EARTH SCIENCES - Notable Research and Discoveries Part 8 docx

opposite page Strain develops along a fault, eventually producing a rupture 1, which quickly reaches the surface 2 and spreads 3, extending throughout the fault 4... earth ScienceS1 San

the world’s climate seems to be in the midst of substantial changes

ClIMatE CHanGE and WatER

flooding low-lying areas

Other impacts of global climate change on the water cycle are less certain Periodic changes in the properties of oceans, such as the warming

a desalination facility, one of the first major invest-10s The worst drought to strike the United States affects

much of the nation, but particularly an area in the Great Plains states of Texas, Oklahoma, Colorado, Kansas, and New Mexico Drying of the soil, cou-pled with poor land management, results in severe dust storms that blanket the dust bowl region

10s After strong episodes of El Niño, researchers begin

to link this phenomenon with storms and droughts

in the United States and elsewhere

10s The MIT professor Edward Lorenz (1917–2008)

discovers the butterfly effect—small changes in weather systems can have enormous consequences

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The U.S government passes the Safe Drinking Wa-ter Act, which regulates water treatment and sets appropriate standards

00 NASA launches the Aqua satellite The collected

data improves weather forecasts and hydrologic modeling and prediction

00 The UN issues its first World Water Development

ignates the years 2005–2015 as the Water for Life Decade, urging conservation and careful manage-ment of water resources

Report, warning of impending shortages, and des-00 In response to serious water shortages, especially

in the western states, the United States establishes NIDIS to coordinate water monitoring and re-search efforts across the country

00 Tampa Bay desalination plant begins operations

ply about 10 percent of the city’s freshwater needs

Egan, Timothy The Worst Hard Time: The Untold Story of Those Who

Survived the Great American Dust Bowl New York: Mariner Books,

2006 This history of the 1930s dust bowl describes the economic,

ecological, and human catastrophe in vivid detail

Environmental Protection Agency “Water.” Available online URL:

http://www.epa.gov/ebtpages/water.html Accessed May 4, 2009

Oki, Taikan, and Shinjiro Kanae “Global Hydrological Cycles and

World Water Resources.” Science 313 (August 25, 2006): 1,068–

Pearce, Fred When the Rivers Run Dry: Water—The Defining Crisis of

the Twenty-First

Public Broadcasting Service “Surviving the Dust Bowl.” Available on-line URL: http://www.pbs.org/wgbh/amex/dustbowl/ Accessed

May 4, 2009 The Internet companion to an episode of American

Ex-perience, these pages include a time line of the events and interviews

with eyewitnesses

http://water.usgs.gov/ Accessed May 4, 2009 Maps, annual water

reports, regional studies, and monitoring data are included in these

extremely informative pages

de Villiers, Marq Water: The Fate of Our Most Precious Resource New

York: Mariner Books, 2001 Earth’s rising population puts added

National Integrated Drought Information System Available online

URL: http://www.drought.gov Accessed May 4, 2009 The NIDIS

enced many earthquakes, including a San Francisco earthquake on April

18, 1906, that destroyed the city and claimed about 3,000 lives

lapsing structures or scattered debris Th e ground shakes or oscillates because of earthquake waves, or seismic waves, which spread out from the earthquake’s origin—the focus (also known as the hypocenter)—

Most of the damage and casualties from earthquakes are due to col-and travel in all directions Many communities that have experienced numerous earthquakes require builders to follow strict codes Buildings and bridges can be designed to resist at least a moderate amount of

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This California highway overpass collapsed during a 1971 earthquake

(R Kachadoorian/USGS)

However, since observations are not always reliable and damage de-precise scale is needed (Bigger earthquakes usually cause much more

The California Institute of Technology researchers Charles

Richter and Beno Gutenberg developed the scale in

accor-dance with the amplitude of the vibrations as measured

by their particular seismometer By comparing instrument

readings rather than subjective observations, the

research-ers could judge the size of any earthquake This method

per-mitted them to distinguish between the numerous smaller

earthquakes and the rare but important major ones without

having to rely on eyewitnesses.

The range of seismic amplitudes is large—the amplitudes

of some seismic waves are huge compared to others A scale

with such a wide range is unwieldy because it must include

enormous numbers as well as tiny ones To make the numbers

more manageable, Richter assigned earthquake magnitudes

based on the logarithm of the amplitude Logarithms compress

the range; for example, the logarithm (base 10) of 10 is 1, and

num-0 value to be a certain extremely small amplitude as recorded

by his instrument when located 62 miles (100 km) from the epicenter An amplitude 10 times greater than this value would register 1 on the Richter scale, 100 times greater would reg- ister 2, 1,000 times greater would register 3, and so on.

A seismic wave’s amplitude depends on the distance from the focus as well as the sensitivity of the recording instru- ment, but a mathematical scale was so useful that scientists adapted the Richter scale for a variety of instruments and distances In each case, seismologists calibrate the output of their instrument to achieve consistent readings of the earth- quake’s intensity that would be observed 62 miles (100 km) from the epicenter There is no minimum or maximum on the scale Although 0 is an extremely small value on the Richter scale—it was about the least that the old instruments could measure—newer instruments are sensitive enough to detect smaller amplitudes, which measure negative values on the Richter scale.

A fault is a crack or fi ssure in which one side or wall moves rela-(160 km) or more Faults oft en occur around plate boundaries, and the

(opposite page) Strain develops along a fault, eventually producing a

rupture (1), which quickly reaches the surface (2) and spreads (3),

extending throughout the fault (4).

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San andreas Fault

Two large tectonic plates, the Pacifi c plate and the North

American plate, meet in California Part of the boundary

in-cludes the San Andreas Fault, as shown in the following fi

g-ure The San Andreas Fault takes its name from San Andreas

Lake, which lies a little south of San Francisco in a valley

cre-ated by the fault Andrew Lawson (1861–1952), a professor

at the University of California, Berkeley, identifi ed the northern

stretch of the fault in 1895 and later discovered it extended

far to the south San Andreas is the backbone or master fault

in the system, running about 800 miles (1,280 km) from

northern California to San Bernardino in the south The fi

s-sure extends to a depth of at least 10 miles (16 km).

Rocks on opposite sides of the San Andreas Fault move past one another horizontally This motion is due to the plate

movement—the Pacifi c plate moves northwestward with

re-spect to the North American plate at a rate of about 2

inch-es (5 cm) per year, as measured in the San Francisco area

Since Los Angeles is on the Pacifi c plate and San Francisco

is on the North American plate, the two cities will slide past

each other in a few million years if the plates continue their

present motion!

In 1906, only 11 years after Lawson’s discovery, this fault became the center of much attention from geolo-

gists—it was the origin of the tragic San Francisco

earth-quake Geologists who flocked to the site found that fences,

streams, and roads that stretched across the fault were no

longer lined up, for one side had suddenly shifted Instead

(continues)

ments mentioned above The product of the area of a fault’s surface

Fault slips are the basis for the moment magnitude measure-and the average distance it moved during a slip is called the moment

The San Andreas Fault extends through coastal California—this fault forms part of the boundary of the Pacifi c plate and the North American plate.

of an earthquake Scientists can estimate the moment from seismo-grams, but they can also determine the moment by studying the fault

itself

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A few earthquakes occur far from any plate boundary, similar to the phenomenon of volcano hot spots The origin of these earthquakes is

not generally well understood But cracks or faults within plates would

explain why these events occur, and in some cases evidence for these

of a continuous road or fence, one side was offset from

the other side, across the fault In some cases, such as

the road at Tomales Bay, the offset was nearly 21 feet (6.4

m)—the center of the road at one side of the fault was a

horizontal distance of 21 feet (6.4 m) from the road at the

other side of the fault!

(continued)

This view shows a portion of the San Andreas Fault at the Carrizo

Plain The fault runs horizontally across the middle of the photograph

Note that the stream channel running vertically is out of alignment

due to movement along the fault (R E Wallace/USGS)

greater power If the primary waves emanating from the earthquake