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An updated magnitude for the Rat Island earthquake of June 13 is now 6.4.
It is very common to have a strong aftershock sequence for events of this size.
There were over 200 aftershocks within the 1st ten hours after the mainshock.
Actually, more than is being reported on the USGS website. However, the aftershock decay rate is very rapid and today, 5 days post the mainshock, there are already much fewer overall aftershocks and especially larger aftershocks.
The USGS website hosts a composite worldwide earthquake catalog. With the stations of global seismic network, the USGS can achieve a uniform earthquake reporting level at about magnitude 4.5. It means that smaller quakes do not get reported in the areas with poor station coverage. USGS also gets earthquake updates from the regional networks such as Alaska regional network. Here we have much denser station coverage than the global network and are able to report much smaller quakes. If you look at aftershock sequence of a M6+ earthquake from an area with dense station coverage, such as central Alaska or California, for example, you'll see a similar picture. Hundreds of aftershocks within the 1st couple of days and decaying rapidly with time. We expect the Rat Islands aftershock sequence to last for a few more months, but at much lower levels of activity than presently.
A similar example of such an aftershock sequence can be found in AEIC or USGS catalogs for the M6.7 Nenana Mountain earthquake that occurred in central Alaska on October 23, 2002.
The current sequence of events is of a different origin than the above mentioned underthrusting events. The faulting parameters estimated from the waveform inversion indicate strike-slip type of motion for both the mainshock and the largest aftershock. It's location, shallow, and above the down-dip end of the locked interface, is more consistent with this event occurring within the crust of overriding North American plate. In the western Aleutians, the crust is partitioned into rotating blocks, such as Buldir Block to the east and Near block to the west of the June 14, 2006 event location. If this event is the manifestation of the block rotation processes, then the NE-striking focal plane is the fault plane for this sequence. It's mechanism is consistent with the clockwise rotation of the crustal blocks.
Originally posted by d1k
Got two new replies from the Alaska Earthquake Information Center people and I think this should put this to rest.
Originally posted by stumason
Well, at least this wont mean an interruption to England's march to victory!
Originally posted by Nygdan
What is the lattitude and longitude of Ratt Island, was it mentioned already, I must've missed it. Does anyone know?
Originally posted by Ptolomeo
Another set of these "aftershocks"
5.8 RAT ISLANDS, ALEUTIAN ISLANDS, ALASKA
5.3 RAT ISLANDS, ALEUTIAN ISLANDS, ALASKA
Besides, all the other quakes in Alaska.