Caroline Holden

Strong shaking in recent New Zealand earthquakes

On 4 September 2010 a surface-rupturing crustal earthquake (Mw 7.1) struck the Canterbury Plains region of New Zealands South Island [Gledhill et al., 2011]. The Canterbury Plains is a region of relatively low seismicity in New Zealand, and the structure that ruptured was a previously unmapped fault (Figure 1a). Fortunately, even though parts of the region experienced liquefaction of unconsolidated sediments and sands—including neighborhoods of the city of Christchurch (population 377,000)—no fatalities occurred. Compared to the average New Zealand aftershock decay model, the aftershock sequence for the 2010 earthquake was relatively underproductive for the first 5 months. But on 22 February 2011 anMw 6.2 aftershock (teleseismic and regional estimates range from (Mw 6.1 to (Mw 6.3 with regional inversions favoring higher values) occurred within kilometers of the center of Christchurch (A. E. Kaiser et al., The (Mw 6.2 Christchurch earthquake of February 2011: Preliminary report, submitted to New Zealand Journal of Geology and Geophysics, 2011). The event increased the productivity of other aftershocks (Figure 1b). This particular aftershock was devastating, generating much more destruction than theMw 7.1 event, including more than 180 fatalities. Recorded peak ground acceleration (PGA) in the city was more than double the acceleration of gravity (g). Many of the poorly consolidated, low-shear-wave-velocity soils liquefied during the shaking. Damage estimates reached approximately US

Earthquakes drive large-scale submarine canyon development and sediment supply to deep-ocean basins

15 billion, making the aftershock New Zealands costliest natural disaster.

The Darfield (Canterbury, New Zealand) Mw 7.1 Earthquake of September 2010: A Preliminary Seismological Report

Coseismic canyon flushing reveals how earthquakes drive canyon development and deep-sea sediment dispersal on active margins. Although the global flux of sediment and carbon from land to the coastal ocean is well known, the volume of material that reaches the deep ocean—the ultimate sink—and the mechanisms by which it is transferred are poorly documented. Using a globally unique data set of repeat seafloor measurements and samples, we show that the moment magnitude (Mw) 7.8 November 2016 Kaikōura earthquake (New Zealand) triggered widespread landslides in a submarine canyon, causing a powerful “canyon flushing” event and turbidity current that traveled >680 km along one of the world’s longest deep-sea channels. These observations provide the first quantification of seafloor landscape change and large-scale sediment transport associated with an earthquake-triggered full canyon flushing event. The calculated interevent time of ~140 years indicates a canyon incision rate of 40 mm year−1, substantially higher than that of most terrestrial rivers, while synchronously transferring large volumes of sediment [850 metric megatons (Mt)] and organic carbon (7 Mt) to the deep ocean. These observations demonstrate that earthquake-triggered canyon flushing is a primary driver of submarine canyon development and material transfer from active continental margins to the deep ocean.