ShakeMap in Nevada
Frequently Asked Questions
How are ShakeMaps used?
Emergency Response: Within minutes after strong ground shaking, ShakeMaps provide emergency responders a map showing where and how large the region of damage may be. With some knowledge of where vulnerable structures are in the affected area, emergency responders can immediately assess the extent of likely problems, focus available resources on greatest needs, and assess whether additional resources will be needed.
Major Public Service Providers: Utilities, transportation agencies, and communications providers can receive the shaking intensity data in ShakeMaps and use it to learn how strong the shaking was at individual facilities. ShakeMaps imported into Geographic Information System software can advise service providers which facilities may need inspection and which others are likely to be okay. Inspection and repair crews can be focused on highest priorities, and minimizing the time that key services are unavailable.
Public Information: When there is news of a large earthquake, people far and wide want more information. People in the region want to know what happened and who may need help; people outside the affected area want to know if the earthquake could have affected family or friends living nearby; and people worldwide want to know what happened. ShakeMaps show immediately the affected area and likely intensity of ground shaking effects.
What do the colors mean on the Rapid Intensity Map?
Inside the dark blue area: A few sensitive individuals (and pets!) may feel the shaking.
Inside the turquoise area: Many are likely to feed the earthquake but few would be frightened.
Inside a yellow area: Shaking could be strong enough to swing hanging lamps and knock over delicate objects.
Inside an orange area: Some damage is expected, such as from larger objects falling over, pictures falling, and possible cracking of plaster.
Inside a red area: Significant damage can occur, including damage or collapse of poor-quality multi-story buildings, damage to bridges, pipelines, and roads. Modern residential structures are likely to be damaged, but are not likely to collapse.
How do we know what the shaking was like? Is it measured everywhere?
Seismologists use the magnitude and location of the earthquake, along with decades of measurements and experience, to predict where and how strongly the ground shook during the earthquake. Maps of the geology of the region are used to improve shaking predictions, lowering or raising estimates locally depending on whether the surface materials are stiff and rock-like or are weak and actually amplify shaking.
In the urban areas of Las Vegas and the Reno-Carson City corridor, real-time recordings of ground shaking will be available to improve on the ShakeMap estimate. For example, the recordings may show that most of the earthquake energy was focused away from the city, and that there was less ground shaking at the surface than expected. In mountain and rural areas where there are few seismic stations, ShakeMaps will show only the predicted levels of shaking. Strong motion recorders are expensive to buy, install, and maintain, so coverage is presently limited in extent and focused on the Las Vegas and the Reno-Carson City areas. Coverage in Nevada has greatly improved as a result of the Advanced National Seismic System (www.anss.org), a U.S. Geological Survey initiative to improve seismic systems nationwide.
Where Can I See Nevada's ShakeMaps?
Visit http://www.seismo.unr.edu/shakemap/shake/index.html.Where Can I See ShakeMaps for California and Other Places?
Visit http://earthquake.usgs.gov/eqcenter/shakemap and then navigate to the location of interest.
Are ShakeMaps Made for International Earthquakes?
The USGS PAGER (Prompt Assessment of Global Earthquakes for Response) program is being developed for this purpose. PAGER is designed to help Federal and International agencies decide which earthquakes among the over 30,000 located by the National Earthquake Information Center could have substantial social impact.
Visit http://earthquake.usgs.gov/eqcenter and go to PAGER to know more about PAGER.
When Are ShakeMaps made?
ShakeMaps are automatically made for earthquakes with Magnitudes > 3.0 in western Nevada and parts of eastern California. The maps are usually available within 6-10 minutes after the earthquake itself. ShakeMaps are normally reviewed minutes to hours later (depending on importance), and a revised map will usually be issued. We revise maps because adjustments are often made to the earthquake location and magnitude compared to the computer-generated automatic solution. ShakeMaps may also be revised if new data relevant to the ground shaking plots becomes available.
Why are many maps made for every event?
Ground motions can be measured in many different ways. Each type of measurement has a different use. The four ShakeMap map types are described below.
[To see a bigger map, please click on each map]
The Instrumental Intensity map gives a quick snapshot of how important an earthquake may be. "Intensity" refers to how strong seismic effects are at the place considered. Near a large earthquake the intensity may be great enough to damage structures; farther away the same earthquake may just rattle the windows. The earthquake "magnitude" is proportional to the energy release at the source, and it does not depend on how strongly or weakly it is felt. "Instrumental Intensity" refers to the intensity we predict based on the earthquake location and magnitude, assisted by any actual ground motion measurements we record. Intensity is often estimated on the "Mercalli Intensity Scale." This scale runs from intensity I, meaning not felt, to intensity X, meaning shaking capable of general devastation of even strong structures. The color scale for intensities and their approximate ground motions are shown at the bottom of each Instrumental Intensity map.
The Peak Acceleration map shows ground accelerations as percentages of the force of gravity. For low-rise buildings the peak acceleration is often the best indicator of the earthquake's potential for causing damage. The acceleration due to gravity is about 980 cm/sec². At the level of about 1 cm/sec² or greater it is common for an earthquake to be felt. On the Peak Acceleration maps the white lines are lines of equal predicted acceleration, much the same as lines of equal elevation on a topographic map. The small triangles, if any are shown, are seismic stations where the acceleration may have been measured. The small open circles are places where the ground acceleration was predicted based on the earthquake location and magnitude. The map itself is formed by using measured ground motions, if available, to modify the predictions, then contouring the acceleration levels.
The Peak Velocity map shows predicted ground velocity in cm/sec. Peak ground velocity is sometimes the best indicator of damage potential for tall structures.
Spectral Response maps are mostly of interest to engineers. They are made only for larger earthquakes. Briefly, they show the acceleration predicted for simple spring-and-mass oscillators of three different periods: 0.3, 1.0, and 3.0 seconds. A ten-story building commonly acts something like a one-second (inverted) pendulum, so the 1-second pseudo-acceleration map would be most relevant for predicting how the earthquake could have affected that building.
What is a Scenario ShakeMap?
In the same way that ground motions can be predicted for a real earthquake, ShakeMap Scenarios are constructed to show predicted results for a hypothetical earthquake. Scenario earthquakes are constructed as "what-if" exercises for emergency planners, public policymakers, and earthquake engineers. Scenario earthquakes made for some Reno area faults can be viewed at http://www.seismo.unr.edu/shakemap/shake/archive/scenario.html , or you can navigate by way of the "Map Archive" and "Earthquake Scenarios" links from our ShakeMap home page.
How is the USGS involved?
The U.S. Geological Survey (USGS) and Caltech scientists developed ShakeMap initially to display ground motions in southern California. The USGS also funded ShakeMap installation and maintenance at UNR through the Advanced National Seismic System (ANSS, www.anss.org). ANSS also funded strong-motion instrumentation that we use to measure strong motions in urban Nevada. The USGS also hosts the national ShakeMap web site which displays ShakeMaps from across the country. Nevada's ShakeMaps joined the national pages in January 2006. They can be viewed at http://earthquake.usgs.gov/eqcenter/shakemap/.
A paper by Glenn Biasi and Kent Lindquist describing Nevada's ShakeMap implementation and its usefulness in seismic hazard planning was prepared for the Basin and Range Province Earthquake Hazard Summit II in May 2004. It explains how the USGS National Mapping Project pages can be used as an input for ShakeMap Scenarios. Download here.
The complete proceedings volume, edited by William R. Lund (20 papers, 64 abstracts, 10 posters) is available on CD from the Utah Geological Survey (http://geology.utah.gov/bookstore/ugs/earthqli.htm). For general information about seismic hazards in the western U.S. see the Western States Seismic Policy Council, www.wsspc.org or the USGS Earthquake Hazard Program Intermountain-West home page at http://earthquake.usgs.gov/regional/imw/.
