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| Titel |
Post-seismic deformation of the Chilean volcanic arc (32°S-38°S): field and numerical studies |
| VerfasserIn |
Matteo Lupi, Daniele Trippanera, Ylona van Dinther, Valerio Acocella, Taras Gerya |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250104343
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| Publikation (Nr.) |
 EGU/EGU2015-5544.pdf |
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| Zusammenfassung |
| Eruptive rates in volcanic arcs increase significantly after subduction zone mega-thrust
earthquakes. Over short time periods the response of the arc is attributed to the
passage of seismic waves and to the elastic deformation of the upper plate. A second
peak of volcanic activity, however, occurs decades to centuries latter. A kinematic
mechanism that controls such a long term response has yet to be proposed and
verified.
In 2010 the M8.8 Maule earthquake struck in Central Chile causing normal stress
reductions in the arc as high as 1MPa (from about 32°S to about 38°S) on optimally oriented
faults. In such regions the shallow (i.e. less than 30 km deep) post-seismic intra-arc seismic
activity increased remarkably in the post-seismic period. We combine classical geological
methods with numerical models of seismic cycles calibrated for the Central Chile
subduction zone to investigate the key processes driving the deformation of the volcanic
arc and the reactivation of volcanic systems over long timescales (e.g. decades to
centuries).
First, we undertook a geological field survey around and across the Nevados de Chillan
volcanic complex, (~36.5°S). We mapped the distribution and orientation of faults
and dikes to better describe the long-term deformation occurring in the this part
of the volcanic arc. We concentrated in this region as the volcano was affected
by the Maule earthquake and its aftershocks. In addition, the volcanic complex
is elongated along a NW-SE direction, which is sub-parallel to the orientation of
basement lineaments that are thought to be reactivated by supra-lithostatic fluid
and magmatic pressures occurring during the post-seismic period. Second, we run
2D numerical simulations of several seismic cycles with a viscous-elasto-plastic
seismo-thermo-mechanical code that accounts for a realistic geometry and rheology of the
compressive margin. The code includes spontaneously developing faults and the
morphology of the volcanic arc, which affects the lithostatic load at shallow depths and
therefore the local distribution of the stresses below the arc. Our field observations
indicate that magmatic activity is strongly affected by the overall tectonic state of the
upper crust. This is in agreement with our numerical experiments pointing out that
upwelling of deep magmas may be controlled by a reduction of the normal effective
stress acting in the shallow crust during the post-seismic periods. In other words,
mega-thrust earthquakes accelerate natural processes (i.e. volcanic activity and the
deformation of the upper crust) that would otherwise occur over far longer timescales. |
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