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Logo Recent Earthquakes in the Intermountain West

Recent Earthquakes FAQ (Frequently Asked Questions)

The Recent Earthquake information system was developed by the USGS through a long process that included input from seismologists, graphic artists, and users. The goal is to provide users with as much information as possible in a timely fashion. Because the number of users continues to grow, some design choices have been made which have not pleased all users, but which will maximize the number of users getting information over the web, especially after felt earthquakes. This system a major step forward for the following reasons:
  • It currently presents data from the University of Utah seismograph network and will expand to include other networks.
  • It offers complete network coverage with no gaps because of an overlapping system of maps.
  • It provides text information on each earthquake and auxiliary information on some of them.
To meet our goal, we had to make many decisions and compromises. We realize that not everyone will agree with our decisions but we do hope that you will read this file and consider why we made them. If you have comments or suggestions please send them to webmaster@seis.utah.edu. We look forward to hearing from you and hope you will find the Recent Earthquake system useful.

How do I find what I want?

NOTE: Our information changes with time. Sometimes when you look at a page your browser will show you an old copy that it has cached. Check the time on the page and in the map. If it was produced over an hour ago, or if you think something has happened since it was produced, then use the reload feature of your browser to get a new version of the file.

To navigate through these maps you should start at the index map or see our list of other sites in the region.

Once you have looked at the index map, click on an area to zoom in. Or, you can select one of the lists of earthquakes below the map.

If you click on the index map and zoom in, you can get more information on any earthquake by either clicking on its map symbol or by clicking on its summary information presented in a list below the map. Or, to move to an adjacent map, you can click on one of the blue arrows near the edges of the map.

If you click on an earthquake (either on a map or in a list) and get a page of detailed information, you should look at the bottom of the page for auxiliary information such as fault plane solutions.

At any time you can use your back button to return to a previous page, but always remember the note above about reloading if a page seems old.

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How can I zoom in further?

There are a variety of special maps listed on each page. These special maps cover selected areas in greater detail. We can't allow arbitrary zooming in because this would mean creating maps for each individual user and our servers could not handle that load.

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What pages should I bookmark?

You may want to bookmark the index page, as well as the more detailed maps for the area where you live and work and others that you find interesting. This may help you get fast access after significant earthquakes when many people are trying to use the Recent Earthquakes system.

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Why are squares used for the earthquakes?

Some users prefer to see earthquakes drawn as circles. We have chosen to use squares, because computer screens are based on a square grid of dots or rasters. This makes it easier to draw a clear square than a circle. To draw a good looking circle requires a technique called anti-aliasing, however this introduces shades of grey into the image which makes the map files larger. That makes them transfer more slowly.

We agree that circles are prettier than squares, and we anticipate that as software and hardware get better and faster, it will be more feasible to use circles. Right now, we have opted for the simplicity and visual clarity of squares.

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How were the symbol sizes chosen?

Some users have noted that the magnitude 1, 2, and 3 earthquakes are drawn with fairly small symbols. This was done because after a large earthquake there will be many small aftershocks. If the aftershocks have large symbols, they may obscure the mainshock on the map. To help prevent this, we have made the small earthquakes have small symbols.

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How were the colors chosen?

Our goal was to highlight the earthquakes while also showing background information such as faults, roads, towns, and bodies of water. We limited our color choices by selecting from the approximately 200 "browser safe" colors that are consistently displayed without dithering by a variety of web browsers. We also attempted to select colors that could be easily distinguished by users with red-green color blindness.

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Why don't the maps show topography?

Some of our older earthquake maps showed topography in the background as either a range of colors or shades of gray. Unfortunately, this popular feature makes the map files about three times larger. These larger files take longer to transfer and, at times of heavy usage, can prevent us from serving many of those who want the earthquake information. While we would like to show the topography, we have concluded that it is more important to provide fast access to the earthquake data to as many people as possible.

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What does "last hour", "last day" and "last week" mean?

Each map shows the time it was created. The phrases "last hour", "last day", and "last week" are with respect to that time. Any earthquakes that occurred within one hour of the creation time are in the "last hour" and are colored red. Those that occurred between 1 and 24 hours before the map was created are in the "last day" and are colored blue. Those that occurred between 24 hours and 7 days (168 hours) before the map was drawn are in the "last week" and are colored yellow.

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How do the earthquakes get here?

Another page describes how the earthquake information gets onto the web server.

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Why do some earthquakes disappear?

The earthquake data shown here is automatically generated and, despite our best efforts, some glitches will create bogus earthquakes. When we find a bogus event, usually by studying the seismograms, we delete it and careful observers may notice that an earthquake has disappeared. This often happens after a large earthquake when our systems don't realize that all of the seismograms were created by a single event. In this case, one earthquake will turn into multiple "events" on the maps. In other cases, problems in our telemetry systems that bring the data from our seismometers to our computers create glitches that also can create bogus events. For these reasons, it is very important to remember that this data is preliminary and when events disappear they weren't real to begin with.

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What are the future plans for this system?

  • Greater plotting precision so we can provide more detailed maps.
  • Plots showing selected seismograms for each event.
  • Expanding the area and number of seismic networks covered.

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Recent Earthquakes home page.





University of Utah Seismograph Stations  «»   135 South 1460 East, Room 705 WBB
Salt Lake City, Utah 84112-0111  «»   Phone 801-581-6274  «»  Fax 801-585-5585
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