Wednesday, December 03, 2014

The Lake Mary Fault Near Flagstaff

There is lots of talk in northern Arizona these days about earthquakes, since a moderate tremor shook Oak Creek Canyon (above) on Sunday, November 30.

This recent event makes me recall the time in 1993 when I taught a course at Yavapai College called "Earthquakes and Volcanoes of Northern Arizona." My research into providing lecture material for the class made me aware how this part of Arizona is very susceptible to strong temblors, as evidenced by a swarm of quakes that occurred near the San Francisco Peaks in 1906 (M6.2), 1910 (M6.0), and 1912 (M6.2). The latter one was so strong some cowboys camped on the north side of Peaks came screaming back into town thinking the world was coming to an end.

Because of my new-found awareness of earthquakes here, I called my home insurance company just to get a quote on earthquake insurance. The voice on the other end of the phone made an audible giggle and said, "You must be from California and new to the area as we don't have earthquakes in Arizona." I slowly gathered myself and told her that I was not new to the area but just curious about how much insurance would be. She replied that she would have do some research as she had never written a policy for earthquake insurance.

A week or more went by and wouldn't you know it, on April 29, 1993, a M5.3 quake rattled just south of the Grand Canyon near Valle, AZ  The quake was widely felt in NorAz and woke me up at about 2 AM. The next day I was reminded about the quote for insurance I never got and so once the offices were open, I called and said, "This is Wayne Ranney calling about a quote I requested." The lady who picked up quickly and excitedly yelled back to me, "HOW DID YOU KNOW??"

Of course, I didn't really know the when, I just knew the why and how. Geology is good for people that way. The end of the story is that the premium was not all that much but the $5,000 deductible (in 1993 dollars) was a deal breaker and I declined to get the insurance. I suspect there are very few policies written in NorAz for earthquake insurance but that there are a flurry of calls to insurance agents this week.

In relation to NorAz earthquakes, please take a look at this four minute video about the Lake Mary fault, located just south of Flagstaff. The production was made in 2011 and funded by the National Earthquake Hazards Reduction Program, with support from the Arizona Geological Survey, Arizona Earthquake Information Center, and AZ Shakes. This fault is about 25 miles long and is currently active, with its last movement in 2011.

We are likely to experience a quake at some time here but the recurrence interval is likely much longer than the average person's attention span for such things. As I travel often to many quake-prone regions - California, South America, the Middle East, the Pacific Rim - I am reminded more often than most of my peers to be earthquake aware all of the time.

Map courtesy of Jeri Young Ben-Horin at AZGS and Lee Allison, AZGS
And here is the latest map showing all of the foreshocks, main event, and aftershocks from the swarm. The foreshock is listed in red circle, M3.5.

1 comment:

  1. Very Interesting, thank you! I love reading and learning about my home state (Native Arizonan).


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