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Lab 4 Natural Hazards - Earth Sciences 1081b 2011 Lab#4...

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Earth Sciences 1081b 2011 Lab #4: Natural Hazards Earth Sciences 1081b Lab 4: Natural Hazards: Earthquakes and Volcanoes (Background Pages for Lab) OVERVIEW Natural hazards occur every day around the world. They include events such as earthquakes, volcanoes, flooding, and storms. These events can occur suddenly or gradually over time. In order to help prevent excessive damage to the population and our surroundings, various properties specific to each event need to be monitored. Today’s lab will focus on earthquakes and volcanoes and the ways in which they are monitored. Earthquakes Earthquakes around the Globe Earthquakes are occurring all of the time, scattered around the world. The majority of these are quite small, < 2.0 M and go undetected. A global network of seismometers has been established with stations on every continent and several on the sea floor. This network detects and locates most earthquakes larger than 4.0 M and many smaller ones. To answer the questions for this lab, you can find out about recent earthquakes around the world from this web site: http://earthquake.usgs.gov/regional/neic/ Earthquakes in Ontario Earthquakes are an important hazard in many parts of the world. Fortunately for us, they tend to be concentrated along plate boundaries and are quite uncommon in our area. Southern Ontario has very few earthquakes, but it is important to understand where and how often they occur in order to plan for the safety of places such as nuclear power plants. Today we will look at how we determine where earthquakes have occurred and where earthquakes are most common. Earthquakes are propagated through the earth as vibrations. Sensitive instruments called seismometers measure these vibrations and translate them into records called seismograms. We can learn many things about earthquakes using these seismograms including: how far away they occurred, how large they were, and what kind of rock they travelled through. Figure 1: Example of a seismogram. http://www.scienceco urseware.org/VirtualE arthquake/VQuakeEx ecute.html
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Earth Sciences 1081b 2011 Lab #4: Natural Hazards An important principle used in studying earthquakes is that different types of vibrations travel at different speeds. P-waves travel by compression and are the fastest and therefore arrive first at any seismometer. S-waves travel by shear and are somewhat slower, arriving after the P-waves (see Figure 1). We use the difference in the arrival times and the knowledge of the speed of the vibrations to determine how far away an earthquake has occurred. As an example, we will here calculate how far away the epicenter of a small earthquake (that occurred at 6:28 am, on May 8, 1996) was located relative to a specific seismic recording station PKRO of the Southern Ontario Seismic Network on the map in Figure 2. Note the location of station PKRO (at Pickering) you will be referring back to it later.
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