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Investigations
of surface strain, plate boundary motion, frictional properties
of faults and mechanical properties of the Earth's crust are necessary
to determine what controls the spatial and temporal patterns of
earthquakes. Space-based observations allow us to measure the entire
earthquake cycle including the aseismic or quiet accumulation of
strain. These new measurements are providing insights into how stress
is transferred between faults, how much strain is released seismically
versus quietly, and potentially how faults fail.
Fully
modeling the earthquake system requires knowledge of the current
and past motions and interactions of faults. It is therefore necessary
to measure the current ongoing deformation associated with plate
tectonics and faults. It is also necessary to obtain detailed topographic
and geomorphic characteristics of faults to better understand the
past earthquake history. Targeted measurements along plate boundary
zones can address how fault systems interact. Because we are discovering
that fault systems can interact over hundreds of kilometers exploratory
measurements are also required until we understand these systems
better.
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For
example, by understanding the stress transients that occur after
major earthquakes, it may be possible to determine more reliably
the probability of future earthquakes occurring at other locations
in the system. Analysis of temporal transients and the spatial complexity
of deformation are likely to reveal properties of the faults and
the Earth's crust. A complete program of study will cover areas
from laboratory measurements, global scale measurements, and large
scale computing to synthesize all aspects of the problem.
Varying
time and space sampling requirements and accuracies dictate specific
observational approaches: GPS networks and INSAR constellations
will be needed to provide dense spatio-temporal sampling and high
accuracy observations of the changes of the Earth's surface. Seismic
networks, borehole arrays, low-frequency sounders, and highly accurate
gravity measurements will enable characterization and change assessment
of the subsurface structure and composition.
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