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Balancing rocks trace history of ‘jumping’ earthquakes

Balancing rocks trace history of ‘jumping’ earthquakes

balancing rocks

The researchers spent 10 years collecting measurements of balancing rocks

US scientists say they have solved the riddle of why a collection of balancing rocks near the San Andreas fault has never been toppled by earthquakes.

Their decade-long study concludes that quakes can stop or “jump” due to interactions between the San Andreas and the neighbouring San Jacinto fault.

Models show that these interactions sent the biggest vibrations around the rock stacks, leaving them intact.

But the connected nature of the faults has implications for quake planning.

The study of precariously balanced rocks was begun in the 1990s by Jim Brune, now an emeritus professor at the University of Nevada and a co-author of the new paper.

“He realised that [these rocks] could be a check on seismic hazard maps, and give long-term indications of ground shaking,” said the study’s lead author Prof Lisa Grant Ludwig, from the University of California, Irvine.

“They are kind of natural seismoscopes – but you have to read them indirectly.

“They don’t tell you an earthquake happened, they tell you ‘an earthquake strong enough to knock me down did not happen’.”

Tipping point

Generally, balancing rocks are not seen within 15km of major faults. But 10 years ago Prof Brune and his colleagues found two sizeable collections of such stones just 7-10km from the San Andreas and San Jacinto faults, in the San Bernardino mountains of California.

The teetering rocks sit less than 10km from two major faults

In the new study, due to be published in the journal Seismological Research Letters, these rocks were carefully catalogued and measured.

Importantly, the team calculated how much force it would take to tip each of the rocks over.

“There are two methods of doing that, one of which is actually trying to tip the thing,” Prof Ludwig said. This meant some nerve-wracking fieldwork, gently pushing the rocks until there was some movement, but not actually tipping them over.

“If my mother had known I was doing that, she would not have been happy,” Prof Ludwig confessed. “You never want to be on the downhill side when you tip it.”

The second method, for rocks too dangerous or difficult to tip, was “photomodelling”: using views from multiple angles to build a 3D model of the balanced stone and calculate its centre of gravity, mass, and so on.

Both these methods, along with some “shake table” simulation experiments, showed that the rocks should have fallen over during quakes as recent as 1812 and 1857.

The famous San Andreas fault stretches 1,300km across California

But various measures can tell us exactly how long the stones have perched in their places – and it is millennia, not centuries.

“One of my former postdocs did an age study of one of the rocks. And it’d been in that position about 18,000 years,” said Prof Ludwig.

So how did these precarious rocks withstand the tens or hundreds of earthquakes that shook the region during that time?

Network of fractures

“The inescapable conclusion was that the ground motions had to be lower than you would expect from typical earthquakes on the San Andreas and San Jacinto faults,” Prof Ludwig explained.

The team’s best explanation for that surprisingly small ground movement – and one supported by computer modelling of big earthquakes – is an interaction between the two faults.

Precarious rocks, like this one in Nevada, can act as natural measures of earthquake strength over time

Precarious rocks, like this one in Nevada, can act as natural measures of earthquake strength over time
“The San Andreas and San Jacinto faults come very close together; they’re only about 2km apart. And it’s been well established, through other earthquakes and modelling studies, that a rupture can jump across [a gap like that]. It’s what’s called a stepover.

“What if the rupture jumped across, or alternatively, stopped at this junction, or started at this junction? All three of those cases would produce lower ground shaking in the area where we found the rocks.”

It is crucial to consider the faults together, Prof Ludwig said – not just to explain the baffling, balancing rocks, but also in order to plan safely for future earthquakes.

“These are really networks of fractures in the earth. Just because we give them different names doesn’t mean that they behave independently.”

Shaky scenario

Dr Lucy Jones is a long-serving seismologist and a science adviser for risk reduction at the US Geological Survey. She said the paper would have “pretty significant implications” for earthquake planning in California.

In particular, Dr Jones said the findings might impact the “ShakeOut scenario” – in which she and others modelled a major San Andreas quake, to support safety drills and procedures.

“I think that this study actually makes the particular ShakeOut scenario less likely, but I’m not sure it means that we’re definitely going to get less ground motion,” Dr Jones told the BBC.

“It isn’t a clear-cut answer as to whether we’ll be better off or worse off. We’re going to need time to look at the permutations.”

Looking beyond individual quakes, Dr Jones said the new study fits into a “pretty well accepted picture” that in the long-term, seismic activity is gradually shifting from the southern stretch of the San Andreas fault across to the younger San Jacinto fault.

“This study is a really cool piece of evidence that maybe the jump is a little further along than we assumed,” she said.

Did you know that pets can often detect ear quakes before they happen? Here’s a story from Animal X about some such pets.


Halloween playlist.

Halloween is almost here.

Jersey Devil

The night when demons and witches, monsters and crytids come out to play.

Trick or treat?

Real or not.

Check out the playlist and decide for yourself.

There are more than 40 great stories in this playlist including the Jersey Devil, Mothman (Winged Creatures), el Chupacabra, Ghostly Creatures, Goat Man, and many more.

 
Halloween Playlist from Animal X. Scary stuff my darlings…. watch, if you dare….

Click on the Playlist dropdown menu at the top of the video to select which scary story you’d like to watch….


 

What do you think of these Halloween stories. Log in and leave a comment.

Here’s some information about the origins of Halloween

Alien Big Cat

Halloween or Hallowe’en (/ˌhæləˈwn, ˈn, ˌhɑːl/; a contraction of “All Hallows‘ Evening“),[6] also known as Allhalloween,[7] All Hallows’ Eve,[8] or All Saints’ Eve,[9] is a yearly celebration observed in a number of countries on 31 October, the eve of the Western Christian feast of All Hallows’ Day. It initiates the triduum of Allhallowtide,[10] the time in the liturgical year dedicated to remembering the dead, including saints (hallows), martyrs, and all the faithful departed believers.[11] Within Allhallowtide, the traditional focus of All Hallows’ Eve revolves around the theme of using “humor and ridicule to confront the power of death.”[12]

Beast of Gevaudan

According to many scholars, All Hallows’ Eve is a Christianized feast initially influenced by Celtic harvest festivals,[13][14] with possible pagan roots, particularly the Gaelic Samhain.[8][15][16] Other scholars maintain that it originated independently of Samhain and has solely Christian roots.[17][18]

Typical festive Halloween activities include trick-or-treating (or the related “guising“), attending costume parties, decorating, carving pumpkins into jack-o’-lanterns, lighting bonfiresapple bobbing, visiting haunted house attractions, playing pranks, telling scary stories, and watching horror films. In many parts of the world, the Christian religious observances of All Hallows’ Eve, including attending church services and lighting candles on the graves of the dead, remain popular,[19][20][21] although in other locations, these solemn customs are less pronounced in favor of a more commercialized and secularized celebration.[22][23][24] Because many Western Christian denominations encourage, although no longer require, abstinence from meat on All Hallows’ Eve,[25][26] the tradition of eating certain vegetarian foods for this vigil day developed, including the consumption of apples, colcannonciderpotato pancakes, and soul cakes.[26][27][28]

Heroic Police Dog Bosun Dies

Retired police dog Bosun, who helped nab the gunman who murdered a detective, has died aged 9. AAP

A Gold Coast police dog who played a key role in the arrest of a gunman who murdered Detective Damian Leeding in 2011 has died.

Retired, heroic police dog Bosun died in the arms of his handler Senior Constable Wayne Algie on Monday.

The German shepherd was nine.

Sen Const Algie described the loyal pooch as a good mate and colleague, adding that he had a great work ethic and would be missed.

“Bosun was much loved by his family at home as well as his QPS family,” he said in a statement on Tuesday.

The police dog had a distinguished career and was well-known for his work helping in the arrest of offenders.

Both Bosun and his handler played a key role in the arrest of the gunman who shot and killed Gold Coast Detective Leeding in May 2011.

The detective was shot in the face after being called to an armed robbery at the Pacific Pines Tavern.
Sen Const Algie and Bosun tracked gunman Phillip Graeme Abell across an exposed paddock and into pitch black bushland where he was arrested.

Abell is serving a life sentence for murder, while his accomplices are also in jail.

In 2012 Bosun spent weeks recovering after being mauled by two dogs during an arrest at Upper Coomera.

That same year he helped officers nab a man, wanted on a string of weapons and theft offences, who ran from police after a pursuit at Pacific Pines.

The famed dog also gave up the bulk of his coat when he was “clipped for a cure” as part of the Leukaemia Foundation’s World’s Greatest Shave fundraiser in 2012.

Bosun, who was awarded the Australian Defence Force Service Medal, had lived with Sen Const Algie since his retirement last year.

Here’s a story from Animal X about other heroic dogs:


Dog Rescued From a Freeway Drain


 
Dog Rescue

This is a nice story about the rescue of a small dog from freeway drain.

Meet Frankie, a tiny black chihuahua who had spent the majority of his life living in an underground sewer system, until one day when an angel came his way. Hope For Paws, an amazing rescue organization in California, got the call about the dog and rescued him from the filth he knew as home.

Frankie’s rescuers took him to a safe place where he was cleaned up and fed. That’s where he met Miley. Miley was an older dog that instantly took tiny Frankie under his paw and showed him kindness.

The pair instantly bonded and Miley taught Frankie that he didn’t have to be frightened any more. Now, they have found a forever home together and are blessed with one another’s friendship every day.

Their story made me smile so big!

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