  The impact of interplanetary (IP) shocks on the Earth's magnetosphere can
greatly disturb the geomagnetic field and electric currents in the
magnetosphere-ionosphere system. At high latitudes, the current systems most
affected by the shocks are the auroral electrojet currents. These currents then
generate ground geomagnetically induced currents (GICs) that couple with and
are highly detrimental to ground artificial conductors including power
transmission lines, oil/gas pipelines, railways, and submarine cables. Recent
research has shown that the shock impact angle, the angle the shock normal
vector performs with the Sun-Earth line, plays a major role in controlling the
subsequent geomagnetic activity. More specifically, due to more symmetric
magnetospheric compressions, nearly frontal shocks are usually more
geoeffective than highly inclined shocks. In this study, we utilize a subset
(332 events) of a shock list with more than 600 events to investigate, for the
first time, shock impact angle effects on the subsequent GICs right after shock
impact (compression effects) and several minutes after shock impact
(substorm-like effects). We use GIC recordings from the Finnish natural gas
pipeline performed near the M\"ants\"al\"a compression station in southern
Finland. We find that GIC peaks (> 5 A) occurring after shock impacts are
mostly caused by nearly frontal shocks and occur in the post-noon/dusk magnetic
local time sector. These GIC peaks are presumably triggered by partial ring
current intensifications in the dusk sector. On the other hand, more intense
GIC peaks (> 20 A) generally occur several minutes after shock impacts and are
located around the magnetic midnight terminator. These GIC peaks are most
likely caused by intense energetic particle injections from the magnetotail
which frequently occur during substorms.
