Scientists have discovered that the Earth's crust is divided into "plates" that have been
gently shifting over the planet's surface for millions of years.
What could this place be where deep within the earth, pressures are causing the crustal
plates to deform?
The ground "bends" to an extent before breaking and "snapping" into a new position.
Seismic vibrations are generated during the faulting process.
Some of the vibrations are so slow that it takes several seconds for one wave to travel
to the next, while others are so fast that they can be heard.
Scientists can see exactly where fissures break through the Earth's crust owing to the
countless small earthquakes that occur in California every year.
Yes!
It is the state of California.
The notorious San Andreas Fault is an example of a continental transform fault.
The San Andreas Fault has been the epicenter of several earthquakes, the deadliest of which
being the 1906 San Francisco quake, which claimed the lives of over 3,000 people.
Since the last earthquake on the San Andreas, seismologists and geologists have been keeping
a careful check on the fault line since they consider it to be nothing less than a ticking
time bomb.
They are aware that an enormous catastrophe might strike at any moment and that California
has to be ready.
Exactly why do scientists worry about the San Andreas Fault line, and what would happen
if the catastrophic disaster they're anticipating actually takes place?
Well then, let's find out!
On April 18, 1906, abrupt displacement along the San Andreas fault caused the devastating
San Francisco earthquake and fire, bringing the fault's existence to global attention
in a spectacular way.
However, due to periodic displacement along the fault, this earthquake was just one of
many that have occurred throughout the fault's lifespan of around 15–20 million years.
The San Andreas fault marks the border between two such plates that meet off the coast of
California.
Earthquakes along the fault line are caused by the northwestward movement of the Pacific
Plate (on the west) compared to the North American Plate (on the east).
The San Andreas is the most important fault in the complex fault system that underlies
the coastal rocks of California.
The whole length of the San Andreas fault system is almost 800 miles, and it goes down
at least 10 miles into the Earth.
From a few hundred feet to a mile in width, the fault is a complicated zone of crushed
and shattered rock.
The San Andreas fault zone is connected to and branched off by a large number of minor
faults.
Small cracks, fault gouge (pulverized rock), and the occasional solid rock chunk may be
seen in nearly every road cut across the zone.
The San Andreas fault runs from northern California southward to Cajon Pass in San Bernardino,
forming a continuous narrow split in the Earth's crust.
Several branching faults, including the San Jacinto and Banning faults, share the movement
of the crustal plates southeastward from Cajon Pass.
The term "San Andreas" is commonly attributed to the northeastern most branch of the fault
zone along this stretch of the fault zone.
A linear depression exposes the presence of the San Andreas fault for most of its length;
from the air, the linear arrangement of lakes, bays, and valleys in this trough is noteworthy.
However, when viewed from the ground, the characteristics are more modest.
Many people passing around Crystal Springs Reservoir, near San Francisco, along Tomales
Bay, or via Cajon or Tejon Passes, for example, may be unaware that they are in the San Andreas
fault zone.
The fault can be identified on the ground by carefully analyzing the terrain.
The fault zone is distinguished by unusual landforms such as long straight escarpments,
narrow ridges, and shallow undrained ponds generated by the settling of small blocks
inside the zone.
Many stream courses veer dramatically to the right as they reach the fault.
The San Andreas fault causes a horizontal motion between blocks on each side of it.
The block on the other side of the fault would appear to have shifted to the right if one
stood on one side of the fault and looked across it.
This kind of fault movement is known as right-lateral strike-slip in the scientific community.
During the 1906 earthquake in the San Francisco area, roadways, railings, and rows of trees
and plants that spanned the fault were offset several yards, while the road at the head
of Tomales Bay was displaced about 21 feet, the highest offset recorded.
The terrain west of the fault migrated substantially northward in each case.
The sudden offset that causes a large earthquake happens on just one portion of the fault at
a time.
Total offset builds in an unequal manner over time, usually due to movement on one and then
another segment of the fault.
The parts that cause major earthquakes stay "locked" and inactive for hundreds or thousands
of years as strain accumulates; eventually, in tremendous lurches, the strain is released,
causing massive earthquakes.
Other segments of the fault, on the other hand, appear to tolerate movement more through
steady creep than by rapid offsets that cause large earthquakes.
In the past, these creeping parts did not cause earthquakes of the magnitude witnessed
on the "locked" sections.
Since its formation around 15-20 million years ago, geologists estimate that the San Andreas
fault has been displaced a total of at least 350 miles due to earthquakes and creep.
Geologically identical terranes on either side of the fault, currently separated by
150 miles, were discovered in studies of a section of the fault between Tejon Pass and
the Salton Sea.
This suggests that certain crustal blocks may have travelled through more than 20 degrees
of latitude.
The pace reflected by these ancient offsets is consistent with the rate recorded during
historical time, which is a challenge to grasp given the magnitude of the movement involved.
As much as 2 inches per year of drift has been measured by surveying efforts.
There are stretches of the San Andreas fault and other plate boundaries where major earthquakes
have not happened for a very long period.
These voids are known to scientists as "seismic gaps" and in many cases they have been able
to accurately predict when huge earthquakes would occur in these voids.
Geological research reveal that significant earthquakes have occurred on the southern
San Andreas fault at around 150-year intervals over the past 1,400 to 1,500 years.
The southern San Andreas hasn't had a major earthquake since 1857, making it a prime target
for a quake in the near future.
Even though it has been less than a century after the devastating 1906 earthquake, the
San Francisco Bay region is still vulnerable to moderate-sized quakes that might cause
significant damage.
Large earthquakes probably won't happen without warning.
Multiple years of increased seismicity, maybe including several foreshocks of roughly magnitude
5 along the fault, may precede such an earthquake.
Also, seismologists anticipate surface changes, such as a reduction in the length of survey
lines across the fault, changes in elevation, and the impact on strainmeters in wells, prior
to the next major earthquake.
The part of the San Andreas fault at Parkfield in central California, where a moderate-size
earthquake has occurred on average every 20-22 years for around the previous 100 years, is
a major place for study on techniques of earthquake prediction.
Numerous terrifying earthquakes, such as the 1857 Fort Tejon quake, the 1906 and 1957 San
Francisco earthquakes, the 1989 Loma Prieta, and the 2004 Park field earthquake, have shook
the area surrounding the San Andreas Fault throughout history.
Scientists have been fretting about the Big One for a while now.
Yuri Fialko, an associate professor at the Scripps Institution of Oceanography's Green
Institute of Geophysics and Planetary Physics, conducted research in 2006 showing that the
San Andreas folded has accumulated enough stress to trigger an earthquake of magnitude
seven or higher.
The study also discovered that the chance of a major earthquake was rising at a rate
that was quicker than experts had predicted.
It was announced a few years ago by the head of the Southern California seismic center
that the San Andreas fault looks to be in a critical state and might produce a significant
earthquake at any time in the coming years.
Experts have cautioned the people that the southern section of the fault looks like it's
locked loaded and ready to go, which is nothing new for Californians as we've established
that the region has weathered its fair number of earthquakes in the past.
If that's the case, then why are seismologists sounding the alarm?
The tension between the plates has been steadily increasing since 1857, when the disastrous
7.8 magnitude 1906 San Francisco earthquake ruptured the fault, and again in the six magnitude
1989 Loma Prieta earthquake.
No earthquake of this size has occurred along the southern San Andreas fault before.
Due to this, experts are speculating that a massive earthquake is coming to this area.
It's feared that this will be The Big One because of the cumulative stress in this area.
Aside from the San Andreas, the Hayward fault, which runs along the base of the Berkeley
hills and right through the University of California, is a ticking time bomb.
It runs beneath a theatre and a few dorms on the stairs of the California Memorial Stadium.
Scientists already know that the Hayward creeps ahead gradually, but they also know that faults
rupture and shatter, and that this rupturing will occur abruptly and without warning.
According to Richard Allen, a Berkeley professor, Hayward is an extremely vulnerable fault line
that hasn't triggered an earthquake since 1868 and is thus due for a large earthquake
in the near future.
Allen predicts that a Hayward earthquake will completely liquefy the stadium field.
Acclaimed specialists have stated unequivocally that huge earthquakes are an unavoidable reality
that Californians cannot prevent, but what residents can do is prepare for such a disaster.
California is constructing three important lines of protection against potentially dangerous
earthquakes.
Buildings in earthquake zones should be designed and constructed to withstand rattling movement.
Lucy Jones spent the whole year of 2014 working with the then-office mayors in Los Angeles
to uncover risks and prepare the city for the inevitable.
Building regulations for older structures can be amended to demand retrofitting to withstand
earthquakes.
Some cities have plans in place to fortify or demolish structures that are prone to collapsing.
The other line of defense is strategic land use, which lessens the negative consequences
of disasters.
Power, communication, and internet networks should be reinforced, and backup systems should
be in place to guarantee that communication is not completely cut off in the event of
an earthquake.
But it's not as simple as it seems; such ideas take billions of dollars in funding and years
to accomplish.
Experts are unsure when the big one will occur or whether it will be as large as they predict.
But, given that California has had its fair share of earthquakes in the past, it's only
natural that residents take every precaution to limit the harm they might wreak.
When do you think the San Andreas fault line, which California sits atop, will finally give
way, causing a devastating earthquake in the state?
Tell us in the comments.