Earthquake 101

Wednesday, August 24, 2011

Yesterday's earthquake didn't lead to any destruction, however there are still many questions New Yorkers have about possible future occurrences.James Gaherty, Lamont Associate Research Professor, Lamont- Doherty Earth Observatory and Lance Jay Brown, architect, co- chairs Design for Risk and Reconstruction committee at AIA New York chapter, professor at City University School for Architecture, answers questions about NYC's building codes. What do you still want to know about earthquakes?


Lance Jay Brown and James Gaherty

Comments [39]

Michael R. Brown from California, U.S.A.

Did you actually read the link to site in the article? It disproves the article's contentions! "Some of these instruments were stationed around the North Anna Nuclear Power plant, but in the 1990’s, due to budget cuts, most of the North Anna sensors were taken off line." *Most* - not *all*. And those were VTSO's sensors - an observatory's seismographs, not the nuke plants safety seismic sensors. This is an irrational moral panic in action. The article conduced to it - it did not even actually state that there were any safety consequences to "all seismographs" being taken offline.

Aug. 25 2011 06:49 PM
Jim Gaherty from Palisades, NY

Carlos' question and Ario's comment are good ones, but let me provide a little context. Seismologist quantify earthquakes using seismic moment, which we like for two reasons: (1) it can be calculated directly from seismograms, and takes into account both the amplitude of the shaking, and it's duration; and (2) it can be related to the product of three simple and basic properties of the earthquake itself -- the rigidity (stiffness) of the rock at the source, the area of the fault surface that slips, and the amount of slip (displacement) that occurred. For the Virginia earthquake, the scalar seismic moment was about 5.8 x 10^17 Newton-meters – we are now working to estimate what this implies for the area of the fault that slipped, and how much slip occurred. For comparison, the Japan earthquake in March had a moment of 6.0 x 10^22 Newton-meters – over 100,000 times larger.
In order to convert this robust estimate of earthquake size to a traditional Richter magnitude scale, we plug it into a logarithmic formula, and obtain Mw, which is comparable to the older versions of Richter magnitude, and allows us to compare quakes of today to quakes from the past. Based on this formula, an earthquake one magnitude unit larger (say Mw of 6.8 instead of 5.8) has a seismic moment that is 10^1.5 times larger (or 31.6 times larger). I think it is fair to say that most of us round this to ~30. Because Mw is a logarithmic formula that puts the earthquakes on the same scale as the original Richter magnitude formulas (of which there are several), then we still call “moment magnitude” a “Richter magnitude”. From Carlos’ question, it is clear that this causes some confusion among people who are really trying to understand the quantitative details.
I hope that this clarifies more than it clouds. For more details, the wikipedia page on Moment magnitude scale isn’t bad:

Aug. 25 2011 02:31 PM
Arlo from Manhattan

To answer Carlos C., yes, we now use the moment magnitude scale, which corresponds closely to the Richter scale over much of the range but not exactly. I'm sure that James Gaherty knows the following but he messed up his explanation: each increase in magnitude (say from 5 to 6) corresponds to a displacement (amplitude of motion) increased by a factor of 10, which corresponds via simple physics to an energy increase of 10 times the square root of ten = 31.6, approximately. Two magnitudes on the moment magnitude scale corresponds to a factor of 1000 in energy. To put this in context, the energy release in a megaton nuclear explosion is about MMS magnitude 6, which is about the size of the Mineral, Virginia earthquake on Tuesday.

Aug. 25 2011 12:52 AM
Carlos C from Weehawken, NJ

Brian's guests today spoke of the Richter scale and how its measurements compare as you move up the scale. Are we still using Richter to quantify the magnitude of a quake? I thought we were on something called the moment magnitude scale. How are the two scales similar, how are they different, and what are the criteria for using one or the other?

Aug. 24 2011 11:21 AM
Nancy from Morristown, NJ

At last, something to make Californians feel superior for 15 minutes!

Aug. 24 2011 11:00 AM
Amy from Manhattan

Carlos & renee, I think we're all talking about the same quake.

Aug. 24 2011 10:57 AM
Gerard Sava from Hasting on Hudson NY

As a former geology major and not ignorant to the fear and exitement around earthquakes, I think the real, actionable news relating the quake was the request from FEMA to limit cell phone use as the networks were heavily congested, limiting access for 911 and important emergency contacts. Nearly 10 years from 9/11 and our individual need for high data ipad pacifiers still can hamstring our societal need for broad shoulders, durable networks and a little perspective on our effect on others.

Aug. 24 2011 10:53 AM
Amy from Manhattan

114 years? There was a quake in NY in the early 1980s. Maybe it was too small to count--I don't remember the Richter number.

Aug. 24 2011 10:48 AM
Mary Ellen Scullard from UWS

What about the safety of all these pre-war buildings (steel cage construction, concrete slabs, brick exterior), 14 floors built in the teens and 1920's? What earthquake codes were they built to, if any?

Aug. 24 2011 10:47 AM
renee from forest hills

Aout 28 years ago we had a 1 pt quake in Queens. I think that the epicenter was in Long Island City.

At that time I learned that NYC is on a fault. And we understand don't build for earthquakes.

Aug. 24 2011 10:46 AM
Sophie from Poughkeepsie, NY

Of course when (if) a true catastrophe hits NYC many will not get out alive.

Aug. 24 2011 10:45 AM
Laura from UWS

Question: How to allocate safety money?

"A nuclear power plant that was shut down after an earthquake struck central Virginia Tuesday had seismographs removed in 1990s due to budget cuts."

Aug. 24 2011 10:45 AM
Sophie from Poughkeepsie, NY

A number of years ago there was an earthquake in Plattsburgh New York, it was felt here in Poughkeepsie.

Aug. 24 2011 10:42 AM
Tony from NJ from New Jersey

I am a structural engineering working in NY and something that is constantly missed in this discussion is that the while the buildings in have been designed for earthquakes since 1995, NY has a very conservative wind code, which has been around much longer and typically the this typically governs the design of buildings in New York, even since 1995 when the earthquake code was introduced.

Aug. 24 2011 10:41 AM
james from Bay Ridge

Was the historically strong earthquake in Colorado just a coincident event, or possibly connected?

Aug. 24 2011 10:40 AM
Pam from ny

A couple of clarifications:
1. I've been told that wood-framed structures are a lot stronger than similar non-wood-framed structures.
2. NY gets a lot of small earthquakes.

Aug. 24 2011 10:39 AM
LCruz from brooklyn

as delightful as it is to not have any serious damage from this recent event, if nothing else, our cell phone dependent culture, myself included should really consider real emergency communications options., as relying on only cell phones is clearly a non starter.

i vote for HAM.

Aug. 24 2011 10:38 AM
Marissa from Manhattan

Seriously, though - we should be much more concerned with flooding from the Hurricane coming this way; that could cause much much more damage than the tiny tremble from the earthquake.

Aug. 24 2011 10:38 AM
Jane from Manhattan

How do the recent instances of companies falsifying concrete testing results affect how those structures might respond to earthquakes?

Aug. 24 2011 10:38 AM
dbbk from bklyn

east coast earthquake zone + lots of old buildings that are not built to withstand earthquakes = another reason to say "no" to hyrdo-fracking....

Aug. 24 2011 10:37 AM
Eric Somers from Poughkeepsie, NY

Does the fact that East Coast rocks transmit the earthquake energy so well means that it dissipates the energy from the primary quake area (kind of the way a heat sink dissipates heat from a hot source)?

Aug. 24 2011 10:37 AM
Carlos from Manhattan

I remember being shaken awake early in the morning by an earthquake as a teenager in the 80's... in the Bronx! So its not the first time!

Aug. 24 2011 10:36 AM
mary ellen from south shore long island

the north shore of long island is rock, the south shore is sand, in a larger earthquake could the south shore "slip" into the ocean in any measure????

Aug. 24 2011 10:36 AM
Alicia from Manhattan

My daughter and I were reading on her bed, on the 12th (top) floor in a 100-year old building on Morningside Heights when we noticed the bed begin to shake slightly--no building sway, however.

My question for this neighborhood--how dangerous is the fault line at 125th Street? Is it possible that we'll have a major quake there?

Aug. 24 2011 10:36 AM
Elaine from Baltimore

If it's 5.8 at the epicenter, how does it decrease in strength the further one gets from the epicenter?

We were rocking in Baltimore!

Aug. 24 2011 10:36 AM
Laura from UWS

I received this e-mail. Can you comment?

"According to the Nuclear Regulatory Commission, Indian Point is designed to withstand a 5.8 earthquake within a 50 mile radius of the plant.This is based on a 5.8 earth quake in New Jersey in 1894. This one was 5.9 and it was 200 miles away. The plant was not at risk, however, it is important to remember that the reactor building is the only building that is covered in the design basis. This means the systems that are needed in an emergency are not covered. Neither is the spent fuel pool or underground pipes. Fire fighting equipment is housed in a cinder block storage building that an earthquake could demolish. Even though this was not a radiological emergency, cell phone lines crashed and it was impossible to make calls, emergency or otherwise. How could the county plan to notify Westchester residents via cell phone have worked in a real emergency? What about notification to those outside the ten mile area? What about parents who work in NYC and their concern for children left in Westchester? What would they do in a radiological emergency? What would any of us in the 50 mile radius do, considering that our roads and bridges cannot even handle an ordinary rush hour?

This unpredictable act of nature brings home the fact that closing a nuclear reactor situated in a 50 mile radius of 20 million people is about a lot more than generating electricity. While we can generate electricity in many different ways, the potential loss of lives and damage to those of us in the Hudson River Valley and New York City is incalculable. While the probability of a natural or human caused catastrophic release of radiation at Indian Point remains low, the impact is simply to much to tolerate. Indian point must be closed.

It is vital for all of us to talk with elected decision makers and remind them of this fact. As this 5.9 earthquake clearly demonstrates, the time for counting megawatts is over."

Aug. 24 2011 10:36 AM
Natalie from Manhattan

If the earthquake was a magnitude of 5.8 in Mineral, VA, does that mean it was also a 5.8 in NYC or is there a way to calculate the magnitude as it got farther away from the center?

Aug. 24 2011 10:35 AM

Lance Jay Brown was ABC yesterday evening sounding impressively indifferent to New York's appalling record of non-inspection, of giving a blanket pass to the abuses of developers, etc.

Is it possible he is unaware of the miserable record of shoddy construction that is endemic to New York? Has he ever heard of Patricia Lancaster?

Aug. 24 2011 10:35 AM
dbbk from bklyn

east coast earthquake zone + lots of old buildings that are not built to withstand earthquakes = another reason to say "no" to hyrdo-fracking....

Aug. 24 2011 10:34 AM
Marissa from Manhattan

I grew up in California and have experienced many earthquakes - I'm surprised of how large a reaction New Yorkers have had to what was a small event (here). Are there any City requirements for retrofitting the brick facades on our older structures, the way there are in California (which has many fewer brick buildings)?

Aug. 24 2011 10:34 AM
Andrew from Greenpoint

What are the fault lines near New York?

Aug. 24 2011 10:34 AM
Joe from Englewood, NJ

Could "apparent magnitude" values be determined, which takes into account the depth of the epicenter and its distance?

Aug. 24 2011 10:34 AM
Laura from UWS

Shouldn't the news media have warned the public to check their hot water heaters for potential gas leaks? And what to do if you smell gas......

If bricks could fall off a chimney, couldn't gas connections come loose?


Aug. 24 2011 10:33 AM
Steve M from Convent Station, NJ

Did the Marcellus Shale Hydraulic Fracturing Or Fracking Process Factor into Yesterdays Earthquake?

Aug. 24 2011 10:33 AM
Pam from NY

At 2 pm, it was reporteds to have been felt in Detroit! How can that be related to bedrock?

Aug. 24 2011 10:33 AM
Laura from UWS

Do you know if anybody is studying animal behavior before this earthquake? This was done after Kobe, Japan earthquake and in California. For example, pet cats running away.

I heard on TV yesterday woman said her dog started barking just before the earthquake.

Aug. 24 2011 10:29 AM
Laura from UWS

Geology question: what was the Earth trying to do?

I understand from TV last night that the extensive rock structure here in the East lets us feel earthquakes over longer distances than out West, but I do not understand the 'geometry' of this quake......Plates? Fault lines?

Also, what's the future going to look like? If San Francisco is moving towards Alaska.......Which way are we going?


Aug. 24 2011 10:25 AM
John A. from suburbs

Is there a number for what the earthquake energy was at Our location? What I perceived seemed like a 4.2 Richter perhaps. (The fact that it was acting over 300+ miles is amazing).
What was the largest east coast earthquake recorded, and the accuracy of such an old estimation.

Aug. 24 2011 10:16 AM

I was in my 4th-floor apartment in Park Slope, Brooklyn. Sitting at my desk, I thought initially that I had somehow jogged my desk, then that somebody was moving something very heavy about. But it continued and got worse and there were no sounds of somebody moving. Then I felt a touch of motion sickness. "Earthquake? No way."

My building is one of _thousands_ of poorly built brick-and-wood-frame constructions in New York. We know from the resignation of Buildings Commissioner Patricia Lancaster that developers _typically_ cut corners and _count_ on inspectors not showing, not caring, or being bought off. This is old New York history. Even supposedly socially responsible institutions, like Trinity Church, have been caught in scandals of shoddy construction.

Shoddy, substandard, and even illegal construction is the NORM in New York City. I find it very difficult to believe that Michael Bloomberg isn't well aware of this — especially given the way he tried ram down New Yorkers' throats the West Side Stadium, the Olympics, and (successfully) Atlantic Railyards.

A severe earthquake — something near and on the order of 6 or higher — in New York might well lead to _thousands_ of deaths -- most avoidable if the city would just _enforce_ existing law.

Aug. 24 2011 10:09 AM

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