geology of the earth 71...2004 sumatra, indonesia 9.0 250,000 2005 n. pakistan 7.6 74,000 2006 java,...
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Canadian Shield
GuianaShield
AmazonianShield
IndianShield
AngaraShield
Arabian Shield
BalticShield
AustralianShield
ChineseShield
Ethiopian Shield
Valley
Equator
Tropic of Cancer
Arctic Circle
Tropic of Capricorn
Antarctic Circle
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12
Holocene 10,000 BP to presentPleistocene
Pliocene
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Miocene
Oligocene
Eocene
Paleocene
Jurassic
Cretaceous
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Tertiary
Quaternary
CEN
OZO
ICM
ESO
ZOIC
PALE
OZO
ICPR
E-CA
MB
RIA
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ERA PERIOD EPOCH
COPYRIGHT PHILIP’S
Pre-Cambrian shields
Sedimentary cover on Pre-Cambrian shieldsPaleozoic (Caledonian and Hercynian) foldingSedimentary cover on Paleozoic folding
Mesozoic folding
Sedimentary cover on Mesozoic folding
Cenozoic (Alpine) folding
Sedimentary cover on Cenozoic foldingIntensive Mesozoic and Cenozoic vulcanism
Principal faults
Oceanic marginal troughs
Midoceanic ridges
Overthrust faults
Earthquake magnitude is usually rated according to either the Richter or the Modified Mercalli scale, both devised by seismologists in the1930s. The Richter scale measures absolute earthquake power withmathematical precision: each step upward represents a tenfold increasein the amplitude of the shockwave. Theoretically, there is no upper limit,but most of the largest earthquakes measured have been rated atbetween 8.8 and 8.9. The 12-point Mercalli scale, based on observedeffects, is often more meaningful, ranging from I (earthquakes noticedonly by seismographs) to XII (total destruction); intermediate pointsinclude V (people awakened at night; unstable objects overturned), VII(collapse of ordinary buildings; chimneys and monuments fall), and IX(conspicuous cracks in ground; serious damage to reservoirs).
Notable Earthquakes Since 1900Year Location Mag. Deaths1906 San Francisco, USA 8.3 3,0001906 Valparaiso, Chile 8.6 22,0001908 Messina, Italy 7.5 83,0001915 Avezzano, Italy 7.5 30,0001920 Gansu (Kansu), China 8.6 180,0001923 Yokohama, Japan 8.3 143,0001927 Nan Shan, China 8.3 200,0001932 Gansu (Kansu), China 7.6 70,0001933 Sanriku, Japan 8.9 2,9901934 Bihar, India/Nepal 8.4 10,7001935 Quetta, India* 7.5 60,0001939 Chillan, Chile 8.3 28,0001939 Erzincan, Turkey 7.9 30,0001960 S. W. Chile 9.5 2,2001960 Agadir, Morocco 5.8 12,0001962 Khorasan, Iran 7.1 12,2301964 Anchorage, USA 9.2 1251968 N. E. Iran 7.4 12,0001970 N. Peru 7.8 70,0001972 Managua, Nicaragua 6.2 5,0001974 N. Pakistan 6.3 5,2001976 Guatemala 7.5 22,5001976 Tangshan, China 8.2 255,0001978 Tabas, Iran 7.7 25,0001980 El Asnam, Algeria 7.3 20,0001980 S. Italy 7.2 4,8001985 Mexico City, Mexico 8.1 4,2001988 N.W. Armenia 6.8 55,0001990 N. Iran 7.7 36,0001992 Flores, Indonesia 6.8 1,8951993 Maharashtra, India 6.4 30,0001994 Los Angeles, USA 6.6 511995 Kobe, Japan 7.2 5,0001995 Sakhalin Is., Russia 7.5 2,0001996 Yunnan, China 7.0 2401997 N. E. Iran 7.1 2,4001998 Takhar, Afghanistan 6.1 4,2001998 Rostaq, Afghanistan 7.0 5,0001999 Izmit, Turkey 7.4 15,0001999 Taipei, Taiwan 7.6 1,7002001 Gujarat, India 7.7 14,0002002 Baghlan, Afghanistan 6.1 1,0002003 Boumerdes, Algeria 6.8 2,2002003 Bam, Iran 6.6 30,0002004 Sumatra, Indonesia 9.0 250,0002005 N. Pakistan 7.6 74,0002006 Java, Indonesia 6.4 6,200
An earthquake off the coast of Sumatra on December 26, 2004, triggered a deadlytsunami that swept across the IndianOcean, causing devastation in manycountries, in particular Sri Lanka, India,Thailand, and Indonesia, where the loss of life was greatest.* now Pakistan
Time, in millions of years before thepresent, is shown on a sliding scale,greatly compressed in the distant past.
Geologists devised their timescale on the basis of relative, not calendar, ages.Accurate dating was impossible and estimates were often bitterly disputed, but the
order in which the rocks were formed could be deduced from careful observation.The advent of radioactive dating – culminating in the 1950s with the
development of a mass spectrometer capable of accurately measuring tinyquantities of isotopes – appears to have settled the arguments. The Earth is
far older than geologists first imagined, but their painstakingly-createdstructure of geological time has withstood the advent of high technology.
The 4.6 billion (4,600 million) years since the formation of the Earth aredivided into four great eras, further split into periods and, in the case
of the most recent era, epochs. The present era is the Cenozoic (“newlife”), extending backward through “middle life” and “ancient life”
to the Pre-Cambrian, named after the Latin word for Wales, the location of some of the earliest known fossils. Most
of the Earth’s geological history is encompassed by the Pre-Cambrian: though traces of ancient life have since
been found, it was largely the proliferation of fossils from the beginning of the Paleozoic era onward, some
570 million years ago, which first allowed precisesubdivisions to be made.
Like the Cambrian, most are named after regionsexemplifying a period’s geology. Others – such
as the Carboniferous (“coal-bearing”) or theCretaceous (“chalk-bearing”) – are more directly
descriptive.
Anchorage1964
San Francisco1906
Managua1972
Mexico City1985
N. Peru1970
S.W. Chile1960
Chillan1939
Valparaiso1906
El Asnam1980
Agadir1960
Avezzano1915
Messina1908
Erzincan1939
N. Iran1990
Tabas1978
Quetta1935 Maharashtra
1993
Bihar1934
Tangshan1976
Gansu1920/1932
Nan Shan1927
Yokohama1923
Los Angeles1994 Kobe
1995
Sakhalin1995
Equator
Tropic of Cancer
Arctic Circle
Tropic of Capricorn
Antarctic Circle
Flores1992
Takhar/Rostaq1998
Izmit1999
Taipei1999
Gujarat2001
Guatemala1976
Sanriku1933
N.E. Iran1968/1997
Yunnan1996
N.W. Armenia1988
S. Italy1980
Khorasan1962
N. Pakistan1974
Baghlan2002
Boumerdes2003
Bam2003
Sumatra2004
N. Pakistan2005
Java2006
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Shockwaves reachthe surface
Epicenter – point onthe surface directlyabove the origin
Origin orfocus
Shockwavestravel outward
Mobile land areas
Submarine zones of mobile land areas
Stable land platforms
Submarine extensions of land platforms
Midoceanic volcanic ridges
Oceanic platforms
Principal earthquakes and dates(since 1900)
1976
X
Subduction zone
Earthquakes are a series of rapidvibrations originating from the slipping or faulting of parts of the Earth’s crustwhen stresses within build up to breakingpoint. They usually happen at depthsvarying from 5 to 20 miles. Severeearthquakes cause extensive damagewhen they take place in populated areas,destroying structures and severingcommunications. Most initial loss of lifeoccurs due to secondary causes such as falling masonry, fires, and flooding.
EARTHQUAKES
GEOLOGICAL TIME
GEOLOGY OF THE EARTH 71
US p70-71 AOW HB IWG '06 21/6/06 2:28 pm Page 71
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