Global Medium-Term Earthquake Forecasting with Every Earthquake a Precursor According to Scale

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Abstract
The “Every Earthquake a Precursor According to Scale” (EEPAS) model uses minor earthquakes in a catalogue to forecast major earthquakes, based on the precursory scale increase phenomenon and associated predictive scaling relations. It has previously been applied to regional earthquake catalogues for medium-term forecasting of earthquakes with target magnitudes exceeding thresholds in the range M 5.0–6.0 using previous earthquakes about two magnitude units below the target threshold, depending on the completeness of the catalogue. Here, we apply it to the ISC-GEM global earthquake catalogue and test its ability to forecast earthquakes with target magnitudes exceeding M 7.5, i.e., the largest and most important earthquakes for assessing earthquake hazard. We use background models based on both smoothed seismicity and spatial variation of strain rate estimates. The models are fitted to the period 1994–2013, with 85 target earthquakes, and tested on the period 2014–2019, with 19 target earthquakes. The EEPAS model shows larger information gains over a smoothed seismicity model than in most regional applications. Also, a hybrid composed of EEPAS, smoothed seismicity and the strain rate outperforms a hybrid consisting only of smoothed seismicity and strain rate components. These preliminary results suggest that EEPAS may be useful for forecasting the largest earthquakes globally but should be followed up by transparent prospective testing. There are several avenues for improvement of EEPAS modeling.
Funding Information
  • Strategic Science Investment Fund
  • National Seismic Hazard Model Revision Project (2020-BD101)
  • Ministry of Business, Innovation and Employment of New Zealand

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