  In the quantum Zeno effect, quantum measurements can block the coherent
oscillation of a two level system by freezing its state to one of the
measurement eigenstates. The effect is conventionally controlled by the
measurement frequency. Here we study the development of the Zeno regime as a
function of the measurement strength for a continuous partial measurement. We
show that the onset of the Zeno regime is marked by a $\textit{cascade of
transitions}$ in the system dynamics as the measurement strength is increased.
Some of these transitions are only apparent in the collective behavior of
individual quantum trajectories and are invisible to the average dynamics. They
include the appearance of a region of dynamically inaccessible states and of
singularities in the steady-state probability distribution of states. These
newly predicted dynamical features, which can be readily observed in current
experiments, show the coexistence of fundamentally unpredictable quantum jumps
with those continuously monitored and reverted in recent experiments.
