What Is an Earthquake? ISCI 2001 Chapter 27 Environmental Geology Earthquakes typically occur at plate boundaries. Earthquakes occur where stressed and deformed blocks of rock are held together by friction. When stress in rock exceeds the friction holding sections of rock together, the rock slips or breaks. This slippage or breakage of rock is an earthquake. What Is an Earthquake? Elastic energy stored in deformed rock is released in the form of seismic waves, mechanical waves similar to shock waves or sound waves. Some seismic waves travel through the Earth, while other seismic waves travel at its surface. Earthquake Vocabulary Seismology: the study of earthquake waves Seismic waves: mechanical waves that distribute the energy released in an earthquake. There are two types: body waves and surface waves. body waves are further classified as S waves and P waves. Focus: the site of the original displacement of rock in an earthquake Earthquake Vocabulary Earthquake Vocabulary Fault: a fracture where rocks on either side have moved relative to one another. Epicenter: the point at Earth's surface directly above an earthquake focus Intraplate quake: an earthquake that occurs away from plate boundaries 1
Earthquake Waves Earthquake Waves New Madrid Earthquake The earthquake occurred in 1811 1812 in New Madrid, Missouri. It was a rare high magnitude, intraplate quake. There were three major quakes with aftershocks. The topography was altered. Over 150,000 acres of forest were destroyed. New Madrid Earthquake There was little loss of human life and property due to sparse settlement of the area at the time. This is an example of a natural event that didn't become disastrous to humans. Why? People were not in the path of destruction. Earthquake Prediction Earthquake Prediction Methods: Measure strain in rocks Map seismic gaps Probabilities of Occurrence (Hazard Maps) Prediction allows risk to be identified within a broad timeframe (30 100 years). 2
Earthquake Prediction Earthquake Measurement Moment magnitude scale Measures energy released in an earthquake Favored by geologists Richter scale just one of several log based scales Measures ground shaking Favored by media Seismometers measure Richter magnitude Earthquake Measurement Tsunami A tsunami is a huge seismic sea wave. is a large, fast moving mass able to travel as far as a mile or more inland. is destructive because it strikes objects on shore with enormous mechanical force. can cause secondary effects. An example is the 2011 tsunami in Japan that damaged the Fukushima Daiichi nuclear power plant. Tsunami Mechanics Tsunami are triggered by a large disturbance, such as a subduction earthquake. Tsunami occur at subduction zones. As a descending plate slips, the overlying plate is deformed. When friction can no longer hold the deformed overlying plate in place, it springs upward. This motion of the overlying plate produces a shock wave or tsunami that propagates across the ocean. When a tsunami reaches shore, it is compressed so that its amplitude greatly increases and its wavelength decreases. It becomes a high speed wall of water. Damage occurs as the tsunami moves on land. 2004 Tsunami A strong tsunami occurred on December 26, 2004. It is called the "Boxing Day" tsunami after the holiday of the same name. A historic magnitude 9.1 subduction earthquake off the coast of Sumatra in Indonesia triggered the Boxing Day tsunami. Tsunami are heavy and fast, so they have enormous momentum and energy. The 2004 tsunami released more energy than all the bomb blasts of World War II. The 2004 tsunami was one of deadliest natural disasters in history. Over 200,000 people were killed in 14 countries. It was the deadliest tsunami ever. 3
2004 Tsunami (a) The December 26, 2004, tsunami began with a strong subduction earthquake off the coast of Sumatra. (b) The tsunami strikes a coastline in Sri Lanka. 2011 Tsunami On March 11, 2011, a 9.0 magnitude earthquake struck off the coast of Japan. The huge earthquake moved Honshu (the main island of Japan) 2.4 m (8 ft) east. It triggered a powerful tsunami that reached heights of over 40 m (130 ft). The tsunami caused meltdowns at three nuclear reactors in the Fukushima Daiichi nuclear power plant complex. The radiation leak required evacuation within a 12 m (20 mile) radius. Volcanoes Volcanoes are essentially vents that allow heat to escape from Earth's interior. Erupted magma is called lava. There are three types of magma: basalt, andesite, and rhyolite. Andesitic and rhyolitic lavas are thicker than basaltic lavas. They can clog a volcano's vent and produce an explosive eruption. Three Kinds of Volcanoes Shield Composite (also called stratovolcano) Cinder cone Appearance Comparison of Volcano Types Shield Composite Cinder Cone Broad and low elevation Plate setting Hot spot in ocean floor Steep-sided and tall Subduction zone or hot spot Steep-sided but small Independent or inside another volcano Type of lava Basalt Basalt and andesite Basalt and andesite, rarely rhyolite Main hazards Toxic gases and lava Toxic gases, lava, pyroclastics, ash Pyroclastics 4
The Ring of Fire The Ring of Fire is a ringshaped region surrounding the Pacific Plate. contains active subduction zones throughout the region. is home to over 75% of the world's volcanoes and 90% of the world's earthquakes. incorporates the West Coast of the United States. Important Volcanic Eruptions Throughout History Eruption at end of Permian period (250 million years ago) lasted for millions of years; triggered climate change; caused a mass extinction that wiped out 90% of life on Earth. Island of Krakatoa in Indonesia was site of explosive eruption in 1883; heard thousands of miles away; triggered tsunami; over 30,000 people killed; Krakatoa completely destroyed. Mt. Thera, Island of Santorini, Greece; 1610 BC; energy release equal to several hundred atomic bombs over a period of less than a second; no written records but probably the strongest explosion ever witnessed by people; altered climate; disrupted human culture; ash deposits 100 feet thick found within a 19 mile radius from the caldera. Important Volcanic Eruptions Throughout History Mt. Tambora, Indonesia; 1815; largest explosion witnessed by people, according to written records; death toll estimated at 71,000 people; summer in 1815 "canceled" in North America and Europe. Yellowstone National Park is situated over a hot spot; three huge calderas in park; oldest caldera is over 60 miles wide and 2 million years old; one formed in a volcanic eruption that produced 600 cubic miles of rock and ash; cooled climate; deposited ash layer covered much of the land area that is now the western and midwestern United States. Mt Vesuvius is the only active volcano in mainland Europe; erupted in 79 AD destroying the Roman cities of Pompeii and Herculaneum; victims buried alive in ash fall. Hurricane Facts A hurricane is a large rotating weather system around a lowpressure zone. Hurricane winds blow over 119 km/h (74 mph). Hurricanes can travel thousands of miles. Hurricanes range from 150 km to 1500 km in diameter. The "eye" (center) of a hurricane can be up to 32 km (20 miles) across. In the "eye," weather is calm with low winds and clear skies. Hurricane Facts Classification of Hurricanes Most of the deaths that occur during hurricanes result from drowning in floods. A hurricane weakens rapidly after it strikes land. Because hurricanes need warm, moist air, hurricane season begins in late summer. The intensity of a hurricane is measured on the Saffir Simpson Scale. This scale measures the wind speed and air pressure of the storm. Based on these characteristics, a hurricane is ranked with a number between 1 and 5. Category 3, 4, or 5 hurricanes are dangerous. 5
Anatomy of a Hurricane The low pressure center of a hurricane is its "eye." Moist air spirals around the eye and is sucked upward across a pressure gradient. The extent of bands of thunderstorms, rain, and wind determines the size of the hurricane. Formation of a Hurricane A hurricane begins to form over warm, moist water, generally in the tropical zone. Water evaporates, rises as water vapor, then condenses to form thunderclouds. Warm, moist air is continually sucked into the low pressure zone below the clouds. Huge collections of thunderclouds develop. The system gains energy as water vapor condenses to form clouds. The energy released by the water vapor when it condenses is called latent heat. Latent heat fuels the hurricane, driving the motion of clouds, rain, and wind. Formation of a Hurricane The Coriolis effect turns the spiral shaped weather system around its low pressure center. The hurricane dies soon after it leaves the open ocean because it no longer can absorb large quantities of warm, moist air. Hurricane Katrina Hurricane Katrina was the costliest hurricane in the history of the United States, with $75 billion in estimated damages. Over 1800 people were killed. There were sustained winds during landfall of 125 mph. The storm surge breached the system of sea walls around New Orleans, so that Gulf waters flooded the city. There was widespread devastation along the central Gulf Coast states. New Orleans, LA, Mobile, AL, and Gulfport, MS, were the cities most affected by Katrina's force. Hundreds of thousands of local residents were left unemployed. Hurricane Katrina (a) Hurricane Katrina in the Gulf of Mexico on August 28, 2005. (b) Hurricane Katrina hammered the city of New Orleans with a 20 ft storm surge. New Orleans sits below sea level and has been protected from flooding by an engineered system of levees and sea walls. But, when the hurricane battered these barrier walls, the structures gave way and seawater rushed into the city. The floodwaters, filthy with floating debris, remained trapped like soup in a bowl within the city walls until the water could be drained.] What Is Climate Change? Weather is the state of the atmosphere at a particular time. Climate is the average weather over several decades or longer. Climate change is a lasting alteration to average weather conditions so that new patterns of temperature, precipitation, humidity, and so on, become established. Climate change also can involve a change in the frequency of extreme weather events over a long (decades or more) time period. 6
Climate Change in Geologic History Climate Change in Geologic History The geologic time scale divides Earth's 4.6 billion year history into time units of different size. Most divisions of the time scale mark major turning points in geologic history or the history of life. The Permian period closes with the Permian extinction, the most severe in history. The Cretaceous period ends with the Cretaceous extinction, the demise of the dinosaurs. Both mass extinctions were a result of climate change. Geologic history shows that climate change can be catastrophic! Ice Ages Earth is now in an interglacial, a period within an ice age. Ice ages are rare in Earth's history. An ice age is a period with cold enough global average temperature that there's extensive glaciation. An interglacial is a pulse of warmer temperatures within an ice age such that glaciers melt back to high latitudes. Humans have existed only within an ice age. Civilization developed in an interglacial period. How will civilization adapt to the climate change that is occurring now? Natural Climate Change Natural drivers of climate change: Solar output (e.g., sunspots) Interactions with space objects (e.g., asteroid impacts) Earth Sun geometry (e.g., Milankovich cycles) Atmospheric chemistry (e.g., greenhouse effect) Volcanic emissions (e.g., end of Permian period) Albedo (e.g., albedo increases during ice ages) Ocean atmosphere interactions (e.g., deep water currents are altered as ice caps melt) Plate tectonics (e.g., positioning of the continents over the equator correlates with higher temperatures due to higher specific heat capacity of water) Albedo: A Factor in Temperature Albedo is a measure of surface reflectivity. Albedo depends on the color and chemical composition of a material. The Greenhouse Effect Short wave radiation from the Sun passes through the atmosphere and is absorbed at Earth's surface. Earth absorbs the short wave radiation and in turn emits long wave (infrared) radiation (also called "terrestrial radiation"). The atmosphere is opaque to long wave radiation because certain atmospheric gases (greenhouse gases) absorb it. The infrared radiation is trapped; that is, it is absorbed and re emitted many times by atmospheric molecules. This warms the atmosphere and is similar to what happens in a florist's greenhouse. 7
Anthropogenic Climate Change Evidence, including chemical analysis of the isotopes in atmospheric carbon dioxide, shows that most of the carbon dioxide in the atmosphere comes from burning fossil fuels. Carbon dioxide emissions from combusting fossil fuels have increased exponentially since the beginning of the Industrial Revolution, as the graph on the left shows. Anthropogenic Climate Change Atmospheric carbon dioxide and average global temperature have shown a close correlation for many thousands of years, as the graph on the right shows. Temperature changes slightly lag carbon dioxide changes. Effects of Climate Change The approximately 1 F increase in global climate has many effects on the world today, including raised sea level, melting sea ice, migration of species, disruption of ecosystems, agricultural effects, increased incidence of extreme weather, economic impacts, and thawing permafrost. The IPCC forecasts a temperature rise of 2.5 F to 10 F over the next century. Some predicted effects are listed in the table. What You Can Do About Climate Change Understand your impact. Consider how your actions and choices affect the climate. Make a difference in your local community and globally too! Work with others on the problem. Find ways to help that you enjoy and feel good about. Give yourself a pat on the back for helping to reduce climate change and protecting life on planet Earth! 8