Spheroidal Source Research Articles

Detecting Transient Uplift at the Active Volcano Ol Doinyo Lengai in Tanzania With the TZVOLCANO Network

AbstractOver the last 7 years, geodetic data have detected periods of uplift and subsidence of the active volcano Ol Doinyo Lengai in Tanzania. Although numerous eruptions of the volcano have occurred historically, a systematic investigation of transient deformation using continuous Global Navigation Satellite System (GNSS) data has not been undertaken. We use the Targeted Projection Operator (TPO) to assess 7 years of continuous GNSS data from the TZVOLCANO network for transient signals and find rapid uplift spanning March 2022–December 2022 and then steady‐state uplift through August 2023. We conduct a nonlinear inversion of the GNSS velocities associated with the transient signal using dMODELS and find consistency with an inflating spheroidal source located 2.3 ± 0.6 km beneath the crater. Prior to March 2022, geodetic data indicated quiescence just below Ol Doinyo Lengai, thus detecting transient deformation with TPO allows for tracking changes in the magmatic system over time in the Natron Rift.

On the Initial Phase of the Ongoing Unrest at Campi Flegrei and Its Relation with Subsidence at Vesuvio (Italy)

The densely inhabited area of Naples (Italy), between the Campi Flegrei and Vesuvio volcanoes, is one of the most hazardous regions in the world. After two decades of sustained subsidence, Campi Flegrei has been experiencing an accelerating uplift since 2005. The uplift is currently associated with unusual seismicity and increased degassing. To try to identify the cause of the shift from subsidence to uplift and explore any connection between Campi Flegrei and Vesuvio, we analysed the ground displacement time series of the two volcanoes from 1993 to 2010, obtained from ERS/ENVISAT Synthetic Aperture Radar imagery. To distinguish between the various sources of deformation, we used simple scatter plots and a blind source separation technique called variational Bayesian independent component analysis (vbICA). We obtained consistent results using both approaches. Specifically, with vbICA, we identified two significant independent components (ICs). IC1 describes the subsidence that occurred at Campi Flegrei prior to 2000, including the mini-uplifts of 2000 and 2005, and part of the post-2005 uplift. The expansion and contraction of two volumes beneath Campi Flegrei satisfy IC1: a sill-shaped volume at a depth of approximately 3 km and a small volume at a depth of 1–2 km, respectively. The two sources of deformation reproduce the large-scale deformation in the Campi Flegrei area and the local deformation in the Solfatara area, respectively. In the Campi Flegrei area, IC2 exhibits primarily uplift, which is concentrated in the eastern part of the caldera. The deformation pattern is complex and difficult to interpret. If we model it using simple spheroidal deformation sources, the pattern suggests that two volumes at depths of approximately 9 and 8 km are experiencing opposite activity, namely contraction (beneath the southwestern part of the caldera) and expansion (beneath the central part of the caldera). In the Vesuvio area, IC2 is consistent with the deformation induced by the contraction of a volume at a depth of around 9 km. The contraction beneath Vesuvio is smaller in magnitude than the expansion/contraction beneath Campi Flegrei. The correlation observed after 2002 between uplift at Campi Flegrei and subsidence at Vesuvio suggests the transfer of magma and/or magmatic fluids between the two plumbing systems at 8–9 km depth. This implies that part of the ongoing unrest at Campi Flegrei may have been promoted by mass transfer from below Vesuvio.

Collagen-mesenchymal stem cell spheroids in suspension promote high adipogenic capacity

Human mesenchymal stem cells (hMSC) represent a unique and promising platform because of their ability to promote soft tissue regeneration, particularly their ability to differentiate into adipocytes, which are important for adipose tissue regeneration. In this context, type I collagen is the most abundant extracellular matrix component of adipose tissue and can act as a natural spheroid source to support the differentiation process of stem cells. However, spheroids based on collagen and hMSCs without numerous pro-adipogenic factors that can induce adipogenesis have not yet been investigated. In this study, we focused on developing collagen-hMSC spheroids capable of differentiating into adipocyte-like cells in a short time (eight culture days) without adipogenic factors, with potential applications in adipose tissue repair. The physical and chemical properties of the spheroids indicated successful cross-linking of collagen. Upon spheroid development, stability, cell viability, and metabolic activity of the constructs were maintained. During adipogenesis, cell morphology shows significant changes, in which cells change from a fibroblast-like shape to an adipocyte-like shape, and adipogenic gene expression after eight days of cell culture. These results support the utility of collagen-hMSC 3 mg ml−1 collagen concentration spheroids to differentiate into adipocyte-like cells in a short time without adverse effects on biocompatibility, metabolic activity, or cell morphology, suggesting that this construct may be used in soft tissue engineering.

The Surface Deformation Signature of a Transcrustal, Crystal Mush‐Dominant Magma System

AbstractThe transcrustal, mush‐dominated magma storage paradigm, which posits liquid melt is heterogeneously distributed within a vertically extensive magma mush, differs significantly from classical geodetic models, where melt is stored within liquid‐dominant chambers within an elastic crust. Here, we present mechanical models consistent with transcrustal melt storage by separating the magmatic system into three domains: liquid melt lenses, surrounding crystal‐dominated poroelastic magma mush, and elastic crust. Our results indicate that pressure changes within the melt lens may induce surface displacements that approximate the displacements predicted by spheroidal pressure sources that mimic the geometry of the mush zone. Adopting constitutive parameters of the mush dependent on mush melt fraction, we show that a magma storage system will have an effective geometry inferred from surface displacements that smoothly transitions from the geometry of the melt lens to the geometry of the mush as mush melt fraction increases. This holds true across multiple storage zone geometries, including a “transcrustal” storage zone with a magma mush that extends deep in the crust. Accounting for the presence of a magma mush can lead to an increase in the estimated volume of injected or withdrawn magma (by several multiples) compared to values obtained using fully elastic models. Comparing erupted magma volumes to source volume changes allows for an estimation of magma compressibility; we show the presence of a mush can increase this estimated magma compressibility by up to approximately 50%, suggesting magmas may have higher bubble fraction than previous geodetically derived estimates.

The 2011 Cordón Caulle eruption triggered by slip on the Liquiñe-Ofqui fault system

Determining the mechanisms that promote large silicic eruptions is one of the biggest challenges in volcanic hazard assessment. The 2011-2012 Cordón-Caulle eruption in Chile was one of the largest silicic eruptions of the 21st century and was characterized by a rapid change from explosive to effusive behavior. This eruption was preceded by inflation from 2007 to 2009, followed by two years of barely any ground deformation. Despite intensive monitoring by geodetic and seismological data, its trigger remains undetermined. Here, we benefit from SAR imagery over the Puyehue Cordón-Caulle Volcanic Complex acquired by ALOS-1, ENVISAT and SENTINEL-1 data, to analyze the temporal and spatial behavior of ground displacements before, during and after the eruption. First, we find that a similar prolate spheroidal source explains the ground deformation for the pre-eruptive and post-eruptive periods. Then, we use 3D numerical elasto-plastic models to assess the failure conditions resulting from the pre-eruptive magma injection. Our results show that such a magma injection was too small to trigger the eruption. Therefore we explore other eruption triggers. Analytical elastic inversion models show that the ground displacements observed during the explosive phase may have been produced by slip motion along a NNW-striking dextral-strike slip, double-branch fault of the north-trending Liquiñe-Ofqui Fault System (LOFS), or along a single southern branch fault of the LOFS and collapse of the caldera. When investigating the elasto-plastic deformation pattern resulting from dextral slip along this branch-fault system, we obtain a sub-vertical dilatational plastic zone that connects the reservoir wall to the surface in a location that coincides with that of the 2011 eruption. Hence, we propose that this LOFS branch-fault eventually destabilized (perhaps weakened by the 2007-2009 episode of magma injection), and then slipped in a way that opened channels for fluid migration from the magma reservoir up to the surface.

Upward Magma Migration Within the Multi-Level Plumbing System of the Changbaishan Volcano (China/North Korea) Revealed by the Modeling of 2018–2020 SAR Data

Changbaishan volcano (China/North Korea border) was responsible for the largest eruption of the first Millennium in 946 CE and is characterized by a multi-level plumbing system. It last erupted in 1903 and presently consists of a cone with summit caldera. An unrest episode occurred between 2002 and 2006, followed by subsidence. Here, we analyze the Changbaishan 2018–2020 deformations by using remote sensing data, detecting an up to 20 mm/yr, NW-SE elongated, Line of Sight movement of its southeastern flank and a −20 mm/yr Line of Sight movement of the southwestern flank. This reveals an unrest occurring during 2018–2020. Modeling results suggest that three active sources are responsible for the observed ground velocities: a deep tabular deflating source, a shallower inflating NW-SE elongated spheroid source, and a NW-SE striking dip-slip fault. The depth and geometry of the inferred sources are consistent with independent petrological and geophysical data. Our results reveal an upward magma migration from 14 to 7.7 km. The modeling of the leveling data of the 2002–2005 uplift and 2009–2011 subsidence depicts sources consistent with the 2018–2020 active system retrieved. The past uplift is interpreted as related to pressurization of the upper portion of the spheroid magma chamber, whereas the subsidence is consistent with the crystallization of its floor, this latter reactivated in 2018–2020. Therefore, Changbaishan is affected by an active magma recharge reactivating a NW-SE trending fault system. Satellite data analysis is a key tool to unravel the magma dynamics at poorly monitored and cross-border volcanoes.

The Christmas 2018 Eruption at Mount Etna: Enlightening How the Volcano Factory Works Through a Multiparametric Inspection

AbstractThe 24–27 December 2018 flank eruption at Mount Etna (Southern Italy) has been investigated through a multidisciplinary approach in which olivine chemical zoning and diffusion chronometry data were integrated with models inferred by GNSS (Global Navigation Satellite System) measurements. Inspection of the olivine chemical zoning from core to rim allowed the identification of some dominant ways of transfer and interaction between magmas pertaining to different magmatic environments. Most of crystal cores are representative of crystallization at pressure of 290–230 and 160–120 MPa. Olivine rims suggest re‐equilibration at shallow pressure (≤30 MPa). Geodetic‐based models indicate pressurization of near‐vertical prolate spheroidal sources centered at ∼7.2 km below sea level (bsl) between 9 June 2017 and 28 June 2018 and later at ∼5.1 km bsl between 28 June 2018 and the eruption onset. Geodetic data also highlight a change in the inflation rate since late June 2018 and later around November 2018, which has been here related to both replenishment phases and magma uprising across the plumbing system. Timescales of magma replenishment are in agreement with prolonged recharge from deep levels upward to shallow environments started about 6 months before the eruption, with further replenishment involving the upper magmatic environments just 3–16 days before the eruption. At present, the eruptive activity at the volcano is primarily controlled by pressure imbalances affecting extensive sections of the plumbing system, with possibility to develop persistent eruptive activity at the summit versus flank eruptions depending on fortuitous interruptions of the steady magma recharge/discharge rate at shallow levels.

Cyclic magma recharge pulses detected by high-precision strainmeter data: the case of 2017 inter-eruptive activity at Etna volcano

Unprecedented ultra-small strain changes (~10−8–10−9), preceding and accompanying the 2017 explosive-effusive activity, were revealed by a high precision borehole strainmeter at Etna. No pre- or co-eruptive deformation was detected by the GPS measurements, which often fail to detect ground deformation engendered by short-term small volcanic events due to their limited accuracy (millimetres to few centimetres). Through the analysis and detection of ultra-small strain changes (few tens of nanostrain), revealed by filtering the raw data, a significant time correspondence with the eruptive activity is observed. For the first time, cyclic fast exponential strain changes, preceding the onset of eruptive events, with a timescale of about 2–7 days, were detected. These variations are attributable to the expansion of the shallow magma reservoir, which is replenished with new magma from depth during the inter-eruptive periods. Interpreting the strain changes in terms of pressurization/depressurization of the chamber due to the cyclic influx and withdrawal of magma, allows placing some constraints on the magma recharge volume rate. A Finite Element model has been developed to simulate the temporal evolution of the strain changes generated by the re-pressurization of a spheroidal magma source using a dynamical approach. An average total mass budget of about 1–2 × 109 kg, which is in the range of the erupted mass, is estimated to be accumulated within a shallow vertically elongated magma chamber during the inter-eruptive periods. Such evidence demonstrates that the near-real time analysis of strainmeter records is remarkable for its ability to record small transients and highlight recharging phases preceding eruptive activity, which would go undetected with other current methodologies. Under these conditions, the ability to simulate inter-eruptive periods offers an opportunity to estimate the magma recharge rate with important implications for volcano hazard assessment.

Horizon quantum mechanics for spheroidal sources

We start investigating the extension of the horizon quantum mechanics to the case of non-spherical sources. We first study the location of trapping surfaces in space-times resulting from an axial deformation of static isotropic systems, and show that the Misner-Sharp mass evaluated on the corresponding undeformed spherically symmetric space provides the correct gravitational radius to locate the horizon. We finally propose a way to determine the deformation parameter in the quantum theory.

Ground deformation source model at Kuchinoerabu-jima volcano during 2006\u20132014 as revealed by campaign GPS observation

We analyzed campaign Global Positioning System observation data in Kuchinoerabu-jima during 2006–2014. Most benchmarks located around Shin-dake crater showed crater-centered radial horizontal displacements. Horizontal displacements at western rim of the Shin-dake crater were tended to be larger compared to those at eastern rim. In addition, benchmark KUC14 which locates near the cliff at Furu-dake showed westward horizontal displacement rather than crater-centered radial (southward) one. Meanwhile, small displacements were detected at the benchmarks located at the foot of Kuchinoerabu-jima. We modeled the observed displacements applying a finite element method. We set entire FE domain as 100 × 100 × 50 km3. We set top of the domain as a free surface, and sides and bottom to be fixed boundaries. Topography was introduced in the area within Kuchinoerabu-jima using digital elevation model data provided by Kagoshima prefecture and elevation information from Google earth, and elevation of the outside area was assumed to be sea level. We assumed a stratified structure based on a one-dimensional P-wave velocity structure. We applied a vertical spheroid source model and searched optimal values of horizontal location, depth, equatorial and polar radiuses, and internal pressure change of the source using the forward modeling method. A spherical source with a radius of 50 m was obtained beneath the Shin-dake crater at a depth of 400 m above sea level. The internal pressure increase of 361 MPa yields its volume increase of 31,700 m3. Taking effects of topography and heterogeneity of ground into account allowed reproduction of overall deformation in Kuchinoerabu-jima. The location of deformation source coincides with hypocenters of shallow volcano-tectonic (VT) earthquakes and the aquifer estimated from a two-dimensional resistivity model by audio-frequency magnetotellurics method. The obtained deformation source may be corresponding to the pressurized aquifer, and shallow VT earthquakes and demagnetization may be caused by pressure and strain accumulation in the rocks around the aquifer. Applying the obtained spherical source to the tilt change before August 3, 2014 eruption, we found that 520 m3 of volcanic materials were supplied toward shallower in 1.5 h before the eruption. The depth and volume change of deformation source before May 2015 eruption detected by precise leveling surveys is deeper and two orders of magnitude greater compared to that before August 2014 eruption.

Co-eruptive subsidence and post-eruptive uplift associated with the 2011–2012 eruption of Puyehue-Cordón Caulle, Chile, revealed by DInSAR

The 2011–2012 eruption of the Puyehue-Cordón Caulle volcanic complex, southern Andes (Chile), was associated with complex surface deformation affecting an area of roughly 50 by 50km. We report here differential SAR interferometry (DInSAR) results of pre-, co- and post-eruptive deformation from ENVISAT ASAR, COSMO-Skymed, and ALOS-2/PALSAR scenes acquired between early 2011 and early 2017. No clear pre-eruptive deformation is observed during five months before the eruption, although some patterns could be interpreted as showing inflation occurring between April and May 2011. Co-eruptive interferograms show a complex deformation pattern consisting in a major deflation lobe (120cm LOS lengthening) centered 10km NW of the eruption vent accompanied by smaller uplift and subsidence regions in the vicinity of the vent. Re-inflation began immediately after the end of the eruption. A first pulse lasted 3years between 2012 and 2015, accumulating ~70cm uplift. We detect here a second pulse, beginning in June 2016 and still ongoing in February 2017, reaching 12cm in half a year. Inverse modeling with spherical cavity and spheroidal sources locates re-inflation sources at a depth ranging between 8 and 11km under the surface. It suggests re-filling of the reservoir occurring after the draining of a shallow magma chamber during the 2011–2012 eruption.

Measurement of three-dimensional surface deformation by Cosmo-SkyMed X-band radar interferometry: Application to the March 2011 Kamoamoa fissure eruption, Kīlauea Volcano, Hawai'i

Abstract Three-dimensional (3D) surface deformation is retrieved for the March 6–10, 2011 (UTC dates), Kamoamoa fissure eruption along the East Rift Zone of Kīlauea Volcano, Hawai'i, through the integration of multi-temporal synthetic aperture radar (SAR) interferometry (InSAR) and multiple-aperture interferometry (MAI) measurements from the COSMO-SkyMed X-band SAR. The measurement accuracies of 1) the individual and multi-stacked MAI interferograms and 2) the 3D deformation, which is measured from COSMO-SkyMed data, are assessed using continuous GPS stations. The root-mean-square (RMS) errors of individual MAI interferograms for descending and ascending data are 2.97 ± 0.6 cm and 3.20 ± 0.62 cm, respectively. The MAI interferograms stacked from multi-temporal observations can produce better results by emphasizing surface deformation signals, with the RMS errors of 1.06 and 1.24 cm for descending and ascending data, respectively. The empirical equations for measurement uncertainties are determined with respect to interferometric coherence for individual and stacked MAI interferograms. An assessment of the 3D components of deformation was performed as well, and RMS errors of 0.75, 0.83, and 0.68 cm were estimated in the east, north, and up directions. A performance test of magma source model parameter estimations was carried out by using the InSAR and 3D measurements. From the 3D deformation field, we found that the magma chamber source at the Kīlauea caldera should be modeled by the spheroid source rather than the simple point source. The performance comparison between the InSAR and 3D modeled results showed that the 3D deformation field allows for precise model parameter estimation.

Deep source model for Nevado del Ruiz Volcano, Colombia, constrained by interferometric synthetic aperture radar observations

AbstractNevado del Ruiz is part of a large volcano complex in the northern Andes of Colombia. Interferometric synthetic aperture radar observations from the RADARSAT‐2 satellite since 2011 show steady inflation of the volcano since 2012 at 3–4 cm/yr. The broad (>20 km) deformation pattern from both ascending and descending track data constrain source models for either point or spheroidal sources, both located at >14 km beneath the surface (mean elevation 4.2 km) and 10 km SW of Nevado del Ruiz, below nearby Santa Isabel Volcano. Stress change computations for both sources in the context of a compressive regional stress indicate that dikes propagating from the source should become trapped in sills, possibly leading to a more complex pathway to the surface and explaining the significant lateral separation of the source and Nevado del Ruiz Volcano.

Aperture-based antihydrogen gravity experiment: Parallel plate geometry

An analytical model and a Monte Carlo simulation are presented of an experiment that could be used to determine the direction of the acceleration of antihydrogen due to gravity. The experiment would rely on methods developed by existing antihydrogen research collaborations. The configuration consists of two circular, parallel plates that have an axis of symmetry directed away from the center of the earth. The plates are separated by a small vertical distance, and include one or more pairs of circular barriers that protrude from the upper and lower plates, thereby forming an aperture between the plates. Antihydrogen annihilations that occur just beyond each barrier, within a “shadow” region, are asymmetric on the upper plate relative to the lower plate. The probability for such annihilations is determined for a point, line and spheroidal source of antihydrogen. The production of 100,000 antiatoms is predicted to be necessary for the aperture-based experiment to indicate the direction of free fall acceleration of antimatter, provided that antihydrogen is produced within a sufficiently small antiproton plasma at a temperature of 4 K.

Present-day deformation of Agung volcano, Indonesia, as determined using SBAS-InSAR

Based on ALOS PALSAR images, time series deformation fields of the Agung volcano area were obtained using SBAS-InSAR in 2007–2009. The time series deformation showed obvious inflation around the Agung volcano area, which was positively correlated with time. We modeled the cumulated deformation interferogram based on Mogi point source and vertical prolate spheroid source. The deformation model indicated that the vertical prolate spheroid model fit the observed deformation reasonably well. The magma chamber was located beneath the center of the volcano at a depth of approximately 5 km beneath the summit.

Continuing inflation at Three Sisters volcanic center, central Oregon Cascade Range, USA, from GPS, leveling, and InSAR observations

Uplift of a broad area centered ~6 km west of the summit of South Sister volcano started in September 1997 (onset estimated from model discussed in this paper) and was continuing when surveyed in August 2006. Surface displacements were measured whenever possible since August 1992 with satellite radar interferometry (InSAR), annually since August 2001 with GPS and leveling surveys, and with continuous GPS since May 2001. The average maximum displacement rate from InSAR decreased from 3–5 cm/yr during 1998–2001 to ~1.4 cm/yr during 2004–2006. The other datasets show a similar pattern, i.e., surface uplift and extension rates decreased over time but deformation continued through August 2006. Our best-fit model to the deformation data is a vertical, prolate, spheroidal point-pressure source located 4.9–5.4 km below the surface. The source inflation rate decreased exponentially during 2001–2006 with a 1/e decay time of 5.3 ± 1.1 years. The net increase in source volume from September 1997 to August 2006 was 36.5–41.9 x 106 m3. A swarm of ~300 small (Mmax = 1.9) earthquakes occurred beneath the deforming area in March 2004; no other unusual seismicity has been noted. Similar deformation episodes in the past probably would have gone unnoticed if, as we suspect, most are small intrusions that do not culminate in eruptions.

Constraints on continued episodic inflation at Long Valley Caldera, based on seismic and geodetic observations

Long Valley Caldera, a large and potentially explosive silicic system, has experienced highly anomalous continued inflation since late 1970s. We characterize an episode of rapid episodic uplift occurring between 2002 and 2003 following similar episodes of 1979–1980, 1983, 1989–1990, and 1997–1998. This most recent episode was the first to be observed by a dense array of 13 continuous Global Positioning System (GPS) stations. Similar to previously observed episodes of deformation, uplift is quasi‐radially symmetric and is mostly explained by a compact pressure source located ∼3 km west of the resurgent dome. The maximum uplift during the 2002–2003 episode is ∼35 ± 8 mm, about 1/3 the magnitude but with a similar time‐dependent behavior as the 1997–1998 episode. The horizontal source location is well constrained at −118.930°, 37.678°, for a small spherical source, and indistinguishable from the location of a vertically dipping prolate spheroidal source. A trade‐off between depth and volume change is observed for both spherical and prolate models, with depth between 7.5 and 13.5 km and a volume change of 0.01–0.03 km3 at 95% confidence. For prolate spheroidal models, depth and volume change are additionally affected by the source axis ratio (b/a), which is greater than 0.55. Though the background seismicity remained low during the 2002–2003 episode, we identified a significant spike in activity during the maximum rate of uplift, similar to observations in both the much larger episodes in 1989–1990, and 1997–1998. More interestingly, we additionally find that all three episodes begin immediately after a short period of seismic quiescence, with background seismicity falling to levels below background levels following the prior uplift event. With the dense GPS coverage, we also identify increased opening of the Mono‐Inyo volcanic chain after the 2002–2003 episode suggesting potential interaction of magmatic fluids between the two systems.

A four-dimensional viscoelastic deformation model for Long Valley Caldera, California, between 1995 and 2000

We investigate the effects of viscoelastic (VE) rheologies surrounding a vertically dipping prolate spheroid source during an active period of time-dependent deformation between 1995 and 2000 at Long Valley caldera. We model a rapid magmatic inflation episode and slip across the South Moat fault (SMF) in late 1997. We extend the spherical VE shell model of Newman et al. [Newman, A.V., Dixon, T.H., Ofoegbu, G., Dixon, J.E., 2001. Geodetic and seismic constraints on recent activity at Long Valley caldera, California: Evidence for viscoelastic rheology. J. Volcanol. Geotherm. Res. 105, 183–206.] to include a prolate spheroid geometry more accurately representing the probable source geometry inferred from other studies. This paper presents the first attempt to geodetically constrain the volcanic deformation source volume at Long Valley, a parameter for hazard assessment. Including fault slip along the SMF explains significant deformation observed with several EDM baselines and components of two continuous GPS time series. Additionally, the model explains the spatial extent of deformation observed by InSAR data covering the 1997–98 inflation episode. For the time period studied, the VE model requires modest pressure changes (maximum of 14.3 MPa) that are far lower than the overburden pressure (∼115 MPa), and less than the maximum for a purely elastic model with the same geometry and elastic strength (∼45 MPa). Thus, the inclusion of a realistic VE component significantly lowers the inferred pressures necessary to explain observed surface deformation. Though our model is non-unique, it is consistent with a broader variety of data compared to purely elastic models. Only right-lateral slip, and not dilitation, was necessary to explain offsets in EDM data near and crossing the SMF.

Analytical and 3-D numerical modelling of Mt. Etna (Italy) volcano inflation

SUMMARY Since 1993, geodetic data obtained by different techniques (GPS, EDM, SAR, levelling) have detected a consistent inflation of the Mt. Etna volcano. The inflation, culminating with the 1998–2001 strong explosive activity from summit craters and recent 2001 and 2002 flank eruptions, is interpreted in terms of magma ascent and refilling of the volcanic plumbing system and reservoirs. We have modelled the 1993–1997 EDM and GPS data by 3-D pressurized sources to infer the position and dimension of the magma reservoir. We have performed analytical inversions of the observed deformation using both spheroidal and ellipsoidal sources embedded in a homogeneous elastic half-space and by applying different inversion methods. Solutions for these types of sources show evidence of a vertically elongated magma reservoir located 6 km beneath the summit craters. The maximum elevation of topography is comparable to such depth and strong heterogeneities are inferred from seismic tomography; in order to assess their importance, further 3-D numerical models, employing source parameters extracted from analytical models, have been developed using the finite-element technique. The deformation predicted by all the models considered shows a general agreement with the 1993–1997 data, suggesting the primary role of a pressure source, while the complexities of the medium play a minor role under elastic conditions. However, major discrepancies between data and models are located in the SE sector, suggesting that sliding along potential detachment surfaces may contribute to amplify deformation during the inflation. For the first time realistic features of Mt. Etna are studied by a 3-D numerical model characterized by the topography and lateral variations of elastic structure, providing a framework for a deeper insight into the relationships between internal sources and tectonic structures.

Unrest at the Campi Flegrei caldera (Italy): A critical evaluation of source parameters from geodetic data inversion

We have analysed the deformation documented during unrest at the Campi Flegrei caldera, Italy, between 1981 and 2001. Via inverse modelling, we constrain the location, geometry and size of the source responsible for the continuing period of surface deformation. We present a critical re-evaluation of results from previously published models and for the first time invert post-1994 data to infer source parameters. Our evaluation is based on constraints from additional horizontal displacement data, mechanical properties of the country rocks, effects of volcanic surface loading and on other geophysical and geochemical observations. We invert leveling and tide-gauge data for a spherical point (Mogi-model) source, a penny-shaped crack and finally a prolate spheroid. Despite the good qualities of fit of both the Mogi-model and the penny-shaped source to the vertical displacement data, our critical evaluation of the implied source properties forces us to reject these models. We propose instead a vertical prolate spheroid located about 800 m East of Pozzuoli at a depth of 2.9 km (95% confidence bound 2.0 to 4.2 km) with an aspect ratio of 0.51 (95% bounds 0.37–0.69) as a more appropriate source model. This model best accounts for the criteria employed and the observed deformation between 1981 and 2001. Combined with results from the inversion of gravity change data (1982–1984) for the spheroidal source, we infer a hybrid nature of the source including both magmatic and hydrothermal components.