People in Indonesia and Thailand gathered on Thursday to mark the 15th anniversary of the Indian Ocean tsunami.The tsunami hit on December 26, 2004.It was caused by a massive 9.1 earthquake off Indonesia's Sumatra island.The huge ocean wave killed about 230,000 people in countries across the Indian Ocean.It was one of the worst natural disasters in modern history.The hardest hit nation was Indonesia, where more than 170,000 people died.Thousands of people gathered Thursday in Indonesia's Aceh province to remember the victims.The governor of the area, Nova Iriansyah, spoke at a ceremony in the town of Sigli.He said no words could describe the feelings people experiencedafter seeing the widespread death and destruction that the tsunami caused.He added: "And now, we can see how people in Aceh were able to overcome suffering and rise again,thanks to assistance from all Indonesians and from people all over the world."Whole villages across Aceh were flattened by the powerful ocean wave.In the years since, the area has been largely rebuilt.About 25,600 buildings – including homes, businesses, government officesand schools – have been built in areas that were mostly destroyed in 2004.Others in Aceh attended memorial ceremonies or religious services.Family members of the dead and religious and community leadersalso presented flowers at mass graves in the capital, Banda Aceh.In Thailand, more than 8,000 people died or went missing in the disaster, including foreign visitors.On Thursday, hundreds of people attended a tsunami memorial ceremonyin the fishing village of Ban Nam Khem, in Phang Nga province.The village lost about half of its population when the tsunami hit.Western visitors and community members attended the ceremony and viewed a collection of victims' photos.A Thai woman handed over an offering of food for Buddhist monks leading the event.Suwannee Maliwan lost both parents and five other family members when the tsunami hit the area."It still haunts me," she told Reuters news agency. "I can remember it all the time."Suwannee added: "Sometimes I dream that a wave is coming. I'm still scared.Sometimes I want to move somewhere else, but it's not possiblebecause I was born here, my mom and dad passed away here."The tourism industry on the popular vacation island of Phuket was crushed by the disaster.But the industry was quickly built back up. It has even grown much larger than it was before.Thai officials used the anniversary to call for more efforts aimed at preventing future disasters.The country's deputy interior minister, Nipon Bunyamanee,said the government "wants to lift safety standards... and build awarenessacross all sectors in preparing and protecting people against disasters."He said December 26 had been declared national accident prevention day.