childs drawing of the letter P


Panic is one of the most significant causes of injury in earthquakes. Trying to run during the violent shaking of a large earthquake often leads to sprained ankles and broken bones. Learn now what to do during an earthquake, practice it now before you need it and you have much better chance of coming through the next earthquake unharmed. For parents, panic is particularly dangerous because your children will follow your lead. If you panic, so will they. Home earthquake drills can help you all stay calm in the next big earthquake. Find sturdy tables in your house and teach your children to go under them if they feel an earthquake. Make your children's bed safe (nothing to fall on it, consider bookcases, pictures and windows) and teach them to stay in bed if the earthquake hits while they are asleep. Once a month, at different times of the day, pretend an earthquake has started and practice duck and cover. You will all feel safer the next time we have a real earthquake.


Every earthquake shows us that preparing before the event can minimize your losses during the event. Several preparedness tips can be found through this Parent's Guide, but it is not complete. Preparing for the earthquake should include eliminating hazards in your house (bolting the house to its foundation, securing water heaters and gas dryers, using florist's putty to secure bric-a-brac and Velcro for computers and televisions), conducting home drills (see Panic) and maintaining supplies (see Electricity, also include water, medicine, tools). The American Red Cross and California Governor's Office of Emergency Services publish excellent guides to home preparedness.


Earthquakes produce three general types of waves (see Waves) to radiate energy. Two are body waves, which means that they travel through the body of the Earth and the other is surface waves, which means that they travel along the surface of the Earth. The two body waves are called P waves (for Primary) and S waves (for Secondary waves). P-waves are compressional waves while S waves are shear waves. Shear waves cannot travel through a fluid so P-waves are the only ones that travel through the Earth's core.

P-waves travel faster, but S waves are usually 2-3 times larger than the P wave. This leads to the characteristic shape of an earthquake on a seismogram with a small P wave followed by a larger S wave. Because the P wave is traveling faster, the time between the P and S wave increases away from the earthquake.

In fact, just like the time between seeing lightning and hearing thunder can be used to estimate the distance to the lightning, the time between the P and S wave can tell you how far away the earthquake is. Local rock type and the depth of the earthquake cause slight variations, but the number of seconds between the P and S wave times 5 is approximately the distance in miles to the earthquake. (Remember that some of that distance may be down into the Earth.)

This relationship between P and S waves also affects some of our perceptions of earthquakes. For instance, people will often report a sharp sound before the earthquake or that they "heard" the earthquake coming. They are not hearing something before the earthquake but are rather hearing the P wave at the beginning and then feeling the S wave. If they had counted the time between the two, they could have figured out how far away the earthquake was! The smaller P wave is also responsible for many of the reports that animals "knew" an earthquake was coming. With their better hearing, animals are more likely to feel and hear the P wave. The human thinks the animal knew before the earthquake happened when actually the animal felt the beginning of the earthquake that the less sensitive human missed.