Abstract - The recent earthquakes in Christchurch, New Zealand, show that active faults, capable of generating large-magnitude earthquakes, can be hidden beneath the Earth’s surface. Here we combine near-surface paleoseismic data with deep (<5 km) onshore seismic-reflection lines to identify sub-resolution active faults and to explore the relations between fault growth over short (<27kyr) and long (>1Ma) timescales in the Taranaki Rift, New Zealand. Displacement rates vary temporally on individual faults by in excess of an order of magnitude over timescales of thousands to millions of years. These changes are attributed to fault interactions rather than to changes in regional strain rates. During the Holocene fault displacement rates were both faster (~50%) and slower (~50%) than their million-year averages. The short-term fault data are incomplete and biased towards the faults that have moved fastest during the Holocene. The integration of different timescale datasets provides a basis for identifying active faults not observed at the ground surface, estimating maximum fault-rupture lengths, inferring maximum short-term displacement rates and improving earthquake hazard assessment.
Abstract of talk given to:
Earthquake Geology and Archaeology: Science, Society and Critical facilities, 2nd INQUA-IGCP 567 International Workshop, Corinth, September 2011.