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an earthquake in joules when Richter magnitude (M) is known: Energy in joules = 1.74 x 10(5 + 1.44*M) Figures 4 and 5 describe the spatial distribution of small and large earthquakes respectively. These maps indicate that large earthquakes have |
distributions that are quite different from small events. Many large earthquakes occur some distance away from a plate boundary. Some geologists believe that these powerful earthquakes may be occurring along ancient faults that are buried deep in the continental crust. |
Recent seismic studies in the central United States have discovered one such fault located thousands of meters below the lower Mississippi Valley. Some large earthquakes occur at particular locations along the plate boundaries. Scientists believe that these areas represent zones |
along adjacent plates that have greater frictional resistance and stress. Figure 4: Distribution of earthquakes with a magnitude less than 5 on the Richter Scale. (Image Source: PhysicalGeography.net) Figure 5: Distribution of earthquakes with a magnitude greater than 7 on |
the Richter Scale. (Image Source: PhysicalGeography.net) The Richter Scale Magnitude, while the most known, is one of several measures of the magnitude of an earthquake. The most commonly used are: - Local magnitude (ML), commonly referred to as "Richter magnitude;" |
- Surface-wave magnitude (Ms); - Body-wave magnitude (Mb); and - Moment magnitude (Mw). Scales 1 to 3 have limited range and applicability and do not satisfactorily measure the size of the largest earthquakes. The moment magnitude (Mw) scale, based on |
the concept of seismic moment, is uniformly applicable to all sizes of earthquakes but is more difficult to compute than the other types. All magnitude scales should yield approximately the same value for any given earthquake. The severity of an |
earthquake can be expressed in terms of both intensity and magnitude. However, the two terms are quite different, and they are often confused. Intensity is based on the observed effects of ground shaking on people, buildings, and natural features. It |
varies from place to place within the disturbed region depending on the location of the observer with respect to the earthquake epicenter while magnitude is related to the amount of seismic energy released at the hypocenter of the earthquake. Although |
numerous intensity scales have been developed over the last several hundred years to evaluate the effects of earthquakes, the one currently used in the United States is the Modified Mercalli (MM) Intensity Scale. The lower numbers of the intensity scale |
generally deal with the manner in which the earthquake is felt by people. The higher numbers of the scale are based on observed structural damage. Structural engineers usually contribute information for assigning intensity values of Vlll or above. The following |
is an abbreviated description of the 12 levels of Modified Mercalli intensity. I. Not felt except by a very few under especially favorable conditions. II. Felt only by a few persons at rest, especially on upper floors of buildings. Delicately |
suspended objects may swing. III. Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibration similar to the passing of a truck. |
Duration estimated. IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably. V. Felt by nearly |
everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop. Vl. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight. Vll. Damage negligible in buildings of good design |
and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken. Vlll. Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in |
poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. IX. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations. |
X. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent. Xl. Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly. Xll. Damage total. Lines of sight and level are distorted. Objects |
thrown into the air. Earthquake Damage and Destruction Earthquakes are a considerable hazard to humans. Earthquakes can cause destruction by structurally damaging buildings and dwellings, fires, tsunamis, and mass wasting (see Figures 6 to 10). Earthquakes can also take human |
lives. The amount of damage and loss of life depends on a number of factors. Some of the more important factors are: - Time of day. Higher losses of life tend to occur on weekdays between the hours of 9:00 |
AM to 4:00 PM. During this time interval many people are in large buildings because of work or school. Large structures are often less safe than smaller homes in an earthquake. - Magnitude of the earthquake and duration of the |
event. - Distance form the earthquake's focus. The strength of the shock waves diminish with distance from the focus. - Geology of the area affected and soil type. Some rock types transmit seismic wave energy more readily. Buildings on solid |
bedrock tend to receive less damage. Unconsolidated rock and sediments have a tendency to increase the amplitude and duration of the seismic waves increasing the potential for damage. Some soil types when saturated become liquefied (Figure 6). - Type of |
building construction. Some building materials and designs are more susceptible to earthquake damage (Figure 7). - Population density. More people often means greater chance of injury and death. The greatest loss of life because of an earthquake this century occurred |
in Tangshan, China in 1976 when an estimated 250,000 people died. In 1556, a large earthquake in the Shanxi Province of China was estimated to have caused the death of about 1,000,000 people. A common problem associated with earthquakes in |
urban areas is fire (Figure 8). Shaking and ground displacement often causes the severing of electrical and gas lines leading to the development of many localized fires. Response to this problem is usually not effective because shock waves also rupture |
pipes carrying water. In the San Francisco earthquake of 1906, almost 90% of the damage to buildings was caused by fire. In mountainous regions, earthquake-provoked landslides can cause many deaths and severe damage to built structures (Figure 9). The town |
of Yungay, Peru was buried by a debris flow that was triggered by an earthquake that occurred on May 31, 1970. This disaster engulfed the town in seconds with mud, rock, ice, and water and took the lives of about |
20,000 people. Another consequence of earthquakes is the generation of tsunamis (Figure 10). Tsunamis, or tidal waves, form when an earthquake triggers a sudden movement of the seafloor. This movement creates a wave in the water body which radiates outward |
in concentric shells. On the open ocean, these waves are usually no higher than one to three meters in height and travel at speed of about 750 kilometers per hour. Tsunamis become dangerous when they approach land. Frictional interaction of |
the waves with the ocean floor, as they near shore, causes the waves to slow down and collide into each other. This amalgamation of waves then produces a super wave that can be as tall as 65 meters in height. |
The US Geological Survey estimate that at least 1,783 deaths worldwide resulted from earthquake activity in 2009. In 2010, the number rose to 226,729 as the result of 222,570 people killed by the Jauary 12, 2010 earthquake in Haiti. The |
deadliest earthquake of 2009 was a magnitude 7.5 event that killed approximately 1,117 people in southern Sumatra, Indonesia on Sept. 30, according to the U.S. Geological Survey (USGS) and confirmed by the United Nations Office for Coordination of Humanitarian Affairs |
(OCHA). However, the number of earthquake-related fatalities in 2009 was far less than the 2008 count of over 88,000. The high number of fatalities in 2008 was primarily due to the devastating magnitude 7.9 earthquake that occurred in Sichuan, China |
on May 12. Although unrelated, the Sept. 30 Indonesian earthquake occurred a day after the year’s strongest earthquake, a magnitude 8.1 on Sept. 29 in the Samoa Islands region. Tsunamis generated by that earthquake killed 192 people in American Samoa, |
Samoa and Tonga. A magnitude 6.3 earthquake hit the medieval city of L’Aquila in central Italy on April 6, killing 295 people. Overall, earthquakes took the lives of people in 15 countries on four continents during 2009, including Afghanistan, Bhutan, |
China, Costa Rica, Greece, Indonesia, Italy, Kazakhstan, Honduras, Japan, Malawi, Samoa, South Africa and Tonga, as well as the U.S. territory of American Samoa. Earthquakes injured people in 11 additional countries, including the mainland United States, where a magnitude 4.4 |
earthquake on May 2 injured one person in the Los Angeles area. The biggest 2009 earthquake in the 50 United States was in the Aleutian Islands of Alaska. The magnitude 6.5 earthquake occurred in the Fox Islands on Oct. 13. |
It was felt at the towns of Akutan and Unalaska, but caused no casualties or damage. The greatest earthquake for the year in the contiguous United States was a magnitude 5.2 event on October 2 in the Owens Valley southeast |
of Lone Pine, California. Because of the sparse population in the epicentral area, this quake caused no damage although it was felt as far away as Merced and Los Angeles, California and Las Vegas, Nevada. A magnitude 9.1 Sumatra-Andaman Island |
earthquake and subsequent tsunami on December 26, 2004 killed 227,898 people, which is the fourth largest casualty toll for earthquakes and the largest toll for a tsunami in recorded history. As a consequence of that earthquake, the USGS has significantly |
improved its earthquake notification and response capabilities. Improvements include the addition of nine real-time seismic stations across the Caribbean basin, a seismic and tsunami prone region near the U.S. southern border, implementation of a 24x7 earthquake operations center at the |
USGS National Earthquake Information Center (NEIC), and development of innovative tools for rapid evaluation of population exposure and damage to potentially damaging earthquakes. The USGS estimates that several million earthquakes occur throughout the world each year, although most go undetected |
because they hit remote areas or have very small magnitudes. The USGS NEIC publishes the locations for about 40 earthquakes per day, or about 14,500 annually, using a publication threshold of magnitude 4.5 or greater worldwide or 2.5 or greater |
within the United States. On average, only 18 of these earthquakes occur at a magnitude of 7.0 or higher each year. In the 2009 year, 17 earthquakes reached a magnitude of 7.0 or higher, with a single one topping a |
magnitude of 8.0. These statistics for large magnitude earthquakes are higher than those of 2008, which experienced only 12 earthquakes over magnitude 7.0 and none over 8.0. Factors such as the size of an earthquake, the location and depth of |
Significant Earthquakes, USGS, 2010 (with additions on two most recent major earthquakes in Haiti and Japan. The following links provide some more information about earthquakes. - American Geophysical Union (AGU) - Animation of P, S & Surface Waves - Animations |
of Seismology Fundamentals - Association of American State Geologists (AASG) - Association of Bay Area Governments (ABAG) - California Geological Survey (CGS) - California Office of Emergency Services (OES) - California Seismic Safety Commission - Center for Earthquake Research & |
Information (CERI) - Central United States Earthquake Consortium (CUSEC) - Consortium of Universities for Research in Earthquake Engineering (CUREE) - COSMOS Virtual Data Center - CREW - Cascadia Region Earthquake Workgroup - Earthquake Engineering Research Institute (EERI) - Earthquake Information |
for 2009, USGS - Earthquake Information for 2010, USGS - Earthquake Monitoring - Earthquakes - Online University - Earthquakes by Bruce A. Bolt Online Companion - Earthquakes Cause over 1700 Deaths in 2009, USGS - Earth Science Education Activities - |
European-Mediterranean Seismological Centre - FEMA - Federal Emergency Management Agency - Finite-source Rupture Model Database - Global Earthquake Explorer - GSA - Geological Society of America - Incorporated Research Institutes for Seismology (IRIS) - International Association of Seismology and Physics |
of the Earth's Interior (IASPEI) - International Seismological Centre (ISC) - John Lahr's Earthquake website - McConnell, D., D. Steer, C. Knight, K. Owens, and L. Park. 2010. The Good Earth. 2nd Edition. McGraw-Hill, Dubuque, Iowa. - Mid-America Earthquake Center |
- Multi-Disciplinary Center for Earthquake Engineering Research (MCEER) - National Geophysical Data Center (NGDC) - NOAA - National Information Centre of Earthquake Engineering (NICEE) - National Science Foundation (NSF) - Natural Hazards Center - Northern California Earthquake Data Center - |
Observatories and Research Facilities for EUropean Seismology (ORFEUS) - Plummer, C., D. Carlson, and L. Hammersle. 2010. Physical Geology. 13th Edition. McGraw-Hill, Dubuque, Iowa. - Project IDA - Quake-Catcher Network - Saint Louis University Earthquake Center - Seattle Fault Earthquake |
Scenario - Seismographs: Keeping Track of Earthquakes - Seismological Society of America (SSA) - Seismo-surfing the Internet for Earthquake Data - Smithsonian Global Volcanism Program - SOPAC (Scripps Orbit and Permanent Array Center) - Southern California Earthquake Center (SCEC) - |
Tarbuck, E.J., F.K. Lutgens, and D. Tasa. 2009. Earth Science. 12th Edition. Prentice Hall, Upper Saddle River, New Jersey. - Tectonics Observatory - Tracing earthquakes: seismology in the classroom - UPSeis Seismology Questions Answered - USGS Earthquake Hazards Program, U.S. |
|Created with the Web Accessibility Wizard||Slide 2 of 21| Eta 6-hour 300 mb heights and wind speed (shaded) valid 5/12 18 UTC. The weather pattern on May 12 featured a large upper-level ridge over the eastern United States. A strong upper jet was located over eastern Canada. Northeast Pennsylvania was |
far removed from the upper jet, but could be considered to be located at the edge of the right entrance region. No upper level divergence associated with the jet was located near northeast Pennsylvania, however the circulation associated with the jet may have acted to increase the low-level southwesterly flow. |
WESTCHESTER, Ill. – A childhood sleep-related breathing disorder (SRBD) is known to have negative consequences on cognitive development, behavior, quality of life and utilization of health care resources. However, a research abstract that will be presented Monday at SLEEP 2007, the 21st Annual Meeting of the Associated... |
a childhood SRBD. The study, conducted by Hawley E. Montgomery-Downs, PhD, of West Virginia University, focused on the parents of those children who underwent overnight polysomnography, who filled out a brief survey about whether the child had been breast, formula or both breast and formula fed as an infant. There were... |
polysomnography was 6.7 years. Fifty-two percent of them were formula fed, 10 percent breast fed and 38 percent both breast and formula fed as infants. It was discovered that children who were breast fed for at least two months as infants had lower rates and less severe measures of an SRBD, and that breast feeding beyo... |
severity. "Prevention of a childhood sleep-related breathing disorder is critically important because the approximately three percent of children who are unable to breathe well while sleeping suffer from frequent sleep interruption and intermittent hypoxia that negatively impacts their cardiovascular function, cognitiv... |
due to the protection against early viral infection that breast feeding provides, or they may be due to the healthful jaw formation that is a result of breast feeding. Investigation of these mechanisms will be the topics of future work. The current findings support another benefit of infant breast feeding." An SRBD may... |
occurs when the airway is partially blocked during sleep. The most common example is snoring. The most severe form of an SRBD is obstructive sleep apnea. It occurs in about one percent to two percent of children. Parents who suspect that their child might be suffering from an SRBD, or another sleep disorder, are encour... |
them to a sleep specialist. The annual SLEEP meeting brings together an international body of 5,000 leading researchers and clinicians in the field of sleep medicine to present and discuss new findings and medical developments related to sleep and sleep disorders. More than 1,000 research abstracts will be presented at... |
the Sleep Research Society. The four-day scientific meeting will bring to light new findings that enhance the understanding of the processes of sleep and aid the diagnosis and treatment of sleep disorders such as insomnia, narcolepsy and sleep apnea. AAAS and EurekAlert! are not responsible for the accuracy of news rel... |
Jamaican sprinter Usain Bolt's record-setting performances have unleashed a wave of interest in the ultimate limits to human running speed. A new study published in the Journal of Applied Physiology offers intriguing insights into the biology and perhaps even the future of human running speed. The newly published evide... |
the critical variable imposing the biological limit to running speed, and offers an enticing view of how the biological limits might be pushed back beyond the nearly 28 miles per hour speeds achieved by Bolt to speeds of perhaps 35 or even 40 miles per hour. The new paper, "The |
biological limits to running speed are imposed from the ground up," was authored by Peter Weyand of Southern Methodist University; Rosalind Sandell and Danille Prime, both formerly of Rice University; and Matthew Bundle of the University of Wyoming. "The prevailing view that speed is limited by the force with which |
the limbs can strike the running surface is an eminently reasonable one," said Weyand, associate professor of applied physiology and biomechanics at SMU in Dallas. "If one considers that elite sprinters can apply peak forces of 800 to 1,000 pounds with a single limb during each sprinting step, it's easy |
to believe that runners are probably operating at or near the force limits of their muscles and limbs," he said. "However, our new data clearly show that this is not the case. Despite how large the running forces can be, we found that the limbs are capable of applying much |
greater ground forces than those present during top-speed forward running." In contrast to a force limit, what the researchers found was that the critical biological limit is imposed by time -– specifically, the very brief periods of time available to apply force to the ground while sprinting. In elite sprinters, |
foot-ground contact times are less than one-tenth of one second, and peak ground forces occur within less than one-twentieth of one second of the first instant of foot-ground contact. The researchers took advantage of several experimental tools to arrive at the new conclusions. They used a high-speed treadmill capable ... |
attaining speeds greater than 40 miles per hour and of acquiring precise measurements of the forces applied to the surface with each footfall. They also had subjects' perform at high speeds in different gaits. In addition to completing traditional top-speed forward running tests, subjects hopped on one leg and ran |
backward to their fastest possible speeds on the treadmill. The unconventional tests were strategically selected to test the prevailing beliefs about mechanical factors that limit human running speeds –- specifically, the idea that the speed limit is imposed by how forcefully a runner's limbs can strike the ground. How... |
researchers found that the ground forces applied while hopping on one leg at top speed exceeded those applied during top-speed forward running by 30 percent or more, and that the forces generated by the active muscles within the limb were roughly 1.5 to 2 times greater in the one-legged hopping |
gait. The time limit conclusion was supported by the agreement of the minimum foot-ground contact times observed during top-speed backward and forward running. Although top backward vs. forward speeds were substantially slower, as expected, the minimum periods of foot-ground contact at top backward and forward speeds w... |
to Matthew Bundle, an assistant professor of biomechanics at the University of Wyoming, "The very close agreement in the briefest periods of foot-ground contact at top speed in these two very different gaits points to a biological limit on how quickly the active muscle fibers can generate the forces necessary |
to get the runner back up off the ground during each step." The researchers said the new work shows that running speed limits are set by the contractile speed limits of the muscle fibers themselves, with fiber contractile speeds setting the limit on how quickly the runner's limb can apply |
force to the running surface. "Our simple projections indicate that muscle contractile speeds that would allow for maximal or near-maximal forces would permit running speeds of 35 to 40 miles per hour and conceivably faster," Bundle said. Peter Weyand is an associate professor of applied physiology and biomechanics in ... |
Annette Caldwell Simmons School of Education & Human Development. Matthew Bundle is an assistant professor of biomechanics in the College of Health Sciences at the University of Wyoming. AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for ... |
Most of us look forward to spring’s arrival: new blooms, new colors and warmer temperatures allowing more outdoor activity. But for the estimated 20 percent of Americans with seasonal allergies, |
spring can be a time of itchy, watery eyes, sneezing and other miseries of the season. Commonly called “hay fever,” these reactions are referred to by doctors as “seasonal allergic |
rhinitis,” where rhinitis means inflammation of the lining of the nose. People can be allergic to all sorts of things, but plant pollens are among the most irritating, and spring |
is their heyday. The American Academy of Allergy, Asthma and Immunology, the official group of doctors specializing in allergy, recommends that you see an allergist if you have prolonged or |
severe symptoms of rhinitis, associated asthma or recurrent sinus infections; if your quality of life is adversely affected; or if the medications you take seem not to be working. But |
Investigate Your Indoor Air Quality You worry about smog and outdoor air pollutants, but do you give indoor air quality a second thought? In the air we breathe outdoors, we know that smog and other pollutants are a big cause for concern. But don't assume that the air quality inside your home is perfectly safe. A number... |
pollute the air, making indoor air quality testing essential for a healthy home. The Clues: Signs of Indoor Air Quality Problems How do you know if you should be concerned about your indoor air quality? Look for these common warning signs that may indicate you have indoor air pollutants: - You feel sick at home and bet... |
even just extra dirt, around heating or cooling units. - Air doesn’t seem to be circulating properly in the house. - You spot mold in your home. - Your indoor air is humid, resulting in condensation. - There’s been damage to a chimney or flue. - Your home’s construction is too tight. - You’ve noticed changes in your he... |
The air in your home always smells old or stuffy. - There’s an odor in the air that you can't get rid of. If you suspect you have an issue with indoor air quality, you can perform tests to see if specific air pollutants are infiltrating your home and possibly affecting your health. Improve the air quality in your home ... |
tasks. The Culprits: Potential Air Pollutants Before you test your indoor air quality, you need to know what you're looking for. Here are some of the most common indoor air pollutants that could be contaminating your home: - Lead and lead dust - Household chemicals - Dust and molds - Pet hair and dander - Rodents and c... |
Originate There are many ways that air pollutants can contaminate the air inside your home. Most often, chemicals or materials inside the home emit gases or particulates. Poor ventilation and circulation don't allow contaminants to flow out of the home; very humid homes and climates are also a breeding ground for conta... |
indoor air quality, particularly when ventilation isn’t good: - Household chemicals, solvents, and cleaning products - Malfunctioning space heaters - Poorly vented furnaces or stoves - Outdoor air pollution that gets in - Pesticide use - Wood, kerosene, oil, gas, and coal burned for heat - Insulation made with asbestos... |
wet - Tobacco products and smoke Having a hard time kicking the smoking habit? Get help here. The Results: Indoor Air Quality and Your Health Indoor air pollutants can affect your entire family's health, by contributing to the development of asthma and other respiratory illnesses. In addition, chronic respiratory disea... |
improve your indoor air quality, consider installing an air cleaning system to remove air pollutants from your home. There are a number of different air cleaning systems and devices that will remove solid and gaseous contaminants from the air. It's also important to make sure that your home is well-ventilated. A poorly... |
levels and can help prevent the growth of mold and mildew in your home. If you think your home is making you sick, you just might be right. Take steps quickly to solve the problem by identifying and then getting rid of indoor air pollutants. Taking action will help you breathe easier. |
Samuel D. Evans West Central Experiment Station University of Minnesota now Emeritus Professor at Morris, Minnesota John F. Moncrief Department of Soil, Water, and Climate University of Minnesota Gyles W. Randall Southern Experiment Station University of Minnesota William E. Lueschen Department of Agronomy and Plant Ge... |
Head of the Southwest Experiment Station at Lamberton Copyright © 2002 Regents of the University of Minnesota. All rights reserved. Management of crop residues with reduced tillage is the most cost-effective method of controlling sediment losses and reducing farming impacts on water quality. Crop residues can also help... |
erosion and can enhance snow entrapment. One of the primary water quality concerns for the Minnesota River and its tributaries is sediment, which contributes increased phosphorus (P) to the system. This increased P stimulates algae growth, which is followed by an increased biological oxygen demand when the algae die an... |
decompose. This can deplete dissolved oxygen levels, resulting in game fish stress or kill. In addition to affecting sediment loss, tillage influences many interacting physical, chemical, and biological properties of soils that can have major impacts on crop production. These properties include temperature, moisture, a... |
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