  Gamma radiation from the Crab pulsar wind nebula (PWN) shows significant
variability at $\sim100$ MeV energies, recently revealed with spaceborne
gamma-ray telescopes. Here we report the results of a systematic search for
gamma-ray flares using a 7.4-year data set acquired with the Fermi Large Area
Telescope. Analyzing the off-pulse phases of the Crab pulsar, we found seven
previously unreported low-intensity flares ("small flares"). The "small
flares'' originate from the variable synchrotron component of the Crab PWN and
show clearly different features from the steady component of the Crab PWN
emission. They are characterized by larger fluxes and harder photon indices,
similar to previously reported flares. These flares show day-scale time
variability and imply a strong magnetic field of $B_{\rm min}\approx
1~\mathrm{mG}$ at the site of the gamma-ray production. This result seems to be
inconsistent with the typical values revealed with modeling of the non-thermal
emission from the nebula. The detection of the "small flares'' gives a hint of
production of gamma rays above $100$ MeV in a part of the nebula with
properties which are different from the main emitters, e.g., due to bulk
relativistic motion.
