  We analyze flare-associated transverse oscillations in a quiescent solar
prominence on 8-9 September, 2010. Both the flaring active region and the
prominence were located near the West limb, with a favorable configuration and
viewing angle. The fulldisk extreme ultraviolet (EUV) images of the Sun
obtained with high spatial and temporal resolution by the Atmospheric Imaging
Assembly (AIA) aboard the Solar Dynamics Observatory, show flare-associated
lateral oscillations of the prominence sheet. The STEREO-A spacecraft, 81.5
degrees ahead of the Sun-Earth line, provides on-disk view of the
flare-associated coronal disturbances. We derive the temporal profile of the
lateral displacement of the prominence sheet by using the image
cross-correlation technique. The displacement curve was de-trended and the
residual oscillatory pattern was derived. We fit these oscillations with a
damped cosine function with a variable period and find that the period is
increasing. The initial oscillation period (P0) is 28.2 minutes and the damping
time (t_D) of 44 minutes. We confirm the presence of fast and slow EUV wave
components. Using STEREO-A observations we derive a propagation speed of 250
km/s for the slow EUV wave by applying time-slice technique to the running
difference images. We propose that the prominence oscillations are excited by
the fast EUV wave while the increase in oscillation period of the prominence is
an apparent effect, related to a phase change due to the slow EUV wave acting
as a secondary trigger. We discuss implications of the dual trigger effect for
coronal prominence seismology and scaling law studies of damping mechanisms.
