# Hellish Northridge Earthquake: Is Los Angeles Safer 20 Years Later?



## mark handler

Hellish Northridge Earthquake: Is Los Angeles Safer 20 Years Later?

http://www.livescience.com/42675-northridge-earthquake-20th-anniversary-science.html







Roaring like a freight train from hell, the Northridge earthquake threw sleeping Angelenos from their beds at 4:31 a.m. on Jan. 17, 1994.

The earthquake's shaking was stronger than the force of gravity, lifting furniture off the floor and buildings off their foundations. Los Angeles firefighters watched their massive fire trucks hop across a station garage in time with the seismic waves.

At least 57 people died and nearly 9,000 people were injured. Some 82,000 buildings were damaged or destroyed. Seven freeway bridges collapsed. With more than $40 billion in property and economic losses, Northridge was one of the most expensive natural disasters in U.S. history.

California geologists say their big cities are overdue for another devastating earthquake. No major earthquake has hit one of the major urban areas since Northridge — and at a magnitude-6.7, it wasn't even the feared "Big One." Twenty years ago, no one knew the Northridge fault existed. Thanks to Northridge, the next one won't be such a surprise. The big question is: Are Californians ready?

Blind thrusts

The Northridge fault is a so-called blind thrust, a fault buried 11 miles (17 kilometers) deep in Earth's crust. Leaving no telltale signs on the surface, geologists had no idea the fault angled beneath the San Fernando Valley, veering northward from Reseda up toward Chatsworth. That angle saved much of Los Angeles 20 years ago, directing the earthquake's energy into the sparsely settled mountains north of the Valley.

The 1994 quake wasn't the first blind thrust to trigger a quake beneath L.A., but it was the most powerful. Northridge swung scientists' attention back toward mapping earthquake hazards directly underneath the Los Angeles area, instead of focusing on the sleeping giant next door, the San Andreas Fault.

"When Northridge occurred, people didn't appreciate these blind thrusts as seismic hazards," said James Dolan, an earthquake geologist at the University of Southern California in Los Angeles. "Northridge really swung the pendulum back [from the San Andreas] to trying to understand the urban fault system in much more detail," Dolan told LiveScience's OurAmazingPlanet. "Although we think these faults aren't going to generate a magnitude-8 earthquake on the scale of the San Andreas, they are literally underneath your feet."

In the past two decades, researchers have done their best to find every fault fracturing Southern California west of the San Andreas Fault. (The eastern part of the state still hides some mysteries, scientists think.) They've also gauged the history of past earthquakes on these faults, when possible, and studied how each fault influences others nearby.

The result looks like a CT scan of the Earth, in which faults are the bones, linked together in a complex framework.

The digital fault model now allows researchers to model how future earthquakes may damage different parts of Los Angeles — one of the vexing problems of the Northridge earthquake. [Video: Scary Scenario – Devasting Earthquake Visualized]

"We have a much clearer picture of what we're up against in terms of the seismic threat facing L.A.," Dolan said. "In some respects it's somewhat worse than what we thought 20 years ago, [because] we know that first of all there are big blind thrust faults underlying most of metropolitan L.A. and we know that at a number of occasions in the past these have ruptured to generate very large magnitude earthquakes."

Basin effects

Before the sun rose on Jan. 17, 1994, the San Fernando Valley looked like a scene from an apocalyptic disaster movie. Dust in the air glowed as more than 1,000 fires burned in the darkness of a city without power. But on the other side of the Santa Monica Mountains, the southern border of the Valley, the city of Santa Monica also suffered a surprising amount of damage. And some pockets in the Valley were left mostly untouched, while others were devastated.

The Northridge earthquake clearly showed how the different soils in an area, and the underlying geologic structures, can magnify an earthquake's strength. In Santa Monica, a lens-shaped fault beneath the mountains focused the seismic waves toward the city the way a magnifying glass can concentrate the sun's rays. In the Valley, the earthquake waves ping-ponged back and forth, bouncing off underground structures and occasionally meeting and intensifying. The strongest ground motion ever recorded in a California earthquake was in the city of Tarzana. The sedimentary layers under Tarzana focused and strengthened the shaking until it was nearly twice that of Earth's gravity.

Today, scientists can predict where such patchwork effects will take place, based on the source and size of an earthquake. For example, even though the towering San Gabriel mountain range separates the San Andreas Fault from Los Angeles, sedimentary basins on the southern side of the mountains, near the city, funnel earthquake energy into L.A.

"We've done a huge number of simulations that really show the importance of these sedimentary basin structures," said Tom Jordan, a seismologist and director of the Southern California Earthquake Center. "Energy can get focused into Los Angeles, so now we take that into account when delineating the [shaking] hazard," Jordan told LiveScience's OurAmazingPlanet.

Building safety

Perhaps the iconic image of the Northridge earthquake is a collapsed parking garage on the California State University, Northridge, campus, folded over on itself like a child's Play-Doh. Another contender is the soft-story apartment building (with parking spaces as the first, "soft" story) that pancaked and flattened cars. [Northridge Earthquake 20th Anniversary in Photos]

But the earthquake also highlighted how vulnerable welds can be in the beam joints of steel-frame structures. Engineers discovered widespread brittle fractures at welds in steel beams, which prompted changes to California's building codes and the way steel-beam buildings are constructed and designed. Thanks to Northridge, steel-frame buildings will perform better in the real Big One.

But despite seismic code upgrades, many buildings are still at risk in Los Angeles and other major cities, according to a study published this week (Jan. 14) in the journal Earthquake Spectra.

"We're not saying that every building constructed before 1994 is going to collapse in an earthquake," Tom Heaton, professor of geophysics and civil engineering at Caltech and a study co-author, said in a statement.  "We're saying that buildings continue to be in use that pose a greater risk of physical injury and financial harm than is necessary."

The next big one

California's urban earthquake faults have been remarkably quiet for the past 20 years. During this time, scientists and emergency planners sought to prepare for the next earthquake disaster. The state runs an annual earthquake drill, the Great ShakeOut, and has installed the framework for an early earthquake warning system similar to Japan's.

Scientists have simulated a magnitude-7.8 earthquake on the southern San Andreas Fault, which they say is about 150 years overdue for a major temblor. A quake such as that would kill 1,800 people and injure 53,000 — relatively minor loss of life in a metropolis of millions, though still a major disaster in the United States.

The big concern is economic loss. California's seismic building code is meant to preserve life, not preserve buildings, and 50 percent of the Los Angeles's structures may be uninhabitable after a San Andreas temblor.

"If you get a large earthquake, we're probably expecting to see damage in many buildings, even in modern buildings," said James Wight, a structural engineer at the University of Michigan. "They are not designed to go damage-free," he told LiveScience's OurAmazingPlanet.

The city's old, brittle water pipes would break, along with its water supply lines from outside, such as the California Aqueduct. With no water for weeks or months, Los Angeles could suffer severe, long-lasting economic losses, similar to New Orleans after Hurricane Katrina, said Lucy Jones, a seismologist with the U.S. Geological Survey.

"At best, it will take us six months to get our water back," Jones told the Los Angeles City Council this week.

"What is at stake is really our whole urban society," Jones said. "Every death in an earthquake is horrible, but people are far more likely to die on our freeways. We are more worried about how society will function afterward."

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


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## cda

Amazing there has not been another one somewhere in calif


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## mark handler

cda said:
			
		

> amazing there has not been another one somewhere in calif


there are earthquakes in CA everyday see attached, JUST NOT BIG ONES


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## cda

Yea knew that

Signed

Ex- Californian


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## mark handler

cda said:
			
		

> Ex- Californian


Yea I knew that TOO


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## Mark K

California needs earthquakes to encourage people to leave the state.  We have too many people.

We need earthquakes to create work for structural engineers.


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## kilitact

This was the second Northridge earthquake, first was in 70, 71


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## mark handler

Mark K said:
			
		

> California needs earthquakes to encourage people to leave the state.  We have too many people.We need earthquakes to create work for structural engineers.


And Architects, Northridge earthquake paid off my first house. ......


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## chris kennedy

That was a good read Mark, thanks.


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## mark handler

The one that will be the wake-up call for the nation will be on the New Madrid Fault or in Yellowstone


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## steveray

I keep telling people over here about the New Madrid....When it can ring church bells 1000 miles away.....WOW!


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## Phil

Here is a brief paper from Computers and Structures Inc. that some might find interesting: Modern Earthquake Codes , History and Development

http://www.csiamerica.com/system/files/technical-papers/mcclure_book_smll_0.pdf .


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## mark handler

http://www.data.scec.org/recenteqs/


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## mark handler

New Madrid Fault vs northridge


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## mark handler

Yellowstone vs Mt St.Helens


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## steveray

That's OK...Iwasn't moving to any of those states anyway


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## mark handler

That's where your food comes from....


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## steveray

mark handler said:
			
		

> That's where your food comes from....


Us yankees are pretty resourceful....I'll eat....


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## mark handler

New Madrid Fault Zone Alive And Active

http://losangeles.cbslocal.com/2014/01/23/study-new-madrid-fault-zone-alive-and-active/

January 23, 2014

LOS ANGELES (AP) — The New Madrid fault zone in the nation’s midsection is active and could spawn future large earthquakes, scientists reported Thursday.

It’s “not dead yet,” said U.S. Geological Survey seismologist Susan Hough, who was part of the study published online by the journal Science.

Researchers have long debated just how much of a hazard New Madrid poses. The zone stretches 150 miles, crossing parts of Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri and Tennessee.

In 1811 and 1812, it unleashed a trio of powerful jolts — measuring magnitudes 7.5 to 7.7 — that rattled the central Mississippi River valley. Chimneys fell and boats capsized. Farmland sank and turned into swamps. The death toll is unknown, but experts don’t believe there were mass casualties because the region was sparsely populated then.

Unlike California’s San Andreas and other faults that occur along boundaries of shifting tectonic plates, New Madrid is less understood since it’s in the middle of the continent, far from plate boundaries.

Previous studies have suggested that it may be shutting down, based on GPS readings that showed little strain accumulation at the surface. Other research came to the same conclusion by blaming ongoing quake activity on aftershocks from the 1800s, which would essentially relieve strain on the fault.

The latest study suggests otherwise. Hough and USGS geophysicist Morgan Page in Pasadena, analyzed past quakes in the New Madrid region and used computer modeling to determine that the continuing tremors are not related to the big quakes two centuries ago.

“Our new results tell us that something is going on there, and therefore a repeat of the 1811-1812 sequence is possible,” Hough said.

The USGS estimates there’s a 7 to 10 percent chance of that happening in the next 50 years.

Arthur Frankel, a seismologist with the USGS in Seattle who had no role in the study, said the latest results seem plausible. His recent field work using GPS shows significant movement of land along the fault in the past decade, indicating a buildup of strain that could lead to potentially dangerous quakes.

Others said this won’t end the debate about the hazards on the New Madrid seismic zone.

Andrew Newman, a geophysicist at the Georgia Institute of Technology, said the method used in the study works well for faults along plate boundaries, but he’s unsure if it applies to enigmatic faults like New Madrid.

(© Copyright 2014 The Associated Press. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.)


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## steveray

They mentioned the New Madrid this AM on CBS news....


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## Alias

mark handler said:
			
		

> The one that will be the wake-up call for the nation will be on the New Madrid Fault or in Yellowstone


Very true.

Sue


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## Alias

And then there was the Loma Prieta earthquake October 17, 1989.  I felt this one and I lived in the Sierras outside Sonora, about 160 miles from the epicenter.

http://earthquake.usgs.gov/regional/nca/1989/

Sue


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## mark handler

Massive Earthquake Could Rock Los Angeles

Dawn Levesque on January 25, 2014.

http://guardianlv.com/2014/01/massive-earthquake-could-rock-los-angeles/

A massive earthquake could rock Los Angeles. In 1994, a substantial earthquake measured 7.3 on the Richter scale, jolting Los Angeles and the surrounding area. The quake caused $40 billion in damage and killed 57 people in southern California. In the past year, Los Angeles has had 291 earthquakes, with the strongest magnitude registered at 4.8 on the Richter scale.

Earthquake seismologists say that if the southern San Andreas Fault ruptures in a particular direction that southern California could expect an earthquake on an unprecedented scale, something not seen in the Los Angeles region in over 300 years.

Up until recently, seismologists had no method of predicting the effects of an earthquake before it happens. The National Science Foundation has created a new computer modeling study with the aim to help engineers design sounder structures. The “supercomputer” simulates how such a quake might progress from the fault line through the city. Such a fissure, as the computer models indicate, could reverberate through the L.A. area, triggering stronger ground motion than previously foreseen. The model shows that shaking in the Los Angeles Basin could feasibly be three times greater on average than in the surrounding L.A. areas.

Earthquake seismologist, Dr. Marine Denolle together with fellow researchers installed a number of seismometers along the San Andreas Fault line to put their method to test. They analyzed how vibrations generated by ocean waves, transmits through the ground. She and her colleagues then applied the collected data to induce 100 computer-simulated magnitude-7 “virtual earthquakes.”

By “synthesizing” the data gathered from the waves, Denolle and her colleagues used the virtual approach to reconstruct what would actually happen should a massive earthquake rock Los Angeles and propagate up the San Andreas Fault. According to Thomas Jordan, director of the Southern California Earthquake Center, it is a process to “trick the earth” with the purpose of giving researchers its response to a large-scale earthquake.

The seismologists have substantiated that with these virtual quakes, the geological structure underneath L.A. does amplify a quake’s shock waves. Angelenos would experience trembling as if they were next to the fault, even at 100 miles away from the actual rupture.

Characteristically, earthquakes create seismic waves that disperse as they radiate away from the source. Major cities such as Paris, Mexico City, Tokyo and Los Angeles lie atop a complex geological structure known as a sedimentary basin that changes the way energy transfers through the ground.

These soft foundations can magnify the extent of damaging cities like Los Angeles experiences during an earthquake. And while most Americans correlate earthquakes only with California,  Denolle’s technique could prove useful for other parts of the United States too.  For instance, both Pennsylvania and Ohio experienced earthquakes last year with a 4.0 magnitude that rattled residents.

The virtual quakes could forecast the threats looming over these states and even cities across the world. It would be especially beneficial to areas that have had no recent history of larger quakes.

earthquake

According to earthquake seismologist, Greg Beroza, the benefit of this research, allows seismologists to “anticipate how the ground will shake” before earthquakes happen as opposed to waiting for an actual earthquake in order to calculate more about their effects.

The importance of predicting shaking from earthquakes is one of the most crucial factors seismologists can do to know how to create structures that will resist the quake shaking. By examining how these ambient waves move underground, researchers could predict the effects of much stronger waves from powerful earthquakes. Additionally, this computer study approach could also replicate “ancient quakes” to cast light on an area’s history.

While an earthquake of unprecedented magnitude could rock Los Angeles, the prospect of virtual earthquake research could significantly modify how buildings are designed in the future to minimize the destruction that rattles Angelenos and people worldwide.

by Dawn Levesque


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## mark handler

For Los Angeles, list is a first step toward improved quake safety

University of California list of L.A.'s older concrete buildings is a starting point on a long and costly road.







ResidentialCommercialIndustrialGovernmentEducationReligious

By Rong-Gong Lin II, Rosanna Xia and Doug Smith

January 25, 2014, 7:25 p.m.

The University of California's release of data on nearly 1,500 older concrete buildings across Los Angeles marks a key step in the city's efforts to improve earthquake safety.

Now the hard part begins.

UC researchers spent several years compiling the list of buildings, a first-of-its-kind effort to help identify a type of building that earthquake experts have long said poses the greatest risk of death.

Of all the older concrete buildings in Los Angeles, the researchers estimated that only about 75 would collapse during a huge quake.

But determining which ones are structurally at risk will require individual inspections.

Experts say the cost for just a preliminary examination could range from $4,000 to $20,000, depending on the size of the building. Retrofitting problem buildings would cost property owners much more, from the tens of thousands of dollars to perhaps more than $1 million for large office or residential towers.

The list underscores the scope of the challenge: More than 220,000 people live or work in the listed buildings, according to a Times analysis of the researchers' data.

For city leaders, the next step is deciding how to inspect and repair the buildings — and who should cover the costs. Mayor Eric Garcetti has said getting quake-vulnerable concrete buildings retrofitted is a top priority and partnered with the U.S. Geological Survey to make recommendations on how to get it done.

Some City Council members have been exploring the idea of a state bond initiative to help defray some of the costs for building owners.

The University of California sent the list of addresses to the city Tuesday, after Los Angeles officials had asked for it. After months of debate about whether to make the list public, UC provided a copy to The Times in response to a public records act request.

The release of the list moves Los Angeles closer to addressing the dangers of concrete buildings after four decades of inaction.

Earlier efforts to identify and fix problem buildings died amid opposition from property owners after the 1994 Northridge quake. Concrete buildings collapsed during both that temblor and the 1971 Sylmar quake, in which hospital buildings crumbled, killing about 50 people.

Concrete buildings can be particularly vulnerable when they lack adequate steel reinforcement. As a result, their frames are brittle and can crumble during heavy shaking. Concrete buildings are found across Los Angeles but particularly in older commercial districts such as downtown, Hollywood and Mid-Wilshire. A Times survey last year found heavy concentrations of concrete residential towers and office buildings in those areas as well in Westwood and Encino.

Los Angeles is now the first city in California with a public list of older concrete buildings, and seismic safety experts said they hope this raises awareness of the issue.

"This challenge our communities face is now out in the open … and tells the community that something needs to be done," said Craig Comartin, a structural engineer and past president of the Earthquake Engineering Research Institute, based in Oakland.

Some Los Angeles officials said the city must act by determining which buildings are actually at risk.

"We need to ensure that, as best as we can, that our residents are safe," Councilman Bernard C. Parks said. "It's absolutely important."

Councilman Mitch Englander said the UC researchers' work gives the city a rare opportunity to move forward, saying the city did not produce a list on its own "because of the political fallout, quite frankly."

"What do you do with it, once you have it? That's the million-dollar question," he added.

Business groups and property owners have long opposed mandatory retrofitting, saying they cannot shoulder the costs alone.

This article is truncated

click on the link for the rest of the article

http://www.latimes.com/local/la-me-adv-earthquake-concrete-list-20140126,0,1704027.story#axzz2rWMW9729


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