at the south end of the Salton Sea is the first of its kind in 30 years. Since the early morning hours more than 200 tremors have rippled through southeastern California. The largest event was a magnitude 5.5 event at 1:57 p.m (PDT). Two other M5 or 5+ events occurred, as well as a number of M4+ events.
Lucy Jones (USGS seismologist) is quoted in “MyDesert.com” as saying that its likely there will be M4 and M5 events before the swarm ends. (Image on the right is a USGS “Did you feel it?” map
showing the precise location of today’s M5.5 tremor.
Index map of recent earthquakes in California and Nevada. Brawley is situated in southcentral most California. The large blue square represents today’s M5.5 event.
Michael Conway (26 August 2012)
A swarm of more than 20 moderate- to small-magnitude earthquakes occurred 35 miles south of Calexico, CA, on the evening of 30 June and morning of 1 July 2012. The swarm began with a M4.6 temblor at 8:25 pm Saturday; the largest quake was a M4.7 at 11:36 pm later that evening. Though poorly constrained the depth to focus was approximately 10 km (6 miles). There were no reports of damage from the nearby communities of Guadalupe Victoria and Mexicali both of Baja California, Mexico.
Most of the 20+ events ranged from M1.5 to M3.0. The swarm occurred at the south end of the Sierra Cucupah along the projection of the Laguna section of the Elsinore fault zone that trends NNW from Baja California to California. On 4 April 2010, a M7.2 earthquake occurred very near to the locus of this
On25 June 2012, at 3:07 pm MST, a small, 2.7 magnitude earthquake struck 9 miles NNW of Paulden, Arizona. There were no reports of damage and USGS’s “Did you feel it” online reporting site only received fewer than 10 responses. AZGS geoscientist Jeri Young used the Arizona Broadband Seismic Network to locate the event precisely (see Google Earth figure to right).
She captured some waveforms from nearby seismometers, too (see below). The area north of Prescott, Arizona is home to the Quaternary Big Chino and Little Chino fault systems, both of which are capable of generating a M6.0+ earthquake.
For some recent videos on the Big and Little Chino fault systems, visit our YouTube channel .
IRIS (Incorporated Research Institutions for Seismology) hosts and distributes a new computer display system, Active Earth Monitor. Designed for K-12 schools, museums, visitor centers and libraries, Active Earth Monitor provides an interactive environment for learning earth science topics.
From IRIS’s description, “All Active Earth Monitor content can be interactive using a touch screen, mouse or trackball. The General Seismicity content can also be displayed as rotating non-interactive content using a standard monitor.”
Active Earth Monitor promises to be a powerful tool for visualizing Earth science processes. Anyone with a computer, monitor, good internet connection, and desire to share information can establish their own Active Earth Monitor. Give it a look.
The US Geological Survey recently released new seismic-hazard maps
for the conterminous U.S. The six map sheets portray “peak horizontal acceleration and horizontal spectral response acceleration for 0.2- and 1.0-second periods with probabilities of exceedance of 10 percent in 50 years and 2 percent in 50 years. All of the maps were prepared by combining the hazard derived from spatially smoothed historic seismicity with the hazard from fault-specific sources.”
Citation: Petersen et al, 2011, Seismic-Hazard Maps for the Conterminous United States, 2008, USGS Scientific Investigation Map 3195.
Mike Conway (2 January 2011)
Science Nation, the National Science Foundation’s online magazine, presents an excellent, short video on drilling into an active fault zone. Researchers from Penn State University examined rock recovered from the Parkfield, California, segment of the San Andreas Fault. What they discovered was incompetent clay-rich material, which explains the aseismic nature of deformation there.
Other fault segments host more competent rock that seize up until increasing stress causes the rock to fail brittlely. Earthquake!
Mike Conway (26 December 2011)
The West Coast Regional Carbon Sequestration Partnership (WESTCARB) is drilling a deep well in the Sacramento-San Joaquin Basin, California, to characterize two potential CO2 storage areas. The first is a depleted natural gas reservoir and the second an underlying saline formation.
Drilling began on 1 December and 0n 21 December the drillers were 7000 feet deep in a mixed sandstone-shale unit.
For daily drilling reports and graphic, visit their Drilling Progress page.
Mike Conway (24 December 2011)
From their introductory page, “Actionable and scalable guidance and tools to the private sector, its owners, managers, and employees about the importance of earthquake mitigation and the simple things they can do to reduce the potential of earthquake damages, injuries, and financial losses.”
The QuakeSmart website includes documents, videos, and artwork. Some prominent chapter headings:
- How Earthquakes Affect Businesses
- How QuakeSmart Can Help
- Step 1: Identify Your Risk
- Step 2: Make a Plan
- Step 3: Take Action
There are three videos including, Mitigation Works for Business.
Mike Conway (24 December 2011)
A small swarm of earthquakes occurred south of Colorado City between December 12th and 13th. The largest event in the swarm was magnitude 3.1, the smallest was 1.7.
|2011||12||13||36.765||-113.018||13.9||0||43||0||2.8||Colorado City, AZ||UU|
|2011||12||13||36.764||-113.017||8.2||23||36||22||3.1||Colorado City, AZ||UU|
|2011||12||12||36.782||-113.001||2.8||9||44||37||1.7||Colorado City, AZ||UU|
|2011||12||12||36.757||-113.02||7.9||8||3||0||2.2||Colorado City, AZ||UU|
This small swarm occurred between the terminus of the Southern Intermontain Seismic Belt (ISB) and the start of the Northern Arizona Seismic Belt. This region regularly experiences small to moderate sized earthquakes. Earlier this summer there were several quakes of similar magnitude in the same area between the Hurricane and Sevier/Toroweap faults.
The National Earthquake Information Center Reports of the southern ISB:
The ISB in southern Utah coincides with a transition between east-west-directed stretching in the Basin and Range to the west and more stable crust of the Colorado Plateau to the east. Tectonic movement on generally north-trending, east- and west-dipping range- and plateau-bounding normal faults, which results in horizontal extension, characterizes this part of Utah. The Sevier Valley is an area of variable and complex deformation involving significant components of folding and both normal and strike-slip faulting. The most prominent geologically young faults in southwestern Utah are the Hurricane and Sevier faults. The Hurricane fault forms the west-facing Hurricane Cliffs, which define the eastern edge of the Basin and Range within the ISB. Faults in the ISB in southern Utah locally show evidence of displacement younger than 10,000 years, but average recurrence intervals are generally longer than those on faults in the ISB in northern Utah. Recurrence intervals for surface faulting on the most active segments of ISB faults in southern Utah are generally many thousand to tens of thousands of years.
|Lisa LinvilleDecember 17, 2011|
The Lake Mary Fault, situated immediately south of Flagstaff, Arizona, represents the greatest earthquake hazard to the more than 70,000 people of Flagstaff and environs. In a new video, Dr. David Brumbaugh, Arizona Earthquake Information Center (AEIC) at Northern Arizona University, narrates the, “Lake Mary Fault – Potential Earthquake Threat to Flagstaff, Arizona”. Since the mid-1980’s, Dr. Brumbaugh has studied faults and monitored earthquakes of northern Arizona using the AEIC seismic network.
As Dave Brumbaugh notes in the video, the maximum probable earthquake of the ~ 25 mile long, Lake Mary fault is estimated at magnitude (M) M6.9 to M7.0. An event of that magnitude would have dire consequences for older structures and for unreinforced masonry buildings in the Flagstaff area. And Flagstaff is no stranger to moderate-sized earthquakes. From 1906 to 1912, three magnitude 6.0 to 6.2 earthquakes occurred within 24 miles of the town.
Mike Conway (9 December 2011)