Presentation on theme: "STAR: lanisotropia sismica come indicatore delle variazione delle proprietà elastiche della crosta Ancona, 23-04-2013 Pastori M., Piccinini D., Guerri."— Presentation transcript:
STAR: lanisotropia sismica come indicatore delle variazione delle proprietà elastiche della crosta Ancona, Pastori M., Piccinini D., Guerri M., Margheriti L., Barchi M.
Equivalent to the birefringence in optics The main technique to study Seismic Anisotropy is based on the Shear Wave Splitting (SWS) phenomena Anisotropic parameters Fast Polarization Direction Fast Polarization Direction typically polarized parallel to the direction of the cracks-fractures Delay Time ( t), Delay Time ( t), the lag of the slower wave, it is a measure of intensity and/or thickness of the anisotropic medium (Crampin & Lovell, 1991) S hmin Vertical Stress Shear Wave Splitting
(Extensive Dilatancy Anisotropy Model; Crampin,1993) 2.Stress open crack EDA Fluid-filled micro-cracks aligned or opened by active stress field 1.Inherited fracture field 3.Time dependent APE Zatsepin & Crampin, 1995) (Anisotropic Poro Elasticity Model; (Zinke and Zoback, 2000) Possible crustal anisotropic causes
Piccinini et al. Computer and Geoscience 2013 OUTPUTS Fast direction and delay times Errors on the parameters Cross correlation Anisomat+ is a set of MatLab scripts that use the cross- correlation method to compute anisotropic parameters: fast direction and delay time 1.Three-component seismogram in SAC format (having the same length) 2.P & S picking 3.Event and Station Coordinates 4.Test incidence angle 5.Test signal quality
Crustal Seismic Anisotropy in the region Comparison between the average values of the anisotropy for the 2010 seismicity (Guerri et al 2012 and the CDC experiment (Pastori et al., 2012). the comparison show a robust agreement both for the average fast directions and for the average delay time values. Green and purple bars represent fats direction and their length is proportional to the delay time.
FastNull Fast directions vs Shmin Guerri et al. 2012
Pietralunga Seismic sequence 2010 Anisotropy in space and time Waveforms picking and locatio by AN Why are ATPI and ATPC different? Lithology? Local stress? 90°flip due to fluid overpressure?
Work in progress … Final remarks Real Time monitoring of anisotropic parameters? The dense seismic network allow to locate many small earthquakes in the S window of each station, giving results all the back-azimuths and well sampling the rock volume Manual pickings seems to give more stable results but on averages the completely automatic procedure give consistent results We should test selection of the results on the base of picking weight or…? At Taboo thanks to the geological-and structural knowledge of the area we should be able to understand why we observe different anisotropic parameters in space and time! Yes go ahead, Lets try it!!! 90°flip for high luid pressure; can we see them?