Impacts of surface fault rupture on residential structures during the 2016 Mw 7.8 Kaikōura earthquake, New Zealand

Russ J Van Dissen,Timothy A Little,Timothy Stahl,Robert M Langridge,Jesse Kearse,Pillar Villamor,Andrew Nicol,Clark Fenton,Mark W Stirling,David J A Barrell,Jarg R Pettinga,Nicola J Litchfield,Andrew King

doi:10.5459/bnzsee.52.1.1-22

Abstract

Areas that experience permanent ground deformation in earthquakes (e.g., surface fault rupture, slope failure, and/or liquefaction) typically sustain greater damage and loss compared to areas that experience strong ground shaking alone. The 2016 Mw 7.8 Kaikōura earthquake generated ≥220 km of surface fault rupture. The amount and style of surface rupture deformation varied considerably, ranging from centimetre-scale distributed folding to metre-scale discrete rupture. About a dozen buildings – mainly residential (or residential-type) structures comprising single-storey timber-framed houses, barns and wool sheds with lightweight roofing material – were directly impacted by surface fault rupture with the severity of damage correlating with both local discrete fault displacement and local strain. However, none of these buildings collapsed. This included a house built directly atop a discrete rupture that experienced ~10 m of lateral offset. The foundation and flooring system of this structure allowed decoupling of much of the ground deformation from the superstructure thus preventing collapse. Nevertheless, buildings directly impacted by surface faulting suffered greater damage than comparable structures immediately outside the zone of surface rupture deformation. From a life-safety standpoint, all these buildings performed satisfactorily and provide insight into construction styles that could be employed to facilitate non-collapse performance resulting from surface fault rupture and, in certain instances, even post-event functionality.

Highlights

The Kaikōura earthquake struck at two minutes past midnight on 14 November 2016
Employing a combination of field observations and a differential Light Detecting and Ranging (LiDAR) digital elevation model (DEM) at the site (Figures 11C & 11D), assuming simple shear, and adopting a sub-vertical fault dip and a horizontal to vertical ratio of displacement of
Based on the building damage examples presented in this paper (e.g. Figures 2, 3 5-18) for the 2016 Kaikōura earthquake, and those presented by Van Dissen et al [21] for the 2010 Darfield earthquake, some pertinent observations can be made regarding the performance of New Zealand residential structures when subjected to surface fault rupture deformation of varying levels of strain and amounts of displacement

Summary

INTRODUCTION

The Kaikōura earthquake struck at two minutes past midnight on 14 November 2016. Its epicentre was located near the South Island township of Waiau (Figure 1) and, with a magnitude of Mw 7.8, it was the largest on-land earthquake to hit New Zealand in more than a century [1, 2]. Harkaway Villa is a timber-framed single-storey house with timber weather board cladding and a corrugated metal roof on framed rafters with internal load-bearing walls (Figures 1, 5 & 6; Table 1) It has a roughly square floor plan (area of ~130 m2), timber strip (plank) flooring, and a timber pile foundation (~60 cm above ground) with joists attached to piles via wire ties and skew nails. Despite this house suffering damage significant enough to be “red tagged”, it - from a life-safety perspective performed commendably It experienced very strong ground shaking, local decimetre-scale surface fault rupture deformation and is located within the hinge zone of a reverse fault scarp that has been classified in other earthquakes as a zone of ‘severe building damage’ [20], yet the villa did not collapse.

Figures in Text

DISCUSSION

CONCLUSIONS