Strides in Earthquake Science

Jan 17, 2014 by Robert Perkins
Strides in Earthquake Science
n overpass that collapsed on Highway 10 (now SR 42) in the Northridge/Reseda area at the epicenter of the earthquake in 1994. Since the quake, the Southern California Earthquake Center, based at USC Dornsife, has created a clearer picture of earthquake risks faced by regions throughout Southern California.

Twenty years ago, a fault that scientists didn't even know existed slipped, triggering a massive 6.7 magnitude earthquake centered beneath the San Fernando Valley, with shockwaves rippling throughout the greater Los Angeles area.

When the strongest shaking ceased, the region had suffered 57 deaths and more than $20 billion in damage. The newly formed Southern California Earthquake Center (SCEC), founded in 1991 and headquartered at USC Dornsife, stepped in to find out exactly what happened and what could be done about it.

Earthquakes cannot be prevented or predicted. However, by beefing up and modernizing the region's seismographic network and then crunching the massive reams of resulting data, scientists from SCEC have been able to piece together a clearer, more granular picture of the varying risk that regions throughout Southern California face due to earthquakes.

That picture can be used to help create appropriate building codes and, in the wake of an , help direct first responders.

"What you have to do in order to get the earthquake rupture forecast—that is, a forecast of how often, how big and where the earthquakes might occur – is to integrate all of this information together," said Thomas H. Jordan, director of SCEC and University Professor in earth sciences at USC Dornsife. "You have to know the faults, the rates of motion and something about the ruptures that occur on them in order to estimate the future probabilities of having earthquakes on these different faults."

To create seismic hazard maps, Jordan and his colleagues use supercomputers to simulate a half million earthquakes at more than nearly 300 sites throughout the Los Angeles region.

"All of the science is being put into products that society can use," Jordan said.

It's not a simple process. As shown in the Northridge quake, an area's risk for heavy shaking doesn't just depend on its proximity to a fault. The type of sediments or rock that an area sits on as well as the geometry of the region can help seismic energy focus and propagate. In 1994, the region's geometry caused an unusual amount of shaking in Santa Monica, resulting in greater damage to the city than surrounding neighborhoods.

In the wake of Northridge, the Southern California Seismographic Network was expanded and modernized—with digital stations replacing the old analog ones. At the time of Northridge, there were six digital stations in use throughout the region. Today, there are more than 400.

The digital stations allow the rapid creation of "ShakeMaps" depicting the pattern of where shaking has occurred. First responders can use these maps to immediately prioritize their response.

"To create the equivalent of this map in '94, it took us two months that involved going out into the field and picking up film," said Lucy Jones, science advisor for risk reduction for the U.S. Geological Survey. "We had to get film recordings, develop them and digitize them, to be able to turn them into this map. This map now happens in a matter of about two to three minutes.

After Northridge, a special focus was also given to so-called "blind-thrust faults"—buried faults that do not appear on the Earth's surface—like the one that caused the quake in 1994. As of today, dozens more have been found.

"One of the major points of emphasis in scientific research after Northridge was to better understand these blind-thrust faults," Jordan said.

Beyond creating hazard maps, SCEC's research has been used to create more realistic earthquake simulations. An example is the simulation used as part of the USGS-developed ShakeOut Scenario, the basis for the original Great Southern California Shakeout in 2008. The massive drill—which has grown statewide and involved 9.6 million participants in 2013 – allows emergency management agencies to estimate and plan for the cascading impacts on the area's infrastructure, according to Kate Long, earthquake program manager for the California Governor's Office of Emergency Services.

And it all begins with the hard work of scientists at SCEC.

"Without the science, without the scenarios, when we exercise we're just guessing," Long said.

Though no one wants to experience another earthquake like Northridge any time soon, Jordan and his colleagues at SCEC are unlikely to run out of temblors to measure and analyze in the Southern California area.

As Jones put it, "Those of us who live in Southern California don't always like to hear what an exciting natural laboratory Southern California is for the scientists, but that's the reality."

Explore further: Eight seconds of terror

add to favorites email to friend print save as pdf

Related Stories

Eight seconds of terror

Jan 17, 2014

(Phys.org) —Twenty years ago this week, in the predawn darkness of Jan. 17, 1994, at five seconds before 4:31 a.m. PST, the ground ruptured violently on a blind thrust fault (a crack in Earth's crust that ...

Longmanshen fault zone still hazardous, suggest new reports

Jan 02, 2014

The 60-kilometer segment of the fault northeast of the 2013 Lushan rupture is the place in the region to watch for the next major earthquake, according to research published in Seismological Research Letters (SRL). Research pape ...

Recommended for you

Fires in the Northern Territories July 2014

2 hours ago

Environment Canada has issued a high health risk warning for Yellowknife and surrounding area because of heavy smoke in the region due to forest fires. In the image taken by the Aqua satellite, the smoke ...

How much magma is hiding beneath our feet?

3 hours ago

Molten rock (or magma) has a strong influence on our planet and its inhabitants, causing destructive volcanic eruptions and generating some of the giant mineral deposits. Our understanding of these phenomena ...

Oso disaster had its roots in earlier landslides

6 hours ago

The disastrous March 22 landslide that killed 43 people in the rural Washington state community of Oso involved the "remobilization" of a 2006 landslide on the same hillside, a new federally sponsored geological study concludes.

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Sinai Construction
3 / 5 (1) Jan 17, 2014
Homeowners in Los Angeles should really take the time, money and effort to have their homes retrofitted against earthquakes. This also goes to the owners of Soft Story buildings. As they say, prevention or mitigation of earthquake damage is infinitely more preferable to dealing with the afterquake injuries and damage.