Module 2, Investigation 1: Earthquake Hazards Introduction Welcome! In the last module, you assumed the role of a volcanologist and learned how volcanoes are described and monitored. You will now assume the role of a seismologist and study how earthquakes affect the Earth. Seismologists are constantly trying to understand earthquake behavior in order to help communities prepare for and respond to earthquakes. You will begin by exploring some of the world's most notorious earthquakes. You will make observations and measurements to examine the different ways that earthquakes have affected people throughout history. You will also consider what factors influence how much damage an earthquake might cause. In the last module, you learned how to use the ruler tool. Don't forget to use this tool whenever you need to make a measurement. Folder 1: Describing Earthquakes 1 Earthquake Anatomy Earthquakes result from the sudden release of energy that is stored within the Earth. The release of energy can occur at various depths below the Earth s surface. This spot in the Earth is called the focus or hypocenter of the earthquake. The spot on the surface of the earth directly above the hypocenter is called the earthquake epicenter. For future reference, record the meanings of these new terms in your field notebook.
Folder 1: Describing Earthquakes 2 Earthquake Magnitude and Intensity People often describe earthquakes according to their magnitude and intensity. Magnitude (M) relates to the amount of energy released at the earthquake's hypocenter. Each earthquake has only one magnitude. Today, scientists use seismograph* data to assign magnitude values according to the Moment Magnitude Scale (MMS). On this scale, each higher number represents an order of magnitude increase in energy, so that an M 9.0 earthquake is much larger than an M 8.0 earthquake. *Refer to your notes on Mount Rainier in the Introduction to Volcanoes module if you can't remember what a seismograph is. Intensity is the severity of an earthquake's effects on the Earth's surface, people, and buildings, which varies from place to place. Because someone's opinion of what they felt during an earthquake can be subjective, scientists have developed the Mercalli Intensity Scale to help calibrate different people's observations, making them more objective. The Modified Mercalli Intensity Scale allows you to assign an intensity value from 1 to 12 according to specific things that happen during the earthquake. Click here to see the Mercalli Intensity Scale. For future reference, record the meanings of the new terms presented in this placemark, including the difference between magnitude and intensity. Folder 2: Shaanxi, China Shaanxi, China In the 16th century, China s economy was booming under the Jiajing Emperor of the Ming Dynasty. On the morning of January 23rd, 1556, without warning, east-central China experienced the deadliest earthquake in recorded history. The epicenter of the estimated M 8.0 earthquake was in the Weihe River Valley in the province of Shaanxi.
Ancient texts record structural damage to homes and temples. Timber frame construction was becoming well developed during the Ming Dynasty, and brick was regularly used in home building. Municipal buildings and temples were typically constructed out of stone and brick. In the cities of Huaxian, Weinan, and Huayin, nearly every building was leveled, killing tens of thousands of people. The earthquake also triggered massive landslides (see video), which added to the estimated 830,000 deaths. Cracks up to 20 m (66 ft) deep opened up on the land surface. Turn on the Shaanxi Earthquake folder to see the geographic extent of the reported damage. Use your measuring tools to make the observations prompted in your field notebook. [Landslide video] Folder 3: San Francisco, California San Francisco, California On April 18, 1906, an M 7.8 earthquake hit the coast of California. The quake created a rupture from San Juan Bautista to Cape Mendocino. In many places, including the fence line in the photo below, the land surface shifted sideways several meters. Scientists were perplexed by these shifts, as well as by the sheer length of the below ground fracture. We will learn more about these fractures, which are called "fault ruptures", in the next investigation. The earthquake s epicenter was near the city of San Francisco. The event lasted less than a minute and included several strong jolts of movement, interspersed with violent shaking. People as far away as southern Oregon, Los Angeles, and central Nevada reported feeling slight vibrations. In San Francisco, many buildings collapsed, and fires caused by ruptured gas lines destroyed even more structures. In the end, approximately 3,000 people died and between 225,000 and 300,000 were left homeless. Click here to view the GigaPan image and explore all the close-up views.
In an analysis conducted shortly after the earthquake, scientists determined that the intensity of the shaking had varied from place to place. Buildings sitting on soft, unconsolidated sediments, like sand and mud deposits, shook more than did those sitting on bedrock. Areas along the shoreline that had been artificially filled in ( reclaimed ) by developers, in order to build more buildings, shook most of all. Turn on the San Francisco folder to see the extent of the rupture. Then open the Geology folder to see the extent of unconsolidated sediments and artificial fill. Try tilting your view to see how the geology relates to the topography. Consider this information and use the measuring tools to make the observations and interpretations prompted in your field notebook. Folder 4: East Indian Ocean East Indian Ocean On December 26th, 2004, an M 9.1 earthquake occurred in the East Indian Ocean. The earthquake was felt through the entire Bay of Bengal, and eastward to Thailand. The earthquake was accompanied by an enormous tsunami (see video). The tsunami killed more people than any other in recorded history. Estimates range from 180,000 to 230,000 deaths and from 1.0 to 1.7 million people displaced in South Asia and East Africa. [Tsunami video] The tsunami spread westward across the Indian Ocean, southward into the Southern Ocean, and westward to the coasts of Australia and New Zealand. Unusually large waves were also recorded along the coasts of North and South America. Turn on the East Indian Ocean folder to view the extent of the area affected by the tsunami and earthquake. Click here to view an animation of the 2004 East Indian Ocean Tsunami. Note that the waves travel out from the point of origin over a period of five hours. The blue color indicates wave crests; red indicates wave troughs. (Animation: National Institute of Advanced Industrial Science and Technology.) Use your Google Earth tools to answer the questions posed in your field notebook. Folder 5: Haiti (National Palace, Port-au-Prince) Haiti On January 12, 2010, an M 7.0 earthquake struck the island nation of Haiti. The vibrations were so intense that most of the buildings in the capital, Port-au-Prince, were leveled. The death toll is estimated at 222,000 people, with 1 million or more left homeless.
Explore the site using the Historical Imagery Timeline feature from the toolbar at the top of your screen (the clock icon). Observe how the National Palace in Port-au-Prince and surrounding areas changed because of the earthquake. Note the number of collapsed buildings. Can you see where people are living? The shaking intensity was not only felt by residents, it was also recorded by a network of seismographs. Scientists at the USGS have developed a method for using the data collected by these instruments within hours of the event to create maps of Modified Mercalli Intensity, called ShakeMaps. ShakeMaps average data to generate intensity estimates for areas in between stations. They are used by federal, state, and local organizations for post-earthquake response and recovery, public information, and scientific research, as well as for disaster planning. View the MMI Values folder to see the network of intensity measurements across Haiti and the Dominican Republic. (Double click on the folder to zoom to the appropriate view.) Next, turn on the USGS ShakeMap folder to see how these values are combined into a ShakeMap for easier viewing. Record your observations and interpretations in your field notebook. Going Further 2: Population Density Population Density First, turn on the Haiti Population Density folder. Then, turn on the USGS ShakeMap folder. Examine these overlays and answer the questions prompted in your field notebook. Summary Let's Reflect! In this investigation, you have visited the sites of some of the most infamous earthquakes on Earth. You ve read about how earthquakes are described, how they affect people and the landscape, and how various factors affect earthquake intensity. Now it is time to summarize what you ve learned about earthquakes in your field notebook. You will want to refer to these notes later.