Klaus Bataille 氏 (Concepcion University)

Large Earthquakes in Chile: and some implications

（2004年07月07日）

The subduction process in Chile is considered a model example of
an oceanic plate subducting beneath a continental plate.
The seismic activity is also considered a model example,
where during the last 500 years evidenced the occurrence of
large earthquakes every 100 years approximately.
However, an anomalously large event took place on the southernmost
part of the contact between the Nazca and Southamerica plate.
This event occurred in May 1960, with a M_w=9.5 rupturing an area of
1000 km long and 200 km wide. Studies of nornal modes, surface waves,
body waves, and geodetic measurements, have complementary shown
the degree of complexity in space and time of the rupture of this event.
However, it is intriguing to note the fact that the Geodetic Moment
is one fifth the Seismic Moment, eventhough it represents the
deformation through a longer time span than compared to just minutes
as for the Seismic Moment determination. Since other large earthquakes
around the globe show similar tendency, this discrepancy is considered
to be a real phenomenon. I suggest that this is a product of
the nonlinear behavior of the elastic material.
To prove this I find the solution for the static displacement,
due to a point source in an infinite nonlinear elastic media,
and show that it depends nonlinearly on M_o/R^2. Using this solution
one can show that the Geodetic and Seismic observations coinciles
reasonably well. If this suggestion is correct, it would imply
that all Geodetic interpretations, especially those causing large
deformations, have to be revised. Not only the total Moment will differ,
but also the distribution in space.