Analysis of Time Dynamical Features in Intraplate Versus Interplate Seismicity: The Case Study of Iquique Area (Chile)
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Pure and Applied Geophysics
Analysis of Time Dynamical Features in Intraplate Versus Interplate Seismicity: The Case Study of Iquique Area (Chile) LUCIANO TELESCA,1 DENISSE PASTE´N,2 Abstract—The intraplate and interplate seismic catalogues of Iquique (Chile) area were investigated by using seismological (b value of the Gutenberg–Richter law), fractal (Allan Factor and detrended fluctuation analysis) and topological (Horizontal Visibility Graph) methods. The two catalogues show different stress state indicated by the different b value, larger for the intraplate seismicity. The interplate seismicity shows significant time-clustering behavior of the earthquake occurrence times at large time scales, while the time distribution of the intraplate earthquakes seems to be featured by random fluctuations without any significant sign of time-clustering. Different role seems to be played by aftershocks in the two investigated seismic zones, revealed by the different time distribution of the aftershock-depleted catalogue of the intraplate zone, which remains Poissonian for most of the time scales, and the interplate zone that still keeps its clustering phenomenon but at higher timescales, thus shortening its clustering time scale range. Furthermore, the interevent times of the interplate catalogue are characterized by persistent dynamics even after removing the aftershocks, while uncorrelated fluctuations characterize the behavior of interevent intervals of the whole as well as aftershock-depleted intraplate catalogue. Additionally, the magnitudes of both catalogues are characterized by time-reversibility before and after the aftershock removal; while the interevent times of intraplate catalogue change their status from time-irreversibility to time-reversibility after removing the aftershocks. The obtained results seem to evidence a different role played by the aftershocks in the intraplate and interplate zones, that needs to be further explored. Keywords: Interplate seismicity, intraplate seismicity, earthquake, time series analysis.
1. Introduction The northern zone of Chile was struck by four major seismic events in the past centuries: in 1543,
1
Institute of Methodologies for Environmental Analysis, National Research Council, 85050 Tito, PZ, Italy. 2 Departamento de Fı´sica, Facultad de Ciencias, Universidad de Chile, Santiago, Chile. E-mail: [email protected]
and VI´CTOR MUN˜OZ2
1615, 1768 and 1877 (Ruiz and Madariaga 2018). The magnitude proposed for the last megathrust occurred in 1877 in the central Andes subduction zone is Mw= 8.7 (Comte and Pardo 1991) and affected Pisagua and Iquique (Vidal Gormaz 1877; Montessus de Ballore 1911–1916). It has still been debating if all these major events were interplate or intraplate intermediate depth (Ruiz and Madariaga 2018). On the other hand, after the 1877 megathrust (that also triggered a large tsunami), earthquakes with magnitudes greater than Mw 7.0 occurred in the northern zone of Chile, such as Tocopilla earthquake in 1967 (Mw 7.4) and 2007 (Mw 7.8), Tarap
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