Alan Pongratz, in collaboration with USGS Hazards Program Geologist Rob Witter, writes:
"Although I am not directly associated with the USGS Hazards Program, I collaborated briefly with USGS Hazards Program Geologist Rob Witter on this event, and he offered the following:
'The map of seismicity surrounding the Bering Sea, below, shows that earthquakes are less common in the region, but not unheard of. Your compilation of earthquakes and the USGS latest earthquakes map and information (click on “View Nearby Seismicity" here) show an interesting swarm southwest of St. Lawrence Island. Most of the earthquakes occured at depths between 15 and 30 km. Chapter 8 in the Geology of Alaska, by Marlow, Cooper and Fisher (1994) reviews the geology of the Bering Sea continental shelf. They say the shelf includes several sediment filled basins, some bounded by normal faults accommodating settlement. Apparently these normal faults are active. However, St. Lawrence Island occurs well away from the closest two basins, Anadyr and Norton Basins, so the seismicity may be on other structures, possibly related to reactivation of faults along an ancient volcanic arc that was active from the Jurassic through to the early Tertiary. Apparently, this volcanism reflects subduction along the Bering Sea shelf margin that ceased in the early Tertiary when subduction along the Aleutian Island Arc initiated.'
He also offered this link to the UAF Alaska Earthquake Center, which contains some additional downloads that can be accessed in the Shakemap tab for this event.
Using some of the tools from above, a simple map (pictured below) was produced showing the island's geology and the relationship to the magnitude 4.9 earthquake's epicenter, as noted from the above references. This small graphic implies that the epicenter lies closely along strike and approximately 25 miles offshore of the known fault shown on the AK State Geologic Map (Scientific Investigations Map 3340, dated 2015), which incorporates exploration and mapping data from USGS Geologists William Patton and Ric Wilson (Scientific Investigations Map 3146, dated 2011).
Although probably not as easily felt throughout the region, there were an additional 20 smaller aftershocks reported by the network over the next 72 hours, ranging from magnitude 2.3 up to magnitude 4.1. Those can be see here
It would be interesting to note if the folks in Gambell felt any, some, or all of the aftershocks, as only the largest 4.9 magnitude event seems to have resulted in any feedback from the public."
The Alaska Earthquake Center has a variety of resources relating to earthquakes, tsunamis,and volcanoes in Alaska. Earthquakes within the past month are displayed on an interactive map with each dot representing a recent earthquake. Click on the earthquake near you, and share your experience! They also share information about why earthquakes happen in Alaska.
The USGS Earthquake Hazard Program provides information on earthquake hazards across Alaska. From their homepage, you can find definitions of common terms, and information on how to read earthquake probability and hazard maps. Also from their homepage, sign up to receive real-time notifications, feeds, and web services.
Observations From Members 