The magnitude of an earthquake depends on the size of the fault and how far the plates move. So how do they measure an earthquake?
They use recordings known as seismograms made on the surface of the earth to measure motion and determine how large the earthquake was. The recordings look like a series of wiggly lines that appear during ground vibration see image below.
A series of short wiggly lines means a small earthquake, and a series with long wiggly lines means a large earthquake. The length of the wiggle depends on the size of the fault, and the size of the wiggle depends on the amount of slip. The magnitude of an earthquake describes how much energy was released based on the maximum motion recorded.
There are different scales used to convey this information, but the moment magnitude scale, abbreviated MW, is preferred because it works over a wider range of earthquake sizes and is applicable globally. Magnitudes are based on a logarithmic scale base What this means is that for each whole number you go up on the magnitude scale, the amplitude of the ground motion recorded by a seismograph goes up ten times.
Using this scale, a magnitude 5 earthquake would result in ten times the level of ground shaking as a magnitude 4 earthquake and 32 times as much energy would be released. Intensity measures the strength of shaking produced by the earthquake at a certain location. Intensity is determined from effects on people, human structures, and the natural environment. This means, how strong an earthquake FEELS to people in a certain location or was there damage to buildings or other structures.
Intensity is measured using a descriptive scale called the Modified Mercalli Intensity Scale. One earthquake will have numerous values for intensity, as it will feel stronger and cause more damage in areas near the epicenter and lessen for areas further away.
Information gathered from people near the earthquake, combined with damage reports, is gathered by zip code and assigned an intensity value see chart below. This information is then mapped to get an overall picture of the earthquake's strength. As soon as an earthquake shakes, an enormous amount of information is gathered from people, equipment and first response organizations.
This information is interpreted by scientists and computers, and then a number of products are available from warnings to maps of the impacted area. Alerts may even be produced before your location is impacted see earthquake early warning.
In most cases, you can sign up to receive real time information through your cell phone, social media, email, etc. Check with your local county emergency management office see Tools and Resources below for websites to see how to sign up.
Other information is accessible virtually immediately online, on television or on the radio. Latest Earthquakes - Worldwide. Induced seismicity is not included in this report because it can increase or decrease over a short period of time and is subject to commercial and policy decisions that could change rapidly. This report looks at the long term while USGS induced seismicity maps are one-year forecasts.
Therefore earthquake hazards and losses are currently higher than what is reflected in this report for Oklahoma, Kansas, Colorado, New Mexico, Texas, and Arkansas where there have been recent occurrences of induced seismicity. Earthquakes in the last decade alone have claimed tens of thousands of lives and caused hundreds of billion dollars of economic impact throughout the globe. In the United States, earthquake risk continues to grow with increased exposure of population and development.
While there is constantly improved understanding of high hazard and risk areas such as Los Angeles, San Francisco and Seattle, there is also high risk of significant damage and loss in regions such as Salt Lake City, St. This high level of risk reflects dense concentrations of buildings and infrastructure. Understanding earthquake hazards is critical for informed policies, priorities, strategies, and funding decisions to protect the most at-risk communities.
Figure This map depicts the difference in USGS estimates of earthquake hazards across the nation in and The new FEMA earthquake loss report includes the data, while the previous report includes the data.
The negative values represent a decrease in estimated hazard since and the positive values represent an increase. Skip to main content. The program highlights the differences between disaster sites and construction sites, and emphasizes the need for workers and employers to have pre-incident training. Businesses and other organizations can register and participate for free. ShakeOut provides an earthquake Drill Manual for Businesses with lessons for workers and employers. A disorganized evacuation can result in confusion, injury and property damage.
An emergency action plan is critical. An emergency action plan checklist can assist this process. USGS updated their U. National Seismic Hazard Maps, which reflect the best and most current understanding of where future earthquakes will occur, how often they will occur, and how hard the ground will likely shake as a result. All states have some potential for earthquakes, 42 of the 50 states have a reasonable chance of experiencing damaging ground shaking from an earthquake in 50 years.
The hazard is especially high along the west coast, intermountain west, and in several active regions of the central and eastern U. The PSA amplifies earthquake safety awareness and the protective actions that people can take to protect themselves in the event of an earthquake. Earthquakes can occur anywhere in California, which means all Californians live with an earthquake risk. In addition to the shaking caused by earthquakes, other things can occur such as landslides, surface fault ruptures and liquefaction--all of which may cause injury or property damage.
Some areas within California are also vulnerable to tsunamis should an earthquake occur. The California Governor's Office of Emergency Services has emergency preparedness and response resources. The state of California also has a Department of Conservation that provides services and information that promote environmental health, economic vitality, informed land-use decisions, and sound management of the state's natural resources.
Specifically, the California Geological Survey CSG has an earthquake website which includes various tools such as ShakeMaps which are a representation of ground shaking produced by an earthquake , probability calculators, shaking hazards, and hazard zones. Oregon is considered a high-risk state for earthquakes. In the last years, the state has experienced several earthquakes over magnitude 5.
0コメント