A strong earthquake hit southern Greece on Valentine's Day about 140 miles southwest of Athens. The epicenter was under the sea, west of the Peloponnese peninsula in southern Greece. The depth of tremor was estimated to be nearly 20 miles beneath the earth's surface, which helped minimize damage. Strong earthquakes are common in Greece because the country lies in one of the world's most active earthquake zones, between Europe and Africa. An earthquake killed 143 persons in Athens in September, 1999.