hquakes, but activity for the past few days has been running higher than normal. Geologists are not certain what the higher numbers of small quakes mean, but they continue to closely monitor the situation.

The Alaska Earthquake Information Center (AEIC) reports that, on Wednesday, June 14, 2006, at 4:18 am UTC (June 13, 8:18 pm ADT) a strong magnitude 6.4 earthquake occurred in the Rat Islands region of the Aleutian Islands. The AEIC's report on the earthquake states: "The mainshock (M6.4) was situated 87 kilometers (54 miles) southeast of Buldir Island. The epicenter was located at 51.86N and 176.92E at shallow depth. This earthquake is the largest to occur in this region since the magnitude 6.8 event on June 14, 2005. ... The AEIC located over a hundred aftershocks of the M6.4 event within the first two days of the sequence. The largest aftershock of magnitude 5.9 occurred 30 minutes after the main shock. ...

"The June 14, 2006 earthquake occurred near the margin of the rupture zone of the M7.7 earthquake of November 17, 2003. The M7.7 event ruptured the boundary between the subducting Pacific and overriding North American plates (approximate extent of the rupture zone is shown by the black line). This region, where the two plates are being forced directly into one another, is one of the world's most active seismic zones. Over one hundred earthquakes of magnitude seven or larger have occurred along this boundary in the past hundred years.

Photo: Recent Alaska shakers

"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." (Editor: You can read more of this report at the AEIC's website here.)

With the exception of Wednesday's 6.4 earthquake in the Rat Islands, the rest of the temblor activity in Alaska does not appear to be increasing stresses along major fault lines, but geologists' understanding of the relationship between outbreaks like this and larger tectonic events is limited. Large earthquakes are sometimes, though not always, preceded by increases in smaller tremors.