About Diego Garcia . .. from another forum --
"As a tsunami leaves the deep water of the open sea and propagates into the more shallow waters near the coast, it undergoes a transformation. Since the speed of the tsunami is related to the water depth, as the depth of the water decreases, the speed of the tsunami diminishes. The change of total energy of the tsunami remains constant. Therefore, the speed of the tsunami decreases as it enters shallower water, and the height of the wave grows. Because of this "shoaling" effect, a tsunami that was imperceptible in deep water may grow to be several feet or more in height."
More at
http://www.wcatwc.gov/physics.htm
further translated into somewhat non-techno babble English:
Tsunamis tend to be higher when the wave can move across extensive shallow water immediately offshore. Although the mathematics is indubitably complicated, the bathymetry of the island approach might deflect a significant portion of the longitudinal wave around the island.
. . . .but it does make sense that islands with steeply sloped bathymetry would experience, on balance, lesser effects. The inhabited, military portions of Diego Garcia probably is quite well elevated above the sea surface, in stark contrast to beach-front dwellings in other parts of the world.
and further on:
Near the island, there is a reef and shallower water in the reef.....would not the tsunami rise up because of this?
The reef may have protected the island and bore the brunt of the tsunami.
As for the seismic equipment: Apparently Diego Garcia had an earthquake in 1983 and it is located on an
ancient volcano.
More Info on Diego Garcia