I was talking to my husband about this Easter Day earthquake from 2 years ago. I was hiking with my (then) fiance, Bob Verish, on the West Mesa just east of the Ocotillo Fault when it struck. The ground motion was so strong I couldn't run over to Bob. Both of us had to get on all fours to maintain balance. Right away we could see dust rising up and out of most of the canyons in all the nearby mountains from numerous rock-falls, and maybe even landslides. The mountain just south of the border was totally covered in dust within minutes. And to think, this dust contains fungi, mold and spores that, if breathed, are life-threatening to infants, elderly and anyone with a compromised immune-system! Little known statistic, but several people died from just such lung infections after the 1987, Whittier Narrows earthquake.
It is intriguing to read about all of the remote sensing by satellite and drones, and how they can measure such small displacements, and then be able to discern a fault from a landslide. We had to take a detour on our way home because the crack in Interstate8 was too big. When we got home in Santee, we found items that had been on a shelf had fallen onto the floor!
Such is life in SoCal (but I'm not complaining, because tornadoes are so rare here;-).
-- Moni
It is intriguing to read about all of the remote sensing by satellite and drones, and how they can measure such small displacements, and then be able to discern a fault from a landslide. We had to take a detour on our way home because the crack in Interstate8 was too big. When we got home in Santee, we found items that had been on a shelf had fallen onto the floor!
Such is life in SoCal (but I'm not complaining, because tornadoes are so rare here;-).
-- Moni
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Baja earthquake shook up view of Southern California faults
Posted by: "Lin Kerns" linkerns@gmail.com lin.kerns
Sun Apr 8, 2012 5:50 am (PDT)
Baja earthquake shook up view of Southern California faults Study of Easter
2010 temblor revealed previously unknown faults
Apr. 8, 2012 |
<http://www.mydesert.com/comments/ >article/20120408 /NEWS0805/ 204080309/ Baja-earthquake- Easter-revealed- unknown-Southern -California- faults
<keith.matheny@thedesertsun. >com
Written by Keith Matheny The Desert Sun
A new scientific study reveals that fault networks near the Salton Sea are
even more complex than previously known � but what that may mean for
earthquake potential in the region remains uncertain.
The U.S. Geological Survey and California Geological Survey released a
study last month that found the Easter Day quake in northern Baja
California on April 4, 2010 � the biggest quake to shake the Coachella
Valley in recent years � triggered surface movement on many faults in the
Imperial and Coachella valleys.
The magnitude-7.2 quake revealed faults southwest of the Salton Sea that
were not previously known to scientists, and confirmed that other known
faults were active, the new research shows.
It's not a finding that will quickly lead to the development of a reliable
earthquake warning system, a primary goal of scientists. But it advances
knowledge and will direct future research on one of the most intricate and
studied fault zones on Earth, scientists said.
The Baja earthquake �has provided a geological treasure trove to our
understanding of what is happening tectonically in this expansive region of
northern Mexico and Southern California,� said state geologist John Parrish
in a statement about the study.
The 2010 Easter Day quake, dubbed the El Mayor-Cucapah quake by scientists,
killed four people and injured more than 100 in Mexico and caused an
estimated $440 million in damage in the Mexicali Valley of Baja California
and $90 million in damage in the Imperial Valley.
The movements the quake caused on Southern California faults occurred at
the surface and were very small, only centimeters. Similar fault movements
were also observed after a magnitude-5.7 aftershock on June 14, 2010.
The discoveries show earth scientists that �the transfer of strain among
the various faults in this region is not as simple as we thought before,�
said Jerry Treiman, a geologist with the California Geological Survey and
co-author of the study.
Earthquakes like the El Mayor-Cucapah quake involve the sudden release of
built-up energy from two of the Earth's tectonic plates moving against each
other as one of the plates slips past the other. The quake was the largest
in the northern Baja region in the past 120 years.
Assisting in locating and mapping the surface movements on Southern
California faults was NASA's UAVSAR, a sensitive radar system flown over
the area at high altitudes on an unmanned aerial vehicle, or drone. Flyover
data was compared with a previous examination of the area in October 2009
after the quakes, Treiman said.
Typical NASA radar images taken from satellites can show ground shifting
down to centimeters, said Michael Rymer, U.S. Geological Survey's lead
geologist on the research. With the drone system, however, �we were seeing
down to millimeters of resolution,� he said.
The images help crews in the field more accurately locate new faults in the
remote Yuha desert west of El Centro near the U.S.-Mexico border, Rymer
said.
*Among the findings:*
� The Ocotillo fault, a known but previously unnamed fault near the
Imperial County town of the same name, was confirmed as an active fault by
its 3.3 inches of movement.
� The Elsinore fault, one of the major northwest-trending faults in the
area, showed movement from the quake extending 2 miles to the southeast
beyond its previously known length.
Slight surface fault movement was discovered as close to the Coachella
Valley as in the Mecca Hills on the San Andreas fault east of Thermal,
Rymer said.
Research shows that historically, the southern San Andreas fault that runs
along the Coachella Valley's northern edge has had a major earthquake every
150 years. But it's been at least 300 years since the last major temblor on
that section of the fault.
But the 2010 event, a so-called triggered slip, occurred near the surface,
from a few hundred meters to about 3 kilometers in depth � not far enough
down to set off a major earthquake on the San Andreas, Rymer said.
�Those big earthquakes happen about 10 to 15 kilometers below the surface,�
he said. �These triggered slips do not affect that area, so they are not
loading or unloading the faults.�
The new faults have now been registered as Alquist-Priolo Earthquake Fault
Zones, in accordance with a 1970s California law to prohibit most
development across active faults, Treiman said.
But many of the new faults are in remote areas of federal land managed by
the U.S. Bureau of Land Management and are unlikely for development.
The study's findings raise questions for scientists to answer through
further research, particularly regarding how strain is distributed across a
wide area of faulting, Treiman said.
Rymer said the new faults could be sites for further seismic review,
including excavation and examination of sediment layers to get a glimpse at
their past eruptions.
�Now that we know about all of these new faults, it may be just the first
step in understanding what the seismic hazard is down there,� he said.
http://www.mydesert.com/article/ 20120408/ NEWS0805/ 204080309/ Baja-earthquake- Easter-revealed- unknown-Southern -California- faults
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