Department of Civil Engineering,California Institute of Technology
Abstract
Abstract. Earthquakes in megacities such as Tehran and Los Angeles pose huge risks that could
jeopardize national prosperity and social welfare. Quantifying urban seismic risk is a dicult problem
because it requires detailed knowledge of the natural and the built environments, as well as an
understanding of both earthquake and human behaviors. Risk assessments can be improved through
international collaborations that combine the expertise of earthquake scientists and engineers. The most
e ective strategies are seismic safety engineering, enforced through stringent building codes and disaster
preparations informed by realistic scenarios of large earthquake cascades. These strategies rely on the
ability to forecast earthquakes and their e ects and to monitor earthquake cascades in near real time. The
practical problems of risk reduction are, thus, coupled to the basic problems of earthquake system science:
the interseismic dynamics of fault systems and the coseismic dynamics of fault rupture and groundmotion
excitation. In the United States, the Southern California Earthquake Center (SCEC) coordinates
an extensive research program in earthquake system science, which includes major e orts to improve
time-dependent earthquake rupture forecasts through better understanding of earthquake predictability
and to develop attenuation relationships that correctly model the physics of seismic wave propagation.
Earthquake system science relies on the premise that detailed studies of fault systems in di erent regions
can be synthesized into a generic understanding of earthquake phenomena. Achieving such a synthesis
will depend on international partnerships that facilitate the development and comparison of well-calibrated
regional models, and it will require the deployment of a cyberinfrastructure that can facilitate the creation
and
ow of information required to predict earthquake behavior. In the not-too-distant future, we will
be able to incorporate much more physics into seismic hazard and risk analysis through physics-based,
system-level simulations.
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