## Improved medium-term earthquake forecasting: Compensating for incomplete contributions of precursory earthquakes

David A. Rhoades, & Annemarie ChristophersenSubmitted August 12, 2018, SCEC Contribution #8405, 2018 SCEC Annual Meeting Poster #050

The EEPAS earthquake forecasting model treats Every Earthquake as a Precursor, According to Scale, of larger earthquakes to follow it in the medium term. It applies empirical predictive relations derived from examples of the precursory scale increase phenomenon to estimate the contribution of an individual precursory earthquake to the future earthquake occurrence rate density at any future time, magnitude and location. The contributions of precursory earthquakes are complete, for a given target earthquake magnitude and future time, if all earthquakes that could contribute to the earthquake occurrence rate density at the target time and magnitude are included in the catalog. If there is a time-lag between the time of the forecast and the target time, then contributions from precursory earthquakes will be incomplete because earthquakes expected to occur during the time-lag will be missing from the catalog. The EEPAS model will therefore tend to under-predict the rate density of earthquakes unless the forecast is compensated for the incompleteness of precursory earthquake contributions. We estimate the completeness of the precursory earthquake contributions at a given target magnitude when forecasting with a given time lag. We also consider two end-members for compensating for incompleteness, by augmenting (1) only the time-varying component, and (2) only the time-varying background component, of the EEPAS model. Using the New Zealand earthquake catalog, we derive an optimal combination of these two end-members for each target magnitude and time lag, and illustrate the effect on forecasts of major earthquakes in central New Zealand using the earthquake catalog up to 2018 to make forecasts with time-horizons out to 2030.

**Key Words**

Earthquake forecasting, New Zealand

**Citation**

Rhoades, D. A., & Christophersen, A. (2018, 08). Improved medium-term earthquake forecasting: Compensating for incomplete contributions of precursory earthquakes. Poster Presentation at 2018 SCEC Annual Meeting.

**Related Projects & Working Groups**

Earthquake Forecasting and Predictability (EFP)