Investigation of the high-frequency attenuation parameter, κ (kappa), from aftershocks of the 2010 Mw 7.1 Darfield, New Zealand earthquake
Abstract
The 3 September 2010 Mw 7.1 Darfield earthquake was felt over 900 km from the source, with maximum felt-intensities estimated to be Modified Mercalli Intensity (MMI) 9 and measured near-field accelerations in excess of 1 g. The mainshock damaged or destroyed over 100,000 buildings and spatially variable shaking and ground damage were observed throughout the city of Christchurch. To record the aftershock sequence, a network of over 180 low-cost, 14-bit accelerometers was deployed in local residences as part of the Quake-Catcher Network Rapid Aftershock Mobilization Project (RAMP). With a large number of sensors covering a city area of ~300 km2, the RAMP collected vast amounts of data and at dense spatial scales. Recent comparison of the time series and response spectra of the 14-bit QCN sensors to the strong motion 24-bit New Zealand GeoNet sensors show similar quality (Cochran et al., 2011). Initial analyses of the data show that aftershocks of magnitude >M4.5 within 30 km of the main network deployment in Christchurch were well recorded by QCN sensors. Utilizing the dense coverage, we investigate local site amplification and shallow site attenuation by analyzing the spectral decay parameter, kappa (κ). We follow the routine outlined in Douglas et al. (2010), and modified from Anderson and Hough (1984), whereby a 5-sec S-wave window is used to calculate the Fourier spectra and κ for each station. The exponential decay in high-frequency energy is proposed to primarily reflect source-station attenuation and local site conditions, but may be partially attributed to the source. First, we will compare data and κ estimates from the low-cost QCN network to the GeoNet network. Then, we will investigate the variation in κ recorded by the QCN and GeoNet stations to determine if κ is influenced primarily by attenuation, local geologic structure, or source properties. Initial κ estimates by two researchers on a subset of the aftershock data range between 0.02 and 0.1 sec. We will correlate these κ values to local site geology and basin velocity model. Preliminary results suggest κ increases as the source-receiver distance increases; however, not all stations display a clear correlation between κ and distance. Future work will include an investigation of κ with source magnitude and consideration of site attenuation in relation to the shallow water table, which has implications for liquefaction hazard.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.S51A2394N
- Keywords:
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- 7200 SEISMOLOGY;
- 7203 SEISMOLOGY / Body waves;
- 7212 SEISMOLOGY / Earthquake ground motions and engineering seismology;
- 7294 SEISMOLOGY / Seismic instruments and networks