(Adds Indonesia withdraws tsunami alert)
JAKARTA, Oct 25 (Reuters) - A powerful earthquake with a magnitude of up to 7.5 under the ocean off Indonesia's Sumatra island on Monday sparked initial tsunami warnings, but the Indonesian earthquake agency later withdrew the alert.
There were no immediate reports of any damage or casualties from the quake, which the earthquake agency measured at 7.2, followed by two aftershocks of magnitude 5.
The agency said the quake hit 78 km (48 miles) west of South Pagai, one of the remote and sparsely developed Mentawai islands, at a depth of 10 km.
The U.S. Geological Survey measured the quake at 7.5, and the Pacific Tsunami Warning Center said a local tsunami watch was in effect but a wider tsunami threat was not seen.
In December 2004, a tsunami caused by an earthquake of more than 9 magnitude off Sumatra killed more than 226,000 people. It was the deadliest tsunami on record.
(Reporting by Telly Nathalia, editing by Andrew Marshall and Michael Roddy)
Our Standards: The Thomson Reuters Trust Principles.
