Nuku'alofa [Tonga] An earthquake measuring 6.4 on the Richter scale struck the Tonga Islands on Monday, according to the National Center for Seismology (NCS). The earthquake occurred at 02:17 Indian Standard Time (IST) and was an earthquake. Depth of 110 kilometers. : Tonga Islands. No casualties have been reported yet. Tonga is part of Oceania and consists of 176 islands, 36 of which are located south of Samoa, southeast of Fiji and New Zealand, according to the United Nations.