1 Introduction
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1.1.1 Overview
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Seismology is used to map the earth’s interior and study the distribution of
physical properties
– The existence of the crust, deeper mantle, liquid outer core, and solid inner core
are inferred from variation in seismic velocity with depth.
• Near the surface - the locations of economic resources (e.g. oil)
• Deeper in the earth - dynamic history and evolution (e.g. mantle
convection)
• The nature of faulting during an earthquake is determined from the
resulting seismograms
Basic ideas – Refraction, Reflection, and Diffraction
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Basic Data - Seismogram
Phase : An individual seismic wave arrival
Magnitude 6 earthquake in Columbia recorded in Colorado (~4900 km)
Study earth structure
Travel time of multiple ScS -> Depth of Core
Amplitude -> the contrast in physical properties between mantle and core
Deep earthquake (650km) in Tonga recorded in Hawaii
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Exploration of the near surface
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Seismic sources
Hypocenter or Focus: The location of an earthquake
Epicenter: The point on the earth’s surface above the hypocenter
Magnitude or Moment: The size of earthquake
1.1.2 Models in seismology
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Limitations on current seismology
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The composition of the Earth
The deep physical processes
Actual fault process
No ability to predict earthquakes
• Because of the complexity of the processes being studied and the
limits of our observations.
• Simplified models to represent key elements of the process
• Inverse and Forward problem.
Forward
Model
Theory
Data
Inverse
• Very difficult (nearly impossible) to get a real model
• Consider issues of precision, accuracy, and uncertainty
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Models improve with time
1. Improvement in data
2. New observational and analytical techniques are introduced
Fitting  # of parameters
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1.2 Seismology and Society
• Seismic exploration
– Oil and other valuable resources
• Earthquake studies
– Seismic Hazard
– Earthquake preparedness strategies
• Nuclear arms control
– Nuclear test monitoring
• Need to know the limit
– Since 1970s the Japanese government has spent more than $1 billion (약 1조원)
on earthquake prediction study.
– Large earthquakes will be preceded by observable precursory phenomena.
– Many seismologists increasingly doubt that such phenomena exist.
1.2.1 Seismic hazards and risks
mb  4
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Hazard and risk
• Hazards
– The intrinsic natural occurrence of earthquakes and the resulting ground motion
and other effects
• Risks
– The danger in the hazard poses to life and property
• The risks are not always proportional to the hazards
• The risks are depending on the populations and construction types.
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1.2.2 Engineering seismology and earthquake engineering
• “Earthquakes don’t kill people; buildings kill people”
• Proper construction is the primary method used to reduce
earthquake risks
• Goal
– Understand the earthquake ground motions that can damage buildings and other
critical structures
– Design structures to survive them or at least ensure the safety of the inhabitants
• Two measures used to characterize the ground motion at a site
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Acceleration (Accelerometer)
Intensity (Don’t need any seismometer)
MMI (Modified Mercalli intensity scale)
MMI I : Shaking not felt, no damage
MMI XII : Damage total, Waves seen on ground surfaces.
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Ms=6.8
~25,000 deaths, but we can expect about only 30 deaths if it happened in California.
(1989 Ms 7.1 Loma Prieta Earthquake killed 63 people)
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지진 취약도
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1.2.3 Highways, bridges, dams, and pipelines
Damage to the Bay Bridge from October 17, 1989, Loma Prieta earthquake
Damage to the Nimitz freeway from October 17, 1989, Loma Prieta earthquake
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Damage to the Hanshin Expressway from Jan. 17, 1995, Kobe earthquake
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What is the cause of the great damage from the earthquake?
Fires burning in San Francisco five hours after the April 18, 1906, earthquake.
Many buildings were damaged by the shaking, but fires that lasted three days are
thought to have done ten times more damage
1.2.4 Tsunamis, landslides, and soil liquefaction
Aerial view of Valdez, Alaska, showing the inundation of the coastline
following the great 1964 earthquake.
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Inundation due to December
24, 2004, Sumatra earthquake
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Damage to apartment buildings caused by soil liquefaction during the June
16, 1964, Niigata (Japan) earthquake.
1.2.5 Earthquake forecasting
• Other geophysical process (e.g. storm)
• Long term average forecast
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Use historic records
Prepare necessary resources
• Short term weather forecasting
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Identify conditions under which a storm is likely to form soon
• Real time monitoring
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People are warned a day or more in advance to make preparations.
• Volcanic Hazard assessment
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Long term :Eruption history
Short term: Precursors such as ground deformation, small earthquakes, and the
release of volcanic gases
Small eruption usually precede a large one
• Real time warning
The giant eruption of May 18, 1980
• 60 deaths including a geologist and citizens who refused to leave.
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How about earthquakes?
• Long term
Successful!
• Short term
Impossible(?)
• Real time warning
OK!
1.
2.
3.
4.
Where?
How often?
How large?
How much ground
motion?
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When large earthquake will occur?
Average time between events is 132 yrs
(intervals vary from 45 to 332 yrs)
Next one? 1989 +/- 105 yrs
Clustered? or not?
Plate motion is constant but earthquake
cycle is not.
What makes earthquake forecasting difficult?
• In case of storm
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Occur frequently on human time scales
Understand their basic physics
• In case of earthquake
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The cycle of earthquakes on a given fault is long on a human time
scale.
Only a few places with a time history long enough to formulate useful
hypotheses
Need more time to test the model
The fundamental physics of earthquake faulting is not yet understood.
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1.2.6 Earthquake prediction
• Specify within certain ranges the location, time and size of an
earthquake a few days to days before it occurs
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Search for precursors
• Foreshocks
• Emission of Radon gas
• P/S velocity ratio
• A decrease in the electric resistivity
• Composition of ground water
• Ground deformation
• What else?
Anomalous behavior
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Parkfield case (M6, 09/28/2004)
Harris and Arrowsmith (2006)
From USGS Web page
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1.2.7 Real-time warning
• For tsunamis
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Tsunami wave is slower than seismic wave
From Alaska to Hawaii (Seismic wave = 7 min, Tsunami = 5.5 hrs)
For Earthquakes
• Application is limited (Source region and urban region is away)
• Automatic warning system
• Stop trains, shut off gas valve, etc
• Rapid estimation of the damages
지진조기 경보의 개념 (J.D. Cooper, 1868)
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지진파의 전파 특성
지진 대비 (지진 조기 경보)
Kanamori, 2005
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지진조기경보 규모 결정
화산 감시와 경보
• 마그마 상승에 의해 암석들이 깨지면서 발생하는 지진파.
• 마그마의 상승과 하강에 따른 지표면의 변화
• 마그마 상승에 의한 압력 하강에 따라 용해되어있던 가스
방출
• 1991년 필리핀 Pinatubo 화산 폭발의 경우
• 300여명 사망
• 경보가 없었을 경우 20,000명 이상 사망 예상
• 화산 감시에 사용된 비용 (약 15억원)
• 경보에 의해 약 5000억 가량 재산 피해를 예방
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화산 감시 (마그마의 상승에 의한 지진 및 변형)
인공위성을 이용한 화산 모니터링
Stanford Univ.
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Monitoring Volcanic Eruptions
Infrasound : low-frequency sound (< 50 Hz)
Infrasonic waves propagate out of
the vent and travel through the atmosphere.
Seismic waves originate from a
diffuse zone and travel through the ground.
Harvard Univ.
1994년 Rabaul Volcano Eruption
Jim Mori, 2010 한국 강연
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1994년 Rabaul Volcano Eruption
Jim Mori, 2010 한국 강연
1994년 Rabaul Volcano Eruption (지표면 상승)
Jim Mori, 2010 한국 강연
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1994년 Rabaul Volcano Eruption (지진 발생빈도 증가)
Jim Mori, 2010 한국 강연
1994년 Rabaul Volcano Eruption
Jim Mori, 2010 한국 강연
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1994년 Rabaul Volcano Eruption
Jim Mori, 2010 한국 강연
1994년 Rabaul Volcano Eruption
Jim Mori, 2010 한국 강연
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화산 감시 및 경보 시스템의 중요성
Jim Mori, 2010 한국 강연
위험한 화산
나폴리의 인구는 약 300만명
단시간 내에 전부
Evacuation하는 것은 거의
불가능
Nature, 2011
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위험한(?) 화산
Science, 2011
1.2.8 Nuclear monitoring and treaty verification
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Regional Moment Tensors
Preliminary results of
moment tensor solutions in
Korean Peninsula using
Korean Regional Networks
(KIGAM and KMA)
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