Ground deformation after a caldera collapse: Contributions of magma inflow and viscoelastic response to the 2015‐2018 deformation field around Bárðarbunga, Iceland

Unrest at B&#225;r&#240;arbunga after a caldera collapse in 2014-2015 includes elevated seismicity beginning about six months after the eruption ended, including nine Mw>4.5 earthquakes. The earthquakes occurred mostly on the northern and southern parts of a caldera ring fault. Global Navigation Satellite System (GNSS, in particular, Global Positioning System; GPS) and Interferometric Synthetic Aperture Radar (InSAR) geodesy are applied to evaluate the spatial and temporal pattern of ground deformation around B&#225;r&#240;arbunga caldera outside the icecap, in 2015-2018, when deformation rates were relatively steady. The aim is to study the role of viscoelastic relaxation following major magma drainage versus renewed magma inflow as an explanation for the ongoing unrest.The largest horizontal velocity is measured at GPS station KISA (3 km from caldera rim), 141 mm/yr in direction N47oE relative to the Eurasian plate in 2015-2018. GPS and InSAR observations show that the velocities decay rapidly outward from the caldera. We correct our observations for Glacial Isostatic Adjustment and plate spreading to extract the deformation related to volcanic activity. After this correction, some GPS sites show subsidence.We use a reference Earth model to initially evaluate the contribution of viscoelastic processes to the observed deformation field. We model the deformation within a half-space composed of a 7-km thick elastic layer on top of a viscoelastic layer with a viscosity of 5 x 1018 Pa s, considering two co-eruptive contributors to the viscoelastic relaxation: &#8220;non-piston&#8221; magma withdrawal at 10 km depth (modelled as pressure drop in a spherical source) and caldera collapse (modelled as surface unloading). The other model we test is the magma inflow in an elastic half-space. Both the viscoelastic relaxation and magma inflow create horizontal outward movements around the caldera, and uplift at the surface projection of the source center in 2015-2018. Viscoelastic response due to magma withdrawal results in subsidence in the area outside the icecap. Magma inflow creates rapid surface velocity decay as observed.We explore further two parameters in the viscoelastic reference model: the viscosity and the "non-piston" magma withdrawal volume. Our comparison between the corrected InSAR velocities and viscoelastic models suggests a viscosity of 2.6&#215;1018 Pa s and 0.36 km3 of &#8220;non-piston&#8221; magma withdrawal volume, given by the optimal reduced Chi-squared statistic. When the deformation is explained using only magma inflow into a single spherical source (and no viscoelastic response), the optimal model suggests an inflow rate at 1&#215;107 m3/yr at 700 m depth. A magma inflow model with more model parameters is also a possible explanation, including sill inflation at 10 km together with slip on caldera ring faults. Our reference Earth model and the two end-member models suggest that there is a trade-off between the viscoelastic relaxation and the magma inflow, since they produce similar deformation signals outside the icecap. However, to reproduce details of the observed deformation, both processes are required. A viscoelastic-only model cannot fully explain the fast velocity decay away from the caldera, whereas a magma inflow-only model cannot explain the subsidence observed at several locations.

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Dynamic Tilt Correction Using Direct Rotational Motion Measurements

Seismological Research Letters ◽

10.1785/0220200132 ◽

2020 ◽

Vol 91 (5) ◽

pp. 2872-2880 ◽

Cited By ~ 2

Author(s):

Felix Bernauer ◽

Joachim Wassermann ◽

Heiner Igel

Keyword(s):

Frequency Domain ◽

Time Domain ◽

Ground Deformation ◽

Time Domain Method ◽

Caldera Collapse ◽

Frequency Domain Method ◽

Test Cases ◽

Ground Acceleration ◽

Data Set ◽

Domain Method

Abstract Inertial sensors like seismometers or accelerometers are sensitive to tilt motions. In general, from pure acceleration measurements, it is not possible to separate the tilt acceleration from the translational ground acceleration. This can lead to severe misinterpretation of seismograms. Here, we present three different methods that can help solving this problem by correcting translational records for dynamic tilt induced by ground deformation with direct measurements of rotational motions: (1) a simple time-domain method, (2) a frequency-domain method proposed by Crawford and Webb (2000) using a coherence-weighted transfer function between rotation and acceleration, and (3) an adapted frequency-domain method that corrects only those parts of the spectrum with coherence between translational acceleration and rotation angle higher than 0.5. These three methods are discussed in three different experimental settings: (1) a reproducible and precisely known laboratory test using a high-precision tilt table, (2) a synthetic test with a simulated volcanic very-long-period event, and (3) a real data set recorded during the 2018 Mt. Kīlauea caldera collapse. All the three test cases show severe influence of tilt motion on the acceleration measurements. The time-domain method and the adapted frequency-domain method show very similar performance in all three test cases. Those two methods are able to remove the tilt component reliably from the acceleration record.

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The application of geodetic observations for near-real time monitoring of Icelandic volcanoes

10.5194/egusphere-egu21-14271 ◽

2021 ◽

Author(s):

Michelle Parks ◽

Benedikt Ófeigsson ◽

Halldór Geirsson ◽

Vincent Drouin ◽

Freysteinn Sigmundsson ◽

...

Keyword(s):

Real Time ◽

Ground Deformation ◽

Current Status ◽

Caldera Collapse ◽

Real Time Monitoring ◽

Volcanic System ◽

Magmatic Intrusions ◽

Reykjanes Peninsula ◽

Magma Migration ◽

Active Volcanoes

Ground deformation is frequently one of the first detectable precursors alerting scientists to changes in behavior or the onset of unrest at active volcanoes. GNSS, InSAR, strain and tilt measurements are routinely used by volcano observatories for monitoring pre-eruptive, co-eruptive and post-eruptive deformation. In addition to monitoring signals related to magma migration, deformation observations are used as an input into geodetic modeling to determine the location and rate of magma accumulation and help define the structure of magma plumbing systems beneath active volcanoes.This presentation will provide an update of how geodetic observations are being used in conjunction with seismicity and gas measurements, for the near-real time monitoring of key Icelandic volcanoes; to determine their current status, identify the onset and likely cause of unrest, locate magmatic intrusions, determine magma volumes and supply rates and assess the likelihood of eruption. An overview of the current status of the following active volcanoes will be provided: Hekla, B&#225;r&#240;arbunga and Gr&#237;msv&#246;tn, along with an update of the recent volcano-tectonic unrest on the Reykjanes Peninsula.Hekla is one of the most active and dangerous volcanoes in Iceland with approximately 18 eruptions since 1104. Over the past few decades, Hekla erupted at almost regular ~10 year intervals, with the last four eruptions occurring in 1970, 1980&#8211;1981, 1991 and 2000. Previous geodetic studies have suggested magma storage at depths of 12-25 km directly beneath the volcanic edifice. However, recent InSAR analysis has detected a localized inflation signal to the west of the volcano. A regional borehole strain meter network has proven instrumental for real-time eruption forecasting at Hekla.In the B&#225;r&#240;arbunga volcanic system, the six-month long effusive 2014-2015 Holuhraun eruption was accompanied by gradual caldera collapse of up to 65 m and was preceded by a two-week period of 48 km long lateral dyke propagation with extensive seismicity and deformation. Geodetic observations indicate that B&#225;r&#240;arbunga began to slowly inflate in July 2015. This may be explained by a combination of renewed magma inflow and viscoelastic readjustment of the volcano.The Gr&#237;msv&#246;tn subglacial volcano is the most frequently erupting volcano in Iceland, with eruptions in 1998, 2004 and 2011. A GPS station shows a prominent inflation cycle prior to eruptions. Observations during the 2011 eruption suggest a pressure drop at a surprisingly shallow level (about 2 km depth) during the eruption, in a similar location as in previous eruptions. Deformation at this volcano has now surpassed that observed prior to historic eruptions and its aviation color code is currently elevated to yellow.In December 2019, the Reykjanes Peninsula entered a phase of volcano-tectonic unrest characterized by seismic swarms, followed in late January 2020 by inflation detected in near-real time by GNSS and InSAR observations. At the time of writing (mid-January 2021) there have been three magmatic intrusions in the vicinity of Svartsengi, an intrusion beneath Kr&#253;suv&#237;k and indications of magma migration at depth along the entirety of the Peninsula.

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Offshore ground movements in the Campi Flegrei caldera during the last ~12 ka

10.5194/egusphere-egu21-15220 ◽

2021 ◽

Author(s):

Camilla Marino ◽

Luigi Ferranti ◽

Jacopo Natale ◽

Marco Sacchi ◽

Marco Anzidei

Keyword(s):

High Resolution ◽

Ground Deformation ◽

Vertical Displacement ◽

Ground Movement ◽

Campi Flegrei ◽

Caldera Collapse ◽

Deformation Pattern ◽

Central Dome ◽

Ground Movements ◽

Campi Flegrei Caldera

Appraisal of morphodepositional markers tied to ancient sea-levels in high-resolution seismic profiles together with geo-archaeological markers along the coast of the Pozzuoli Bay provided insights into the vertical deformation of the submerged part of the Campi Flegrei caldera (Southern Italy).The collapse of the central part of the Campi Flegrei caldera is associated with the eruption of the Neapolitan Yellow Tuff (NYT) at ~15 ka. The NYT caldera collapse was followed by central dome resurgence associated with alternations of fast uplift and subsidence displacements that accompanied with discrete phases of intra-caldera volcanic activity. Previously, the evolution of ground movement in the Campi Flegrei caldera has been reconstructed using marine deposits uplifted onland or archaeological evidence and historical accounts and thus offers a mainly 2D appraisal of the deformation pattern. However, a complete reconstruction of post-collapse deformation suffers of the limitation that nearly two-thirds of the caldera are submerged beneath the Pozzuoli Bay.We contribute to fill this gap by providing a reconstruction of offshore and coastal deformation through estimation of the vertical displacement of morphodepositional markers in high-resolution seismic reflection profiles and geoarchaeological markers directly surveyed at shallow depths. Our interpretation reveals the occurrence of different sediment stacking pattern whose provides evidence of rapid and oscillating ground movements. Whereas the offshore morphodepositional markers provide displacement information for the last ~12 ka, for the last ~2 ka our interpretation is supported by ancient Roman sea-level indicators. The multi-dataset analysis has allowed disentangling the signal related to the post-caldera dynamics from a broader deformation signal that affects this part of the extensional margin of the Apennines.The integration of offshore data in the study of past episodes of ground deformation, by yielding a more complete picture of the ground motions associated to the post-collapse evolution of the Campi Flegrei caldera, bears a significant contribution for a 3D reconstruction of this high-risk resurgence caldera. Besides, the multidisciplinary approach presented here can be relevant for investigations of other calderas spanning the sea-land transition.

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The role of slurry TBM parameters on ground deformation: Field results and computational modelling

Tunnelling and Underground Space Technology ◽

10.1016/j.tust.2016.01.007 ◽

2016 ◽

Vol 57 ◽

pp. 257-264 ◽

Cited By ~ 18

Author(s):

Michael A. Mooney ◽

Jacob Grasmick ◽

Bernadette Kenneally ◽

Yong Fang

Keyword(s):

Ground Deformation ◽

Computational Modelling ◽

Deformation Field

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Multiscale edge-detection methods for the geometrical constraint of deformation sources in the volcanic environment

10.5194/egusphere-egu2020-536 ◽

2020 ◽

Author(s):

Andrea Barone ◽

Raffaele Castaldo ◽

Maurizio Fedi ◽

Susi Pepe ◽

Giuseppe Solaro ◽

...

Keyword(s):

Edge Detection ◽

Ground Deformation ◽

A Priori ◽

Geometrical Model ◽

Deformation Field ◽

Detection Methods ◽

Hazard Evaluation ◽

Geometrical Parameters ◽

A Priori Information ◽

Priori Information

The development of the satellite remote sensing technologies is providing a great contribution to monitor volcanic phenomena. Specifically, the large amount of the ground deformation field data (i.e., DInSAR measurements) holds information about the changes of physical and geometrical parameters of deep and shallow volcanic reservoirs; therefore, the exploitation of these data becomes an important task since they actively contribute to the hazard evaluation.Currently, DinSAR measurements are mostly used for modeling the volcanic deformation sources through the optimization and the inversion procedures; although the latter provide a physical and geometrical model for the considered volcanic site, their results strongly depend on the availability of a priori information and on the considered assumptions about the physical settings; therefore, they do not provide a single solution and they unlikely guarantees a correct analysis&#160; for the multi-source cases.In this scenario, we consider a new methodology based on the use of edge-detection methods for exploiting DInSAR measurements and characterizing the active volcanic sources. Specifically, it allows the estimation of the source geometrical parameters, such as its depth, horizontal position, morphological features and horizontal sizes, by using Multiridge, ScalFun and Total Horizontal Derivative (THD) methods. In particular, it has been proved the validity of Multiridge and ScalFun methods for modeling the point-spherical source independently from its physical features, such as the pressure variation, the physical-elastic parameters of the medium, such as the shear modulus, and low signal-to-noise ratio.Now, we extend the proposed Multiridge and ScalFun methods from the hydrostatic-pressure point source to the tensile one, and then to the others (rectangular tensile-fault and the prolate spheroid analytical models) in order to investigate volcanic sources as sills, dikes and pipes.Specifically, after the analysis of the physical and mathematical features of the considered models, we apply Multiridge and ScalFun methods to the synthetic vertical and E-W components of the ground deformation field. We carefully evaluate the advantages and the limitations which could characterize these cases, showing how to solve critical aspects. We especially focus on the sill-like source, for which the edge-detection methods provide very satisfying results. In addition, we perform a joint exploitation of the edge-detection methods to model the deformation source of Fernandina volcano (Galapagos archipelago) by analyzing COSMO-SkyMed acquisitions related to the 2012-2013 time interval.In conclusion, this approach allows retrieving univocal information about the geometrical configuration of the analyzed deformation pattern. We remark that, although a subsequent analysis is required to fully interpret the ground deformation measurements, this methodology provides a reliable geometrical model, which can be used as a priori information to constrain the entire interpretation procedure during next analyzes.

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The mechanics of Campi Flegrei unrests as related to plastic behaviour of the caldera borders

Annals of Geophysics ◽

10.4401/ag-3738 ◽

1999 ◽

Vol 42 (3) ◽

Author(s):

S. M. Petrazzuoli ◽

C. Troise ◽

F. Pingue ◽

G. De Natale

Keyword(s):

Shear Stress ◽

Half Space ◽

Ground Deformation ◽

Point Of View ◽

Campi Flegrei ◽

Caldera Collapse ◽

Homogeneous Half Space ◽

Ground Deformations ◽

Plastic Zones ◽

Differential Uplift

We present here a model which explains the mechanism of generation of unrest episodes at Campi Flegrei caldera from a mechanical point of view. The mechanism involves the effects of plastic zones at the borders of the inner collapsed area on both static deformations and seismicity. The large amount of ground uplift observed necessarily calls for plastic effects. These effects are interpreted as concentrated at the caldera borders: the generation of such plastic zones is simulated in terms of the mechanisms leading to the caldera collapse. In order to simulate the influence of such plastic zones on both ground deformations and seismicity we model them as surfaces of discontinuities free from shear stress within an elastic homogeneous half-space. The presence of such discontinuities allows the inner caldera block to move differentially from the outer areas, by slip along the plastic bordering zones. Such a differential uplift of the central block causes the concentration of the ground deformation. Our model explains a lot of puzzling observations at Campi Flegrei in terms of the effects of the caldera structure. The model is applicable to other caldera areas, which show typical evidence for the effects of such discontinuity zones, during unrest episodes.

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3D Coseismic Deformation Field and Source Parameters of the 2017 Iran-Iraq Mw7.3 Earthquake Inferred from DInSAR and MAI Measurements

Remote Sensing ◽

10.3390/rs11192248 ◽

2019 ◽

Vol 11 (19) ◽

pp. 2248 ◽

Cited By ~ 1

Author(s):

Zhiheng Wang ◽

Rui Zhang ◽

Yuxin Liu

Keyword(s):

Ground Deformation ◽

Source Parameters ◽

Field Measurements ◽

Parameters Estimation ◽

Deformation Field ◽

Coseismic Deformation ◽

United States Geological Survey ◽

Data Sets ◽

Coseismic Slip ◽

Main Fault

The coseismic slip on the main fault related to the 2017 Iran-Iraq Mw7.3 earthquake has been investigated by previous studies using DInSAR (differential interferometric synthetic aperture radar) ground deformation measurements. However, DInSAR observation is not sensitive to the ground deformation in the along-track (AT) direction. Therefore, only the one-dimensional (1D) DInSAR coseismic deformation field measurements, derived in the LOS (line-of-sight) direction of radar, was applied in source parameters estimation. To further improve the accuracy of the fault slip inversion, the 3D (three-dimensional) coseismic deformation fields were reconstructed in the first place, by a combined use of the DInSAR and MAI (multiple aperture InSAR) measurements. Subsequently, the LOS and 3D deformation data sets were used as the constraint respectively, to perform a two-step inversion scheme to find an optimal geometry and slip distribution on the main fault. The comparative analysis indicated that the 3D coseismic deformation data sets improved the inversion-accuracy by 30%. Besides, the fault invention results revealed a deep dislocation on a NNW trending fault (the strike is 352.63°) extending about 60 km, along the fault dips 14.76° to the ENE. The estimated seismic moment is 8.44 × 1019 Nm (Mw7.3), which is close to the solution provided by USGS (United States Geological Survey). The slip distributed at the depth between 12 and 18 km, and the peak slip of 6.53 m appears at the depth of 14.5 km left near the epicenter. Considering the geological structure in the earthquake region and fault source-parameters, it comes to a preliminary conclusion that the ZMFF (the Zagros Mountain Front fault) should be responsible for the earthquake. In general, this paper demonstrated the superiority of using the 3D coseismic deformation fields on source parameters estimation.

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