Spectral scaling of the aftershocks of the Tocopilla 2007 earthquake in northern Chile

Abstract

SUMMARY We study the scaling of spectral properties of a set of 68 aftershocks of the 2007 November 14 Tocopilla (M 7.8) earthquake in northern Chile. These are all subduction events with similar reverse faulting focal mechanism that were recorded by a homogenous network of continuously recording strong motion instruments. The seismic moment and the corner frequency are obtained assuming that the aftershocks satisfy an inverse omega‐square spectral decay; radiated energy is computed integrating the square velocity spectrum corrected for attenuation at high frequencies and for the finite bandwidth effect. Using a graphical approach, we test the scaling of seismic spectrum, and the scale invariance of the apparent stress drop with the earthquake size. To test whether the Tocopilla aftershocks scale with a single parameter, we introduce a non‐dimensional number, , that should be constant if earthquakes are self‐similar. For the Tocopilla aftershocks, Cr varies by a factor of 2. More interestingly, Cr for the aftershocks is close to 2, the value that is expected for events that are approximately modelled by a circular crack. Thus, in spite of obvious differences in waveforms, the aftershocks of the Tocopilla earthquake are self‐similar. The main shock is different because its records contain large near‐field waves. Finally, we investigate the scaling of energy release rate, Gc, with the slip. We estimated Gc from our previous estimates of the source parameters, assuming a simple circular crack model. We find that Gc values scale with the slip, and are in good agreement with those found by Abercrombie and Rice for the Northridge aftershocks.

Global rupture parameters for deep and intermediate‐depth earthquakes

“…Our estimates of are on the order of 0.1–1000 MJ/m 2 for the slip range analyzed. The values are on the same order of magnitude of previous fracture energy estimations from seismological data [ Abercrombie and Rice , ; Tinti et al ., ; Lancieri et al ., ; Prieto et al ., ; Viesca and Garagash , ], laboratory experiments [e.g., McGarr et al ., ], and geological observation [e.g., Di Toro et al ., ; Andersen et al ., ].…”

“…Assuming η = 0.46 [ Brune , ] reduces equation to the fracture energy representation of Lancieri et al . [].…”

Taxonomy of : A Review of Definitions and Estimation Approaches Targeted to Applications

“…In source studies, removing the attenuation term is fundamental in order to study self-similarity of the source spectrum; this can be done by inverting for the theoretical Q , using empirical Green's functions (EGFs) or multiple EGFs to remove path and site effects, measuring spectral parameters from the coda, or using κ r to correct for high-frequency attenuation (e.g., Irikura, 1986;Abercrombie, 1995;Mayeda and Walter, 1996;Hough, 1997;Lancieri et al, 2012). In the generation of synthetic ground motion using point-source or finite-fault stochastic or hybrid simulation approaches, κ 0 is applied as a low-pass filter to constrain high frequencies, affecting peak ground motion and spectral shape (Boore, 1986;Beresnev and Atkinson,2005;Mai et al, 2010;Schmedes et al, 2010;Foster et al, 2012), imposing such a constraint is necessary to achieve realistic results at high frequencies.…”

A Study on the Variability of Kappa ( ) in a Borehole: Implications of the Computation Process

“…κ is also necessary to constrain the attenuation, peak ground acceleration (PGA), and spectral shape of synthetic accelerograms generated with stochastic methods in ground-motion simulation studies (e.g., Boore, 2003). It is also computed on an individual event basis (without the regression that gives κ 0 ) to correct records for site effects before these can be used in studying the spectral characteristics of the seismic source (e.g., Margaris and Hatzidimitriou, 2002;Oth et al, 2010;Lancieri et al, 2012). Finally, κ 0 may be used as an indicator of local site conditions by comparing values at specific sites with typical values, especially given empirical correlations of κ 0 with V S30 such as those introduced by Silva et al (1998).…”