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| Titel |
The far-field deformations associated with the seismic cycle: The lessons from the postseismic deformations of the recent giant subduction earthquakes |
| VerfasserIn |
O. Trubienko, L. Fleitout, J. D. Garaud, C. Vigny |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250070661
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| Zusammenfassung |
| The strains associated with the seismic cycle are often modeled using an elastic behaviour:
For example, elastic backslip is often used to model the interseismic phase. The study of the
huge post-seismic deformations following the Aceh earthquake has unambiguously shown
that relaxation in the asthenosphere with transient viscosities of the order of 3. 1018Pas is
necessary to reproduce the pattern of far-field deformations.
With the help of 2D and 3D finite element programs, we compute the deformations
through the whole seismic cycle for recurring earthquakes in the case where the
asthenosphere deforms according to the viscoelastic rheology deduced from the postseismic
of Aceh. We show that there are sizable perturbations of the horizontal interseismic velocities
over a zone much broader (broader than 1000 km) than in the elastic backslip case. Morover,
for subduction earthquakes, postseismic centimetric subsidence is predicted in the far-field
while a slight upward velocity is expected at the end of the cycle. The typical interseismic
velocity pattern across a fault consists in a region with a sharp gradient over a few hundred
km from the fault and a region with a smaller gradient but extending typically more than
1000km from the fault. The predicted extent and relative velocity accomodation
across this broad low velocity gradient region is function of the period of seismic
cycle.
We reinterpret the GPS velocities measured before the three recent giant subduction
earthquakes as the counterparts of the present-day observed postseismic velocities: the
northward velocities of the Sunda block with respect to South China observed before 2004
are shown to have the same amplitude as the velocities predicted for the interseismic
phase of the Andaman-Sumatra subduction seismic cycle. The same is true for
the pre-2011 westward velocity of the west coast of Honshu with respect to the
Amurian plate. As a consequence, the estimates of the long-term shortening velocity
across the Japan basin should be revised. The eastward velocity with respect to a
South-America reference frame, observed before 2010 as far East as Buenos Aeres, is
also the counterpart of the westward post-seismic velocity presently measured in
Argentina.
The velocity pattern measured by GPS a few thousand km away from faults generating
large earthquakes is strongly affected by the seismic cycle.
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