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 uncertainty 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, 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.
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: http://www.youtube.com/user/azgsweb
Mike Conway (22 October 2011)
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 of 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.
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)
A swarm of more than 60 mostly small magnitude earthquakes, the lion’s share smaller than 3.0 M events, occurred over the past week about 4 to 6 miles northwest of Pinnacles, California. Pinnacles is situated along the San Andreas fault system in central California. The events began on 22 August and continued through the morning of 28 August. Nine events were in the 3.0 to about 3.6 range. The largest event, which occurred just after midnight (PDT) on 27 August, was a 4.6 M event. Shaking was light, nonetheless more than 2000 people reported it to USGS’s “Did you feel it”.
Mike Conway (28 August 2011)
Media attention today focused like a laser on the 5.8 M Mineral, Virginia, earthquake that shook the Eastern seaboard from Atlanta, Georgia, to Maine. And that is as it should be, the event rocked Washington D.C. and New York City and send thousands of people scurrying into the streets. The USGS’s “Did you feel it” recorded nearly 14,000 reports from 3754 zip codes and 33 cities. While strong shaking was localized, moderate shaking was reported widely. For additional information and maps visit the USGS’s events page.
The Mineral earthquake overshadowed what otherwise was a newsworthy seismic swarm of moderate- to low-magnitude events on the Colorado-New Mexico border 9 miles WSW of Trinidad, Colorado. (Broadband seismometers of the Arizona Integrated Seismic Network nicely captured the Mineral event and the two largest Trinidad events.)
The Trinidad swarm began with a 4.6 M event at 5:30 p.m. (MDT) on 22 August and continued through 8:11 a.m. (MDT) the next morning. In all, 11 events occurred. The largest event was a 5.3 M that occurred at 11:46 p.m. (MDT) on the evening of 22 August; this is also the largest event reported for the area since 1973. Small to moderate magnitude earthquake are not uncommon here – unlike the rare 5.8 M near Mineral, Virginia – and eight M 4.x events have occurred over the past decade.
The causative fault(s) lack any surface expression and thus are not included on the interactive USGS Quaternary fault map of Colorado-New Mexico. Nonetheless, the past day’s events and those of a swarm in 2001 are consistent with a north-northeast trending fault system, congruent with east-west extension responsible for forming the Rio Grande Rift.
Michael Conway (23 August 2011)
Earthscope’s mission is to explore the structure and evolution of the North American continent. Their chief tool is the portable array of 400 seismometers, USArray, rolling across the country from west to east. The first footprint was established in 2007 in the western-most U.S. Since then the stations have rolled on and are now deployed from Texas and North Dakota in the west to Alabama and Wisconsin in the east.
Data from USArray fuels models of the structure, i.e., fault distribution and geometry, of the Earth’s crust. If that seems a bit esoteric, those data provide insight into seismic, volcanic and landslide hazards in the continental U.S. This type of large-scale science research has the potential to benefit us all directly or indirectly for generations.
Check out this really fascinating animation of USArray capture of seismic wave propagation from an M 6.0 earthquake near Wells, Nevada on 21 February 2008 (animation).
Background. From the USArray website, “Each of the Transportable Array stations consists of a three-component broadband seismometer with associated signal processing, power, and communications equipment. In the early phase of the experiment, significant effort was devoted to the design of the temporary vaults to house the instruments, which resulted in a configuration that provides both high-quality data and a data return of greater than 90%.”
Michael Conway (21 August 2011)
The Quake Catcher Network (QCN) is hard at work in the San Francisco Bay area recruiting citizen scientists, deploying low-cost strong motion seismometers, and capturing earthquake data. From QCN website, “The Quake-Catcher Network is a collaborative initiative for developing the world’s largest, low-cost strong-motion seismic network by utilizing sensors in and attached to internet-connected computers.”
And as part of their program, they focus on recruiting schools and thereby getting teachers and students involved. Currently, the program is piloting in parts of western and central U.S. — California, Oregon, Washington, the Wasatch fault in Utah, and the New Madrid fault zone of Missouri – where the probability of large-magnitude earthquakes are greatest.
Sounds like a truly excellent program. Their sponsors include NSF, IRIS, Southern California Earthquake Center, O-NAVI, and United Parcel Service (UPS)
Check them out at Quake Catcher Network.
FEMA training in Somerton, AZ, today focused on ATC-20; evaluating building safety/integrity following an earthquake. Chiefly we reviewed the ATC-20 form and engaged in discussion on how to recognize building type – i.e., material (wood, steel, concrete, unreinforced masonry) — and how to recognize potential structural and non-structural hazards. We were then presented with a suite of slides of damaged buildings and using the ATC-20 posting system — green – inspected and safe for occupation; yellow – safe for limited entry; red – unsafe, no egress – made selections based on ATC-20 criteria regarding building safety.
Mike Griffin also introduced the electronic version of Rapid Observation of Vulnerability and Estimation of Risk (ROVER), which uses Windows mobile smartphone to gather and transfer data. The open source software remains in development stage but FEMA plans to release it later in 2011.
Mike Conway (11 August 2011)
I joined about 45 others today in Somerton, AZ, to participate in FEMA 154 – Rapid Visual Screening of Buildings for Potential Seismic Hazards. Gretchen Robinson of Yuma County Office of Emergency Management hosted the event and Mike Griffin, P.E., conducted the training. The participants represented Yuma county and local municipal agencies, including the Somerton Fire Dept
After lunch, we applied the RVS tool to several nearby buildings. It was a challenge but we passed the test.
For more information on FEMA 154
Mike Conway (10 Aug 2011)
Even by Gulf of California’s standards, today was a busy day for seismicity. USGS reports that three magnitude 4+ events occurred near the mouth of the Gulf. The action started at 17:44 UTC with a M 5.9 event, it was followed up by 4.3 M and a 5.0 M events at 18:57 and 19:40 UTC. The three events were shallow, occurring from 10-12 km deep.
Mike Conway (26 July 2011).