DSpace Angular :: Browsing by Author "Venegas Aravena, Patricio"

Browsing by Author "Venegas Aravena, Patricio"

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Analytical relation between b-value and electromagnetic signals in pre-macroscopic failure of rocks: insights into the microdynamics' physics prior to earthquakes
(2023) Venegas Aravena, Patricio; Cordaro, Enrique G.; Pontificia Universidad Católica de Chile. Departamento de Ingeniería Estructural y Geotécnica, Escuela de Ingeniería
Field measurements in subduction regions have revealed the presence of non-seismic pre-earthquake signals such as electromagnetic or acoustic emission, gas liberation, changes in Earth's surface temperature, changes at the ionospheric level, or fluid migration. These signals are commonly associated with impending earthquakes, even though they often rely solely on temporal and spatial correlations in impending earthquake zones without a comprehensive understanding of the underlying lithospheric processes. For example, one criticism is the measurement of increasing electromagnetic signals even in the absence of observable macroscopic stress changes, which challenges the conventional understanding that macroscopic stress changes are the primary energy source for non-seismic pre-earthquake signals. To address this gap, rock experiments provide valuable insights. Recent experiments have shown that rocks can become electrified under constant macroscopic stress changes, accompanied by a decrease in the b-value, indicating multiscale cracking. This suggests the existence of small-scale dynamics that generate electromagnetic signals independently of large-scale stress variations. In that sense, multiscale thermodynamics offers a valuable perspective in describing this multiscale phenomenon. That is why the main goal of this work is to demonstrate that the electromagnetic signals before macroscopic failures are not independent of the cracking generation because the origin of both phenomena is the same. In particular, we present analytical equations that explain the physical connection between multiscale cracking, the generation of electromagnetic signals, and its negative correlation with acoustic emission before the macroscopic failure of rocks even when the macroscopic load is constant. In addition, we also show that the thermodynamic fractal dimension, which corresponds to the global parameter that controls the cracking process, is proportional to the b-value when the large-scale crack generation is considerably larger than the small-scale cracks. Thus, the decreases in the b-value and the increases in the electromagnetic signals indicate that rocks irreversibly prepare to release energy macroscopically. These findings could be related to the dynamics at lithospheric scales before earthquakes.
Fractal clustering as spatial variability of magnetic anomalies measurements for impending earthquakes and the thermodynamic fractal dimension
(2022) Venegas Aravena, Patricio; Cordaro, Enrique Guillermo; Laroze, David
Several studies focusing on the anomalies of one specific parameter (such as magnetic, ionospheric, radon release, temperature, geodetic, etc.) before impending earthquakes are constantly challenged because their results can be regarded as noise, false positives or are not related to earthquakes at all. This rise concerns the viability of studying isolated physical phenomena before earthquakes. Nevertheless, it has recently been shown that all of the complexity of these pre-earthquake anomalies rises because they could share the same origin. Particularly, the evolution and concentration of uniaxial stresses within rock samples have shown the generation of fractal crack clustering before the macroscopic failure. As there are studies which considered that the magnetic anomalies are created by lithospheric cracks in the seismo-electromagnetic theory, it is expected that the crack clustering is a spatial feature of magnetic and non-magnetic anomalies measurements in ground, atmospheric and ionospheric environments. This could imply that the rise of multiparametric anomalies at specific locations and times, increases the reliability of impending earthquake detections. That is why this work develops a general theory of fractal-localization of different anomalies within the lithosphere in the framework of the seismo-electromagnetic theory. In addition, a general description of the fractal dimension in terms of scaling entropy change is obtained. This model could be regarded as the basis of future early warning systems for catastrophic earthquakes.
Large earthquakes are more predictable than smaller ones
(2025) Venegas Aravena, Patricio; Zaccagnino, Davide
Large earthquakes have been viewed as highly chaotic events regardless of their magnitude, making their prediction intrinsically challenging. Here, we develop a mathematical tool to incorporate multiscale physics, capable of describing both deterministic and chaotic systems, to model earthquake rupture. Our findings suggest that the chaotic behavior of seismic dynamics, that is, its sensitivity to initial and boundary conditions, is inversely related to its magnitude. To validate this hypothesis, we performed numerical simulations with heterogeneous fault conditions. Our results indicate that large earthquakes, usually occurring in regions with higher residual energy and lower b-value (i.e., the exponent of the Gutenberg-Richter law), are less susceptible to perturbations. This suggests that a higher variability in earthquake magnitudes (larger b-values) may be indicative of structural complexity of the fault network and heterogeneous stress conditions. To further validate our findings, we compare our theoretical predictions with real seismicity in Southern California; specifically, the relationship between the b-value and the fractal dimension of hypocenters with our model predictions finding good agreement. The statistical similarities observed between the simulated and real earthquakes support the hypothesis that large earthquakes may be less chaotic than smaller ones; hence, more predictable.
Long-term magnetic anomalies and their possible relationship to the latest greater Chilean earthquakes in the context of the seismo-electromagnetic theory
(2021) Cordaro, Enrique Guillermo; Venegas Aravena, Patricio; Laroze, David
Several magnetic measurements and theoretical developments from different research groups have shown certain relationships with worldwide geological processes. Secular variation in geomagnetic cutoff rigidity, magnetic frequencies, or magnetic anomalies have been linked with spatial properties of active convergent tectonic margins or earthquake occurrences during recent years. These include the rise in similar fundamental frequencies in the range of microhertz before the Maule 2010, Tōhoku 2011, and Sumatra–Andaman 2004 earthquakes and the dramatic rise in the cumulative number of magnetic anomalous peaks before several earthquakes such as Nepal 2015 and Mexico (Puebla) 2017. Currently, all of these measurements have been physically explained by the microcrack generation due to uniaxial stress change in rock experiments. The basic physics of these experiments have been used to describe the lithospheric behavior in the context of the seismo-electromagnetic theory. Due to the dramatic increase in experimental evidence, physical mechanisms, and the theoretical framework, this paper analyzes vertical magnetic behavior close to the three latest main earthquakes in Chile: Maule 2010 (Mw 8.8), Iquique 2014 (Mw 8.2), and Illapel 2015 (Mw 8.3). The fast Fourier transform (FFT), wavelet transform, and daily cumulative number of anomalies methods were used during quiet space weather time during 1 year before and after each earthquake in order to filter space influence. The FFT method confirms the rise in the power spectral density in the millihertz range 1 month before each earthquake, which decreases to lower values some months after earthquake occurrence. The cumulative anomaly method exhibited an increase prior to each Chilean earthquake (50–90 d prior to earthquakes) similar to those found for Nepal 2015 and Mexico 2017. The wavelet analyses also show similar properties to FFT analysis. However, the lack of physics-based constraints in the wavelet analysis does not allow conclusions that are as strong as those made by FFT and cumulative methods. By using these results and previous research, it could be stated that these magnetic features could give seismic information about impending events. Additionally, these results could be related to the lithosphere–atmosphere–ionosphere coupling (LAIC effect) and the growth of microcracks and electrification in rocks described by the seismo-electromagnetic theory.
Natural Fractals as Irreversible Disorder: Entropy Approach from Cracks in the Semi Brittle-Ductile Lithosphere and Generalization
(2022) Venegas Aravena, Patricio; Cordaro, Enrique G.; Laroze, David
The seismo-electromagnetic theory describes the growth of fractally distributed cracks within the lithosphere that generate the emission of magnetic anomalies prior to large earthquakes. One of the main physical properties of this theory is their consistency regarding the second law of thermodynamics. That is, the crack generation of the lithosphere corresponds to the manifestation of an irreversible process evolving from one steady state to another. Nevertheless, there is still not a proper thermodynamic description of lithospheric crack generation. That is why this work presents the derivation of the entropy changes generated by the lithospheric cracking. It is found that the growth of the fractal cracks increases the entropy prior impending earthquakes. As fractality is observed across different topics, our results are generalized by using the Onsager’s coefficient for any system characterized by fractal volumes. It is found that the growth of fractality in nature corresponds to an irreversible process.
On the limits of knowledge and the evolution of the physical laws in non-Euclidean universes
(2025) Venegas Aravena, Patricio; Cordaro, Enrique G.
The anthropic principle suggests that the universe's fundamental constants are precisely fine-tuned to allow for life. However, by incorporating a dynamic physical perspective of nature, such as the multiscale thermodynamic principle known as Principium Luxuriæ, it is found that fundamental constants and forces of the universe may evolve over time in a non-Euclidean universe. If the universe has this geometry, it would have profound implications, which are discussed in this paper. For example, that the conditions conducive to life are not static and finely tuned but rather transient, undermining the need for a fine-tuned universe. Given that multiscale thermodynamics requires external forces, it's plausible that the universe's expansion could be linked to the existence of other phenomena such as other universes acting as external forces, each with their own evolving laws of physics. This suggests that life might be a transient and coincidental occurrence across multiple universes, if they exist. Additionally, the ever-evolving physical laws limit our ability to fully comprehend the universe at any given time. As we inevitably overlook certain aspects of reality, physical systems cannot be fully explained by the sum of their parts. Consequently, emergent phenomena like consciousness could not be studied from a self-referential perspective, as there will always be elements beyond our understanding.
Subduction as a Smoothing Machine: How Multiscale Dissipation Relates Precursor Signals to Fault Geometry
(2023) Venegas Aravena, Patricio; Cordaro, Enrique G.
Understanding the process of earthquake preparation is of utmost importance in mitigating the potential damage caused by seismic events. That is why the study of seismic precursors is fundamental. However, the community studying non-seismic precursors relies on measurements, methods, and theories that lack a causal relationship with the earthquakes they claim to predict, generating skepticism among classical seismologists. Nonetheless, in recent years, a group has emerged that seeks to bridge the gap between these communities by applying fundamental laws of physics, such as the application of the second law of thermodynamics in multiscale systems. These systems, characterized by describing irreversible processes, are described by a global parameter called thermodynamic fractal dimension, denoted as D. A decrease in D indicates that the system starts seeking to release excess energy on a macroscopic scale, increasing entropy. It has been found that the decrease in D prior to major earthquakes is related to the increase in the size of microcracks and the emission of electromagnetic signals in localized zones, as well as the decrease in the ratio of large to small earthquakes known as the b-value. However, it is still necessary to elucidate how D, which is also associated with the roughness of surfaces, relates to other rupture parameters such as residual energy, magnitude, or fracture energy. Hence, this work establishes analytical relationships among them. Particularly, it is found that larger magnitude earthquakes with higher residual energy are associated with smoother faults. This indicates that the pre-seismic processes, which give rise to both seismic and non-seismic precursor signals, must also be accompanied by changes in the geometric properties of faults. Therefore, it can be concluded that all types of precursors (seismic or non-seismic), changes in fault smoothness, and the occurrence of earthquakes are different manifestations of the same multiscale dissipative system.
The Multiscale physics behind the Rikitake time, general friction law, and precursory-coseismic energy scaling
(2025) Venegas Aravena, Patricio
Earthquakes, capable of causing widespread devastation, are complex multiscale phenomena. The Gutenberg-Richter law describes the power-law relationship between earthquake frequency and magnitude, while fault roughness, also exhibiting power-law behavior, influences rupture processes. The Rikitake time, an empirical relationship linking earthquake magnitude to the time required for stress accumulation, is affected by these multiscale characteristics. However, the underlying physics of this relationship remains poorly understood. This study demonstrates that the Rikitake time can be derived from the principles of multiscale thermodynamics, where energy dissipation at various scales governs system evolution. This supports the notion that faults evolve into smoother interfaces, capable of storing more stress prior to large earthquakes due to friction increase. Moreover, it also shows that multiscale thermodynamics can accurately describe different friction laws that are commonly employed in seismic modeling. It is also found a scaling between precursor and coseismic activity. This research provides a general friction law that incorporates multiscale thermodynamic principles, offering a deeper understanding of earthquake dynamics.
The Multiscale Principle in Nature (Principium luxuriæ): Linking Multiscale Thermodynamics to Living and Non-Living Complex Systems
(2024) Venegas Aravena, Patricio; Cordaro, Enrique G.
Why do fractals appear in so many domains of science? What is the physical principle that generates them? While it is true that fractals naturally appear in many physical systems, it has so far been impossible to derive them from first physical principles. However, a proposed interpretation could shed light on the inherent principle behind the creation of fractals. This is the multiscale thermodynamic perspective, which states that an increase in external energy could initiate energy transport mechanisms that facilitate the dissipation or release of excess energy at different scales. Within this framework, it is revealed that power law patterns, and to a lesser extent, fractals, can emerge as a geometric manifestation to dissipate energy in response to external forces. In this context, the exponent of these power law patterns (thermodynamic fractal dimension 𝐷 ) serves as an indicator of the balance between entropy production at small and large scales. Thus, when a system is more efficient at releasing excess energy at the microscopic (macroscopic) level, 𝐷 tends to increase (decrease). While this principle, known as Principium luxuriæ, may sound promising for describing both multiscale and complex systems, there is still uncertainty about its true applicability. Thus, this work explores different physical, astrophysical, sociological, and biological systems to attempt to describe and interpret them through the lens of the Principium luxuriæ. The analyzed physical systems correspond to emergent behaviors, chaos theory, and turbulence. To a lesser extent, the cosmic evolution of the universe and geomorphology are examined. Biological systems such as the geometry of human organs, aging, human brain development and cognition, moral evolution, Natural Selection, and biological death are also analyzed. It is found that these systems can be reinterpreted and described through the thermodynamic fractal dimension. Therefore, it is proposed that the physical principle that could be behind the creation of fractals is the Principium luxuriæ, which can be defined as “Systems that interact with each other can trigger responses at multiple scales as a manner to dissipate the excess energy that comes from this interaction”. That is why this framework has the potential to uncover new discoveries in various fields. For example, it is suggested that the reduction in 𝐷 in the universe could generate emergent behavior and the proliferation of complexity in numerous fields or the reinterpretation of Natural Selection.
The role of residual energy in heterogeneous self-arrested seismic ruptures
(2024) Venegas Aravena, Patricio; Crempien de la Carrera, Jorge; Hurtado Sepúlveda, Daniel; Pontificia Universidad Católica de Chile. Escuela de Ingeniería
Understanding the causes of strong ground motion is crucial for mitigating earthquake damage and devastation. This necessitates unraveling the physics of the seismic source, the primary driver of ground shaking variations. However, limited data from real earthquakes compels researchers to develop computational tools for deeper exploration. Crucially, simulations lack empirical constraints due to constant parameters or arbitrary domain limitations, leading to potentially inaccurate representations of real-world earthquakes and erroneous interpretations. This work aims to identify the rupture process characteristics that closely resemble natural earthquakes using empirical tests. The chosen test, the Somerville (or asperity) criteria, stipulates that 20-30% of the ruptured area releases over 50% of the seismic moment. Dynamic simulations revealed two rupture types: self-arrested, which halt before reaching the domain boundaries, and runaway, which traverse the entire domain. Only self-arrested ruptures met the Somerville criteria. Moreover, their parameters exhibited stronger correlation during evolution, suggesting runaway ruptures might not be physically realistic due to seemingly independent parameter evolution. Limited by the difficulty of generating self-arrested ruptures in dynamic simulations, simpler kinematic simulations were also explored. Both approaches revealed that the spatial distribution of residual energy (available energy minus dissipation) acts as the key constraint governing rupture parameters during arrest.

Browsing by Author "Venegas Aravena, Patricio"

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