AZGS Web Posts

M2.8 aftershock to Duncan earthquake

Arizona Geology Blog - Wed, 2014-09-03 11:20
There was another measurable Duncan aftershock last night about 7p.m.  The M2.8 followed a M2.6 event that morning.   [Right, orange star marks epicenter. Credit, USGS]




Categories: AZGS Web Posts

Small aftershock in Duncan area

Arizona Geology Blog - Tue, 2014-09-02 15:01
A M2.6 earthquake on the Arizona-New Mexico border is likely an aftershock from the June 28, M5.3 Duncan earthquake.  Because of it's small size and the limited seismic station coverage in the area, we suspect the location is not well constrained.     The quake hit at 9:21 a.m. this morning.  We expect aftershocks will continue for weeks to months.  [Right, orange star marks epicenter. Credit, USGS]
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Portable seismometers pulled from Duncan, heading to Napa

Arizona Geology Blog - Sat, 2014-08-30 20:38
AZGS geologists Jeri Young and Phil Pearthree pulled out four of the seven portable seismometers deployed in the area around June's M5.2 earthquake near Duncan, Arizona.  The portable instruments were installed in July to monitor the aftershocks from the June 28 event, detect small events, and provide accurate locations for all of the aftershocks.

However, the PASSCAL facility that owns the instruments needs to redeploy them in the Napa California area to monitor the aftershocks from last weeks M6.1 earthquake there.

Since they were installed, the portable instruments have recorded hundreds of aftershocks, with the largest a M4.1 event [right.  waveforms of aftershock as recorded by different stations]

Categories: AZGS Web Posts

New Geologic Map of Black Peak and Bobs Well 7.5" quadrangles released

Arizona Geology Blog - Sat, 2014-08-30 10:07
AZGS has published a new geologic map of the Black Peak and Bobs Well 7.5" quadrangles as a digital map.  It is available at our online repository for free viewing and downloading.


Most of the map area is covered by sand dunes and related features of Cactus Plain. The dune field of Cactus Plain is on a low plateau formed primarily on older eroded sediments, with minor bedrock hills protruding from the plain locally. The oldest late Cenozoic deposits in Cactus Plain are undeformed fan deposits composed primarily of crystalline metamorphic clasts, obviously derived from the east and northeast. These deposits are overlain by, and locally may interfinger with, fine-g rained clay, silt, sand and minor limestone deposits that we consider to be part of the Bouse Formation. Bouse carbonate deposits are also extensively exposed on the flanks of Black Peak and related hills near the northern margin of the map area. On the western, north eastern, and southern margins of Cactus Plain, there are extensive well-rounded, lithologically diverse gravel and sand deposits that we tentatively correlate with the early Pliocene Bullhead alluvium. T h is major river aggradation sequence is found all along the Colorado River below the mouth of the Grand Canyon (House et al., 2008; Howard et al., in prep.).
The map was funded in part by the StateMap component of the National Cooperative Geologic Mapping Program managed by the USGS.

Ref: Pearthree, P.A. and Spencer, J.E., 2014, “Geologic Map of the Black Peak and Bobs Well 7.5 Quadrangles, La Paz County, Arizona,” Arizona Geological Survey Digital Geologic Maps DGM-108 v1, scale 1:24,000.
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