The Northridge Earthquake: 18th Anniversary

[HurricaneJosh]

Today marks the 17th anniversary of the great Northridge Earthquake. The event has a special place in my heart because, although I've been in a gazillion hurricanes, the Northridge Quake remains my scariest and most hair-raising natural-disaster experience.

SUMMARY

It struck suddently at 4:30:55 am PST on 17 January 1994. The 6.7 shock was centered within the L.A. city limits and caused very-strong to violent shaking over the entire Metro region. The quake was short-lived but its shallow depth produced surprisingly intense surface motion for an event of its magnitude. There were numerous building collapses, multiple freeway failures, 57 deaths, 9,000 injured, 20,000 left homeless, and damages totaling ~$20 billion-- all within approx. 15 seconds. The city was under curfew and martial law for several days, with large swaths looking like bombed-out war zones.

Shaking was felt across much of the Western USA. This map shows the reported shaking in the L.A. Metro region, by ZIP code.

TRIVIA

* This was the first quake to occur directly under an urban area in the USA since the Long Beach Earthquake of 1933.

* The epicenter was later calculated to be in Reseda-- however, it's still called the Northridge Earthquake.

* The ground acceleration-- i.e., the ferocity of the shaking-- was the highest ever instrumentally recorded in an urban area in North America.

PERSONAL ACCOUNT

I grew up in NY and had never been in a quake when this one hit. (I'd moved to L.A. a year and a half before.) In the map above, I was in an area of VII (very strong) to VIII (severe) shaking-- perhaps 12 mi from the epicenter, a little S of the area of IX (violent) shaking that occurred in the San Fernando Valley.

It struck suddenly, in the middle of the night. I awoke as things-- books and CDs-- were falling on me. Within a second or two the shaking got really, really bad and the whole house-- an old wooden bungalow-- was jumping up and down. I held onto the bed as it pushed away from the wall. A lamp hit me in the head. The motion was fast, jerky, and erratic-- in multiple directions, with a strong vertical component. The walls were bending-- everything was in motion. The banging and rumbling sounds were ferocious-- like a train going by. I thought the house might come down. Outside it was like 4th of July, with transformers exploding up and down Santa Monica Boulevard.

I was totally freaked. When the shaking calmed I jumped out of bed (now in the middle of the room) and tore out of the house with my roommates-- while transformer explosions continued to light up the city.

Aside from the mess of broken dishes and fallen pictures, our house did fairly well-- although screens had been knocked off the windows and we had a hole in the roof where the chimney had separated from the house. The people across the street had a broken window. Several blocks away, a house had collapsed. A couple of miles away, a one-mile section of the elevated 10 freeway had fallen to the ground.

It was a big one. Those fifteen seconds or so were the scariest of my life-- way worse than any hurricane I've been in.

Do any of the other Southern Californians have recollections to share?

Sources: Personal recollections, USGS, SCEDC, & Wikipedia article.

[aslkahuna]

Exactly one year later to the day, a similar earthquake (though on a different type fault) struck Kobe Japan. Up until that second earthquake, the Japanese had been crowing about how their construction practices and earthquake drills meant that Japan would never experience the type and amount of damage to buildings and infrastructure that California did in the 1989 and 1994 shocks. Since Kobe, the Japanese have been very quiet on this score as Kobe proved to be far worse in terms of damage and particularly casualties it was a bitter shock to Japan. Earthquakes are definitely the scariest of all natural disasters since there's practically no warning unless you can understand dogs and birds. Even a modest 5.9 like I experienced in San Jose CA in 1955 can be scary when the epicenter is close (in my case 1.5 blocks away).

Steve

[MJW155]

Stop being a wuss Josh. It was only 15 seconds.

Didn't the Good Friday earthquake last 4 minutes or something like that? That's insane.

Seriously, I have no idea how people can live in earthquake prone areas. It would be one thing if you even got a 2 min. warning but it's instantaneous. Being in bed at night probably makes it that much worse. I guess people rationalize it by saying it only happens once every 50 years or whatever. Scary ****.

[aslkahuna]

The March 27, 1964 shock was a classic megathrust earthquake in a subduction zone with a magnitude of 9.2 at least 15000 times more potent than 1994. Post shock analysis showed that an area the size of the entire state of California had undergone structural changes in the 1964 shock. As far as lasting only 15 seconds, that can seem like an eternity when you are being shaken up and expecting everything to collapse on you.

Steve

[MJW155]

The March 27, 1964 shock was a classic megathrust earthquake in a subduction zone with a magnitude of 9.2 at least 15000 times more potent than 1994. Post shock analysis showed that an area the size of the entire state of California had undergone structural changes in the 1964 shock. As far as lasting only 15 seconds, that can seem like an eternity when you are being shaken up and expecting everything to collapse on you.

Steve

See Josh, you are being a wuss. Imagine being in a quake 15000x stronger.

[aslkahuna]

A MM6.7 earthquake is nothing to sneeze at nobody's a wuss if the first earthquake they have ever felt is of that magnitude and it scares the crap out of them.

Steve

[Normandy]

I may be off base here, but I remember reading that despite the 6.7 magnitude the shaking was very severe, even more so than the Chilean earthquake that happened last year (or year before, dont remember).

[HurricaneJosh]

Exactly one year later to the day, a similar earthquake (though on a different type fault) struck Kobe Japan. Up until that second earthquake, the Japanese had been crowing about how their construction practices and earthquake drills meant that Japan would never experience the type and amount of damage to buildings and infrastructure that California did in the 1989 and 1994 shocks. Since Kobe, the Japanese have been very quiet on this score as Kobe proved to be far worse in terms of damage and particularly casualties it was a bitter shock to Japan. Earthquakes are definitely the scariest of all natural disasters since there's practically no warning unless you can understand dogs and birds. Even a modest 5.9 like I experienced in San Jose CA in 1955 can be scary when the epicenter is close (in my case 1.5 blocks away).

Steve

Yep, I remember that-- the way the Japanese were so smug until the Kobe quake. Actually, Los Angeles performed remarkably well given that violent shaking occurred over a large, dense urban area. Yeah, a lot of buildings collapsed-- but most got through OK from a structural standpoint (despite broken windows, etc.). L.A. did as well as it could have, and it remains one of the most earthquake-resistant cities in the world.

Stop being a wuss Josh. It was only 15 seconds.

Didn't the Good Friday earthquake last 4 minutes or something like that? That's insane.

Seriously, I have no idea how people can live in earthquake prone areas. It would be one thing if you even got a 2 min. warning but it's instantaneous. Being in bed at night probably makes it that much worse. I guess people rationalize it by saying it only happens once every 50 years or whatever. Scary ****.

Yeah, the suddenness is the thing. It's a tremendous, life-changing experience, and it starts up in the space of one second. So in one second you go from your everyday life to a code-red emergency. No other experience is quite like that.

See Josh, you are being a wuss. Imagine being in a quake 15000x stronger.

People are often confused about this topic, so let me explain it:

The Richter magnitude is a measure of the total energy released in the event-- not how violent the shaking is at the surface, at a given location. The motion "violence" is measured by the Modified Mercalli (MM) scale, which is what the map in Post 1 shows. While there's a rough correlation between Richter magnitude and MM intensity, it's not a perfect correlation-- so some smaller quakes can produce extremely violent shaking. (Other factors include depth and soil composition.)

The Northridge quake (6.7) produced MM IX shaking. The tremendous Chilean quake of last year (8.8) produced the same level of shaking: MM IX. The Chilean quake shook a larger area and lasted longer than Northridge, but it was no more violent than Northridge. So, what we experienced in L.A. in 1994 was just as violent as what Chileans experienced in their quake in 2010.

It's just like how two hurricanes can have the same max winds, but one is tiny and one is enormous. The Northridge quake was relatively small (compared to the Chilean quake), but that didn't matter to us Angelenos, because that "small" quake happened right under the city. We had a direct hit; we were "in the eyewall".

A MM6.7 earthquake is nothing to sneeze at nobody's a wuss if the first earthquake they have ever felt is of that magnitude and it scares the crap out of them.

Steve

Thank you.

I may be off base here, but I remember reading that despite the 6.7 magnitude the shaking was very severe, even more so than the Chilean earthquake that happened last year (or year before, dont remember).

No, you are not off base-- you are basically right. See above.

[Kennethb]

Being from Louisiana, earthquakes are very rare here and if so, rarely felt. However I was in an earthquake in Mexico City in 1977. Fortunately the epicenter was off to the southwest so we were not in the worse part. Still it was very unnerving and we had some after shocks.

The most ironic thing about an earthquake is that it can occur on a bright, sunny day, with no warning.

[MJW155]

A MM6.7 earthquake is nothing to sneeze at nobody's a wuss if the first earthquake they have ever felt is of that magnitude and it scares the crap out of them.

Steve

I know. I'm just busting his chops. It would scare the crap out of me too.

The Richter magnitude is a measure of the total energy released in the event-- not how violent the shaking is at the surface, at a given location. The motion "violence" is measured by the Modified Mercalli (MM) scale, which is what the map in Post 1 shows. While there's a rough correlation between Richter magnitude and MM intensity, it's not a perfect correlation-- so some smaller quakes can produce extremely violent shaking. (Other factors include depth and soil composition.)

The Northridge quake (6.7) produced MM IX shaking. The tremendous Chilean quake of last year (8.8) produced the same level of shaking: MM IX. The Chilean quake shook a larger area and lasted longer than Northridge, but it was no more violent than Northridge. So, what we experienced in L.A. in 1994 was just as violent as what Chileans experienced in their quake in 2010.

It's just like how two hurricanes can have the same max winds, but one is tiny and one is enormous. The Northridge quake was relatively small (compared to the Chilean quake), but that didn't matter to us Angelenos, because that "small" quake happened right under the city. We had a direct hit; we were "in the eyewall".

Oh OK, that makes perfect sense. My cousin who grew up in NJ was living in Seattle when they had that big earthquake a few years ago. He worked above the 20th floor of a building and was scared enough to think the entire building was going to fall over.

[HurricaneJosh]

Unfortunately, there's just not a lot of video footage from the Northridge quake. However, here are some decent clips of the Kobe, Japan, quake. The Kobe quake about the same size and violence as the Northridge quake-- so what you see below is about what we experienced in L.A.

What's scary is that inanimate, everyday objects seem to spring to life: doors, cupboards, cabinets, dishes, bottles, etc., all spring to life and become dangerous projectiles. Could you imagine standing in the candy aisle in 7-Eleven and suddenly having things go nutty like that? Or imagine it happening while you're sleeping-- which was the case for most of us during Northridge. You're just like, "WTF???"

http://www.youtube.com/watch?v=yJPS4lokxtw

[HurricaneJosh]

Being from Louisiana, earthquakes are very rare here and if so, rarely felt. However I was in an earthquake in Mexico City in 1977. Fortunately the epicenter was off to the southwest so we were not in the worse part. Still it was very unnerving and we had some after shocks.

The most ironic thing about an earthquake is that it can occur on a bright, sunny day, with no warning.

Yeah, and there's actually a widespread perception among Southern Californians that quakes only happen when it's hot and dry out. Sometimes when we get really warm, still nights, locals will say it's "earthquake weather". This is just a superstition, and I think it stems from the fact that significant quakes in any one location are rare, and in Southern California, they usually occur during warm, dry weather because that's just the kind of weather we're usually having.

I know. I'm just busting his chops. It would scare the crap out of me too.

It's cool-- I knew you were joking around.

Oh OK, that makes perfect sense. My cousin who grew up in NJ was living in Seattle when they had that big earthquake a few years ago. He worked above the 20th floor of a building and was scared enough to think the entire building was going to fall over.

And comparing that quake (the Nisqually) with Northridge perfectly illustrates my earlier point. The Nisqually quake was bigger than Northridge on the Richter scale, but it wasn't as violent as Northridge. Compare the approximate shake maps for the two events, and you can see how violent Northridge was:

[MJW155]

How long did it take for you to get back into your normal routine? Was it hard falling to sleep at night?

[HurricaneJosh]

How long did it take for you to get back into your normal routine? Was it hard falling to sleep at night?

The city was under a curfew and martial law for a few days-- you weren't allowed to be out after dark-- and most stores were closed because there was so much damage to shelves, windows, and merchandise-- so we had to eat whatever was in the house (which wasn't much). I lived near a 7-Eleven and it was totally trashed-- the shelves had tipped over like dominoes, I think-- so they sold water from the doorway.

Believe it or not, I think we went back to work the next day or the day after, because we had a hard-azzed employer-- a shark-like Hollywood publicist who put his business before all else. Work was unpleasant. We were in a tower on Sunset Boulevard, and we were having lots of aftershocks for days and weeks-- several of them over 5.0, big enough to knock over heavy filing cabinets-- and people would get very upset. Each time a tremor started up, everyone would dive under their desks, the women would scream, etc. It might sound funny, but the homes of several people in my office had been trashed or very badly damaged, and people were just on the edge. It was like a post-traumatic stress thing.

Sleeping was also a problem. The slightest aftershock sent us all springing to our feet, wide awake. And since we were having sh*tloads of aftershocks, it meant crappy, light, interrupted sleep. We were extremely sensitive to the slightest signals. This lasted for weeks or even months.

[MN Transplant]

Not really related to the topic, but appropriate for a weather board - it was cold that day in the upper Midwest. I remember sitting at home for two or three days watching the quake coverage because the governor had closed all schools in MN.

[Ed Lizard]

The Northridge quake was on a blind thrust fault. Oil company geologists knew the faults were there, the USGS geologists were much more vague. The faults tend to shift porous and permeable rock that can hold oil against impermeable shales, forming a trap, and when oil wells are drilled and logged, sub-surface maps are produced. After the quake, the USGS and Cal-Tech were asking for, and receiving, the more detailed oil company maps.

The Temblor Sands in the Western San Joaquin Valley in the foothills are oil and gas bearing because of their proximity to the San Andreas, the oil fields around Long Beach are from traps along the fault that produced a significant quake in the area about 70 years ago, and the oil fields closer to Bakersfield are near the White Wolf fault.

The earthquake near the oilfields in Coalinga, CA was a surprise, I don't think even the oil company geologists who knew about the faults knew they were active.

[aslkahuna]

In comparing the Nisqually WA shock with the Northridge, one also has to remember that the former was at a greater depth than the latter. Vertical accelerations in the Northridge shock exceeded 1G such an occurrence was noted in the San Fernando shock of 1971 which was of similar magnitude on a similar fault with very similar damage and casualty figures. The White Wolf Fault produced the July 1952 shock which was MM 7.5 one of only 4 CA earthquakes in recorded history of that magnitude or greater that shock was also a surprise since fault is only 34 miles in length. Most big CA shocks are in the 6.5-7.4 range.

Steve

[HurricaneJosh]

In comparing the Nisqually WA shock with the Northridge, one also has to remember that the former was at a greater depth than the latter. Vertical accelerations in the Northridge shock exceeded 1G such an occurrence was noted in the San Fernando shock of 1971 which was of similar magnitude on a similar fault with very similar damage and casualty figures. The White Wolf Fault produced the July 1952 shock which was MM 7.5 one of only 4 CA earthquakes in recorded history of that magnitude or greater that shock was also a surprise since fault is only 34 miles in length. Most big CA shocks are in the 6.5-7.4 range.

Steve

Yep, I remember hearing that the Northridge quake was relatively shallow, which is one of the reasons it shook so harshly at the surface.

The other big factor was the soil composition in certain areas: Sherman Oaks and Santa Monica saw pockets of particularly heavy shaking due to looser, softer ground in those areas. I think soil composition also had something to do with the spectacular collapse of a large section of the elevated 10 freeway at La Cienega Blvd.

[aslkahuna]

Bad ground (loose unconsolidated or poorly consolidated fill) is where the damage to the 880 Freeway, the Bay Bridge and the Marina District to South of Market in the Oakland-SFO areas occurred despite being 60 miles from the epicenter of the 1989 Lome Prieta 6.9 shock. In fact, short of levelling all of the structures in the Marina District (not going to happen) and removing the old fill and replacing with new (not going to happen) the Marina District is going to be another disaster when the next big shock hits SFO. The fill there consists of debris from 1906 that was shoved into the Bay and covered with dirt-definitely bad ground. As far as the Bay Bridge is concerned, the Cantlivered span on the Oakland side where the collapse occurred in 1989 is being replaced with a modern suspension structure seated in bed rock. The suspension section west of Yerba Buena Island is on solid bedrock. The GG Bridge seems okay.

Steve

[Mallow]

Yep, I remember hearing that the Northridge quake was relatively shallow, which is one of the reasons it shook so harshly at the surface.

The other big factor was the soil composition in certain areas: Sherman Oaks and Santa Monica saw pockets of particularly heavy shaking due to looser, softer ground in those areas. I think soil composition also had something to do with the spectacular collapse of a large section of the elevated 10 freeway at La Cienega Blvd.

Right.

Soil composition is a significant factor, but the effects are very localized. There are areas in the Puget Sound region near the epicenter of the Nisqually quake which are composed of low-lying, waterlogged soils, and these areas were hit hardest by the quake (not surprisingly). But the soil composition differences don't show up as well on the maps you posted, since one zip code might cover myriad soil types, and the shaking over the entire zip code (especially larger ones) will tend to "average out", so to speak.

The bigger effect you're seeing in the maps is related to the depth. I'd like to further your hurricane analogy... a deep, strong (moment magnitude) earthquake is like a large, deep cyclone, a la Hurricane Katrina. Significant impacts are felt over a very wide area, but the intensity near the epicenter (ignoring the impacts of soil) is not as severe as one might expect, and not significantly more severe than areas nearby. A shallow but weaker (moment magnitude) earthquake is like a compact, intense cyclone, a la Hurricane Charley. Significant impacts occur over a much smaller region, but the intensity near the epicenter is very severe, and falls off quickly with distance from the epicenter.

In general, shallower quakes tend to have more severe shaking in a more localized area, whereas deeper quakes tend to have less severe shaking but over a much broader area. This holds true in pretty much every case I've seen.

Examples of the shallow kind are Northridge, and the recent Haiti earthquake, as well as the Kobe earthquake. Examples of the deeper kind of quakes include Nisqually, the Chilean earthquake, and the Indonesian earthquake which caused the tsunami.

Almost always, earthquakes with very high ratings on the moment magnitude scale (>8.0) are deep earthquakes, since they're caused by slipping along deep subduction zones. They are so much more "powerful" because they release their energy over such a large area, not necessarily because the shaking at any one location is extreme. A 7.0 earthquake with an epicenter near the surface and right below you would have extremely violent shaking, even while an 9.0 quake generally wouldn't (because it's much deeper).

[HurricaneJosh]

Right.

Soil composition is a significant factor, but the effects are very localized. There are areas in the Puget Sound region near the epicenter of the Nisqually quake which are composed of low-lying, waterlogged soils, and these areas were hit hardest by the quake (not surprisingly). But the soil composition differences don't show up as well on the maps you posted, since one zip code might cover myriad soil types, and the shaking over the entire zip code (especially larger ones) will tend to "average out", so to speak.

They actually show up pretty well on the ZIP code map for urban areas like L.A., where each ZIP code covers a relatively small area. For example, the dark-orange ZIP codes right near the beach are Santa Monica, which was one of the violent pockets I mentioned. The dark-orange ZIP codes a little above the Los Angeles label are Sherman Oaks, the other pocket I mentioned.

The bigger effect you're seeing in the maps is related to the depth. I'd like to further your hurricane analogy... a deep, strong (moment magnitude) earthquake is like a large, deep cyclone, a la Hurricane Katrina. Significant impacts are felt over a very wide area, but the intensity near the epicenter (ignoring the impacts of soil) is not as severe as one might expect, and not significantly more severe than areas nearby. A shallow but weaker (moment magnitude) earthquake is like a compact, intense cyclone, a la Hurricane Charley. Significant impacts occur over a much smaller region, but the intensity near the epicenter is very severe, and falls off quickly with distance from the epicenter.

In general, shallower quakes tend to have more severe shaking in a more localized area, whereas deeper quakes tend to have less severe shaking but over a much broader area. This holds true in pretty much every case I've seen.

Examples of the shallow kind are Northridge, and the recent Haiti earthquake, as well as the Kobe earthquake. Examples of the deeper kind of quakes include Nisqually, the Chilean earthquake, and the Indonesian earthquake which caused the tsunami.

Almost always, earthquakes with very high ratings on the moment magnitude scale (>8.0) are deep earthquakes, since they're caused by slipping along deep subduction zones. They are so much more "powerful" because they release their energy over such a large area, not necessarily because the shaking at any one location is extreme. A 7.0 earthquake with an epicenter near the surface and right below you would have extremely violent shaking, even while an 9.0 quake generally wouldn't (because it's much deeper).

Agreed with the above. The hurricane analogy plays through nicely-- Northridge really was the "Charley" of earthquakes-- and your thoughts are in line with what Steve and I posted. We Pacific-side dudes know how to talk quakes!

I'm glad that we cleared up that it's not all about Richter magnitude! That myth has to go!

[HurricaneJosh]

Today is the 18th anniversary of this violent quake that made a direct hit on L.A.

Can't believe it was almost two decades ago. It's still so vivid in my mind-- those fifteen seconds of complete craziness.

[am19psu]

IMBY weenie

[HurricaneJosh]

IMBY weenie

It was a legitimate event.

P.S. Where you been all day?

[am19psu]

It was a legitimate event.

P.S. Where you been all day?

Whatever. I'm looking forward to you starting a thread about some 7" snowstorm in Prague.

(P.S. Getting my azz kicked with non-wx stuff at work. This is my first break all day and I'm just eating lunch now)

[Srain]

Whatever. I'm looking forward to you starting a thread about some 7" snowstorm in Prague.

(P.S. Getting my azz kicked with non-wx stuff at work. This is my first break all day and I'm just eating lunch now)

[HurricaneJosh]

I thought this would be a thread of historical remembrance. Instead it's trollytrollz.

[Hoosier]

It's weird. I remember that week very well because of the extreme cold...or so I thought. I don't remember seeing any earthquake coverage and I assume it was a big national story.

[HurricaneJosh]

It's weird. I remember that week very well because of the extreme cold...or so I thought. I don't remember seeing any earthquake coverage and I assume it was a big national story.

Oh, it was. I know just because of what friends in NY told me. It was one of those big, nonstop stories on the TV news-- before the 24-hr cable news fad-- with a huge, banner headline on the front page of the NYT. It was a big story. The nation's second-largest city was smashed up, paralyzed, and under curfew for days.

[mappy]

Josh, I just stumbled across this thread. Thanks for sharing.

My father was in San Fran for the earthquake that struck during the World Series (I can't remember the year). He said it was one of the worst things he had ever experienced and he went to Vietnam, and grew up in the plains and experienced plenty of tornadoes.

Two seperate years I went to CA for spring break, San Diego one year and San Fran the second. I told him prior to the San Fran trip how much I had wanted to experience an earthquake, nothing major, just a tremor. My father called me a f-in moron. He never liked talking about the quake (or his time at war) but he made sure to tell me ALL about the San Fran quake so I wouldn't hope for one while I was out there.

Based on his story, I'm glad it never happened while I was there. And now I can say I did experience a quake, in MD (who would have thought?)