ALBERT

Description: The emission of electrical signals during application of mechanical stress to brittle geo-materials (the so-called pressure-stimulated current; PSC) can provide significant information regarding the mechanical status of a studied rock sample. PSCs originate as a result of the opening of cracks and microfractures in rock. In this study, such electrical signal emissions are detected and studied when rock samples are subjected to step-wise mechanical stress, increased from low stress levels vL up to higher stress levels vH. This increase is performed at high stress rates and consequently the stress is maintained practically constant for a long period. During this time, the applied stress reaches its maximum value, and the emitted PSC decays gradually and relaxes back to a minimum value. The conducted experiments suggest that the characteristics of the relaxation processes of the PSC depend directly on the high level of the applied stress that is maintained constant after the application of each stress step. Analysis of the macroscopic parameters that characterize the relaxation phenomenon of the PSC provides clear information regarding the proximity of the applied stress to the fracture limit of the rock sample.

Description: Observational studies from rock fractures to earthquakes indicate that fractures and many large earthquakes are preceded by accelerating seismic release rates (accelerated seismic deformation). This is characterized by cumulative Benioff strain that follows a power law time-to-failure relation of the form C(t) = K + A(Tf – t)m, where Tf is the failure time of the large event, and m is of the order of 0.2-0.4. More recent theoretical studies have been related to the behavior of seismicity prior to large earthquakes, to the excitation in proximity of a spinodal instability. These have show that the power-law activation associated with the spinodal instability is essentially identical to the power-law acceleration of Benioff strain observed prior to earthquakes with m = 0.25-0.3. In the present study, we provide an estimate of the generic local distribution of cracks, following the Wackentrapp-Hergarten-Neugebauer model for mode I propagation and concentration of microcracks in brittle solids due to remote stress. This is a coupled system that combines the equilibrium equation for the stress tensor with an evolution equation for the crack density integral. This inverse type result is obtained through the equilibrium equations for a solid body. We test models for the local distribution of cracks, with estimation of the stress tensor in terms of the crack density integral, through the Nash-Moser iterative method. Here, via the evolution equation, these estimates imply that the crack density integral grows according to a (Tf – t)0.3-law, in agreement with observations.  

Description: Author(s): Georgios Michas and Filippos Vallianatos Earthquake time series are widely used to characterize the main features of regional seismicity and to provide useful insights into earthquake dynamics. Properties such as intermittency and nonstationary clustering are common in earthquake time series, highlighting the complex nature of the earthqua... [Phys. Rev. E 98, 042107] Published Wed Oct 03, 2018

Description: Observational indications support the hypothesis that many large earthquakes are preceded by accelerating-decelerating seismic release rates which are described by a power law time to failure relation. In the present work, a unified theoretical framework is discussed based on the ideas of non-extensive statistical physics along with fundamental principles of physics such as the energy conservation in a faulted crustal volume undergoing stress loading. We define a generalized Benioff strain function Ω ξ ( t ) = ∑ i = 1 n ( t ) E i ξ ( t ) , where Ei is the earthquake energy, 0 ≤ ξ ≤ 1 . and a time-to-failure power-law of Ω ξ ( t ) derived for a fault system that obeys a hierarchical distribution law extracted from Tsallis entropy. In the time-to-failure power-law followed by Ω ξ ( t ) the existence of a common exponent mξ which is a function of the non-extensive entropic parameter q is demonstrated. An analytic expression that connects mξ with the Tsallis entropic parameter q and the b value of Gutenberg—Richter law is derived. In addition the range of q and b values that could drive the system into an accelerating stage and to failure is discussed, along with precursory variations of mξ resulting from the precursory b-value anomaly. Finally our calculations based on Tsallis entropy and the energy conservation give a new view on the empirical laws derived in the literature, the associated average generalized Benioff strain rate during accelerating period with the background rate and connecting model parameters with the expected magnitude of the main shock.

Description: The Yellowstone Park volcanic field is one of the most active volcanic systems in the world, presenting intense seismic activity that is characterized by several earthquake swarms over the last decades. In the present work, we focused on the spatiotemporal properties of the recent earthquake swarms that occurred on December–January 2008–2009 and the 2010 Madison Plateau swarm, using the approach of Non Extensive Statistical Physics (NESP). Our approach is based on Tsallis entropy, and is used in order to describe the behavior of complex systems where fracturing and strong correlations exist, such as in tectonic and volcanic environments. This framework is based on the maximization of the non-additive Tsallis entropy Sq, introducing the q-exponential function and the entropic parameter q that expresses the degree of non-extentivity of the system. The estimation of the q-parameters could be used as a correlation degree among the events in the spatiotemporal evolution of seismicity. Using the seismic data provided by University of Utah Seismological Stations (UUSS), we analyzed the inter-event time (T) and distance (r) distribution of successive earthquakes that occurred during the two swarms, fitting the observed data with the q-exponential function, resulting in the estimation of the Tsallis entropic parameters qT, qr for the inter-event time and distance distributions, respectively. Furthermore, we studied the magnitude-frequency distribution of the released earthquake energies E as formulated in the frame of NESP, which results in the estimation of the qE parameter. Our analysis provides the triplet (qE, qT, qr) that describes the magnitude-frequency distribution and the spatiotemporal scaling properties of each of the studied earthquake swarms. In addition, the spatial variability of qE throughout the Yellowstone park volcanic area is presented and correlated with the existence of the regional hydrothermal features.

Description: Entropy, Vol. 20, Pages 721: Complexity of the Yellowstone Park Volcanic Field Seismicity in Terms of Tsallis Entropy Entropy doi: 10.3390/e20100721 Authors: Kalliopi Chochlaki Georgios Michas Filippos Vallianatos The Yellowstone Park volcanic field is one of the most active volcanic systems in the world, presenting intense seismic activity that is characterized by several earthquake swarms over the last decades. In the present work, we focused on the spatiotemporal properties of the recent earthquake swarms that occurred on December–January 2008–2009 and the 2010 Madison Plateau swarm, using the approach of Non Extensive Statistical Physics (NESP). Our approach is based on Tsallis entropy, and is used in order to describe the behavior of complex systems where fracturing and strong correlations exist, such as in tectonic and volcanic environments. This framework is based on the maximization of the non-additive Tsallis entropy Sq, introducing the q-exponential function and the entropic parameter q that expresses the degree of non-extentivity of the system. The estimation of the q-parameters could be used as a correlation degree among the events in the spatiotemporal evolution of seismicity. Using the seismic data provided by University of Utah Seismological Stations (UUSS), we analyzed the inter-event time (T) and distance (r) distribution of successive earthquakes that occurred during the two swarms, fitting the observed data with the q-exponential function, resulting in the estimation of the Tsallis entropic parameters qT, qr for the inter-event time and distance distributions, respectively. Furthermore, we studied the magnitude-frequency distribution of the released earthquake energies E as formulated in the frame of NESP, which results in the estimation of the qE parameter. Our analysis provides the triplet (qE, qT, qr) that describes the magnitude-frequency distribution and the spatiotemporal scaling properties of each of the studied earthquake swarms. In addition, the spatial variability of qE throughout the Yellowstone park volcanic area is presented and correlated with the existence of the regional hydrothermal features.

Description: 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.

Description: Geosciences, Vol. 8, Pages 52: A Non-Extensive Statistical Mechanics View on Easter Island Seamounts Volume Distribution Geosciences doi: 10.3390/geosciences8020052 Authors: Filippos Vallianatos In the volcanic complex processes, inherent long-range interactions exist suggesting that Non-Extensive Statistical mechanics could be used to describe fundamental properties of the system. Based on the non-extensive Tsallis entropy a frequency-volume distribution function is suggested for the Easter Island-Salas y Gomez seamounts chain. Our results demonstrate the applicability of fundamental principles of Tsallis entropy to derive the cumulative distribution of seamounts volumes. The work suggests that the processes responsible for hotspot seamount formation are complex and the cumulative frequency-volume distribution of seamounts in the Easter Island/Salas y Gomez Chain (ESC) are well-described by a q-exponential function. The analysis leads to a non-extensive index q = 1.54 in agreement with that presented in other geodynamic or laboratory scale effects.

Description: Geosciences, Vol. 8, Pages 107: A Transient ElectroMagnetic (TEM) Method Survey in North-Central Coast of Crete, Greece: Evidence of Seawater Intrusion Geosciences doi: 10.3390/geosciences8040107 Authors: Despina Kalisperi Maria Kouli Filippos Vallianatos Pantelis Soupios Stephen Kershaw Nikos Lydakis-Simantiris Seawater intrusion into near-shore aquifers is one of the main environmental problems that affect Mediterranean islands. Crete is the biggest and most populated island of Greece, characterized by limited surface waters and strong dependence on groundwater sources as the primary source of natural water supply for extensive agricultural activity and human use. Freshwater demand in Crete has increased notably the last decades. The Geropotamos aquifer is located on the north-central coast of Crete and freshwater management is in a delicate balance with saltwater at coastal areas of the aquifer due to the scarce precipitation and high evaporation as well as the intense over exploitation of the groundwater resources. The geological setting of the study area is considered complex and the local tectonic regime is characterized by two sets of faults orientated NW-SE and NE-SW. Investigation of the aquifer using a survey grid of 1179 Transient ElectroMagnetic soundings (TEM) in 372 sites, has resulted in 1D models, and 2D/3D visualization of geoelectric structures, depicting the zones of salination of groundwater in the aquifer. Geological mapping, hydro-lithological data and geochemical analysis of 24 water samples (22 boreholes and 2 springs) are in agreement with results obtained from TEM soundings, supporting our interpretation that the aquifer is degraded by saline intrusion which likely occurs along fractures in a fault zone, emphasising the critical role of fracture pathways in salination problems of coastal aquifers.