USGS Frequently Asked Questions - Frequently Asked Questions

Why are we having so many earthquakes? Has earthquake activity been increasing? Does this mean a big one is going to hit? OR We haven't had any earthquakes in a long time; does this mean that the pressure is building up and a big one is coming?

Tue, 22 May 2012 08:41:00 -0600

A temporary increase or decrease in seismicity is part of the normal fluctuation of earthquake rates. Niether an increase or decrease worldwide is a positive indication that a large earthquake is imminent.

The NEIC now locates about 20,000 earthquakes each year, or approximately 55 per day. Because of the improvements in communications and the increased interest in natural disasters, the public now learns about earthquakes more quickly than ever before.

According to long-term records (since about 1900), we expect about 16 major earthquakes in any given year, which includes 15 earthquakes in the magnitude 7 range and one earthquake magnitude 8.0 or greater. In the past 38 years, from 1973 through 2011, our records show that we have exceeded the long-term average number of major earthquakes only 8 times, in 1976, 1990, 1995, 1999, 2007, 2009, 2010, and 2011.

The year with the largest total was 2010, with 24 earthquakes greater than or equal to magnitude 7.0. In other years the total was well below the 16 per year expected based on the long-term average: 1989 only saw 6, while 1988 saw only 7 major earthquakes.

See the NEIC Earthquake Facts and Statistics Web page for the tables of earthquake counts by magnitude and year.

What does an earthquake feel like?

Tue, 22 May 2012 14:39:00 -0600

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 difficult to stand up. The contents of your house will be a mess.

A large earthquake far away will feel like a gentle bump followed several seconds later by stronger rolling shaking that may feel like sharp shaking for a little while.

A small earthquake nearby will feel like a small sharp jolt followed by a few stronger sharp shakes that pass quickly.

A small earthquake far away will probably not be felt at all, but if you do feel it, it will be a subtle gentle shake or two that is easier to feel if you're still and sitting down.

The type of crustal material the seismic waves travel through on their way to you, and the type of shallow crustal structure that is directly below you will also influence the shaking you feel. Soft thick sediments will amplify the shaking and hard rock will not. If the energy happens to bounce around and get focused on where you are, that will also amplify the shaking. Low-level vibrations that last for more than a few seconds is not indicative of an earthquake, but is more likely a man-made environmental source.

I want to buy a topographic map. How do I get it?

Fri, 05 Aug 2011 13:19:00 -0600

You can purchase topographic maps several ways:

Download or online from the USGS Store at http://store.usgs.gov

Click on Maps in the left margin or click on the Map Locator near the center of the screen. Topographic maps in GeoPDF format are available for free download by using the Map Locator. Be sure to see our next generation of topographic maps by clicking on US TOPO.

You can order by mail or fax:

Instructions are available at http://ask.usgs.gov/prices/faqs_prices_usgs_products.html#11.

Contact a map dealer (a list is available in the left margin of the USGS Store).

Information on acquiring historical USGS topographic maps may be found at http://nationalmap.gov/historical/.

Information about additional USGS maps and publications can be found at http://www.usgs.gov/pubprod.

For more assistance on ordering please visit http://ask.usgs.gov/prices/faqs_prices_usgs_products.html or call 1-888-ASK-USGS (1-888-275-8747).

How are floods predicted?

Fri, 09 Sep 2011 08:26:00 -0600

Floods are a dangerous hazard throughout the world, and most people underestimate the power of flood waters. On average, in the United States, about 165 people are killed and about $2 billion of damage occurs each year.

Several types of data can be collected to assist hydrologists predict when and where floods might occur. The first is monitoring the amount of rainfall occurring on a realtime basis. Second, monitoring the rate of change in river stage on a realtime basis can help indicate the severity and immediacy of the threat. Third, knowledge about the type of storm producing the moisture, such as duration, intensity and areal extent, is valuable for determining possible severity of the flooding. And fourth, knowledge about the characteristics of a river's drainage basin, such as soil-moisture conditions, ground temperature, snowpack, topography, vegetation cover and impermeable land area, can help to predict how extensive and damaging a flood might become.

The National Weather Service collects and interprets rainfall data throughout the United States and issues flood watches and warnings as appropriate. The National Weather Service uses statistical models and flood histories to try to predict the results of expected storms. The USGS maintains a network of streamflow-gaging stations throughout the country for which the discharge and stage are monitored. Flood estimation maps are generally produced by estimating a flood with a certain recurrence interval or probability and simulating the inundation levels based on flood plain and channel characteristics. More information on floods is available from the USGS Hydrologic Information Center at http://www.nws.noaa.gov/oh/hic and from the USGS national home page at http://water.usgs.gov. For more information on real-time flood monitoring, please see

Where does the USGS monitor stream water quality in real time? How can I see these sites on a map and get to the data?

Fri, 09 Sep 2011 15:06:00 -0600

Continuous real-time water quality information is at http://water.usgs.gov/waterwatch/wqwatch/. These data are limited to measurable characteristics such as temperature, turbidity, specific conductance (salinity), dissolved oxygen, and pH (acidity).

WaterQualityWatch is a USGS web site that provides access to real time water-quality monitor data collected in surface waters throughout the United States as part of the USGS mission to describe water resources.

Measurements include streamflow (through WaterWatch) water temperature, specific conductance, pH, dissolved oxygen, and turbidity. These measurements are available at more than 1,300 sites in streams with watersheds as small as a few square miles to more than 1,000,000 square miles in the Mississippi River as it enters the Gulf of Mexico.

Continuous real-time water-quality data are used for decisions regarding drinking water, water treatment, regulatory programs, recreation, and public safety. Additionally, links to other USGS technical resources and how these measurements are used as surrogates to obtain real-time computations or estimates of other water quality constituents are provided.

What was the extent of ash deposition from the largest Yellowstone eruptions?

Fri, 21 Oct 2011 10:01:00 -0600

During the three giant caldera-forming eruptions that occurred between 2.1 million and 640,000 years ago, tiny particles of volcanic debris (volcanic ash) covered much of the western half of North America, likely a third of a meter deep several hundred kilometers from Yellowstone and several centimeters thick farther away (Figure 3). Wind carried sulfur aerosol and the lightest ash particles around the planet and likely caused a notable decrease in temperatures around the globe.

How Hot Is A Volcano?

Fri, 23 Sep 2011 10:37:00 -0600

Lava and Lava Flows

The temperature of basalt lava at Kilauea reaches 1,160 degrees Celsius (2,120 degrees Fahrenheit). -- USGS/VHP Website, 1998
The tube system (lava tubes) of episode 53 (Pu'u O'o eruption, Hawaii) carried lava for 10 kilometers (6 miles) from the vent to the sea. So efficient were the tubes in containing heat that lava cooled only 10 degrees Celsius across that distance. When it reached the ocean, the lava was still a sizzling 1,140 degrees Celsius (2,085 degrees Fahrenheit). -- USGS/HVO Volcano Watch, November 14, 1987
The temperature of the lava in the tubes is about 1,250 degrees Celsius (2,200 degrees Fahrenheit). -- USGS/HVO Volcano Watch, June 4, 1998
By way of its color, incandescent rock gives a crude estimate of temperature. For example, orange-to-yellow colors are emitted when rocks (or melt) are hotter than about 900 degrees Celsius (1,650 degrees Fahrenheit). Dark-to-bright cherry red is characteristic as material cools to 630 degrees Celsius (1,165 degrees Fahrenheit). Faint red glow persists down to about 480 degrees Celsius (895 degrees Fahrenheit). For comparison, a pizza oven is operated at temperatures ranging from 260 to 315 degrees Celsius (500 to 600 degrees Fahrenheit). -- USGS/HVO Volcano Watch, November 14, 1997
Lava sampling can be risky, so why do we bother to do it? Hot lava samples provide important information about what's going on in Kilauea's magma chambers. ... We know from laboratory experiments that the more magnesium there is in magma, the hotter it is. Chemical analysis therefore provides the means, not only to determine the crystallization history of lava, but also to establish the temperature at which it was erupted. ... Episode 54 lavas are chemically different from lavas erupted over the last 12 years. Chemical analyses show that magma was supplied by two distinct magma bodies that have resided for years beneath Napau Crater, where eruptions last occurred in 1983 and in 1968. Lava nearest Pu'u O'o erupted at 1,125 degrees Celsius to 1,130 degrees Celsius (2,057 to 2,066 degrees Fahrenheit) and contains crystals of olivine, feldspar and pyroxene. Calculations show the source of this lava was intruded at the beginning of the Pu'u O'o eruption in January 1983. The lava erupted from the west wall of Napau tapped a second magma body that was possibly emplaced in August 1968. This magma, which had been cooling and crystallizing for a longer time, erupted with more abundant feldspar and pyroxene crystals and at lower temperatures of 1,110 to 1,120 degrees Celsius (2,030 to 2,048 degrees Fahrenheit). -- USGS/HVO Volcano Watch, March 14, 1997

What are the likely effects of the dead and dying marshes if one or more hurricanes make landfall on the Louisiana coast or during normal winter storm fronts in the coming year?

Tue, 30 Aug 2011 09:10:00 -0600

There is great concern that the dead marsh areas could be seriously affected by major storm events. Local, state, and federal agencies are working together to determine what, if any, short-term measures can be implemented, and to put in place long-term remediation strategies. The Governor's Office has requested consideration of an emergency funding allocation through federal sources to provide for immediate assistance.

What should I know about wildfires and debris flows?

Fri, 18 May 2012 09:16:00 -0600

Wild land fires are inevitable in the western United States. Expansion of human development into forested areas has created a situation where wildfires can adversely affect lives and property, as can the flooding and landslides that occur in the aftermath of the fires. There is a need to develop tools and methods to identify and quantify the potential hazards posed by landslides produced from burned watersheds. Post-fire landslide hazards include fast-moving, highly destructive debris flows that can occur in the years immediately after wildfires in response to high intensity rainfall events, and those flows that are generated over longer time periods accompanied by root decay and loss of soil strength. Post-fire debris flows are particularly hazardous because they can occur with little warning, can exert great impulsive loads on objects in their paths, and can strip vegetation, block drainage ways, damage structures, and endanger human life. Wildfires could potentially result in the destabilization of pre-existing deep-seated landslides over long time periods.

Learn more at the following USGS Web sites:

Post-Wildfire Landslide Hazards: http://landslides.usgs.gov/research/wildfire/

Methods for the Emergency Assessment of Debris-Flow Hazards from Basins Burned by the Fires of 2007, Southern California. http://pubs.usgs.gov/of/2007/1384/

Landslide Hazards Overview (in Spanish and English)

“Landslide Hazards” (English): http://pubs.usgs.gov/fs/fs-0071-00/fs-0071-00.pdf

“Peligros de Deslizamientos” (Spanish): http://pubs.usgs.gov/fs/2000/0072/report.pdf

How does the use of pesticides affect our Nation's water quality?

Thu, 12 Jan 2012 12:52:00 -0600

Information on pesticides and herbicides and on nutrients is available from the USGS National Water-Quality Assessment Program

Why are there no entries for caves or military installations in the Geographic Names Information System Database?

Fri, 13 Jan 2012 08:30:00 -0600

Entries for these categories are in the database, but are not available at the public Web site. In response to the 1988 National Cave Management Resources Act, an Interior Department Regulation (43 CFR Subtitle A, Part 37) forbids employees from releasing information regarding the location of a cave classified as significant on Federal lands. The regulation has been extended to all caves on Federal lands that have not been so classified as, "being under consideration for such classification."

The GNIS database does not have presently the capability or the resources to determine which caves exist on Federal lands and are administered by Federal agencies as contrasted with those on other lands. Therefore, until further notice, features classified as "cave" are not retrievable at the Web site.

Information regarding the location of caves in the GNIS must be requested in writing from the office of the Secretary of the Interior. Each request will be analyzed on a case-by-case basis. The address is U.S. Department of the Interior, Secretary of the Interior, 1849 C Street NW, Washington, D.C. 20240.

Information from this database regarding military installations must be requested in writing from the Associate Director for Geospatial Data at the U.S. Geological Survey, 12201 Sunrise Valley Drive, Reston, VA 20192. Each request will be evaluated on a case-by-case basis. This does not apply to military installations classified as historic, for which information is available from the GNIS database.