Worldwide earthquake forecasts

Yan Y. Kagan

Published 2017, SCEC Contribution #6260

We review global earthquake forecast as it was developed by our UCLA
group since 1970s. We discuss the new results on earthquake
magnitude/moment distribution, especially the determination of
maximum/corner moment magnitude. Recent successes of global geodetic
surveys allow us to construct a high resolution map of the Earth
surface displacement and, after converting this map to earthquake rate,
combine these maps with those based on seismicity smoothing. Thus we
are constructing and testing a Global Earthquake Activity Rate model as
a function of the magnitude at 0.1 by 0.1 degree resolution. Nicknamed
"GEAR", the model relies on a global strain rate model (GSRM) and the
instrumental earthquake catalogs. Thus, for our forecast we use
datasets that provide uniform global coverage: seismic catalogs, global
plate boundary models, and Global Positioning System (GPS) geodetic
velocities. After testing, the model can be used by Global Earthquake
Model foundation (GEM) and others in seismic hazard estimation. GEAR
covers magnitudes 5.8 and larger, the periods are from years to decades
with no explicit time-dependence. The normalized magnitude distribution
at each location is a combination of the tapered Gutenberg-Richter
distributions with b-values and the corner magnitudes determined by a
few global parameters that depend on the tectonic style and the focal
mechanism proportion. The seismic and strain-rate components of the
model are specified separately and then combined optimally to fit an
earthquake occurrence over the last several years. GEAR performs well
in quasi-prospective tests using the GCMT catalog after 2005 and the
GEM catalog from 1918 to 1976; GEAR will be rigorously tested
prospectively against future earthquakes. Because of its simplicity,
GEAR can serve as a well-vetted reference model and as a
null-hypothesis against which more complex models can be tested. With
its high spatial resolution, GEAR can also be compared to detailed
regional models. We also discuss potential methods to improve and
extend the forecasts. Such methods include extending the forecast to
lower magnitudes, introducing focal mechanisms into prediction methods,
and making the short-term forecast an integral part of the practical
forecast implementation.

Key Words
Probability distributions, Seismicity and tectonics, Statistical seismology, Dynamics, seismotectonics, Subduction zones, Maximum/corner magnitude.

Kagan, Y. Y. (2017). Worldwide earthquake forecasts. Stochastic Environmental Research and Risk Assessment (SERRA), 31(6), 1273-1290.

Related Projects & Working Groups
B. Collaboratory for the Study of Earthquake Predictability (CSEP)