Geology Vocabulary

Here is some vocabulary to help you along the way as you continue to explore the geology of the Santa Monica Mountains. We'll be adding to it from time to time, so be sure to check back again. Enjoy!


Active Fault: Having had significant movement and / or an earthquake in the last 10,000 years.

Farallon Plate: An oceanic plate beneath the Pacific Ocean, about the size of Oregon.

Fault: A fracture in the Earth's crust where both sides of the split have moved in opposite directions.

Holocene: A geologic epoch that includes from the last 10,000 years to present.

Modified Mercalli Intensity Scale (MMI): A scale developed for urban areas to represent the amount of destruction and damage following an earthquake. These numbers are always written in Roman numerals. The scale ranges from I (not felt) to a X+ (extreme shaking). An MMI of IV is about the threshold in which most people start to feel an earthquake.

North American Plate: The continental plate of North America.

Pacific Plate: Oceanic plate north of the Farallon Plate under the Pacific Ocean.

Oligocene Epoch: 33- 23.8 million years ago.Subduct: the process of one tectonic plate descending and sliding beneath another plate.

Richter Scale: Created in 1935 by Charles Richter at Cal Tech, this logarithmic scale was devised to measure the energy output of an earthquake. The scale ranges from 0.0 to 10.0. Each increase in an earthquake magnitude (4.0 to 5.0) is equal to a 10 times increase in wave amplitude. Because of the math associated, this also means that a 5.0 has 31 times more energy than a 4.0!

Surface Rupture: A visible surface feature of a fault formed during an earthquake.

Transferred Lithosphere: The remnants of the plate that is left behind as the ridge travels northeastward.

Transverse Range: Mountains that run in an East-West direction instead of a North-South direction.

Quaternary: A geologic period that includes from the last 1.65 million years to present.

Last updated: March 1, 2015

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