Do great earthquakes occur on the Alpine Fault in central South Island, New Zealand?

Abstract

Geological observations require that episodic slip on the Alpine fault averages to a long-term displacement rate of 2-3 cm/yr. Patterns of seismicity and geodetic strain suggest the fault is locked above a depth of 6-12 km and will probably fail during an earthquake. High pore-fluid pressures in the deeper fault zone are inferred from low seismic P-wave velocity and high electrical conductivity in central South Island, and may limit the seismogenic zone east of the Alpine fault to depths as shallow as 6 km. A simplified dynamic rupture model suggests an episode of aseismic slip at depth may not inhibit later propagation of a fully developed earthquake rupture. Although it is difficult to resolve surface displacement during an ancient earthquake from displacements that occurred in the months and years that immediately surround the event, sufficient data exist to evaluate the extent of the last three Alpine fault ruptures: the 1717 AD event is inferred to have ruptured a 300-500 km length of fault; the 1620 AD event ruptured 200-300 km; and the 1430 AD event ruptured 350-600 km. The geologically estimated moment magnitudes are 7.9 ± 0.3, 7.6 ± 0.3, and 7.9 ± 0.4, respectively. We conclude that large earthquakes (M w >7) on the Alpine fault will almost certainly occur in future, and it is realistic to expect some great earthquakes (M w ≥8).

Review Article: Potential geomorphic consequences of a future great (<i>M</i><sub>w</sub> = 8.0+) Alpine Fault earthquake, South Island, New Zealand

“…This displacement is predominantly coseismic as little to no aseismic slip has been detected on the central and northern sections of the Alpine Fault (Beavan et al, 1999). Individual earthquake ruptures are estimated to result in 8-9 m dextral displacement with 2-3 m vertical displacement suggesting magnitudes of M w ∼ 8 (Adams, 1980b;Hull and Berryman, 1986;Cooper and Norris, 1990;Sutherland and Norris, 1995;Sutherland et al, 2007). Rockfall deposits and other off-fault evidence similarly suggest that such events have M w ∼ 8 (Adams, 1980b;Sutherland, 1994;Beavan et al, 1999;Leitner et al, 2001), though recent work indicates a slightly higher magnitude may be possible (De Pascale and Langridge, 2012).…”

Shear behavior of DFDP-1 borehole samples from the Alpine Fault, New Zealand, under a wide range of experimental conditions

“…Major earthquakes (M w > 7.0) are inferred to have occurred over the past 8,000 years with a recurrence of ~260-400 years (Bull 1996;Berryman et al 2012). No large earthquake has occurred in the past 300 years, suggesting that a hazardous, large-magnitude earthquake on the Alpine Fault may be imminent (Sutherland et al 2007(Sutherland et al , 2012Townend et al 2009Townend et al , 2013. Geodetic measurements along the central segment of the fault indicate that the Alpine Fault is fully locked at depths of 5-8 km and partially locked up to ~18 km, and is loaded from below by the lower crust at a rate representing 50-70 % of the plate convergence rate (Beavan et al 1999Norris and Cooper 2000;Wallace et al 2007).…”

“…The Deep Fault Drilling Project (DFDP) was initiated in 2011 to investigate the Alpine Fault in New Zealand via coring, sampling, and wireline logging (Townend et al 2009). The Alpine Fault is a highly appropriate target for study due to its status as a major plate boundary fault capable of large (M w ~ 8) earthquakes, as well as the inference that it may be nearing the end of its earthquake cycle (Sutherland et al 2007;De Pascale and Langridge 2012).…”

Liquefaction Features Produced by the 2010–2011 Canterbury Earthquake Sequence in Southwest Christchurch, New Zealand, and Preliminary Assessment of Paleoliquefaction Features

“…1). The Pacific and Australian plates are converging obliquely at ∼35-40 mm=year , with up to 80% of the total rate being accommodated by the strike-slip/reverse Alpine fault (e.g., Beavan et al, 2007;Sutherland et al, 2007;Wallace et al, 2007) and, farther north, by the Marlborough strike-slip fault system (Hope, Clarence, Awatere, and Wairau faults; Langridge et al 2003;Fig. 1b).…”