Stochastic ground motion modelling of the largestM_w5.9 + aftershocks of the Canterbury 2010–2011 earthquake sequence

Abstract

The 2010-2011 Canterbury earthquake sequence includes the 22 February 2011 Christchurch aftershock (M w 6.2), the June 2011 M w 6.0 aftershock and the December 2011 magnitude (M L ) 5.8 and 6.0 aftershocks. These events caused widespread liquefaction, landslides and heavy building damage and collapse. To better understand the contributions of the source, path and site effects to these damaging ground motions, we compute broadband synthetic seismograms for the largest M w 5.9 + aftershocks of the 2010-2011 Canterbury earthquake sequence at near-source sites. We employ a stochastic approach to compute the seismograms that is not only controlled by detailed source models but also by regional parameters derived using spectral inversion of the extensive Canterbury strong-motion dataset. Our results show that using appropriate stress drop value and site-specific amplification functions helps greatly to reproduce key engineering parameters such as peak ground accelerations (PGAs) and response spectra. ARTICLE HISTORY

Rockfall Activity Rates Before, During and After the 2010/2011 Canterbury Earthquake Sequence

“…Holden and Kaiser (2016) used detailed source models combined with calibrated, region‐specific parameters to develop synthetic seismograms. Comparing the synthetic seismograms (corrected for site effects) with ground motion recordings for several CES events in the greater Canterbury region indicated that they capture key aspects of the ground motion, including PGA and spectral content (Holden & Kaiser, 2016). Given the generally high shear wave velocity of the basaltic materials at the study sites (Massey et al., 2017), we adopted free‐field ground motion parameters assuming rock free‐field site conditions (i.e., without site or topographic effects) to estimate ground shaking in the rock slopes.…”

“…Given the generally high shear wave velocity of the basaltic materials at the study sites (Massey et al., 2017), we adopted free‐field ground motion parameters assuming rock free‐field site conditions (i.e., without site or topographic effects) to estimate ground shaking in the rock slopes. Holden and Kaiser (2016) simulated key earthquakes from the CES, including events of 22 February, 16 April, 13 June, and 23 December 2011 and a later moderate‐intensity event on 14 February 2016. Debris was observed to have fallen from the sites' large slopes during each of these earthquakes.…”

“…The CES commenced on 4 September 2010 with the M W 7.1 Darfield earthquake, centered 45 km west of the Port Hills (Figure 2), which caused damaging levels of ground shaking (the maximum recorded horizontal peak ground accelerations (PGA) of 1.25 g) and liquefaction in Christchurch but relatively few rockfalls in the Port Hills (Massey et al., 2014). The damage and loss inflicted by the Darfield earthquake were eclipsed by the M W 6.2 Christchurch earthquake of 22 February 2011, which occurred directly under the Port Hills, generating extreme near‐field ground motions with PGAs exceeding 2.0 g (Holden & Kaiser, 2016). Five other major earthquakes in the sequence caused notable rockfalls in the Port Hills; these were the M W 5.0 on the 16 April, M W 6.0 on the 13 June, M W 5.8 and M W 5.9 on 23 December 2011, and the M W 5.7 on the 14 February 2016 “Valentine's day” (Figure 2).…”

“…(c) Location of the large (numbered MC1 to MC69) and major (named by their locations) rock slopes analyzed in this study. The background hillshade model is derived from the 2011 airborne lidar survey and the contours are horizontal peak ground acceleration (m/s 2 ) for the 22 February 2011 earthquake, from Holden and Kaiser (2016).…”

Introduction toNZJGGspecial issue in honour of John Beavan's scientific contributions

“…In addition to new insights into the evolution of the complex earthquake sequence, John's work underpins ongoing efforts to forecast what might be expected to occur in future earthquakes in that area as the Canterbury earthquake sequence evolves. Holden & Kaiser (2016) undertake stochastic ground motion modelling of many of the largest aftershocks in the Canterbury sequence. To help constrain these models, they use detailed source information underpinned by John's geodetic work on the Canterbury sequence.…”