Rapid recovery of high resolution topographic and kinematic data from the Kaikoura earthquake, New Zealand

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Early in the morning of 14th November 2017, a Magnitude 7.8 earthquake occurred in the South Island of New Zealand. The earthquake started around 9 km north of Culverden, and rupture on the fault plane propagated rapidly northwards in a complex pattern along a series of nine separate faults, with dramatic surface ruptures (with up to ~10m of horizontal slip) and large-scale landsliding between Kaikoura and Blenheim. Only two fatalities were recorded, one as a result of a heart attack, and one in Kaikoura when a historic homestead collapsed. The earthquake is remarkable for several reasons - it is probably the largest earthquake event dominated by horizontal movement to occur at a time and location where there were many scientific instruments already operating to record the seismic waves and determine the ground motion. The earthquake occurred mostly on land, meaning that we are may be able to reconstruct what the sense of movement was from features such as roads and fences that were broken and moved during the event. Furthermore, the event was complex, with slip on multiple faults of different type, and with large variations in slip over short distances.However, many aspects of the surface record which may be used to determine the sense of movement are relatively short-lived. They are gradually reduced in size and sharpness, and eventually destroyed or distorted by surface processes such as slope wash during heavy rain and by anthropogenic remediation such as repairing highways and repositioning broken fences. Following the movement that occurs during the earthquake, a slower motion known as post-seismic slip can occur on timescales of weeks and months. The next winter season will obliterate many of the finer surface features. These are very important for the detailed interpretation of how and when the earthquake rupture developed, and include soft features on fault scarps and landscape surfaces, for example where these are composed of gravel.We plan to undertake two main tasks: i) to record key selected examples of these temporary landscape features before they are destroyed by surface processes, as soon after the event as is possible, to help tell the difference between initial fault slip during the earthquake from post-seismic movement, and ii) to emplace a number of semi-permanent GPS recorders which record their ground position to within a few cm, to capture the rate and timing of post-seismic movement over a period of around 3 months. Both of these tasks are critically time-dependent for reasons of preservation (weathering and erosion) and contamination (e.g. new deposition of sediment above the surface features). Undertaking this research soon will allow us to record the maximum amount of data useful for understanding the detail of the earthquake event. This can help in interpreting other earthquakes, and in gaining an improved understanding of what happened during ancient seismic events, so that we are able to improve seismic hazard assessment. This assists local and central governments, along with authorities and suppliers of services such as roads, railways, power, water etc. to plan more accurately for future earthquake events, and consequently improve the likely outcomes for members of the public in those regions.