Archive for October, 2011

Chino Valley 3.5 M Earthquake: 25 October 2011


A 3.5 M earthquake occurred roughly 20 miles north of Prescott, Arizona, on Tuesday, 25 October 2011. The USGS put the focus – i.e. depth – at about 3.1 miles, with an CV did you feel it mapuncertainty of nearly 2 miles.

Anecdotal reports from northern Chino Valley-Prescott area, where more than 600 people reported to USGS’s “Did you feel it?, indicate that the tremor was strongly felt there. A former Californian called our office and said, “this was as big a jolt as some earthquakes I felt in California”. In the Prescott courthouse, people on the 4th floor were sufficiently concerned to consider evacuating the building. They didn’t.

Tuesday’s earthquake coincided with the recent release of two videos, products of AZGS’s AZ Shakes earthquake outreach program, describing the geometry, structure, recurrence, and the probable maximum magnitude earthquake of the Little Chino and Big Chino faults (see our blog of 22 October). The earthquake does not appear to have been on either of those faults, but it was situated a few miles from the Big Chino Fault. As Phil Pearthree (Chief of AZGS Environmental Geology) pointed out, the Big Chino fault is capable of producing an earthquake with a magnitude up to 6.5 or 7.0. It’s been at least 20,000- to 30,000-years since a major earthquake on that fault.

We are coordinating with Yavapai Counties Emergency Management Dept. on a brochure promoting earthquake preparedness in Yavapai County. Our target release date is late November.

Resources:  The Little Chino and Big Chino fault videos available at AZGS’s YouTube channel.

Mike Conway (29 October 2011)

Chino Valley, Arizona, Fault Videos

Chino Valley Fault Videos

Chino Valley, Arizona, is home to two fault systems, the Little Chino and Big Chino faults, capable of delivering moderate to large earthquakes, with a maximum likely magnitude of 6.5+.  Prescott, 30 miles to the south, could be adversely impacted by rupture of either one of the faults.  Brian Gootee walks along a roadcut that exposes multiple fault features of the Little Chino fault, and describes the complexity, recurrence period and potential hazard of future events.  

chino valley pics

A fault scarp – 40 feet high – marks the central segment of the Big Chino fault.  Phil Pearthree, Chief of AZGS Environmental Geology, points out salient features and describes the behavior of Basin and Range faults in central Arizona.  From Prescott’s Courthouse square, Phil discusses the possible impact of a magnitude 6.5+ earthquake on the town and its community.

Check out the videos at our AZGS Youtube Channel:

Mike Conway (22 October 2011)

BioBlitz ~ Saguaro National Park

National Geographic and Saguaro National Park near Tucson, Arizona, joined forces to inventory flora and fauna.  Beginning on the morning of 21 October and running through the early afternoon ofbioblitz 22 October, the organizers enlisted the aid of thousands of Tucson-area residents to count saguaro, palo verde, ocotillo, prickly pear, creosote, gila monsters, kangaroo rats, snakes and more over hundreds of square miles of the Sonoran Desert.   Roughly 2000 school kids, K-8, participated, too.

Arizona Geological Survey hosted an exhibit of Tucson Mountain-area rocks and soils.   We had samples of four parent rocks and four derivative in situ soils for students to match up.  Using color, texture and composition, the kids did an outstanding job.  We showcased our baby mammoth – a museum quality, to scale model – and described pre-historic southern Arizona ecosystems that included: mammoth, mastodon, dire wolf, American Lion, camel, horse, sloth, bison and savannah-like grasslands.  One of the chief questions we put to our audience, “where did these animals and plants go”.   Extinction was a common answer, but most were uncertain as to why the megafauna became extinct.  DSC02295

As part of the BioBlitz Speaker series, I outlined the geologic history of the Tucson area over the past 300 million years.

Our hats are off to BioBlitz organizers with National Geographic and Saguaro National Park for a marvelous event that engaged thousands of people.  

Mike Conway (22 October 2011)


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