M3.3 Earthquake & aftershocks in northwestern-most Arizona

M3.3 Earthquake & 7 aftershocks (8/28/2017)

At 7:03 a.m. on 28 August, a magnitude 3.3 earthquake occurred in the northwest corner of Arizona about 20 miles SSE of Mesquite, Nevada. Seven smaller aftershocks followed on the heels of the initial event (Table 1, Figure 1). 

According to AZGS geologist Jeri Young, the earthquakes occurred just west of the Grand Wash Fault.  The range of depths, from 0 to 13 km is not uncommon ‘due to the westward stepping off the Colorado Plateau here.’

Table 1*. Earthquake events of NW Arizona of 8/28/2017 

MAGNITUDE (ML)            DATE               LAT        LONG       DEPTH (km)

0.8                        8/28/2017           36.593   -113.848              9.7

1.1                        8/28/2017           36.584   -113.866              13.3

1                            8/28/2017           36.609   -113.813              13.2

0.3                        8/28/2017           36.638   -113.832              12.1

0.2                        8/28/2017           36.611   -113.854              0

1.3                        8/28/2017           36.627   -113.823              12.3

1.2                        8/28/2017           36.622   -113.826              6.1

3.3                        8/28/2017           36.572   -113.887              3.8

*Data derived from the Arizona Broadband Seismic Network by Jeri Young (AZGS).

Remembering M. Lee Allison: one year later

Lee Allison examining a diversion ditch, Flagstaff, AZ. 

A year ago today Lee Allison, Director of the Arizona Geological Survey and State Geologist, passed away 3 days after suffering a tragic accident at his home. We cannot adequately express the scope of this tremendous loss to the AZGS and staff members. Lee was unique and irreplaceable, a dynamo who was primarily responsible for the survival and growth of the AZGS during the 10+ years when he was Director. For Lee, challenges were opportunities to do more, and obstacles never stopped him from going forward. The AZGS became involved in areas of research and outreach that we never would have imagined before his arrival, and the profile of the AZGS was raised within Arizona, nationally, and internationally.

Fortunately for us who have had to carry on without him, the legacy of Lee’s dynamic tenure as Director was incredibly influential as the state legislature considered re-establishing a state appropriation for the AZGS this past spring. It was much easier to explain the critical value the AZGS provides to the State of Arizona because of the work we completed under Lee’s leadership, addressing many different aspects of geology and its impact on society and commerce. Lee truly viewed geology as underpinning modern society, and he never passed up an opportunity to make that argument in public forums. (Photo by A. Youberg, 8/25/2010)

Phil Pearthree
AZGS Director & State Geologist

Eldred Dewey Wilson & the Proterozoic ‘Mazatzal Revolution’

Study area map of Wilson (1937)

In 1937, geologist Eldred Dewey Wilson coined the phrase ‘Mazatzal Revolution’ to describe mountain building along the western edge of the North American craton. While the Mazatzal Revolution occurred in the Proterozoic - more than 1.6 billion years ago - it continues to influence Arizona geology and mineral exploration to this day. Wilson’s 1937 Ph.D. research is now available online for the first time.

In about 1920, twenty-two-year old Eldred Dewey Wilson joined a handful of geologists - N.H. Darton, Carl Lausen and Olaf P. Jenkins, among them – wrestling with the complex geology of the rugged mountains of southern and central Arizona. Wilson was an assistant geologist at the Arizona Bureau of Mines and working on his M.S. thesis, ‘The Mazatzal Quartzite, a new pre-Cambrian formation of central Arizona’ at the University of Arizona. In 1924 Wilson was promoted to geologist at the Bureau, where he remained, with a short leave of absence to begin his doctoral research in 1931-1932 at Harvard University, until his death in 1965.
 
Wilson set out in 1930 to address, ‘the chief features of pre-Cambrian regional structure within part of central Arizona’, for his Ph.D. dissertation – ‘‘The Pre-Cambrian Mazatzal Revolution in Central Arizona’. His field area included the Mazatzal Mountains, Pine Creek, eastern Tonto Basin or northern Sierra Ancha, Del Rio, and the southern Black Hills areas, all of which contained extensive outcrops of Proterozoic-age rocks. Wilson concluded from his observations of the field relationships of rocks and structures that the ‘principal features of regional structure originated from a great pre-Cambrian crustal disturbance’, which he called the ‘Mazatzal Revolution’.

Wilson’s ‘Mazatzal Revolution’ was an early contribution to deconstructing the processes responsible for the geology of central Arizona. He noted, ‘The subparallel folds, thrust faults, and imbricate, steeply dipping reverse faults clearly resulted from intense north­west-southeastward regional compression. The transverse faults are believed to have been formed, also during the compression, by shearing normal to the trend of the folds.’

Wilson hypothesized, too, that, ‘structural weaknesses inherited from the Mazatzal Revolution may have influenced the localization of many of Arizona's prevailingly north­eastward-trending veins and the pattern of the Tertiary Basin and Range faulting.’ The orogenic Mazatzal Revolution continues to impact Arizona geology today. 

E.D. Wilson ca. 1960s.

Reynolds & Others (2013) on Eldred Dewey Wilson’s contribution to Arizona geology. Wilson published a number of important papers on Arizona geology. According to Reynolds and others (2013), Eldred D. Wilson provided the first geologic map and cogent discussion of the geology and mineral resources of southern Yuma County: “Wilson mapped this hitherto unknown area of southwestern Arizona from 1929-1932. In the process, he discovered a new set of mountains that had been overlooked by previous geologists and explorers. He named this range the Butler Mountains after G. M. Butler, former Director of the Bureau and Dean of the College of Mining and Engineering (Wilson, 1931). Wilson was the first person to describe and map the geology of a large number of mountain ranges in southwestern Arizona. The data from Wilson's 1933 geologic map were incorporated into the 1969 state geologic map.” 

See James T. Forrester and Richard E. Moore’s ‘Memorial to Eldred Dewey Wilson 1898-1967’ for more about the life and times of Dr. Wilson.

Note: AZGS thanks an anonymous patron who arranged at his/her own expense with Harvard University to scan Wilson’s dissertation and secure copyright permission from Dewey Wilson to re-release Dr. Wilson’s work as CR-17-C. 

References 
 
Forrester, J.T. and Moore, R.E., 1965 Memorial to Eldred Dewey Wilson 1898-1967. Geological Society of America Bulletin, V. 76, p. 187-191. 

Reynolds, S., Spencer, J.E., Richard, S.M., Pearthree, P.A. 2013, The Geological Exploration of Arizona: The Role of State and Federal Surveys and the Geologic Map of Arizona, Arizona Geology Magazine, Winter 2013.

Wilson, E.D., 1922, The Mazatzal Quartzite, a new pre-Cambrian formation of central Arizona. Univ. of Arizona M.S. thesis, 40 p.

Wilson, E.D., 1937, The Pre-Cambrian Mazatzal Revolution in Central Arizona. Ph.D. Dissertation, Harvard University, Cambridge, MA, 335 p.