Elaine Meinel Supkis
8.0 earthquake in ocean off of the Island of Tonga which rises out of the turbulent seas right on the outer edge of where the swift-moving Australian Plate is shoving into the great Pacific Plate. The upper end of the Pacific Plate had a series of 6+ magnitude quakes on the Aluetian volcano arc over a week ago and for the last five days, the entire west coast of South America shook like jelly, repeatedly so it is no suprise to see the third corner of the Pacific Plate triangle blowing out with a huge quake.
A strong earthquake measuring 8.0 has rocked the Pacific island nation of Tonga, reports say.
The US Geological Survey said the quake was centred about 155km (95 miles) south of the island of Neiafu and north-east of the capital, Nuku'alofa.
It struck at 0426 local time (1526 GMT), the USGS said.
There was no immediate word of damage or casualties, but tsunami alerts were in effect for Tonga, Fiji, New Zealand, Samoa and Hawaii.
"We have a tsunami warning for Fiji and New Zealand and for the rest of the Pacific we have a tsunami watch," ocean scientist Nathan Becker of the Pacific Tsunami Warning Center, based in Hawaii, told the AFP news agency.
Earthquakes as strong as magnitude 8.0 could trigger a lethal tsunami, depending on conditions and the nature of the quake.
The nature of tsunamis is, if there is little displacement, then there isn't much of a wave. One can't tell, though, until long after, when the waves strike so the prudent thing to do is to run for them thar hills if there are any.
The problem with most islands riding on the outer edge of the Pacific/Australian plate boundry is they have no hills to run to. The populations have not lived all that long, less than 1,000 years, much less, on these islands. The precarious toehold grasped by island-hopping Polynesian peoples can be wiped out if a 9+ event like the one that decimated the islands around Sumatra.
03-MAY-2006 15:26:35 -20.03 -174.23 8.0 16.1 TONGA ISLANDS
01-MAY-2006 21:40:47 -28.30 -176.94 5.2 10.0 KERMADEC ISLANDS REGION
01-MAY-2006 02:24:41 -28.42 -176.84 5.3 35.0 KERMADEC ISLANDS REGION
30-APR-2006 19:33:19 -15.58 -173.14 6.3 10.0 TONGA ISLANDS
30-APR-2006 15:08:39 -15.36 -173.68 5.5 10.0 TONGA ISLANDS
30-APR-2006 14:52:14 -19.73 -177.94 4.3 526.1 FIJI ISLANDS REGION
27-APR-2006 19:13:10 -16.05 -173.79 5.3 75.2 TONGA ISLANDS
27-APR-2006 19:13:02 -16.07 -173.77 5.4 10.0 TONGA ISLANDS
A number of the preliminary shocks occured at the all-popular 10 km level. For some reason, this depth is a strong cut-off point for our crust. Like when you slice bread, there is the brown top and then a transistion layer and then the bread itself. The foreshocks were at several depths so this was a major realighnment of the uppermost layers. It is very odd how the Australian plate has this sharp dagger edge to the outermost corner. It looks a lot like the transition point between Africa and Saudi Arabia.
Click on picture to enlarge.
South America has been most active and some of the greatest mountain raising events are occuring on the leading western edge. It looks to my untrained eye as if South America is rotating away from Antarctica which it probably joined back 60 million years ago and the upper half is spinning east while the lower half is rotating west. This is probably why the isthmus is so convaluted like a swan's neck.
It is quite possible that more than once, continents swung around instead of moving forwards, it would make sense since many things in nature, when crowded, tend to rotate rather then move forwards unless there is a bottleneck, even then, there is this eddy effect if any edges are rough.
Person said a typical year for earthquakes consists of 18 major temblors (magnitude 7.0 to 7.9) and one great quake (8.0 or higher). During the first two months of 2001, there were seven earthquakes with magnitudes of 7.0 or higher, and two others with magnitudes of 6.8. The highest magnitude of any quake in February 2001 was the magnitude 7.3 in Southern Sumatra.
It is interesting that a typical year had "great quakes" that are now virtually ignored today. A mere 6.8 garners virtually no notice these days! The last 30 days, we had 14 6+ events. Three +7 events this month. This must be an exciting time to be working in the field of geology. If one can get a job, that is! We have to keep remembering, the most interesting planet in this arm of the galaxy is one we call "Earth."