# GLG310 Structural Geology 2004 Geologic Blocks and Strike and Dips Lab

### Introduction to Structural Planes

You can divide even the most complicated geologic structure into a series of linear or planar elements, so the fundamental geometric features are lines and planes. We have to know how to describe their orientation.

Let's look at the basic concept of strike and dip with this little movie: Strike and Dip QuickTime VR Movie

Here are some definitions:

Strike and dip symbols have 3 parts:

Here are some common symbols whose usage is well established by convention:

Strike and dip notation
1. Strike notation.
(a) N65 W, 25 S ("Quadrant"): the bearing of the strike direction is 65 degrees west of north and the dip is 25 degrees in a southerly direction. For a given strike, there are only two possible dip directions, one on each side of the strike line. Hence it is necessary only to identify which side by two letters. If the strike direction is nearly N-S or E-W, then a single letter is appropriate; if the strike direction is close to the 45 degree directions (NE or NW) then two letters are preferred.
(b) 295, 25 S ("azimuth"): the azimuth of the strike direction is 295 degrees measured clockwise from north and the dip is 25 degrees toward the south. Usually the trend of the northernmost end of the strike line is given, but the azimuth of the opposite end of the line may also be used, as in 115, 25 S.

2. Dip notation.
(a) 25, S25W: the dip is 25 degrees and the trend of the dip direction has a bearing of 25 degrees west of south.
(b) 25/205 ("dip and dip direction"): the dip is 25 degrees and the trend of the dip direction has an azimuth of 205 degrees measured clockwise from north. To avoid confustion, dip angles should always be given with two digits and the trend with three, even if this requires leading zeros.

Let's practice:

### Geologic Blocks

The major effort of this lab is to work through the Interactive Geologic Blocks 3d Laboratory exercise and to fill out the worksheet that we have handed out as you go. You can work in groups like last time.

http://geology.asu.edu/%7Esreynolds/blocks/home.htm
You will turn in the worksheets.

### Homework

Do this Strike and dip conversion exercise and complete the Geologic Blocks worksheets to be turned in next Thursday at the beginning of lab.