Earthquake Rupture of Multiple Faults and Implications for Seismic Hazard in New Zealand

Session: Cryptic Faults: Assessing Seismic Hazard on Slow Slipping, Blind or Distributed Fault Systems
Type: Oral
Date: 4/28/2020
Time: 05:00 PM
Room: 240
Description: 

The 2016 Kaikōura Earthquake ruptured at least 17 separate faults and reminded the global seismology community of the possibility of large earthquakes that rupture multiple faults. It is clear from the Kaikōura event that such ruptures can be complex, however, questions remain about how common multi-fault ruptures are and whether we should expect similarly complex ruptures in the future? To address these questions, we have analysed eight moderate to great historical earthquakes (Mw 6.5-8.2) that ruptured the ground surface in New Zealand post 1840. Of these earthquakes five ruptured at least three faults (Wairarapa 1855, Hawkes Bay 1931, Edgecumbe 1987, Darfield 2010 and Kaikōura 2016) and show a strong age-dependence with all but one post-dating 1930. The importance of these multi-fault events over the last ~90 years may reflect the improving quality and quantity of the available data rather than a change in the style of surface-ruptures. Independent of these sampling biases it is clear that rupture of multiple faults during individual earthquakes has been common in New Zealand during the last ~180 years. Multi-fault ruptures occur for a range of fault types, with variable fault displacement rates and in different tectonic settings. In some cases, co-rupture of the Hikurangi subduction thrust may have facilitated (and linked) rupture of more than one fault (Wairarapa 1855, Hawkes Bay 1931 and Kaikōura 2016), whereas other events were far removed from subduction (Edgecumbe and Darfield), and the subduction-thrust cannot have directly contributed to the observed complex rupture geometries. Consistent with the subduction hypothesis we suggest that fault intersections promote multi-fault ruptures, increasing both rupture lengths and earthquake magnitudes. Future multi-fault ruptures can be expected in parts of New Zealand where active faults are hard-linked or closely spaced (e.g., 5 km).

Presenting Author: Andy Nicol

Authors