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  • 1
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    In:  Geophys. Res. Lett., Berlin, Schweizerbart'sche Verlagsbuchhandlung, vol. 28, no. 23, pp. 4379-4382, pp. L07302, (ISSN 0016-8548, ISBN 3-510-50045-8)
    Publication Date: 2001
    Keywords: Earthquake ; Source ; China ; Tectonics ; GRL ; 1242 ; Geodesy ; and ; gravity ; Seismic ; deformations ; (7205) ; 7215 ; Seismology ; Earthquake ; parameters
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  • 2
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    In:  Tectonophys., Stuttgart, Pergamon, vol. 388, no. 5, pp. 21-31, pp. 1244, (ISSN: 1340-4202)
    Publication Date: 2004
    Keywords: Velocity depth profile ; Geothermics ; Physical properties of rocks ; Tectonics ; China ; rheology, ; seismicity, ; strength ; profile ; composition
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  • 3
    Publication Date: 2005
    Keywords: Earthquake ; Tsunami(s) ; Earthquake hazard ; Indonesia ; Banda ; Aceh ; seismic Moment ; Surface waves ; Source ; Modelling ; Crustal deformation (cf. Earthquake precursor: deformation or strain) ; slow ; red ; silent ; contribution ; Camp
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  • 4
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    In:  Science, Roma, Polish Geothermal Association, vol. 301, no. 5633, pp. 630-633, pp. L18613, (ISSN: 1340-4202)
    Publication Date: 2003
    Keywords: Plate tectonics ; Seismicity ; Subduction zone ; Gravimetry, Gravitation ; Friction ; Geol. aspects ; topography ; FLORENZO
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  • 5
    Publication Date: 2016-05-09
    Description: The M w 8.4 Illapel earthquake occurred on 16th September was the largest global event in 2015. This earthquake was not unexpected because the hypocenter was located in a seismic gap of the Peru–Chile subduction zone. However, the source model derived from 3D spectral-element inversion of teleseismic waves reveals a distinct two-stage rupture process with completely different slip characteristics as a composite megathrust event. The two stages were temporally separated. Rupture in the first stage, with a moment magnitude of M w 8.32, built up energetically from the deeper locked zone and propagated in the up-dip direction toward the trench. Subsequently, the rupture of the second stage, with a magnitude of M w 8.08, mainly occurred in the shallow subduction zone with atypical repeating slip behavior. The unique spatial-temporal rupture evolution presented in this source model is key to further in-depth studies of earthquake physics and source dynamics in subduction systems.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Publication Date: 2012-09-11
    Description: The oceanic asthenosphere is characterized as a low viscosity channel down to 200–300 km depth separating the cold lithosphere from above, and it is intimately linked to a layer of low seismic velocity and prominent seismic anisotropy observed globally beneath ocean basins. While subduction of tectonic plates in convergent margins is well recognized, the fate of oceanic asthenosphere remains enigmatic. We demonstrate that subduction of the oceanic asthenosphere characterized by weak azimuthal anisotropy and strong radial anisotropy explains the essence of sub-slab shear-wave splitting patterns, where the fast splitting direction changes from predominantly trench-parallel (or sub-parallel) under relatively steep subduction zones to frequently trench-normal under shallow subduction zones. To explain the observed splitting time, the thickness of the subducted asthenosphere is estimated to be 100 ± 50 km.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
    Publication Date: 2012-05-09
    Description: Slow slip events (SSEs) are recently discovered in the transition zone downdip of the locked zone where megathrust earthquakes repeatedly occur at subduction zone interface. Structural changes from the locked zone to the transition zone and the nature of in situ deformation in the transition zone, however, remain unclear. We model teleseismic converted P-to-S waves to investigate seismic structural transition and anisotropy associated with shear deformation near the deep locked zone and the transition zone beneath southern Mexico. The deep locked zone appears to be consistent with normal oceanic crust velocity. In the transition zone, we find that seismic anisotropy larger than 5% is associated with the ultra-slow velocity layer (USL) near the top of the subducted oceanic crust. The foliation plane is plunging 20 ± 10 degrees steeper than the plate interface, and it is consistent with crystallographic preferred orientation developed in S-C mylonites. We suggest that long-term SSEs likely coincide with a near-lithostatic semiductile talc-rich shear zone.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
    Publication Date: 2011-12-23
    Description: Anisotropic uppermost mantle in young subducted slab underplating Central Mexico Nature Geoscience 5, 55 (2012). doi:10.1038/ngeo1342 Authors: Teh-Ru Alex Song & YoungHee Kim Knowledge of the rate of plate-spreading at mid-ocean ridges is critical for estimating plate motions and the outward flux of heat from Earth’s interior. Magnetic lineations and anisotropy—crystals that have aligned themselves with mantle flow—preserved in oceanic lithosphere provide a means for estimating plate-spreading rates up to 180 million years ago. However, reconstructions beyond this time are difficult because most older oceanic lithosphere has been subducted into the mantle. Here we use converted seismic waveforms to show that anisotropy is preserved in the subducted part of the Cocos Plate beneath Central Mexico. We observe strong P- and S-wave anisotropy in the topmost 2–6 km of the subducted oceanic mantle. The strength of the anisotropy is comparable to that measured in the surface portion of the Cocos Plate. We also show that P-wave azimuthal anisotropy and plate-spreading rate at present-day mid-ocean ridges exhibit a linear relationship. On the basis of this relationship, we suggest that the subducted portion of the Cocos Plate formed at a half-spreading rate of about 8 cm yr−1 at the East Pacific Rise, about 15 million years ago. Our results imply that subducted oceanic lithosphere could preserve an archive of ancient plate-spreading rates on Earth.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 9
    Publication Date: 2019-10-15
    Description: Long period volcanic tremors (LPTs), typically termed as VLP, have been widely observed in many volcanic systems around the world. LPTs in different volcanic settings are often repetitive, suggesting a nondestructive source and providing critical insights into the fluid dynamic processes operating inside a volcanic system. Recently, a deep triggering source of LPT has also been discovered, located between the LPT source and the magma chamber. These diverse and rich signals not only help monitor the state of shallow volcanic conduit and its link to upcoming eruptions. it also helps understand causal triggering of LPT and potentially intra-crustal transport of magma. Given diverse and rich signals within the Aso volcanic system, we further explore other possible sources in the tidal period. We analysed continuous data recorded at two borehole tiltmeters installed at Aso volcano, during the period of 2011-2016. We first perform a polarisation analysis of the ground tilt, filtering in the frequency bands matching the medium-long period tidal constituents, Mm, Mf and S1. The results evidence a well-defined direction of the tilting plane at both sites, with minor fluctuations occurring in 2012 and 2014. Moreover, we investigated the tilt time series the 1-8 hour band. There is a clear variation in azimuth orientation in at least one of the two tiltmeters and these azimuthal variations occur roughly from September 2013 at least until November 2014. In the meantime, LPTs were strong and more active, ash eruption occurred at the end of August 2014, followed by a major Strombolian eruption episode starting at the end of November 2014. In this time interval between September 2013 and November 2014, we further discovered a sequence of nearly monochromatic signals, with repetitive waveforms, a typical period of about 2 hours and a duration of about 9 hours. We extracted these signals and will compare their timing against the LPT catalog we constructed previously. Moreover, we will perform waveform correlation in order to quantify the degree of similarity among these monochromatic signals. Finally, we will attempt to reconcile all these observations in terms of the volcano dynamics and of its different eruptive styles during the 2011-2016 eruption cycle.
    Description: Published
    Description: Vienna
    Description: 4V. Processi pre-eruttivi
    Keywords: Aso volcano ; Tilt oscillations
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Abstract
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  • 10
    Publication Date: 2023-09-07
    Description: Ground deformation in volcanic areas induced by geothermal fluid circulation can reveal useful information about the dynamical processes occurring in the subsurface hydrothermal system. In the present work, we investigate tiltmeter time-series recorded at Aso Volcano during 2011–2016, a time interval during which different phases of volcanic activity occurred. We performed polarization analysis of the data and identified peculiar long-lasting (hours) transients, defined as Very-Long-period Tilt Pulses. The transients were further characterized in terms of waveform cross-correlation, particle tilt pattern, energy, and time distributions. The analyses indicate that such signals, which appear like deflation–inflation (DI) events, are associated with a Poissonian process whose underlying dynamics evolves over time always driven by a Poissonian mechanism. The obtained results have been interpreted in light of the available geophysical, geochemical and volcanological information. In this framework, the Very-Long-period Tilt Pulses may be ascribed to the depressurization/pressurization of the shallow hydrothermal system according to a fault-valve mechanism, which was active with different efficiency throughout eruptive and inter-eruptive phases.
    Description: Published
    Description: 132
    Description: 4V. Processi pre-eruttivi
    Description: JCR Journal
    Keywords: Aso Volcano ; Tiltmeter data ; Polarization analysis ; Clusters ; Inflation ; Deflation ; 04.08. Volcanology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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