interseismic strain accumulation and the earthquake potential on the southern san andreas fault system the southern section of the san andreas fault is the only part of the fault that hasn t ruptured in historic times for this reason it is believed to pose the largest seismic risk in california although whether tectonic stress is actually accumulating there is a topic of heated debate using data from radar interferometry satellites yuri fialko has produced a detailed map of surface deformation in the area that shows that elastic stress is accumulating at a fairly high rate during the past 300 years a displacement of 6 to 9 metres has built up this suggests that the southern san andreas fault is nearing the end of the interseismic phase of the earthquake cycle and that increased seismic activity of some kind can be expected the san andreas fault in california is a mature continental transform fault that accommodates a significant fraction of motion between the north american and pacific plates the two most recent great earthquakes on this fault ruptured its northern and central sections in 1906 and 1857 respectively the southern section of the fault however has not produced a great earthquake in historic times for at least 250 years assuming the average slip rate of a few centimetres per year typical of the rest of the san andreas fault the minimum amount of slip deficit accrued on the southern section is of the order of 7 10 metres comparable to the maximum co seismic offset ever documented on the fault1 2 here i present high resolution measurements of interseismic deformation across the southern san andreas fault system using a well populated catalogue of space borne synthetic aperture radar data the data reveal a nearly equal partitioning of deformation between the southern san andreas and san jacinto faults with a pronounced asymmetry in strain accumulation with respect to the geologically mapped fault traces the observed strain rates confirm that the southern section of the san andreas fault may be approaching the end of the interseismic phase of the earthquake cycle

diagnostic analysis and spectral energetics of a blocking event in the glas climate model simulation abstract we examine diagnostically the structure and spectral energetics of an amplified persistent blocking ridge and trough pattern that occurred in one of the glas climate simulations this particular model simulation was performed by shukla and bangaru 1979 to study the sensitivity of the quasi stationary waves to the north pacific sea surface temperature anomalies the spectrally filtered hovmoller diagram shows that wavenumbers 2 and 3 in the anomaly run become stationary near their climatological locations the constructive interference of wavenumbers 2 and 3 forms two persistent blocking ridges one in the west coast of north america and the other in western europe spectral energetics analysis of this blocking case shows that a2i and a3 the available potential energy of wavenumbers 2 and 3 are supplied by the conversion from zonal available potential energy k2 and k3 the kinetic energy of thew two waves are maintained by different processes k2 is maintained by conversion from a2 to k2 a

coupled magma chamber inflation and sector collapse slip observed with synthetic aperture radar interferometry on mt etna volcano 1 volcanoes deform dynamically due to changes in both their magmatic system and instability of their edifice mt etna features vigorous and almost continuous eruptive activity from its summit craters and periodic flank eruptions even though its shape is that of a large stratovolcano its structure features two rift systems and a flank collapse structure similar to hawaiian shield volcanoes we analyze european remote sensing ers satellite differential interferometric synthetic aperture radar insar data 1993 1996 for mt etna spanning its quiescence from 1993 through the initiation of renewed eruptive activity in late 1995 we use synthetic aperture radar sar data from both ascending and descending ers satellite tracks comparison of independent interferograms covering the first 2 years of the inflationary period shows a pattern consistent with inflation of the volcano calculation of the tropospheric path delay based on meteorological data does not change this interpretation interferograms from late summer 1995 1996 show no significant deformation joint inversion of interferograms from ascending and descending satellite tracks require both inflation from a spheroidal magmatic source located beneath the summit at 5 km below sea level and displacement of the east flank of etna along a basal decollement both sources of deformation were contemporaneous within the resolution of our data and suggest that inflation of the central magma chamber acted to trigger slip of etna s eastern flank these results demonstrate that flank instability and recharge of a volcano s magma system must both be considered toward understanding how volcanoes work and in their hazard evaluation

numerical modelling of melting processes and induced diapirism in the lower crust summary the processes of partial melting and magmatic diapirism within the lower crust are evaluated using a numerical underplating model fully molten basalt t 1200 c is emplaced at the moho beneath a solid granite t 750oc in order that a melt front grows into the granite if diapirism does not occur this melt front in the granite reaches a minimal depth in the crust before like in the molten basalt crystallization takes place the density contrast between the partially molten granite layer and the overlying solid granite can lead to a rayleigh taylor instability rti which results in diapiric rise of the partially molten granite assuming a binary eutectic system for both the granite and the underplating basalt and a temperature and stress dependent rheology for the granite we numerically solve the governing equations and find a that diapirism occurs only within a certain but possibly realistic range of parameters and b that if diapirs occur they do not rise to levels shallower than 15 or perhaps 12km the growth rate depends on the degree of melting and the thickness of the partially molten layer as well as the viscosity of the solid and the partially molten granite from a comparison of the growth rate with the velocity of a stefan front it is possible to predict whether a melt front will become unstable and result in diapiric ascent or whether a partially molten layer is created which remains at depth we carry out such a comparison using our thermodynamically and thermomechanically consistent model of melting and diapirism

interferometric synthetic aperture radar insar atmospheric correction gps moderate resolution imaging spectroradiometer modis and insar integration atmospheric effects represent one of the major limitations of repeat pass interferometric synthetic aperture radar insar in this paper gps and moderate resolution imaging spectroradiometer modis data were integrated to provide regional water vapor fields with a spatial resolution of 1 km 1 km and a water vapor correction model based on the resultant water vapor fields was successfully incorporated into the jet propulsion laboratory california institute of technology roi pac software the advantage of this integration approach is that only one continuous gps station is required within a 2030 km 1354 km modis scene application to ers 2 repeat pass data over the los angeles southern california integrated gps network scign area shows that this integration approach not only helps discriminate geophysical signals from atmospheric artifacts but also reduces water vapor effects significantly which is of great interest to a wide community of geophysicists

decadal volcanic deformation in the central andes volcanic zone revealed by insar time series 1 decadal trends of volcanic deformation in the central andes volcanic zone cvz are identified with interferometric synthetic aperture radar insar stacks and time series velocity maps covering an area 19 s 27 s and 66 w 69 w we combine over 750 ers and envisat interferograms from two descending and three ascending tracks these tracks cover 100 000 km 2 and span 1992 2011 our analysis extends observations at cerro blanco uturuncu and lazufre volcanic centers and uncovers two previously undocumented deformation centers cerro overo in northern chile and putana volcano in southwest bolivia cerro overo exhibits a transition from steady 0 4 cm yr deflation to 0 5 cm yr inflation over several years putana volcano underwent a short lived episode of uplift between 13 september 2009 and 31 january 2010 with a maximum uplift of 4 0 cm cerro blanco continues 1 0 cm yr deflation since 1995 uplift at lazufre began between 1997 and 2000 and has gradually accelerated to 3 5 cm yr since 2005 uturuncu volcano continues 1 0 cm yr monotonic uplift since 1992 and shows evidence for a broad moat of subsidence surrounding the uplifting region four of the nine deformation events in the cvz are not obviously associated with a particular volcanic edifice furthermore there is significant spatial and temporal variability of these deformation events within a small geographic area

diapiric ascent of silicic magma beneath the bolivian altiplano 1 the vertical transport of large volumes of silicic magma which drives volcanic eruptions and the long term compositional evolution of the continental crust is a highly debated problem in recent years dyking has been favored as the main ascent mechanism but the structural connection between a distributed configuration of melt filled pores in the source region and shallow magma reservoirs remains unsolved in the central andes inversion of a new high resolution bouguer anomaly data over the altiplano puna magma body apmb reveals 15 km wide vertically elongated low density 3d structures rooted at the top of the apmb at 20 km depth we integrate our gravity inversion with the available geophysical geological and petrological observations and in agreement with petrological mechanical considerations propose that in this region of the andes partially molten granitic bodies ascend diapirically through the hot ductile mid upper crust

atmospheric propagation heterogeneities revealed by ers 1 interferometry spaceborne synthetic aperture radar sar repeat pass interferometry is a technique based on the exploitation of the interference pattern of two sar images acquired in similar geometric conditions at two different dates this measure contains geometric atmospheric topographic and land deformation information in this paper we focus on the atmospheric information first we show theoretically that an adequate processing is sufficient to remove homogeneous atmospheric effects and that heterogeneities as tropospheric turbulences rain falls and ionospheric phenomena can be detected with sar interferometry then we interpret several observations and we present interferometric images of cumulus and turbulences due to relief sar interferometry could be a new remote sensing tool for the study of tropospheric turbulences at a high horizontal resolution 40 m

atmospheric effects in interferometric synthetic aperture radar surface deformation and topographic maps interferogram images derived from repeat pass spaceborne synthetic aperture radar systems exhibit artifacts due to the time and space variations of atmospheric water vapor other tropospheric variations such as pressure and temperature also induce distortions but the effects are smaller in magnitude and more evenly distributed throughout the interferogram than the wet troposphere term spatial and temporal changes of 20 in relative humidity lead to 10 cm errors in deformation products and perhaps 100 m of error in derived topographic maps for those pass pairs with unfavorable baseline geometries in wet regions such as hawaii these are by far the dominant errors in the spaceborne imaging radar c and x band synthetic aperature radar sir c x sar interferometric products the unknown time delay from tropospheric distortion is independent of frequency and thus multiwavelength measurements such as those commonly used to correct radar altimeter and global positioning system gps ionospheric biases cannot be used to rectify the error in the topographic case the errors may be mitigated by choosing interferometric pairs with relatively long baselines as the error amplitude is inversely proportional to the perpendicular component of the interferometer baseline for the sir c x sar hawaii data we found that the best longest baseline pair produced a map supporting 100 m contouring whereas the poorest baseline choice yielded an extremely noisy topographic map even at this coarse contour interval in the case of deformation map errors the result is either independent of baseline parameters or else very nearly so here the only solution is averaging of independent interferograms so in order to create accurate deformation products in wet regions many multiple passes may be required rules for designing optimal data acquisition and processing sequences for interferometric analyses in nondesert parts of the world are 1 to use the longest radar wavelengths possible within ionospheric scintillation and faraday rotation limits 2 for topography maximize interferometer baseline within decorrelation limits and 3 for surface deformation use multiple observations and average the derived products following the above recipe yields accuracies of 10 m for digital elevation models and 1 cm for deformation maps even in very wet regions such as hawaii

sombrero uplift above the altiplano puna magma body evidence of a ballooning mid crustal diapir the altiplano puna ultralow velocity zone in the central andes south america is the largest active magma body in earth s continental crust space geodetic observations reported an uplift in the altiplano puna proper at a rate of 10 mm year however the nature of the inferred inflation source has been uncertain we present data showing that the uplift has persisted at a nearly constant rate over the past two decades and is surrounded by a broad zone of subsidence we show that the ongoing uplift and peripheral subsidence may result from a large mid crustal diapir fed by partial melt from the altiplano puna magma body

evidence for on going inflation of the socorro magma body new mexico from interferometric synthetic aperture radar imaging interferometric synthetic aperture radar insar imaging of the central rio grande rift new mexico usa during 1992 1999 reveals a crustal uplift of several centimeters that spatially coincides with the seismologically determined outline of the socorro magma body one of the largest currently active magma intrusions in the earth s continental crust modeling of interferograms shows that the observed deformation may be due to elastic opening of a sill like intrusion at a rate of a few millimeters per year despite an apparent constancy of the geodetically determined uplift rate thermodynamic arguments suggest that it is unlikely that the socorro magma body has formed via steady state elastic inflation

dauphine twinning as evidence for an impact origin of preferred orientation in quartzite an example from vredefort south africa large meteorite impacts cause great changes to geologic features on earth ranging from cratering and ejecta blankets to phase transformations in minerals in this report we describe the effect of a shock wave on the crystallographic orientation of quartz crystals in quartzite from the vredefort impact site in south africa preferred orientation of bulk quartzite samples was measured by time of flight neutron diffraction with a random distribution of c axes a weak but distinct difference between the orientation distribution of positive and negative rhombs was observed as illustrated with pole figures and inverse pole figures results for the natural vredefort sample are compared with deformation

model experiments on the impact of pacific sea surface temperature anomalies on blocking frequency abstract sensitivity experiments with a perpetual january version of a low resolution general circulation model are conducted to investigate the influence of pacific sea surface temperature sst anomalies on blocking in the northern hemisphere six 1200 day integrations each of which contains a different specified sst anomaly superimposed upon a fixed climatological sst distribution are compared with a 1200 day control simulation to examine the impact of both equatorial pacific and midlatitude north pacific anomalous forcing an ensemble of eight independent 90 day realizations is extracted from each simulation distributions of the ensemble mean differences in the total number of blocking days from the control simulation are presented along with estimates of the statistic significance of these differences pacific sst anomalies do not strongly affect the total number of days in which a block is present anywhere over the north pacific basin but they apparently can affect the preferred regions over th

giant magmatic water reservoirs at mid crustal depth inferred from electrical conductivity and the growth of the continental crust the formation of the continental crust at subduction zones involves the differentiation of hydrous mantle derived magmas through a combination of crystallization and crustal melting however understanding the mechanisms by which differentiation occurs at depth is hampered by the inaccessibility of the deep crust in active continental arcs here we report new high pressure electrical conductivity and petrological experiments on hydrated andesitic melt from uturuncu volcano on the bolivian altiplano by applying our results to regional magnetotelluric data we show that giant conductive anomalies at mid crustal levels in several arcs are characterized by relatively low amounts of intergranular andesitic partial melts with unusually high dissolved water contents 8 wt h2o below uturuncu the altiplano puna magma body apmb displays an electrical conductivity that requires high water content up to 10 wt dissolved in the melt based on crystal liquid equilibria and melt h2o solubility experiments such a super hydrous andesitic melt must constitute about 10 of the apmb the remaining 90 being a combination of magmatic cumulates and older crustal rocks the crustal ponding level of these andesites at around 6 kbar pressure implies that on ascent through the crust hydrous magmas reach their water saturation pressure in the mid crust resulting in decompression induced crystallization that increases magma viscosity and in turn leads to preferential stalling and differentiation similar high conductivity features are observed beneath the cascades volcanic arc and taupo volcanic zone this suggests that large amounts of water in super hydrous andesitic magmas could be a common feature of active continental arcs and may illustrate a key step in the structure and growth of the continental crust one sentence summary geophysical laboratory conductivity and petrological experiments reveal that deep electrical conductivity anomalies beneath the central andes cascades and taupo volcanic zone image the ponding of super hydrous andesitic melts which contributes to the growth of continental crust

uturuncu volcano bolivia volcanic unrest due to mid crustal magma intrusion uturuncu volcano sw bolivia is a dormant stratovolcano 85 km3 dominated by dacitic lava domes and flows 39ar 40ar ages show that the volcano was active between 890 ka and 271 ka with the lavas becoming younger and less extensive at higher elevations there are current signs of unrest between 1992 and 2006 geodetic satellite measurements record an ongoing 70 km deformation field with a central uplift rate of 1 to 2 cm yr deformation indicates volume changes of 400 x 108 m3 over 14 years an average of 1 m3 s 10 2 km3 yr the deformation is attributed to magma intrusion into the altiplano puna regional crustal magma body deformation models indicate a source at depths of 17 to 30 km beneath current local relief in a reconnaissance survey persistent seismic activity mean of 2 6 earthquakes per hour with a maximum of 14 per hour was recorded at about 4 km depth below the center of the uplift 4 km sw of the volcano s summit the seismic events have a normal b value 1 04 and activity is attributed to brittle deformation in the elastic crust above the active deep magma intrusion the porphyritic dacite lavas 64 68 sio2 have a plagioclase orthopyroxene biotite magnetite ilmenite assemblage and commonly contain juvenile silicic andesite inclusions cognate norite nodules and crustal xenoliths temperature estimates are in the range 805 to 872 c for the dacites and about 980 c for the silicic andesites the dacite magmas formed by fractional crystallization of andesite forming norite cumulates and involving partial melting of crust compositions and zoning patterns of orthopyroxene and plagioclase phenocrysts indicate that compositional variation in the dacites is caused by magma mixing with the silicic andesite reversely zoned orthopyroxene phenocrysts in the andesitic end member are explained by changing oxidation states during crystallization fe3 fe2 ratios from orthopyroxene crystals and fe3 in plagioclase provide evidence for a relatively reduced melt that subsequently ascended degassed and became more oxidized as a consequence of degassing the geophysical and petrological observations suggest that dacite magma is being intruded into the altiplano puna regional crustal magma body at 17 km or more depth consistent with deformation models in the late pleistocene dacitic and andesitic magmas ascended from the regional crustal magma body to a shallow magma system at a few kilometers depth where they crystallized and mingled together the current unrest together with geophysical anomalies and 270 ka of dormancy indicate that the magmatic system is in a prolonged period of intrusion such circumstances might eventually lead to eruption of large volumes of intruded magma with potential for caldera formation

an insar based survey of volcanic deformation in the central andes we extend an earlier interferometric synthetic aperture radar insar survey covering about 900 remote volcanos of the central andes 14 27 s between the years 1992 and 2002 our survey reveals broad 10s of km roughly axisymmetric deformation at 4 volcanic centers two stratovolcanoes are inflating uturuncu bolivia and hualca hualca peru another source of inflation on the border between chile and argentina is not obviously associated with a volcanic edifice here called lazufre and a caldera cerro blanco also called robledo in northwest argentina is subsiding we explore the range of source depths and volumes allowed by our observations using spherical ellipsoidal and crack like source geometries we further examine the effects of local topography upon the deformation field and invert for a spherical point source in both elastic half space and layered space crustal models we use a global search algorithm with gradient search methods used to further constrain best fitting models inferred source depths are model dependent with differences in the assumed source geometry generating a larger range of accepted depths than variations in elastic structure source depths relative to sea level are 8 18 km at hualca hualca 12 25 km for uturuncu 5 13 km for lazufre and 5 10 km at cerro blanco deformation at all four volcanoes seems to be time dependent and only uturuncu and cerro blanco were deforming during the entire time period of observation inflation at hualca hualca stopped in 1997 perhaps related to a large eruption of nearby sabancaya volcano in may 1997 although there is no obvious relation between the rate of deformation and the eruptions of sabancaya we do not observe any deformation associated with eruptions of lascar chile at 16 other volcanoes that had recent small eruptions or fumarolic activity or associated with a short lived thermal anomaly at chiliques volcano we posit a hydrothermal system at cerro blanco to explain the rate of subsidence there for the last decade we calculate the ratio of the volume of magma intruded to extruded is between 1 10 and that the combined rate of intrusion and extrusion is within an order of magnitude of the inferred geologic rate

impact of localized tropical and extratropical sst anomalies in ensembles of seasonal gcm integrations a series of 120 day ensemble integrations of a general circulation model designed to assess the impact of geographically localized sea surface temperature sst anomalies in both the tropics and extratropics are described these experiments contribute firstly to an appraisal of the relative roles of tropical and extratropical sst anomalies on interannual variability of the large scale circulation in the northern extratropics and secondly to an assessment of the role of quasi stationary diabatic heating anomalies on model systematic error including blocking activity overall it is found that sst anomalies associated with el nino and la nina have a larger and more reproducible impact on the extratropics than the chosen extratropical sst anomalies these extratropical anomalies were localized to the north west pacific and north west atlantic with realistic amplitude however unlike earlier studies a response to the extratropical north pacific sst anomalies has been obtained over the north pacific which is correlated with the sign of the imposed sst anomaly the response to extratropical sst anomalies in the north west atlantic are similar to the results obtained from an earlier study the downstream responses to the extratropical pacific and atlantic sst anomalies are qualitatively similar to one another overall it is concluded that the northern large scale flow is influenced by such extratropical sst anomalies the response to idealized tropical sst anomalies was also studied in particular a localized anomaly over indonesia had a very substantial impact on the hadley circulation on zonal flow and on blocking frequency over the north pacific and europe this response was such as to reduce model systematic error locally in the vicinity of the sst anomaly remotely around the tropics and remotely in the extratropics a similar though weaker impact on euro atlantic blocking was obtained with an idealized caribbean sst anomaly further statistical and dynamical analyses suggested that the extratropical response to the indonesian sst anomaly occurs through the creation of two distinct planetary scale regimes in one of which the formation of blocks is much favoured by increased ridges on the north eastern side of the oceans

mitigation of atmospheric phase delays in insar data with application to the eastern california shear zone we present a method for estimating radar phase delays due to propagation through the troposphere and the ionosphere based on the averaging of redundant interferograms that share a common scene estimated atmospheric contributions can then be subtracted from the radar interferograms to improve measurements of surface deformation inversions using synthetic data demonstrate that this procedure can considerably reduce scatter in the time series of the line of sight displacements we demonstrate the feasibility of this method by comparing the interferometric synthetic aperture radar insar time series derived from ers 1 2 and envisat data to continuous global positioning system data from eastern california we also present results from several sites in the eastern california shear zone where anomalous deformation has been reported by previous studies including the blackwater fault the hunter mountain fault and the coso geothermal plant

the central andean altiplano puna magma body receiver function analysis of 14 teleseismic events recorded by 6 temporary passcal broadband stations within the altiplano puna volcanic complex apvc shows a consistent 2 s negative polarity p to s conversion for all stations for all available azimuths forward modeling of the largest amplitudes suggests that this conversion is produced by the top of a very low velocity zone at a depth of 19 km with a vs 0 5 km s and a thickness of 750 810 m we interpret the characteristics of the low velocity zone low vs areal extent and flatness to be consistent with a sill like magma body on the basis of additional data from the german ancorp experiment the altiplano puna magma body appears to underlie much of the apvc and it may therefore be the largest known active continental crustal magma body

deflation and inflation of a large magma body beneath uturuncu volcano bolivia insights from insar data surface lineaments and stress modelling summary the voluminous ash flow eruptive products in the central andes imply that there are major magma bodies however how these magma bodies develop and change in time and space are not understood in this study we analyse the deformation activity of the uturuncu volcano sw bolivia from 2003 to 2009 using a satellite radar interferometry insar data set we find that the strength and the pattern of the present deformation can be explained by a pressurized source such as an inflating flat topped magma body at 22 9 km depth below the surface furthermore we examine the optical remote sensing data to perform a lineament analysis which shows in a geographic information system gis that a girdle of river streams and faults encircle the volcano at radial distance of approximately 15 km using numerical stress models we locate a magma body beneath the volcano and find that the lineaments are best explained by a deflating flat topped magma body at approximately 18 2 km depth which is consistent with the insar study thus both the independent analysis of insar and lineament data suggest the presence of a horizontally extended flat topped magma body beneath uturuncu the location depth is in agreement with or just above a prominent seismic low velocity zone consequently although the sign of deformation caused by the herein constrained magma body differs the similar geometry and similar location suggest them to be similar possibly indicating longevity of a magma storage region

the large scale surface uplift in the altiplano puna region of bolivia a parametric study of source characteristics and crustal rheology using finite element analysis 1 this paper focuses on the driving mechanism behind a 70km wide region of ground uplift centered on uturuncu volcano in the altiplano puna region of southern bolivia we present a series of forward models using finite element analysis to simultaneously test for first order parameters that help constrain a viable model for the observed maximum line of sight uplift rate of 1 2cm yr between 1992 and 2006 stresses from pressure sources with finite geometries are solved numerically accounting for both homogeneous and heterogeneous mechanical rock properties in elastic and viscoelastic rheologies crustal heterogeneity is constrained by seismic velocity data that indicate the presence of a large low velocity zone the altiplanopuna magma body at depths of 17km below the surface a viscoelastic rheology is employed to account for time dependent deformation and an inelastic crust comparing homogeneous and heterogeneous models demonstrates the significant impact of a mechanically weak source depth layer which alters surface displacement patterns by buffering subsurface deformation elastic model results guide the source parameters tested in the viscoelastic models and demonstrate a range of possible causative source geometries our preferred model suggests that pressurization of a magma source extending upward from the altiplano puna magma body is causing the observed surface uplift and alludes to a continued increase in this pressure to explain both the spatial and temporal patterns we also demonstrate how a pressure time function plays a first order role in explaining the observed temporal deformation pattern

variations in the long term uplift rate due to the altiplano puna magma body observed with sentinel 1 interferometry abstract we present new interferometric synthetic aperture radar insar observations of surface deformation in the altiplano puna region south america where previous studies documented a broad uplift at an average rate of 10 mm yr we use data from the sentinel 1 satellite mission to produce high resolution velocity maps and time series of surface displacements between years 2014 2017 the data reveal that the uplift has slowed down substantially compared to the 1992 2010 epoch and is characterized by short term fluctuations on time scales of months to years the observed variations in uplift rate may indicate a non steady supply of melt and or volatiles from the partially molten altiplano puna magma body apmb into an incipient diapir forming in the roof of the apmb

shallow seismicity triggered seismicity and ambient noise tomography at the long dormant uturuncu volcano bolivia using a network of 15 seismometers around the inflating uturuncu volcano from april 2009 to 2010 we find an average rate of about three local volcano tectonic earthquakes per day and swarms of 5 60 events a few times per month with local magnitudes ranging from 1 2 to 3 7 the earthquake depths are near sea level more than 10 km above the geodetically inferred inflation source and the altiplano puna magma body the mw 8 8 maule earthquake on 27 february 2010 triggered hundreds of earthquakes at uturuncu with the onset of the love and rayleigh waves and again with the passage of the x2 x3 overtone phases of rayleigh waves this is one of the first incidences in which triggering has been observed from multiple surface wave trains the earthquakes are oriented nw se similar to the regional faults and lineaments the b value of the catalog is 0 49 consistent with a tectonic origin of the earthquakes we perform ambient noise tomography using love wave cross correlations to image a low velocity zone at 1 9 to 3 9 km depth below the surface centered slightly north of the summit the low velocities are perhaps related to the hydrothermal system and the low velocity zone is spatially correlated with earthquake locations the earthquake rate appears to vary with time a seismic deployment from 1996 to 1997 reveals 1 5 earthquakes per day whereas 60 events day were seen during 5 days using one seismometer in 2003 however differences in analysis methods and magnitudes of completeness do not allow direct comparison of these seismicity rates the rate of seismic activity at uturuncu is higher than at other well monitored inflating volcanoes during periods of repose the frequent swarms and triggered earthquakes suggest the hydrothermal system is metastable