The Add Feature(s) box lists features that can be overlaid on your base map. You can add more than one feature at a time. To do so, hold down the CTRL key on PCs or the Command key on Macs and click on several features. To deselect a feature, click on it again. If you only have one feature selected, click on No Features to deselect it. Note that the feature(s) will not display until you have clicked on the Make Changes button (or pressed the Enter key on some systems).
Once a feature is 'turned on', it will appear on all subsequent maps until it is deselected. For example, if you turn on Earthquakes, earthquake sites will appear on every map until you deselect Earthquakes.
The features are described below.
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No Features: This turns off all features
Major Rivers: Shows data from the World Data Bank II or CIA Data Bank (WDB), which contain coastlines, lakes, political boundaries, and rivers.
Coast Lines: Shows data from the World Vector Shoreline (WVS), which contains shorelines between saltwater and land (i.e., no lakes), and the World Data Bank II or CIA Data Bank (WDB), which contain coastlines, lakes, political boundaries, and rivers.
Political Lat/Long: Shows major cities, country, and state boundaries along with a latitude and longitude grid. Latitude lines are generally horizontal and go from 0 degrees at the equator to +90 degrees at the North Pole and -90 degrees at the South Pole. Longitude lines are generally vertical with 0 at the prime meridian at Greenwich, England, going to -180 degrees westward and +180 degrees eastward. Why do we generally say horizontal and vertical? Since we use an equal area projection for the zoom maps, the longitude lines will converge as you select a map near the poles. The view is much as if you were looking at a portion of a globe - it's less distorted than the typical Mercator projection seen on the World Map view. City locations, populations, and names, and country centroid positions and names are from ESRI's ArcWorld data set provided in ArcView 3.0 (redistribution permitted). Country boundaries are supplied with GMT.
Tectonic Plates: The light blue lines show a continuous plate tectonic boundary model where each major plate is completely outlined. The plate boundaries, however, are still being studied and techniques, such as precise surveying using GPS and more detailed geologic and topographic / bathymetric maps, allow scientists to define smaller plates and more complex geologic structures. A newer, more detailed tectonic plate boundary model from the PLATES Project is shown in red, yellow, and dark blue lines. These lines are discontinuous and can differ significantly from the continuous model.
The earth's surface is divided into seven large and many small moving plates. The plates, each about 50 miles thick, move relative to one another at an average of a few inches a year. The three types of movement at the plate boundaries are described below.
At convergent boundaries, plates move toward each other and collide. Where an oceanic plate collides with a continental plate, the oceanic plate tips down and slides beneath the continental plate, forming a deep ocean trench. Major mountain systems, such as the Himalayas, are formed where continental plates collide.
At divergent boundaries, such as at the Mid-Atlantic Ridge, plates move away from each other. Where plates diverge, hot, molten rock rises and cools, adding new material to the edges of the oceanic plates. This process is known as sea-floor spreading.
At transform-fault boundaries, plates move horizontally past each other. The San Andreas Fault zone is one such example; the Pacific Plate on which Los Angeles sits is moving slowly northwestward relative to the North American Plate on which San Francisco sits.
For more information, access the USGS Major Tectonic Plates of the World and Information on Plate Tectonics websites, the NASA Digital Tectonic Activity Map of the Earth website, or open the This Dynamic Planet PDF file.
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Focal Mechanisms: The blue and white earthquake focal mechanism "beach balls" mark the location, size, and sense of motion of over 80,000 of the large (moment magnitudes > 5.5) earthquakes from the Harvard Centroid-Moment (CMT) earthquake catalog. Using a global array of seismographs and looking at the directions of the first motions of the recorded seismic wave, scientists can determine the likely orientation and sense of motion of the fault where an earthquake occurred. The orientation of the fault is indicated on the focal mechanism by the lines between blue and white sections. The diameter of the circle indicates the relative magnitude of the earthquake, with larger earthquakes having larger diameters. Because the method is ambiguous, two possible fault surfaces are always shown. You can think of the white section moving in toward the center of the beach ball and the blue away from the center. With a normal fault, for example, the white wedge in the middle drops vertically.
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Earthquakes: Shows over 442,000 earthquake locations from 1961 to 2001, color-coded by depth. Light green dots are shallow events, grading smoothly to red for events around 400 km in depth, and to magenta for events around 670 km in depth. The size of each event's dot is scaled to magnitude on zoomed-in maps. The earthquake hypocenters are from USGS's National Earthquake Information Center (NEIC), catalog for 1961-2001.
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Stress Axes: Shows the contemporary tectonic stress directions from the International Lithosphere Program (ILP) World Stress Map project. Colored lines show the orientations of the maximum horizontal tectonic stress. They are derived from earthquake focal mechanisms (63%), well bore breakouts and drilling-induced fractures (23%), in-situ stress measurements (9%), and young geologic data (5%). For stresses determined from earthquake focal mechanisms, the relative magnitude of the stresses can be resolved in three dimensions and the sense of faulting can be determined. For these measurements, the tectonic regimes are indicated by the color coding (dark blue, pink, and red). For measurements where only the horizontal stress directions can be determined, the lines are light blue.
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Volcanoes: Shows the locations of active volcanoes (active in the last 10,000 years), from the Smithsonian Global Volcanism Program.
To close this window, click on the X at the end of the menu bar or in the upper right corner of the window.