Preseismic electromagnetic signals in terms of complexity

Abstract

There is a recent thesis in the literature that an important organization of a physical system precedes a catastrophic event. In this context, one can search for signatures that imply the transition from a normal state to a main catastrophic event (e.g., earthquake). Experimental techniques are thus useful in corroborating theories from observed data. For example, recent results indicate that preseismic electromagnetic time series contain information characteristic of an ensuing earthquake event. Hereby, we attempt to demonstrate that an easily computable complexity measure, such as T-complexity or approximate entropy, gives evidence of state changes leading to the point of global instability. The appearance of a precatastrophic state is characterized by significant lower complexity in terms of T-complexity and approximate entropy. The present study confirms the conclusions of previous works based on an independent linear fractal spectral analysis. This convergence between nonlinear and linear analysis provides a more reliable detection concerning the emergence of the last phase of the earthquake preparation process. More precisely, we claim that our results suggest an important principle: significant complexity decrease and accession of persistency in electromagnetic (EM) time series can be confirmed at the tail of the preseismic EM emission, which could be used as diagnostic tools for the Earth's impending crust failure. Direct laboratory and field experimental data as well as theoretical arguments support the conclusions of the present analysis.

Tsallis and Levy statistics in the preparation of an earthquake

“…of the Athens EQ is consistent with other precursors that are imposed by data from other disciplines such as: (i) seismology in terms of cumulative Benioff "strain", (ii) infrared remote sensing, (iii) synthetic aperture radars interferometry, and (iv) ultra low-frequency seismic electric signals (SES) (Karamanos et al, 2006). Notice, these measurements could indicate the possible position of the epicenter and the magnitude of the impending EQ, while the analysis of MHz-KHz EM emissions particularly point to way of estimating the time to global failure.…”

“…However, the collection of a volume of appropriate EM data for statistical purposes requires some decades of years at least. Indeed, due to their absorption these signals are associated with surface EQs of magnitude 6 or larger that occur on land or closed to coastline (Karamanos et al, 2006). However, such EQs occur rarely in Greece, so that a statistical evaluation stemming from the EM data is practically impossible (Karamanos et al, 2006).…”

“…Indeed, due to their absorption these signals are associated with surface EQs of magnitude 6 or larger that occur on land or closed to coastline (Karamanos et al, 2006). However, such EQs occur rarely in Greece, so that a statistical evaluation stemming from the EM data is practically impossible (Karamanos et al, 2006). This fact obliges us to attempt a multidisciplinary evaluation of seismogenic origin of the detected candidate precursory EM emissions.…”

“…These precursors are detectable both at a laboratory and a geophysical scale. It is by now recognized that the pre-fracture kHz-MHz EM time series contain valuable information about the fracture EQ preparation process (Kapiris et al, 2004;Karamanos et al, 2005Karamanos et al, , 2006. Being non-destructive, monitoring techniques based on these fracture-induced fields are a basis for a fundamental understanding of fracture mechanism and for development consecutive models of rock/focal area behavior.…”

“…An antipersistent behavior (Contoyiannis et al, 2005;Karamanos et al, 2006) implies a set of fluctuations tending to induce a stability within the system, i.e., a nonlinear negative feedback in the underlying fracto-EM mechanism, which "kicks" the opening cracks away from extremes. The observed antipersistency, which is rooted in the heterogeneity of the system, enables the fracture in highly heterogeneous systems to be described via an analogy with thermal continuous phase transitions.…”