Rethinking earthquake prediction
Sykes LR, Shaw BE, Scholz CH
PURE AND APPLIED GEOPHYSICS
155: (2-4) 207-232 AUG 1999
Abstract:
We re-examine and summarize what is now possible in predicting
earthquakes, what might be accomplished (and hence might be possible in
the next few decades) and what types of predictions appear to be inherently
impossible based on our understanding of earthquakes as complex phenomena.
We take predictions to involve a variety of time scales from seconds to
a few decades. Earthquake warnings and their possible societal uses differ
for those time scales. Earthquake prediction should not be equated solely
with short-term prediction-those with time scales of hours to weeks-nor
should it be assumed that only short-term warnings either are or might
be useful to society. A variety of "consumers" or stakeholders are likely
to take different mitigation measures in response to each type of prediction.
A series of recent articles in scientific literature and the media claim
that earthquakes cannot be predicted and that exceedingly high accuracy
is needed for predictions to be of societal value, We dispute a number
of their key assumptions and conclusions, including their claim that earthquakes
represent a self-organized critical (SOC) phenomenon, implying a system
maintained on the edge of chaotic behavior at all times. We think this
is correct but only in an uninteresting way, that is on global or continental
scales. The stresses in the regions surrounding the rupture zones of individual
large earthquakes are reduced below a SOC state at the times of those events
and remain so for long periods. As stresses are slowly re-established by
tectonic loading, a region approaches a SOC state during the last part
of the cycle of large earthquakes. The presence of that state can be regarded
as a long-term precursor rather than as an impediment to prediction. We
examine other natural processes such as volcanic eruptions, severe storms
and climate change that, like earthquakes, are also examples of complex
processes, each with its own predictable, possibly predictable and inherently
unpredictable elements. That a natural system is complex does not mean
that predictions are not possible for some spatial. temporal and size regimes.
Long-term, and perhaps intermediate-term, predictions for large earthquakes
appear to be possible for very active fault segments. Predicting large
events more than one cycle into the future appears to be inherently difficult,
if not impossible since much of the nonlinearity in the earthquake process
occurs at or near the time of large events. Progress in earthquake science
and prediction over the next few decades will require increased monitoring
in several active areas.