Dead Plants Hold Earthquake Secrets
Scott Haefner, USGS
View looking southeast along the surface trace of the San Andreas fault in the Carrizo Plain, north of Wallace Creek.
April 19, 2012 --
Forty years ago this week, the crew of Apollo 16 captured this image of Earth rising above the lunar landscape. The Apollo missions enabled humanity to see for the first time our planet as it appears from space. As Apollo 13 commander Jim Lovell once said: “When I was orbiting the moon and could put my thumb up to the window and completely cover the Earth, I felt a real sense of my own insignificance. Everything I'd ever known could be hidden behind my thumb.” As we approach Earth Day on April 22, we look at the efforts of people throughout the ages to explore, understand and portray our world and its place in the Universe.
Trustees of the British Museum (image rotated
Babylonia Believed to be the earliest known representation of Earth, this stone tablet from Babylon shows the world as a disc, surrounded by a ring of water called the "Bitter River." The world is dominated by the area surrounding Babylon itself, and the Euphrates River bisects most of the inner circle. Unearthed in southern Iraq in the late 1800s, the tablet is housed in the British Museum.
Sixteenth-century interpretation of Ptolemy's
Celestial Spheres In his 2nd century treatise, the "Almagest," Claudius Ptolemy proposed an explanation for the apparent movement of stars and planets, in which Earth was central and immovable, and surrounded by, at progressively greater distances, the Moon, Mercury, Venus, the Sun, Mars, Jupiter, Saturn and a sphere of ‘fixed stars.’ This geocentric view of the cosmos did not meet its first real challenge until Copernicus proposed that the planets revolved around the Sun, and Galileo used his telescope to observe the phases of Venus.
Library of Congress, via the History Blog
Flat Earth The Greek philosopher Aristotle determined that Earth was spherical and not flat almost 2,500 years ago. The notion of a flat earth retained at least a few die-hard devotees for a surprisingly long time. For example, this 1893 map by Orlando Ferguson, recently acquired by the Library of Congress, cites “Scripture that condemns the globe theory” and promotes a book that “knocks the globe theory clean out.”
ANALYSIS: What if Earth Were a Cube?
De Costa, B.F. (September 1879). "The Lenox G
Lenox Globe It is popularly believed that ancient cartographers filled in unknown and unexplored areas of the world with the phrase ‘Here be dragons’. In fact, only one known ancient map – the so-called Lenox Globe, which is believed to date to around 1510 - displays the phrase ‘HC SVNT DRACONES’, from the Latin “hic sunt dracones.” (The phrase is written near the equator on the eastern cost of Asia.) Some nineteenth-century writers, however, believed that it referred, not to dragons, but to the ‘Dagroians’, a people who “feasted upon the dead and picked their bones.”
PHOTOS: Sea Monsters Real & Imagined
Image Database of the Kano Collection, Tohoku
Terra Australis Incognita In this copy of a 1602 map that was created on behalf of China’s Wanli emperor by Italian Matteo Ricci and collaborators, the familiar outlines of most of the world’s continents are coming into shape, although obviously many details remain unfinished. To the map’s makers, however, the likes of Australia, New Zealand and Antarctica are not even figments of the imagination, replaced instead by an enormous southern landmass. The notion of an unknown southern land – a terra australis incognita - was first mooted by Aristotle in 322 BCE; not until 1820 did Fabian von Bellingshausen become the first man to see the Antarctic continent.
South Pole For centuries, gaps in maps were filled by explorers who set out across land and sea, often at immense personal risk. The true nature of “Terra Australis” had long been established by the time Robert Falcon Scott and comrades stood at the South Pole on Jan. 17, 1912; but existing knowledge could not diminish the terrible toll the conditions exacted on the men. “Great God!” wrote Scott in his journal, “this is an awful place.” All five members of Scott’s polar team died before they could reach their base camp.
PHOTOS: Forgotten Discoveries of Scott's Antarctica
Moscow at night Time and technology have enabled us to explore, not just across the surface of the globe or even beneath its waves, but from on high. Here, Moscow is seen at night from the International Space Station, flying at an altitude of approximately 240 miles on March 28, 2012. A solar array panel for the space station is on the left side of the frame. The Aurora Borealis, airglow and daybreak frame the horizon.
Pale Blue Dot In contrast to earlier suppositions about our place in the firmaments, we know now that our globe is not at the center of the cosmos, and that other celestial bodies are not attached to interlaced spheres that rotate around us. We are but one world among many, in one solar system among many, in one galaxy among many. In this image, taken by the Voyager I spacecraft from a distance of 4 billion miles, Earth is but a speck – a pale blue dot – in the cosmic night.
NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring
Blue Marble If satellite images of Earth now seem almost routine, they never lose their ability to enthrall. This picture of the western hemisphere was captured on January 25 by NASA’s latest Earth observation satellite, Suomi NPP. By February 1, it had registered over 3 million views on Flickr – testament to the beauty and fascination of our Blue Marble.
PHOTOS: Earth's Blue Marble Beauty
With a few tricks borrowed from the oil industry, scientists are hoping to one day better understand why earthquakes start and stop.
Geologists would love to know what controls earthquakes. But one of the best ways to answer that question — drilling into faults — is expensive and difficult. An easier alternative is to study faults exposed on Earth's surface, and look at "fossilized" earthquakes preserved along the faults.
But faults can be several feet wide and filled with crushed-up rock, or they can be inch-thick cracks. How does someone walk up to a crack, point a finger at it and determine an earthquake occurred there?
Sometimes, the tremendous heat created during an earthquake melts rock inside a fault. "That was the gold standard," said Heather Savage, a geophysicist at Lamont-Doherty Earth Observatory in New York. "When you get the melt, it means the fault slipped fast."
(Faults get hot because of friction. Just as rubbing your hands warms them on a winter's day, earthquakes heat the Earth when two sides of a fault slide past each other during a quake.)
But there are plenty of old faults exposed on Earth's surface and very little of this melted rock, called pseudotachylyte, Savage said.
So, over the past few years, Savage and her colleagues have devised a new way to find old earthquakes. It turns out that earthquakes can "cook" dead plants and algae trapped in a fault, similar to how organic material transforms over eons into oil.
And because heat from an earthquake is linked to fault strength, Savage is also testing whether this cooked organic matter reveals clues about fault strength during past earthquakes. [Image Gallery: This Millennium's Destructive Earthquakes]
"Temperature rise during an earthquake says something about the strength of the fault when it was slipping, and that is a big unknown in earthquake science," Savage told LiveScience's OurAmazingPlanet. "These kinds of questions are really fundamental if we're ever going to get better at making accurate earthquake predictions."
The technique could prove especially handy at subduction zones — the source of the world's biggest earthquakes — which are often rich in organic material scraped off the ocean floor.
In Alaska, a 60-million-year old subduction zone between the Pacific and North American plates now sits exposed above shoreline at Pasagshak Point on Kodiak Island. This is one of the only places in the world where pseudotachylyte is found on a subduction zone. Savage and her colleagues tested their earthquake "biomarker" method here, comparing the temperature recorded by organic matter to that from the pseudotachylyte at one section of the fault.
The drilling site offshore of Japan, where researchers pierced through the plate boundary that caused the 2011 Tohoku earthquake.IODP/JAMSTEC
The organic chemistry was borrowed from the oil industry, which has invested millions in measuring how rocks are heated based simply on the properties of organic matter in those rocks — though the cooking usually takes millions of years, not seconds and minutes, like earthquakes.
In Alaska, the biomarkers were diamondoids, carbon and hydrogen heated until they take on the same basic structure as diamonds. By modeling the heat needed to create diamondoids, Savage and her colleagues estimate the earthquake they found was about a magnitude 7 or magnitude 8, with a temperature rise of between 1,540 and 2,140 degrees Fahrenheit (840 to 1,170 degrees Celsius) and between 3 to 30 feet (1 to 9 meters) of movement. The findings were published Jan. 6 in the journal Geology. [Shine On: Photos of Dazzling Mineral Specimens]
"We're very excited; it's one of the first times we've been able to do this with a new method," Savage said.
Savage noted that this earthquake thermometer only works on faults in sedimentary rocks that carry organic material, and that not all earthquakes will generate a lot of heat. In California, along an ancient strand of the San Andreas Fault called the Punchbowl Fault, the team found a temperature rise of only 1,150 F (625 C), despite geologic evidence of past earthquakes.
The group has several new projects in the works. They're investigating rocks from Japan's JFAST drilling site, at the source of the 2011 Tohoku earthquake, and working on the San Andreas Fault deep drilling project, to see if the slow-moving part of the San Andreas Fault ever had large earthquakes. They are also running laboratory tests to customize those petroleum-industry chemical equations and to better understand the link between temperature on faults and organic matter. And someday, Savage would like to create a "heat map" of a fault.
"We're hoping that being able to walk up to an outcrop and fingerprint this kind of slip, which may help tell us how earthquakes get started, and maybe how they stop," Savage said.
"A fault plane is hundreds of kilometers long and tens of kilometers wide, and maybe the strength of that fault is determined by very small patches holding most of the resistance to sliding," Savage said. "Understanding how stress is distributed on faults is a very important question toward understanding when a fault is getting close to actually having an earthquake."
Original article at LiveScience's OurAmazingPlanet.
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