Introduction

An Earthquake is the result of movement of the Earth's crust. This movement can often be observed at the surface of the earth as slip, which is the movement of one part of the Earth's surface relative to another. The amount and extent of the slip of a fault line is what determines the energy released by a earthquake and hence its magnitude.

Aftershocks are smaller earthquakes that occur after large earthquake. These earthquakes are usually adjustments to the new stress conditions created by the large quake.

In this lab we will look at how both slip and aftershocks can be used to gain a better picture of the extent and size of a large earthquake. Three earthquakes that will be looked at are the 2004 Parkfield Earthquake (magnitude 6.0), the 2002 Alaska Earthquake (Magnitude7.9) and the 2004 Sumatra Earthquake (magnitude 9.1).

Using World Wind

The EarthQuake Plug-In

In versions of NASA World Wind 1.34 and above the earthquake plug in is automatically installed with the program. If you are running an earlier version here is a link to the plug-in web site where it can be downloaded and installed onto you computer. The Plug in has two separate parts a "seven day list: of recent earthquakes and a historical earthquake data base.

Much of the following information is taken from the Earth Is Square web site at http://www.earthissquare.com/WorldWind/index.php

Historical Earthquake survey

The second of the two earthquake plug-in is the USGS Historical Query Plug-In. With this plug-in you can query USGS earthquake data all the way back to 1973.

The Historical Earthquake query can be accessed by clicking on the plug in menu and selecting the historical earthquake query option. this will bring up the control screen for the earthquake query.

Search Method- Allows you to focus your earthquake search in one of three ways

Global search- will look for earthquakes across the entire globe

Rectangular search- Allows you to define a rectangle in which historical earth quakes will be queried. the dimensions of the rectangle can types in by hand or generated by drawing a box on the globe.

Radial search- allows you to define a circle in which earthquakes will be queried. you can type in the center point and radius or select the center of the circle in World Wind

Search limiters- allows to limit which earthquake are displayed based on different parameters.

Starting Year - Month - Day - Set the earliest date for which earthquakes will be displayed

Ending Year- Month- Day - set the latest date for which an earthquake is displayed

Min - Max Depth - defines at depth range you want to display earthquakes

Min - Max Magnitude - defines the magnitude of the earthquakes that are displayed.

Once the search is conducted the symbols will appear on the globe. On the query panel a count of how many earthquakes were found is displayed as well of a list of the five largest earthquakes.

And your World Wind globe will look like this:


The results have a different appearance than the RSS plug-in. The colors again relate to age and the size is related to the magnitude. But what is new are the shapes, the shapes are related to the depths the earthquakes happened.

Earthquake Occurrence

Part 1: Introduction

Part 2: Parkfield

Part 3: Alaska

Part 4: Sumatra

Question Sheet