Andreas Tzanis | Searcharxiv

arXiv2019

On the Statistical Nature and Dynamics of Seismogenesis in the NW Circum-Pacific Belt: A Study Based on Non-Extensive Statistical Physics

We inquire the statistical nature and dynamics of shallow and deep seismogenesis along major plate margins of the NW Circum-Pacific Belt, by examining whether earthquakes are generated by Poisson processes and are independent (uncorrelated), or by Complex processes and are dependent (correlated). Analysis is based of Non Extensive Statistical Physics and the complete and homogeneous catalogue of the Japan Meteorological Agency for the period 2002-2016.5. Emphasis is given to background seismicity recovered by removing aftershocks with stochastic declustering. Long-term correlation and long-range interaction is mostly weak to moderate in shallow background seismicity. Conversely, deep seismicity is mostly uncorrelated (quasi-Poissonian), particularly in Wadati-Benioff zones. As function of time, shallow background seismicity exhibits persistent weak to moderate correlation; sub-crustal background seismicity is generally quasi-Poissonian but may dynamically transition to moderate-significant in association with temporal clusters of large earthquakes. A universal such effect was observed ahead of the 2011.19 Tohoku mega-earthquake. These results contrast observations along the Pacific-North American transformational plate boundaries of California and Alaska which are generally correlated, suggesting that the geodynamic setting is essential in the development of self-organization and Complexity. Moreover, observations appear consistent with simulations of small-world fault networks in which free boundary conditions at the surface allow for Complexity to develop, while fixed boundary conditions at depth do not.

physics.geo-ph↗

arXiv2014

The Characteristic States of the Magnetotelluric Impedance Tensor: Construction, Analytic Properties and Utility in the Analysis of General Earth Conductivity Distributions

It is shown that the Magnetotelluric (MT) impedance tensor admits an anti-symmetric generalized eigenvalue - eigenstate decomposition consistent with the anti-symmetry of electric and magnetic fields referred to the same coordinate frame: this is achieved by anti-diagonalization through rotation by 2x2 complex operators of the SU(2) rotation group. The eigenstates comprise simple proportional relationships between linearly polarized eigenvalues of the input magnetic and output electric field along the locally resistive and conductive propagation path into the Earth, respectively mediated by the maximum and minimum characteristic values of the tensor (eigen-impedances). It is shown from first principles that the eigen-impedances are expected to be positive real (passive) functions, analytic in the entire lower-half complex frequency plane and with singularities confined on the positive imaginary frequency axis. Insofar as the impedance tensor is generated by isometric transformation of the eigen-impedances, it is also passive. The expected passivity is an effective means of appraising measured tensors for compliance with the basic tenets of the MT method: it can be violated only in the presence of sources in the Earth. In addition to extrinsic effects (e.g. noise), it is demonstrated with examples, that such sources may be secondary large or small scale inductive phenomena generated by realistic conductivity configurations. However, they may not be time-independent effects taking place in a passive induction context, such as steady-state current channelling, galvanic distortion and electric field reversals. In general, to assert whether violation of passivity has occurred, it is necessary to decompose the impedance tensor, refer it to its intrinsic coordinate frame and evaluate the compliance of the eigen-impedances with their expected analytic properties

physics.geo-ph↗