  We follow the eruption of two related intermediate filaments observed in
H$\alpha$ (from GONG) and in EUV (from SDO/AIA) and the resulting
large-amplitude longitudinal oscillations of the plasma in the filament
channels. The events occurred in and around the decayed active region AR12486
on 2016 January 26. Our detailed study of the oscillation reveals that the
periods of the oscillations are about one hour. In H$\alpha$ the period
decreases with time and exhibits strong damping. The analysis of 171~\AA\
images shows that the oscillation has two phases, an initial long period phase
and a subsequent oscillation with a shorter period. In this wavelength the
damping appears weaker than in H$\alpha$. The velocity is the largest ever
detected in a prominence oscillation, approximately 100 $\mathrm{\, km \,
s^{-1}}$. Using SDO/HMI magnetograms we reconstruct the magnetic field of the
filaments modeled as flux ropes by using a flux-rope insertion method. Applying
seismological techniques we determine that the radii of curvature of the field
lines in which cool plasma is condensed are in the range 75-120~Mm, in
agreement with the reconstructed field. In addition, we infer a field strength
of $\ge7$ to 30 gauss, depending on the electron density assumed; that is also
in agreement with the values from the reconstruction (8-20 gauss). The poloidal
flux is zero and the axis flux is of the order of 10$^{20}$ to 10$^{21}$ Mx,
confirming the high shear existing even in a non-active filament.
