elements seismology
18
CHAPTER 2 ELEMENTS OF SEISMOLOGY
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Transcript of elements seismology
CHAPTER 2ELEMENTS OF SEISMOLOGY
WHAT IS SEISMOLOGY?
•Seismology is a science dealing with all aspects of earthquakes
• Multidisciplinary science, links physics with other geosciences (geology, geography)
•Large span of amplitudes ( ~ 10-9 – 101 m)
• Very large span of wave periods ( ~ 10-3 – 104 s)
• Very young science (second half of the 19th century)
EL
EM
EN
TS
O
F
SE
ISM
OL
OG
Y1. THEORY OF PLATE TECTONICS
2. EARTHQUAKE FAULTS
THEORY OF PLATE TECTONICS
PL
AT
E T
EC
TO
NIC
SPLATE TECTONICS theory is very young (1960-ies)
It provides answers to the most fundamental questions in seismology:
Why earthquakes occur?
Why are earthquake epicenters not uniformly distributed around the globe?
At what depths are their foci?
•By definition the word "plate" in geologic terms means a large slab of solid rock. "Tectonics" is a part of the Greek root for "to build" and together the terms define how the Earth's surface is built up of moving plates.The theory of plate tectonics itself says that the Earth's lithosphere is made up individual plates that are broken down into over a dozen large and small pieces of solid rock.
TECTONIC PLATES
•Plate tectonics is the scientific theory that attempts to explain the movements of the Earth's lithosphere that have formed the landscape features we see across the globe today.
TECTONIC PLATES
•These fragmented plates ride next to each other on top of the Earth's more fluid lower mantle to create different types of plate boundaries that have shaped the Earth's landscape over millions of years.
TECTONIC PLATES
MA
jOR
TE
CT
ON
IC P
LA
TE
S
MAJOR TECTONIC PLATES EARTHQUAKE EPICENTRES
OCEAN-BOTTOM AGE VOLCANOES
ONE YEAR OF SEISMCITY
MAJOR TECTONIC PLATES EARTHQUAKE EPICENTRES
TE
CT
ON
IC P
LA
TE
S Tectonic plates are
large parts of litosphere ‘floating’ on the astenosphere
Convective currents move them around with velocities of several cm/year.
The plates interact with one another in three basic ways:
1. They collide2. They move away from each other3. They slide one past another
INT
ER
AC
TIN
G P
LA
TE
S Plates moving past
each other do so along the TRANSFORM FAULTS.
The earthquakes may be very strong.
EXAMPLES: San Andreas Fault (Pacific – North American plate)
EARTHQUAKE FAULTS
• Earthquakes occur at FAULTS.
• Fault is a weak zone separating two geological blocks.
• Tectonic forces cause the blocks to move relative one to another.
HO
W E
AR
TH
QU
AK
ES
O
CC
UR
S?
?
•In geology, a fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement along the fractures as a result of earth movement
FAU
LTS
