Feature Article

A Nation Unprepared

[TamilNet, Monday, 27 December 2004, 00:10 GMT]
As with any natural hazard, the more informed the public is, the better are the chances for survival. Sri Lanka's National Aquatic Resources Research & Development Agency (NARA) or the Meteorology Department do not have the resources to receive early warning information released by International Monitoring stations that monitor seismic activity so that Sri Lanka's citizenry can be alerted in time of impending tsunamic waves. Had these organizations taken a few diligent steps Sunday's tsunamic disaster may have been reduced to just loss of property, and loss, perhaps, of few lives.

TsunamiPacific Tsunami Warning Center (PTWC) of the National Oceanic and Atmospheric Agency of the US Government provides such early warning messages.

Established in 1949, the PTWC in Ewa Beach, Hawaii, provides warnings for tsunamis to most countries in the Pacific Basin as well as to Hawaii and all other US interests in the Pacific outside of Alaska and the US West Coast. Those areas are served by the West Coast / Alaska Tsunami Warning Center (WC/ATWC) in Palmer, Alaska. The International Tsunami Information Center (ITIC) established in 1965 by the IOC (Intergovernmental Oceanographic Commission) of UNESCO, is the third such group that monitors seismic activity.

The ITIC also assists Member States in establishing national warning systems, and makes information available on current technologies for tsunami warning systems.

Although the main focus for PTWC or ITIC is US's interests in Pacific, the regions they monitor seismic activity include those that impact coastal regions of Sri Lanka. More specifically, Sunday's oceanic earthquake measuring 8.5 Richter scale off the west coast of Sumatra was detected and a news bulletin published within 15 minutes of the onset of the quake. The details of the bulletin follow:


"....TSUNAMI BULLETIN NUMBER 001
PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS
ISSUED AT 0114Z 26 DEC 2004
AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS
ORIGIN TIME - 0059Z 26 DEC 2004
COORDINATES - 3.4 NORTH 95.7 EAST
LOCATION - OFF W COAST OF NORTHERN SUMATERA
MAGNITUDE - 8.0
EVALUATION
THIS EARTHQUAKE IS LOCATED OUTSIDE THE PACIFIC. NO DESTRUCTIVE TSUNAMI THREAT EXISTS BASED ON HISTORICAL EARTHQUAKE AND TSUNAMI DATA."

One can see from the text that there was 15minute delay (0059Z to 0114Z) from the onset of seismic activity to when the warning message was generated. This bulletin was later updated at 0204Z with a magnitude adjustment to 8.5. Note that (Z) Zulu time is the same as Greenwich Mean Time (GMT), and Sri Lanka's local time is GMT+6 hrs, meaning the earthquake occured at Sri Lanka's time 6hrs 59 minutes.

The first issue in question is why Sri Lanka authorities did not make arrangements with organizations such as PTWC or ITIC to provide alerts on seismic activities in regions relevant to Sri Lanka?

The next issue is even if one successfully received the alert, how much time is left for the shockwave to travel from the point where the earthquake was, to the disaster area? A brief description of the speed of travel of tsunami 'wave' is useful.

Tsunami differ from normal wind-generated waves (the waves everyone has observed on the beach) because of their longer periods and wave lengths. In fact, wind-generated waves usually have periods (time between two successive waves) of 5 to 20 seconds and a wavelength (distance between two successive waves) of 100 to 200 meters. A tsunami can have a period in the range of 10 minutes to 2 hours and a wavelength in excess of 500 km.

Tsunami
Tsunami
It is because of their long wavelengths that tsunami behave as shallow-water waves characterized by a very small ratio between the water depth and the wave's wavelength. These shallow-water waves have constant characteristics: first of all, their speed is proportional to the depth of the water while the rate at which the wave loses its energy is inversely related to its wavelength. This means that, since a tsunami has a very large wavelength, it will lose little energy as it propagates. Hence in very deep water, a tsunami will travel great transoceanic distances at high speeds and with limited energy loss.

For example, when the ocean is 6000 m deep, unnoticed tsunami travel about 890 km/hr, the speed of a jet airplane. As the tsunami crosses the deep ocean, its length from crest to crest may be a hundred miles or more, and its height from crest to trough will only be a few feet or less. They can not be felt aboard ships nor can they be seen from the air in the open ocean. In the deepest oceans, the waves will reach speeds exceeding 970 km/hr.

In the case of Sunday's event, assuming a conservative estimate of tsunami speed of 850km/hr, the shockwave would have taken little less than two hours to travel the approximately 1600km between Sumatra and East coast of Sri Lanka hitting Sri Lanka's east coast at local time 9am Sunday (6hr 59m + 2 hrs).

In this specific case, 1.75hrs (ie. 2 hrs less 15 minutes to account for the alert delay) would have been more than adequate to warn most of the vulnerable coastal residents to move to high lands 50' to 60' above the mean sea level. A disaster of the present magnitude could well have been prevented or in the least the losses minimized. That is if it turned out to be a real tsunami, which it did.

Pundits may point out that in the U.S's reporting system from 1950's a 75% false alarm rate has prevailed, and this undermines the credibility of the warning system, and place citizens at physical risk of accidental injury or death during the evacuation. The local hazard management experts should accept this risk but actively participate in experimenting with other new technologies to improve hazard prediction and evacuation techniques.


External Links:
NOAA: Deep-ocean Assessment and Reporting of Tsunamis
ITIC: International Tsunami Information Center
SpaceUK: tsunami
NOAA: TSUNAMI BULLETINS

 

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