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SPECFEM / specfem2d

SPECFEM2D simulates forward and adjoint seismic wave propagation in two-dimensional acoustic, (an)elastic, poroelastic or coupled acoustic-(an)elastic-poroelastic media, with Convolution PML absorbing conditions.
https://specfem.org
GNU General Public License v3.0
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Correction for 2D calculation and the 3D wavefield #1091

Open pasansherath opened 3 years ago

pasansherath commented 3 years ago

Hi,

This is a general question rather than an issue in SPECFEM2D.

I was reading a paper that used a finite difference method to calculate synthetic seismograms (Ohira et al 2017). The authors there say that they applied a correction (division by offset^0.5) to the synthetic seismograms to correct for the difference of geometrical effects for the 2D calculation and the actual 3D wavefield. Is this applicable to SPECFEM2D as well?

Thanks very much.

Pasan

Ohira, A., Kodaira, S., Nakamura, Y., Fujie, G., Arai, R., & Miura, S. (2017). Evidence for frozen melts in the mid-lithosphere detected from active-source seismic data. Sci Rep, 7(1), 15770. https://doi.org/10.1038/s41598-017-16047-4

Mau-dvr75 commented 2 years ago

Hi. The "real" Earth is a 3D medium and specfem2D simulates wave propagation in 2D. In 3D a simple source may be seen as a point source while 2D a simple source may be seen as "line source" because of the one invariant direction. Of course there is a difference between geometrical spreading considering 2D vs 3D, so you have to apply a geometrical and phase correction to your 3D data in order to "transform it" to 2D data. There are several kinds of corrections that gives good results, as the one you mention in the cited paper.