The crust and upper mantle in southeastern Asia is highly
heterogeneous, presenting a challenge for path calibration, but it is well
surrounded by earthquake sources, and a significant number of high quality
broadband digital stations exist.
Using a finite-frequency 2D approximation (NACT, Li and Romanowicz, 1995),
we have already developed a 3D radially anisotropic model in a large
region (longitude 30 to 150 degrees and latitude -10 to 60 degrees) from
the existing long period waveform database in the range of 60 s to 400 s.
The database was collected at Berkeley over the last 10 years
for the construction of global mantle tomographic models (Li and Romanowicz, 1996;
Megnin and Romanowicz, 2000; Gung et al., 2003; Panning and Romanowicz, 2004),
and to it are added data from 20 new events in the period up to to 2005.
A data set of 38826 3-component waveforms recorded at 169 stations from 393 events
was used in the waveform inversion.
The data have been processed with an automated algorithm, which removes glitches
and checks for many common problems related to timing, poor instrument response,
and excessively noisy windows. A weighting scheme has been applied to ensure
even distribution of data across the region. The model is parameterized
laterally in spherical spline level 6, which corresponds to lateral
resolution of km. And the corresponding radially anisotropic model
is parameterized in the spline level 5, which corresponds to a lateral resolution of km.
In this study we will use a newly developed "non-linear" 3D Born approximation (N-Born) to refine
the above NACT model (Panning et al., 2007).
Raypath coverage in the subregion. The background grey raypath coverage
is denoted for NACT and the black raypath coverage is for N-Born. Stations and events
are required to be in the large region for the N-Born inversion, and so the
N-Born raypath coverage is a subset of that of NACT.
Berkeley Seismological Laboratory
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