Active Faulting and Earthquakes in Arizona

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Active Faulting and Earthquakes in Arizona

• J Ramón Arrowsmith
• Associate Professor of Geology Department of
  Geological Sciences
• Arizona State University
• ramon.arrowsmith_at_asu.edu
• http//activetectonics.la.asu.edu
• http//earthquakes.asu.edu

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outline

• Overview of western US plate boundaries
• Arizona faults and seismicity
• Notable historic Arizona seismicity
• 2 important areas Western Grand Canyon and
  Flagstaff
• Summary

Acknowledgements

• Phil Pearthree, Chris Menges, David Brumbaugh
• Arizona Geological Society
• US National Science Foundation grants ITR/IMAP
  (GEO) Collaborative research Creation of a
  geospatial data system for the transition between
  the Colorado Plateau and the Basin and Range
  Provinces (Geoinformatics in Action)--EAR-0112960
  and ITR Collaborative research GEON a research
  project to create cyberinfrastructure for the
  geosciences--EAR-0225543.

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Plate Tectonic history of Western North America,
38 Ma to present sets configuration for ongoing
deformation
--From Tanya Atwater http//emvc.geol.ucsb.edu/
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Arizona is not on the plate boundary
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Quaternary faults from USGS (http//qfaults.cr.usg
s.gov/)
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Seismicity gtM4 since 1900 (ANSS/CNSS Worldwide
Earthquake Catalog)
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Crustal motion relative to Stable North America
(http//epicenter.usc.edu/cmm3/)
Largest velocity 49 mm/yr
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Arizona is surrounded by relatively more rapidly
deforming crust
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Q or QT units and Q faults
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Important historic Arizona Earthquakes
http//www.azgs.state.az.us/Spring2000.htm
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Historic earthquakes near Flagstaff (Intensity
gtVII) Jan. 25, 1906 great rocking motion
September, 1910 Numerous shocks, severe north
of San Francisco Peaks August 18, 1912
1910
1906
1912
--AEIC
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1887 Pitaycachi, Sonora earthquake, M7.4 great
destruction near epicenter
the walls of the saloon did a two-step and the
floor did a shimmeynear Sierra Vista AZ
(McGarvin, 1987)
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1887 Pitaycachi, Sonora earthquake
http//nisee.berkeley.edu/elibrary/index.html
(Steinbrugge Collection)
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1887 Pitaycachi, Sonora earthquake scarp Late
Pleistocene paleoevent (?)
http//nisee.berkeley.edu/elibrary/index.html
(Steinbrugge Collection)
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View North along Hurricane Fault near Cottonwood
Creek
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Moriah Knoll Basalt New 40Ar/39Ar date of
0.850.06 Ma 154-204 m offset (paleoslope or
no) Approximately 0.15 to 0.25 mm/yr offset rate
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• Morphologic dating of fault scarps along the
  Hurricane Fault zone, Shivwitz segment
• Assume that sediment flux is proportional to
  local slope, no flow in or out of plane of
  profile. Find best fit model profile.
• Sed. Flux rate constant is k (1.1 m2/ky)depends
  on climate, scarp material and aspect)
• kt controls final form
• -gt 0.060.21 mm/yr offset rate for 6-80 ka

Diffusion erosion
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Paleoseismic trench investigation
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Paleoseismic trench investigation
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Most Recent Earthquake colluvial wedge (2.3-3.4 m
offset at about 8900-10,400 calBPminimum age)
Penultimate Earthquake colluvial wedge (1.2-2.3 m
offset)
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• Most Recent Event 2.3-3.4 m offset (M7-7.2)
  8900-10,400 calBP
• 10 kyr recurrence interval
• Steady deformation over Quaternary

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Flagstaff area from the south
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Lake Mary Fault and Flagstaff earthquake hazards
(with D. Brumbaugh, NAU)
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Walnut Canyon
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Observatory Road site
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COARSE Collaboration
Matt Fouch, ASU Hersh Gilbert, UAGeorge Zandt,
UASusan Beck, UAEd Garnero, ASU

• Constrain first-order crust and upper mantle
  structure
• Provide regional images for focused EarthScope
  effort

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Q or QT units and Q faults
Arizona Seismicity Relatively low rate, long
recurrence, edge of Basin and Range Distributed
in Southern Colorado Plateau, possibly driven by
topographic/crustal thickness gradient Watch out
for an event in Southern California!
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Complete Bouger Anomalyproxy for crustal
thickness (Yoburn, et al., in press)
Arizona Seismicity Relatively low rate, long
recurrence Distributed in Southern Colorado
Plateau, possibly driven by topographic/crustal
thickness gradient Watch out for an event in
Southern California!
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Peak ground acceleration (g) with 2 probability
of exceedence in next 50 yrs (USGS)
http//earthquake.usgs.gov/hazmaps/products_data/

Arizona Seismicity Relatively low rate, long
recurrence Distributed in Southern Colorado
Plateau, possibly driven by topographic/crustal
thickness gradient Watch out for an event in
Southern California!
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Interested in more information?

• M-34-Earthquake Hazards Map, by P.A. Pearthree
  and D.B. Bausch, 1999, scale 11,000,000. 6.00
• http//www.azgs.state.az.us