Source characteristics, regional attenuation and site influences on ground motion during the Canterbury earthquake sequence, New Zealand

The Canterbury earthquake sequence beginning with the 2010 Mw 7.1 Darfield earthquake is one of the most well-recorded crustal earthquake sequences in a low-strain-rate region worldwide. Understanding the physical influences on ground motion during this sequence is crucial in assessing the ongoing seismic hazard and can also provide valuable insights for analagous regions worldwide. We use a generalized spectral inversion approach to separate and quantify source, path and site characteristics for Canterbury. Results were obtained utilizing a subset of the rich GeoNet accelerogram database consisting of > 200 earthquakes (Mw 3 - 7.2) and > 2300 source-station paths. Source characteristics derived for the Canterbury sequence indicate that earthquakes are associated with higher than average stress drops (median value ~5 MPa) and close to self-similar behaviour. Furthermore, higher stress drop values tend to be observed at the edges of major fault ruptures. Non-parametric attenuation functions derived from the inversion illustrate regional characteristics, including strong high-frequency attenuation and the influence of regional mid-crustal structure. Linear site response factors spanning a range of rock and soil conditions show that local amplification effects also played a significant role in the variations in ground motion observed within Christchurch city, although nonlinear/liquefaction effects dominated at deep soil sites during the strongest shaking.