  The study of quasi periodic oscillations (QPOs) plays a vital role in
understanding the nature and geometry of the Comptonizing medium around
black-hole X-ray binaries. The spectral-state dependence of various types of
QPOs (namely A, B, & C) suggests that they could have different origins. The
simultaneous presence of different types of QPOs would therefore imply the
simultaneous occurrence of different mechanisms. In this work we study the
radiative properties of two non-harmonically related QPOs in the black-hole
binary GRO J1655--40 detected at the peak of the ultraluminous state during the
2005 outburst of the source. The two QPOs have been previously identified as
types B & C, respectively. We jointly fit the phase-lag and rms spectra of the
QPOs and the time-averaged spectrum of the source with the time-dependent
Comptonization model vkompth to infer the geometry of the media producing the
QPOs. The time-averaged spectrum required a hot disk of 2.3 keV and a steep
power law with index 2.7, revealing that the source was in an ultraluminous
state. The corona that drives the variability of the type-B QPO is smaller in
size and has a lower feedback fraction than the one that drives the variability
of the type-C QPO. This suggests the simultaneous presence of a horizontally
extended corona covering the accretion disk and a vertically elongated jet-like
corona that are responsible for the type-C & B QPOs, respectively.
