  We present best-fit values of porosity -- and the corresponding effective
thermal inertiae -- determined from three different depths in Europa's
near-subsurface (~1-20 cm). The porosity of the upper ~20 cm of Europa's
subsurface varies between 75-50% ($\Gamma_{eff}\approx50-140$ J m$^{-2}$
K$^{-1}$ s$^{-1/2}$) on the leading hemisphere and 50-40%
($\Gamma_{eff}\approx140-180$ J m$^{-2}$ K$^{-1}$ s$^{-1/2}$) on the trailing
hemisphere. Residual maps produced by comparison with these models reveal
thermally anomalous features that cannot be reproduced by globally homogeneous
porosity models. These regions are compared to Europa's surface terrain and
known compositional variations. We find that some instances of warm thermal
anomalies are co-located with known geographical or compositional features on
both the leading and trailing hemisphere; cool temperature anomalies are well
correlated with surfaces previously observed to contain pure, crystalline water
ice and the expansive rays of Pwyll crater. Anomalous regions correspond to
locations with subsurface properties different from those of our best-fit
models, such as potentially elevated thermal inertia, decreased emissivity, or
more porous regolith. We also find that ALMA observations at ~3 mm sound below
the thermal skin depth of Europa (~10-15 cm) for a range of porosity values,
and thus do not exhibit features indicative of diurnal variability or residuals
similar to other frequency bands. Future observations of Europa at higher
angular resolution may reveal additional locations of variable subsurface
thermophysical properties, while those at other wavelengths will inform our
understanding of the regolith compaction length and the effects of external
processes on the shallow subsurface.
