Crustal versus asthenospheric relaxation and post-seismic deformation for shallow normal faulting earthquakes:the Umbria-Marche (central Italy) case

Details Crustal versus asthenospheric relaxation and post-seismic deformation for shallow normal faulting earthquakes:the Umbria-Marche (central Italy) case Crustal versus asthenospheric relaxation and post-seismic deformation for shallow normal faulting earthquakes:the Umbria-Marche (central Italy) case

Jun 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000geoji.141f...7r&link_type=abstract

Geophysical Journal International, Volume 141, Issue 3, pp. F7-F11.

Astronomy and Astrophysics

Astronomy

1

Central Italy, Earth Models, Earthquakes, Post-Seismic Relaxation

Scientific paper

Following a normal mode approach for a stratified viscoelastic earth, we investigate the effects induced by shallow normal faulting earthquakes, on surface post-seismic vertical displacement and velocity at the surface, when stress relaxation occurs in the crust or in the asthenosphere. The modelled earthquake is a moderate one characteristic of some slowly deforming plate boundaries in the central Mediterranean region. We focus on the Umbria-Marche (central Italy) region where deep seismic reflection studies (CROP03) and the 1997 earthquake sequence clearly show a seismogenic layer decoupled from the lower crust by a sizeable transition zone. Accordingly, the crust is subdivided into three layers: an elastic upper crust, a transition zone and a low-viscosity lower crust. The fault is embedded in the upper crust. The layered viscoelastic structure of the crust and mantle imposes a pattern and scale on the modelled coseismic and post-seismic deformation with a major contribution from the transition crustal zone and low-viscosity lower crust, stress relaxation in the mantle being negligible. We show that significant vertical deformation rates of the order of 1mmyr-1 could be expected for a shallow and moderate event such as the recent Umbria-Marche earthquake for viscosity values of 1019 and 1018Pas in the crustal transition zone and lower crust, respectively.

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