In this work a multidisciplinary study of the December 26th, 2004 Sumatra
earthquake has been carried out. We have investigated both the effect of the
earthquake on the Earth rotation and the stress field variations associated
with the seismic event.
In the first part of the work we have quantified the effects of a water
mass redistribution associated with the propagation of a tsunami wave on the
Earth’s pole path and on the length-of-day (LOD) and applied our modeling
results to the tsunami following the 2004 giant Sumatra earthquake. We
compared the result of our simulations on the instantaneous rotational axis
variations with some preliminary instrumental evidences on the pole path
perturbation (which has not been confirmed yet) registered just after the
occurrence of the earthquake, which showed a step-like discontinuity that
cannot be attributed to the effect of a seismic dislocation.
Our results show that the perturbation induced by the tsunami on the
instantaneous rotational pole is characterized by a step-like discontinuity,
which is compatible with the observations but its magnitude turns out to be
almost one hundred times smaller than the detected one. The LOD variation
induced by the water mass redistribution turns out to be not significant because the total effect is smaller than current measurements uncertainties.
In the second part of this work of thesis we modeled the coseismic and
postseismic stress evolution following the Sumatra earthquake. By means of
a semi-analytical, viscoelastic, spherical model of global postseismic deformation
and a numerical finite-element approach, we performed an analysis
of the stress diffusion following the earthquake in the near and far field of
the mainshock source. We evaluated the stress changes due to the Sumatra
earthquake by projecting the Coulomb stress over the sequence of aftershocks
taken from various catalogues in a time window spanning about two years
and finally analyzed the spatio-temporal pattern.
The analysis performed with the semi-analytical and the finite-element
modeling gives a complex picture of the stress diffusion, in the area under
study, after the Sumatra earthquake. We believe that the results obtained
with the analytical method suffer heavily for the restrictions imposed, on the
hypocentral depths of the aftershocks, in order to obtain the convergence of
the harmonic series of the stress components. On the contrary we imposed no
constraints on the numerical method so we expect that the results obtained
give a more realistic description of the stress variations pattern.
| Identifer | oai:union.ndltd.org:unibo.it/oai:amsdottorato.cib.unibo.it:864 |
| Date | 09 June 2008 |
| Creators | Pisani, Anna Rita <1973> |
| Contributors | Piersanti, Antonio, Bonafede, Maurizio |
| Publisher | Alma Mater Studiorum - Università di Bologna |
| Source Sets | Università di Bologna |
| Language | English |
| Detected Language | English |
| Type | Doctoral Thesis, PeerReviewed |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
Page generated in 0.0022 seconds