How To Draw Strike And Dip

In order to understand geology, we need to retrieve nigh the rocks below our feet in three dimensions. Those spatial relationships— what's on height of what, how rocks are faulted or folded— requite us all kinds of interesting information. While maps are useful in all kinds of ways, they're a niggling lacking in the 3-D section. And so when we've measured the orientation of a rock layer, we need a fashion to represent that on a map. Here's a basic primer on how that's washed.

The geological lingo for this is "strike and dip". The words may be confusing at first, simply it'due south really quite uncomplicated. Let'southward start with some nice, horizontal sedimentary rocks. Pretend the top of this cake is the surface of the Earth. Picture a kangaroo hopping beyond information technology, if that helps or entertains yous.

Let's picture a single layer of that rock and tilt it downward to the right. The tilt of that layer is what we call "dip". We draw this layer every bit dipping to the right, because that'south the direction it's tilted downwards toward. We measure out the dip as the angle between the layer and horizontal.

Now, permit'southward try to imagine looking at that same tilted layer from directly in a higher place it. Again, it'due south dipping downward to the right. Draw a horizontal line across that layer— that'due south what nosotros call the "strike". (Don't worry virtually why we use that word.) In this instance, the strike is north-south. That means this layer is dipping to the e.

Here'south a block made of tilted layers instead of horizontal ones. The top of the block is still the surface of the Earth, but I've sliced out a piece of the block to assistance united states of america visualize this ameliorate. Imagine you lot're looking at a cliff.

When you look at the side of the block, you tin see the dip. When you await at the top of the block (the surface), you can run into the strike. Click the epitome below to explore a existent outcrop of sandstone and siltstone from the Oregon coast that looks a lot like this. Exist certain to zoom in and get a closer wait.

Hither'southward an annotated image of that outcrop, but to brand sure you can come across the strike and dip. Yous can click on this prototype to see more photos from this spot. If you lot click this link, y'all can check out the surface area with Google Earth.

Geologists carefully measure the strike and dip on an outcrop similar that using a tool called a Brunton compass, pictured below.

One time you've made the measurements, y'all can display them on a geologic map— which was our goal at the start of this post. Strike is easy enough, since it's a compass management. If we measured the rock striking n-south, we would draw a short, vertical line on the map in the location of our measurement (assuming up is north). If the rock was dipping 45 degrees to the east, we would add a tick marking at the midpoint of our strike line, pointing east. Think of the tick mark as an arrow pointing in the direction a ball would roll if you could prepare it on that stone layer. Just below that we would write the measured dip: "45". It would expect something like the case below. The different colors on the map stand for the different rock layers exposed at the surface, simply like looking at ane of the block diagrams from higher up. Without the strike and dip symbol, nosotros would have no idea if those layers were dipping to the west, to the east, or were vertical. Simply past adding this simple symbol, we can understand something well-nigh the 3-D orientation of the rocks.