Prospective Evaluation of Global Earthquake Forecast Models:Two Years of Observations Provide Preliminary Support for Merging Smoothed Seismicity with Geodetic Strain Rates

The Global Earthquake Activity Rate (GEAR1) seismicity model uses an optimized combination of geodetic strain rates, hypotheses about converting strain rates to seismicity rates from plate tectonics, and earthquake-catalog data to estimate global mw ≥ 5.767$ shallow (≤ 70 km) seismicity rates. It comprises two parent models: a strain rate-based model, and a smoothed-seismicity based model. The GEAR1 model was retrospectively evaluated and calibrated using earthquake data from 2005-2012, resulting in a preferred log-linear, multiplicative combination of the parent forecasts. Since October 1, 2015, the GEAR1 model has undergone prospective evaluation within the Collaboratory for the Study of Earthquake Predictability (CSEP) testing center. We present initial prospective forecast test results for the GEAR1 model, its tectonic and seismicity components, and for the first iteration of the strain rate-based model, during the period October 1, 2015 to September 7, 2017. During the evaluation period, observed earthquakes are consistent with the GEAR1 forecast and comparative test results likewise support that GEAR1 is more informative than either of its components alone. Based on a combination of retrospective and prospective testing, the tectonic forecasts do not effectively anticipate observed spatial earthquake distribution, largely due to over-localization of the model with respect to observed earthquake distributions.