Introduction to the Special Issue on the 2004 Sumatra–Andaman Earthquake and the Indian Ocean Tsunami

The great Sumatra–Andaman earthquake of 26 December 2004 (UTC 00:58:53) was a momentous event, whether measured by scientific or human standards. Sadly, what is currently regarded as the third largest earthquake in recorded history led to the worst tsunami disaster in recorded history, with the loss of more than 200,000 lives and devastation throughout the Bay of Bengal. About three months later, on 28 March 2005, the Nias–Simeulue earthquake, near the southern end of the 2004 rupture, shocked the region again. Fortunately, this Mw 8.7 earthquake, the second largest earthquake in the past decade, was less destructive. These earthquakes and resulting tsunamis have been a sobering reminder to many in the community of earthquake scientists that the subject of our professional lives can have enormous impact on humanity. Hopefully, the legacy of the science presented in this volume will be a greater understanding of earthquake and tsunami processes that will be useful in advancing the resilience of our communities to Nature’s violence. The 2004 and 2005 earthquakes and tsunami revealed much that we did not know about great subduction zone events. Both the length of the 2004 rupture (perhaps as great as 1600 km) and its duration (upward of 600 sec) exceeded any previously recorded. Although the issue of whether the 2005 earthquake was an aftershock or triggered by the 2004 earthquake is currently debated, the 2005 earthquake was a significant event that may rank as one of the largest aftershocks ever recorded. The 2004 rupture extended through sections of the Sunda megathrust that had ruptured separately in earlier large earthquakes. The limited historical records and tectonic characteristics of this section of the megathrust had led many of us to believe that it was incapable of producing a giant earthquake. Nonetheless, such unanticipated natural events often lead to unanticipated advances in human knowledge. Fortunately, advances in geophysical instrumentation and field techniques made these the bestrecorded great earthquakes and tsunami in history and set the stage for the work represented here. The articles in this volume embody key aspects of the current state of knowledge about earthquakes and tsunamis. Topics include determinations of the spatial extent and evolution of the 2004 and 2005 ruptures from seismographic, geodetic, tsunami, and field observations, catalogs of previous and subsequent regional seismic activity, and evidence for previous tsunamis and deformation. Although the 2004 Sumatra–Andaman earthquake is the best-recorded great earthquake in history, its analysis posed many challenges, as many standard techniques proved inadequate to deal with such a giant event. Hence, this issue contains articles that present new techniques and unique datasets used and developed for this particular earthquake.