Ch+14

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Click here to download a pdf version of the slide show, with three slides per page and lines for notes.

Ch 14 Handout media type="custom" key="27790643"

[|How the Japan Earthquake Shortened Days on Earth]

[|Could a 9.0 Earthquake Happen In the United States?]

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Geology of the Cajon Pass media type="custom" key="28273695"

 Liquefaction

Liquefaction is a process in which water saturated sediment or soil temporarily loses strength and acts as a fluid. Though most commonly associated with earthquakes, liquefaction can occur whenever there is shear stress on a saturated soil/sediment.

Liquefaction most often occurs in loose, granular soils, often with poor drainage. These soils most often occur in swampy/marshy areas or in areas of reclaimed land (land that used to be underwater but was filled in for development). Because these loose soils have a tendency to compress when sheared, during an earthquake or any period of repeated loading and unloading of stress, the pore pressure increases which results in the loss of strength of the soil

Some large earthquakes can cause what are called sand boils, sometimes called sand blows or sand volcanoes. This is where the shaking causes sand and water to force its way to the surface causing a fountain of sand and water, sometimes several meters high.

The most dramatic effect of liquefaction occurs when large buildings are built in unstable areas. When the soil beneath these buildings liquefies, the buildings often do not collapse outright, but end up tilted or completely toppling over, leaving the building structurally intact.

The photo is from the 1964 Niigata, Japan earthquake. What you see is the tilting/toppling of buildings due to liquefaction. Note the buildings did not structurally collapse, they just fell over, like cutting down a tree.

---Adam

Photo Credit: Earthquake Engineering Research Center, University of California, Berkeley

Further Reading:

@http://www.sciencedaily.com/articles/e/earthquake_liquefaction.htm

@http://earthquake.usgs.gov/learn/glossary/?term=liquefaction

@http://www.ce.washington.edu/~liquefaction/html/what/what1.html

http://geomaps.wr.usgs.gov/sfgeo/liquefaction/aboutliq.html#niigata Mapping Seismic Activity: Vulnerable vs. Non-Vulnerable Regions

The study of plate tectonics offers an interesting view on our planet’s past, present, and future seismic activity. The larger and expanded map indicates the probable intensity of earthquakes that could happen in the next 50 years, starting from 2004. The green lines represent the earth’s plate boundaries and the shaded colors rangin g from grey to orange represent the probable intensity of an earthquake in that specific region. Each red dot on the map represents a recorded seismic event since 1900 that had a Seismic Moment Magnitude above 8.5. Dr. Jean-Paul Rodrigue, the author of this map, explains that it is a matter of when, rather than if, that these endangered areas face some sort of seismic activity in the near future.

Although there are vulnerable areas in middle Asia, the Middle East, and Europe, with very distinguishable seismic activity, such as Italy for example, most areas that have had either previous or predicted earthquakes exist on the edges of the Pacific Ocean in a region called the Ring of Fire, depicted in the zoomed-in second map. This horseshoe shaped border of most of the Pacific Ocean stretches for 40,000 km (≈25,000 miles) and contains 75% of the earth’s active and dormant volcanoes. Notice that out of the documented 16 earthquakes that had magnitudes higher than 8.5, 12 occurred almost directly on the Pacific Ring of Fire. This is no coincidence. A collection of convergent, divergent, and transform boundaries create this highly active ring where powerful earthquakes shake the ground and active volcanoes reshape terrains.

Recently within the Ring of Fire, Asia has suffered from catastrophic earthquakes and tsunamis generated from deep-sea earthquakes. Mount Ruapehu in New Zealand has continued to be one of the most active volcanoes on earth with consistent annual eruptions, and Chile has had some of the most spontaneous seismic activity in the world. It is hard to not become a little daunted by the events that have occurred within the Ring of Fire, especially for those who reside directly on and near the plate boundaries. One cannot help but to question where the next site of devastation will occur. With that said; continued research and mapping of seismic activity will generate more data and scientific breakthroughs which in turn will increase the predictability of dangerous seismic activity.

--Pete D

Photo Credits: 1. Dr. Jean-Paul Rodrigue, Hofstra University  http://people.hofstra.edu/geotrans/eng/ch9en/conc9en/plate_tectonics.html 2. Dr. Jean-Paul Rodrigue, Hofstra University  http://people.hofstra.edu/Jean-paul_Rodrigue/GESA/topic1/ringoffire.html

References: <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">1. @http://education.nationalgeographic.com/education/encyclopedia/ring-fire/?ar_a=1 <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">2. @http://pubs.usgs.gov/fs/2005/3045/ <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">3. @http://www.volcanolive.com/active2.html <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">4. @http://volcanoes.usgs.gov/activity/status.php

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<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">A TALE OF TWO LAVAS

<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">This striking image taken from space by the International Space Station Mission 16 team shows the Harrat Khaybar volcanic field located north of Medina, Saudi Arabia. This north-south oriented volcanic field covers more than 14,000 km2 and contains examples of scoria cones, basaltic shield volcanoes, domes, tuff cones, several whaleback lava flows, and one stratovolcano. The e <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">ruptions have taken place over the last 5 million years, with the most recent eruption recorded between 600 and 700 AD. The area is not involved with the opening of the Red Sea, but it is a more recent rift zone.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">We can learn a lot about the history of this lava field just by looking at the image. One of the most obvious features is the contrast in color between the volcanoes on the left and the right of the photo (north is indicated by the arrow on the bottom right). The colors indicate the types of lava that were involved in the eruptions. The lighter colors are more indicative of eruptions of felsic lava, which is higher in silica and water and much thicker. Rock types in the area include benmoreite, trachyite and comendite (a type of light blue-grey rhyolite). The large, round Jabal Bayda' crater in the upper left is an example of a tuff cone, formed by pyroclastic eruptions, which may indicate more abundant water in the past. Jabal Abyad at the bottom left of the image is an example of a lava dome, formed by thicker lava flows.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">The darker rock on the right is basalt, indicative of mafic lava flows which are higher in iron and magnesium. Mafic lava is lower in viscosity, and eruptions are generally less explosive. Because the darker basalt from the Jabal al Qidr stratovolcano is overlapping the lighter rock, we know that the mafic lava eruptions were more recent. The lack of vegetation indicates a very arid climate.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">-Amy

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">References:

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> http://www.volcanodiscovery.com/harrat_khaybar.html

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> http://earthobservatory.nasa.gov/IOTD/view.php?id=8650

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> http://www.saudicaves.com/lava/introobl.htm

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Image courtesy of ISS Expedition Crew 16, provided by the Image Science & Analysis Laboratory, Johnson Space Center

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<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;">Into the volcano …

<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;">Volcanoes are beautiful, but deadly. As if to re-emphasise this, news is coming in as I write of five fatalities on the slopes of Mount Mayon, a volcano two hundred miles south-east of Manila, in the Philippines. A brief one-minute phreatic eruption tragically caught a group of climbers ascending the mountain, noted for its perfectly-shaped cone.

<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;">Elsewhere in the news, NASA ha <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;">ve reported new Landsat images of an eruption of Paluweh volcano in Indonesia, taken on April 29th 2013. As well as visible light images a new detector employing a thermal infrared sensor was exploited. Comparing the two sets of images reveals the boundaries between hot volcanic activity and the cooler volcanic ash clouds, ejected into the cooler reaches of the high atmosphere. The white dot at the volcano vent corresponds to the hot lava at the central cone, while the dark cloud is the cooler ash drifting in the wind.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;">The thermal infrared sensor can pick up variations in temperature of around one tenth of a degree Celsius, and will be used in future to make accurate measurements of Earth's surface temperature while accounting for atmospheric variations in temperature. It is being used as part of NASA's Landsat Data Continuity Mission, for long-term remote observation of our planet.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;">~SATR

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;">Image: NASA

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;">Links:

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;"> @http://www.nasa.gov/mission_pages/landsat/news/indonesia-volcano.html

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;"> @http://www.bbc.co.uk/news/world-asia-22430378

<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;">Volcano in a Corn Field

<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;">In honor of Cinco de Mayo, here’s a story about a volcano in Mexico. This is Paricutín, located in central Mexico in the Michoácan-Guanajuato volcanic field. It may look like any other small cinder volcano, but this one is unique in one very special way. The entire life cycle from birth to extinction of this volcano was witnessed by humans.

<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;">The story begins in a cornfie <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;">ld near the village of Paricutín in February, 1943. A farmer, Dionisio Pulido and his wife Paula witnessed ash and stones exploding out of a fissure in their field. Residents of the area watched in dismay as the volcano grew to over 16 meters in a week. The volcano quickly took over the cornfield, and then eventually buried the villages of Paricutín and San Juan Parangaricutiro. After one year, the volcano was over 336 meters tall. Eruptions of lava and ash continued for 8 years, and then the volcano became silent in 1952.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;">Paricutin is a monogenetic volcano, one that erupts for a short period of time, but never erupts again. Monogenetic volcano fields occur where the magma supply is low or vents are not large enough to give a continuous supply of magma to a single volcano. The Michoácan-Guanajuato volcanic field in Mexico is a monogenetic field with over 1400 vents. The area averages around 2.5 cinder cones every 100 square kilometers. Although the life of any single volcano is short, a monogenetic field can actively produce eruptions for millions of years.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;">-Amy

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;"> http://www.geology.sdsu.edu/how_volcanoes_work/Paricutin.html

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;"> http://vulcan.wr.usgs.gov/Glossary/VolcanicFields/description_volcanic_fields.html

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;">Image of Paricutin erupting at night in 1943, Courtesy NGDC/NOAA slide archive and Wikimedia Commons <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif;">





.An interactive copy of this map is posted here: []



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<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">A new story for the West Coast of North America

<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">You know what? The West Coast of North America is a mess.

<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">Well, maybe not from whatever perspective you’re thinking…my apologies to everyone I just (quasi-deliberately) offended, let’s be a little more specific. From a geologic perspective, the West Coast of North America is a mess.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">If you look at the Andes Mountains, they are something of a clean story. For hundreds of millions of years, there has been subduction of an oceanic plate beneath South America, building the mountain range we see today. Oh, there are a few plateaus, there are a few volcanoes, but overall, it’s a thin mountain range that doesn’t intrude much into the continent.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">Compared to that, the Rocky Mountains in North America are a nightmare. The Andes are about 500 kilometers wide, while the Rocky Mountains in places stretch nearly 2000 kilometers into the continent.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">There are a number of causes for this huge damage zone in North America, but a big part of the puzzle is stuff that wasn’t always part of North America. Docked to the west coast of North America, there are a series of what are called “accreted terranes”. They have names like Stikina, Wrangellia, etc. These accreted terranes can be understood as ocean island chains that rode in on the subducting oceanic plate, slammed into the continent, but couldn’t make it down the subduction zone and wound up stuck where they arrived.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">The image you see here is a beautiful shot from the National Park Service of a place in Wrangell-St. Elias national park (see the name?). The rocks that make up this shot are part of one of those accreted terranes. They rode in on a plate that was being subducted and stuck in place.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">So, all of these terranes have been accreted in North America, but South America doesn’t have them. Obviously, that brings up the question “Why”?

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">New research published in the journal Nature tries to answer that question with a new model for subduction along the North American coast.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">Once a plate is subducted, most of the evidence of that plate disappears. Piecing together a plate that has been subducted is an arduous challenge. Prior to this paper, the basic model for the Pacific Ocean involved 3 plates: the Pacific plate, the Kula plate, and the Farallon plate. The Kula plate is basically gone today, while there are a few fragments of the Farallon plate left, such as the Juan de Fuca plate currently subducting beneath Washington, Oregon, and British Columbia.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">Although tracking down a subducted plate is difficult, there is one tool that might help called seismic tomography. Seismic tomography involves measuring the speed of earthquake waves very precisely as they travel through the Earth and using those speeds to understand the material the waves travel through. Subducted plates have a very distinct signature, so they can be fairly easily detected using this technique.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">These authors performed seismic tomography underneath the Western U.S. and North Pacific Ocean and found something that seems a bit startling; extra plates! Underneath the North Pacific there are what appear to these authors to be multiple old, subducted plates, and there are other fragments of plates deep beneath North America.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">If the authors’ identification of these plates is correct…that means there was more subduction happening in what is today the Pacific Ocean than anyone thought. Subduction within oceanic plates tends to create island arcs; the same type of material seen off the coast of Asia today in the Philippines or Japan, and the same type of material that was repeatedly accreted to North America.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">This work might give an answer for why there is so much stuff stuck to North America. If the simple “Pacific-Kula-Farallon” model was much more complicated, if the Farallon plate was broken into many pieces with subduction zones in-between, that could create the island arcs that slammed into North America and became the accreted terranes. The authors actually give names to some of these subducted plate fragments: the Angayucham and Mezcalera plates. They could have even played a very important tectonic role; if they were attached to North America while they were being subducted, they could have applied a force to the continent that helped open up the Atlantic Ocean 200+ million years ago.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">It’s an interesting story and one that will be worked on, particularly now that things have names (that always helps!). If the story is right, it’s one that can only be told using information trapped a thousand kilometers deep in the Earth’s mantle. From the surface, all we can see is that North America is a mess, but maybe for once the mantle has made things simpler and told a story we’d otherwise never see.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">-JBB

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">Photo Source, public domain photos provided by the National Park Service: <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;"> @http://www.nps.gov/common/uploads/photogallery/akr/park/wrst/3BF3A378-1DD8-B71C-07A66530C4E13429/3BF3A378-1DD8-B71C-07A66530C4E13429-large.jpg

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">Full paper: <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;"> @http://www.nature.com/nature/journal/v496/n7443/full/nature12019.html

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">News & Views summary: <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;"> @http://www.nature.com/nature/journal/v496/n7443/full/496035a.html

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;">Sciencedaily article: <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 11.199999809265137px;"> @http://www.sciencedaily.com/releases/2013/04/130403141402.htm



<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">SAN ANDREAS FAULT: Caution! Fault Crossing Road!

<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">We geologists love it when a road-cut opens up some fascinating display of the earth showing off, and this panoramic photo shows one of the most tremendous displays of tectonic forces visible anywhere on the earth: a cross-section through the San Andreas Fault.

<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Forces? What is a tectonic force, anyway? <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">The pushing and shoving of the tectonic plates are a kind of force that are not easily transmitted through solid rock – just push against a solid wall and you can feel the force of your push, but not much happens to the wall. Tectonic plates are far more massive than you, and they keep on pushing for millions of years. Now imagine trying to bend one of the bricks in the wall into one of the squiggly shapes observed along this roadcut, and you can begin to envision the power of tectonic movements. When deformed by the San Andreas fault, the rocks in this outcrop were fully lithified and about as strong as bricks.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">The tectonic forces responsible for the San Andreas date to about 30 million years ago with the “consumption” of the Farallon Plate beneath North America and change in orientation of plate collision (try our recent post @http://tinyurl.com/dy8nn83 for a summary of the regional geology): by about 20 million years ago, the forces between the Pacific and North American plates began to move in a horizontal fashion, developing a right-lateral movement zone at the plate boundary – the “proto” San Andreas fault. Today’s expression of the fault dates to about 5 - 10 million years in age and averages a rate of motion on the order of ~5 cm/year.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Whatever rocks get caught up between these moving plates become the folded, distorted, broken, stretched, and strained mash-up observable along this ~600m long road cut. Here, the Pacific Plate and North American plates themselves are occluded by younger sediments deposited over and covering the fault zone; the rocks of the roadcut consist of sandstones and gypsum-bearing clays of Pliocene age (~5 – 2.5 million years old). The plates are moving down below, and the trace of their boundary is translated through these surface sediments as an immense rupture, the San Andreas. These covering sediments have been greatly deformed by the fault movement, folded and cut by numerous sub-faults. To the right of the panorama, a “sag pond” is visible (sag ponds are water-filled depressions that develop within broad fault zones, though this one is now also used as a reservoir).

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Running ~1300km NNW across California, the San Andreas is one of the world’s best known, most highly studied, and seismically dangerous faults.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Annie R <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Photo by Adriano DeFreitas: Panorama of the San Andreas fault exposed in roadcut along the California SR14 highway: used with thanks, and thanks as well to Moorpark College. http://www.edmar-co.com/adriano/field/VasquezRocks/vasquez.html

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">More information on the San Andreas and on the Palmdale roadcut at: <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> http://pubs.usgs.gov/gip/earthq3/move.html <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> @http://academic.emporia.edu/aberjame/student/nester1/images.htm <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> @http://seismo.berkeley.edu/blog/seismoblog.php/2008/12/09/beware-fault-xinghttp://strike-slip.geol.ucsb.edu/KESSEL/palmdaleroadcut.html

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">. <span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Trading obsidian in worlds old and new.

<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Obsidian is a silica rich volcanic glass that has been prized for millennia because it can easily be shaped into a point, thanks to its property of conchoidal fracture (shaped like a shell). Its use in tools dates from the lower Palaeolithic, 2.6-1.7 million years ago, long before the appearance of modern humans. Being easier to work than flint, easy to car <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">ry and high in value, it was probably the first trade item in history. Since it has only limited sources, wherever a felsic volcano has erupted and the lava has rapidly cooled to a glass, it is widely used to trace early exchange networks.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Peoples who lived near a source became rich from it, and one of the earliest known towns, Catal Huyuk (7500-5600 BCE) in modern Turkey was built upon the resulting wealth. Obsidian was also passed around in the Americas soon after man's currently recognised arrival. Some of these prehistoric exchange networks are now emerging from the fogs of time, with a little help from Archaeology's friends in the Earth sciences.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Geochemical fingerprinting of volcanic rocks for both major and trace elements is a standard tool of Earth science. Back in the 1960's, Colin Renfrew (Britain's most influential prehistorian of the last century) realised that this could be used to trace distribution routes, and be of particular importance in prehistoric studies. The abundance of obsidian artefacts in excavations worldwide set Renfrew onto his idea in the first place. It is plentiful, easily traced and can be analysed non-destructively. This idea had been applied worldwide by many archaeologists, and this method is now a standard tool of the discipline.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">The analysis is done using a LAICPMS (explained in the first part of this series at http://tinyurl.com/c9nba7f ) for trace elements and X-ray fluorescence for the major elements. This last methods bombards the sample with radiation to excite the electrons within. These electrons absorb the energy of the rays and jump to a higher energy level. When they fall back to their default state each element gives off radiation of a characteristic wavelength. A spectrometer then measures and collates these, and delivers a printout of the samples relative elemental composition.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Meaningful data from the Paleolithic is more scarce, as the world was less densely populated, peoples nomadic and artefact finds more isolated. The Neolithic era starting in 11000 BCE saw the first towns appear, including Jericho and Catal Huyuk. It was a time of early agriculture and evolving trade in the Near East, with obsidian the main long distance good. It was used for both hunting and agricultural implements, as well as luxury goods like mirrors. A bit earlier in the Americas, similar trade in this raw material for tool making was starting with the Clovis culture, spreading out from the obsidian sources in the west.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Obsidian distribution networks have been traced all over the Americas, from California and Oklahoma to the southern cone in Argentina. It allows us to trace movement patterns, and by dating artefacts using C14 from associated organic remains such as charcoal, to learn how sources us changed over time. In some periods all the obsidian used was local, at others some pieces came from far away.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">In the Mediterranean there are several major sources, each with its own dispersion pattern. They include some of the Greek islands, Sardinia, Cappadocia and Anatolia (Hassan Dag being the volcano near Catal Huyuk). They can be distinguished from each other using trace elements such as yttrium, barium and zirconium. In Sardinia and Melos, the changing pattern of use of different lava flows as sources has also been traced, along with the different places each of these were traded to.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Using Sardinia as an example, three main sources were exported, called SA, SB and SC. Southern France liked using SA (95%), while SC was more common in Northern Italy (50%). The reasons for these preferences are unknown. Maybe they reflect choice at the customer end, or that they follow the routes chosen by different traders using one source and travel pattern.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">In Anatolia the two main source areas had different routes and dispersion patterns, which evolved through time. Experts theorise that in all early obsidian trade, hunting parties played a big part in the physical movement of goods. The trade evolved from a limited amount in the early Paleolithic through to agricultural tools in early pre-metalworking farming communities. The routes widened from lines along the coasts and rivers to a more trellis like pattern over time, eventually covering the whole Levant (Lebanon, Syria) as far as the Euphrates river in modern Iraq.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">As the technology has gotten cheaper, analysis of the entire excavated artefact assemblage from a site has become more common, allowing us to recognise the occasional piece from further away. Before, when only a few pieces per site were analysed, the sample chosen might not have been representative. Combined with stratigraphy it allows us to constrain when a source was exploited.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">The use of obsidian fades during the transition from hunter gathering to agriculture as metals began to spread, and these imported artefacts gradually disappear from the archaeological record. Long distance exchange networks begin to be replaced by trade, mediated by money as societies began to differentiate out of the Neolithic into the copper and bronze age.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Loz

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Image: Obsidian Clovis point, USA, circa 11000BCE, made from Black Tank obsidian sourced 50 miles away.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Credit: Dan Boone/Rvan Belknap

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> http://geokult.com/2011/06/26/hasan-dag-and-catal-huyuk/

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> http://shell.cas.usf.edu/~rtykot/PR22%20-%20AccChemRes%202002.pdf

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> http://shell.cas.usf.edu/~rtykot/PR91%20Tykot%202011.pdf

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> http://www.archatlas.org/ObsidianRoutes/ObsidianRoutes.php

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> @https://inlportal.inl.gov/portal/server.pt?open=514&objID=1269&mode=2&featurestory=DA_164833

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> @http://goafar.org/AFAR/Reading_files/Obsidian-The%20Metal%20of%20the%20Maya.pdf

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> <span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">VASQUEZ ROCKS: The World’s Poster Child for Tectonics

<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Located about 40 km north of Hollywood, California and 15 km southwest of the San Andreas Fault are some the world’s most recognizable rock formations; these are the rugged San Vasquez Rocks.

<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">The stones themselves are rather unremarkable on first sight: basically, they’re sandstones of about 25 million years of age with a fairly strong tilt, <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> dipping away from a larger anticline. Okay, there are many Oligocene rock formations scattered around the earth with similar tilts and folds. The Vasquez Rocks contain clues to their depositional environment with ample mudcracks, ripple marks, crossbeds and graded beds – always geological fun to find in the field, but by no means rare phenomena. Their rugged topography is due to differential erosion; okay, so what else is so outlandish that these rocks deserve such special tectonic recognition?

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">The North American Plate was once separated from the Pacific Plate by another plate named the Farallon. About 25 million years ago (yes, the same age as the Vasquez sediments), the Farallon plate was over-ridden by the North American Plate and subducted to great depths (you can see a series of cross-sections of these tectonic motions on our recent Earth Story post: http://tinyurl.com/c6jq4yj ). Below and within the sedimentary rock formations of Vasquez are basalts; these basalts intruded into the broken cracks and fractures forming above this subducting plate. The relentless movement of the North American Plate continued, and continues still, with the San Andreas fault zone now taking the place of a plate contact between the North American Plate and Pacific plate. The early days of the Vasquez formation records this phase of geologic history, and its sedimentary record includes several mega-cycles of uplift, erosion, and deposition as the new plate margin evolved. A Google Earth view of the Aqua Dulce area shows the anticlinal form of the outcropping Vasquez Rocks as a product of motion between the North American Plate and Pacific Plate along the San Andreas fault.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Perhaps you’re scratching your head at this point, and wondering where on earth you've seen these rocks before? In addition to seeing them “on earth,” they’re also highly visible amongst alien planets. Being conveniently accessible to movie and TV studios, as well as being fairly easy for actors and camera crews to scramble over, the Vasquez Rocks are filmed so frequently as to have become an icon for several Star Trek episodes, Bonanza, and have been used as stunt doubles for Tibet, Egypt and other desert countries.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">So, the next time you’re watching the TV and the Vasquez Rocks are featured, remember that they’re not famous only for the battle between Captain Kirk and the Gorn, but also as a geologic landmark known the world over.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Annie R

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Photo: from Wiki Commons by a photographer who identifies him/herself as hear2heal: <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Thanks to the Tectonophysics Page for reminding me how special these rocks are: @https://www.facebook.com/TectonophysicsOfficial?fref=ts

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">More information on the World’s Most Highly Recognizable Tectonic Locality: <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> @http://geology.campus.ad.csulb.edu/VIRTUAL_FIELD/Vasquez/vasqmain.htm <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> @http://www.edmar-co.com/adriano/field/VasquezRocks/vasquez.html <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> @http://www.scvresources.com/geology/aguadulce/

<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">The Creeping Imperial Fault

<span style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Southeast of the Los Angeles basin and due East from San Diego lies California’s Imperial Valley. It is heavily irrigated, as you see from the small irrigation ditch featured in this photo. The land is quite flat and has been filled in with sediment from the Colorado River. Thanks to irrigation channels leading from the Colorado, the area has become a rich area for gro <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">wing plants and vegetables.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">But, many unseen geological features lurk beneath the surface of the Imperial Valley. The San Andreas Fault enters the northwestern tip of this Valley, but then breaks off into a couple different segments along the coastline of the Salton Sea. South of the Salton Sea, the fault reorganizes into a system that travels into Mexico known as the Imperial Fault.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">In this photo of what appears to be a simple Imperial Valley irrigation ditch, you’ll notice that the concrete has cracked and there are plants growing through the concrete along these fractures.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">This irrigation ditch sits directly atop of the Imperial Fault. This picture was taken from the “North American” plate side of the fault, looking across at the Pacific plate, so the land to the top of this image is moving to the right relative to the viewer (the San Andreas system being a right-lateral fault).

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">The fault hasn’t had a major earthquake since a magnitude 6.4 event in 1979, which happened before this channel was built, but it’s still there and still slowly creeping. Concrete doesn’t handle shear stress very well, so here it’s cracking due to that slow motion. The Fault hasn’t had large motions since 1979, but it still creeps along, allowing very subtle motions to take place while the stress builds up that will eventually drive a larger earthquake.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">This fault also offsets a nearby rail line and telephone poles, some of which were built before the 1979 quake and are offset by a meter or more. There is also, for some reason, a buried high pressure gas line at this location.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">-JBB

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">Image credit: Me, image owned by the author of this post.

<span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;">1979 Earthquake details: <span class="text_exposed_show" style="background-color: #ffffff; color: #333333; font-family: 'lucida grande',tahoma,verdana,arial,sans-serif; font-size: 12.800000190734863px;"> @http://www.data.scec.org/significant/imperial.html

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<span style="background-color: #ffffff; color: #171717; font-family: Arial,Tahoma,Verdana,Helvetica,sans-serif; font-size: 14px;">This incredible shot was submitted by photographer Andrew Hara to //National Geographic’s//‘Your Shot’ column this week. <span style="background-color: #ffffff; color: #171717; font-family: Arial,Tahoma,Verdana,Helvetica,sans-serif; font-size: 14px;">Based in Hawaii, Hara was legally able to get close to the red-hot lava of the Kilauea Volcano because of his volunteer position in the Hawaii Volcanoes National Park, where this relatively young volcano is situated. To get there, he had to cautiously hike through a closed-off area of the national park and don a respirator to protect himself from the volcanic ash. Then he drew in closer for this one-in-a-million selfie. <span style="background-color: #ffffff; color: #171717; font-family: Arial,Tahoma,Verdana,Helvetica,sans-serif; font-size: 14px;">“I carefully set the timer for two minutes and walked around to the farther, visually stable edge of the crater to create this self-portrait,” Hara told // National Geographic .// “It is quite an experience when Earth feels incredibly large and one feels microscopic and insignificant in comparison." []

BELL MOUNTAIN, APPLE VALLEY CA: =[|BELL MOUNTAIN]= media type="custom" key="27790647" =Japan 2011 Tsunami:= =[|How Collective memory saved lives during the 2011 tsunami]= media type="custom" key="27790655" =Early Earthquake Warning App= =[|Early Earthquake Warning App]=

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=Plate Boundary Map:= media type="youtube" key="aaL-S88hZys" width="560" height="315" =[|Plate Boundary Map]= [|Newport Inglewood Fault] media type="custom" key="27765841"