Investigation of the high-frequency attenuation parameter, κ (kappa), from aftershocks of the 2010 Mw 8.8 Maule, Chile earthquake

Abstract

The Bío Bío region of Chile experienced a vigorous aftershock sequence following the 2010 February 27 M w 8.8 Maule earthquake. The immediate aftershock sequence was captured by two temporary seismic deployments: the Quake Catcher Network Rapid Aftershock Mobilization Program (QCN RAMP) and the Incorporated Research Institutions for Seismology CHile Aftershock Mobilization Program (IRIS CHAMP). Here, we use moderate to large aftershocks (M L ≥ 4.0) occurring between 2010 March 1 and June 30 recorded by QCN RAMP and IRIS CHAMP stations to determine the spectral decay parameter, kappa (κ). First, we compare waveforms and κ estimates from the lower-resolution QCN stations to the IRIS CHAMP stations to ensure the QCN data are of sufficient quality. We find that QCN stations provide reasonable estimates of κ in comparison to traditional seismic sensors and provide valuable additional observations of local ground motion variation. Using data from both deployments, we investigate the variation in κ for the region to determine if κ is influenced primarily by local geological structure, path attenuation, or source properties (e.g. magnitude, mechanism and depth). Estimates of κ for the Bío Bío region range from 0.0022 to 0.0704 s with a mean of 0.0295 s and are in good agreement with κ values previously reported for similar tectonic environments. κ correlates with epicentral distance and, to a lesser degree, with source magnitude. We find little to no correlation between the site kappa, κ 0 , and mapped geology, although we were only able to compare the data to a low-resolution map of surficial geology. These results support an increasing number of studies that suggest κ observations can be attributed to a combination of source, path and site properties; additionally, measured κ are often highly scattered making it difficult to separate the contribution from each of these factors. Thus, our results suggest that contributions from the site, path and source should be carefully considered when interpreting κ values.

Low stress drops observed for aftershocks of the 2011 Mw 5.7 Prague, Oklahoma, earthquake

“…An initial κ is measured on individual records based on the Anderson and Hough [] ( κ , AH ) procedure using an automated linear regression routine described in Neighbors et al []. As the horizontal spectra are corrected with the median H / V spectral ratio for the station, we refer to this κ as a residual κ ( κ , AH , H / V ) that potentially reflects source‐dependent variations (i.e., magnitude scaling) [e.g., Purvance and Anderson , ], azimuthal path variations [e.g., Castro et al , ], or near‐source scattering [e.g., Kilb et al , ].…”

“…We require three or more stations to have recorded the event to solve for each of the parameters ( M 0 , f 0 , and κ ). We also impose the criterion that an event has a single M 0 and f 0 for each iteration, but allow κ to vary across station‐event pairs to reflect variations in source, path, and site effects [e.g., Neighbors et al , , ]. Due to the nonlinear appearance of κ in the Anderson and Hough [] adaptation of the Brune model, we linearize the form of equation with respect to κ by taking the natural logarithm:…”