SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Seismic wave Propagation and Imaging in Complex media: a European network EBRU BOZDA Ğ Early Stage Researcher Host Institution: Utrecht University Place of Origin: Istanbul, Turkey Appointment Time: February 2005 Project: Testing and Improving Tomographic Models Using Numerical 3D Wave Propagation Task Groups: TG Planetary Scale Cooperation: Oxford University EBRU BOZDA Ğ Early Stage Researcher Host Institution: Utrecht University Place of Origin: Istanbul, Turkey Appointment Time: February 2005 Project: Testing and Improving Tomographic Models Using Numerical 3D Wave Propagation Task Groups: TG Planetary Scale Cooperation: Oxford University

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Crustal corrections predicted by ray theory and finite frequency theory compared to measured time shifts from SEM seismograms using Crust2.0 Ebru Bozdağ Jeannot Trampert SPICE Utrecht University, Utrecht, the Netherlands

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Crustal corrections are important in surface wave tomography  Crustal structures have a strong effect on surface waves.  Inverting for crust and mantle is difficult. Therefore crustal corrections are preferred.  Phase delays from the crust are removed in surface wave tomography to identify mantle structure.

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland The objective Investigate how far  great circle approximation  exact ray theory and  finite frequency theory predict crustal corrections using the SEM (Komatitsch and Tromp, 2002) seismograms computed in 1D (PREM) and 3D (PREM+Crust2.0) earth models.

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Data generation Earthquakes & Stations VIC CMA SEP CRT XZNG WIA SOA NCN IJR SIR IJR 11 earthquakes 253 stations Synthetic seismograms using SEM  Synthetic seismograms from 1D earth model PREM (Dziewonski and Anderson, 1981)  3D crustal model Crust2.0 (Bassin et al., 2000) is superimposed on top of PREM model and synthetic seismograms are computed for PREM+Crust2.0 model

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Measuring time shifts as a function of frequency PREM PREM+Crust2.0 Cross-correlation of the seismograms Time-variable filter to extract the fundamental mode Rayleigh wave Phase correction to PREM seismograms Unwrap the phase Measure the phase of the cross-correlation PREM+Crust2.0 - PREM PREM+Crust2.0 – PREM+Corr.

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Great Circle Approximation (GCA) Exact Ray Theory (ERT) Finite Frequency Theory (FFT) Methods used for crustal corrections

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Calculation of local phase velocity perturbations  At each grid point of Crust2.0, we superimpose the crustal model (plus topography) onto PREM and solve for the exact eigenfrequencies in that 1D earth model.  We thus generate exact local phase velocities at each grid point which are used to calculate crustal corrections along rays.

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland A spherical harmonic expansion of the local phase velocities is used to simulate the smoothing of Crust2.0 in SEM Rayleigh, 40s Without smoothing Smoothing with spherical harmonic expansion dc/c 0

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Ray paths showing the time shifts computed for 150 s using GCA for one earthquake Time shifts from PREM+Crust2.0 – PREM seismograms Time shifts after correction (PREM+Crust2.0 - PREM+GCA) time shift (s)

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Time shifts as a function of distance calculated for 150 s using GCA (l=40) Black lines: average uncertainties of the measurements of Trampert & Woodhouse Blue bars: before correction (PREM+Crust2.0 - PREM) Red bars: after correction (PREM+Crust2.0 – PREM+GCA) dt=±5.9 s dt=±7.2 s dt=±10.6 s dt=±19.4 s dt=±22.7 s dt=±27.8 s 90% 76% 81% 89% 92% 96%

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Black lines: average uncertainties of the measurements of Trampert & Woodhouse Blue bars: before correction (PREM+Crust2.0 - PREM) Red bars: after correction (PREM+Crust2.0 – PREM+GCA) Time shifts as a function of distance calculated for 40 s using GCA (l=40) dt=±4.8 s dt=±7.2 s dt=±11.2 s dt=±17.8 s dt=±20.8 s dt=±24.8 s 59% 55% 69% 50% 62% 78%

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Oceans-continents 150 s, GCA, l=40 Blue bars: before correction (PREM+Crust2.0 - PREM) Red bars: after correction (PREM+Crust2.0 - PREM+GCA)

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Oceans-continents 40 s, GCA, l=40 Blue bars: before correction (PREM+Crust2.0 - PREM) Red bars: after correction (PREM+Crust2.0 - PREM+GCA)

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Comparison of methods (150 s, l=40) GCA vs. FFT GCA vs. ERT FFT vs. ERT GCA vs. FFT (major arc)

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Comparison of methods (40 s, l=40) GCA vs. FFT (major arc) GCA vs. ERTFFT vs. ERT GCA vs. FFT

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Conclusions  No pronounced difference between GCA, ERT or FFT corrections  Corrections at 150 sec are better than at 40 sec  Corrections get worse as distance increases  We will now check if the imperfect corrections will lead to a detectable mantle signal