[Arrual (OP)]

Is it possible to have an earthquake that could effect the nation even global??

[CliffordK]

It might depend on the size of the nation.  Does Luxemburg or San Marino get earthquakes?  I believe the quakes dissipate on land over a few hundred miles. 

To some extent, countries around the Pacific swap Tsunami waves.  So, while the shaking of an Earthquake decreases quickly, the effects of the Tsunami can be felt at quite a distance.

The 1964 Alaska Quake caused a Tsunami that killed several people in both Oregon and California, quite some distance from the epicenter.  Waves were recorded in Hawaii and Japan, although minimal in Japan. 

Oregon and Washington have an interesting phenomenon in that they lie on the quietest part of the Pacific Ring of Fire.  The current theory is that Earthquakes do occur with a periodicity of 300 to 900 years, and every Earthquake may be a 9+ Earthquake.  The last one to hit the region was just over 300 years ago, and the next one could break all the "rules".  If the entire subduction zone of the Juan De Fuca plate (Cascadia subduction zone) is affected, then an area from Southwest Canada to Northern California could feel the effects. 

The 2004 Indian Ocean Quake had a fault rupture that was about 250 miles (400 km) long.

Not an ordinary quake, but a large meteor impact could have global effects, and the Theia Impact Theory is that essentially the entire Earth's surface became liquefied with the impact.

[evan_au]

There are several slumbering "supervolcanoes" around the world; if one of these exploded, the ash could cause severe damage at national and worldwide scales. A well-known one with a track record of large eruptions lies under Yellowstone National Park in the USA.

There is a theory that one such eruption at Toba (Indonesia) may have killed as much as 60% of the world's human population at that time.