ABSTRACT:

This paper examines the potential impacts of tsunamis to the infrastructure and operations at Apra Harbor, Guam. An assessment of plate tectonics and historical records indicates that destructive tsunamis to Apra Harbor will likely originate from the Mariana, Philippine, and Japan subduction zones. Numerical modeling of tsunamis from 100-year earthquakes at these three source regions show inundation of the low lying eastern shores of the inner and outer harbors as well as coupled oscillations and a hydraulic jump between the two harbor basins. High velocity flows may persist at the commercial port and the outer and inner harbor entrances due to resonance.

INTRODUCTION

Guam lies at the southern end of the Mariana Island chain in the western Pacific. The island is approximately 50 km long and 6 to 14 km wide covering an area of 540 sq km. Apra Harbor on the western side is the only deep-water port on the island and a vital transportation hub in the region. The aerial photo in Figure 1 shows the layout of the harbor and the vicinity. The entrance is approximately 0.7 km wide. The outer harbor, which is 6 km by 2 km, is surrounded by the Orote Peninsula to the southwest and Cabras Island and Glass Breakwater to the north. The north side of the outer harbor is home to the commercial port, which handles 90% of the import to Guam. The 2 km by 1.3 km inner harbor is the location of Naval Base Guam. Shallow reefs are visible along most of the coastlines and in the outer harbor from the aerial photo. Guam's location near active subduction zones makes it susceptible to earthquake-related hazards. The waves reached 1.8 m elevation at the shore washing cars into the ocean.

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