About Earthquakes

Earthquakes are one of the most destructive natural disasters.  For example one of the largest quakes in history was the 1906 earthquake that devastated the city of San Francisco.

The risk of earthquakes is highest along fault lines. In places that are prone to earthquakes like those along the tectonic plates, people prepare for earthquakes, cities construct buildings designed to withstand large earthquakes, and schools teach children what to do if a quake strikes.

Scientists conduct studies to help cities like San Francisco and Los Angeles, located on the San Andreas Fault, to be prepared for a large magnitude earthquake.  The San Andreas Fault is a crack in the earth’s crust that is close to 590 miles long (or 950 kilometers).

The damage caused by an earthquake is dependent on the magnitude and how close the epicenter is to populated areas.  The epicenter of an earthquake is the location on the surface directly above where the rocks deep below the surface of the ground begin to break apart.

In order to determine the location of an epicenter, researchers have buried sensitive devices called seismometers all over the earth that detect and record the slightest motion of the earth.  Every hour numerous tiny earthquakes occur which are detected by these scientific instruments, although they are not be felt by people.  Signals from seismometers are transmitted via satellite or phone line to a central computer providing scientists with the magnitude and epicenter of each earthquake.

What Is An Earthquake Like

People often ask what an earthquake feels like, and of course, there is not a definitive answer for that question.  When major earthquakes occur, they don’t always feel the same.  Some quakes have more of a rolling feel, while others have more of a shaking back and forth movement.  There are many factors involved that determine what people feel when a quake strikes.

How close is the epicenter
How deep is the focus of the quake
The density of the ground (rock, sand, clay, etc.)
Did it occur on a major or minor fault line
Was it a tectonic or volcanic earthquake

What We Feel During An Earthquake

The motion people feel during an earthquake is the result of the shockwaves listed below.  The first motion usually felt during an earthquake is a jolt caused by the push-pull shockwave from the P-Wave as it reaches the surface.  The second jolt is is from the other type of body wave, the S-Wave.

The L-Waves, or Surface Waves, will then be felt typically as a rolling and swaying.

The stronger the quake, the longer the motion felt during the quake will last.  A major earthquake can last several minutes.

In addition to the motion felt during an earthquake, seismic waves are sometimes audible, having been described by those who have experienced a major earthquake as sounding like thunder, a locomotive, or cannon fire.

3 Types Of Shockwaves Create Different Types Of Motion

Earthquakes produce three different types of shockwaves that travel outward from the focus of the quake, both horizontally and vertically, and each can only move through certain layers of the earth.

P-Waves, or Primary Waves, are similar to sound waves and are longitudinal, high frequency waves, with a short wavelength. These waves can pass through solids and liquids. P-Waves produce relatively small ground displacement.

S-Waves, or Secondary Waves, are also high frequency, short wavelength waves; however, they are transverse instead of longitudinal. These waves move in all directions away from the source.
These waves cannot move through liquids and the density of the ground they move through determines the speed in which they travel.  S-Waves move the ground in a sideways motion, for example leaving walls and fences in an S-shaped manner.

L-Waves, also referred to as Surface Waves, are low frequency transvere vibration with a long wavelength. The motion of these type of waves move similar to the waves of the sea, causing the ground to move in a circular motion which then triggers a rising and falling motion which visibly looks like waves moving across the ground.

It is these L-Waves/Surface Waves which cause the majority of damage caused by earthquakes.  There are several types of surface waves, but the two most common are R-Waves, or Raleigh waves, and L-Waves, Love waves, named after the scientists who discovered them.

R-Waves continuously move forward, and cause the earth to move vertically similar to a twig in a pond bobbing up and down after a stone is tossed in the water.  L-Waves also move in a forward motion, but these waves cause the earth to move back and forth horizontally.

Earthquake Prediction

The USGS and other seismologists state that earthquakes are not predictable.  Scientists conduct extensive studies and are able to determine the likelihood that a major earthquake is likely to occur in a particular area over a span of years, but they have not yet been able to develop a method of detection where an earthquake warning could be issued.

Caltech seismologist, Kate Hutton, said in an interview with Xinhua in March 2011 that scientists agree that a major earthquake is overdue somewhere along the San Andreas Fault.  According to Hutton, while scientists are able to make long time predictions, they are not able to predict earthquakes on a short time basis like a weather forecast.

Some of the factors involved in scientific studies related to earthquake prediction are plate tectonics, past history of earthquake occurrences, monitoring the buildup of stress and strain in various fault areas.


Dogs & Animals Sense Earthquakes Moments Before

Dogs can sense earthquakes moments before a quake strikes. Throughout history you will find recorded evidence that our canine friends have alerted us to earthquakes and other natural disasters, like tsunamis, by displaying considerable agitation just prior the occurrence of such an event.

In the video clip above you see footage from a security camera as it captures Sophie the dog bolting to find her master just moments before a 6.5 magnitude earthquake struck in Eureka, California on January 9, 2010.

Scientists are learning that dogs have a sixth sense which enables them to know what’s happening before humans can detect it.  Dogs’ extraordinary senses are immensely invaluable and have already been used by scientists to successfully predict earthquakes.

The intelligence of the canine species along with the dogs’ ability to communicate with people, is what sets them apart from other domestic species.

Other animals are also able to detect the initial motion of an earthquake which are called P-waves, the fastest moving waves of an earthquake that are too small for human detection.  These ultrasonic waves travel much faster than the following S-waves which cause the strongest ground shaking.

Throughout history, almost all civilizations have observed unusual animal behavior preceding an earthquake.  A fairly recent example was in the Tamilnadu 2004 tsunami when a herd of 500 blackbucks fled from coastal areas to a nearby hilltop.

What To Do In An Earthquake

The KCAL9 News report above was aired after a 5.4 earthquake in Chino Hills, California, although it was later revised to a magnitude of 5.5.

-If you are indoors…

Take cover underneath a heavy table or desk and hold on, if it moves try to stay under it.
Studies have proved that a sturdy table is the most likely place for survival during a quake.  Aside from the obvious protection from falling debris, the space under the table can also provide you with air space if the building collapses.

If you are unable to get under a table or desk then try to take shelter in a door frame or near an inner wall, especially an inner corner or doorway that is away from windows.  While doorways are no longer considered as the number one location to seek shelter in an earthquake it is the next best thing.

Watch for falling objects, hanging objects, bookcases, and other large furniture items that could fall and trap you.  Also watch for falling structural debris like fireplace bricks, or a chimney, light fixtures, wall hangings, bookshelves, cabinets or closets with swinging doors.

If possible find something that you can use to shield your head and face from broken glass, falling debris, and even the dust stirred up if the building collapses.

What Not To Do…

If the power is out use a flashlight. DO NOT use candles, matches, or lighters during or after an earthquake. Possible gas leaks could trigger an explosion.

If you are in the kitchen, quickly turn off the stove.

-If you are in a high rise…

First get under a desk, and if circumstances allow get under a desk that is away from windows and outside walls.
During the quake do not exit the building because there is greater risk of injury and death due to falling debris outside the building from breaking glass and large portions of the structure coming down.

-If you are in a crowded public place…

The first instinct is to run to the nearest exit or doorway; however, in a large crowd of people, everyone will be panicking and rushing the exits. This creates another disaster within a disaster where people become trapped or even trampled.

Look for someplace where you can take cover, or at the very least try to find something you can shield your face and head from falling debris.

-If you are in a store surrounded by shelves of inventory…

It’s difficult to make a standard recommendation because each scenario will be unique; however, here are some possibilities to think through ahead of time so you can be ready to make the best possible choice in that moment a large quake hits.

After watching a number of videos of earthquakes in warehouses and stores with aisles of product, typically there are a few sections on some aisles that are free from debris. For the most part, the shelving units themselves withstood the quakes. There were of course, some exceptions where portions of the shelving collapsed or broke apart. Most of the aisles were typically full of product that had fallen from the shelves.  Even the space right next to the shelves was covered in debris.

You will need to make a split second decision based on the following:

  • the amount of shaking
  • how crowded the area is
  • how far away are you from an exit
  • should you even consider exiting based on if you are in a high rise building
  • is there a table or countertop close be to take shelter under

Suggested safety tips to take in a warehouse during a major earthquake:

  • If circumstances allow try to exit the warehouse
    Of course this depends on if there would be greater risk outside the building due to falling debris, for example if the location is in a high rise district, etc.
  • If unable to exit safely, look for a table or countertop to take shelter under.
  • Take shelter within the shelving unit itself
    If product on the shelves are not too heavy, push the items off the shelf and crawl into the shelf for shelter from falling debris until the shaking stops.  If you have a choice, don’t use the bottom shelf or you will most likely be blocked in from everything that has fallen on the floor.  But, if the bottom shelf is your only option…go for it.
  • If all of the above actions are not possible, the next best thing to do is to stand right next to the shelving unit itself.  This will at least give you a better chance of avoiding direct impact of falling items.  The initial impact of falling debris typically hits near the center of the aisle and then rolls to the edges.

If you are in your car during a major quake…

If you are driving when an earthquake happens, pull over and stop as quickly as it is safe to do so.  As much as is possible, stop your car in the safest possible area such as the shoulder of the road or curbside while keeping away from utility poles and overhead wires, as well as avoiding underpasses and overpasses.

Stay in your car during the quake and apply the parking brake.
Listen to the radio for emergency information about the earthquake.

After the shaking has stopped and conditions appear safe enough for you to drive, be very cautious and watchful for any hazards created by the earthquake such as large cracks in the pavement, downed utility wires, and collapsed overpasses or bridges.


How To Prepare For An Earthquake

It’s very important to know how to prepare for an earthquake because once a quake strikes you most likely will not have the opportunity to go out and purchase the emergency supplies you will need to hold you over for a few days until power and water can be restored or until aid can reach you. Therefore, you must prepare for a number of different possible scenarios.

To be prepared for an earthquake is much more involved than just gathering essential food, water, and medical supplies.  It is important to have a emergency plan in place.  There are a number of issues which need to be addressed ahead of time.

A well prepared earthquake plan should include first aid and CPR training well in advance of an emergency medical condition or injury incurred after a major earthquake.  It is important for each member of your household to know what to do if the earthquake occurs when you aren’t together.  It is often impossible to make local calls after a quake, so you’ll want to designate and emergency contact out of the area to help communicate your loved ones, etc.

Consider the following possible scenarios:

If the epicenter of the quake is near your location you will be dealing with severe damage to structures, roadways, power outages, no water supply, etc.

Your area might experience moderate damage, but utility services such as power and water may be unavailable for a number of days.

Phone lines and cell phone signals may be down or jammed and you may not be able to contact emergency services or loved ones.

After a quake you may or may not be able to travel by automobile.

Gas stations and markets will be damaged or have no power after a major quake and it is probable you will not be able to get gas or food after a quake occurs.

Emergency paramedics or ambulance services may not be able to be reached or may not be able to gain access to your area.

How to prepare an earthquake plan:

  • Know what to do during an earthquake:
    First and foremost you will want to equip yourself with the knowledge of what to do during an earthquake, as discussed above.  Know where the safest place is in your home or office to take cover during a quake.
  • Make it a habit to keep a half tank of gas in your car
  • Have an earthquake supply kit that contains at least these basic supplies:
    Food, water, and personal hygiene items for at least 3 days.  For a more detailed list of suggested items to have in an earthquake supply kit see the following section below.
  • Store your earthquake supply kit in a location that could be
  • Also have an earthquake kit for each vehicle you own
  • Take a first aid and CPR course
  • Consider online document storage of scanned and digital copies of important records, contacts, and priceless photos or arrange to keep copies of these records at a separate location.  If you prefer not to store such items online, store these items instead in a fireproof safe.  Since earthquakes come without warning you have no opportunity to gather important paperwork, precious family photos, medicines, phone numbers of doctors, veterinarian, insurance company, and so on.
  • Establish a plan of where to meet family and loved ones in case an earthquake occurs during work or school hours and you’re not together when a quake strikes.
  • Anchor collectibles, figurines, and other breakable shelf items with museum wax
  • Use earthquake safety straps to secure the TV, computer, printer, etc.  Also secure bookshelves or other heavy furniture items to the wall with furniture brackets or heavy duty straps.
  • Secure your water heater with water heater safety straps

Earthquake List

  • First Aid Kit
  • 1 gallon of water per person, per day
  • Non-perishable food items
  • Spare eyeglasses
  • Medications
  • Out of town contact number
  • Pet food
  • Pet crate
  • Hand operated can opener
  • Battery operated or a hand-cranked radio
  • Work gloves (in case you need to clear rubble)
  • Sturdy shoes in case you need to walk to safety
  • Spare clothes
  • Battery operated or hand-cranked flashlight/lantern
  • Comfort items such as playing cards or games, books, etc.
  • Solar powered battery charger for batteries, cellphones, and laptops
  • Extra batteries
  • Portable camping toilet and chemicals
  • Toilet paper
  • Hygiene items
  • Dry shampoo
  • Cash