c and o isotopes that agree with other interpretations of paleoenvironment such as high frequency covariance in c and o that corresponds with changes in the mg concentration of carbonates using these strategies we have determined that diagenesis has not affected the isotopic composition of carbonates in the late miocene pliocene thakkhola graben in southern tibet and the oligocene to pliocene linxia basin in northeastern tibet in the case of paleogene basins in east central tibet however ambiguity in data precludes the determination of diagenetic effects d 2004 elsevier b v all rights reserved

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

major ion bulk deposition around an active volcano mt etna italy bulk atmospheric deposition of major cations na k ca mg and anions cl f so4 were measured at 15 sites around an active volcano mount etna from 2001 to 2003 their composition indicates several natural sources among which deposition of plume derived volcanogenic gas compounds is prevalent for f cl and s plume derived acidic compounds are also responsible for the prevailing acidic composition of the samples collected on the summit of the volcano ph in the 2 45 5 57 range cation species have complex origin including deposition of plume volcanogenic ash and aerosols and soil dust wind re suspension of either volcanic or carbonate sedimentary rocks

slow slip history for the mexico subduction zone 2005 through 2011 to further our understanding of the seismically hazardous mexico subduction zone we estimate the first time dependent slip distributions and coulomb failure stress changes for the six major slow slip events sses that occurred below mexico between late 2005 and mid 2011 slip dist ributions are the first to be estimated from all continuous gps data in central and southern mexico which better resolves slow slip in space and time than was previously possible in this region below oaxaca slip during previously un modeled sses in 2008 9 and 2010 11 extended farther to the west than previous sses this constitutes the first evidence that slow slip accounts for deep slip within a previously noted gap between the oaxaca and guerrero sse source regions the slip that we estimate for the two sses that originated below guerrero between 2005 and 2011 agrees with slip estimated in previous mostly static offset sse modeling studies however we show that both sses migrated eastward toward the oaxaca sse source region in accord with previous work we find that slow slip below guerrero intrudes up dip into the potentially seismogenic region presumably accounting for some of the missing slip within the well described guerrero seismic gap in contrast slow slip below oaxaca between 2005 and 2011 occurred mostly down dip from the seismogenic regions defined by the rupture zones of large thrust earthquakes in 1968 and 1978 and released all of the slip deficit that accumulated in the down dip region during this period

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

chemical composition of precipitation at mt vesuvius and vulcano island italy volcanological and environmental implications natural precipitation and water samples from passive devices were collected at mt vesuvius and vulcano island italy during the period 2004 2006 in order to investigate its possible interactions with fumarolic gases evidence of chemical reactions between fumarolic fluids and rain samples before and after its deposition into the sampling devices was found at vulcano island very low ph values down to 2 5 and significant amounts of chlorine and sulfate up to 22 meq l were measured at sampling points located close to the fumarolic field in contrast anthropogenic contributions and or dissolution of aerosols both maritime and continental influence the chemistry of rainwaters at mt vesuvius which show inter annual variations that are highly consistent with those recorded at the coastal site at vulcano island chemistry of waters directly exposed to fumarolic fluids may then give useful information about its temporal evolution holding the signal of the maximum chemical event occurred in the meanwhile in addition the observation of the health status of vegetation colonizing the immediate surroundings of the fumarolic fields due to its strong dependence on the interactions with these fluids may work as a possible biomarker of volcanic activity

major impact of volcanic gases on the chemical composition of precipitation in iceland during the 2014 2015 holuhraun eruption the holuhraun eruption in 2014 15 was the largest in iceland for more than 200 years it resulted in emissions of large quantities of volcanic gases into the atmosphere 11 mt so2 0 1 mt hcl and 0 05 mt hf during the eruption the volcanic gases had major effects on f so4 and to a lesser extent cl concentrations in precipitation throughout iceland effects not observed in recent decades the concentrations of f cl and so4 n 705 reached values of 444 m 12 270 m and 17 324 m during the eruption and were on average 20 times higher for f and so4 and much lower for cl compared to pre eruption times the concentrations of major cations si na k ca mg al and fe n 151 in the precipitation were taken as having originated from seawater spray and dissolution of rock dust and aerosol based on the mixing model developed here it is demonstrated that the source of the enrichment of f and so4 was indeed the volcanic gas emissions with 60 100 mol of so4 and f in the precipitation originated from volcanic gas whereas the cl originated mostly from seawater spray making the volcanic gas input of cl relatively less important than for f and so4 the results showed that large volcanic eruptions can have major effects on atmospheric chemistry and impact the composition of precipitation

chemical characterisation of rainwater at stromboli island italy the effect of post depositional processes abstract volcanoes emit fluids and solid particles into the atmosphere that modify the chemical composition of natural precipitation we have investigated the geochemistry of stromboli s rainfall during the period from november 2014 to march 2016 using a network of a new type of sampler specifically designed for operations on volcanic islands we found that most of the chemical modifications are due to processes occurring after the storage of rainwater in the sampling bottles these processes include dissolution of volcanogenic soluble salts encrusting volcanic ash and a variable contribution of sea spray aerosol our data showed noticeably less scatter than has previously been achieved with a different sampling system that was more open to the atmosphere this demonstrates the improved efficacy of the new sampler design the data showed that post depositional chemical alteration of rain samples dominates over processes occurring during droplet formation ad precipitation this has important implications for the calculation of fluxes of chemicals from rainfall in volcanic regions

transient deformation in southern mexico in 2006 and 2007 evidence for distinct deep slip patches beneath guerrero and oaxaca 1 we model three slow slip events in 2006 and 2007 recorded by continuous gps stations in central and southern mexico to test for overlap between their source regions along the mexican subduction interface and whether they intrude upward into the rupture zones of previous large earthquakes inverse modeling yields source regions beneath central oaxaca for two of the three slow slip events sse where a previously described sse occurred in 2004 and beneath guerrero for the third where slip events previously occurred in 2001 2002 and possibly 1998 along with previously published results our work suggests there are persistent differences between the depths and magnitudes of transient slip beneath oaxaca and guerrero transient slip beneath oaxaca in 2004 2006 and 2007 had a common source region downdip from the seismogenic zone and released elastic strain energy equivalent to mw 7 0 earthquakes equaling most or all energy that accumulated below the seismogenic zone transient slip beneath guerrero in 2006 had a larger moment magnitude mw 7 3 and extended somewhat farther updip possibly to seismogenic depths transient slip thus appears to relieve some elastic strain that accumulates at shallow levels in the guerrero seismic gap we find no evidence for spatial or temporal correlations of slow slip along these two widely separated source regions although better data are needed to test more definitively for any interaction between them

slow slip event in the mexican subduction zone evidence of shallower slip in the guerrero seismic gap for the 2006 event revealed by the joint inversion of insar and gps data slow slip events sses in subduction zones have been observed in the last decade with continuous gps stations some of them could be related to the lateral segmentation of subduction interface that seems to be a critical parameter for the propagation of large subduction earthquakes in 2006 one of the largest sses recorded so far was captured by a dozen continuous gps stations in the guerrero area mexico along the mexican subduction zone previous studies based on these data suggested a lateral variation of the updip depth of the see at the guerrero seismic gap but suffered from a lack of resolution east of the gap here we show the ability of insar technique to capture a part of the 2006 sse cumulative displacement east of the guerrero gap by a stacking approach we processed long strip envisat interferograms corrected for orbital errors and interseismic signal using gps data we first use a forward modelling approach to test insar sensitivity to the amount of slip depth and width of the slipping area on the subduction interface due to its high spatial resolution insar allows one to comprehensively sample the north south spatial wavelength of the sse deformation complementing the sparse gps network insar locates the maximum of uplift and subsidence caused by the sse more precisely than the gps data giving better constraints on the updip slip limit of the sse we then inverted the insar and gps data separately to understand how each inversion resolves the slip at depth finally we performed a joint inversion of insar and gps data which constrained the sse slip and its location on the plate interface over the entire guerrero area the joint inversion shows significant lateral variation of the sse slip distribution along the trench with a shallower updip edge in the guerrero seismic gap west of acapulco and a deeper slip edge further east

atmospheric dispersion environmental effects and potential health hazard associated with the low altitude gas plume of masaya volcano nicaragua masaya volcano 560 m a s l nicaragua re sumed its degassing activity in mid 1993 with the con tinuous emission of so 2 at rates increasing from 600 metric tons t day 1 7 0 kg s 1 in 1995 to 1800 t day 1 21 0 kg s 1 in 1999 the low altitude gas plume is typically blown westward by the prevailing wind across the masaya caldera and las sierras high lands which are at a higher elevation than the gas vent in this study the areal distribution of atmospheric so 2 concentrations was monitored within 44 km of the vent with a network of passive samplers measured so 2 air concentrations ranged from 2 to 90 ppbv in 1998 and from 2 to 230 ppbv in 1999 the data suggest that the volcanic emissions influenced air quality across a 1 250 km2 area downwind local topography exerts a strong control on plume dispersal and hilltops are particularly prone to fumigation and thus to high ambient so 2 lev els in a zone 22 km2 in size located within 15 km of the source the response of vegetation to sustained exposure to high atmospheric dose of volcanic so 2 and hf result ed in a strong reduction in the number of plant communi ties a transition zone of somewhat indefinite boundary surrounds the devastated zones and exhibits vegetation damage in the form of leaf injury in addition to the envi ronmental impacts of the volcanic emissions both short and long term public health hazards may exist in areas most exposed to the plume the harmful effects of the volcanic emissions on cultivated vegetation could be di minished by using windbreaks made of gas tolerant trees and shrubs such as eugenia jambos brosimum utile and clusia rosea the current gas crisis at masaya volcano provides an unique opportunity for investigating the at mospheric environmental and medical impacts of volca nic gases and aerosols

triggering of tremors and slow slip event in guerrero mexico by the 2010 mw 8 8 maule chile earthquake 1 we investigate the triggering of seismic tremor and slow slip event in guerrero mexico by the february 27 2010 maule earthquake mw 8 8 triggered tremors start with the arrival of s wave generated by the maule earthquake and keep occurring during the passing of scs ss love and rayleigh waves the rayleigh wave dispersion curve footprints the high frequency energy envelope of the triggered tremor indicating a strong modulation of the source of tremors by the passing surface wave this correlation and modulation by the passing waves is progressively lost with time over a few hours the tremor activity continues during the weeks months after the earthquake gps time series suggest that the second sub event of the 2009 2010 sse in guerrero is actually triggered by the maule earthquake the southward displacement of the gps stations starts coincidently with the earthquake and tremors the long duration of tremors indicate a continuing deformation process at depth which we propose to be the second sub event of the 2009 2010 sse we show a quasi systematic correlation between surface displacement rate measured by gps and tremor activity suggesting that the nvt are controlled by the variations in the slip history of the sse this study shows that two types of tremors emerge 1 those directly triggered by the passing waves and 2 those triggered by the stress variations associated with slow slip this indicates the prominent role of aseismic creep in the mexican subduction zone response to a large teleseismic earthquake possibly leading to large scale stress redistribution

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

complex characteristics of slow slip events in subduction zones reproduced in multi cycle simulations 1 since the discovery of slow slip events along subduction zone interfaces worldwide dense geodetic and seismic networks have illuminated detailed characteristics of these events and associated tremor high resolution observations of tremor where the spatial temporal evolution is presumed to reflect that of the underlying slow slip events show highly complex patterns in which the origins remain poorly understood we present a new computationally efficient modeling technique that reproduces many features of observed slow slip events including slow initiation coalescence of separate events and rapid back propagation of renewed slip over previously slipped regions rapid back propagation speeds are explained as a consequence of rate and state dependent frictional healing consistent with analytical solutions developed in support of the simulations

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

multi event simulations of slow slip events for a cascadia like subduction zone 1 we employ the earthquake simulator rsqsim which incorporates rate and state dependent friction to investigate characteristics of slow slip events sses along a cascadia like mega thrust the simulations consist of 100 000 sses with equivalent moment magnitudes mw4 0 7 0 the largest simulated sses mw6 4 7 0 have inter event times of 19 months durations of 10 40 days mean slips of 2 2 4 1 cm and along strike propagation speeds of 7 20 km day which are comparable to observations from cascadia the simulations show quiescence after mw 6 4 sses followed by a progressive increase in both the magnitude and frequency of sses prior to the next large event small sses below mw5 6 develop in an incoherent manner and have irregular geometries while larger sses show highly coherent growth of the slip region and spontaneous but transient event to event segmentation the change in event characteristics at mw5 6 corresponds to a break in the scaling of seismic moment with slip fault area and duration

formation of rock coatings induced by the acid fumarole plume of the passively degassing volcano of la fossa vulcano island italy at la fossa volcano vulcano island and in the surrounding environment rock coatings rc develop owing to exposure of the ground surface to a volcanic acid plume this plume is produced by the passive degassing of la fossa active cone proximal and distal with respect to the high temperature fumarolic field rc have been identified which differ in mineralogy texture and chemical composition proximal rc are characterised by high silica content massive texture and strong leaching at the expense of the pyroclastic material distal rc are characterised by the presence of silica jarosite and minor goethite laminated texture and less developed evidence of leaching the rc are produced by direct interaction between the acid fumarolic aerosol and rocks and by reaction of dews and rains acidified by the absorption of acid gases so2 hcl hf of the fumarole plume with volcanic material proximal rc are produced at conditions of ph 2 distal rc form at ph 2 3 based on the presence of jarosite although the occurrence of goethite in some samples suggests higher values of ph the influence of the volcanic plume in the development of these rc is indicated also by the coincidence of the rc areal distribution with the distribution of the volcanic plume controlled by the local wind field this is furthermore supported by the presence in rc of chloride and or sulphur bearing compounds enriched in volatile elements and metals commonly carried by volcanic aerosols

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

gps constraints on 34 slow slip events within the cascadia subduction zone 1997 2005 1 refinements to gps analyses in which we factor geodetic time series to better estimate both reference frames and transient deformation resolve 34 slow slip events located throughout the cascadia subduction zone from 1997 through 2005 timing of transient onset is determined with wavelet transformation of geodetic time series thirty continuous stations are included in this study ranging from northern california to southwestern british columbia our improvements in analysis better resolve the largest creep events and also identify many smaller events at 48 5 n latitude a 14 month average recurrence interval has been observed over eight events since 1997 farther north along vancouver island a host of smaller events with a distinct 14 month periodicity also occurs in southern washington state some of the largest transient displacements are observed but lack any obvious periodicity in their recurrence along central oregon an 18 month recurrence is evident while in northern california an 11 month periodicity continues through 2005 we invert gps offsets of the 12 best recorded events for thrust slip along the plate interface using a cross validation scheme to derive optimal smoothing parameters these 12 events have equivalent moment magnitudes between 6 3 and 6 8 and have 2 3 cm of slip unlike other subduction zones no long duration events are observed and cumulative surface deformation is consistently less than 0 6 cm the many newly resolved smaller transient events in cascadia show that slow slip events occur frequently with gps best capturing only the largest events it is likely that slow slip events occur more frequently at levels not detectable with gps

remote triggering of tremor along the san andreas fault in central california received 30 august 2008 accepted 16 april 2009 published 18 july 2009 1 we perform a systematic survey of triggered tremor along the san andreas fault in central california for the 31 teleseismic earthquakes with mw 7 5 since 2001 we identify 10 teleseismic events associated with clear triggered tremor about 52 of the tremor is concentrated south of parkfield near cholame where ambient tremor has been identified previously and the rest is widely distributed in the creeping section of the san andreas fault north of parkfield tremor is generally initiated and is in phase with the love wave particle velocity however the pattern becomes complicated with the arrival of the rayleigh waves and sometimes tremor continues after the passage of the surface waves we identify two cases in which tremor is triggered during the teleseismic pkp phase these results suggest that while shear stress from the passage of the love waves plays the most important role in triggering tremor in central california other factors such as dilatational stresses from the rayleigh and p waves also contribute we also examine the ambient tremor occurrence rate before and after the teleseismic events and find a transient increase of stacked tremor rate during the passage of the teleseismic surface waves this observation implies that the occurrence time of tremor is temporally advanced by the dynamic stresses of the teleseismic waves the amplitude of the teleseismic waves correlates with the occurrence of triggered tremor and the inferred tremor triggering threshold is 2 3 kpa the relatively low triggering threshold indicates that the effective stress at the tremor source region is very low most likely due to near lithostatic fluid pressure

temporal variations of non volcanic tremor nvt locations in the mexican subduction zone finding the nvt sweet spot epicentral locations of non volcanic tremors nvt in the mexican subduction zone are determined from the peak of the energy spatial distribution and examined over time nvt is found to occur persistently at a distance of 215 km from the trench which we term the sweet spot because this region probably has the proper conditions i e temperature pressure and fluid content for the nvt to occur with minimum shear slip high energy nvt episodes are also observed every few months extending 190 km to 220 km from the trench with durations of a few weeks during the 2006 slow slip event sse the duration and the recurrence rate of the nvt episodes increased low energy episodes were also observed independent from the high energy episodes 150 km to 190 km from the trench during the 2006 sse both the high and low energy episodes were made up of many individual nvt s that had a range of energy release rates however the highest energy release rates of the high energy episodes were consistently double those of the low energy episodes and the persistent activity at the sweet spot we suggest that all of the high energy episodes are evidence of small short repeat interval sse given this model the increased recurrence rate of the high energy nvt episodes during the 2006 long term sse implies that short term sse s also increase during the sse and are therefore triggered by the sse

environmental impact of magmatic fluorine emission in the mt etna area universita degli studi di palermo italy istituto nazionale di geofisica e vulcanologia sezione di palermo unione europea fondo sociale europeo

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

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

slow slip evolves into megathrust earthquakes in 2d numerical simulations 1 slow slip events sse in many subduction zones incrementally stress the adjacent locked megathrust suggesting that they could potentially either trigger or evolve into damaging earthquakes we explore this with 2d quasi dynamic simulations with rate state friction dilatancy and coupled 1d pore fluid and heat transport steady state weakening friction allows transient slip to nucleate but is inhibited by dilatant strengthening and destabilized by thermal pressurization sse spontaneously nucleate in low effective stress velocity weakening lesvw regions if the dimension of the lesvw is relatively small the sse are trapped at its updip end imparting a strong stress concentration in the locked zone after several centuries sse penetrate into the region of higher effective stress where thermal pressurization eventually leads to dynamic rupture for larger lesvw regions sse tend to increase in length with time ultimately higher slip speeds enhance thermal weakening leading to dynamic instability within the sse zone in both cases the onset of the ultimate sse is essentially indistinguishable from preceding events

space time correlation of slip and tremor during the 2009 cascadia slow slip event 1 episodic tremor and slip ets involving transient deformations accompanied by emergent low frequency tremor occurs in subduction zones around the world ets events increase the shear stress on locked megathrusts and may potentially trigger damaging earthquakes despite the clear association of tremor and slip the physical relationship between them is unresolved tremor appears to result from slip on small asperities on the plate interface due to either creep on the surrounding fault or stress increases ahead of the propagating slow slip front previous studies of migrating slow slip events have not had sufficient spatial and temporal resolution to differentiate between these two models to address this we invert gps data from the august 2009 ets event in central cascadia for the space time evolution of fault slip rate we find a correlation in both space and time between tremor epicenters and the independently determined position of high fault slip rate this supports the first hypothesis that tremor asperities are loaded directly by slow slip rather than by stress increases ahead of the slip front and provides new insights into the mechanics of ets

volcanic plume fingerprint in the groundwater of a persistently degassing basaltic volcano mt etna abstract the chemical composition of the groundwater at mt etna was investigated in order to determine the extent to which the persistent plume affects the chemical composition of circulating waters samples from 31 springs and wells were collected during june and july 2014 and analyzed for their chemical compositions the content of dissolved elements derives from the bulk deposition wet and dry deposition at the recharge areas as well as from the weathering of volcanic rocks during the infiltration and transport of groundwater in its early phase the chemical weathering of volcanic rocks and ashes is promoted by the acid rain that characterizes the area and subsequently by the huge amount of deep magmatic carbon dioxide co 2 coming up through the volcanic edifice and dissolving in the water the high content of chlorine is mainly derived from interactions between the plume and rainwater while the total alkalinity can be completely ascribed to the dissociation of carbonic acid h 2 co 3 after the hydration of co 2 the relative contributions of plume derived elements weathering and co 2 driven weathering has been computed for each element in addition the comparison between the chemical compositions of the bulk deposition and of groundwater provides a new understanding about the mobility of volatile elements the proposed approach has revealed that the persistent plume strongly affects the chemical composition of groundwater at mt etna and probably also at other volcanoes characterized by huge open conduit degassing activity

two successive slow slip events evidenced in 2009 2010 by a dense gps network in guerrero mexico a large slow slip event sse had been expected for the guerrero gap for 2010 it was actually observed with an onset in july 2009 comparison with the preceding large sses which occurred in 2002 and 2006 highlights both persistent characteristics of the guerrero sses e g the localization of slip in the seismogenic part of the subduction interface and also particularities of the 2009 2010 event namely two distinct slip patches on the fault interface moving consecutively the long gps time series and the density of the gps network provide evidence that the guerrero sses like classical earthquakes have complex features despite having very short and relatively regular repeat times 4 yr guerrero sses appear aperiodic a shorter loading time before the 2009 2010 event than before the 2006 sse seems to produce consistently reduced surface displacements for a group of stations in a core zone

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