Annual Meeting - SCEC.org

Poster Abstracts
earthquake in February, which caused the loss of more than 180 lives, and the June Mw 6.0 earthquake; both of these major
aftershocks occurred directly under the city of Christchurch. The sequence of events is occurring in what is a moderate hazard
area in the New Zealand National Seismic Hazard Model (NSHM). With significant rebuilding effort required due to the
damage from the sequence, a reinvestigation of the NSHM was requested in terms of the NZ building code, and in terms of
probabilities of future liquefaction. Initially a very tight time frame (on the order of weeks) was given for the update to the
model. On this short schedule, modifications were made to both the ground motion prediction equation and to the source
models.
All larger earthquakes in the sequence to date have had large apparent stresses based on energy magnitudes; we have scaled
the predicted ground-motions to account for this. Additionally we have developed a composite source model of differing
clustering scales that consists of four sub-models: 1) the NSHM fault model including conditional probabilities of rupture on
key faults; 2) a short-term clustering model to account for immediate aftershock clustering; 3) a medium-to-long-term
clustering model to account for more distant and clustering on a longer time scale; and 4) a smoothed seismicity model based
on a non-declustered catalog to allow for the expectation of increased seismicity in the coming decades. This preliminary work
has resulted in an increase in the official building code requirements by about 1/3. The work is currently being re-evaluated
with additional alternatives and uncertainties being considered. Due to the nature of the sequence, and the fact that the hazard
is dominated by events with M