Indonesia's most catastrophic earthquake-the 2004 M9.1-9.3 Andaman–Sumatra (or Boxing Day) megathrust earthquake and tsunami in northern Sumatra and the Andaman Sea/Nicobar Island area, which killed hundreds of thousands 1-resulted in a direct economic loss to Indonesia of about USD 4 billion, 2 with much of the damage and loss caused by the tsunami. On average, Indonesia has been hit by loss-causing earthquakes every one to two years since 1992, when the M7.8 Nusa Tenggara Timur earthquake off the north coast of Flores Island killed more than 2,500 people and caused significant property damage on Flores and Babi islands from both shaking and tsunami. Since 1970 (when earthquake reporting in the region began to improve), more than 25 earthquakes have caused significant deaths and/or losses. The high seismicity rate throughout Southeast Asia has, of course, led to frequent losses from earthquakes in Indonesia. On average, an earthquake larger than M7.5 occurred every two to three years in the last 100 to 200 years. The Southeast Asia region has produced an estimated 18 earthquakes larger than M8.0 in the last 200 years, two thirds of which have occurred since 1900 and four since the year 2000. Large dots indicate events larger than M7.0 since 1800 events larger than M8.0 since 1900 are labeled.
Active faults and historical seismicity in the Southeast Asia region. The Southeast Asia region also hosts some of the largest active crustal faults in the world, such as the Sumatra and Sula-Sorong faults. Their rapid convergence toward the Sunda plate has created volcanically and seismically active subduction zone faults-more than 9,000 km (6,600 miles) in total-along the island arcs, from western Indonesia eastward to the Philippines. The thousands of islands that make up the Republic of Indonesia are surrounded by several tectonic plates, including the Indo-Australia plate, the Pacific plate, the Philippine Sea plate, and the Sunda plate (Figure 1).
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