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Following the November 14 2016 Mw7.8 Kaikoura earthquake, field expeditions were undertaken using Unmanned Aerial Vehicles (UAVs) to map 25 sites of scientific interest with a plan area of 7.2 km2. A total of 23,172 images collected by the UAVs were used as input in Structure-from-Motion (SfM) to create 3D models of the target areas with a focus on landslides and fault rupture. Two sites are presented in more detail as examples of the data generated; a section of the Kekerengu fault that ruptured during the earthquake, and the Limestone Hills landslide. The sites were mapped at high resolution with ground sampling distance that varied from 0.5 to 7.0 cm/pixel. The developed SfM models were compared to 1-m aerial LiDAR data and the results were found to be comparable. However, the higher resolution of the SfM digital surface model (DSM), paired with the imagery facilitated more detailed interpretations, highlighting the usefulness of the UAV-enabled SfM as a mobile and effective technique for documenting perishable post-earthquake reconnaissance data.
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Landslides caused by the Mw7.8 Kaikōura earthquake and the immediate response
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.
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- Award ID(s):
- 1719496
- PAR ID:
- 10149620
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Date Published:
- Journal Name:
- Bulletin of the New Zealand Society for Earthquake Engineering
- Volume:
- 50
- Issue:
- 2
- ISSN:
- 1174-9857
- Page Range / eLocation ID:
- 106 to 116
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5459/bnzsee.50.2.106-116
