Preprints
https://doi.org/10.5194/nhess-2021-403
https://doi.org/10.5194/nhess-2021-403

  04 Jan 2022

04 Jan 2022

Review status: this preprint is currently under review for the journal NHESS.

Pseudo-prospective testing of 5-year earthquake forecasts for California using inlabru

Kirsty Bayliss, Mark Naylor, Farnaz Kamranzad, and Ian Main Kirsty Bayliss et al.
  • School of GeoSciences, University of Edinburgh

Abstract. Probabilistic earthquake forecasts estimate the likelihood of future earthquakes within a specified time-space-magnitude window and are important because they inform planning of hazard mitigation activities on different timescales. The spatial component of such forecasts, expressed as seismicity models, generally rely upon some combination of past event locations and underlying factors which might affect spatial intensity, such as strain rate, fault location and slip rate or past seismicity. For the first time, we extend previously reported spatial seismicity models, generated using the open source inlabru package, to time-independent earthquake forecasts using California as a case study. The inlabru approach allows the rapid evaluation of point process models which integrate different spatial datasets. We explore how well various candidate forecasts perform compared to observed activity over three contiguous five year time periods using the same training window for the seismicity data. In each case we compare models constructed from both full and declustered earthquake catalogues. In doing this, we compare the use of synthetic catalogue forecasts to the more widely-used grid-based approach of previous forecast testing experiments. The simulated-catalogue approach uses the full model posteriors to create Bayesian earthquake forecasts. We show that simulated-catalogue based forecasts perform better than the grid-based equivalents due to (a) their ability to capture more uncertainty in the model components and (b) the associated relaxation of the Poisson assumption in testing. We demonstrate that the inlabru models perform well overall over various time periods, and hence that independent data such as fault slip rates can improve forecasting power on the time scales examined. Together, these findings represent a significant improvement in earthquake forecasting is possible, though this has yet to be tested and proven in true prospective mode.

Kirsty Bayliss et al.

Status: open (until 17 Feb 2022)

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Kirsty Bayliss et al.

Model code and software

Pseudo-prospective testing of 5-year earthquake forecasts for California using inlabru - data and code Kirsty Bayliss, Mark Naylor, Farnaz Kamranzad and Ian Main https://doi.org/10.5281/zenodo.5793157

Kirsty Bayliss et al.

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Short summary
We develop earthquake forecasts that include different spatial information (e.g. fault locations). We test different spatial components and input earthquake catalogues. The performance of these models are then tested over three different periods. We find that our models perform well, with the forecasts using simulated-catalogues performing better than those built on regular grids because the they capture more uncertainty. This suggests our approach can improve earthquake forecasting.
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