AIM second annual meeting September 29-30, 2011 Prague

1. AIMsecond annual meeting September 29-30, 2011 Prague The computation of the elementary synthetic seismogramsfor Isola MT inversions in Dobrá Voda regionusing the 3D finite-difference method Martin GÁLIS1,2 Lucia FOJTÍKOVÁ1,3 Jiří ZAHRADNÍK4 1 Geophysical Institute, Slovak Academy of Sciences, Bratislava 2Comenius University Bratislava 3Institute of Rock Structure and Mechanics,Academy of Sciences of the Czech Republic, Prague 4Charles University Prague in cooperation with industrial partner: JurajSEKEREŠ DagmarSEKEREŠOVÁ Progseis, Ltd.,Trnava, Slovakia

2. introduction the area of our interest the region with significant seismic activity with respect to Slovak territory (1906 Ms 5.7) used names Dobra Voda or Little Carpathians or Male Karpaty

3. introduction motivation 3 methods for moment tensor inversionwere tested and comparedwith respect to their accuracy and stability : FOCMECPg and Pn wave polarities AMT P-wave amplitudes ISOLA full waveform

4. recent earthquakes national network MKNET introduction motivation

5. introduction ISOLA first step synthetic elementary seismogramsare computed for a set of stations elementary seismogram =ground motion at the stationdue to one elementary focal mechanism

6. introduction ISOLA first step synthetic elementary seismogramsare computed for a set of stations elementary seismogram =ground motion at the stationdue to one elementary focal mechanism second step the coefficients of the linear combination of synthetic elementary seismograms are find by minimization of the misfit between the real data and synthetics

7. introduction motivation ISOLA is distributed as a package with a programs to computethe elementary seismogramsonly for 1D medium the limitations of 1D medium with respect to realistic 3D structures are obvious therefore we decided to try to use ISOLA with synthetics for 3D medium

8. from model definition to computational model model by Geofyzika, 1985

9. from model definition to computational model extended model

10. from model definition to computational model 2D interpolation spline interpolation - presence of false details, high-frequency content

11. from model definition to computational model 2D interpolation spline interpolation - presence of false details, high-frequency content bi-linear interpolation on quadrilaterals - presence of stair-likestructures

12. from model definition to computational model 2D interpolation spline interpolation - presence of false details, high-frequency content bi-linear interpolation on quadrilaterals - presence of stair-like structures linear interpolation on triangles with the same orientation - generally good results, but still some local sharp corners

13. from model definition to computational model 2D interpolation linear interpolation on triangles with adapted orientation for each quadrilateralthe orientationwith smaller gradient at the triangle’s contact is used for the interpolation

14. from model definition to computational model 2D interpolation linear interpolation on triangles with adapted orientation

15. from model definition to computational model 3D interpolation and smoothing we applied 2D interpolation in successive steps to xy, xz and yz planes to obtain a 3D grid with spacing 100m we applied volumetric smoothing to remove the artifacts of linear interpolation(discontinuous derivatives at the triangle edges)

16. Vp[km/s] 6 5 4 3 2 from model definition to computational model model visualization depth = 0 km 31 km 51 km

17. Vp[km/s] 6 5 4 3 2 from model definition to computational model model visualization depth = 1 km 31 km 51 km

18. Vp[km/s] 6 5 4 3 2 from model definition to computational model model visualization depth = 2 km 31 km 51 km

19. from model definition to computational model Vp to Vs the model by Geofyzika is defined only in terms of Vp (P-wave) velocity for 3D model we used the same Vp / Vs ratio as for 1D model: Vp / Vs = 1.75

20. from model definition to computational model Vp to density density [g.cm-3] Vp [m.s-1]

21. finite-difference method brief info we used FD scheme and program developed in Bratislavamainly by Peter Moczo and Jozef Kristek

22. finite-difference method brief info we used FD scheme and program developed in Bratislavamainly by Peter Moczo and Jozef Kristek in two recent exercises, ESG2006 and E2VP-Cashima project, participated teams using different numerical methods (finite-difference, finite-element,spectral element, discontinuous galerkin, pseudo-spectral)

23. finite-difference method brief info we used FD scheme and program developed in Bratislavamainly by Peter Moczo and Jozef Kristek in two recent exercises, ESG2006 and E2VP-Cashima project, participated teams using different numerical methods (finite-difference, finite-element,spectral element, discontinuous galerkin, pseudo-spectral) these exercises showed thatif our FD scheme was applicable to the problem configuration (for example if planar free surface was an acceptable approximation)it was the most accurate and the most efficient method

24. results V14

25. results comparison of 1D and 3D synthetic seismograms SMOL – very close bedrock station Z NS EW

26. results comparison of 1D and 3D synthetic seismograms HRAD – distant bedrock station Z NS EW

27. results comparison of 1D and 3D synthetic seismograms SPAC – distant station on sediments Z NS EW

28. conclusions we prepared the 3D computational modelof the Dobra Voda regionfor 3D FD computations (however the model should be considered as very preliminary) we applied the 3D FD method to compute 3D synthetic elementary seismograms for ISOLA moment tensor inversion we tested this procedure on two events, V03 and V14 (the results of the analysis will be presented in next talk) we are ready to apply this procedure to more events with the same model or with improved model once it will be available

29. thank you for the attention