Hamed O. Ghaffari

Complex aperture networks

A complex network approach is proposed for studying the shear behavior of a rough rock joint. Similarities between aperture profiles are established, and a functional complex network—in each shear displacement—is constructed in two directions: parallel and perpendicular to the shear direction. We find that the growth of the clustering coefficient and that of the number of edges are approximately scaled with the development of shear strength and hydraulic conductivity, which could possibly be utilized to estimate and formulate a friction law and the evolution of shear distribution over asperities. Moreover, the frictional interface is mapped in the global–local parameter space of the corresponding functional friction network, showing the evolution path and, eventually, the residual stage. Furthermore, we show that with respect to shear direction, parallel aperture patches are more adaptable to environmental stimuli than perpendicular profiles. We characterize the pure-contact profiles using the same approach. Unlike the first case, the later networks show a growing trend while in the residual stage; a saturation of links is encoded in contact networks.

Analysis of aperture evolution in a rock joint using a complex network approach

A complex network approach to characterize a rough fracture is developed. Some metric spaces (similarity measurements) between apertures profiles are set up, and a general evolutionary network in two directions (parallel and perpendicular to the shear direction) is constructed. Evaluation of the network shows the connectivity degree (distribution of edges) of network, after a transition step, falls into a stable state that coincides with a Gaussian distribution. Based on this event, and real observations of the complex network changes, an algorithm is proposed in which evolution of a network is accomplished using preferential and random attachments of edges, while the number of nodes is fixed. Evolution of clustering coefficients and number of edges display similar patterns observed in shear stress, hydraulic conductivity and dilation changes, which can be engaged to estimate shear strength distribution of asperities. Distinguishing the contact profiles and their changes, despite the former case, disclosed growing networks, which can shed light on the details of changes within intra-topology of profiles.

Application of soft granulation theory to permeability analysis

This paper describes application of information granulation theory, on the design of rock engineering flowcharts. Firstly, an overall flowchart, based on information granulation theory has been highlighted. Information granulation theory, in crisp (non-fuzzy) or fuzzy format, can take into account engineering experiences (especially in fuzzy shape-incomplete information or superfluous), or engineering judgments, in each step of designing procedure, while the suitable instruments modeling are employed. In this manner and to extension of soft modeling instruments, using three combinations of Self Organizing Map (SOM), Neuro-Fuzzy Inference System (NFIS), and Rough Set Theory (RST) crisp and fuzzy granules, from monitored data sets are obtained. The main underlined core of our algorithms are balancing of crisp(rough or non-fuzzy) granules and sub fuzzy granules, within non fuzzy information (initial granulation) upon the open-close iterations. Using different criteria on balancing best granules (information pockets), are obtained. Validations of our proposed methods, on the data set of in-situ permeability in rock masses in Shivashan dam, Iran have been highlighted.

Complex networks and waveforms from acoustic emissions in laboratory earthquakes

We report some new applications of functional complex networks on acoustic emission waveforms from frictional interfaces. Our results show that laboratory faults undergo a sequence of generic phases as well as strengthening, weakening or fast-slip and slow-slip leading to healing. Also, using functional networks, we extend the dissipated energy due to acoustic emission signals in terms of short-term and long-term features of events. We show that the transition from regular to slow ruptures can have an additional production from the critical rupture class similar to the direct observations of this phenomenon in the transparent samples. Furthermore, we demonstrate detailed sub-micron evolution of the interface due to the short-term evolution of rupture tip, which is represented by phenomenological description of the modularity rates. In addition, we found nucleation phase of each single event for most amplified events follows a nearly constant time scale, corresponding to initial strengthening of interfaces.

Observation of the Kibble-Zurek Mechanism in Microscopic Acoustic Crackling Noises.

Characterizing the fast evolution of microstructural defects is key to understanding “crackling” phenomena during the deformation of solid materials. For example, it has been proposed using atomistic simulations of crack propagation in elastic materials that the formation of a nonlinear hyperelastic or plastic zone around moving crack tips controls crack velocity. To date, progress in understanding the physics of this critical zone has been limited due to the lack of data describing the complex physical processes that operate near microscopic crack tips. We show, by analyzing many acoustic emission events during rock deformation experiments, that the signature of this nonlinear zone maps directly to crackling noises. In particular, we characterize a weakening zone that forms near the moving crack tips using functional networks, and we determine the scaling law between the formation of damages (defects) and the traversal rate across the critical point of transition. Moreover, we show that the correlation length near the transition remains effectively frozen. This is the main underlying hypothesis behind the Kibble-Zurek mechanism (KZM) and the obtained power-law scaling verifies the main prediction of KZM.

Microscopic evolution of laboratory volcanic hybrid earthquakes

Characterizing the interaction between water and microscopic defects is one of the long-standing challenges in understanding a broad range of cracking processes. Different physical aspects of microscopic events, driven or influenced by water, have been extensively discussed in numerical calculations but have not been accessible in micro-scale experiments. Through the analysis of the emitted ultrasound excitations during the evolution of individual dynamic microcracking events, we show that the onset of a secondary instability – known as hybrid events in coda part of the recorded waveforms occurs during the fast equilibration phase of the system, which leads to (local) sudden increase of pore water pressure in the process zone. As a result of this squeezing-like process, a secondary induced instability akin to the long period event occurs. This mechanism is consistent with observations of hybrid earthquakes found in volcanic settings. Introduction Critical challenges remain in the study of dynamic interactions between in-situ liquids and moving defects (fractures and micro-defects such as dislocations and other topological defects) and in triggering the nucleation and/or movement of defects [1-3]. Such interactions might emit broadband phononic excitations which mirror the complexity of the source dynamics from which they are derived as well as the environment in which the sources propagate. An important manifestation of these excitations in the geosciences is the study of the seismic response of rocks in the presence of pore fluids. Seismological observations of earthquakes associated with active volcanism have exposed a wide variety of physical phenomena that are manifested as seismic activity [4-5]. In particular, Low-Frequency (LF) earthquakes have been associated with so-called slow slip events in subduction zones and as a consequence of fluid movement during volcanic unrest [6-7]. LF events also known as longperiod (i.e., dominant low frequency component in the energy spectrum) and very long-period events, are observed on all types of active volcanoes, often in swarms preceding eruption. Such LF events differ from Volcanotectonic seismicity (VT events) in terms of both their characteristic frequency range and extended harmonic (coda) signature [4,6-7] and have been postulated to be generated from fluid flow and resonance in fractures and conduits within the edifice. Finally, the third type of seismicity shows features of both HF seismicity and also LF harmonic tremor. Known as hybrid events, this type of seismicity is characterized by a high frequency, VT-like onset and a LF-like coda, suggesting that hybrid generation is stimulated by stress regimes leading to both rock failure, and also where fluids are present in order to generate LF and tremor [4,5-8]. Laboratory manifestations of LF, VT, and hybrid seismicity are accessible by recording the Acoustic (phonon) Emissions (AEs) – the laboratory analogue of seismic events in Earth’s crust and a commonly-used proxy in laboratory rock physics [9]. The high resolution andCharacterizing the interaction between fluids and microscopic defects is one of the long-standing challenges in understanding a broad range of cracking processes, in part because they are so difficult to study experimentally. We address this issue by reexamining records of emitted acoustic phonon events during rock mechanics experiments under wet and dry conditions. The frequency spectrum of these events provides direct information regarding the state of the system. Such events are typically subdivided into high frequency (HF) and low frequency (LF) events, whereas intermediate “Hybrid” events, have HF onsets followed by LF ringing. At a larger scale in volcanic terranes, hybrid events are used empirically to predict eruptions, but their ambiguous physical origin limits their diagnostic use. By studying acoustic phonon emissions from individual microcracking events we show that the onset of a secondary instability–related to the transition from HF to LF–occurs during the fast equilibration phase of the system, leading to sudden increase of fluid pressure in the process zone. As a result of this squeezing process, a secondary instability akin to the LF event occurs. This mechanism is consistent with observations of hybrid earthquakes.

Advances in Time Series Analysis and Its Applications

1School of Electrical Engineering and Automation, Tianjin University, Tianjin 300072, China 2School of Mathematics and Statistics, University of Western Australia, Crawley, WA 6009, Australia 3Mineral Resources, CSIRO, Kensington, WA 6151, Australia 4Potsdam Institute for Climate Impact Research, 14473 Potsdam, Germany 5Tianjin University of Science and Technology, Tianjin 300222, China 6Department of Civil Engineering, University of Toronto, Toronto, ON, Canada M5S 3E3

Modeling of Social Transitions Using Intelligent Systems

In this study, we reproduce two new hybrid intelligent systems, involve three prominent intelligent computing and approximate reasoning methods: Self Organizing feature Map (SOM), Neuro-Fuzzy Inference System and Rough Set Theory (RST), called SONFIS and SORST. We show how our algorithms can be construed as a linkage of government-society (or any other similar systems) interactions, where government catches various states of behaviors: ldquosolid (absolute) or flexiblerdquo. So, transition of society, by changing of connectivity parameters (noise) from order to disorder is inferred.