29th December 2004, 12:02 AM
A little more information on EQ and Tsunamis:
Originally Posted by jsbn
1) Not all submarine earthquakes causes tsunamis. Quoting from an article off the New York Times: There is no direct connection between an earthquake magnitude and a resulting tsunami. Not all quakes under the ocean lift the ocean floor to displace the water needed to create a tsunami. Read here. Earthquakes can be categorized into two groups: one that creates forces of a horizontal nature (called the P-waves) and the other causes vertical displacements The latter is the more lethal form of earthquakes, resulting in more extensive damage to property and lives than the former. The type of EQ that leds to a tsunami can be associated as a severe form of the latter EQ,
2) The lack of advance warning, in addition to , was due in part to there not being a tsunami research centre responsible for detecting the risk of tsunamis in the Indian Ocean. Historically, tsunamis were largely observed in the Pacific Ocean. On top of that, modeling tsunamis are largely conducted using data on historical occurrences; researcher use seismographs to estimate the strength and location of earthquakes and observe the presence of a tsunami. Using these data, they formulate a forecast on the probability of a tsunami following an EQ. Given that tsunamis in the Indian Ocean are rare, there was probably no data that might help to predict this one.
29th December 2004, 12:16 AM
Adding to the above post:
Technically, there's no sure way of predicting a tsunami. In the open ocean, tsunamis are not directly visible on the surface of the water. The nature of shockwaves causes travelling regions of high water pressure underwater which does not affect the waves on the surface. It's only nearer the coastlines when the energy is directed and converted by the continental slope into increased kinetic energy in the waves.
So the size of the tsunami is also largely determined on the underwater slope of the coast lines, any obstructions like outlying coral reefs and the also the geography of the coastline (wavefront convergences and concentration).
29th December 2004, 12:45 AM
Stumbled upon this rather interesting bit of statistic. The incidence of major EQ (> 7) has been fairly consistent in the last couple of years. This trend has been observed for the past 100 years since 1900.
29th December 2004, 03:51 PM