  We analyze the galactic cosmic ray (GCR) density and its spatial gradient in
Forbush Decreases (FDs) observed with the Global Muon Detector Network (GMDN)
and neutron monitors (NMs). By superposing the GCR density and density gradient
observed in FDs following 45 interplanetary shocks (IP-shocks), each associated
with an identified eruption on the sun, we infer the average spatial
distribution of GCRs behind IP-shocks. We find two distinct modulations of GCR
density in FDs, one in the magnetic sheath and the other in the coronal mass
ejection (CME) behind the sheath. The density modulation in the sheath is
dominant in the western flank of the shock, while the modulation in the CME
ejecta stands out in the eastern flank. This east-west asymmetry is more
prominent in GMDN data responding to $\sim$ 60 GV GCRs than in NM data
responding to $\sim$ 10 GV GCRs, because of softer rigidity spectrum of the
modulation in the CME ejecta than in the sheath. The GSE-y component of the
density gradient, $G_y$ shows a negative (positive) enhancement in FDs caused
by the eastern (western) eruptions, while $G_z$ shows a negative (positive)
enhancement in FDs by the northern (southern) eruptions. This implies the GCR
density minimum being located behind the central flank of IP-shock and
propagating radially outward from location of the solar eruption. We also
confirmed the average $G_z$ changing its sign above and below the heliospheric
current sheet, in accord with the prediction of the drift model for the
large-scale GCR transport in the heliosphere.
