FAQ: M7.9 Earthquake Event, 11/3/02

 

The Alaska Earthquake Information Center at the UAF Geophysical Institute located a strong earthquake that occurred on Sunday, November 3rd at 1:12 pm Alaska Standard Time in the central region of Alaska.

 

Q: How big was the earthquake and where was it located?

A: The earthquake was a magnitude (M) 7.9 and was located along the Denali Fault, 92 miles south of Fairbanks, 176 miles north-northeast of Anchorage, and 43 miles east of Denali Park at a depth of 4.2 km (3 mi).  The earthquake is the largest earthquake recorded in the world in 2002.

Q: How long did the earthquake last?

A: At the epicenter, the earthquake lasted somewhere between 1.5 – 2 minutes and the resulting rupture was approximately 330 km (206 mi.) long.  Depending on location, the earthquake’s duration was longer due to the travel rates of the P-Wave and S-Wave generated by the event.  In Fairbanks, the earthquake lasted over 3 minutes.

 

Q: Where was the earthquake most intensely felt?

A: The areas that reported the maximum impact were the villages of Slana and Mentasta, where the intensity was gauged to be around seven on a scale of one-to-ten.  Other communities who experienced strong intensity included Tok, Paxson, Cantwell and Northway.  Fairbanks averaged an intensity of five and Anchorage an intensity of four.


Q: How far away was the earthquake felt?

A: There were reports of the earthquake being felt on land as far as Washington (in high-rise buildings), and on water as far as Louisiana and Texas.

 

Q: Where can I report what I felt?

A: Log onto www.aeic.alaska.edu and click on “Did you feel the shaking?” to report your experiences.

 

Q: Where can I find out about damage as a result of the earthquake?

A: Contact the state Division of Emergency Services at (907) 428-7000 or (800) 478-2337, or visit them online at www.ak-prepared.com.

 

Q: How far did the earth move?

A:     Overall, the geologists found that measurable scarps indicate that the north side of the Denali fault moved to the east and vertically up relative to the south. Maximum offsets on the Denali fault were 22 feet at the Tok Highway cutoff and were 6.5 feet on the Totschunda fault. The largest offsets were in the region between the Richardson Highway and the Tok Cutoff Highway.  This variance will continue to change as aftershocks help the land along the fault fit back together and settle.

 

Q: How long can we expect aftershocks to occur from this earthquake?

A: Frequent aftershocks are expected to occur for the next few months, and will eventually taper off in frequency but continue to occur for up several years. 

 

Q: Will another large earthquake happen soon and where will it occur?

A: Though seismologists cannot predict exactly when and where the next earthquake will occur, we can expect another significant earthquake in Alaska on any given day. Alaska has more earthquakes than any other region in North America and is by far the most active state in the U.S.; more than 10,000 earthquakes are located on average in Alaska each year.  Of those, an average of five per year will be a M6 – 7, up to one per year will be a M7 – 8, and one per 13 years will be larger.

 

Q: Was this earthquake linked to the M6.7 event that happened the week before?

A: Yes, the epicenter of the M6.7 that occurred on Oct. 23 was immediately west of that of the M7.9 along the Denali fault.  The M6.7 ruptured 40 km (25 mi) of land west of the epicenter, and the M7.9 ruptured approximately 330 km (206 mi.) of land east of the epicenter toward the trans-Alaska pipeline.

 

Q: When was the last earthquake of this magnitude along the Denali fault?

A: The M7.9 shock is the largest earthquake on the Denali fault since at least 1912, when a M7.2 earthquake occurred in the general vicinity of the fault more than 50 miles to the east of today’s epicenter.  Since there was only one seismograph operating in Alaska at that time and no reports of surface faulting in the remote Alaska Range, the location of the 1912 shock is not well constrained. 

 


Q: What was the magnitude of the 1964 earthquake?

A: On March 27, 1964 Alaska experienced an earthquake of M9.2, the second largest earthquake ever to occur in recorded history.  Excluding activity in the Aleutian Islands, the recent earthquake of M7.9 was the largest earthquake in Alaska since 1964.

 

Q: Why do we have earthquakes in Alaska?

A: In Alaska, the Pacific plate is actively subducting under the North American plate.  There are also several faults in Alaska, including the Denali fault where the M7.9 earthquake recently occurred.  These geological factors create frequent earthquakes along the plate boundary in south central Alaska, along the Aleutian chain, and in interior Alaska along seismic zones and faults such as Salcha, Fairbanks and Minto Flats.

 

Q: How often do earthquakes occur in Alaska?

A: Alaska has more earthquakes than any other region in North America and is by far the most active state in the U.S.; more than 10,000 earthquakes are located on average in Alaska each year.  Of those, an average of five per year will be a M6 – 7, one per year will be a M7 – 8, and one per 13 years will be larger. Alaska has 11 percent of the world’s earthquakes, and 52 percent of all the earthquakes that occur in the U.S.  In fact, three of the six largest earthquakes in recorded history were in Alaska.

 

Q: What does the Alaska Earthquake Information Center do when there’s an earthquake?

A: Using computer software and a network of 300 seismometers statewide, AEIC locates all earthquakes that occur in Alaska every day.  When an earthquake occurs, a signal is sent from seismometers to our lab where the data is interpreted into information about the event.  Within 30 minutes, that information is disseminated to the public and several governmental agencies via email, fax, phone and on the Web.

 

Q: Where can I find out more about this and other earthquakes?

A: Visit AEIC online at www.aeic.alaska.edu for current earthquake information.




Page created by the GI Information Office
Updated: October 2006