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 Enter 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. Note that USArray & Other, PBO GPS, PBO Strain, and SAFOD show EarthScope activities and data.
|
|
No Features: Turns off all features.
USArray & Other: The United States Seismic Array is a dense network of seismic stations that will allow scientists to image the details of Earth structure beneath North America. Over a decade, a transportable array of 400 broadband seismometers will cover the continent with a uniform grid of 2000 sites. By studying the recorded waveforms of earthquakes and large explosions from mines and quarries, scientists will be able to identify and map subtle differences in the velocity and amplitude of seismic energy traveling through Earth, which should result in a vastly improved ability to resolve geological structures throughout the entire crust and upper mantle and into earth’s deepest interior. More information is available at EarthScope: USArray.
PBO GPS: PBO is a distributed observatory of high-precision geodetic instruments designed to image the ongoing deformation of western North America. The geodetic network will extend from the Pacific coast to the eastern edge of the Rocky Mountains, and from Alaska to Mexico. Two instrument systems—Global Positioning System (GPS) technology at about 875 sites, and ultra-low-noise strainmeters at 180 locations—will provide superior time resolution. A sparse GPS network at active volcanoes and the most active earthquake faults will provide complete spatial coverage. PBO will significantly improve our ability to image and characterize the slow deformation that accompanies earthquakes and volcanic events. The data will elucidate the poorly understood processes that precede earthquakes and volcanic eruptions, and could provide a firm basis for their prediction. The broad geographic coverage will permit quantitative understanding of tantalizing connections observed between activity in different regions. Complementary geological investigations will link present-day deformation to longer-term processes that have shaped the plate-boundary region. More information is available on the UNAVCO, Inc. map coordinates reference for the proposed PBO site and the EarthScope: PBO website. Note that the blue dots will be new PBO stations; the green dots are existing stations that will be upgraded for PBO.
PBO Strain: Shows the Plate Boundary Observatory GPS receiver and borehole strainmeter clusters centered in the most tectonically active areas. The red triangles are laser strainmeters, whereas the pink triangles are borehole strainmeters. More information is available on the UNAVCO, Inc. map coordinates reference for the proposed PBO site and the EarthScope: PBO website.
SAFOD: The X shows the location of the San Andreas Fault Observatory at Depth (SAFOD) site (USGS). SAFOD is a 4-km-deep observatory drilled directly into the San Andreas fault zone near the nucleation point of the 1966 magnitude 6 Parkfield earthquake. The project will reveal the physical and chemical processes acting deep within a seismically active fault. Initially, fault-zone rocks and fluids will be retrieved for laboratory analyses, and intensive downhole geophysical measurements will be taken within and adjacent to the active fault zone. The observatory’s long-term monitoring activities will include decades of detailed seismological observations of small- to moderate-sized earthquakes, and continuous measurement of pore pressure, temperature and strain during the earthquake cycle. SAFOD will provide direct information on the composition and mechanical properties of faulted rocks, the nature of stresses responsible for earthquakes, the role of fluids in controlling faulting and earthquake recurrence and the physics of earthquake initiation and growth. Drilling, sampling, downhole measurements and long-term moni- toring will allow testing of a wide range of hypotheses about faulting and earthquake generation, and the pursuit of a scientific basis for earthquake hazards assessment and prediction. More information is available on the EarthScope: SAFOD website.
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.
 |
 |
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.
 |
 |
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.
 |
 |
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.
 |
 |
Volcanoes: Shows the locations of active volcanoes (active in the last 10,000 years), from the Smithsonian Global Volcanism Program.
Volcanoes & Names: Shows volcanoes that have shown some tectonic activity in the past 10,000 years. Some are just steam fields rather than actual volcanoes but have potential to be active. The information comes from the Smithsonian Global Volcanism Program.
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.
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.
Major Rivers: Shows data from the World Data Bank II or CIA Data Bank (WDB), which contain coastlines, lakes, political boundaries, and rivers.
To close this window, click on the X at the end of the menu bar or in the upper right corner of the window.