1.0 Introduction

On September 29, 2009, at 6:48 am (local time) an Mw 8.0 earthquake located 190 km north of Pago Pago, American Samoa generated a tsunami. The earthquake was located at the convergence of the Pacific and Australian plates, where the Pacific plate is subducting beneath the Australia plate at the Tonga trench.

The first tsunami waves arrived in Pago Pago Harbor at approximately 7:08 am (local time), about 20 minutes after the earthquake. In the aftermath of the tsunami, 123 people died in Western Samoa and 32 in American Samoa, making this the deadliest tsunami in the Samoa Region in living history.

A reconnaissance team was mobilized to the affected region in the days that followed the earthquake and tsunami. The GEER team was assembled to investigate the geotechnical effects of both the earthquake event and the tsunami effects on the coastal environment. The team also made observations on structural engineering and lifeline aspects, although these were not the primary focus.

The GEER team was comprised of Jennifer L Donahue, PhD, PE from Geosyntec Consultants and Michael Olsen, PhD from Oregon State University. The team members were selected to provide needed expertise in geotechnical engineering, LIDAR mapping, and earthquake ground motions.

The GEER team employed a number of useful technologies to facilitate effective reconnaissance. Each team member utilized a common GPS unit and laptop with a Google Earth GIS database to track visited locations. The team also deployed with LIDAR equipment to map areas of tsunami devastation to include scour, erosion, and structural damage.

This report represents the GEER findings. Following this introduction, Chapter 2 describes the geologic and tectonic setting, moment tensor solutions for the main shock. Chapter 3 describes the LIDAR equipment and its use in mapping the tsunami effects. Chapter 4 describes the villages visited in both Western Samoa and American Samoa and the impacts of the earthquake or tsunami on each. Chapter 5 presents the geo-hazards and damage patterns found on both islands. Chapter 6 describes the effects of public education and the ensuing response in American Samoa. Chapter 7 describes the current efforts for rebuilding and reconstruction. Finally, Chapter 8 describes the GEER Reconnaissance Team.