Signal Hill is known for being tall and for having oil. If you haven't already, check out my other nearby earthcache about Signal Hill's Oil field at Discovery Well Park (GC5W3HY). Signal Hill stands hundreds of feet above the rest of the Los Angeles Basin. So what makes it so tall? The answer lies beneath our feet.
Before I go into any more details lets first discuss the basic fundamentals of how fault lines are created and now they work. The answer can be found in your kitchen, literally. When boiling pasta on the stove, the hotter pasta floats to the surface then when it cools it sinks. This effect has a name. Convection currents in your pot at home and in the earth are nearly identical. There are a few difference though. One is with water, rather than boiling rocks and the other is that one is less a few inches while one is miles deep. Convection currents are continues cycles in the earth's mantel that make hotter rock rise, and cooler rock fall and the cycle begins over and over again. When this happens, it causes fractures in the earth's crust. When fractures occur, a fault line is created.
Now at this point I'm sure you are asking, "What is a fault line?" Well, it is place where two tectonic plates meet and create friction. When this friction is released, an earthquake is formed. This friction is formed by these convection currents. When they move in a circular pattern in one direction, they can push rock with them. When tension is released you get an earthquake in an that moves in waves on the X, Y, and Z axises. X is up or down, Y is right or left, and Z is pivoting side to side. Faults generally move at a constant rate of 2 centimeters per year. Depending on the pressure, it can create a magnitude 1 earthquake on the Richter Scale or a 10. A 10 has never happened in recorded history, but is believed to have only occur when large meteors hit the earth. The largest earthquake ever recorded happened in Chile on May 22, 1960. It happened in open waters, just off the coast in the Pacific where it created a Tsunami. You can see my earthcache about that Tsunami here. A Richter Scale works like this. Say there was a 5.0 earthquake, which are common, and a 7.0, a little less. A 7.0 on the Richter scale is 100 times greater of that of a 5.0 on the same scale. Each decimal point in-between is twice as as bad as the preceding one.
Southern California is prone to earthquakes due to the fact that there are many fault lines. The most famous is the San Andreas Fault, about 50 miles away from here. The fault line that created Signal Hill is called the Newport-Inglewood Fault. It starts just off the coast in Newport Beach and heads north west towards the east portions of Inglewood.
Fault zones and oil field DO have a correlation as to where they are both found. This is one of the many reasons why Signal Hill has so many oil rigs. If there is a fault near the coastline, there is a higher chance for oil to be found nearby. Although this might not be the case as several other factors go into how deep oil may be such as the type of rock that the oil is under and duration that the dead material is under high temperatures. With the help of seismic activity, oil can literally be driven out of the ground as seen with the nearby La Brea Tar Pits. Above is a map of fault lines and known oil fields. See a correlation?
Sometimes, the fault is jagged and isn't a perfect strait line as you can see when the fault approaches Signal Hill above. When this happens, two outcomes are extremely likely. A sag pond may form due to the breaking apart of land OR a large hill or mountain due to the compression of land. Obviously, a sag pond isn't occurring.
Now, at this site you will be on top of Signal Hill, which was created by a convergent step in the fault. Convergent means that the two plates are moving towards each other and a divergent means they are moving away from each other. Convergent steps create hills and divergent steps created valleys, which collect water. You must understand that this isn't a plate boundary, it's a fault within a plate. The only plate boundary in California is along the San Andreas Fault that divides the North American plate to the east, and the Pacific Plate to the west. Signal Hill is on the Pacific Plate.
The way to tell what each form is simple. First you must know that there are two types of transform faults. We'll use the San Andreas Fault for example as it's more widely known. The San Andreas is a right-lateral fault. This means, of you are on one side of the fault and look to the other side, you will notice that the other side is moving to the right relative to you. You will see the trees, houses, and even roads move to the right while you are standing still. Now, this doesn't happen overnight. It takes millions of years to make this happen. The same thing occurs when it's a left-lateral fault. The only difference is that it moves to the left, relative to you. You can even try this at home. Just like when you push to sides of the same piece of paper together and you get a ridge in the paper, the same happens here. The only difference is the size and scale.
To determine if a sag pond or hill will form, you will need to look at aerial photos and maps. Transform faults usually are parallel (for the most part) north and south. To make things simpler, think of the fault as a straight road that heads north and south. If the north part of the road is to the west/below the south facing part of the road, hills will form due to compression because of the relative motion. If the north part of the road is to the east/above the south part of the road, a valley will form due to decompression because of the relative motion. Look at the diagram and notice how and where the relative motion is on each plate.
Works Cited
http://scedc.caltech.edu/significant/
https://www.priweb.org/ed/pgws/backyard/signal_hill/signal_hill_oil.html
TO LOG A FIND ON THIS CACHE YOU MUST E-MAIL (NOT THE GEOCACHING.COM MESSAGE CENTER) ME THE CORRECT ANSWERS BEFORE YOU LOG A FIND. ANY INCORRECT ANSWERS WILL RESULT IN A DELETED LOG
**No group emails will be accepted as for me, this is a form of cheating. If this happens, all your logs will be deleted. Any incorrect or inaccurate answer will result in a deleted log, so don't let this happen to you!**
1. "Newport-Inglewood Fault - Signal Hill" on the first line of your email.
2. Using the view as a point of reference look for any other compressional hills or sag ponds that are similar to Signal Hill. If not, why don't you see any. If so, tell me where you see them and why you think there is one at that location.
3. On the plaque, an elevation was recorded along with when it was recorded. Using this information, calculate the difference in elevation of Signal Hill from the year the elevation was recorded to the current year. Consider that the Newport-Inglewood Fault moves at 2 centimeters per year. Hint: the base year is given to you on the plaque.
4. From your answer above, is Signal Hill growing or shrinking AND do you agree with what the answer is based on your own observations? Explain.
5. What is the percent grade of Signal Hill?
* NOTE - You will likely not receive an email back from me, unless I need clarification on your answers. Please, don't wait for me to tell you you have it correct or not. I do review you emails within 12 hours of getting them in my inbox and with other of my earthcaches, it has become too hard to do. As soon as you send the email, you can log this earthcache.
