Litchfield, N.J.; Smith, W.D.; Berryman, K.R. 2009 Return times for high levels of ground-shaking (>/- MM7) in the Waipaoa and Waitaki River catchments. Lower Hutt, N.Z.: GNS Science. GNS Science report 2009/03 87 p.
Abstract: Moderate to large earthquakes can have a significant impact on sedimentary systems, by causing widespread ground shaking, which can result in landsliding and ultimately, delivery of sediment to river channels. Thus, a first step to quantifying impacts on a sedimentary system is to identify how often and where, moderate to large earthquakes occur within the major source areas of the sedimentary systems. We undertake this for two contrasting tectonically active sedimentary systems in New Zealand, the Waipaoa sedimentary system in the North Island East Coast (NIEC) and the Waitaki sedimentary system in the Central South Island (CSI). In particular, we calculate return times for high levels of strong ground shaking (>/- 7 Modified Mercalli Intensity, MMI) in the major source areas of these sedimentary systems, the Waipaoa River catchment and the Waitaki River catchment. We calculate MMI (rather than any other measure of strong ground shaking such as peak ground accelerations, PGA, or velocities, PGV, or duration) because studies of earthquake-triggered landslides have shown that landslide damage generally scales with MMI. To illustrate this we also review moderate to large historical earthquakes and their landscape impacts (e.g., landsliding) in and around the NIEC and CSI study areas. (auth/DG)