Characteristics of strong ground motion from the sequence of New Zealand earthquake: 2010, M_W7.0, main shock and 2011, M_W6.1, aftershock

The New Zealand earthquake of September 3, 2010, M_W7.0 occurred in the South Island of New Zealand with depth of 10 km. The February 21, 2011, South Island, New Zealand, earthquake occurred as a part of the aftershock sequence of the 2010 M_W7.0 mainshock (Darfield earthquake of 2010). This largest M_W 6.1 aftershock (Christchurch earthquake of 2011) is significantly closer to the main population center of Christchurch, New Zealand, than is the September 2010 mainshock, however, violent M_W6.1 aftershock was caused by movement along a fault that does not appear to have broken the surface. Considering the amplification of shallow velocity structure (v_S30), we compared the observed horizontal PGAs (peak ground acceleration) and PGVs (peak ground velocity) of both the mainshock and aftershock with NGA (next generation attenuation), respectively. The near-field strong ground motion of the aftershock is higher than the observations of mainshock. For the New Zealand sequence, two special finite fault models, dynamical composite source model (DCSM) and scholastic finite-fault model (SFFM), are constructed for Darfield and Christchurch earthquake of 2010 and 2011, respectively. For comparison purpose, we also conducted the broadband ground motion predictions for the station of Heathcote Valley Primary School (HVSC) and Greendale station (GDLC), which are the nearest stations from the epicenter of mainshock and aftershock, respectively. We compared the advantage and limitation of the DCSM and SFFM, respectively, for developing appropriate technique to generate the shaking map in real time and for earthquake early warning.