  Motivated by the question of how to distinguish seismically between
monolithic and cluster models of sunspots, we have simulated the propagation of
an $f$-mode wave packet through two identical small magnetic flux tubes (R=200
km), embedded in a stratified atmosphere. We want to study the effect of
separation $d$ and incidence angle $\chi$ on the scattered wave. We have
demonstrated that the horizontal compact pair of tubes ($d/R=2$, $\chi=0$)
oscillate as a single tube when the incident wave is propagating, which gives a
scattered wave amplitude of about twice that from a single tube. The scattered
amplitude decreases with increasing $d$ when $d$ is about $\lambda/2\pi$ where
$\lambda$ is the wavelength of the incident wave packet. In this case the
individual tubes start to oscillate separately in the manner of near-field
scattering. When $d$ is about twice of $\lambda/2\pi$, scattering from
individual tubes reaches the far-field regime, giving rise to coherent
scattering with an amplitude similar to the case of the compact pair of tubes.
For perpendicular incidence ($\chi=\pi/2$), the tubes oscillate simultaneously
with the incident wave packet. Moreover, simulations show that a compact
cluster oscillates almost as a single individual small tube and acts more like
a scattering object, while a loose cluster shows multiple-scattering in the
near-field and the absorption is largest when $d$ within the cluster is about
$\lambda/2\pi$. This is the first step to understand the seismic response of a
bundle of magnetic flux tubes in the context of sunspot and plage
helioseismology.
