Internationales Qualitäts-Netz: GeorisikenSPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
Seismic wave Propagation and Imaging in Complex media: a European network
EBRU BOZDA
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
compared to measured time shifts
from SEM seismograms using Crust2.0
Ebru Bozda
Jeannot Trampert
SPICE
www.spice-rtn.org
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.
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SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
The objective
predict crustal corrections using the SEM (Komatitsch and Tromp, 2002) seismograms computed in 1D (PREM) and 3D (PREM+Crust2.0) earth models.
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SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
Data generation
Earthquakes & Stations
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
CMA
SEP
CRT
XZNG
WIA
SOA
NCN
IJR
SIR
IJR
VIC
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SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
Measuring time shifts as a function of frequency
Cross-correlation
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
Methods used for crustal corrections
Great Circle Approximation (GCA)
Exact Ray Theory (ERT)
Finite Frequency Theory (FFT)
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.
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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
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
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
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
Black lines: average uncertainties of the measurements of
Trampert & Woodhouse
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
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
Oceans-continents
Blue bars: before correction
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
Oceans-continents
Blue bars: before correction
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
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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. ERT
FFT vs. ERT
GCA vs. FFT
SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland
Conclusions
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
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