Exploring the Earth Using Seismology - IRIS · analyzing the ground motion created by large...
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0∞ 30∞ 60∞ 90∞ 120∞ 150∞ 180∞ Seismic stations farther away from the earthquake record P, S and Surface waves minutes after the earthquake occurred. Because P waves and S waves travel at different speeds, the arrival times between the P, S and Surface waves become greater with increasing distance. Long-term measurements of P waves traveling throught the inner core (PKIKP waves) suggest that the inner core may rotate faster than the Earth’s outer layers. 0 minutes 180∞ 150∞ 120∞ 90∞ 60∞ 30∞ 0∞ 10 minutes 20 minutes 30 minutes 0 minutes 10 minutes 20 minutes 30 minutes Exploring the Earth Using Seismology Christel B. Hennet, IRIS Consortium; Lawrence W. Braile, Purdue University WATCH EARTHQUAKES AS THEY OCCUR At the IRIS website (www.iris.edu) you can monitor global seismicity in near real-time, view records of ground motion, visit seismic stations around the world, and learn more about earthquakes. THE NORTHRIDGE EARTHQUAKE In the early morning of January 17, 1994, a magnitude 6.7 earthquake changed the Northridge area east of Los Angeles forever. The quake left 51 people dead and 7,000 injured. It also caused over $20 billion in damage to buildings, highways and bridges. Although moderate in size, the Northridge earthquake was one of the costliest natural disasters in the United States. The Northridge earthquake destroyed man-made structures and took lives, but it also helped build mountains. During the earthquake crustal material was moved 3 meters upward along a fault that ruptured 18km below the surface. On the surface, the Santa Susana Mountains north of Los Angeles rose by as much as 70 cm and moved almost instantaneously northwest by as much as 21 cm. The damage incurred due to the Northridge earthquake is over $20 billion. HOW ARE EARTHQUAKES RECORDED? Seismometer recording horizontal ground motion Seismometer recording vertical ground motion Temporary seismograph installment Seismometers are installed in a sheltered location with good coupling to the ground An important tool to study the Earth’s interior is the seismograph. The seismograph is an instrument that records ground motion, or seismic waves, generated by earthquakes. Seismographs can be installed permanently or temporarily. Temporary installments are used to answer scientific questions of geological interest such as here near the base of the Nangar Parbat massif in northeast Pakistan. Permanent installments are used to study the overall structure of the Earth’s interior. Seismographs used in permanent installments are deployed at fixed locations around the world. Modern seismographs record and amplify seismic waves electronically, and can detect ground motion as small as 0.00000001 cm (distances of the order of atomic spacing.) The principle by which a seismometer works can be thought of as a heavy mass freely attached to a frame fixed to the Earth. When seismic waves reach the seismometer, the frame moves along with the ground. The heavy mass inside the frame remains stationary because of its inertia. The relative motion between the frame and the mass is a P wave Compressions Dilatations Undisturbed medium S wave Double amplitude Wave length Love wave Rayleigh wave SEISMIC WAVES During an earthquake seismic waves radiate outward in all directions. The waves that travel through the interior of the Earth are called body waves, while those that travel along the surface are called surface waves. There are two main types of body waves: compressional waves (also called P waves) and shear waves (also called S waves). P waves travel by compressing and dilating the material through which they propagate. S waves travel by particles trying to slide past each other similar to when one shakes a rope up and down or from side to side. P waves can travel through solid and fluid materials, S waves can only travel through solids. P waves travel faster than S waves. Surface waves are confined to the surface of the Earth. In one kind of surface wave (called Rayleigh wave), the particle motion is elliptical. In another kind of surface wave (called Love wave), the particle motion is sideways. Surface waves travel slower than P waves and S waves. Design and illustration: Keaton Drew Design Introduction Earthquakes are a constant reminder that we are living on the rigid crust of a cooling planet. By studying rocks near the surface of the Earth, geologists can infer the Earth’s interior structure to about 100 km depth. But what lies below? By analyzing the ground motion created by large earthquakes around the world, seismologists can explore the Earth's interior to its very center. The Earth The schematic on the left shows the basic structure of Earth's interior. Energy released by earthquakes creates seismic waves which travel through the Earth and are reflected and refracted at boundaries that separate regions of different materials. Shown here are the paths for seismic waves from the 1994 Northridge earthquake that were recorded at seismic stations around the world. Seismic station locations are marked as triangles and some are labeled with their station codes. Seismograms for these seismic stations are shown on the right. The Seismogram Section Below, each horizontal trace shows the arrival of seismic waves from the Northridge earthquake. The traces are the actual ground motion recorded at the seismic stations shown on the Earth. Some traces are labeled with the location of the seismic station at which they were recorded. The direct ray paths for P, S and Surface waves are shown in green. Seismologists compare the arrival times and amplitudes of seismic waves from many stations to infer the seismic velocity and hence the structure of Earth’s deep interior. HOW OFTEN DO EARTHQUAKES OCCUR? Large earthquakes occur about once a year. Smaller earthquakes such as magnitude 2 earthquakes, occur several hundred times a day. To create a mountain system might take several million medium size earthquakes over tens of millions of years. We describe the size of an earthquake using the extended Richter Magnitude scale, shown on the left hand side of the figure. The larger the number, the bigger the earthquake. The scale on the right hand side of the figure represents the amount of high explosives required to produce the energy released by the earthquake. The 1994 earthquake in Northridge, California, for example, was about magnitude 6.7. Earthquakes this size occur about 20 times each year worldwide. Although the Northridge earthquake is considered moderate in size, it caused over $20 billion in damage. The earthquake released energy equivalent to almost 2 billion kilograms of explosives, about 100 times the amount of energy that was released by the atomic bomb that destroyed the city of Hiroshima during World War II. 2 6 4 8 10 9 7 5 3 56 1,800 56,000 1,800,000 56,000,000 1,800,000,000 56,000,000,000 1,800,000,000,000 56,000,000,000,000 Number of Earthquakes per Year (worldwide) 1,000,000 100,000 12,000 2,000 200 20 3 <1 Energy Release (equivalent kilograms of explosive) Magnitude major earthquake severe economic impact large loss of life strong earthquake damage ($ billions) loss of life moderate earthquake property damage light earthquake some property damage minor earthquake felt by humans great earthquake near total destruction massive loss of life Chile (1960) Alaska (1964) Kobe, Japan (1995) San Francisco, CA (1906) New Madrid, MO (1812) Long Island, NY (1884) Large Lightning Bolt Average Tornado Hiroshima Atomic Bomb Mount St. Helens Eruption Loma Prieta, CA (1989) Charleston, SC (1886) Oklahoma City Bombing Moderate Lightning Bolt Krakatoa Eruption World’s Largest Nuclear Test (USSR) Earthquakes Energy Equivalents Northridge (1994) San Fernando Valley Northridge IRIS is a university research consortium dedicated to monitoring the Earth and exploring its interior through the collection and distribution of geophysical data. IRIS programs are conducted in partnership with the US Geological Survey, and are supported by the National Science Foundation and other federal agencies, universities, and private foundations. Copies of this poster can be obtained from; the IRIS Consortium, 1200 New York Ave., NW, Suite 800, Washington, DC 20008 (202) 682-2220. Santa Susana Mountains San Fernando Fault Santa Susana Fault San Gabriel Fault Hinge Spring The Global Seimographic Network is an international scientific program to monitor the Earth and explore it’s interior. Data from the network are used for scholarly research, education, earthquake hazard mitigation, and to verify compliance with the Comprehensive Test Ban Treaty. GLOBAL SEISMOGRAPHIC NETWORK WHERE DO EARTHQUAKES HAPPEN? Earth’s outer surface, the Earth’s crust, is broken into what geologists call tectonic plates. These plates move under, over, or slide past each other. The plates are driven by hot mantle materials that convect. The relative motion of plates is associated with earthquakes. Most earthquakes occur along the edges of large plates. The arrows on the map above indicate how fast the plates are moving in millimeters per year. African Plate Nazca Plate Pacific Plate South American Plate North American Plate Cocos Plate Caribbean Plate Antarctic Plate Somali Plate Philippine Plate Indo-Australian Plate Eurasian Plate Arabian Plate Scotia Plate Juan de Fuca Plate 10 23 29 79 106 46 32 12 6 11 8 8 14 54 59 74 9 9 9 21 105 102 Northridge Rupture Earthquake focus North 18km Needles, California (NEE) Tucson, Arizona (TUC) Corvallis, Oregon (COR) Cathedral Cave, Missouri (CCM) College Outpost, Alaska (COL) Harvard, Massachusetts (HRV) Adak, Alaska (ADK) San Juan, Puerto Rico (SJG) Chiang Mai, Thailand (CHTO) Wright Valley, Antarctica (VNDA) Narrogin, Australia (NWAO) Lobatse, Bot swana, Africa (LBTB) Taipei, Taiwan (TATO) Enshi, China (ENH) Tibet, China (LSA) Beijing, China (BJI) Nana, Peru (NNA) Albuquerque, New Mexico (ANMO) La Paz, Bolivia (LPAZ) Rarotonga, Cook Islands (RAR) Yuzhno Sakahlinsk, Russia (YSS) Kongsberg, Norway (KONO) Matsushiro, Japan (MAJO) Taburiente, Canary Island, Spain (TBT) San Pablo, Spain (PAB) Obninsk, Russia (OBN) Charters Towers, Australia (CTAO) Palmer Station, Antarctica (PMSA) P w a v e r e f l e c t e d o n c e a t t h e Ea r t h ' s s u r f a c e ( P P w a v e ) P wave diffracted around the core-mantle boundary (P diff wave) S wave diffracted around the core-mantle boundary (S diff wave) d i r e c t c o m p r e s s i o n a l w a v e ( P w a v e ) d i r e c t s h e a r w a v e ( S w a v e ) S w a v e r e f l e c t e d o n c e a t t h e E a r t h ’ s s u r f a c e ( S S w a v e ) s u r f a c e w a v e DISTANCE from earthquake (1 ∞ =111 km) P w a v e tr a v e r s i n g t h e o u t e r a n d i n ne r c o r e ( P K I K P w a v e ) P wave traversing the outer core (PK P w a v e ) TIME since earthquake occured (travel time) S O U T H A F R I C A S u rfa c e Earthquake Epicenter Northridge, California TEIG SRR PFO JTS PAYG BOCO NNA RPN LPAZ LVC TRQA PLCA PTGA SDV CPUP EFI EFI HOPE HOPE SUR ASCN ASCN BOSA LBTB TSUM BDFB HKT NEE TUC ANMO COR CCM COL HRV ADK SAML LSZ SHEL SHEL NWAO LBTB SJG NNA RAR LPAZ YSS KONO MAJO TBT PAB OBN BJI TATO ENH CTAO PMSA LSA CHTO VNDA P wave, S wave P wave, S wave P wave, S wave P diff wave P wave, S wave PKP wave PKIKP wave Seismic stations close to the earthquake record strong P, S and Surface waves in quick succession just after the earthquake occurred. The sharply decreasing P and S wave amplitudes seen at stations beyond about 100∞ (1,100 km) from the earthquake indicate the existence of the Earth’s outer core. Although P waves travel through the outer core (PKP waves), S waves do not. Because liquids cannot support shear motion, the absence of S waves traveling through the outer core indicates that the outer core is fluid. INNER CORE composed mostly of solid iron, P wave velocities around 11 km/s, S wave velocities around 3.5 km/s OUTER CORE composed mostly of liquid iron, P wave velocities increase from 8 km/s to 10 km/s, S wave velocity is 0 km/s (no S waves) MANTLE composed of magnesium-iron silicate material, P wave velocities increase from 8 km/s to 13 km/s, S wave velocities increase from 4.5 km/s to 7 km/s CRUST composed of mostly granitic and basaltic rock, extends from Earth's surface to about 50 km depth, P wave velocities increase from 6 km/s to 8 km/s, S wave velocities increase from 3.5 km/s to 4.5 km/s 50 KM 2,900 KM 5,100 KM 6,370 KM P P w a v e , S S w a v e LZH LBTB LPAZ PLCA VNDA BJT KMI ANTO BILL CHTO CMB COR GRFO KBS KEV KIP MA2 MAKZ NWAO PAB PAS PMG SNZO TBT TIXI TSUM ULN YAK ABKT CMLA JTS MSVF TAU BGCA SBA HRV MAJO DBIC ENH HIA MDJ ANMO CASY CCM DPC INCN KONO PMSA SPA RAYN HKT PTGA SSPA TUC PFO WRAB QIZ BDFB BOSA CPUP LSA WMQ XAN SSE FURI ADK AFI BOCO COLA CTAO DAV GNI GUMO HNR KIEV KMBO LSZ LVC PET PTCN RAR SDV SFJ SJG TATO TEIG WAKE XMAS YSS AAK ALE ARU ASCN BORG BRVK COCO EFI ERM ESK FFC KDAK KIV KURK LVZ MSEY NIL NNA NRIL OBN RPN SHEL SUR TLY HOPE PAYG ABUS MBWA MSKU MACQ QUE Socorro Tarawa Uganda Cape Verde Is. Kwajalein Gissar Funafuti NDI Sulawesi TRQA BEC BHL DWPF JOHN KOD KOWA Kanton RAO Midway POHA RCBR TRIN TRIS SAML WSAR Jos Diego Garcia Abha Nukuhiva SHIO
Transcript of Exploring the Earth Using Seismology - IRIS · analyzing the ground motion created by large...
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Seismic stations farther away from the earthquake record P, S and Surface waves minutes
after the earthquake occurred.
Because P waves and S waves travel at different speeds, the arrival times
between the P, S and Surface waves become greater with increasing distance.
Long-term measurements of P waves traveling throught the inner core (PKIKP waves) suggest that the inner core may rotate faster than the Earth’s outer layers.
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Exploring the Earth Using Seismology
Christel B. Hennet, IRIS Consortium;Lawrence W. Braile, Purdue University
WATCH EARTHQUAKES AS THEY OCCUR
At the IRIS website (www.iris.edu) you can monitor global
seismicity in near real-time, view records of ground
motion, visit seismic stations around the world, and learn
more about earthquakes.
THE NORTHRIDGE EARTHQUAKEIn the early morning of January 17,
1994, a magnitude 6.7 earthquake
changed the Northridge area east of
Los Angeles forever. The quake left
51 people dead and 7,000 injured. It
also caused over $20 billion in
damage to buildings, highways and
bridges. Although moderate in size,
the Northridge earthquake was one
of the costliest natural disasters in
the United States.
The Northridge earthquake destroyed
man-made structures and took lives,
but it also helped build mountains.
During the earthquake crustal
material was moved 3 meters
upward along a fault that
ruptured 18km below the
surface. On the surface, the
Santa Susana Mountains
north of Los Angeles rose by
as much as 70 cm and moved
almost instantaneously northwest by
as much as 21 cm.
The damage incurred due tothe Northridge earthquake is over $20 billion.
HOW ARE EARTHQUAKES RECORDED?
Seismometer recording horizontal ground motion
Seismometer recording vertical
ground motion
Temporary seismograph installment
Seismometers are installed in a sheltered location with good coupling to the ground
An important tool to study the Earth’s
interior is the seismograph. The
seismograph is an instrument that
records ground motion, or seismic waves,
generated by earthquakes. Seismographs
can be installed permanently or
temporarily. Temporary installments are
used to answer scientific questions of
geological interest such as here near the base of the Nangar Parbat massif in
northeast Pakistan.
Permanent installments are used to study the overall structure of the
Earth’s interior. Seismographs used in permanent installments are deployed at
fixed locations around the world. Modern seismographs record and amplify
seismic waves electronically, and can detect ground motion as small as
0.00000001 cm (distances of the order of atomic spacing.)
The principle by which a
seismometer works can be thought of
as a heavy mass freely attached to a
frame fixed to the Earth. When
seismic waves reach the seismometer,
the frame moves along with the
ground. The heavy mass inside the
frame remains stationary because of
its inertia. The relative motion
between the frame and the mass is a
P wave
Compressions
Dilatations
Undisturbed medium
S wave
Double amplitudeWave length
Love wave
Rayleigh wave
SEISMIC WAVES
During an earthquake seismic
waves radiate outward in all
directions. The waves that travel
through the interior of the Earth are
called body waves, while those that
travel along the surface are called
surface waves.
There are two main types of
body waves: compressional waves
(also called P waves) and shear
waves (also called S waves). P waves
travel by compressing and dilating
the material through which they
propagate. S waves travel by
particles trying to slide past each
other similar to when one shakes a
rope up and down or from side to
side. P waves can travel through
solid and fluid materials, S waves
can only travel through solids. P
waves travel faster than S waves.
Surface waves are confined to
the surface of the Earth. In one
kind of surface wave (called
Rayleigh wave), the particle motion
is elliptical. In another kind of
surface wave (called Love wave), the
particle motion is sideways. Surface
waves travel slower than P waves
and S waves.
Design and illustration: Keaton Drew Design
Introduction
Earthquakes are a constant reminder that we are living on the
rigid crust of a cooling planet. By studying rocks near the
surface of the Earth, geologists can infer the Earth’s interior
structure to about 100 km depth. But what lies below? By
analyzing the ground motion created by large earthquakes
around the world, seismologists can explore the
Earth's interior to its very center.
The EarthThe schematic on the left shows the basic structure of Earth's interior. Energy released by earthquakes creates seismic waves which travel through the Earth and are reflected and refracted at boundaries that separate regions of different materials. Shown here are the paths for seismic waves from the 1994 Northridge earthquake that were recorded at seismic stations around the world. Seismic station locations are marked as triangles and some are labeled with their station codes. Seismograms for these seismic stations are shown on the right.
The Seismogram SectionBelow, each horizontal trace shows the arrival of seismic waves from the Northridge earthquake. The traces are the actual ground motion recorded at the seismic stations shown on the Earth. Some traces are labeled with the location of the seismic station at which they were recorded. The direct ray paths for P, S and Surface waves are shown in green. Seismologists compare the arrival times and amplitudes of seismic waves from many stations to infer the seismic velocity and hence the structure of Earth’s deep interior.
HOW OFTEN DO EARTHQUAKES OCCUR?
Large earthquakes occur about once a year. Smaller earthquakes such as magnitude
2 earthquakes, occur several hundred times a day. To create a mountain system
might take several million medium size earthquakes over tens of millions of years.
We describe the size of an earthquake using the extended Richter Magnitude
scale, shown on the left hand side of the figure. The larger the number, the bigger
the earthquake. The scale on the right hand side of the figure represents the amount
of high explosives required to produce the energy released by the earthquake.
The 1994 earthquake in Northridge, California, for example, was about
magnitude 6.7. Earthquakes this size occur about 20 times each year worldwide.
Although the Northridge earthquake is considered moderate in size, it caused over
$20 billion in damage. The earthquake released energy equivalent to almost 2 billion
kilograms of explosives, about 100 times the amount of energy that was released by
the atomic bomb that destroyed the city of Hiroshima during World War II. 2
6
4
8
10
9
7
5
3
56
1,800
56,000
1,800,000
56,000,000
1,800,000,000
56,000,000,000
1,800,000,000,000
56,000,000,000,000
Number of Earthquakes per Year (worldwide)
1,000,000
100,000
12,000
2,000
200
20
3
<1
Energy Release(equivalent kilograms of explosive)
Magnitude
major earthquakesevere economic impactlarge loss of life
strong earthquakedamage ($ billions)loss of life
moderate earthquakeproperty damage
light earthquakesome property damage
minor earthquakefelt by humans
great earthquakenear total destructionmassive loss of life
Chile (1960)
Alaska (1964)
Kobe, Japan (1995)
San Francisco, CA (1906)New Madrid, MO (1812)
Long Island, NY (1884)
Large Lightning Bolt
Average Tornado
Hiroshima Atomic Bomb
Mount St. Helens Eruption
Loma Prieta, CA (1989)Charleston, SC (1886)
Oklahoma City BombingModerate Lightning Bolt
Krakatoa Eruption
World’s Largest Nuclear Test (USSR)
E a r t h q u a k e s E n e r g y E q u i v a l e n t s
Northridge (1994)
San Fernando ValleyNorthridge
IRIS is a university research consortium dedicated to monitoring the Earth and exploring its interior through the collection and distribution of geophysical data. IRIS programs are conducted in partnership with the US Geological Survey, and are supported by the National Science Foundation and other federal agencies, universities, and private foundations. Copies of this poster can be obtained from; the IRIS Consortium, 1200 New York Ave., NW, Suite 800, Washington, DC 20008 (202) 682-2220.
SantaSusana
Mountains
SanFernandoFault
SantaSusanaFault
SanGabrielFault
HingeSpring
The Global Seimographic Network is an international scientific program
to monitor the Earth and explore it’s interior. Data from the network are
used for scholarly research, education, earthquake hazard mitigation, and
to verify compliance with the Comprehensive Test Ban Treaty.
GLOBAL SEISMOGRAPHIC NETWORK WHERE DO EARTHQUAKES HAPPEN?
Earth’s outer surface, the Earth’s crust, is broken into what geologists call
tectonic plates. These plates move under, over, or slide past each other. The
plates are driven by hot mantle materials that convect. The relative
motion of plates is associated with earthquakes. Most earthquakes occur
along the edges of large plates. The arrows on the map above indicate how
fast the plates are moving in millimeters per year.
Afr ican Plate
Nazca Plate
Pacif ic PlateSouthAmerican
Plate
NorthAmerican
Plate
Cocos Plate
Caribbean Plate
Antarct ic Plate
Somali Plate
PhilippinePlate
Indo-Austral ian Plate
Eurasian Plate
ArabianPlate
Scotia Plate
Juan de Fuca Plate
10
23 29
79 106
4632
12
6 11
8
8
14
54
59
74
9
9
921
105
102
NorthridgeRupture
Earthquakefocus
North
18km
Needles, California (NEE)
Tucson, Arizona (TUC)
Corvallis, Oregon (COR)
Cathedral Cave, Missouri (CCM)
College Outpost, Alaska (COL)
Harvard, Massachusetts (HRV)
Adak, Alaska (ADK)
San Juan, Puerto Rico (SJG)
Chiang Mai, Thailand (CHTO)
Wright Valley, Antarctica (VNDA)
Narrogin, Australia (NWAO)
Lobatse, Bot swana, Africa (LBTB)
Taipei, Taiwan (TATO)
Enshi, China (ENH)
Tibet, China (LSA)
Beijing, China (BJI)
Nana, Peru (NNA)
Albuquerque, New Mexico (ANMO)
La Paz, Bolivia (LPAZ)
Rarotonga, Cook Islands (RAR)
Yuzhno Sakahlinsk, Russia (YSS)
Kongsberg, Norway (KONO)
Matsushiro, Japan (MAJO)
Taburiente, Canary Island, Spain (TBT)
San Pablo, Spain (PAB)
Obninsk, Russia (OBN)
Charters Towers, Australia (CTAO)
Palmer Station, Antarctica (PMSA)
P w
av
e r e
f l ec
t ed
on
ce
at t h
e E
art h
' s s
urf a
ce
( PP
wa
ve
)
P w
ave diffracted around th
e core-m
antle
boundary (P
diff wave)
S wave diffracted around the core-m
antle
boundary (Sdiff w
ave)
dir
ec
t c
om
pr
es
sio
na
l
wa
ve
(
P
wa
ve
)
di r e
ct s
he
ar w
av
e ( S
wa
ve
)
S wave re f lec ted once a t the Ear th ’s sur face (S
S w
ave)
s u r f a c e wa v e
DI
ST
AN
CE
f
ro
m
ea
rt
hq
ua
ke
(
1∞
=1
11
k
m)
P w
ave
trave
rsing th
e o
ute
r
an
d in
ner co
re (P
KIK
P w
ave
)
P w
ave traversing th
e outer co
re (PK
P w
ave)
T I M E s i n c e e a r t h q u a k e o c c u r e d ( t r a v e l t i m e )
S O U T H
A F R I C A
Surface
Earthquake EpicenterNorthridge, California
TEIG
SRR
PFO
JTSPAYG
BOCO
NNA
RPN
LPAZ
LVC
TRQA
PLCA
PTGA
SDV
CPUP
EFIEFI
HOPEHOPE
SUR
ASCNASCN
BOSA
LBTB
TSUM
BDFB
HKT
NE
E
TUC
AN
MO
CO
R
CC
M
COL
HRV
ADK
SAML
LSZ
SHELSHEL
NWAO
LBTB
SJG
NNA
RAR
LPAZ
YSS
KONO
MAJO
TBT
PAB
OBN
BJI
TATO
ENH
CTAO
PMSA
LSA
CHTO
VNDA
P wave, S wave
P wave, S wave
P wave, S w
ave
Pdiff w
ave
P wave, S wave
PK
P w
ave
PK
IKP
wave
Seismic stations close to the earthquake record strong P, S and Surface waves in quick succession just after the earthquake occurred.
The sharply decreasing P and S wave amplitudes seen at
stations beyond about 100∞ (1,100 km) from the
earthquake indicate the existence of the Earth’s outer core.
Although P waves travel through the outer core (PKP waves), S
waves do not. Because liquids
cannot support shear motion, the absence of S waves tra
veling through the outer core
indicates that the outer core is fluid.
INNERCOREcomposed mostlyof solid iron,P wave velocitiesaround 11 km/s,S wave velocitiesaround 3.5 km/s
OUTERCOREcomposed mostly ofliquid iron, P wavevelocities increase from8 km/s to 10 km/s,S wave velocity is0 km/s (no S waves)
MANTLEcomposed of magnesium-ironsilicate material, P wavevelocities increase from 8 km/sto 13 km/s, S wave velocitiesincrease from 4.5 km/s to 7 km/s
CRUSTcomposed of mostlygranitic and basalticrock, extends from Earth's surface toabout 50 km depth,P wave velocitiesincrease from6 km/s to8 km/s, S wavevelocities increasefrom 3.5 km/s to 4.5 km/s
50 KM
2,900 KM
5,100 KM
6,370 KM
PP
wave
, SS
wave
LZH
LBTB
LPAZ
PLCA
VNDA
BJT
KMI
ANTO
BILL
CHTO
CMBCOR GRFO
KBSKEV
KIP
MA2
MAKZ
NWAO
PABPAS
PMG
SNZO
TBT
TIXI
TSUM
ULN
YAK
ABKTCMLA
JTS
MSVF
TAU
BGCA
SBA
HRVMAJO
DBIC
ENH
HIAMDJ
ANMO
CASY
CCM
DPC
INCN
KONO
PMSA
SPA
RAYNHKT
PTGA
SSPATUCPFO
WRAB
QIZ
BDFB
BOSACPUP
LSA
WMQ
XANSSE
FURI
ADK
AFI
BOCO
COLA
CTAO
DAV
GNI
GUMO
HNR
KIEV
KMBO
LSZ
LVC
PET
PTCNRAR
SDV
SFJ
SJGTATO
TEIG WAKE
XMAS
YSSAAK
ALE
ARU
ASCN
BORG BRVK
COCO
EFI
ERM
ESKFFCKDAKKIV
KURK
LVZ
MSEY
NIL
NNA
NRILOBN
RPN
SHEL
SUR
TLY
HOPE
PAYG
ABUS
MBWA
MSKU
MACQ
QUE
Socorro
TarawaUganda
Cape Verde Is.Kwajalein
Gissar
Funafuti
NDI
Sulawesi
TRQA
BEC BHLDWPF
JOHNKOD
KOWA
Kanton
RAO
Midway
POHA
RCBR
TRINTRIS
SAML
WSAR
Jos
Diego Garcia
Abha
Nukuhiva
SHIO
