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EarthCache

A View By De-Fault

A cache by SAMO-NPS
Hidden : 7/6/2009
In California, United States
Difficulty:
1 out of 5
Terrain:
2.5 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

Welcome to the Santa Monica Mountains National Recreation Area EarthCaching Program. This earthcache site is available year round. This cache is on trail. Please do not travel off trail for your safety and preservation of resources.

Located at Ranch Sierra Vista / Satwiwa this cache provides views of the mountains, canyons, the Pacific Ocean and, on clear days, the Channel Islands can be seen from this trail.

Information regarding Rancho Sierra Vista and Satwiwa

Pets are permitted on a leash no longer than 6 feet (2 meters). Bicycles and horses are not permitted to this cache
• Rancho Sierra Vista / Satwiwa is open daily from sunrise to sunset.
• All plant material, rocks, animals, and historical features are protected by law and may not be collected or disturbed.
• Safety information:
- Poison Oak can be found in this area. It is identified by three leaves ranging in color from green to crimson. The plant is deciduous, so it does lose its leaves in the winter.
- Watch out for mountains lions, rattlesnakes and ticks.

Satwiwa Native American Culture Center Information:
Open weekends from 9AM – 5PM
Phone number: 805-375-1930

National Park Service Visitor Center Information:
Open daily from 9 AM – 5PM.
Address: 401 West Hillcrest Drive, Thousand Oaks, CA, 91360
Phone number: 805-370-2301
www.nps.gov/samo

In emergency: dial 911

Vocabulary:
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!
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.
Quaternary: A geologic period that includes from the last 1.65 million years to present.
Holocene: A geologic epoch that includes from the last 10,000 years to present.
Fault: A fracture in the Earth’s crust where both sides of the split have moved in opposite directions.
Surface Rupture: A visible surface feature of a fault formed during an earthquake.
Active Fault: Having had significant movement and / or an earthquake in the last 10,000 years.
Sycamore Canyon Fault: An approximately 13-mile long fault that runs northeast to southwest on the western edge of the Santa Monica Mountains range.
Boney Mountain Fault: An approximately 9-mile long fault that runs northeast to southwest on the western edge of the Santa Monica Mountains range.
Santa Monica Mountains Blind Thrust Fault: A 32-mile long fault that runs east – west under the Santa Monica Mountains that has no visible surface rupture.

Geological information:
California, especially the Los Angeles Area is home to movie stars, famous beaches, traffic, and earthquakes. Earthquakes are as much as part of this landscape as oak trees and coastal sage scrub. It can even be reasoned that without earthquakes, that the Mediterranean ecosystem, which the Los Angeles Area and the Santa Monica Mountains are a part of, would never have evolved. Earthquakes, volcanoes, and even plate tectonics created this Mecca of sun that millions of people call home.

An earthquake. The ground is shifting. The land is shaking. Rocks are splitting. Objects and buildings are swaying. The Earth is in fact, moving. Earthquakes are the only natural disaster whereby we have no idea where the next one is going to be. Kind of. ”When is the “Big One” going to hit Los Angeles?” is a question for the ages, but we can study the past as a way of looking to the present and future.

Let’s propose it this way.” Is there going to be an earthquake in California today?” Yes, anywhere from 75 – 125 earthquakes occur in California a day. However, most of them are too small to feel. “Is there going to be an earthquake in the Los Angeles Area today?” Yes, there are 1 – 10 earthquakes each day in the Los Angeles Area. Yet again, most are too small to feel. But it is the ones that are felt that we become concerned about. “So, when is going to happen?” “How big will it be?”

The site you are visiting is looking out at two major fault lines with another under your feet. Do you see them? Most likely not. Two of them are hidden beneath vegetation and the other is underground. So how do we know they are there and how does this relate to the “Big One?”

The two faults that you are looking towards that have surface ruptures are the Sycamore Canyon Fault and the Boney Mountain Fault. The road you can see leads into Sycamore Canyon. The mountain face to your left, at the base, is the Boney Mountain Fault. It’s not exactly what we think of when we think “fault”. Instead, the image that comes to mind is the San Andreas Fault. Yet, with these two fault lines, they are not considered active faults. These two faults are potentially active faults in that they last had a significant earthquake in the Quaternary period, between 11,000 and 1.65 million years ago (Jennings, 1994). This means, the faults could have an earthquake, but they haven’t in a while.

The Sycamore Canyon Fault is approximately 13 miles long (Jennings and Strand, 1969) and has offset the surrounding rocks and geology about 5,000 feet (Sonneman, 1956). The Boney Mountain Fault is approximately 9 miles long (Jennings and Strand, 1969) but has offset the surrounding rocks and geology about 9,000 feet (Sonneman, 1956). These two faults are what define Sycamore Canyon from here to the ocean directly south of where you are standing.

The other significant fault in the area is underneath your feet. The Santa Monica Mountains Blind Thrust Fault is a 32-mile long fault that has no surface rupture (Saikai, 1999). This means that there is fault line running almost the entire length of the Santa Monica Mountain range that we cannot see. Should we be concerned standing here? No, because remember earthquakes happen all the time. But remember we can study the past to learn about the future.

Seismology is the study of earthquakes and the structure of the earth. Through this study we can analyze and understand how the earth moves. The two most common scales that are used to measure an earthquake are the Richter Scale and the Modified Mercalli Intensity Scale (MMI). The Richter Scale is what most people are familiar with. 5.0, 6.2, 7.1 is usually how we hear about earthquakes through media. The scale, designed as a way to quantitatively explain earthquake intensity using seismometers, devices that record earthquakes, for scientific understanding. The MMI was created as a way to qualitatively explain earthquake intensity in urban areas, how do the people perceive the earthquake. So what does this mean for the three faults we’re talking about? First off the mountains are 16-24 million years old and were created by volcanoes. (See the Inspiration Point EarthCache to learn how.) They have since have been eroding away. At one point these mountains were over 10,000 feet high. But in that time, millions of years, the rate at which they have eroded has change. Today, it is about 0.5 ± 0.3 mm per year or 1636 feet every million years for the last 100,000 years (Meigs et al., 1999). On the other hand the Santa Monica Mountains are growing at about 0.5 ± 0.4 mm per year, or 1636 feet every million years for the last 100,000 years (Meigs et al., 1999). And what accounts for this growth are earthquakes. The mountains are growing at about the same speed in which they are eroding away.

This growth comes from faults and the earthquakes that are produced from it. The story doesn’t end there. The largest of the three faults we are looking at is the most recently active, the Santa Monica Mountains Blind Thrust Fault, ruptures on average every 740 years (Dolan et al., 1995). And when these earthquakes occur, how big should we expect them? Most scientists agree that the largest magnitudes produced by these faults would around a 6.0 – 6.2 for the Sycamore Canyon and Boney Mountain Faults (Slemmons, 1977) and 7.2 for the Santa Monica Mountains Blind Thrust (Dolan et al., 1995).

So back to the “Big One” and the area you’re standing on. In 1995, a study was done by James Dolan and others that shows after they analyzed 51 different sources that in the last 200 years there should have been 17 major earthquakes in the Los Angeles Area; there have been two. In the future there will earthquakes. This location preserves the scenery that was created by the forces that control our planet. We’ll have to wait and see what happens next, because tomorrow there will still be earthquakes.

Quiz
To earn your certificate for this cache click the link below and take the quiz.

A View By De-Fault Quiz

Q: From This EarthCache site, point at the Sycamore Canyon Fault. What direction are you pointing?
Q: In the narrative, it states that the mountains are neither growing nor shrinking. Select the geological feautures you can see from this EarthCache site that illustrate this theory.
Q: The Chumash took a traditional route to the ocean for trade. Which direction do you think they traveled from the villages closest to this cache site?

Links:
Santa Monica Mountains Homepage
GPS Activities in the Santa Monica Mountains
Recent Earthquakes in California and Nevada
U.S. Geological Survey Earthquake Hazards Program

Sources:
- Dolan, J.F., Seih, K., Rockwell, T.K., Yeates, R.S., Shaw, J., Suppe, J., Hufrile, G.J., and Gath, E.M., 1995, Prospects for Larger or More Frequent Earthquakes in the Los Angeles Metropolitan Region, Science, V. 269, p. 199-205
- Dolan, J.F., and Pratt, T.L., 1997, High-resolution seismic reflection profiling of the Santa Monica Fault Zone, West Los Angeles, California, Geophysical Research Letters, V. 24, N. 16, p. 2051-2054
- Jennings, C.W., and Strand, R.G., compilers, 1969, Geologic Map of California, Olaf P. Jenkins edition; Los Angeles Sheet: California Division of mines and Geology Map, scale 1:250,000
- Jennings, C.W., complier, 1994, Fault activity map of the California and adjacent area: California Department of conservation, Division of Mike and Geology, California Geologic Data Map Series, map no. 8
- Meigs, A., Brozovic, N., and Johnson, M.L., 1999, Steady, balanced rates of uplift and erosion of the Santa Monica Mountains, California, Basin Research, V. 11, p. 59-73
- Sonneman. H. S., 1956, Geology of the Boney Mountain Area, Santa Monica Mountains, California, University of California, Los Angeles Master of Arts in Geology Thesis, p. 63-64
- Saikia, C. K., 1999, Generation of strong motion time histories from postulated large earthquakes (Mw =7) on the Santa Monica Mountain Fault System, URS Greiner Woodward Clyde, Pasadena, CA, 91101
- USGS Earthquake Hazards Program has created some of the graphics that are included in this cache.

Additional Hints (Decrypt)

Ba Uvqqra Inyyrl Bireybbx Genvy ba ACF ynaq.

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)

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Inventory

There are no Trackables in this cache.

 

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64 Logged Visits

Found it 60     Write note 3     Publish Listing 1     

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Current Time:
Last Updated: on 9/2/2014 6:34:53 PM Pacific Daylight Time (1:34 AM GMT)
Rendered From:Unknown
Coordinates are in the WGS84 datum