Acehtsunami

Earthquake with a preliminary magnitude of 5.7 strike the Caribbean island of Puerto Rico early Sunday, the U.S. Geological Survey said.

The quake hit at 1:16 a.m. (0516 GMT) four miles (six kilometers) from the small community of Espino on the western part of the island and 63 miles (101 kilometers) from the capital, San Juan. It was recorded at a depth of 68 miles (110 kilometers).

There were no immediate reports of damage and injuries.

The West Coast and Alaska Tsunami Warning Center said it did not guess a tsunami, but local tsunamis triggered by underwater landslides were possible in coastal areas close to the epicenter.

Tsunamis are different from wind-generated waves, which many of us may have observed on a local lake or at a coastal beach, in that they are characterized as shallow-water waves, with long periods and wave lengths.The wind-generated swell one sees at a California beach, for example, seeded by a storm out in the Pacific and rhythmically rolling in, one wave after another, might have a period of about 10 seconds and a wave length of 150 m.

A tsunami, on the other hand, can comprise a wavelength in excess of 100 km and period on the order of one hour.

As a result of their long wave lengths, tsunamis usually behave as shallow-water waves.A wave becomes a shallow-water wave when the ratio between the water depth and its wave length gets very less.Shallow-water waves travel at a speed that is equal to the square root of the product of the acceleration of gravity (9.8 m/s/s) and the water depth.

If the first part of a tsunami to reach land is a trough known as drawback, rather than a wave crest. The water along the shoreline recedes dramatically, exposing usually submerged areas.

A drawback generally occurs because the tectonic plate on one side of the fault sinks suddenly during the earthquake, causing the overlaying water to propagate outwards with the trough of the wave at its front. This is why there would not be any drawback when the tsunami traveling on the other side arrives ashore, as the tectonic plate is “raised” on that side of the fault line.

Drawback starts to begin before the wave arrives at an interval equal to half of the wave’s period. If the slope of the coastal seabed is small, drawback can exceed about hundreds of meters. People who are unaware of the danger sometimes remain near the shore to satisfy their curiosity or to collect fish from the exposed seabed. During the Indian Ocean tsunami, the sea withdrew and a number of people went onto the exposed sea bed to investigate. Photos show people walking on the normally submerged areas with the advancing wave in their background.

Coastal areas in India are extensive and support some of the most diverse and valuable coastal resources. These rich coastal biodiversity and their invaluable support to multiple uses of human activities for many centuries present a challenge to managers/planners and developers of these areas in the many ways these areas are conserved and developed.

The richness of biodiversity, the large variation in the types of coastal zones within a state, varied human populations and diverse regional economies among regions within states are some of the main reasons why the Coastal Regulation Zone (CRZ) notification of 1991 came into play.

While acknowledging the difficulties in implementing the regulations and the need to develop a better and more robust notification, the Ministry of Environment and Forests (MoEF) has announced a draft ‘Coastal Management Zone Notification, 2008’ that would come into force after considering comments and oppositions, received by June 30, 2008. It is envisaged that the new notification would replace the 1991 CRZ notification and contain various plans on how coastal areas will be managed.

The stated objective of the proposed Costal Management Zone (CMZ) notification of 2008 is “protection and sustainable development of the coastal stretches and marine environment through sustainable coastal zone management practices based on sound scientific principles taking into account the vulnerability of the coast to natural hazards, sustainable livelihood security for local communities, and conservation of ecologically and culturally significant coastal resources.”

While addressing this, it is important to remember coastal systems extend beyond jurisdictional boundaries and are affected by local users and decisions made by different levels of government. The management of coastal systems thus requires many agencies, at different levels to be involved. The system is highly interconnected and no single agency has the necessary controls.

We would like to initiate a discussion amongst members of the Water and Disaster Management Communities and invite recommendations and suggestions on providing sensible and scientifically valid solutions for managing various conflicting interests in coastal areas and on regulatory mechanisms.

Keeping this in mind, members could begin by considering the implications on the following:

· Biodiversity conservation

· Land use changes

· Coastal and fisheries livelihood

· CRZ vs. CMZ

· Collective and individual role and responsibility of the various government agencies in ICZM