Authors:Somayeh Ahmadzadeh, Stefano Parolai, Gholam Javan-Doloei, Adrien Oth First page: 668 Abstract: A nonparametric generalized inversion technique (GIT) has been used to derive attenuation characteristics, source parameters and site amplification effects from S wave spectra of the 2006 Silakhor earthquake aftershocks recorded at 10 temporary stations in the epicentral area of the main shock along the main recent fault in Zagros region. We apply a total number of 971 spectral amplitudes from 213 aftershocks with ML 1.5-4.4 in the frequency range 0.5–35Hz. The obtained nonparametric attenuation curves decay monotonically with distance for the entire frequency range and the estimated S wave quality factor shows low Q values with fairly strong frequency dependence. We fit the omega-square source model to the inverted source spectra to derive earthquake source parameters. The estimated stress drops range from 0.04 to 5.3 MPa with an average of 0.9 MPa, within the range typically observed for crustal earthquakes in other regions of the World. The evaluated apparent stresses vary from 0.009 to 0.9 MPa and its relation with stress drops is generally consistent with the theoretically expected relation assuming Brune model. The local magnitude ML shows a linear correlation with the moment magnitude MW that underestimates the MW scale by about 0.1-0.5 magnitude units for MW 1.5-3.0. We found a gradual increase in corner frequency values against seismic moments that may be considered as an evidence for a deviation from self-similarity scaling though the magnitude range of this study is fairly small to deduce a firm conclusion. The comparison of estimated GIT site amplification functions with the evaluated horizontal to vertical (H/V) spectral ratios shows different levels of amplification in site responses due to amplification of the vertical component; however, the overall shape of site spectra provided by both methods are relatively similar. PubDate: 2017-12-21 DOI: 10.4401/ag-7520 Issue No:Vol. 60, No. 6 Sup (2017)

Authors:Vito Zago, Giuseppe Bilotta, Annalisa Cappello, Robert Anthony Dalrymple, Luigi Fortuna, Gaetana Ganci, Alexis Hérault, Ciro Del Negro First page: 669 Abstract: Complex fluid dynamics encompasses a large variety of flows, such as fluids with non-Newtonian rheology, multi-phase and multi-fluid flows (suspensions, lather, solid/fluid interaction with floating objects, etc), violent flows (breaking waves, dam-breaks, etc), fluids with thermal dependencies and phase transition or free-surface flows. Correctly modeling the behavior of such flows can be quite challenging, and has led to significant advances in the field of Computational Fluid Dynamics (CFD). Recently, the Smoothed Particle Hydrodynamics (SPH) method has emerged as a powerful alternative to more classic CFD methods (such as finite volumes or finite elements) in many fields, including oceanography, volcanology, structural engineering, nuclear physics and medicine. With SPH, the fluid is discretized by means of particles and thanks to the meshless, Lagrangian nature of the model, it easily allows the modeling and simulation of both simple and complex fluids, simplifying the treatment of aspects which can be challenging with more traditional methods: dynamic free surfaces, large deformations, phase transition, fluid/solid interaction and complex geometries. In addition, the most common SPH formulations are fully parallelizable, which favors implementation on high-performance parallel computing hardware, such as modern Graphics Processing Units (GPUs). We present here how GPUSPH, an implementation of the SPH method that runs on GPUs, can model a variety of complex fluids, highlighting the computational challenges that arise in its applications to problem of great interest in volcanology. PubDate: 2017-12-21 DOI: 10.4401/ag-7362 Issue No:Vol. 60, No. 6 Sup (2017)

Authors:Sankar N Bhattacharya First page: 670 Abstract: We consider transversely isotropic media with vertical axis of symmetry (VTI). Solutions of P-SV equation of motion in a homogeneous VTI medium contain depth decay factors r1 and r2, which sometimes become complex depending on VTI parameters. In this case, r1 and r2 are complex conjugates. Using this property, we obtain dispersion equation of Rayleigh waves with real terms for a layered VTI half space through Thomson-Haskell method with reduced delta matrix. Phase and group velocities as well as surface ellipticity of Rayleigh waves are computed in real domain for a few oceanic and continental VTI structures of the earth. Present computation in real domain is similar to that in a layered isotropic half space using the same method. Thus it is presumed that such computation in a layered VTI half space will allow efficient evaluation of a VTI structure of the earth. PubDate: 2017-12-21 DOI: 10.4401/ag-7444 Issue No:Vol. 60, No. 6 Sup (2017)

Authors:Tushar Andriyas First page: 672 Abstract: comparison of solar wind conditions, geomagnetic response, and auroral boundary movement, using a similar number of sawtooth events and shock induced substorm triggers is carried out. 81% of the sawtooth onsets were triggered at low latitudes compared to 33% for onsets during shocks. Results of superposed epoch analysis indicated that the mean interplanetary magnetic field (IMF) Bz remained strongly southward during sawtooth events while it was southward during the loading period and turned northward 20 minutes prior to the onset, during the shock triggered events. During both the event types, the mean energy available in the solar wind was found to be above the substorm threshold level. Relatively high levels of solar wind density indicated to the magnetosphere being compressed to a larger degree during substorms initiated by shocks. The high latitude indices were elevated during sawtooth events with 2-3 hr fluctuations was observed in the AL and PCN indices but AU index after the onset remained at similar levels. SYM-H remained below storm time values during shock related onsets but was much stronger and remained above the storm threshold during sawtooth events, that they occurred embedded in a geomagnetic storm. Comparatively higher mean values of ASYM-H indicated to a much stronger asymmetric ring current during sawtooth events. Mean boundary locations during sawtooth events were located a few degrees equatorward of those during the shock related onsets. Oval in the dawn, dusk, and midnight sectors was much thicker during sawtooth events with clear widening around the onset during both event groups but the thickness in noon sector was similar and remained steady during the epoch window during both the event groups. Elevated driving during sawtooth events was also indicative in a greater stretching and relaxation of the magnetic field lines at geosynchronous orbit in the midnight sector. PubDate: 2017-12-21 DOI: 10.4401/ag-7481 Issue No:Vol. 60, No. 6 Sup (2017)

Authors:Valeria Paoletti, Maurizio Fedi, Giovanni Florio First page: 674 Abstract: We carried out a study of the structures of the volcanic island of Ischia by the analysis and interpretation of high-resolution aeromagnetic data and by a newly compiled in-land gravity data set. The comparison between the vertical gradient of gravity data and pole-reduced magnetic data was performed through semblance analysis and highlighted a correspondence between the main magnetic and gravity highs over the lava and green tuff deposits (e.g., Punta Imperatore, Mt. Trippodi, Zaro, Mt. Rotaro, Mt. Epomeo). Our analysis also highlighted the simultaneous presence of a magnetic minimum and a gravimetric maximum in the central part of the island, mainly visible in the long-period components of the two data sets. This may be due to the existence of a partially demagnetized structure with positive density contrast, representing the island's igneous basement. The boundaries of the lava and tuffs deposits of the island were clearly pointed out by the maxima of the total horizontal gradient maps of magnetic and gravity data. Those maxima also show the position of several lineaments, in good agreement with the mapped faults of the island. PubDate: 2017-12-21 DOI: 10.4401/ag-7550 Issue No:Vol. 60, No. 6 Sup (2017)

Authors:Filippos Vallianatos First page: 675 Abstract: It is being increasingly recognized that geological media are inherently rough with persistent, long-range spatial correlations in physical properties, including electrical conductivity, which spans many decades in length scale. In the present study, the ideas of a multi-scaled geological medium and the anomalous diffusion of EM eddy currents applied, in Keritis Basin (Western Crete, Greece), a complex geological system surrounded by normal faults and with the majority of formations to be calcareous and karstified. We present evidence of a multi-scaled hierarchical structure,based on observed q-exponential distributions of the resistivity, supporting our motivation to introduce fractional diffusion ideas and non-extensive statistical physics to describe the geoelectrical structure of karstified Keritis basin. The essential goal of this paper is to test in a real geological complex formation the TEM response in terms of the rough geological medium where the conductivity of the ground has a spatial distribution, which is described by a roughness parameter,and to better understand the geoelectrical properties of complex geological structure introducing the ideas of fractional diffusion and non extensive statistical physics. PubDate: 2017-12-21 DOI: 10.4401/ag-7551 Issue No:Vol. 60, No. 6 Sup (2017)