Landslides caused by the Mw7.8 Kaikōura earthquake and the immediate response

Abstract

Tens of thousands of landslides were generated over 10,000 km2 of North Canterbury and Marlborough as a consequence of the 14 November 2016, Mw7.8 Kaikōura Earthquake. The most intense landslide damage was concentrated in 3500 km2 around the areas of fault rupture. Given the sparsely populated area affected by landslides, only a few homes were impacted and there were no recorded deaths due to landslides. Landslides caused major disruption with all road and rail links with Kaikōura being severed. The landslides affecting State Highway 1 (the main road link in the South Island of New Zealand) and the South Island main trunk railway extended from Ward in Marlborough all the way to the south of Oaro in North Canterbury.
 The majority of landslides occurred in two geological and geotechnically distinct materials reflective of the dominant rock types in the affected area. In the Neogene sedimentary rocks (sandstones, limestones and siltstones) of the Hurunui District, North Canterbury and around Cape Campbell in Marlborough, first-time and reactivated rock-slides and rock-block slides were the dominant landslide type. These rocks also tend to have rock material strength values in the range of 5-20 MPa. In the Torlesse ‘basement’ rocks (greywacke sandstones and argillite) of the Kaikōura Ranges, first-time rock and debris avalanches were the dominant landslide type. These rocks tend to have material strength values in the range of 20-50 MPa.
 A feature of this earthquake is the large number (more than 200) of valley blocking landslides it generated. This was partly due to the steep and confined slopes in the area and the widely distributed strong ground shaking. The largest landslide dam has an approximate volume of 12(±2) M m3 and the debris from this travelled about 2.7 km2 downslope where it formed a dam blocking the Hapuku River. The long-term stability of cracked slopes and landslide dams from future strong earthquakes and large rainstorms are an ongoing concern to central and local government agencies responsible for rebuilding homes and infrastructure. A particular concern is the potential for debris floods to affect downstream assets and infrastructure should some of the landslide dams breach catastrophically.
 At least twenty-one faults ruptured to the ground surface or sea floor, with these surface ruptures extending from the Emu Plain in North Canterbury to offshore of Cape Campbell in Marlborough. The mapped landslide distribution reflects the complexity of the earthquake rupture. Landslides are distributed across a broad area of intense ground shaking reflective of the elongate area affected by fault rupture, and are not clustered around the earthquake epicentre. The largest landslides triggered by the earthquake are located either on or adjacent to faults that ruptured to the ground surface. Surface faults may provide a plane of weakness or hydrological discontinuity and adversely oriented surface faults may be indicative of the location of future large landslides. Their location appears to have a strong structural geological control. Initial results from our landslide investigations suggest predictive models relying only on ground-shaking estimates underestimate the number and size of the largest landslides that occurred.

The 2016 Kaikōura Earthquake Revealed by Kinematic Source Inversion and Seismic Wavefield Simulations: Slow Rupture Propagation on a Geometrically Complex Crustal Fault Network

“…The 2016 Kaikōura, New Zealand, earthquake struck the east coast of the northern South Island on 13 November 11:02 (universal time meridian). The damaging earthquake generated large (>10 m) fault displacements, widespread strong ground motion, and a regional tsunami (Hamling et al, ; Kaiser et al, ), triggered over 100,000 landslides in the epicentral region (Dellow et al, ) and large‐scale (>15,000 km 2 ) slow slip events on the Hikurangi subduction interface (Wallace et al, ) and tremor and widespread seismic activation over much of the North Island (Wallace et al, ). The Kaikōura earthquake occurred in a complex tectonic region that marks the transition from the Hikurangi subduction zone to the north and the transpressional Alpine fault‐dominated continental transform in central South Island.…”

Transport infrastructure performance and management in the South Island of New Zealand, during the first 100 days following the 2016 Mw 7.8 “Kaikōura” earthquake

“…Co-seismic landslides ( Figure 5c) and rockfalls ( Figure 5d) closed the road in a number of places, and have presented one of the greatest challenges in repairing the road requiring a substantial amount of time and effort to clear. A more complete summary of landslides and their impacts is presented in Dellow et al [4].…”

“…Initial estimates suggest between 80,000 and 100,000 landslides were triggered by the earthquake, within an area of 10,000 km 2 , with most of the co-seismic landslides located within an area of 3,600 km 2 (Figure 2) [1]. Five landslides were more than 1,000,000 m 3 in size, and 50 large landslide dams were identified [1,4].…”

Geotechnical aspects of the 2016 Kaikōura earthquake on the South Island of New Zealand

“…A drive-through survey was conducted along State Highway 1 (SH1) south of Blenheim. Typical damage (excluding the major impacts of fault rupture and landslides described in Dellow et al 2017) included cracking along the roadside as well as settlements of up to ~30cm in the bridge approaches. Detailed inspections were not generally carried out in this area except near the location of the strong ground motion station at the Ward Fire station (WDFS).…”

“…These aspects are outside the scope of this paper. Landslide and fault ruptures on the South Island are discussed in Dellow et al [2] and Stirling et al [3] respectively. Impacts of liquefaction on the North Island (which includes the CentrePort facility) are presented in Cubrinovski et al [4].…”