This map depicts reports from residents who felt the earthquakes that happened Sunday night.

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Three earthquakes rattle North Valley

11/7/2015

Elizabeth Medora
Staff

NORTH VALLEY – “What was that?!” was the resounding question on Sunday night after three earthquakes rattled the North Valley and beyond, startling local residents. No damage has been reported from the quakes, and the quakes did not break the surface of the ground.

According to the Arizona Geological Survey, the three earthquakes all occurred about 3-11 miles north of Black Canyon City. The resulting tremors were felt widely, with reports of feeling the quakes coming north of Flagstaff and south of Casa Grande. Residents reported hearing loud booms and feeling their houses shake, with the shaking continuing for about 45 seconds during the second quake.

The U.S. Geological Survey is referring to the three quakes as a foreshock, mainshock, and aftershock. The foreshock, 3.2 magnitude and depth between 0.6-3 miles, happened about 9 p.m. on Sunday night. The mainshock (the second earthquake), which had a magnitude of 4.1 and depth of approximately seven miles, occurred about 11:20 p.m. on Sunday. The third earthquake, 4.0 magnitude and depth of approximately three miles, hit about 11:45 p.m. on Sunday.

According to the AZGS, the U.S. Geological Survey initially located the epicenters and depth to focus. Research Geologist Dr. Jeri Young used 15 Arizona-based seismometers from the Arizona Broadband Seismic Network and the Arizona Earthquake Information Center to refine the locations of the three earthquakes.

The closest known active fault is the Horseshoe Fault, according to the Arizona Geological Survey. This fault is located 22 miles SSE of the mainshock. 

Since Black Canyon City is located near the epicenters of the quakes, residents there felt the earthquakes especially hard. Black Canyon City residents described hearing a sound like a loud wind, saying it was “very noisy.” Several people reported feeling all three quakes distinctly.

Black Canyon City resident Christina noted that her neighbors’ animals became very noisy, as if something was bothering them. Christina described hearing a “huge boom” and then feeling her 13-foot travel trailer shaking. She noted that her home is located approximately 2.5 miles from the epicenter.

While Arizona isn’t known for earthquakes, it’s not uncommon for some areas to experience them. According to the U.S. Geological Survey, no Arizona earthquakes in recorded history have caused any deaths. Some of the past earthquakes have caused damage, however. While earthquakes can’t be predicted, seismic activity can be monitored, which the Arizona Geological Survey does through the use of broadband seismometers, which are located around the state. The broadband seismometers can record ground motion from local, regional, and global earthquakes.

Local residents may not be quite done with this latest earthquake. The AGS noted that aftershocks will continue for several months. Most aftershocks likely won’t be felt, but Black Canyon City and surrounding area residents may feel some of the aftershocks. 

For North Valley residents, feeling an earthquake of this magnitude is an uncommon and unforgettable experience.

After recounting what she felt and researched the night of the earthquakes, Christina, like many other residents, concluded, “I won’t soon forget it.”

Want to learn more about earthquakes in Arizona? Visit the Arizona Geological Survey’s earthquake page at www.azgs.az.gov/hazards_earthquakes.shtml.