Earthquake California: An investigative look at the forces ...



Earthquake California: An investigative look at the forces behind continental drift.Guiding Question: Will part of California eventually, over time break off into the Pacific Ocean? Explain.Background Research: CaliforniaBefore you read the article, think about the following:How fast are the plates moving?Where is the fault located?What direction are the plates moving? Is there any evidence about rocks to support your thinking?The San Andreas Fault is the boundary between the Pacific Plate and the North American Plate. It slices California in two sections from Cape Mendocino to the Mexican border. San Diego, Los Angeles and Big Sur are on the Pacific Plate, while San Francisco, Sacramento and the Sierra Nevada are on the North American Plate. Despite San Francisco’s legendary 1906 earthquake, the San Andreas Fault does not go through the city, however communities like Desert Hot Springs, San Bernardino, Wrightwood, Palmdale, and Bodega Bay lie squarely on the fault and are sitting ducks.The plates are slowly moving at a couple of inches a year, which is about the same rate that your fingernails grow. This is not a steady motion, it is the average motion. For years the plates will be locked with no movement at all. Suddenly the built-up strain breaks the rock along the fault and the plates slip a few feet all at once. The breaking rock sends out waves in all directions and it is the waves that we feel as earthquakes.In many places like the Carrizo Plain (San Luis Obispo County) and the Olema Trough (Marin County), the fault is easy to see as a series of scarps and pressure ridges. In other places, it is more subtle because the fault hasn’t moved in many years and is covered with alluvium, or overgrown with brush. In San Bernardino and Los Angeles Counties, many of the roads along the fault cut through great mountains of gouge, the powdery, crumbled rock that has been pulverized by the moving plates.The hallmark of the San Andreas Fault is the different rocks on either side of it. Being about 28 million years old, rock from great distances have been juxtaposed against rocks from very different locations and origins. The Salinian block of granite in central and northern California originated in Southern California, and some even say northern Mexico.My Notes:University Research: Types of plate boundariesRead through the passage, and complete the CDT (Convergent, Divergent, Transform) Table on the following page3218814901164There are three major ways plates can interact with one another. They could diverge, meaning they can move away from one another resulting in a divergent plate boundary, they can converge, meaning they move towards one another resulting in a convergent plate boundary, or they can move parallel to one another, resulting in a transform plate boundary. Each of these different interactions results in different consequences for Earth’s continental crust.The most common divergent boundaries are mid-ocean ridges. Shallow earthquakes and minor, basaltic lava flows characterize divergent boundaries at mid- ocean ridges. The seafloor at the ridges ishigher than the surrounding plain because the rocks are hot and thus less dense and more buoyant, riding higher in the underlying mantle. As the rocks move away from the spreading center, they cool and become denser and less buoyant. Typically, these types of plate boundaries only produce around 5% of all seismic energy released in a given year and recently determined that they have a moderate amount of volcanic activity.Convergent boundaries are the most geologically active, with different features depending on the type of crust involved. Typically, 90% of all seismic energy released by Earthquakes is resulted from convergent plate boundaries. These earthquakes tend to occur deeper in the crust than at other boundaries. There are different types of convergent plate boundaries, which are explained below.Oceanic meets continental are subduction zones, where dense oceanic crust is diving beneath more buoyant continental crust. These boundaries are characterized by a very deep ocean trench next to a high continental mountain range, large numbers of earthquakes and large numbers of volcanoes. Oceanic meets more oceanic occur when two plates converge along a boundary where the crust on both sides is oceanic, a subduction zone also occurs, but the result is slightly different. Since the densities of the two plates are similar, it is usually the plate with the older oceanic crust that is subducted (goes under) because that crust is colder and denser.Earthquakes progress from shallow to deep moving away from the trench like in the oceanic-continental convergence, and volcanoes form an island arc. Continental meets continental occurs when two pieces of continental crust converge, the result is a great pileup of continental material. Both pieces of crust are buoyant and are not easily subducted, resulting in large mountain ranges.Transform plate boundaries occur when 2 plates move horizontally past one another. This is a very rare occurrence on continents and makes up only about 5% of all seismic energy released in any given year. Not many volcanoes are found in this region due to the movement of the plates and most earthquakes that occur are very shallow. A transform plate boundary is typically marked in some places by linear valleys along the boundary where rock has been ground up by the sliding. In other places, transform boundaries are marked by features like stream beds that have been split in half and the two halves have moved in opposite directions.While completing the chart below, fill in what features you would find at these types of boundariesConvergentDivergentTransformUSGS Research: DataYou are provided with data for 3 locations, Chili in South America (Pacific Ocean side of South America),Reykjanes Ridge (In the Atlantic Ocean, North to Iceland), and California. All data shown indicates every major earthquake in the region with a magnitude of 6.5 or greater from 1930 – 2014.LocationNumber of EarthquakesAverage DepthAverage MagnitudeChili, South America11354 km7.0Reykjanes Ridge, Iceland416 km6.7California, United States137 km6.8Geological Survey (Map) Data4572006729Figure 1 to the left shows the area of Chili studied for this data set in table 3. Each triangle indicates an active volcano along the fault zone.Figure 2 (below) shows the current active volcanoes in the California region. Each dark triangle indicates an active volcano. Pay attention to the linear valley (Sierra Nevada Mountains) along the location near the San Andreas Fault- it aligns with the volcanoes.21920201812394297679258316Figure 3 to the right indicates all tectonic plates and their names for reference. The locations of these plates have changed over the years due to continental drift as a result ofearthquakes. 200-300 million years ago, the Earth’s surface looked quite different, known as Pangea. All of the continents at this time were combined, forming one super-continent.45720026081Figure 4 to the left shows the location of Iceland in the middle of the Atlantic Ocean. Running through the middle of the island is the Reykjanes Ridge, which is part of a mid ocean ridge. A mid ocean ridge occurs when two oceanic plates are at a divergent plate boundary.457200219878Figure 5 (above) is from the USGS, indicating the average depth of all earthquakes from 1975-1995.Investigative Reporting from National GeographicRift Valley versus Mid-Ocean RidgesA rift valley forms where the Earth’s crust, or outermost layer, is spreading or splitting apart. This kind of valley is often narrow, with steep sides and a flat floor.Rift valleys differ from river valleys and glacial valleys because they are created by tectonic activity and not by the process of erosion.Rift valleys are created by plate tectonics. Tectonic plates are the huge rocky slabs made up of the Earth's crust and upper mantle. Where plates move apart, the Earth’s crust separates, or rifts. Rift valleys can lead to the creation of entirely new continents, or deepen valleys in existing ones.Many rift valleys have been found underwater, along the large ridges that run throughout the ocean. These mid-ocean ridges are formed as tectonic plates move away from one another at divergent plate boundaries. As the plates separate, molten rock from the Earth’s interior may well up and harden as it contacts the sea, forming new oceanic crust at the bottom of the rift valley. In order for a rift valley to be considered a mid-ocean ridge, it must be a divergent plate boundary at 2 oceanic plates.This occurs along the northern crest of the Mid-Atlantic Ridge (Reykjanes Ridge), where the North American plate and the Eurasian plate are splitting apart. The Mid-Atlantic Ridge rifts at an average of 2.5 centimeters (1 inch) per year. Over millions of years, the Mid-Atlantic Ridge has formed rift valleys as wide as 15 kilometers (9 miles).3790950302587In the Pacific Ocean, the East Pacific Rise has created rift valleys where the Pacific plate is separating from the North American plate, Riviera plate, Cocos plate,Nazca plate, and Antarctic plate. (The Pacific plateisthe largest on Earth.) Like many underwater rift valleys, the East Pacific Rise is dottedwith hydrothermal vents. The geologic activity beneath the underwater rift valley creates these vents, which spew super-heated water and sometimes-toxic vent fluids into the ocean.There are only two rift valleys on Earthwithin continental crust, the Baikal Rift Valley andtheEast African Rift (Right). Tectonic activity splitscontinental crust much in the same way it does along mid-ocean ridges. As the sides of a rift valley move farther apart, the floor sinks lower.The deepest continental rift valley on Earth is the Baikal Rift Valley in the Siberian region of northeastern Russia. Lake Baikal, the deepest and oldest freshwater lake in the world, lies in the Baikal Rift Valley. Here, the Amur plate is slowly tearing itself away from the Eurasian plate, and has been doing so for about 25 million years. The deepest part of Lake Baikal is 1,187 meters (3,893 feet), and getting deeper every year. Beneath this is a layer of soft sediment reaching several kilometers. The actual bottom of the rift extends about 10 kilometers (6.2 miles) deep.So, what is the difference between a rift valley and a mid-ocean ridge?Research ExpectationsYour group is to furnish a report, answering the guiding question, “Will part of California eventually, over time break off into the Pacific Ocean?” Your report must include only data derived from the previous 6 pages of information including the background research, university research, USGS Data, Geological Survey Data, and Investigative Reporting Data. No other outside sources may be used. All statements must be supported by data included on those 4 pages, and online sources. All resources must be documented. Speculation and opinion are not allowed. Your report must follow the claim/evidence/justification model as indicated below.Your ReportIn Background Research of California, where is the fault located?Does the fault run through any major cities?What information do you know about the rock formations?How much does the fault move each year?In University Research, have the students identify what the 3 different types of plate boundaries are.Where is most of the energy from an Earthquake released? (What type of plate boundary?)What can the reading tell us about the volcano locations?What does the reading tell us about the depth of an earthquake?Evidence:All data collected over the course of the lab goes in this box. This data can include (but not limited to)Data from data tables (you may not want the entire data table, but you could average the data or make a generalization)Data from Maps (You can copy a section of the map and highlight it here)Key pieces of data from the readingsBackground research about CaliforniaJustification:Why your claim is correct in paragraph form while reflecting on the data. You MUST connect the evidence to your answer!The following KEY VOCABULARY must be included:ConvergentDivergentTransformMid-ocean ridgeSea floor spreadingVolcanoes or Mountain BuildingContinental DriftGuiding Question: Will part of California eventually, over time break off into the Pacific Ocean?Our Claim: This is where your answer to the question goes after completion of lab. ................
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