Advertisements
Archive | San Andreas Fault RSS for this section

#Satellite images show giant #crack caused by #earthquake in #MojaveDesert, #California, #USA

Before and after imagery of the epicentre of the recent Ridgecrest Earthquake. Pic: Planet Labs Inc

Before and after images show the epicentre of Friday’s quake. Pic: Planet Labs Inc

The impact of Southern California’s strongest earthquake in 20 years has been revealed after satellite images showed how a huge crack emerged in the Earth’s surface.

The US state was rocked by two powerful earthquakes of magnitudes 7.1 and 6.4 last week along with hundreds of aftershocks.

The stronger quake on Friday struck 11 miles from the city of Ridgecrest, with satellite images by Planet Labs Inc showing the large crack that was ripped open in the Mojave Desert.

Move the slider from left to right to see the difference in images of the epicentre before and after the quake.

The US Geological Survey has reportedly said the crack is not a new fault line and the recent quake activity is not related to the dangerous San Andreas fault.

Before last week, the last time an earthquake above a magnitude of 6 struck Southern California was in 1999 when a 7.1 magnitude event – dubbed the Hector Mine quake – was recorded.

Friday’s quake ruptured gas lines and sparked numerous fires in Ridgecrest, about 125 miles from Los Angeles.

RIDGECREST, CALIFORNIA - JULY 04: A local resident inspects a fissure in the earth after a 6.4 magnitude earthquake struck the area on July 4, 2019 near Ridgecrest, California. The earthquake was the largest to strike Southern California in 20 years with the epicenter located in a remote area of the Mojave Desert. The temblor was felt by residents across much of Southern California. (Photo by Mario Tama/Getty Images)
The 6.4 quake caused a fissure near Ridgecrest in the earth last Thursday

Offices in central LA were shaken for around 30 seconds by the tremors, and the quake was also felt in the Hollywood Hills, Las Vegas and parts of Mexico.

It came after Southern California was struck by a 6.4-magnitude quake on Thursday, which was followed by a strong 5.4-magnitude aftershock in the early hours of the next morning.

The force of the earthquake left a crack through this highway Pic: Karaleigh Roe
The force of the earthquake cracked a road Pic: Karaleigh Roe

There were minor injuries but no reports of anyone seriously hurt or killed.

Fears of a large quake had grown recently after 1,000 small tremors were reportedly recorded in Southern California over three weeks.

The “swarmageddon” produced earthquakes with an average magnitude of 3 last month, the LA Times reported.

Fissures that opened up under a highway during a powerful earthquake that struck Southern California are seen near the city of Ridgecrest, California, U.S., July 4, 2019. REUTERS/David McNew
There have no reports of any fatalities

California officials are spending more than $40m (£32m) on an earthquake early warning system that – in addition to alerting the public – could also be used to automatically halt trains and open fire station doors moments before a major tremor actually strikes.

Emergency management officials have said they intend to have the statewide warning system in place by mid-2021 to serve California’s roughly 40 million residents.

Courtesy of Sky News

https://tinyurl.com/y5zgpfvb

Advertisements

MAGNITUDE 6.3 ANDREANOF ISLANDS, ALEUTIAN IS.

Subject to change
Depth: 60 km

Distances: 3779 km NE of Tokyo, Japan / pop: 8,337,000 / local time: 12:35:16.8 2018-08-23

4512 km NE of Pyongyang, Korea, Democratic People’s Republic of / pop: 3,222,000 / local time: 12:05:16.8 2018-08-23
4526 km NE of Seoul, Korea, Republic of / pop: 10,350,000 / local time: 12:35:16.8 2018-08-23
Global view Regional view

Major earthquake ‘certain’ to hit Southern California, study says

‘No getting out of this’: Major earthquake ‘certain’ to hit Southern California, study says
San Andreas fault © Francois Gohier / http://www.globallookpress.com
It is simply a matter of time before a major earthquake hits Southern California, according to a new study by the US Geological Survey (USGS), which examined patterns of historic quakes. The only question is how long it will be before the ‘Big One’ strikes.
 
The study – the most extensive of its kind – examined a section of the San Andreas fault that runs along Interstate 5, near Frazier Mountain in northeast Kern County.
 
“One of the reasons why this location is of importance is because in Southern California, the Big Bend, Carrizo, and Mojave sections of the San Andreas Fault accommodate 50-70% of plate motion. This means that the seismic hazard is high,” according to Temblor. 
 
To understand the size and likelihood of future earthquakes striking the area, the researchers looked into the past, by digging more than 30 trenches to trace ancient temblors.
 
“To get 1,200 years of records, we have to do lots of excavations and go quite deep,” said the study’s lead author, USGS research geologist Kate Scharer, as quoted by the Los Angeles Times.
 
Scharer and her team found 10 major earthquakes over a 1,000-year period. They were able to date the temblors by examining charcoal and plant remains found at each horizon.
 
The most common magnitude found at the site was 7.5.
 
A 7.9 earthquake in 1857 – the last major temblor to strike – was so powerful that it caused the soil to liquefy and trees to sink and uproot. The shaking lasted between one and three minutes.
 
Since then, land on either side of the fault has been pushing against the other at a rate of more than 1in per year, accumulating energy which will be suddenly released in a major earthquake that would move land along the fault line by many feet.
 
A repeat of the 1857 quake could move the land as much as 20ft, damage aqueducts that ferry water into Southern California from the north, disrupt transmission lines, and damage Interstate 5.
 
Although the researchers noted that a big earthquake is certain, they couldn’t predict when it will happen because they “don’t happen like clockwork.”
 
For instance, while there was once a gap of just 20 years between two temblors, another pair saw a gap of 200 years between them.
 
The average interval between quakes was found to be approximately 100 years, meaning the gap separating today from the 1857 earthquake is already 60 years more than the average.
 
“Longer gaps have happened in the past, but we know they always do culminate in a large earthquake. There’s no getting out of this,” Scharer said.
 
She went on to urge similar studies to take place so that scientists can gain a greater understanding of the San Andreas Fault, in order to “properly design infrastructure, like highways, water, and power lines, so that it can survive the next earthquake.”
 
The San Andreas Fault extends roughly 1,300km (800 miles) through California. It has three segments, each with a varying degree of earthquake risk. The most significant is the southern segment, which passes within about 56km (35 miles) of Los Angeles.
Courtesy of rt.com

A SECOND fault line running parallel to San Andreas has just been identified

the-san-andreas-fault
The San Andreas Fault. Credit: US Geological Survey
Just days after a cluster of more than 200 small earthquakes shook the Salton Sea area of Southern California, scientists have found evidence of a second fault line that runs parallel to the massive San Andreas Fault – one of the state’s most dangerous fault lines.
 
The new fault appears to run right through the 56-km-long Salton Sea in the Colorado Desert, to the west of the San Andreas Fault. Now that we know it’s there, seismologists will be forced to reassess earthquake risk models for the greater Los Angeles area.
 
“This previously unidentified fault represents a new hazard to the region and holds significant implications for fault models … and, consequently, models of ground-motion prediction and southern San Andreas Fault rupture scenarios,” the team from the Scripps Institution of Oceanography and the Nevada Seismological Laboratory reports.
 
Now known as the Salton Trough Fault, the newly mapped fault has been hidden for all this time because it’s submerged beneath the Salton Sea – a vast, salty rift lake that formed as a result of all the tectonic activity in the area.
 
The team had to use an array of instruments, including multi-channel seismic data, ocean-bottom seismometers, and a surveying method called light detection and ranging (LiDAR), to precisely map fault inside several sediment layers both in and surrounding the lakebed.
 
“The location of the fault in the eastern Salton Sea has made imaging it difficult, and there is no associated small seismic events, which is why the fault was not detected earlier,” says Scripps geologist Neal Driscoll.
 
Oddly enough, the fact that we now know there’s an extra fault line running parallel to the San Andreas Fault doesn’t necessarily mean the area is more prone to earthquakes than we originally thought.
 
It might actually solve the mystery of why the region has been experiencing LESS earthquakes than expected.
 
As the team explains, recent research has revealed that the region has experienced magnitude-7 earthquakes roughly every 175 to 200 years for the last 1,000 years. 
 
But that’s not been the case more recently. In fact, a major rupture on the southern portion of the San Andreas Fault has not occurred in the last 300 years, and researchers think the region is long overdue for a major quake.
 
Now they have to figure out what role the Salton Trough Fault could have played in all that.
 
“The extended nature of time since the most recent earthquake on the Southern San Andreas has been puzzling to the earth sciences community,” said one of the Nevada team, seismologist Graham Kent. 
 
“Based on the deformation patterns, this new fault has accommodated some of the strain from the larger San Andreas system, so without having a record of past earthquakes from this new fault, it’s really difficult to determine whether this fault interacts with the southern San Andreas Fault at depth or in time.”
fault-lines
A map of the new fault line, STF. Credit: Sahakian et. al.
On Monday morning, ominous rumblings started to emanate from deep underneath the Salton Sea, and then a ‘swarm’ of small earthquakes – three measuring above magnitude 4 – ruptured at the nearby Bombay Beach.
 
The ruptures continued for roughly 24 hours, with more than 200 small earthquakes having been recorded in the area.
 
These small earthquakes – or temblors – were not very severe, but this is just the third time since records began in 1932 that the area has experienced such an event. And this one had more earthquakes than both the 2001 and 2009 events.
 
The event caused the US Geological Survey to increase the estimated risk of a magnitude 7 or greater earthquake in the next week from to between 1 in 3,000 and 1 in 100. To put that in perspective, without any quake swarms, the average risk for the area sits at around 1 in 6,000.
 
Fortunately, the increased risk now appears to have passed, and according to the Los Angeles Times, California governor’s Office of Emergency Service just announced that the earthquake advisory period is now officially over.
 
Of course, for those living in the area, it’s cold comfort, because the southern San Andreas Fault is still “locked, loaded, and ready to go”. Let’s hope the discovery of the Salton Trough Fault will make it easier for seismologists to at least predict when that will happen.
Courtesy of sciencealert.com