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

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.

In the short term, during the time-period of the urgency grant, the direct beneficiaries will be our project partners GNS Science (New Zealand), our industry partner Geospatial Research Ltd (GRL, UK), as well as the local rural landowners around the rupture on the northern extend of the South Island of New Zealand.

GNS Science will benefit from an increased number of fault observations, increasing their capacity to respond to this major event, and enabling more of the massive long fault rupture to be covered in a timely fashion before erosional processes start to diminish it and the offsets are contaminated by further fault slip processes. Also, the proposal provides the opportunity to test the accurate measurement of fault offsets using topography models acquired at a range of very high resolutions (sub meter to centimetre scale) - techniques that may be of use in future earthquake and fault studies, as well as for validating the effectiveness of the airborne LiDAR datasets being acquired at the metre scale to detect smaller deformation signals.

Our collaboration with our industrial project partner provides the opportunity to test and validate newly developed instrumentation for measuring positions accurately (from Global Navigation Satellite Systems, GNSS) measuring ground displacements after a major onshore earthquake. This will benefit the company by both opening up new technologies for commercial applications and also potential new customers in New Zealand (such as our other project partner, GNS Science). This will be timely in preparation for the recently "gone live" EU Galileo satellite system, which offers the prospect of much increased accuracy of positioning for commercial users over the coming two years.

The local rural landowners would be beneficiaries of the work through the mapping of the extent of distributed fault damage to rural residential land, which is included in the Earthquake Commissions (EQC) insurance coverage.

For the post project, medium term, timescale of a few years, the beneficiaries would expand to encompass the populations of both the South and North islands of New Zealand as the short-term benefits are propagated through the advice provided by GNS to local and national governments. This will be of particular importance to the capital city (Wellington, population 400,000), where the stress from this recent earthquake has increased on those in and around the city of Wellington.
Longer Term and indirect impacts and benefits:

Over the much longer term, far beyond the timescale of the urgency project, into the next decade, the beneficiaries could potential expand more globally to encompass those organisations charged with updating earthquake rupture forecasts and the populations that these forecasts are designed to help protect. Updates to national scenarios would benefit with improved forecasts that are more likely to include the potential for these large complex earthquake rupture events. This will benefit populations by improving the preparedness for large earthquakes, resulting in reductions in fatalities, injuries and property losses. The outputs of this proposal will be a part of a much greater whole of research where we build upon recent work the investigators have done on understanding the biggest jump that is possible between faults in earthquake ruptures.