Two large and shallow earthquakes struck off Indonesia’s Sumatra island early Wednesday, the U.S. Geological Survey reported, but no tsunami warning was issued. The quakes, of magnitude 6.8 and 6.9, struck within six minutes of one another from 5:23 a.m. (22:23 GMT Tuesday).  The Indian Ocean Tsunami Warning and Mitigation System said there was “no threat to countries in the Indian Ocean.” There was a “low likelihood of casualties and damage,” the USGS added. The Southeast Asian archipelago experiences frequent seismic and volcanic activity due to its position on the Pacific “Ring of Fire,” where tectonic plates collide. In 2018, a 7.5-magnitude quake and subsequent tsunami on Sulawesi island left more than 4,300 people dead or missing. A devastating 9.1-magnitude quake struck off the coast of Sumatra in 2004, triggering a tsunami that killed 220,000 throughout the region, including around 170,000 in Indonesia.