AbstractA tsunami is a set of ocean waves caused by any large, abrupt disturbance of the sea surface (NOAA, 2007). A very large disturbance can cause local devastation and export tsunami destruction even to thousands of miles away.Predicting when and where the next tsunami will strike are impossible, but once the tsunami is generated, forecasting tsunami arrival and impact is possible through modeling and measurement technologies.The recent development of real-time deep ocean tsunami detectors and tsunami inundation models has given coastal communities the means to reduce the impact of future tsunamis.1. IntroductionThe word tsunami is a Japanese word, represented by two characters: tsu, meaning, “harbor”, and nami meaning, “wave”.In the past, tsunamis were often incorrectly referred to as “tidal waves” by many people. Tsunamis, however, are not caused by the tides nor are related to the tides; although a tsunami striking a coastal area is influenced by the tide level at the time of impact. Tides are the result of gravitational influences of the moon, sun, and planets (NOAA, 2007).A tsunami is a set of ocean waves caused by any large, abrupt disturbance of the sea surface (NOAA, 2007). A very large disturbance can cause local devastation and export tsunami destruction even to thousands of miles away. If the disturbance is close to the coastline, however, local tsunamis can demolish coastal communities within minutes. Predicting when and where the next tsunami will strike are impossible, but once the tsunami is generated, forecasting tsunami arrival and impact is possible through modeling and measurement technologies.1.1 ObjectivesThis study primarily aims to identify the root of tsunamis and how they are formed. Due to the fact that tsunamis cannot be predicted nor prevented, it is important that precautionary measures are taken to enable swift evacuation of coastal areas.This study also examines the possible methods for detecting the arrival of tsunamis using modern technology and determines, whether or not, these equipment are effective and useful. Studies on the possibility of predicting the onset of tsunamis are also scrutinized.1.2 Scope and LimitationThe information obtained in this experiment is obtained from evaluations of past tsunami disasters; these evaluations were made weeks and even months since the disaster, and so the information obtained may have discrepancies compared to what really happened in when the disaster struck.2. Review of Related Literature
2.1. Generation of TsunamisA tsunami is a series of waves with very long wave lengths and long periods that are generated in a body of water by a disturbance that displaces the water. A tsunami can be generated by any disturbance that displaces a large water mass from its equilibrium position. Tsunamis are primarily associated with earthquakes in oceanic and coastal regions, landslides, volcanic eruptions, nuclear explosions, and even impacts of objects from outer space like meteorites, asteroids, and comets (Ward & Asphaug, 1999; Ward, 2000; Watts, 2000; NOAA, 2007).Earthquakes generate tsunamis when the sea floor abruptly deforms and displaces the water above it from its equilibrium position. Waves are formed as the displaced water, which acts under the influence of gravity, attempts to regain its equilibrium. The main factor which determines the initial size of a tsunami is the amount of vertical sea floor deformation, which is controlled by the earthquake’s magnitude, depth, fault characteristics and coincident slumping of sediments or secondary faulting. Other factors that influence the size of a tsunami along the coast are the shoreline, the velocity of the sea floor deformation, the water depth near the earthquake source, and the efficiency which energy is transferred from the earth’s crust to the water column (NOAA, 2007).When a tsunami finally reaches the coastline, it may appear as a rapidly rising or falling tide or a series of breaking waves. Reefs, bays, entrances to rivers, undersea features and the slope of the beach all help to modify the height of the tsunami as it approaches the shore. Tsunamis rarely become great, towering breaking waves, as they sometimes break far offshore, or they may form into a bore: a step-like wave with a steep breaking front.A bore can happen if the tsunami moves from deep water into a shallow bay or river. The water level on shore can rise many feet, and in extreme cases, water level can rise to more than 50 feet (15 m) for tsunamis of distant origin and over 100 feet (30 m) for tsunami generated near the earthquake’s epicenter. Tsunamis may reach a maximum vertical height onshore above sea level, called a run-up height, of 30 meters (98 ft) (Borrero, 2004; NOAA, 2007).2.1.1. Earthquake-generated tsunamisEarthquakes are the most common cause for tsunamis. Earthquakes occur whenever one of the many tectonic plates that make up the Earth’s crust subducts under an adjacent plate; this newly formed area is then called the “subduction zone”. The overriding plate then gets squeezed as its leading edge is dragged down while the area behind it swells upward, building stress for over long periods of time.After decades, or even centuries of built up stress, an earthquake finally occurs along the subduction zone, because the leading edge of the overriding plate eventually breaks free from the subducting plate. This movement then raises the sea floor and displaces a great mass of seawater upwards, while also relieving the tension as the rest of the overriding plate collapses, thereby the lowering the coastal areas (Atwater et al 2005).2.1.2. Landslide-generated tsunamisSubmarine landslides, which often occur alongside a large earthquake, can sometimes also create a tsunami. The tsunami created are often termed “surprise tsunami” and can be initiated far outside the epicenter of an associated earthquake or be greater than predicted as according to the magnitude of the earthquake.During a submarine landslide, the equilibrium sea-level is distorted by sediment moving along the sea-floor. Gravitational forces then propagate the tsunami given the initial disturbance of the sea-level. What makes this cause for a tsunami dangerous is that it arrives without any precursory seismic warning at all (Ward & Asphaug, 1999; Ward, 2000; Watts, 2000; NOAA, 2007).2.1.3. Tsunamis generated from volcanic eruptions