The ESV, Jr. opens with a map of the North American continent displayed. You can choose from a variety of base maps by making selections in the Select a Base Map list box. Examples include "Face of the Earth" and "Earth at Night" satellite imagery, global topography, geoid, sea-floor age, strain rate, and seismic hazard maps. Once you make a selection, a thumbnail view will display to the right. If you preview a number of maps, be sure that the one you want to view is highlighted at the end. To deselect a base map, click on the name again. To see your new map, you must click on the Make Changes button.
Note that any features or velocities selected previously will display on the new base map. To turn them off, deselect them in the Feature(s) or Velocities list box or click on No Features or No Plate Velocities.
The maps are described below. Each link takes you directly to it.
Face of the Earth & Relief: Shows the natural, cloudless, color of the land and ice surfaces of the earth. The source of this 1-km resolution digital image is the ARC Science Simulations Face of the Earth ™ (Copyright 1999). ARC created this composite image from thousands of global AVHRR (Advanced Very High Resolution Radiometry) satellite images. The image was constructed from the five AVHRR data channels (one visible, one near infrared, and three infrared) in a manner that resulted in a very accurate surface color. For this map option, colorscaled bathymetry was added for the oceans. The entire image was then mixed with gray shaded relief.
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Color Topography: Shows the elevation of the land (topography) and sea floor depths (bathymetry), based on the global digital elevation model (DEM) GTOP030. GTOPO30 has a horizontal grid spacing of 30 arc seconds (about 100 pixels/° resolution, or about 1 kilometer). For this map option, the color scale shows the elevation, and gray shaded relief was mixed in.
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Gray Topography: Same as Color Topography, but uses a gray scale to represent elevation and bathymetry (sea floor depth) mixed with gray shaded relief.
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Gray Shaded Relief: Shows the surface roughness of the earth derived from GTOP030. Shading is represented as if there were a light source to the northeast and helps provide a perception of depth.
Face of the Earth: Same as Face of the Earth and Relief, but without the relief and ocean bathymetry. The map lets you see shallow areas in the ocean as well as muddy areas at the mouths of rivers.
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Earth at Night: Shows a true color, cloudless, nighttime view of the continents and oceans from the Defense Meteorological Satellite Program (DMSP) satellite imagery (6.67 pixels/° resolution). The images show artificial lighting from population centers and blue background from the reflection of starlight off of land, water, and ice.
SeaWIFS 1997: These maps are derived from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) satellite. Changes in color in the world's oceans and lakes represent concentrations of chlorophyll and other plant pigments in the water. They are used to determine phytoplankton production, which provides information on biological systems and patterns in the ocean. On land, the color scale gives the normalized difference land vegetation index where the minimum values are barren land. SeaWiFs data are time-dependent and provide valuable information on climate change. Two images are provided, one for 1997 and one for 2000.
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SeaWIFS 2000: Same as SeaWIFS 1997, but for the year 2000.
Ocean Floor Age: Shows digital isochrones (areas of similar age) of the world's ocean floor. The colors give the age of the ocean floor in Myr (millions of years before present day), determined from magnetic anomalies measured by ships, satellite altimetry data, and a self-consistent plate tectonic plate model. Areas with no data are shown in gray. Oceanic areas in white or black are mostly continental crust currently below sea level. The resolution of the map is 0.1 degrees.
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Strain Rate: The strain rate model shows the rate at which the surface of the earth is deforming, determined from Global Positioning System (GPS) and other geodetic data, geologic fault slip rates, and earthquake moment tensors. This global strain rate map, along with the strain style map and the velocity vectors (see the Add Velocities section) are from the International Lithosphere Project (ILP), "Global Strain Rate Map" project. The colors range from low to high strain rate; black areas have zero strain rate and can be considered to be rigid. The resolution of the map is 5 pixels/°.
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Strain Style: Shows the style of deformation from the strain rate model described in the Strain Rate section. The color scale provides a sense of the type of earthquakes that one might expect. For example, red areas are undergoing contraction and could lead to reverse faulting if stresses are accumulating.
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Geoid: Shows the undulations of the geoid - an equipotential surface that approximates where sea level would be in the absence of land. The height of the geoid (and the variations or undulations shown on the map) reflect the variation of the gravity field of the earth. The gravity field can provide information about the composition and geodynamic processes occurring within the planet. The colors of the map give the geoid height in meters. The resolution of the map is 4 pixels /°and is derived from the NASA Earth Geopotential Model 1996 (EGM96).
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Seismic Hazard: Shows the seismic hazard potential from the ILP (International Lithosphere Program) Global Seismic Hazard Assessment Program (GSHAP). The source data has a 10 pixels/° resolution. Seismic hazard is represented as the peak ground acceleration, in meter/second**2, with a 10% chance of exceedance in 50 years (corresponding to a return period of 475 years) and a prediction maximum set to 1 g=9.8 meter/second**2. For example, an area in pink (the maximum) has a 10% chance of experiencing an earthquake with a large ground acceleration of 9.8 meters/second**2 (one g of acceleration) in the next 50 years. The models are derived from efforts to determine where earthquakes occur, how large they might be, and how often they occur using historical seismicity catalogs, geologic data (such as trenching data), and geodetic deformation data.
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To close this window, click on the X at the end of the menu bar or in the upper right corner of the window.