While not as dramatic at the Japan Earthquake today was probably pretty hairy for the people living in a part of the southwest pacific. The islands of Vanuatu and the Loyalty Islands are used to having an earthquake or two. Today started out with a 5.0 earthquake in Vanuatu waters but then the action moved south and west a bit and there was a 7.1 magnitude quake in the waters off of the Loyalty Islands which was followed closely by 10 earthquakes in the range from 5.0 to 5.8.
This follows a similar set of quakes just a few hundred miles north at the end of last month with 8 earthquakes over 5 in just a day. In February there was a similar grouping of 6 5.0 or larger earthquakes, with the initial quake of 5.9 and a bunch of less than 5’s. There was also a set of a 7, a bunch of 5’s a 6 and a bunch less than 5 at almost the same spot as todays cluster of quakes back in January. And earlier in January another cluster just a few degrees north of that cluster. The longest was the cluster from October 7 to 31 and it did expand a degree or two while happening. It started with a 5.1 followed by a 7.7, 17 hours later which then was followed almost immediately by a ton of aftershocks including 2 more high 7 quakes, 4 6+ quakes and many 5+. This pattern of clusters of earthquakes goes back as far as the data I can find, moving up and down the fault line of Vanuatu and the Loyalty islands.
While there have been clusters of quakes on this part of the fault line for as far back as the data I have seen, most years have maybe 1 of these clusters, some none at all. Starting in 2008 there started to be more than 1 each year, 2008 had 3, 2009 had 2 one of which was huge, 2001 had 3, one starting Christmas day and continued into January 2011 with aftershocks right up to Jan 25. Then the Feb 4 through 9 cluster which was followed by the April 29 cluster. Then today there is the newest start of a cluster. Each of these clusters, separated by time and location is a singular event but being on the same fault they are related. (I’m using data extracted from USGS archives.)
So does this mean that the fault along that part of the pacific is going through a cascade or earthquake storm? There is some data that may point to that but the activity is not clear cut north to south or south to north. It seems to happen in one spot for a few days then the next cluster occurs either north or south. Looking at the quake reports, the topology and map of the faults in the area, all of these quakes are on a single fault where the pacific plate boundary folds in on itself. This means that the area is very geologically active with complex movements.
The pacific plate meets New Zealand and the plate boundary goes north through Tonga to American Samoa where it does a bend back on itself back toward Fiji where it then bends back from southward to northward up through between the Loyalty Islands and Vanuatu. I’m still digesting data. I am looking for movement data, data on the movement of the plates as one passes under the other (and in some spots here that is the the pacific subducting, but in others it is riding over the Australian plate. )
I will post more when I know more.