Forecasting earthquake behavior on the Alpine Fault, New Zealand

Nicolas C. Barth, Jamie Howarth, Keith B. Richards-Dinger, Sean Fitzsimons, & Glenn P. Biasi

Published August 15, 2018, SCEC Contribution #8809, 2018 SCEC Annual Meeting Poster #038

New Zealand’s Alpine Fault is perhaps the world’s best example of a relatively simple, hypermature, active continental plate boundary transform. A 4000-year paleo-earthquake record from the Alpine Fault reveals the extent of the last 19 surface rupturing earthquakes along 300 km of the Central and South Westland sections of the fault; this record illuminates the most periodic earthquake recurrence behavior yet observed on a natural fault (coefficient of variation of 0.23 for the Central section), while also indicating these past earthquakes exhibit a range of rupture lengths and magnitudes. Importantly, the Central-South Westland section boundary (defined by a change in fault geometry and slip rake) behaves as an earthquake gate: about half (48%) of the recorded earthquakes rupture through the boundary as ~Mw 8 multi-section earthquakes and half (52%) terminate against the section boundary as ~Mw 7.5 single-section earthquakes with these two earthquake modes clustering in time. In other words, the central Alpine Fault exhibits a strong time dependence to earthquake return but the event magnitude and distribution may depend more strongly on the sequence of past earthquakes. We utilized the best constraints on fault geometry (fault strikes, fault dips, seismogenic depths) and fault kinematics (geological slip rates, slip rakes) along the full ~880 km length of the Alpine Fault to simulate 100,000 years of Alpine Fault earthquake behavior using the quasi-dynamic earthquake simulation code RSQSim. We find remarkable agreement in earthquake recurrence interval, recurrence interval coefficient of variation, single event displacement, and the pattern of rupture between the paleo and synthetic earthquake records, which builds confidence that our data-rich simulations can be used to enhance earthquake forecasting. The last three earthquakes on the Alpine Fault have been ~Mw 8 multi-section events, a mode that our 100 kyr simulation shows is followed by another Mw 8 multi-section event 82 (+13/-18) % of the time. We use simulation-based extension of the recent rupture history of the Alpine Fault to produce three complementary time and mode dependent probabilities concerning rupture of the Alpine Fault’s Central section in the next 50 years: (1) a 7 (+5/-5) % probability that no earthquake Mw > 7 occurs, (2) a 17 (+2.7/-3.7) % probability of a major (~Mw 7.5) earthquake occurring, and (3) a 76 (+12/-17) % probability of a multi-section great (Mw ~8) earthquake.

Key Words
earthquake simulation, earthquake forecasting, earthquake gate, Alpine Fault

Citation
Barth, N. C., Howarth, J., Richards-Dinger, K. B., Fitzsimons, S., & Biasi, G. P. (2018, 08). Forecasting earthquake behavior on the Alpine Fault, New Zealand. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Forecasting and Predictability (EFP)