New Earthquake Model Predicts a Bigger Quake: Why?

It's not that earthquake faults in California are more dangerous than before. It's just that scientists are better now at measuring their potential for disaster.

Earlier this week, the U.S. Geological Survey released a new study, which concluded that California faces a bigger chance of experiencing a powerful earthquake in the next 30 years than previous studies had predicted.

Non-seismologists who just glanced at the news headlines about the study -- including ours -- may have been left worrying that the risk of "The Big One" is now greater, due to some alarming change in Earthquake faults.

But the explanation is actually more complicated, though not necessarily more comforting. The upside is that recent discoveries about the nature of earthquakes and how they spread, coupled with advances in supercomputer software and monitoring technology, now enable scientists to make more accurate predictions about future quakes.

The Third Uniform California Earthquake Rupture Forecast, also known as UCERF3, used those conceptual and technological advances to predict that the chances of an 8.0 or greater event -- roughly, the equivalent of the San Francisco earthquake of 1906 -- rocking the state in the next 30 years has increased from 4.7 percent to 7.0 percent. Meanwhile, the chances of significant but less-than-catastrophic quakes in the 6.5 to 7.0 range actually has gone down slightly in the new forecast.

The big reason for the difference from previous forecasts is that scientists have figured out how to solve a longstanding limitation in earthquake prediction models, according to Tom Jordan, a University of Southern California professor of earth sciences and one of the study's authors.

On the simplest level, an earthquakes can occur when a portion of a single fault ruptures. But scientists have known since the early 1900s that earthquakes also have the capability to jump from one fault to other nearby ones and become more powerful, almost the way that a single burning house can ignite nearby houses as well. This phenomenon was illustrated by the June 1992 Landers earthquake, a 7.3 event which actually resulted in ruptures of five different faults, and involvement of numerous smaller ones as well.

Although scientists for long have known about this phenomenon, it wasn't until recent years that they understood how frequently it occurred, and what proximity was required for a quake to jump from one fault to others. As a result, they were compelled to stick to conventional models based on the potential of single fault events.

That sort of modeling, because it didn't account for the energy in earthquake faults that might end up being used in large multi-fault events, resulted in forecasts that slightly overestimated the number of moderate-intensity quakes, and underestimated the number of big ones, Jordan explains. "We called that overestimation the 'bulge,'' Jordan explains. "We couldn't quite get the data to match what we were observing in the real world."

But adjusting the forecasting method to account for these systemic, multi-fault quakes was a challenging task, according to Tom Parsons, a USGS research geophysicist who also was involved in the study.

Researchers spent years writing complex software for supercomputers, so that they could run models that incorporated the multi-fault effect, he said. Additionally, for the first time they incorporated data gathered by Global Positioning System satellites.

The new model also benefits from scientists' realization that the earthquake fault system in California is far more complex than once believed. The latest model takes into account about 300 different faults in California, compared to 200 for the 2007 forecast and just 16 for the inaugural 1988 report.

The upshot is that "we're far less likely to be surprised by a rupture" in the future, Parsons says. Both scientists are optimistic that the new modeling method will result in more accurate forecasts in other parts of the world as well.

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.

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.

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.

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?

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

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.

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