Earthquakes in the Brooks Range
The Brooks Range today is nearly aseismic. The following figure from the USGS shows earthquake epicenter locations for events from 1977 to 1997. Virtually all events are shallow (<33 km), and occur in the crust. Most seismicity is clustered in the western part of the Brooks Range. A second small cluster in the NE Brooks Range corresponds to an area where thrust faulting is thought to be active today. The Harvard Seismology website (
http://www.seismology.harvard.edu/) lists 28 CMT solutions for earthquakes in the northern Alaska (62 to 72 latitude; -170 to -140 longitude) during the period 1976-2002. The number of thrust, normal and strike-slip events were as follows:|
Thrust |
Normal |
Strike-Slip |
|
6 |
5 |
17 |
From this limited data, it appears that strike-slip faulting is currently the dominant type of faulting. Since we know from geological observations that strike-slip faulting has dominated the deformation of most of Alaska since the mid-Cenozoic, the dominance of strike-slip fault motions is not surprising.
Earthquakes in Alaska, 1977-1997. From
http://gldss7.cr.usgs.gov/neis/general/seismicity/us.html
In southern Alaska, minor earthquakes are a daily occurrence. However, the Brooks Range experiences almost no seismicity, even when considering magnitudes as low as 2.0. The following figure illustrates the earthquake occurrences in Alaska in a typical month. For a current "last month map", click on the link below the figure.
Earthquakes in Alaska during March 2002. From
http://www.giseis.alaska.edu/Seis/html_docs/last_months_earthquakes.html|
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