On April 18, 1906, an estimated 7.8 magnitude earthquake struck along the San Andreas Fault in California, just off the coast of San Francisco.
It only lasted for forty-two seconds, but the resulting fires burned for days. More than 3000 people died.
What Causes Earthquakes?
All land on Earth (including the sea floor) floats around on the surface as gigantic separate sections called tectonic plates. These plates move at an average of about 1-2 inches per year and usually slide over and under each other with little trouble.
In some cases, however, the plates press against each other or stick together, and pressure starts to build. When the pressure has built up to the breaking point, the plates will suddenly shift. These plate shifts lead to one of two kinds of earthquakes—thrust quakes or slip quakes—depending on how the plates move past each other.
Thrust quakes occur when one plate runs directly into another, and the pressure is released by a plate bursting over or under the opposing one.
Slip quakes occur when two plates under stress suddenly move sideways in relation to each other to relieve the pressure. This results in the “ripped earth” images typical of disaster movies.
Where and when Earthquakes Occur?
Every US state has some seismic activity, but the most active are the ones along the Pacific Ocean (Alaska the most of all, then California). The second strongest earthquake in US history (estimated at an 8.1 magnitude) is the New Madrid quake of 1811, which struck Missouri.
There are earthquakes occurring all over the world all of the time. Fortunately, these are very tiny quakes, and most people aren’t even aware of them. Unfortunately, we are still unable to predict when a dangerous earthquake will occur with any exactness.
How are Earthquakes Measured?
The “local magnitude” scale was developed in 1935. Commonly known as the “Richter scale” after one of its developers, it aimed to quantify medium intensity quakes (those of a magnitude between 3 and 7 on the scale).
The Richter scale goes from 1 to 9+, and it is a logarithmic scale, which means that each number is a factor of ten higher than the previous one, compounded by each step.
This means that a magnitude 6 quake will shake with 10 times the amplitude of a magnitude 5, and 100 times more than a 4. As our measuring of earthquakes became finer, inherent limitations in the Richter scale became more apparent (in particular, quantifying quakes stronger than a 7), so the Richter scale was replaced with the moment magnitude scale.
For most quakes, the two scales line up pretty well, but the MMS allows more precise measurement of larger earthquakes. Non-scientific reports tend to still use the Richter designations, but in most cases, the differences are minor.
We tend not to notice quakes below a 3. 4s will rattle interiors, but usually, cause no damage. A 5s can cause damage, but usually no loss of life. Anything higher and you start to see substantial, if not catastrophic, damage and death.
Earthquake preparedness plan before, during and after: Protecting your Home
In the United States, areas that get a lot of quakes have evolved their building standards to help mitigate the potential damage. Even older buildings can be retrofitted with modern safety equipment. It’s not cheap, but it can cut the cost of your insurance, and it’s less expensive than replacing the whole house.
Apart from meeting building codes, homeowners should attach safety straps to the back of large items such as bookcases, hutches, wardrobes, grandfather clocks, etc. These are strong nylon webbing straps that will catch the item before it can pitch all the way over. Cabinet doors can be latched to prevent their swinging open.
Open-faced storage units can have short rails installed at the front of their shelves to help stop items from sliding out. Heavier items should be kept on the lowest shelves. There are films available that can be applied to windows.
They won’t necessarily prevent them from breaking, but they will keep shards of glass from flying into the room. Utility companies can advise you on automatic cutoffs that will engage if your water, gas, or power lines break.
How To Protecting Yourself during An Earthquake
If you are indoors when an earthquake occurs, get under a sturdy desk or table; anything that will give you literal breathing room even if it is buried by debris.
What Not To Do During An Earthquake
DO NOT take shelter in a doorway.
They aren’t any stronger than the rest of the house, and you can be injured by falling debris on both sides.
Similarly, do not hide under a bed, as it can collapse on top of you. If you’re caught in bed, your best bet is to cover your body with blankets and your head with pillows. If no sheltering table is available, the best position inside a building is an interior corner (if the ceiling collapses, the joined walls should angle it away from you).
Crouch in the corner with your arms over your head. When the quake is over, evaluate your home for damage. If there is structural damage, get out immediately until it has been repaired.
If you are outside when a quake strikes, your best option is to get into a sheltered doorway (archways are strongest). Many modern buildings are designed to absorb the sudden movements caused by the earth shifting under them, but the sudden stresses can pop windows out of their frames.
Office windows are solid plates that can easily weigh three hundred pounds or more, and you don’t want to be on the sidewalk when they fall. Other potential hazards include signs, balconies, decorative facades, etc. If you are driving, brake quickly but smoothly and pull over as far as you can.
Stop the car and remain inside until everything stops shaking (beware of aftershocks). Driving after an earthquake is not advised until you have ascertained the safety of your route, as bridges, overpasses, and other infrastructure may be damaged, or blocked by debris.
If you become trapped by falling debris, remain as calm as possible to conserve your energy. Banging things together (particularly metal objects) will attract attention. Wait until you hear people nearby before banging or yelling in order to save your strength. Trying to dig your way out is not recommended, as you can destabilize the pile on top of you.
After an earthquake strikes, you will be in the same situation as with pretty much any other disaster, in that your next steps are to treat injuries, stay fed and hydrated, and begin recovery efforts.
The warnings about being aware of electrical and gas hazards from broken supply lines are especially strident after a quake since most of those runs are underground. Same thing with the water supply: treat all water as contaminated until tested and cleared by the authorities.
If you think you will have to face an earthquake, your emergency disaster survival kit should especially include sturdy clothing, including heavy work boots and gloves, dust masks, and eye protection. This will help prevent injury during the cleanup.
As you have seen, you will have no warning to be able to evacuate before an earthquake occurs, so the best way to be prepared is just that… be prepared.
We hope you’ve enjoyed this post, and have found the information in it to be helpful. Join us tomorrow for a thought experiment about paying for goods and services in a post-modern society. We look forward to seeing you then!