Was that just an earthquake? Here's how to confirm what really shook you up

SAN FRANCISCO – Was that an earthquake you just felt or merely a big truck rumbling by?

You don't have to wonder – the U.S. Geological Survey is on the case and can almost immediately tell you whether there's been an earthquake nearby. You can also be part of the survey's data gathering by reporting what you experienced on its Did You Feel It? page.

It's not just Los Angeles and San Francisco – earthquakes happen all the time, often in places that we don't think of as seismically active. While the West Coast up into Alaska frequently rocks and rolls, quakes aren't uncommon elsewhere. Other quake-prone areas include Charleston, South Carolina, eastern Massachusetts, the St. Lawrence River area and the central Mississippi River Valley, according to Michigan Tech.

Fracking and the disposal of waste fluids that are byproducts of oil production are increasing the risk of smaller temblors, known as induced earthquakes in areas that aren't typically seismically active. Texas has the most induced earthquakes in the United States, but they also occur in Arkansas, Colorado, Kansas and Oklahoma.

About 55 earthquakes a day – 20,000 a year – are analyzed by the National Earthquake Information Center. Most are tiny and barely noticed by people living where they happen. But some are strong enough to shake things off walls, cause cracks in foundations and, in the worst cases, bring entire buildings down.

Here's how to tell if you just went through one.

Was that an earthquake? How to check

The easiest way to see whether there was a magnitude 2.5 or greater earthquake near you in the past 24 hours is to go to the USGS Latest Earthquakes page. It's rare to notice an earthquake of less than magnitude 3, though they happen all the time.

The USGS page opens with a map of the world, centered on the United States. A red dot means an earthquake happened within the past hour, a yellow dot within the past day. The magnitude of the quake is indicated by the size of the circle – the larger the circle, the more powerful the quake.

Click on a dot and a box opens up on the left hand side of the page telling you the earthquake's magnitude, location, when it happened local time as well as Coordinated Universal Time (UTC) and its depth.

Click on the location and you'll get more information about that specific temblor, including a map and recent nearby earthquakes.

Did you feel it?

If you felt an earthquake, USGS runs a citizen science program that collects information from those who were nearby to aid research. The page is called Did You Feel It? and asks a series of questions about where you were when it happened, what it felt like and what happened around you.

These range from "Did you hear creaking or other noises?" to "Did objects rattle, topple over, or fall of shelves?" to " things like Did pictures on walls move or get knocked askew? and "Was a heavy appliance (refrigerator or range) affected?"

These answers help USGS create more accurate earthquake maps that show what people experienced and the extent of possible damage.

Get alerted to earthquakes before they happen

For the more than 50 million residents of California, Oregon and Washington – and anyone visiting – it's also possible to get an early warning for some significant quakes.

MyShake is an app available from the University of California, Berkeley that relies on ShakeAlert data from USGS. It detects some earthquakes early enough that alerts can be delivered to phones and automated systems, sometimes seconds before strong shaking arrives. That can be enough time to get to safety.

If you're near a coming quake, your phone will buzz and emit a warning tone. The alert tells users to Drop! Cover! and Hold On!

An example of a MyShake earthquake alert on a phone. The app, powered by data from the U.S. Geological Survey, can warn residents in California, Oregon and Washington of a possible nearby earthquake.

There are lots of quakes; we don't feel them all

Worldwide, there are on average about 16 major earthquakes in any given year, 15 in the magnitude 7.0 range and one 8.0 or greater, according to records going back to 1900.

The United States typically has about 63 earthquakes magnitude 5.0 to 5.9 each year, according to the U.S. Geological Survey, about five 6.0 to 6.9 and fewer than one from 7.0 to 7.9.

What does magnitude mean in an earthquake?

Magnitude is a measurement of the strength of an earthquake. Officially it's called the moment magnitude scale. It's a logarithmic scale, meaning each number is 10 times as strong as the one before it. So a 5.0 earthquake is 10 times stronger than a 4.0.

• Below 2.5: Generally not felt
• 2.5 to 5.4: Minor or no damage
• 5.5 to 6.0: Slight damage to buildings
• 6.1 to 6.9: Serious damage
• 7.0 to 7.9: Major earthquake. Serious damage.
• 8.0 or greater: Massive damage, can destroy communities

You might also have heard the term "the Richter Scale" used to describe earthquakes, but it is no longer commonly used because it was only valid for certain earthquake frequencies and distance ranges. Magnitude has replaced it, expressed as "a 4.0 magnitude earthquake."

This article originally appeared on USA TODAY: Was that just an earthquake? Here's how to confirm what really shook you up