  We present an observational analysis of numerical simulations of galaxy
cluster mergers. We identify several observational signatures of recent merger
activity, and quantitatively assess the uncertainty introduced into cluster
mass estimates when invoking the commonly held assumptions of hydrostatic
equilibrium, virial equilibrium, spherical symmetry and isothermality. We find
that mergers result in multiple X-ray peaks, long-lived elongation of the X-ray
emission as well as isophotal twisting and centroid shifting to a degree
consistent with recent observations. We also find an enlargement of the X-ray
core relative to the dark matter core. Mergers result in non-isothermal
clusters exhibiting observable inhomogeneities in the emission-weighted X-ray
temperature of several keV on linear scales of less than 0.5 Mpc. The resulting
gas dynamics are extremely complex, and we present an example of what might be
observed by a high resolution X-ray spectrograph. We further speculate that the
gas dynamics, via shocks, bulk flows and turbulence, play an important role in
the evolution of cluster galaxies and associated radio sources, particularly
wide-angle tailed (WAT) sources and radio halos. We find that X-ray based by
cluster mass estimates made under equilibrium assumptions can be uncertain 50\%
or more in the first 2 Gyrs after a merger and by up to 25\% after 2 Gyrs
depending on the details of the analysis and projection effects. Uncertainties
can be considerably larger if the temperature is not well constrained.
