Indonesia stays alert for possible tsunami waves after a 7.3-magnitude earthquake hit the Molucca Sea at 10:31 a.m. Saturday. The quake struck 155 km northwest of Kota Ternate at a depth of 35 km.

An hour later, a 4.8-magnitude quake followed near the same area.

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An official from Indonesia's meteorological agency said they have issued an early tsunami warning.

Earthquakes with magnitudes greater than 4.5 can generate secondary shockwaves which can do additional damage. These waves may occur hours, days, weeks or months after the main quake.

Although warnings said that "the initial wave may not be the largest", the waves could last for hours and may cause additional damages.

The Global Disaster Alert and Coordination System(GDACS)  issued a Green Earthquake Alert which means that the quake can have a low humanitarian impact.

Half an hour later, a 5.9-magnitude earthquake struck 60 km south of Molibagu. More than an hour later, a 4.3-magnitude quake occured 111km northwest of Tobelo and a 4.7-magnitude 138km east of northeast of Bitung.

No casualties were reported so far but officials say a possible tsunami could affect parts of other countries such as the Philippines, Palau, Japan, Taiwan and Papua New Guinea, where a 6.6-magnitude quake recently hit.

Indonesia is located within the The Pacific Ring of Fire. This is an area where earthquakes and volcanic eruptions frequently occur. Other countries that suffer from hazardous earthquakes are the Philippines and Japan.

The actual movement of the ground is not the usual cause of earthquake casualties. The usual causes are falling debris and weak building constructions. The quake may also cause fires and landslides to occur.

In 2004, a 9.0-magnitude quake hit the Indian Ocean near the the island of Sumatra. It sent powerful shock waves in every direction. The energy released was estimated to have been equal to 23, 000 Hiroshima-type atomic bombs.

More than 100,000 people died and the killer waves were described to be the most destructive in history.

TagsIndonesia, Tsunami, earthquake