Science of Tsunami Hazards (May 2022)
EVALUATION OF TSUNAMI SOURCE MECHANISMS ALONG THE TONGA TRENCH AND VOLCANIC ARC – Case Study: Earthquake and Tsunami of 29 September 2009
Abstract
The present report provides an evaluation of the tectonics of the upper part of the Tonga Trench and Volcanic Arc Region. The overall tectonics of the region are dominated by the convergence of the Pacific and Australia plates. The active westward movement of the Pacific oceanic lithosphere underneath the Australian plate has formed an extensive tectonic boundary. The boundary consists of the Tonga-Kermadec Subduction Zone, marked by a great trench and its associated adjacent volcanic arc. The eastern edge of the Australia plate is a collection of smaller micro-plates that move with respect to each other, and with the Pacific plate and the interior of the Australia plate. Many earthquakes along the boundaries of these tectonic boundaries have generated relatively small tsunamis. However, on 29 September 2009 a major 8.3 Richter magnitude earthquake near the upper segment of the Tonga trench generated an unusually destructive tsunami. Large waves struck coastal villages and towns in Samoa, American Samoa and the island Kingdom of Tonga, causing extreme damage and many deaths at Pago Pago harbor, the village of Leone and elsewhere. The destruction by this particular event was unprecedented. A tsunami warning issued by the Pacific Tsunami Warning Center did not reach the affected region in time for people to evacuate. The following report documents the tectonics of subduction along the northern segment the Tonga Trench and Volcanic Arc, the source mechanism of the 2009 tsunami, and a brief history of past events. Furthermore, and in view of the tsunami generated by the 15 January 2022 eruption/explosion of the submarine volcano Hunga-Tonga-Hunga-Ha'apai near Tonga, the present report provides a preliminary evaluation of stresses along a cross-section in the middle segment of the Tonga trench from Pacific plate subduction along the spreading center of Lau Basin, for a report under preparation pertaining to tsunami generation mechanisms along the adjacent volcanic arc.
