Plate Tectonics: Science Background


Faults and Plate Tectonics
Azimuth
Crustal motion vectors
Frames of reference
Latitude/Longitude
Space geodesy and GPS
Vectors
   

Note that this section is under development. Some information and links have been added. More will be developed soon.

Faults and plate tectonics: This Dynamic Earth: The Story of Plate Tectonics (a United States Geological Survey, USGS, website) has general background on the theory of plate tectonics.

Azimuth: The concept of azimuth has been developed to permit precise descriptions of direction. The underlying principle is that a complete circle can be divided into 360 degrees (360°) of arc. Each degree can be further divided into 60 minutes (60') and each minute can be divided into 60 seconds (60"). If due north is designated as 0°, then 90° points to the east, 180° points to the south, 270° points to the west, and 360° points, once again, to the north. At any given time, if you think of your location as lying at the center of a circle, the direction (azimuth) to any feature can simply be described by its angle of arc in degrees. A typical azimuth could be 37° 5' 15", which would indicate an arc of 37 degrees, 5 minutes, and 15 seconds. Azimuth can be measured directly off a map, using a protractor or calculated, using simple trigonometric relations.

Crustal motion vectors: This section provides a general description of GPS vectors and what they signify, and observed vs. model vectors. (See if Bill Holt can briefly describe the compilation of observed GPS vectors and basics of their model velocity field.)

Frames of reference

 

Latitude/Longitude: The most important use of any map is to locate your position on the Earth's surface. The most commonly used location system is the longitude-latitude system. This system of location was developed by sailors who needed a means of describing their location at sea. In short, the system is based on the principle of intersecting N-S and E-W lines of known position.

The N-S lines, referred to as longitudinal lines or meridians, are actually circles that pass through the north and south poles. The meridian that passes through Greenwich, England has been designated arbitrarily as the 0° meridian and any point along that meridian is said to have a longitude of 0°. The 0° meridian is also called the prime meridian.

If you could place yourself above the North Pole and look down upon the intersecting meridians, it would look like a giant compass with meridians extending in all directions. The longitude of any meridian is based on the angle of arc (in degrees, minutes, and seconds) and direction (east or west) between it and the prime meridian. Note that the longitude increases from west to east (or left to right on a map) for meridians lying to the east of the prime meridian, but increases from east to west (or right to left on a map) for meridians lying to west of the prime meridian (for example, the United States).

The other half of the system, the E-W lines, are referred to as latitudinal lines or parallels. Parallels are circles, parallel to the equator, that encircle the Earth at successively closer distances to both the north and south pole. By definition, parallels are perpendicular to meridians. The equator is designated as having a latitude of 0°. The latitude of all other parallels is then based on how far (once again in terms of degrees, minutes, and seconds) they lie to the north or south of the equator.
Now that the entire earth has been divided into N-S running meridians and E-W running parallels, the position of any point at sea or on land can be uniquely described by the longitude and latitude of the intersecting meridians and parallels. The locations of meridians and parallels are often shown along the edges of maps.

Space geodesy and GPS: The GPS tutorial, a website developed by Trimble Navigation, Inc., has general information on the Global Positioning System (GPS).

Vectors