第71回統計地震学セミナー / The 71st Statistical Seismology Seminar

Date&Time
2018年11月6日(火)
/ 6 November, 2018 (Tue) 16:00 – 17:00

Admission Free,No Booking Necessary

Place
統計数理研究所 セミナー室5 (D313)
/ Seminar room5 (D313) @ The Institute of Statistical Mathematics
区切り線
Speaker
David Harte
(GNS Science, New Zealand)
Title
Evaluation of Earthquake Stochastic Models Based on Their Real-Time Forecasts: A Case Study of Kaikoura 2016
Abstract

The M7.8 Kaikoura NZ earthquake started at 2016-11-13 11:02:56 (UTC) with epicentre (173.02 deg E, 42.69 deg S), 15km NE of Culverden, and lasted for about two minutes. It caused multiple fault ruptures to the north as far as Seddon (150km from epicentre), the location of a large sequence in 2013. Since the mainshock, the bulk of the aftershock activity has also migrated to the north.

We analyse real-time probability forecasts produced during the Kaikoura 2016 aftershock sequence, based on a spatial ETAS model. Forecasts were derived by simulating the model forward over the required time interval multiple times. Each forecast was evaluated at the end of the forecast time interval by comparing with the number of events that eventually occurred. Further, the spatial and temporal forecast characteristics were evaluated by comparing the actual log-likelihood with those of the simulations.

We show that the model was forecasting too fewer aftershocks immediately after the mainshock, and too many aftershocks in the later stages of the sequence. The too fewer aftershocks is probably caused by many missing smaller events early in the sequence and an initial large under-estimate of the mainshock magnitude, being 6.6 with a final solution of 7.8 three days later. Various catalogue, model and methodological problems become evident during such a real-time experiment and these are also discussed.