Some interesting follow-up yesterday on last Halloween's earthquake swarm near Sunset Crater. We were meeting at ASU with Arizona's earthquake seismologists to discuss plans for maintaining the Arizona Integrated Seismic Network.
The NAU group had
described the swarm thusly:
In the early morning hours of October 31, 2009 (UTC), a series of micro-earthquakes occurred in a region approximately 15 miles northeast of Flagstaff, Arizona near Sunset Crater National Monument. The Arizona Earthquake Information Center has identified over 100 micro earthquakes and has satisfactorily located about two dozen events occurring over a time span of six hours. The depths of the well located earthquakes are within the mid-crust and range from 17 km to 27 km. The largest events where of duration magnitude (Md) 2.5 and would not have been felt by local residents. The majority of the events had duration magnitudes less than 2.0, and the location of these events cannot be determined with the available data. However, these smaller earthquakes are thought to have occurred in the vicinity of the larger events.
According to Dave Brumbaugh, who manages the seismic network at NAU, the quake swarm outlined a northeast trending line, which contrasts with the northwest trending fractures associated with Sunset Crater.
Did the Halloween swarm represent deep magma movement or associated fracturing? Hard to know, but even if it were, it's not time to worry about an eruption. This is simply a fascinating geologic event.