The Southern California Integrated GPS Network Education Module

Exploring the use of space technology in earthquake studies

Plate tectonics

Structure of the Earth

Geophysical studies have uncovered much new information about the Earth's interior, including its composition and mechanical properties.

History of plate tectonics

Plate tectonic theory had its roots in Alfred Wegener's erroneous "continental drift" theory (1915) but since the 1950's, geologic and geophysical evidence has helped it gain widespread acceptance as a model of Earth processes.

Plates

Plate tectonic theory tries to account for the movement of plates over time. According to this model, the lithosphere is divided into 7 major and several minor plates which move in relation to one another.

Plate boundaries

Plate boundaries are wide zones of deformation where two or more plates interact. They are found at the edge of plates and are characterized by three distinct motions.

Forces

Forces create stress, which acts to change the volume and/or shape of a material. There are three different stresses which act upon a material in three distinct ways.

Faults

Faults are surfaces along which rocks have been fractured and displaced. There are three main types of faulting and each type is associated with one of the three plate boundaries.

Hypercard resources

Animations of tectonic phenomena, courtesy of the United States Geological Survey.

Earthquakes

What are earthquakes?

Earthquakes are the Earth's natural means of releasing the stress that is built up due to plate motions.

Types of earthquakes

There are many different types of earthquakes and each type is the result of different geologic and non-geologic causes.

Forces

A force can be thought of as a push or pull and has both a magnitude and direction, so therefore it is a vector.

What causes stress?

Much of the stress in plates is caused by tectonic motion, but some stresses occur as the result of non-tectonic processes, especially in the interior of plates, far from plate boundaries.

Elasticity

Materials have different properties which allow them to undergo elastic, plastic, or brittle deformation, depending on the amount and type of stress applied.

Waves

Three types of waves are produced when stress is released as energy in earthquakes. Each of these waves travel in different directions and velocities within the Earth.

Detection and recording

Earthquakes can vary in size and various methods are used to measure and record the energy released in earthquakes. Using seismological instruments, the earthquake's size and location can be determined.

Measurement

Energy released in an earthquake can be measured in several ways. Intensity, magnitude, and seismic moment are three common ways to describe an earthquake's energy.

A new type of measurement

GPS is another tool used by scientists to measure the horizontal and vertical motion of the crust. It can be used to monitor these motions both during and in between earthquakes.

GPS

What is GPS?

The Global Positioning System (GPS) is a navigation and precise positioning tool developed by the Department of Defense in 1973. It was originally used only by the military, but now has wider uses including scientific and recreational.

How does it work?

The Global Positioning System is made up of three main parts. These include the satellites (which send radio signals to the Earth that describe their orbital position and time), the ground station (comprised of an antenna and receiver) and the data center (where ground stations are monitored and controlled and the data retrieved and analyzed).

GPS in earthquake studies

The Global Positioning System can be applied to scientific studies of earthquakes and faults. The Southern California Integrated GPS Network (SCIGN) is an example of how scientists are using GPS in order to study tectonic motion on a regional scale.

Using GPS to measure earthquakes

GPS (and more specifically SCIGN) does not measure the actual ground shaking during an earthquake, but rather the final displacement of the stations caused by the permanent deformation of the Earth's crust during an earthquake.

Space Technology at Work

What is SCIGN?

The Southern California Integrated GPS Network (SCIGN) is a dense array of GPS stations in the Los Angeles Basin and surrounding region which continuously records the millimeter-scale deformation of the Earth's crust caused by tectonic motion. The data collected are used by scientists to study mechanics of faults as well as to estimate seismic hazard in the region.

Who runs it? Who has access?

SCIGN is operated by the Jet Propulsion Laboratory (JPL), the US Geological Survey (USGS), and the Scripps Institute of Oceanography (SIO) under the umbrella of the Southern California Earthquake Center (SCEC). Data are freely available to the public and may be used as long as the user acknowledges SCIGN and its funders as the source.

What happens to the SCIGN data?

Data are continuously recorded by stations and are processed daily at the three SCIGN data centers (at JPL, the USGS, and Scripps) and are made publicly available via the world wide web or anonymous ftp.

How are the SCIGN data used?

SCIGN data are used by scientists to study plate motions, model faults and fault mechanics, identify blind thrust faults, and to help determine the seismic hazard potential posed by faults in Southern California.

More information about SCIGN

Explore these web pages to learn more about SCIGN and its participants.

About this module
Table of Contents
Title page

Last modified on 8/13/98 by Maggi Glasscoe (scignedu@jpl.nasa.gov)