Earthquakes: How to prepare yourself

Aug 24, 2011

Did you find yourself unprepared as to what to do when a 5.8-magnitude earthquake struck the East Coast yesterday? Learn tips on how you should prepare should another earthquake or aftershocks appear again. Chat with seismic analyst Anthony Guarino Wednesday, Aug. 24 at 11 a.m. ET.

Have a question? Ask now.

Hello, my name is Anthony Guarino, a Caltech Seismic Analyst and Duty Seismologist. I am here and look forward to answering a few of your questions.

What to do in the event of an aftershock?

The proper procedure is to drop, cover, and hold on. This means get under a desk or sturdy table, cover under it, and hold on to the desk or table. DO NOT RUN OUT OF A BUILDING DURING AN EARTHQUAKE. This is the most dangerous thing you can do, as the facades of the buildings are usually the first to go. 2 women were killed in San Simeon, CA during a M6.5 earthquake while running out of a building. Everyone inside survived without a scratch.

Mr. Guarino, Are aftershocks ever as strong as the quake itself? Also, one of the guys at my office said yesterday that the earthquake yesterday may just be a "foreshock", in which case the "real" earthquake will be bigger. How likely is that ?

An aftershock is an earthquake that is smaller than the main shock. If a larger earthquake occurs, we call the new event a mainshock and any earlier events foreshocks. 

As for your other question, in most cases, any earthquake has about a 5% chance (1 in 20) to being a foreshock for something larger. This probability decreases rapidly with time, so today the odds are significantly less (maybe 1-2% in most cases). 

The east coast is a little different, because we don't have enough data (not enough earthquakes) to know if this probability fits. It is still unlikely, although possible, that yesterday's event could be a foreshock to something larger.

First of all, there was no prediction for this 5.9 magnitude earthquake. Why?

No seismologist can predict any earthquake. It is just not possible (although we can use probabilities, which tell us that a certain earthquake may occur within 50-100 years at a certain % in a certain area). 

Here in Southern California, we have 30+ earthquakes per day on average.

Good morning, I was working at my computer my home on the 26th floor of a high rise yesterday when the quake. Interesting waving effect. As I considered moving to an inner room, I realized entrances to both kitchen and bath were just beyond the double 8-foot bookcases waving away. I decided to stay put but drop down and cover myself in case the wall of windows shattered. They did not but what if they had? What can I keep close by to protect myself from potentially shattering glass if I happen to find myself in this situation again? I was prepared for the earthquake but not for the gap in exiting to a safer location; for that, I am reconsidering my furniture arrangements. Thank you

You did the correct thing. Drop, cover under a table or desk, and hold on to that object, as it will move around during a large event. Stay away from any objects that will fall or break near you. 

During the 1994 M6.7 Northridge earthquake, the most common injury was glass cuts to the feet, as the event happened in the very early morning. I was told this by an ER Dr. on duty at the hospital closest to the epicenter. So, it's a good idea to keep a pair of old shoes tied to the foot of your bed if you live in an earthquake prone area.

Should I run downstaires as soon as possible, I live at the 11th floor?

No, the correct thing to do in any earthquake in the US is to drop, cover, and hold on. Get under something sturdy and wait it out. Once the shaking has stopped, you can evacuate a building, but the largest aftershocks tend to occur soon after the mainshock, so staying indoors is a good idea, since there may be downed power lines and other hazardous objects outdoors. Many newer buildings are fairly earthquake safe. Older buildings should be retrofitted for an event.

Does rocky soil take the shock better than softer soil?

Hard rock, like on the eastern seaboard, propagate waves more efficiently (i.e. they move faster through more dense rock). They do not shake as intense as soft sedimentary rock or sandy soils, which is why yesterday's event was felt over the entire eastern seaboard, whereas the same even in LA would only be felt a 100-200 miles, generally speaking.

How much warning time would you have if this earthquake was a magnitude 7+ in the same location? With a early warning system like Japan has?

This is an excellent question. We have an earthquake early warning system in S. CA that we are beta testing right now. It is operational, but only scientists are testing it.

If the early warning system that we have set up was in operation on the east coast, Washington DC would have had about 30 seconds of warning that the shaking was on the way.

Early warning doesn't work for events at the epicenter, but are designed to work for earthquakes at a distance that may do damage (i.e. 25 miles or more). 

Early warning is not a prediction, but a warning telling you that the earthquake has already begun, and the shaking is on the way. Think of it like lightning and thunder. The damaging earthquake waves move at about the speed of sound (thunder), whereas we can send data telling us the event has occurred at nearly the speed of light (lightning). So, like with a storm, when you see the flash of light, the thunder comes later, depending on how far the storm is. Earthquake early warning (EEW) works the same way.

In Japan, it saved countless lives during their recent M9.0. They televised it, and you can see the youtube video of their parliment in session, the warning on the TV, then the shaking more than a minute later. Just check youtube for "Japan Earthquake Early Warning."

My husband keeps saying that our DC townhouse (built in 1885) is likely to withstand an earthquake better than many of the newer buildings in the city. He argues it is more solid and better built. I am skeptical. Is it reasonable to expect that techniques used in older buildings would make them safer during earthquakes?

This depends on the size of the building and how far the earthquake is (as well as how big it is, obviously). So, think of throwing a rock into a pond. Very close to the splash, the waves are very close together. Further away from the splash, the waves get further apart, and they decrease in height. So, this means that big buildings far away may shake more intensely than smaller buildings. 

Scientists used to believe that the more rigid a building was, the stronger it was. Now we know that the building should move with the event. We have giant shock absorbers as well as giant metal concave dishes that the feet of the building sit in, so when the shaking starts, the building moves with the shaking.

Mexico City had severe damage to buildings between 10-20 stories during the 1980's, and there were ~10,000 people killed, but the earthquake was all the way off of the west coast of Mexico! Remember that Mexico City is in the middle of the country, nowhere near the ocean. 

So, smaller buildings did great, as did the skyscrapers, but mostly those buildings that resonated between 10-20 stories were the buildings that collapsed (apartments and hospitals, where many people were at the time).

I'm a decade+ out of california, but the rule used to be, after an earthquake, you're generally safer inside than outside (breaking glass and falling power lines are usually the issue outside, whereas inside you're not usually in danger of the building collapsing). So, why did everyone evacuate outside today? Did the rules change, or is it different here because buildings aren't built to the same specifications as they are in california?

No, the rules haven't changed. DROP, COVER, AND HOLD ON (under a desk and hold on to it, for example). The people that ran outside did the wrong thing.

Why did the earthquake energy go so far north but not as far south? I would have thought it would be like a pepple in a pool and ripple in a circle but it didn't.

This can be due to a few factors. One is the fault ruptured and pushed the energy north. Another is that older geological structures may have reflected energy (the east coast ripped apart from Pangaea several million years ago). 

I would encourage you to use a search engine to observe the wave propagation for the Sumatra earthquake. There are good animations on the web that show how it is more like dropping a large 2x4 piece of wood into a swimming pool. The maximum energy radiates in two directions, perpendicular to the length of the wood.

Having been raised in SF Bay Area, we were taught as little kids to get under our desks, but then as we got older they said if you can, get under a doorway. I've kinda held to that ever since, and yesterday that is where I went. However, today I read something saying that going under a strong table or desk is better than a doorway. What do you think?

The door frame is a falacy that originated due to early CA adobe buildings. The door frames were made of wood, but the rest of the building was made of clay. When the earthquake collapsed the building, all that was left was the wooden door frame. 

DROP, COVER, AND HOLD ON (under a desk/table and hold on to it as it moves). This is what you should do during an earthquake. 

So we're suddenly going to start preparing for earthquakes around here like we're in California? This was a once in a lifetime event, why overreact? I've seen articles about getting earthquake insurance, earthquake emergency supply kits, etc. Seems like a bunch of people profiteering off of fear from a freak event.

You should have an emergency kit for any type of disaster, not just an earthquake. The east coast has a big storm on the way, which will likely do more damage than this earthquake. You should always be prepared. 

Most people on the east coast will feel moderately intense shaking sometime in their lifetime. This isn't just a freak event. There have been earthquakes on the east coast for millions of years, but they just happen less frequently. 

I encourage you to check out, which has a HUGE list of events that have happened on the east coast since 1800.

New Madrid, MO, had three events in the mid to high M7 range that damaged property over much of the east coast. It caused waves to move up the Mississippi River, giving the illusion that it was flowing backwards.  

What is best to do when there's an earthquake?

DROP, COVER, AND HOLD ON. Get under a sturdy table and hold onto it.

What's the biggest mistake you saw yesterday in the DC area in terms of readiness for the earthquake from an individual and regional standpoint?

People running out of buildings during the shaking. They should have dropped, covered under a sturdy table, and held on.

Why is Virginia an east coast hotspot for earthquakes? How can Appalachian faults be reactivated now?

It, along with every other state (except maybe Florida), has earthquakes. NYC even has earthquakes of a moderate size, although it has been many generations since the last. Boston has fairly large quakes infrequently, as does NC and MD.

I have often scoffed at my father's childhood training in case of a nuclear attack--the whole duck-and-cover under a desk. But guess who was far better prepared for yesterday's EQ?

Drop and cover is different from drop, cover, and hold on. In an earthquake, you don't just drop and cover, but you hold onto the object. One of the most common fatalities in Haiti were crush fatalities (many of those who got under their small schooldesks survived.)

How do we know that yesterday's earthquake was the "big one" and not just a foreshock with something bigger to come?

It was not a large earthquake by seismology standards. When a M7+ event happens (say on the New Madrid Fault Zone in MO), then you will be seeing damage at significant distances.

There was just a M7.0 earthquake in S. America a few minutes ago, but that event was near the boarder of Peru and Brazil. Many S. American countries have large events (up to M9.5, which happened in Chile in 1960). This is the about the largest earthquake we can have on earth, because to have a big quake, you need a big fault rupture. There aren't any larger faults, so that is about the maximum (save for Alaska, and a couple other places that have faults the same size). M9.5 is about the largest.

Mr. Guarino - the news yestereday said the earthquake in Japan several months ago was "50,000 times stronger" than the quake we had yesterday. Can you explain how the Richter scale works, and keep in mind I'm a novice! It's difficult/impossible to conceive of something that strong!

Actually, we don't use the "Richter" scale any longer. That was dependent on a specific instrument calibrated here in Pasadena at a place that is no longer owned by Caltech. 

The Moment Magnitude scale (developed by my collegue Dr. Hiroo Kanamori), is the scale that we use for most big events. Each whole number increases the energy by a factor of 32, whereas the ground shaking increases by a factor of 10. This means we would need 10 M4.8 events to equal the energy released in yesterday's event, or about 1,000 M3.8 events, or about 32,000 M2.8 events to release the same energy. 

Mr. Guarino, how does one know that what one is feeling is an earthquake? Here in New York, I figured it out right away, but most people did not know. Most of my neighbors thought it was blasting from the Second Avenue Subway. And since 9/11, when there is some unexplained problem, New Yorkers do not stick around inside a building in Midtown or Downtown waiting to find out what it is. Probably a thousand of our neighbors died in the South Tower that day precisely because they followed instructions to remain inside.

That's a tough question, but remaining inside is always the protocol for an earthquake. I have never experienced a blast, but an earthquake will last longer, generally. If you have a computer and access, you can always check the USGS website, where it will usually pop up within 1 or 2 minutes of the event. 

Given my fabulous decorating sense, all my tables are glass. I could turn over a sofa (into like a teepee), but if I'm not near one, is getting near an interior wall or exterior wall best? Also, in a three level home with a basement, which is the safest level to be on? Thanks!

It depends on how far the event is and how big it is. The best thing in this case would probably to just get away from anything that may break, and try to get some cover. You won't have time to flip your couch, and we don't encourage people to get next to a wall and crouch down. There isn't any evidence that this works any better than being any other place (save for under a sturdy desk or table). 

Most buildings are built to withstand most earthquakes. Also, if it is a very large event, you will not be able to walk. You will get thrown to the ground, as they did in Japan. You may be able to crawl, but certainly not run in a very large event (which is unlikely but still possible on the east coast). 

Is there a known fault associated with this earthquake?

This occurred on the Virginia Fault Zone, a known area of many faults. They are not well mapped, as there is much overgrowth of vegitation. Also, most of these faults are millions of years old, whereas in CA we have some that are only a few hundred years old. 

You say shelter in place. I am reading recommendations from Chile that say to go, in an orderly fashion of course, to a park or some open space. Indeed these are the images we saw during the South American earthquakes: people in parks.

Most of the time, the event that you are experiencing will be the largest event (except a few percent of the time). So, shelter in place is fine in most cases. After some of the larger aftershocks subside, then using a park or some other open space is a great idea. Chile had many magnitude 7-8 aftershocks right after their M9.5 in 1960.

Do you think a big earthquake will happen again?

I can say with nearly scientific certainty (which is rare) that there will be more events on the east coast in the future (maybe not the near future, but the future nonetheless).

Thank you all for your questions. Some great questions were asked. I encourage all to watch the Japan Earthquake Early Warning video on YouTube when you get a chance. It will show you how Washington DC would have had about a half of a minute warning that the shaking was on the way if the system was in place (like it is in CA, where we are beta testing it). 

Thanks again for the great questions. Have a great earthquake-free day, and spread the message about drop, cover, and hold on! Thank you. Good bye. -Anthony Guarino, Caltech

In This Chat
Anthony Guarino
Anthony Guarino is a seismic analyst/duty seismologist who has worked for Caltech Seismology for nearly 10 years and holds a degree in Geophysics.
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