Earthquake Hazards

FAQ

How can I make my own seismometer?

It is relatively easy to acquire the necessary materials and build your own seismometer. The links here are to various sources with information on how to build a seismometer. They range from very simple and inexpensive to sophisticated and pricey. Model Seismograph - Classroom Demonstration Build your own Seismograph Station Build Your Own...

What was the first instrument that actually recorded an earthquake?

The earliest seismoscope was invented by the Chinese philosopher Chang Heng in A.D. 132. This was a large urn on the outside of which were eight dragon heads facing the eight principal directions of the compass. Below each dragon head was a toad with its mouth opened toward the dragon. When an earthquake occurred, one or more of the eight dragon-...

What is a Geoid? Why do we use it and where does its shape come from?

Geoid illustration Contrast of the Geoid model with an Ellipsoid and cross-section of the Earth's surface. (Public domain.) A geoid is the irregular-shaped “ball” that scientists use to more accurately calculate depths of earthquakes, or any other deep object beneath the earth’s surface...

What is a seismic zone, or seismic hazard zone?

Although you may hear the terms “seismic zone” and “seismic hazard zone” used interchangeably, they really describe two slightly different things. A seismic zone is used to describe an area where earthquakes tend to focus; for example, the New Madrid Seismic Zone in the Central United States. A seismic hazard zone describes an area with a...

What is seismic hazard? What is a seismic hazard map? How are they made? How are they used? Why are there different maps, and which one should I use?

Seismic hazard is the hazard associated with potential earthquakes in a particular area, and a seismic hazard map shows the relative hazards in different areas. The maps are made by considering what we currently know about: Past faults and earthquakes The behavior of seismic waves as they travel through different parts of the U.S. crust The near-...

What are the earthquake hazards/risks where I live?

Determining your risk with regard to earthquakes, or more precisely shaking from earthquakes, isn't as simple as finding the nearest fault. The chances of experiencing shaking from an earthquake and/or having property damage is dependent on many different factors. The National Hazard Maps use all available data to estimate the chances of shaking (...

How will my house hold up in an earthquake? Can the USGS send someone out to evaluate my property?

Published maps will only provide generalized, uninterpreted information about specific areas. Every property consists of a unique combination of geologic and structural factors that must be considered to determine what might happen to a house during an earthquake. Therefore, an individual site study is necessary. Geologic factors include: type of...

How do I decide whether or not to get earthquake insurance?

You should consider the following factors when deciding whether or not to get earthquake insurance: proximity to active earthquake faults seismic history of the region (frequency of earthquakes) time since last earthquake building construction (type of building and foundation) architectural layout materials used quality of workmanship extent to...

How do earthquakes affect buildings?

Ground shaking is the primary cause of earthquake damage to man-made structures. Many factors influence the strength of earthquake shaking at a site including the earthquake's magnitude, the site's proximity to the fault, the local geology, and the soil type . More than 250 structures throughout the United States have been outfitted with seismic...

What is the likelihood of a large earthquake at location X?  Is it safe to go to X since they've been having a lot of earthquakes lately?

The National Seismic Hazards Mapping project provides an online web tool for determining the probability of a large earthquake within 50 kilometers (~31 miles) of a specific location over a certain time period. The calculation is based on the latest available information from seismic hazard data. Unified Hazard Tool - Earthquake Hazard and...

What is the probability that an earthquake will occur in the Los Angeles Area? In the San Francisco Bay area?  

Los Angeles area: Within the next 30 years the probability is: 60% that an earthquake measuring magnitude 6.7 46% that an earthquake measuring magnitude 7 31% that an earthquake measuring magnitude 7.5 will occur in the Los Angeles region. San Francisco Bay area: Within the next 30 years the probability is: 72% that an earthquake measuring...

What is the probability that an earthquake is a foreshock to a larger earthquake?

Worldwide the probability that an earthquake will be followed within 3 days by a large earthquake nearby is somewhere just over 6%. In California, that probability is about 6%. This means that there is about a 94% chance that any earthquake will NOT be a foreshock. In California, about half of the biggest earthquakes were preceded by foreshocks;...

Are earthquake probabilities or forecasts the same as prediction?

No. Probabilities and forecasts are rather like climate probabilities and weather forecasts, while predictions are more like statements of when, where, and how large, which is not yet possible for earthquakes. Probabilities describe the long-term chances that an earthquake of a certain magnitude will happen during a time window. Most earthquake...

Can the National Seismic Hazard Maps be used as an earthquake forecast tool for the near future?

Not really. This web site is designed to display the probability of different sources that might occur in a several-year to several-decade period. The model bases all probability estimates on mean rate of earthquakes over long periods. As you shorten the time window, you should expect greater and greater fluctuations in what may be observed from...

How do I get earthquake hazard maps for locations outside of the U.S.?

We know of no current "zone" designations for sites outside of the United States. For locations outside the United States for which seismic design is required for military facilities, there exists a standard based on probabilistic spectral ordinates in the manner of the International Building Code and are declared to reflect the 2015 version of...

How are engineers working to make roads and buildings safer?

Earthquake engineers are working to make roads and buildings safer in the event of a major earthquakes. This includes both improving the design of new buildings and bridges as well as strengthening older units to incorporate the latest advances in seismic and structural engineering. The Federal Emergency Management Agency plays a central role in...

What is the USGS doing to mitigate and respond to earthquake hazards?

The U.S. Geological Survey performs the following functions related to earthquake hazard mitigation: Receives, analyzes, maintains, and distributes data on earthquake activity worldwide. Satellites link our National Earthquake Information Center in Golden, Colorado to a network of seismograph stations. These stations, located throughout the world...

At what magnitude does damage begin to occur in an earthquake?

It isn't that simple. There is not one magnitude above which damage will occur. It depends on other variables, such as the distance from the earthquake, what type of soil you are on, etc. That being said, damage does not usually occur until the earthquake magnitude reaches somewhere above 4 or 5.

What does an earthquake feel like?

The way an earthquake feels depends on where you are, where the earthquake is, and how big the earthquake is: A large earthquake nearby will feel like a sudden large jolt followed quickly by more strong shaking that may last a few seconds or up to a couple of minutes if it's a rare great event. The shaking will feel violent and it will be...

What are those booms I sometimes hear before or during an earthquake?

"Booms" have been reported for a long time, and they tend to occur more in the Northeastern US and along the East Coast. Of course, most "booms" that people hear or experience are actually some type of cultural noise, such as some type of explosion, a large vehicle going by, or sometimes a sonic boom, but there have been many reports of "booms"...