Modeling of the source mechanism of the April 5, 2003 paroxysmal eruption at Stromboli volcano (Italy) by the inversion of broadband seismic data

Abstract: On April 5, 2003, one of the largest eruptions in the last decades was observed at Stromboli volcano, Italy. The eruption occurred in a period of anomalous volcanic activity, after a previous explosion in December 2002 interrupted the typical moderate "Strombolian" behaviour. An exhaustive analysis of the available broadband seismic data is here presented and related to the observed eruption phases. Prominent features of the seismic signals include a very long period signal a few tens of seconds prior to the explosive eruption, as well as a strong energetic signal a few seconds after the onset of the eruption

Influence of topograhy on the seismic waveforms associated to eruptive events at Stromboli volcano

The steep topography, which characterizes certain volcanic areas, may strongly influence the displacement field associated to seismic signals. As a consequence, the interpretation of seismic data for the inversion of the seismic source and the crustal structure properties should carefully take into account these effects. We propose a set of numerical simulations for seismic wave propagation in a 3-D homogeneous model of Stromboli volcano, Italy, based on the application of a pseudospectral technique. The model assumes a topography with a discretization of 100 m on the horizontal directions, and 1 m on the vertical direction, while bathymetry is not yet included. We estimate the surface displacement field for different seismic sources, reproducing possible phenomena occurring during an eruptive process. These include purely isotropic sources, the realistic inclusion of an additional deviatoric CLVD component, which may take into account the effects of explosive events in presence of conduits and the final fall-out of material at the volcanic surface. Different durations of the source time function are tested in order to compare the effects of topography for seismic radiations with a variable range of frequency content. The comparison of results highlights the effects, which are strictly related to the presence of a steep topography

Estimation of long period volcanic sources by a frequency domain inversion approach

The high interest of volcanologists to understand the physical phenomena which governs long period (LP) events is related to the fact that they may be directly generated by fluid transfer and could be indicators of the level of activity in the volcano and in some cases could act as precursor to eruptions. The wide variety of waveforms and spectral contents existing for LP events, as well as the existence of alternative models to explain the observations make it interesting to develop new inversion schemes. We propose an inversion methodology to determine source mechanisms and study these events through an exhaustive source inversion by using synthetic and observed data. Our method for source inversion is based on a frequency domain approach, which has its main advantage in reducing computational requirements. The resulting source mechanism is represented by the sum of two time-dependent terms: a full moment tensor and a single force. The method has been applied to different sets of synthetic and observed data, including data from Kilauea volcano. Green’s functions have been calculated using different layered crustal models, which have been proposed for volcanic areas. Inversion tests are established to check the stability of the method and the possibility of retrieving all source components. The method has been finally applied to volcanic data and results are interpreted in terms of possible source models

Source inversion of seismic events recorded in the Larderello geothermal area

The Larderello geothermal field is a wide thermal anomaly located in the western part of Tuscany (Italy). Geophysical investigations in this area suggest a crustal thinning and intrusion of hot mantle material into the crust. The local seismicity, monitored since 1978 by a network of 26 short period almost vertical seismic stations, is characterized by a several hundred of M 1.5 events per year, never exceeding M=3.2 in the past 25 years. At December 2004 ENEL and INGV started a scientific collaboration, which includes also exchange of selected datasets. One of the main tasks is to perform source inversion of low magnitude seismic events recorded in the Larderello geothermal area. This is of particular interest, because such earthquakes could show similarities with seismic events recorded on active volcanoes. In order to record also seismic events below magnitude M = 1 the gain of the ENEL-seismic network is set rather sensitive. This implicates that seismograms of events with magnitudes M > 2.0 are recorded by the entire network, but at low epicentral distances the traces are often saturated, making a waveform inversion impossible. On the other hand, smaller events are not strong enough to be recorded also at the more external stations of the network. In both cases this trade-off results in a limited number of vertical component recordings available for the inversion. A further difficulty by performing source inversion of small seismic events is to fit the high frequencies. Therefore we applied the moment tensor (MT) inversion both in the time domain as well as in the frequency domain and compared the results. Source inversion was performed both for the full MT as well as by introducing constraints for doubles couple e/o CLVD. The source inversions of events occurred in the Travale area show a high double couple percentage and show no indications for an isotropic source. This seems to indicate a source mechanism which is typical for tectonic events

Control of Au nanoantenna emission enhancement of magnetic dipolar emitters by means of VO2 phase change layers

Active, ultra-fast external control of the emission properties at the nanoscale is of great interest for chip-scale, tunable and efficient nanophotonics. Here we investigated the emission control of dipolar emitters coupled to a nanostructure made of an Au nanoantenna, and a thin vanadium dioxide (VO2) layer that changes from semiconductor to metallic state. If the emitters are sandwiched between the nanoantenna and the VO2 layer, the enhancement and/or suppression of the nanostructure’s magnetic dipole resonance enabled by the phase change behavior of the VO2 layer can provide a high contrast ratio of the emission efficiency. We show that a single nanoantenna can provide high magnetic field in the emission layer when VO2 is metallic, leading to high emission of the magnetic dipoles; this emission is then lowered when VO2 switches back to semiconductor. We finally optimized the contrast ratio by considering different orientation, distribution and nature of the dipoles, as well as the influence of a periodic Au nanoantenna pattern. As an example of a possible application, the design is optimized for the active control of an Er3+ doped SiO2 emission layer. The combination of the emission efficiency increase due to the plasmonic nanoantenna resonances and the ultra-fast contrast control due to the phase-changing medium can have important applications in tunable efficient light sources and their nanoscale integration

Tuning ZnO nanorods photoluminescence through atmospheric plasma treatments

Room temperature atmospheric plasma treatments are widely used to activate and control chemical functionalities at surfaces. Here, we investigated the effect of atmospheric pressure plasma jet (APPJ) treatments in reducing atmosphere (Ar/1 parts per thousand H-2 mixture) on the photoluminescence (PL) properties of single crystal ZnO nanorods (NRs) grown through hydrothermal synthesis on fluorine-doped tin oxide glass substrates. The results were compared with a standard annealing process in air at 300 degrees C. Steady-state photoluminescence showed strong suppression of the defect emission in ZnO NRs for both plasma and thermal treatments. On the other side, the APPJ process induced an increase in PL quantum efficiency (QE), while the annealing does not show any improvement. The QE in the plasma treated samples was mainly determined by the near band-edge emission, which increased 5-6 fold compared to the as-prepared samples. This behavior suggests that the quenching of the defect emission is related to the substitution of hydrogen probably in zinc vacancies (V-Zn), while the enhancement of UV emission is due to doping originated by interstitial hydrogen (H-i), which diffuses out during annealing. Our results demonstrate that atmospheric pressure plasma can induce a similar hydrogen doping as ordinarily used vacuum processes and highlight that the APPJ treatments are not limited to the surfaces but can lead to subsurface modifications. APPJ processes at room temperature and under ambient air conditions are stable, convenient, and efficient methods, compared to thermal treatments to improve the optical and surface properties of ZnO NRs, and remarkably increase the efficiency of UV emission. (c) 2019 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)

Fabrication of biocompatible free-standing nanopatterned films for primary neuronal cultures

Devising and constructing biocompatible devices for nervous system regeneration is an extremely challenging task. Besides tackling the issue of biocompatibility, biomaterials for neuroscience applications should mimic the complex environment of the extracellular matrix, which in vivo provides neurons with a series of cues and signals to guide cells towards their appropriate targets. In this work, a novel nanopatterned biocompatible poly-ε-caprolactone (PCL) film is realized to assist the attachment and growth of primary hippocampal neurons. Costly and time-consuming processes can be avoided using plasma-surface nanotexturing obtained by a mixed gas SF6/Ar at -5 °C. The intrinsic composition and line topography of nanopatterned PCL ensure healthy development of the neuronal network, as shown by confocal microscopy, by analysing the expression of a range of neuronal markers typical of mature cultures, as well as by scanning electron microscopy. In addition, we show that surface nanopatterning improves differentiation of neurons compared to flat PCL films, while no neural growth was observed on either flat or nanopatterned substrates in the absence of a poly-d-lysine coating. Thus, we successfully optimized a nanofabrication protocol to obtain nanostructured PCL layers endowed with several mechanical and structural characteristics that make them a promising, versatile tool for future tissue engineering studies aimed at neural tissue regeneration

Seismic and Tsunamigenic Characteristics of a Multimodal Rupture of Rapid and Slow Stages

On 12 August 2021, a >220 s lasting complex earthquake with Mw > 8.2 hit the South Sandwich Trench. Due to its remote location and short interevent times, reported earthquake parameters varied significantly between different international agencies. We studied the complex rupture by combining different seismic source characterization techniques sensitive to different frequency ranges based on teleseismic broadband recordings from 0.001 to 2 Hz, including point and finite fault inversions and the back-projection of high-frequency signals. We also determined moment tensor solutions for 88 aftershocks. The rupture initiated simultaneously with a rupture equivalent to a Mw 7.6 thrust earthquake in the deep part of the seismogenic zone in the central subduction interface and a shallow megathrust rupture, which propagated unilaterally to the south with a very slow rupture velocity of 1.2 km/s and varying strike following the curvature of the trench. The slow rupture covered nearly two-thirds of the entire subduction zone length, and with Mw 8.2 released the bulk of the total moment of the whole earthquake. Tsunami modeling indicates the inferred shallow rupture can explain the tsunami records. The southern segment of the shallow rupture overlaps with another activation of the deeper part of the megathrust equivalent to Mw 7.6. The aftershock distribution confirms the extent and curvature of the rupture. Some mechanisms are consistent with the mainshocks, but many indicate also activation of secondary faults. Rupture velocities and radiated frequencies varied strongly between different stages of the rupture, which might explain the variability of published source parameters

The November 2017 Mw 5.5 Pohang earthquake: a possible case of induced seismicity in South Korea

The Mw 5.5 earthquake that struck South Korea in November 2017 was one of the largest and most damaging events in this country over the last century. Its proximity to an Enhanced Geothermal Systems site, where high pressure hydraulic injection had been performed during the previous two years, raises the possibility that this earthquake was anthropogenic. We have combined seismological and geodetic analyses to characterize the mainshock and its largest aftershocks, constrain the geometry of this seismic sequence and shed light on its casual factors. According to our analysis it seems plausible that the occurrence of this earthquake was influenced by these industrial activities. Finally we found that the earthquake transferred static stress to larger nearby faults, potentially increasing the seismic hazard in the area

Drainage of a deep magma reservoir near Mayotte inferred from seismicity and deformation

The dynamics of magma deep in the Earth’s crust are difficult to capture by geophysical monitoring. Since May 2018, a seismically quiet area offshore of Mayotte in the western Indian Ocean has been affected by complex seismic activity, including long-duration, very-long-period signals detected globally. Global Navigation Satellite System stations on Mayotte have also recorded a large surface deflation offshore. Here we analyse regional and global seismic and deformation data to provide a one-year-long detailed picture of a deep, rare magmatic process. We identify about 7,000 volcano-tectonic earthquakes and 407 very-long-period seismic signals. Early earthquakes migrated upward in response to a magmatic dyke propagating from Moho depth to the surface, whereas later events marked the progressive failure of the roof of a magma reservoir, triggering its resonance. An analysis of the very-long-period seismicity and deformation suggests that at least 1.3 km3 of magma drained from a reservoir of 10 to 15 km diameter at 25 to 35 km depth. We demonstrate that such deep offshore magmatic activity can be captured without any on-site monitoring