Thomas Tartaron / Google Earth

Archaeologists discovered Korphos-Kalamianos, the spectacularly preserved ancient harbor town of the Mycenaeans, the civilization on which many ancient Greek legends were based.

By Becky Oskin
LiveScience

The grand Mycenaens, the first Greeks, inspired the legends of the Trojan Wars, "The Iliad" and "The Odyssey." Their culture abruptly declined around 1200 B.C., marking the start of a Dark Ages in Greece.

The disappearance of the Mycenaens is a Mediterranean mystery. Leading explanations include warfare with invaders or uprising by lower classes. Some scientists also think one of the country's frequent earthquakes could have contributed to the culture's collapse. At the ruins of Tiryns, a fortified palace, geologists hope to find evidence to confirm whether an earthquake was a likely culprit.

Tirynswas one of the great Mycenaean cities. Atop a limestone hill, the city-state's king built a palace with walls so thick they were called Cyclopean, because only the one-eyed monster could have carried the massive limestone blocks. The walls were about 30 feet (10 meters) high and 26 feet (8 m) wide, with blocks weighing 13 tons, said Klaus-G. Hinzen, a seismologist at the University of Cologne in Germany and project leader. He presented his team's preliminary results April 19 at the Seismological Society of America's annual meeting in Salt Lake City. [History's Most Overlooked Mysteries]

Hinzen and his colleagues have created a 3-D model of Tiryns based on laser scans of the remaining structures. Their goal is to determine if the walls'collapse could only have been caused by an earthquake. Geophysical scanning of the sediment and rock layers beneath the surface will provide information for engineering studies on how the ground would shake in a temblor.

The work is complex, because many blocks were moved by amateur archaeologist Heinrich Schliemann in 1884 and later 20th-century restorations, Hinzen said. By combing through historic photos, the team found unaltered wall sections to test. They also hope to use a technique called optical luminescence dating on soil under the blocks, which could reveal whether the walls toppled all at the same time, as during an earthquake.

"This is really a challenge because of the alterations. We want to take a careful look at the original conditions," Hinzen told OurAmazingPlanet.

Another hurdle: finding the killer quake. There are no written records from the Mycenaean decline that describe a major earthquake, nor oral folklore. Hinzenalso said compared with other areas of Greece, the region has relatively few active faults nearby. "There is no evidence for an earthquake at this time, but there was strong activity at the subduction zone nearby," he said.

The Mycenaean preference to place their fortresses atop limestone hills surrounded by sediment would concentrate shaking, even from distant earthquakes, Hinzen said. "The (seismic) waves get trapped in the outcrop and this can do a lot of damage. They are on very vulnerable sites," he said.

The researchers also plan to study the ancient Mycenaean city of Midea. The group has done similar work investigating ancient earthquakes in Turkey, Germany and Rome.

Email Becky Oskin or follow her @beckyoskin. Follow us @OAPlanet, Facebook and Google+. Original article on LiveScience's OurAmazingPlanet.

• The 7 Most Mysterious Archaeological Discoveries on Earth
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USGS

The beautiful Wasatch Range looms over Salt Lake City, Utah.

By Becky Oskin
LiveScience

Two faults bounding Utah's biggest city may combine to produce especially powerful earthquakes, geologists will report in Salt Lake City Wednesday at the annual meeting of the Seismological Society of America.

Utah's biggest earthquake fault runs east of Salt Lake City, at the base of the steep Wasatch Mountains. About 75 percent of the state's population lives near the 240-mile-long (385 kilometers) Wasatch Fault, according to the Utah Geological Survey. Its last big earthquake hit in 1600, 247 years before Mormon settlers arrived.

To the west, in urban Salt Lake City, a 4-mile-wide (6 km) zone of fault segments called the West Valley Fault Zone stretches north-northwest for 9 miles (14 km) beneath the valley.

Trenches along a portion of the West Valley Fault Zone, near Salt Lake City's airport, reveal that both the West Valley and Wasatch faults seem to rupture simultaneously during earthquakes, scientists will report at the meeting.

While dating techniques can't confirm that the earthquakes were synchronous, instead of within a few days, month or years, modeling suggests they strike at the same time, said Christopher DuRoss, study co-author and a geologist at the Utah Geological Survey.

"Based on models of how the crust would behave, we expect the West Valley Fault Zone would rupture instantaneously with the Salt Lake City segment," DuRoss told OurAmazingPlanet.

Two faults, more shaking
If both fault zones ruptured during an earthquake, it would mean more shaking for Salt Lake City, which sits atop soft lake sediments, the kind that experience liquefaction during severe earthquakes. In the 2011 Christchurch, New Zealand earthquake, liquefaction destroyed the city's downtown core. In Salt Lake City, planners are also concerned about the risk of flooding from waves in the Great Salt Lake and landslides in mountain canyons during a major earthquake.

Residents of Salt Lake will get a better picture of their risk when the Utah Geological Survey and U.S. Geological Survey release updated hazard maps in 2014, which are based on today's presentation and other recent work, DuRoss said. [What's the Most Earthquake-prone State in the U.S.?]

Mike Hylland / Utah Geological Survey

The Wasatch and West Valley fault zones near Salt Lake City may rupture at the same time, new research reveals.

The Wasatch Fault is divided into 10 segments, which mostly act independently, researchers think. The 25-mile-long (40 km) Salt Lake City segment is thought to be one of the most hazardous, with the probability of a large quake (magnitude 7.0) put at 16.5 percent in the next 100 years, according to the Utah Geological Survey. However, that earthquake forecast is now out-of-date, thanks to new research, and will be updated next year by the Working Group on Utah Earthquake Probabilities, DuRoss said.

Trenches find big quakes
DuRoss and study co-author Michael Hylland looked at the link between the Wasatch Fault and the West Valley Fault Zone with trenches dug near the Salt Lake City airport, where the shrinking Great Salt Lake has exposed West Valley fault traces. For the Wasatch fault, the team dug new trenches near the University of Utah.

Disturbed sediment layers indicate four big earthquakes on the West Valley Fault broke ground in the past — 15,700, 13,000, 12,300 and 5,500 years ago, said Hylland, also a geologist at the Utah Geological Survey. Radiocarbon and optical luminescence dating ties the broken ground to earthquake records in trenches along the Salt Lake City section of the Wasatch Fault.

More complete sediment records exist for the Salt Lake City section of the Wasatch Fault, with nine prehistoric temblors found, Hylland said.The last big earthquake on the Salt Lake City segment was 1,400 years ago. The quakes hit every 1,300 to 1,500 years, researchers think.

"From what we can see, it looks like the frequency is about the same" on the two fault zones, Hylland told OurAmazingPlanet. "What it really comes down to is 'how active is the Salt Lake City segment?'" Hylland said. "That's the real driver of the hazard for Salt Lake Valley."

The separate faults likely merge into a single fault deep beneath the valley, Hylland said. The West Valley Fault angles to the east, and the Wasatch Fault dips to the west.

Movement on both faults is up-down. They are both normal faults, sliding one block of the Earth's crust away from another block during an earthquake.

Email Becky Oskin or follow her @beckyoskin. Follow us @OAPlanet, Facebook and Google+. Original article on LiveScience's OurAmazingPlanet.

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K.-G. Hinzen et al.

The top three photos are of the Roman mausoleum at Pinara. The middle three images are reconstructions from laser scans of the mausoleum. The bottom three images are from a computer model of the mausoleum, including hypothetical missing parts.

By Charles Q. Choi
LiveScience

The way the massive stone blocks making up a Roman mausoleum in Turkey were knocked off-kilter reveals clues to the power of the earthquake that rocked the structure.

Analyzing other ancient ruins for such damage could help shed light on the history of earthquakes in a region, which could yield insights on what risks that area faces in the future, the scientists who examined the mausoleum said.

The ruins of the city of Pinara date back at least 2,500 years to the ancient realm of Lycia in what is now southwest Turkey. It eventually became part of the Roman Empire.

"Pinara is a very exciting place because it has not been excavated yet," said Klaus-G. Hinzen,  a seismologist at the University of Cologne in Germany. "You feel closer to ancient times than you would strolling through a museum with great artifacts."

Hinzen and his colleagues analyzed a Roman mausoleum in Pinara. Built under a sheer cliff nearly 330 feet (110 meters) high, it has a commanding view of the nearby forum and castle and the mountain range to the east.

The mausoleum is mostly intact, but shows signs of damage. Most of its blocks have shifted heavily; some have fallen off its walls, and the front section of the mausoleum is collapsed, including its pillars.

Scientists were uncertain how the mausoleum was damaged. An earthquake seemed a likely culprit, but the cliff the mausoleum is built under is honeycombed with numerous other tombs, and damage from falling rock also seemed a plausible cause.

To help solve the mystery, researchers constructed a 3-D model of the mausoleum based on 90 million data points from nine laser scans of the structure.

"Some objects we laser-scanned in Pinara caused more gardening work than geophysical work — we had to remove vegetation to get the laser beam a straight view to the targets," Hinzen said.

The scientists deduced the mausoleum was once made of about 180 stone blocks. Computer simulations analyzing the way it warped revealed that rockfall was not the likely major cause of its damage. Instead, it was likely an earthquake, and based on the level of damage the structure experienced, the simulations suggest the quake was potentially a magnitude 6.3 temblor. [Video: What Earthquake 'Magnitude' Means]

"I was astonished by the sensitivity with which the model of the building reacts to small changes in the ground motion," Hinzen told OurAmazingPlanet. "It is fascinating to watch the movements of the blocks during the calculations. Sometimes when you watch a block or column, you think, now it must topple, but at the end it doesn't."

These findings could help inform seismologists about the likely earthquake hazard this southwestern region of Turkey faces. Such work could also provide information on the effects of ancient earthquakes elsewhere in the world.

"Currently we are testing the hypothesis that the Mycenaean culture was brought to an end, at least in part, by strong earthquakes on the Peloponnese in Greece," Hinzen said. "We're concentrating our work on the Mycenaean citadels of Tiryns and Midea, a project in cooperation with archaeologists from Heidelberg University and Greece."

Hinzen and his colleagues Helen Kehmeier and Stephan Schreiber detailed their findings in the April issue of the journal Bulletin of the Seismological Society of America.

Follow OurAmazingPlanet @OAPlanet, Facebook and Google+.Original article at LiveScience's OurAmazingPlanet.

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Heritage Auctions

The tyrannosaur of the minerals, this gold nugget in quartz weighs more than 70 ounces (2 kilograms).

By Becky Oskin, OurAmazingPlanet

Earthquakes have the Midas touch, a new study claims.

Water in faults vaporizes during an earthquake, depositing gold, according to a model published in the March 17 issue of the journal Nature Geoscience. The model provides a quantitative mechanism for the link between gold and quartz seen in many of the world's gold deposits, said Dion Weatherley, a geophysicist at the University of Queensland in Australia and lead author of the study.

When an earthquake strikes, it moves along a rupture in the ground — a fracture called a fault. Big faults can have many small fractures along their length, connected by jogs that appear as rectangular voids. Water often lubricates faults, filling in fractures and jogs.

About 6 miles (10 kilometers) below the surface, under incredible temperatures and pressures, the water carries high concentrations of carbon dioxide, silica and economically attractive elements like gold.

Shake, rattle and gold
During an earthquake, the fault jog suddenly opens wider. It's like pulling the lid off a pressure cooker: The water inside the void instantly vaporizes, flashing to steam and forcing silica, which forms the mineral quartz, and gold out of the fluids and onto nearby surfaces, suggest Weatherley and co-author Richard Henley, of the Australian National University in Canberra.

While scientists have long suspected that sudden pressure drops could account for the link between giant gold deposits and ancient faults, the study takes this idea to the extreme, said Jamie Wilkinson, a geochemist at Imperial College London in the United Kingdom, who was not involved in the study.

"To me, it seems pretty plausible. It's something that people would probably want to model either experimentally or numerically in a bit more detail to see if it would actually work," Wilkinson told OurAmazingPlanet.

Previously, scientists suspected fluids would effervesce, bubbling like an opened soda bottle, during earthquakes or other pressure changes. This would line underground pockets with gold. Others suggested minerals would simply accumulate slowly over time.

Weatherley said the amount of gold left behind after an earthquake is tiny, because underground fluids carry at most only one part per million of the precious element. But an earthquake zone like New Zealand's Alpine Fault, one of the world's fastest, could build a mineable deposit in 100,000 years, he said.

Surprisingly, the quartz doesn't even have time to crystallize, the study indicates. Instead, the mineral comes out of the fluid in the form of nanoparticles, perhaps even making a gel-like substance on the fracture walls. The quartz nanoparticles then crystallize over time. [Gold Quiz: From Nuggets to Flecks]

Even earthquakes smaller than magnitude 4.0, which may rattle nerves but rarely cause damage, can trigger flash vaporization, the study finds.

"Given that small-magnitude earthquakes are exceptionally frequent in fault systems, this process may be the primary driver for the formation of economic gold deposits," Weatherley told OurAmazingPlanet.

The hills have gold
Quartz-linked gold has sourced some famous deposits, such as the placer gold that sparked the 19th-century California and Klondike gold rushes. Both deposits had eroded from quartz veins upstream. Placer gold consists of particles, flakes and nuggets mixed in with sand and gravel in stream and river beds. Prospectors traced the gravels back to their sources, where hard-rock mining continues today.

But earthquakes aren't the only cataclysmic source of gold. Volcanoes and their underground plumbing are just as prolific, if not more so, at producing the precious metal. While Weatherley and Henley suggest that a similar process could take place under volcanoes, Wilkinson, who studies volcano-linked gold, said that's not the case.

"Beneath volcanoes, most of the gold is not precipitated in faults that are active during earthquakes," Wilkinson said. "It's a very different mechanism."

Understanding how gold forms helps companies prospect for new mines. "This new knowledge on gold-deposit formation mechanisms may assist future gold exploration efforts," Weatherley said.

In their quest for gold, humans have pulled more than 188,000 tons (171,000 metric tons) of the metal from the ground, exhausting easily accessed sources, according to the World Gold Council, an industry group.

Email Becky Oskin or follow her @beckyoskin. Follow us @OAPlanet, Facebook or Google+. Original article on LiveScience's OurAmazingPlanet.

• 50 Amazing Facts About Earth
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U.S. Navy / Petty Officer 2nd Class Philip A. McDaniel

A village near the coast of Sumatra lays in ruin on Jan. 2, 2005, as a result of the tsunami that struck Southeast Asia on Dec. 26, 2004.

By Becky Oskin
Our Amazing Planet

The earthquakes that rocked Tohoku, Japan in 2011, Sumatra in 2004 and Chile in 1960 — all of magnitude 9.0 or greater — should not have happened, according to seismologist's theories of earthquake cycles. And that might mean earthquake prediction needs an overhaul, some researchers say.

All three earthquakes struck along subduction zones, where two of Earth's tectonic plates collide and one dives beneath the other. Earlier earthquakes had released the pent-up strain along Chile's master fault, meaning no big quakes were coming, scientists had thought. Japan and Sumatra both sat above on old oceanic crust, thought to be too stiff for superquakes.

And records of past quakes, combined with measurements of the speed of Earth's tectonic plates, suggested the Tohoku and Sumatra-Andaman regions couldn't make quakes larger than 8.4, almost nine times smaller than a magnitude 9.0 temblor.

"These areas had been written off as places incapable of producing a great earthquake," said Chris Goldfinger, a marine geologist at Oregon State University in Corvallis.

USGS

The Cascadia subduction zone: producer of massive earthquakes.

But the events of 1960, 2004 and 2011 showed that these faults were capable of producing some of the most destructive earthquakes in recorded history, suggesting earthquake researchers need to rethink aspects of how they evaluate a fault's earthquake potential.

"It's time to come up with something new," Goldfinger told OurAmazingPlanet.

Faults are like batteries
When two tectonic plates collide, they build up strain where a fault sticks, or locks, together. Earthquakes release this strain, which is a form of energy.

For decades, scientists assumed faults acted like rubber bands, steadily building up strain and then releasing it all at once, Goldfinger said. The longer the time since the last earthquake, the larger the next earthquake would be, the model predicted. [ Video: What Does Earthquake 'Magnitude' Mean? ]

The problem was researchers failed to recognize that faults can store energy like a battery, Goldfinger said. And just like batteries, they can discharge energy in small amounts, or all at once, he explained.

Goldfinger and other researchers now think if a "small" quake hits, it may not release all of the accumulated energy in a fault. (On a subduction zone, a small quake can still register in the magnitude-8.0 range, which is devastating to nearby cities.)

Thus, a fault can "borrow" stored energy from previous strain-building cycles, generating larger earthquakes than expected, such as those that hit Sumatra and Tohoku, Goldfinger and his colleagues propose in a study published in the January/February 2013 issue of the journal Seismological Research Letters.

"Those models were already being called into question when Sumatra drove one stake through their heart, and Tohoku drove the second one," said Goldfinger, the lead author of the study.

Superquakes and supercycles
Goldfinger said scientists' failure to recognize that faults could store energy comes from a lack of data. Historic earthquake records go back only 100 years, he noted. Geologists are only now getting histories that reach back thousands of years, via techniques that decode evidence of past earthquakes in sediments.

"What is happening on a short-term timescale is actually imposed on a long-term cycle," he said.

Goldfinger calls these long-term histories supercycles, and the unusually large and rare earthquakes that discharge the battery are superquakes. The sequence, size and location of quakes vary from one supercycle to the next, he said.

Seismologist Marco Cisternas first proposed that faults could store energy in 2005, with a study showing that the magnitude 9.5 Chile earthquake in 1960, the largest on record, released more energy than had been stored since its most recent quake, in 1837. Tsunami deposits in Chile indicate the last superquake occurred in 1575, and smaller quakes since then had only partly released the strain built up on the fault, his study found.

In Sumatra, south of the Andaman region, analyses of corals uplifted and killed during earthquakes also indicated that the subduction zone undergoes supercycles, according to a 2008 study led by geologists at the Earth Observatory Institute in Singapore. Each series of quakes in the region lasts between 30 and 100 years, according to the study. The supercycles unfold every 200 years or so.

Forecasting the future
Goldfinger and his colleagues have evidence that the Cascadia Subduction Zone, which stretches from Northern California to British Columbia, is also in the middle of an earthquake supercycle.

Over the past 10,000 years, 19 superquakes and four supercycles have occurred along the zone, Goldfinger said.

"These would typically be of a magnitude from about 8.7 to 9.2, really huge earthquakes," Goldfinger said. "We've also determined that there have been 22 additional earthquakes that involved just the southern end of the fault. We are assuming that these are slightly smaller, more like 8.0, but not necessarily. They were still very large earthquakes that if they happened today could have a devastating impact," he said.

The present cycle seems like it's gently ratcheting downward, Goldfinger said. "This would suggest that we're not due for a giant (quake) anytime soon, but the model has no predictive value," he said.

The battery model of earthquake energy storage and discharge makes it difficult for scientists to forecast future earthquakes, as there's no explanation yet for why faults would behave this way, Goldfinger said. Plus, it's hard to say how much energy a fault's battery stores. "We haven't yet figured out how to effectively put a voltmeter on a fault and say how charged it is," Goldfinger said.

But with more detailed records of past earthquakes, such as those in Sumatra and Cascadia, Goldfinger believes scientists can give better estimates of seismic hazards, and prevent surprises like Sumatra and Tohoku.

"The long records are revealing very useful things," he said. "We're not sure what's driving the long-term cycling, but at least we can tell people what to prepare for," Goldfinger said.

Reach Becky Oskin at boskin@techmedianetwork.com. Follow her on Twitter @beckyoskin. Follow OurAmazingPlanet on Twitter @OAPlanet. We're also on Facebook   and Google+.

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