Tsunami causes devastation near the coast of the sea as the speed of the sonic waves generated at the epicentre is

Tsunamis are categorized as long-period shallow-water waves because their wavelength is significantly greater than the ocean depth [t2, t6]. The speed of a tsunami wave is mathematically defined by the formula v = ∑(g!! d), where 'g' is the acceleration due to gravity and 'd' is the water depth [t2, t7]. Consequently, the speed of the wave is directly proportional to the depth of the sea; it travels faster in deep oceans (up to 800-1000 km/h) and slows down as it approaches shallow coastal waters [c1, c3, t1]. As the wave slows down near the coast, its energy is conserved by increasing its amplitude (height), a process known as the shoaling effect, which leads to coastal devastation [c2, c5, t6]. The distance from the epicentre affects arrival time but does not define the inherent speed-depth relationship [t2, t8].

Sources

1. [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 8: Natural Hazards and Disaster Management > Characteristics of Tsunami Waves > p. 33
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 15: Tsunami > Propagation of The Waves > p. 191
3. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 15: Tsunami > Normal Waves vs Tsunami Waves > p. 192
4. [4] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 15: Tsunami > Normal Waves vs Tsunami Waves > p. 193
5. [5] http://www.maine.gov/mema/maine-prepares/preparedness-library/tsunami-wave-mechanics
6. [6] https://www.ncei.noaa.gov/products/natural-hazards/tsunamis-earthquakes-volcanoes/tsunamis/travel-time-maps