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Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of kilometres long1. Previous models of rifting events indicate either lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens2, 3, 4, or magma flowing vertically into dykes from an underlying source5, 6, with the role of topography on the evolution of lateral dykes not clear. Here we show how a recent segmented dyke intrusion in the Bárðarbunga volcanic system grew laterally for more than 45 kilometres at a variable rate, with topography influencing the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred primarily over 14 days, was revealed by propagating seismicity, ground deformation mapped by Global Positioning System (GPS), interferometric analysis of satellite radar images (InSAR), and graben formation. The strike of the dyke segments varies from an initially radial direction away from the Bárðarbunga caldera, towards alignment with that expected from regional stress at the distal end. A model minimizing the combined strain and gravitational potential energy explains the propagation path. Dyke opening and seismicity focused at the most distal segment at any given time, and were simultaneous with magma source deflation and slow collapse at the Bárðarbunga caldera, accompanied by a series of magnitude M > 5 earthquakes. Dyke growth was slowed down by an effusive fissure eruption near the end of the dyke. Lateral dyke growth with segment barrier breaking by pressure build-up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries.

Surges are common at all the major ice caps in Iceland. Ice masses of gigatons may shift from the upper part of the outlet glacier towards the terminus in a few months, advancing the glacier front by up to several kilometres. The advancing ice front may be up to 100m thick, increasing the load on crustal rocks correspondingly. We use the observed change in crustal loading during a surge of the western part of the Vatnajökull ice cap, Iceland, during 1993–1995 and the corresponding elastic crustal deformation, surveyed with interferometric synthetic aperture radar, to investigate the material properties of the solid Earth in this region. Crustal subsidence due to the surge reaches ∼75mm at the edge of the Síðujökull outlet glacier. This signal is mixed with a broad uplift signal of ∼12mmyr−1, relative to our reference area, caused by the ongoing retreat of Vatnajökull in response to climate change. We disentangle the two signals by linear inversion. Finite element modelling is used to investigate the elastic Earth response of the surge, as well as to confirm that no significant viscoelastic deformation occurred as a consequence of the surge. The modelling leads to estimates of the Young's modulus and Poisson's ratio of the underlying Earth. Comparison between the observed and modelled deformation fields is made using a Bayesian approach that yields the estimate of a probability distribution for each of the free parameters. Residuals indicate a good agreement between models and observations. One-layer elastic models result in a Young's modulus of 43.2–49.7 GPa (95 per cent confidence) and Poisson's ratio of 0–0.27, after removal of outliers. Our preferred model, with two elastic layers, provides a better fit to the whole surge signal. This model consists of a 1-km-thick upper layer with an average Young's modulus of 12.9–15.3 GPa and Poisson's ratio of 0.17, overlying a layer with an average Young's modulus of 67.3–81.9 GPa and Poisson's ratio of 0.25.

International audience; The Tungurahua volcano, in Ecuador, has been experiencing a substantial activity period since 1999, with several eruptions, including those of 2006 and 2008. We use a persistent scatterers approach to analyze a time series of Envisat synthetic aperture radar (SAR) data over the period 2003-2009, to investigate surface deformation in the region of the volcano. We measure a continuous large-scale uplift with a maximum line of sight displacement rate of about 8 mm/yr, which is the first evidence of a sustained inflation in the Andes for an active volcano encompassing several eruptions. We model this signal as magma emplacement in a permanent storage zone at 11.5 km below sea level, with a net inflow rate of 7 million m3/yr. The paroxysmal eruptions in 2006 and 2008 did not seem to disrupt this long-term signal. However, we observe significant deformation during the 2006 eruption consistent with an additional intrusion of 4.5 million m3 of magma. © 2014. American Geophysical Union.

The Arctic environment offers the biggest challenge for In-SAR; huge seasonal change, ice and snow cover for much of the year, and large variations in soil moisture. Yet the Arctic is often seen as a barometer for climate change and therefore being able to exploit technologies such as InSAR provides invaluable information not only for the communities involved, but also for climate change science as a whole. Furthermore, InSAR's unmatched spatial coverage make it an obvious choice for covering vast landmasses such as the Canadian Archipelago.

Twenty years of continuous Earth observation by satellite SAR have resulted in numerous new insights into active volcanism, including a better understanding of subsurface magma storage and transport, deposition of volcanic materials on the surface, and the structure and development of volcanic edifices. This massive archive of data has resulted in fundamental leaps in our understanding of how volcanoes work – for example, identifying magma accumulation at supposedly quiescent volcanoes, even in remote areas or in the absence of ground-based data. In addition, global compilations of volcanic activity facilitate comparison of deformation behavior between different volcanic arcs and statistical evaluation of the strong link between deformation and eruption. SAR data are also increasingly used in timely hazard evaluation thanks to decreases in data latency and growth in processing and analysis techniques. The existing archive of SAR imagery is on the cusp of being enhanced by a new generation of satellite SAR missions, in addition to ground-based and airborne SAR systems, which will provide enhanced temporal and spatial resolution, broader geographic coverage, and improved availability of data to the scientific community. Now is therefore an opportune time to review the contributions of SAR imagery to volcano science, monitoring, and hazard mitigation, and to explore the future potential for SAR in volcanology. Provided that the ever-growing volume of SAR data can be managed effectively, we expect the future application of SAR data to expand from being a research tool for analyzing volcanic activity after the fact, to being a monitoring and research tool capable of imaging a wide variety of processes on different temporal and spatial scales as those processes are occurring. These data can then be used to develop new models of how volcanoes work and to improve quantitative forecasts of volcanic activity as a means of mitigating risk from future eruptions.

FUTUREVOLC is a collaborative project funded through the FP7 Environment Supersite Concept call encompassing 26 partners in 10 countries. The main objectives of FUTUREVOLC are to establish an integrated volcanological monitoring procedure through European collaboration, develop new methods to evaluate volcanic crises, increase scientific understanding of magmatic processes and improve delivery of relevant information to civil protection and authorities. FUTUREVOLC is in the first of its 3.5 year duration, therefore this paper presents aims and expectations rather than results.

International audience; Nyamulagira, located in the east of the Democratic Republic of Congo on the western branch of the East African rift, is Africa's most active volcano, with an average of one eruption every 3 years since 1938. Owing to the socio-economical context of that region, the volcano lacks ground-based geodetic measurements but has been monitored by interferometric synthetic aperture radar (InSAR) since 1996. A combination of 3D Mixed Boundary Element Method and inverse modelling, taking into account topography and source interactions, is used to interpret InSAR ground displacements associated with eruptive activity in 1996, 2002, 2004, 2006 and 2010. These eruptions can be fitted by models incorporating dyke intrusions, and some (namely the 2006 and 2010 eruptions) require a magma reservoir beneath the summit caldera. We investigate inter-eruptive deformation with a multi-temporal InSAR approach. We propose the following magma plumbing system at Nyamulagira by integrating numerical deformation models with other available data: a deep reservoir (c. 25 km depth) feeds a shallower reservoir (c. 4 km depth); proximal eruptions are fed from the shallow reservoir through dykes while distal eruptions can be fed directly from the deep reservoir. A dyke-like conduit is also present beneath the upper southeastern flank of Nyamulagira.

Stress is the most commonly reported precipitating factor for seizures. The proconvulsant actions of stress hormones are thought to mediate the effects of stress on seizure susceptibility. Interestingly, epileptic patients have increased basal levels of stress hormones, including corticotropin-releasing hormone (CRH) and corticosterone, which are further increased following seizures. Given the proconvulsant actions of stress hormones, we proposed that seizure-induced activation of the hypothalamic-pituitary-adrenal (HPA) axis may contribute to future seizure susceptibility. Consistent with this hypothesis, our data demonstrate that pharmacological induction of seizures in mice with kainic acid or pilocarpine increases circulating levels of the stress hormone, corticosterone, and exogenous corticosterone administration is sufficient to increase seizure susceptibility. However, the mechanism(s) whereby seizures activate the HPA axis remain unknown. Here we demonstrate that seizure-induced activation of the HPA axis involves compromised GABAergic control of CRH neurons, which govern HPA axis function. Following seizure activity, there is a collapse of the chloride gradient due to changes in NKCC1 and KCC2 expression, resulting in reduced amplitude of sIPSPs and even depolarizing effects of GABA on CRH neurons. Seizure-induced activation of the HPA axis results in future seizure susceptibility which can be blocked by treatment with an NKCC1 inhibitor, bumetanide, or blocking the CRH signaling with Antalarmin. These data suggest that compromised GABAergic control of CRH neurons following an initial seizure event may cause hyperexcitability of the HPA axis and increase future seizure susceptibility.

A broad uplift occurs in Iceland in response to the retreat of ice caps, which began circa 1890. Until now, this deformation signal has been measured primarily using GPS at points some distance away from the ice caps. Here, for the first time we use satellite radar interferometry (interferometric synthetic aperture radar) to constrain uplift of the ground all the way up to the edge of the largest ice cap, Vatnajokull. This allows for improved constraints on the Earth rheology, both the thickness of the uppermost Earth layer that responds only in an elastic manner and the viscosity below it. The interferometric synthetic aperture radar velocities indicate a maximum displacement rate of 24 +/- 4 and 31 +/- 4 mm/yr at the edge of Vatnajokull, during 1995-2002 and 2004-2009, respectively. The fastest rates occur at outlet glaciers of low elevation where ice retreat is high. We compare the observations with glacial isostatic adjustment models that include the deglaciation history of the Icelandic ice caps since 1890 and two Earth layers. Using a Bayesian approach, we derived probability density functions for the average Earth model parameters for three satellite tracks. Based on our assumptions, the three best fit models give elastic thicknesses in the range of 15-40 km, and viscosities ranging from 4-10x1018 Pa s.

Subsidence within the main caldera of Askja volcano in the North of Iceland has been in progress since 1983. Here, we present new ground- and satellite-based deformation data, which we interpret together with new and existing micro-gravity data, to help understand which processes may be responsible for the unrest. From 2003 to 2007, we observe a net micro-gravity decrease combined with subsidence and from 2007 to 2009 we observe a net micro-gravity increase while the subsidence continues. We infer subsidence is caused by a combination of a cooling and contracting magma chamber at a divergent plate boundary. Mass movements at active volcanoes can be caused by several processes, including water table/lake level movements, hydrothermal activity and magma movements. We suggest that, here, magma movement and/or a steam cap in the geothermal system of Askja at depth are responsible for the observed micro-gravity variations. In this respect, we rule out the possibility of a shallow intrusion as an explanation for the observed micro-gravity increase but suggest magma may have flowed into the residing shallow magma chamber at Askja despite continued subsidence. In particular, variable compressibility of magma residing in the magma chamber as well as compressibility of the surrounding rock may be the reason why this additional magma did not create any detectable surface deformation.

Ice retreat on volcanoes reduces pressure at the surface of the Earth and induces stress changes in magmatic systems. The consequences can include increased generation of magma at depth, increased magma capture in the crust, and modification of failure conditions of magma chambers. We review the methodology to evaluate each of these effects, and consider the influence of ongoing ice retreat on volcanoes at the Mid-Atlantic divergent plate boundary in Iceland. Evaluation of each of these effects requires a series of assumptions regarding the rheology of the crust and mantle, and the nature of magmatic systems, contributing to relatively large uncertainty in response of a magmatic system to climate warming and associated ice retreat. Pressure release melting due to ice cap retreat in Iceland may at present times generate a similar amount of magma as plate tectonic processes; larger than realized previously. However, new modelling shows that part of this magma may be captured in the crust, rather than being erupted. Gradual retreat of ice caps do steadily modify failure conditions at magma chambers, which is highly dependent on their geometry and depth, as well as the details of ice load variations. A model is presented where long-term ice retreat at Katla volcano decreases the likelihood of eruption, as more magma is needed in the magma chamber to cause failure than in the absence of the ice retreat.

Terrestrial Radar Interferometry (TRI) has several advantages for measuring glacier velocity. These ground-based systems alleviate problems associated with the long revisit times of satellites, and provide higher spatial sampling compared to GPS-based approaches. TRI is the technique of choice for rapidly moving glaciers, especially their terminal zones, which tend to exhibit high spatial and temporal variability. In this study, we use the Gamma Portable Radar Interferometer (GPRI) to measure the velocity of Breidamerkurjokull, a marine-terminating outlet glacier on the southeastern coast of Iceland, and compare it to TerraSAR-X data taken shortly after. We document significant temporal and spatial variability of ice velocity within 800 meters of the calving front.

Many calderas in the world show long-term unrest in the form of elevated rates of deformation and seismicity, related to pressure changes and magma movements within their magmatic plumbing systems. We present new observations of the style of deformation at the Askja caldera, Iceland, since 2000, using interferometric analysis of synthetic aperture radar images (InSAR) acquired by the Canadian RADARSAT-2 satellite. When combined with previously acquired detailed geodetic observations, by various techniques, we obtain an overview of Askja's behaviour through more than four decades. The combined dataset reveals that, during this non-eruptive period, Askja continuously subsides at a rate of 2.5–3 cm/yr in 2000–2009, somewhat lower than the ~ 5 cm/yr rate inferred for the 1983–1998 period. This behaviour of Askja is evaluated and compared to those of other restless calderas. The wrapped interferograms show three main features: (1) concentric fringes depicting subsidence in the centre of the main Askja caldera, (2) oval fringes elongated along the rift portraying subsidence and (3) subsidence in an area north of the Vatnajokull glacier. The average line-of-sight (LOS) velocity from ground to satellite was used as input for inverse modelling, of a deflating pressure source beneath the caldera, embedded in a homogeneous, elastic half-space. Two different source geometries were tested: a point pressure source and a horizontal penny shaped crack. The concentric fringes centred in the Askja caldera are best fit by a point source located at 65.05°N 16.78°W, at a depth of 3.2–3.8 km with a volume decrease of 0.0012–0.0017 km3/yr from 2000 to 2009, consistent with previous studies. Provisional 2D FEM models including structural complexities in the crustal layers indicate that the tectonic setting of Askja plays an important role in the continuous, long-term high subsidence rates observed there. In order to fully understand the cause and effects of the complicated tectonic setting we encourage the use of a more realistic rheological model of the area, which could lead to reinterpretation of previous model results.

[1] Hekla volcano is one of the most active volcanoes in Iceland. The most recent eruption occurred from 26 February to 8 March 2000 when about 0.19 km3 of magma was erupted. We present deformation data from multitemporal analyses of synthetic aperture radar (SAR) images acquired between 1993 and 2008, focusing on pixels with low-phase variance (using persistent scatterer and small baseline approaches). Prior to and after the 2000 eruption, we find a broad area of inflation around the volcano (radius about 20 km), with satellite line-of-sight (LOS) shortening of up to 5 mm/yr. We interpret this signal as the result of pressure increase in a deep-seated magma chamber, which we model as a spherical source at 14–20 km depth increasing in volume by 0.003–0.02 km3/yr. Within a ∼6 km radius of the summit of the volcano, a LOS lengthening is superimposed on the broad inflation signal, which correlates partly with recent lava flows. We interpret this signal as the result of thermally contracting lava flows, combined with viscoelastic yielding due to the load of the volcano and its lavas. Coeruptive deflation during the 2000 eruption was similar to the cumulative inflation from 1993 to 2000 and is consistent with a spherical magma chamber at 14–18 km depth that decreases in volume by 0.04–0.08 km3. Interferograms spanning the 2000 eruption show a local coeruptive deformation signal near the eruptive fissure. This is consistent with a dike opening from the surface to depths up to 5.8 km with a volume of 0.005–0.006 km3.

International audience; Despite the ability of synthetic aperture radar (SAR) interferometry to measure ground motion with high-resolution, application of this remote sensing technique to monitor andesitic stratovolcanoes remains limited. Specific acquisition conditions characterizing andesitic stratovolcanoes, mainly vegetated areas with large elevation ranges, induce low signal coherence as well as strong tropospheric artefacts that result in small signal-to-noise ratio. We propose here a way to mitigate these difficulties and improve the SAR measurements. We derive ground motions for two of the most active Mexican stratovolcanoes: Popocatepetl and Colima Volcano, from the time series of SAR data acquired from December 2002 to August 2006. The SAR data are processed using a method that combines both persistent scatterers and small baseline approaches. Stratified tropospheric delays are estimated for each interferogram using inputs from the global atmospheric model NARR, up to a maximum of 10 rad/km. These delays are validated using spectrometer data, as well as the correlation between the wrapped phase and the elevation. The tropospheric effect is removed from the wrapped phase in order to improve the unwrapping process. On Popocatepetl, we observe no significant deformation. The Colima summit area exhibits a constant subsidence rate of more than 1 cm/year centered on the summit but enhanced (reaching more than 2 cm/year) around the 1998 lava flow. We model this subsidence considering both a deflating magma source at depth and the effect of the eruptive deposits load.

The load of lava emplaced over periods of decades to centuries induces a gradual viscous response of the Earth resulting in measurable deformation. This effect should be considered in source model inversions for volcanic areas with large lava production and flow emplacement in small centralized regions. If deformation data remain uncorrected, constructive load and pressure source interference may result in an overestimate of depth and volume of a magma reservoir whereas destructive signal interference may cause these values to be underestimated. In both cases the source geometry preference could be biased. The ratio of horizontal and vertical displacements aids the identification of composite signals. We provide a method to quantify and remove the lava load deformation signals, using deformation at Hekla volcano, Iceland as an example.

Gradual inflation of magma chambers often precedes eruptions at highly active volcanoes. During such eruptions, rapid deflation occurs as magma flows out and pressure is reduced. Less is known about the deformation style at moderately active volcanoes, such as Eyjafjallajökull, Iceland, where an explosive summit eruption of trachyandesite beginning on 14 April 2010 caused exceptional disruption to air traffic, closing airspace over much of Europe for days. This eruption was preceded by an effusive flank eruption of basalt from 20 March to 12 April 2010. The 2010 eruptions are the culmination of 18 years of intermittent volcanic unrest. Here we show that deformation associated with the eruptions was unusual because it did not relate to pressure changes within a single magma chamber. Deformation was rapid before the first eruption (5 mm per day after 4 March), but negligible during it. Lack of distinct co-eruptive deflation indicates that the net volume of magma drained from shallow depth during this eruption was small; rather, magma flowed from considerable depth. Before the eruption, a ∼0.05 km(3) magmatic intrusion grew over a period of three months, in a temporally and spatially complex manner, as revealed by GPS (Global Positioning System) geodetic measurements and interferometric analysis of satellite radar images. The second eruption occurred within the ice-capped caldera of the volcano, with explosivity amplified by magma-ice interaction. Gradual contraction of a source, distinct from the pre-eruptive inflation sources, is evident from geodetic data. Eyjafjallajökull's behaviour can be attributed to its off-rift setting with a 'cold' subsurface structure and limited magma at shallow depth, as may be typical for moderately active volcanoes. Clear signs of volcanic unrest signals over years to weeks may indicate reawakening of such volcanoes, whereas immediate short-term eruption precursors may be subtle and difficult to detect.

SUMMARY On 2008 May 29 an earthquake doublet shook the southwestern part of Iceland. The first main shock originated beneath Mt Ingolfsfjall, located near the western margin of the South Iceland Seismic Zone (SISZ) approximately 40 km east of the capital Reykjavik. Immediate aftershock activity was recorded by the SIL seismic network, operated by the Icelandic Meteorological Office (IMO), with both N–S and E–W structures illuminated over a broad area. A continuous GPS (CGPS) network, also operated by the IMO, recorded coseismic offsets with up to 200 mm of horizontal motion at the closest stations. We estimate the coseismic surface deformation observed by campaign and continuous GPS and satellite radar data (InSAR). We invert the geodetic data to find the optimal geometry, location and slip on the main faults, accounting for variation in the elastic parameters of the crust with depth. Our models indicate that most of the slip occurred on two N–S structures spaced ∼5 km apart. From a joint inversion of GPS and InSAR data for variable slip models we find that most of the slip for the first (Ingolfsfjall) event was concentrated at 2–4 km depth with a maximum of 1.9 m, whereas the slip on the second (Kross) fault was located deeper, at 3–6 km depth with up to 1.4 m of motion. The models give similar geodetic moments for the two main events, equivalent to a moment magnitude of Mw5.8 and Mw5.9 for the first and second event, respectively. Our estimated composite moment therefore equals a Mw6.1 for the doublet, smaller than the Mw6.3 estimated from teleseismic data (e.g. NEIC and Harvard). The geodetic data support rupture on two main faults and analysis of high-rate (1 Hz) CGPS data suggests that slip on the second fault initiated within 3 s of the first main shock. Static Coulomb failure stress calculations indicate that the first event caused a stress increase in the area of the main asperity (i.e. at the location of the largest slip patch) on the second fault. However, we cannot rule out dynamic stress triggering due to the short time between the two main events. The 2008 May 29 earthquake doublet appears to be a continuation of the earthquake sequence that started in 2000 June, when two Mw6.5 events struck the eastern and central part of the South Iceland Seismic Zone, in the span of 81 hr. The 2000 June–2008 May sequence has released about half of the moment accumulated by plate motion since the previous earthquake sequence in 1896–1912. Therefore, continued earthquake activity with moderate size events rupturing N–S faults in the SISZ in the coming decades is likely.

The Katla volcano is covered by the Mýrdalsjokull ice cap and is currently one of the most active volcanoes in Iceland. It has erupted twenty times the past 1,100 years. The neighbouring volcano Eyjafjallajokull has erupted twice, simultaneously with Katla. As glaciers cover both volcanoes, their eruptions are phreato-magmatic by nature. The volcanoes are located directly south of where surface expressions of the rift cease. Seismically, Katla is one of the most active volcanoes in Iceland, showing an annual cycle in activity, observed from at least 1960 and less pronounced since 2004. From 1999 to late 2004, GPS measurements revealed steady inflation of the volcano, showing uplift and outward horizontal displacement. Until 1990s, Eyjafjallajokull had been seismically quiet for several decades. Seismic activity there was high in 1994 and again in 1999, related to the emplacement of two intrusions.

We investigated the surface deformation of the northern Taiwan area, including the Taipei basin and its surrounding mountainous areas of the last fifteen years using the ERS-1, ERS-2 and ENVISAT SAR images. Although the Taipei basin now is well developed and amenable to research gathering using the Differential Interferometric Synthetic Aperture Radar (DInSAR) technique, the mountainous areas surrounding the basin are densely covered with various vegetation throughout different seasons inducing high noise ratio in interferograms. Therefore the DInSAR technique is ineffective for observation of surface deformations of these areas. As a result, we developed the Persistent Scatterer (PS) InSAR technique to extract the phase signal of the chosen PS points for this study. Our analysis result shows that the atmospheric disturbance and DEM residual can be successfully reduced and the precise information of surface deformation can be effectively obtained by the PSInSAR technique not only in the basin but also in the mountainous areas. Integrating the DInSAR and PSInSAR results, we observed conspicuous deformation events in northern Taiwan including: (1) the slight uplift in the Western Foothills, the Tatun volcanoes, the Linkou Tableland and the Taoyuan area; (2) the subsidence at the border of the Taipei basin; and (3) relative slight uplift rebound in the center of Taipei basin. The displacements along the Shanchiao, Chinshan, and Kanchiao Faults are large enough to be observed; the Taipei, Hsinchuang, and Nankang Faults are too small and cannot be discerned. Further comparison between the DInSAR, PSInSAR, and their corresponding leveling data shows a very coincidental pattern and measurably improves the authenticity of radar interferometry.

In this study we investigate the effects of unilateral voluntary contraction (VC) and electromyostimulation superimposed on VC (EV) training on maximal voluntary (MVC) force and cross-sectional area (CSA), as assessed by magnetic resonance imaging of knee extensors. Thirty young men were randomly assigned to either a control group (CG), VC group (VG), or EV group (EVG). The VG and EVG trained the right leg isometrically three sessions per week for 6 weeks. After training, MVC increased in the right leg in the VG and in both legs in the EVG, and EVG was significantly different from CG (all P0.01). Increased CSA was found only in the right leg in the VG and EVG (P0.01), and correlated with improvements of MVC (r = 0.49, P = 0.01). It appeared that the EV training was equally effective as VC at increasing MVC and CSA, while having a greater cross-education effect. Increased strength without muscle hypertrophy in the unexercised leg of the EVG indicated that neural adaptation was responsible for the cross-education effect.

Synthetic aperture radar (SAR) interferometry is a technique that provides high-resolution measurements of the ground displacement associated with many geophysical processes. Advanced techniques involving the simultaneous processing of multiple SAR acquisitions in time increase the number of locations where a deformation signal can be extracted and reduce associated error. Currently there are two broad categories of algorithms for processing multiple acquisitions, persistent scatterer and small baseline methods, which are optimized for different models of scattering. However, the scattering characteristics of real terrains usually lay between these two end-member models. I present here a new method that combines both approaches, to extract the deformation signal at more points and with higher overall signal-to-noise ratio than can either approach alone. I apply the combined method to data acquired over Eyjafjallajökull volcano in Iceland, and detect time-varying ground displacements associated with two intrusion events.

The problem of phase unwrapping in two dimensions has been studied extensively in the past two decades, but the three-dimensional (3D) problem has so far received relatively little attention. We develop here a theoretical framework for 3D phase unwrapping and also describe two algorithms for implementation, both of which can be applied to synthetic aperture radar interferometry (InSAR) time series. We test the algorithms on simulated data and find both give more accurate results than a two-dimensional algorithm. When applied to actual InSAR time series, we find good agreement both between the algorithms and with ground truth.

Neonatal stroke presents with seizures and results in neurologic morbidity, including epilepsy, hemiparesis, and cognitive deficits. Stem cell-based therapy offers a possible therapeutic strategy for neonatal stroke. We developed an immature mouse model of stroke with acute seizures and ischemic brain injury. Postnatal day 12 CD1 mice received right-sided carotid ligation. Two or 7 days after ligation, mice received an intrastriatal injection of B5 embryonic stem cell-derived neural stem cells. Four weeks after ligation, hemispheric brain atrophy was measured. Pups receiving stem cells 2 days after ligation had less severe hemispheric brain atrophy compared with either noninjected or vehicle-injected ligated controls. Transplanted cells survived, but 3 out of 10 pups injected with stem cells developed local tumors. No difference in hemispheric brain atrophy was seen in mice injected with stem cells 7 days after ligation. Neural stem cells have the potential to ameliorate ischemic injury in the immature brain, although tumor development is a serious concern.

[1] While conventional interferometric synthetic aperture radar (InSAR) is a very effective technique for measuring crustal deformation, almost any interferogram includes large areas where the signals decorrelate and no measurement is possible. Persistent scatterer (PS) InSAR overcomes the decorrelation problem by identifying resolution elements whose echo is dominated by a single scatterer in a series of interferograms. Existing PS methods have been very successful in analysis of urban areas, where stable angular structures produce efficient reflectors that dominate background scattering. However, man-made structures are absent from most of the Earth's surface. Furthermore, existing methods identify PS pixels based on the similarity of their phase history to an assumed model for how deformation varies with time, whereas characterizing the temporal pattern of deformation is commonly one of the aims of any deformation study. We describe here a method for PS analysis, StaMPS, that uses spatial correlation of interferogram phase to find pixels with low-phase variance in all terrains, with or without buildings. Prior knowledge of temporal variations in the deformation rate is not required for their identification. We apply StaMPS to Volcan Alcedo, where conventional InSAR fails because of dense vegetation on the upper volcano flanks that causes most pixels to decorrelate with time. We detect two sources of deformation. The first we model as a contracting pipe-like body, which we interpret to be a crystallizing magma chamber. The second is downward and lateral motion on the inner slopes of the caldera, which we interpret as landsliding.

[1] Sierra Negra volcano in Isabela island, Galapagos, erupted from October 22 to October 30 in 2005. During the 8 days of eruption, the center of Sierra Negra's caldera subsided about 5.4 meters. Three hours prior to the onset of the eruption, an earthquake (Mw 5.4) occurred, near the caldera. Because of the large and complex phase gradient due to the huge subsidence and the earthquake, it is difficult to form an interferogram inside the caldera that spans the eruption. The deformation is so large and spatially variable that the approximations used in existing InSAR software (ROI, ROI_PAC, DORIS, GAMMA) cannot properly coregister SAR image pairs spanning the eruption. We have developed here a two-step algorithm that can form intra-caldera interferograms from these data. The first step involves a “rubber-sheeting” SAR image coregistration. In the second step we use range offset estimates to mitigate the steep phase gradient. Using this new algorithm, we retrieve an interferogram with the best coverage to date inside the caldera of Sierra Negra.

Interferometric synthetic aperture radar, or InSAR, is a visual geodetic technique permitting detailed mapping of motion over wide areas. InSAR has been limited to regions without much vegetation, which shields the ground from the radar signals and contributes random motions to the observed deformation. The resulting "decorrelation" of the echoes precludes accurate displacement measurements in these areas. Decorrelation also occurs in interferograms with acquisitions separated too far in the sky. Yet certain points, denoted persistent scatterers, in a radar image are stable, do not decorrelate, and form a network of fiducial points that allow measurements in otherwise poor-quality interferograms. We have generalized an algorithm to find networks of stable points in natural terrain, rather than in urban areas, and applied the method to spaceborne satellite data. Using modern information theory to optimize persistent scatterer detection, we can now find many, many more such points than previously possible. We have applied this improved algorithm to the San Francisco Bay segments of the San Andreas and Hayward faults, and in both cases find that a large number of stable points are seen in the vegetated areas that have to date resisted InSAR analysis. Our method of integrating information theoretic estimation and detection theory to all parts of the method, improves the identification, filtering, and phase unwrapping of the observations. Identification of stable true-ground scattering points permits mapping of subtle surface motions and deformations and also of "bare-Earth" topography.

[1] We present here a new InSAR persistent scatterer (PS) method for analyzing episodic crustal deformation in non-urban environments, with application to volcanic settings. Our method for identifying PS pixels in a series of interferograms is based primarily on phase characteristics and finds low-amplitude pixels with phase stability that are not identified by the existing amplitude-based algorithm. Our method also uses the spatial correlation of the phases rather than a well-defined phase history so that we can observe temporally-variable processes, e.g., volcanic deformation. The algorithm involves removing the residual topographic component of flattened interferogram phase for each PS, then unwrapping the PS phases both spatially and temporally. Our method finds scatterers with stable phase characteristics independent of amplitudes associated with man-made objects, and is applicable to areas where conventional InSAR fails due to complete decorrelation of the majority of scatterers, yet a few stable scatterers are present.

Shallow magma bodies that feed regularly erupting volcanoes are usually considered enduring features that grow steadily between eruptions. Measurements of deformation at Santorini, however, reveal sudden rapid magma accumulation after half a century of rest.

Rapid convergence between the Eurasian plate and the Philippine Sea plate in the northern Longitudinal Valley near the city of Hualien in eastern Taiwan has produced prominent fault scarps and large earthquakes (M≥7). This study attempts to more thoroughly understand the surface deformation activities near the faults and their relation to earthquakes near Hualien City using a stable target, multi-temporal radar interferometry method to extract the surface deformation information in this area. Our results indicate that the extracted deformation signals were comparable with those in our leveling data and have a very high spatial density (exceeding 70 point km^(-2)). Additionally, all faults in the northern Longitudinal Valley and Hualien City were not deformed monotonically. Rather, deformation time series are complex and frequent activities affected the general trends wherein, for example, 2005 earthquake swarm produced more than 10 mm of displacement near the Milun fault. Moreover, deformation rates in the study area generally ranged from around 10-20 mm yr^(-1) of relative displacement rates along the radar line of sight between the western part of Hualien City near the Central Range and the eastern part during the decade, while only the Mingyi fault displayed monotonic fault activities with change of displacement rates of approximately 5-10 mm yr^(-1) across the fault.

[1] The inconsistency in depth between geodetic and seismic models of the 1989 Kilauea earthquake has long been puzzling. Previous attempts to incorporate elastic heterogeneity have deepened geodetic models substantially, bringing them closer to the seismic depth. However, recent studies that have included heterogeneity for other faults indicate that the effect is not so great. We show here that elastic heterogeneity has a relatively minor effect on the geodetic model depth for this earthquake also. However, by combining three different sets of geodetic data we are able to get a more accurate estimate of the depth, which does in fact coincide with the hypocentral depth at the 95% confidence level. When we consider that static elastic parameter values are commonly less than dynamic values, the agreement is even better. Furthermore, the depth is consistent with the earthquake having occurred at the interface between the volcanic pile and the pre-volcanic seafloor.

Some observations of the phenomenon known as ‘inversion’ in records of scintillation of signals from the sources Cassiopeia A and Cygnus A are reviewed briefly. It is shown that the phenomenon is more likely to be explained by the finite angular diameters of these sources than, as suggested by previous authors, by the aperture size of the antenna used in making the observations. An experiment is suggested which should distinguish between these and other criteria which can bring about the observation of inversion.

The landslide activity in the area of Bolshoy Sochi (Big Sochi) situated at the Black Sea coast of the Great Caucasus has been studied using the StaMPS PS-InSAR method. We incorporated three sets of radar images from the satellites with different wavelengths ALOS, Envisat and Terra-SAR-X from both ascending and descending tracks which cover the time period from January 2007 to September 2012. Comparative investigation of surface displacements obtained from all the data sets is presented. Areas where high surface displacement rates have been located on the base of the satellite data coincide well with zones of high landslide activity according to ground observations. We constructed time series for the two landslides: in the Baranovka and Mamaika villages where considerable surface movements had been observed during the time of acquisitions. Analysis of the time series made it possible to determine periods of activity and relative stability of the landslides and compare them with ground observations.

Eighteen long stay male patients (diagnosis chronic schizophrenia) were involved in a six month token economy prior to random assignment to one of three experimental groups to investigate the importance of social reinforcement and other token-related variables in maintaining improvements brought about by the token system. Assessment included standardised psychiatric rating scales, nurse rating scales, and behavioural measures. Analysis of variance suggests the full token economy system produced significant improvements, but that the social factors involved in token exchanges were not demonstrably important sources of reinforcement. and that none of the variables studies at the experimental phase were critical factors. Once patients returned to a complete token system, results indicate that this may have more value in the promotion of work activities rather than social responding. It is argued that the token system provides a necessary clear structure within which nurses can encourage continuous improvements with long stay patients.

Europe's Sentinel-1A spacecraft and its extraordinary images of slip from the South Napa earthquake herald a new era of space-based surveillance of faults.