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Natural Hazards and Disasters Chapter 4 Earthquake Prediction and Mitigation. Predicted Earthquake Arrives on Schedule. Early afternoon February 4, 1975: officials in Haicheng, China issued warning to expect large earthquake in next two days, asked people to remain outside

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natural hazards and disasters chapter 4 earthquake prediction and mitigation
Natural Hazards and Disasters

Chapter 4

Earthquake Prediction

and Mitigation

predicted earthquake arrives on schedule
Predicted Earthquake Arrives on Schedule
  • Early afternoon February 4, 1975: officials in Haicheng, China issued warning to expect large earthquake in next two days, asked people to remain outside
  • Prediction based on
    • Increase in small earthquakes
    • Rise in elevation, ground tilting near fault
    • Changes in groundwater levels, magnetic field
    • Strange animal behavior
  • 7:36 pm: magnitude 7.3 earthquake struck
    • 90% of buildings damaged or destroyed
    • 2,014 deaths, 27,500 injuries, out of 3 million people
predicted earthquake arrives on schedule1
Predicted Earthquake Arrives on Schedule
  • Early 1976: officials in Tangshan, China issued forecast to expect large earthquake later that year
  • On July 26, scientist noticed changes in electrical properties of ground, issued warning of impending earthquake
  • Warning did not reach Tangshan before magnitude 7.6 earthquake struck
  • Tangshan (city of 1 million) was destroyed
    • More than 250,000 people killed
    • 164,000 people injured
predicting earthquakes
Predicting Earthquakes

Scientists cannotpredict date and time when earthquake will strike, but do understand which regions are likely to experience earthquakes

Objective is to provide reasonably reliable warning of impending earthquake

earthquake precursors
Earthquake Precursors
  • Research continues to explore phenomena that warn of imminent earthquake
  • Track fault movement to anticipate when it will break
    • Monitor deformation with GPS (Global Positioning System)
  • Anticipate accumulation of stress necessary to break fault loose at predictable time
    • Stress applied at constant rate does not produce results at constant rate
    • Far more complicated conditions include juxtaposing different rock types with different strengths, changing stress patterns after nearby earthquakes
earthquake precursors2
Earthquake Precursors

earthquake precursors3
Earthquake Precursors
  • Swarms of minor earthquakes or foreshocks may announce onset of fault slippage
    • Swarms precede 1/3-1/2 of earthquakes overall but only small percentage of large earthquakes
    • Difficult to distinguish from background activity
    • Study of microearthquakes identifies previously unknown faults
    • Impossible to determine in advance if a given small earthquake is foreshock or ordinary small earthquake
earthquake precursors4
Earthquake Precursors
  • Change in levels of radon is possible earthquake precursor
    • Rare gas forms as part of uranium’s decay chain
    • Forms no chemical compounds
    • Remains trapped in rock until escapes along fracture
    • Formation of new fractures before large earthquake may allow radon to escape closer to ground surface (and may cause drop in water table)
    • Changes detectable as increase in radioactivity of groundwater wells
earthquake precursors5
Earthquake Precursors

Radon concentration changes in ground water prior to and after the 1966 Tashkent earthquake in the USSR

Radon concentrations prior to the Songan-Pingwu earthquakes in China. The arrows indicate the time and magnitude of the earthquakes

Gray 1996. A Review of Two Methods of Predicting Earthquakes.

earthquake precursors6
Earthquake Precursors

Vertical movements of bench marks along the west coast of Japan near the June 1964 Niigata earthquake. Changes in level (in centimeters) before and after the earthquake are shown on the right

Gray 1996. A Review of Two Methods of Predicting Earthquakes.

  • Change in ground elevation is possible earthquake precursor
    • In 1975, geologists noticed rise in surface elevation near Palmdale, California
    • Accompanied by drop in groundwater level, increase in background radiation
    • No recent earthquakes on adjacent fault might indicate that earthquake was overdue
    • No earthquake has occurred in time since then
earthquake precursors7
Earthquake Precursors
  • Zone of high fluid pressure may localize fault movement
    • Pumping water into ground has inadvertently triggered earthquakes
    • Addition of fluids into area of fault increases pore-fluid pressure and decreases strength of fault until it breaks
    • Suggestion that deliberate injections into fault may trigger smaller earthquakes and relieve stress, may preempt large earthquakes
    • Consequences are too serious to attempt
    • Too many smaller earthquakes would be necessary to relieve stress
earthquake precursors8
Earthquake Precursors
  • Combination of factors monitored by UCLA team
    • Increase in frequency of small earthquakes
    • Clustering of small earthquakes in time and space
    • Nearly simultaneous earthquakes over large parts of region
    • Increase in ratio of medium-magnitude earthquakes to small-magnitude earthquakes for region
  • Two successful predictions in 2003
  • Unsuccessful prediction for 2004
  • Still being tested
early warning systems
Early Warning Systems

Large earthquake 100 km or more away could be detected in time to give useful warning

Earthquake waves travel 4 km/s, take 25 seconds to travel 100 km

Enough time for early warning system to shut down critical facilities

prediction consequences
Prediction Consequences
  • Short-term forecasts or warnings also raise complex political issues
  • Possible consequences of announcing reliable prediction days in advance:
    • Hysterical public reaction
    • Major physical and economic damage
  • With current state of knowledge, earthquakes are inherently unpredictable in short term
earthquake probability
Earthquake Probability

Can make reasonable reliable forecasts

Statement of where and how frequently an event is likely to occur and how large it is likely to be

Understand tectonic environment

Establish record of past events

forecasting where faults will move
Forecasting Where Faults Will Move

Digging steps into the trench at Tule Pond (Tyson Lagoon), Hayward fault, Fremont, CA. photo by Jennifer Adleman, USGS.

  • Paleoseismology: study of prehistoric fault movements
    • Expose fault by digging trench across it
    • Study offset of sediment layers by fault movement
    • Larger offset correlates to larger earthquake
forecasting where faults will move1
Forecasting Where Faults Will Move
  • Seismic gaps: segments of active fault that lack historic (or recent) earthquakes
    • More likely to be location of next large earthquake
    • 1989 Loma Prieta earthquake filled in earlier identified ‘Southern Santa Cruz Mountains gap’
forecasting where faults will move2
Forecasting Where Faults Will Move
  • Migrating earthquakes: earthquakes occur sequentially from one end of the fault to the other
    • North Anatolian fault in Turkey runs east-west for 900 km (comparable to San Andreas fault)
    • Earthquakes from east to west, from 1939 to 1999
earthquake frequency
Earthquake Frequency
  • Knowledge of past earthquakes makes it possible to estimate recurrence interval for earthquakes of various sizes
  • Can statistically estimate probability that earthquake of a particular size will strike a particular region within a specified time period
  • Some faults exhibit regular patterns of activity, though often not too reliably
    • Parkfield section of San Andreas fault: experienced a moderate earthquake every 22 years, until 38 year interval ended in 2004
    • Tokyo, Japan experiences strong earthquakes about every 70 years, with most recent expected in 1993 – hasn’t occurred yet
earthquake frequency1
Earthquake Frequency
  • North Anatolian fault in Turkey has periods of activity and inactivity
  • Coast of northern California, Oregon, Washington and southern British Columbia experiences major earthquakes at long intervals, with last earthquake 300 years ago
  • Paleoseismology of Reelfoot Fault in Tennessee shows three major earthquake sequences in last 2400 years, with recurrence interval of 500-1000 years
earthquake frequency2
Earthquake Frequency
  • Fresh appearance of Wasatch Front and other clues indicate large but infrequent earthquakes through urban areas of Utah
populations at risk
Populations at Risk

Probability of where and when an earthquake will strike used to construct risk map

populations at risk1
Populations at Risk

Highest-risk U.S. areas include heavily populated coast of California

the san francisco bay area
The San Francisco Bay Area
  • Wide zone of San Andreas Fault (SAF) system includes nearly entire San Francisco Bay area
  • SAF began to move 16 million years ago, has caused thousands of earthquakes since then
  • Gutenberg-Richter frequency vs. magnitude relationship indicates that any 100 km long segment of SAF should release energy equivalent to
    • One magnitude 6 earthquake every 8 years
    • One magnitude 7 earthquake every 60 years
    • And one magnitude 8 earthquake every 700 years
    • Many segments overdue
the san francisco bay area1
The San Francisco Bay Area

Hayward Fault splays north on east side of San Francisco Bay through Hayward, Oakland, Berkeley, Richmond

Magnitude 7 earthquake on Hayward Fault could kill several thousand people, destroy 57,000 structures

Rodgers Creek Fault extends north from Hayward Fault, also through rapidly growing populations

Over 1836-1906: magnitude 6-7 earthquakes every 10-15 years

Over 1911-1979: no magnitude 6 or higher earthquakes

Over 1979-1989: four magnitude 6-7 earthquakes

Currently in cluster of strong earthquakes?

the san francisco bay area2
The San Francisco Bay Area
  • Forecast that before 2032:
    • 21% probability of magnitude 6.7 or larger earthquake on San Andreas Fault
    • 27% probability of magnitude 6.7 or larger earthquake on Hayward-Rodgers Creek Fault
    • 11% probability of magnitude 6.7 or larger earthquake on Calaveras Fault
  • Or in summary
    • 62% probability of magnitude 6.7 or larger earthquake somewhere in San Francisco Bay area
the los angeles area
The Los Angeles Area

San Andreas Fault is 50 km northeast of Los Angeles

Many related thrust faults cross Los Angeles basin

Moderate earthquakes (like 1994 magnitude 6.7 Northridge earthquake) are likely every 10 years

Far too few moderate earthquakes in 1857-2007 to account for observed strain across region

Moderate earthquakes may occur in clusters

minimizing earthquake damage
Minimizing Earthquake Damage

Primary cause of death and damage is from collapse of buildings and other structures

Aftermath includes fire, disease epidemics

Load-bearing masonry walls can shake apart and collapse

Bridge decks and parking garage floors can be shaken off unanchored supports

External walls are loosely attached to framework and can collapse

Reinforced concrete can break, leaving steel unenclosed so it can buckle and fail

Weak floors, unbraced windows can not resist lateral movements

structural damage and retrofitting
Structural Damage and Retrofitting

Shattering windows are major source of injuries – safety glass becoming more common

Older buildings have loosely-resting beams – can pull out, collapse

Older houses are not bolted down – can be shaken off their foundations

Overhanging parapets or external décor can be easily shaken off, fall onto sidewalk, parked cars

structural damage and retrofitting1
Structural Damage and Retrofitting

Buildings can be constructed to withstand severe earthquake

Wood-frame houses are flexible enough to bend without shattering

Welded or bolted steel frames can resist collapse

Retrofitting old, existing buildings can be much more expensive than building new ones at higher standard

structural damage and retrofitting2
Structural Damage and Retrofitting
  • Tall buildings can collapse if upper floors are moving in one direction while ground snaps back in other direction
  • Computer modeling shows whiplash effect on 20-story L.A. building, built according to latest codes
  • Amount of sway depends on frequency of earthquake waves
    • If natural vibration frequency of building matches frequency of ground shaking, resonance can greatly amplify shaking of building
    • Tall buildings most vulnerable to lower frequencies
structural damage and retrofitting3
Structural Damage and Retrofitting
  • FEMA issued new steel construction guidelines in 2001 for areas prone to earthquakes
  • Engineers use base isolation to protect buildings from shaking ground
    • Can be done in new construction or as part of retrofitting
earthquake preparedness
Earthquake Preparedness
  • Evaluate structural weaknesses in home and retrofit
    • Walls should be anchored to floors and foundation
    • Bolt bookcases and water heaters to walls
    • Secure chimneys and vents with brackets
    • Make water and gas mains flexible
  • Consider purchasing earthquake insurance
    • Most well-built wood-frame houses will not collapse, but may be rendered uninhabitable or worthless
    • Extremely expensive, not part of homeowners insurance
    • Covers only cost of house, not land
earthquake preparedness1
Earthquake Preparedness
  • Plan what to do when earthquake strikes
    • If indoors, stay there
    • Usually not enough time to get out
    • Longer-lasting earthquakes accompanied by stronger ground motions that would make it very difficult to stay mobile
    • Lie down next to sturdy object, under table or desk, in doorway
    • If you do leave a building, avoid elevators and run for open ground
by the numbers
By the Numbers

Frequency of Building Vibration

Buildings of different heights sway at different frequencies

During earthquake, ground vibrates at different frequencies in response to different types of earthquake waves

Buildings should avoid shaking at similar frequency as ground

Short, rigid building on soft sediment often does well in earthquake

Tall, flexible building on bedrock often does well in earthquake

land use planning and building codes
Land Use Planning and Building Codes

Best defense against deaths, injuries and property damage

Should require structures framed in wood, steel or reinforced concrete

Should forbid masonry walls of brick, concrete blocks, stone or mud that support roofs

Uniform Building Code provides seismic zonation map of U.S. indicating construction standards

Enforcement of building codes often issue

Modern, strongly enforced construction codes  significant damage but few deaths

Poor-quality construction and little enforcement of construction codes  high death tolls

land use planning and building codes1
Land Use Planning and Building Codes

Zoning should strictly limit development along active faults, areas prone to landslides, on soft mud or fill

Such dangerous areas could be used as parks, golf courses

Many cities grew in dangerous areas before dangers were understood

Increasing problem of millions living in hazardous environments

case in point
Case in Point

Earthquake Fills a Seismic Gap: Loma Prieta Earthquake, California, 1989

Just before start of Game Three of World Series between San Francisco Giants and Oakland Athletics

Jarring arrival of P wave was followed 10 seconds later by intense shaking of S wave  earthquake about 80 km away, in Santa Cruz mountains

2.25 mile stretch of upper deck of freeway in Oakland collapsed, killing 42 motorists (would have been many more in ordinary rush hour traffic, if not for World Series game)

Buildings in Marina District were badly damaged, because located on soft fill

case in point1
Case in Point

Earthquake Fills a Seismic Gap: Loma Prieta Earthquake, California, 1989

case in point2
Case in Point

Earthquake Fills a Seismic Gap: Loma Prieta Earthquake, California, 1989

62 people killed, 3757 people injured, 12,000 displaced from homes

963 homes destroyed, $6 billion in property damage

Offset of fault began at 18 km depth, did not reach surface

Working Group on California Earthquake Probabilities had already identified fault segment as one likely to produce earthquake of magnitude 6.5 or higher between 1988-2018

case in point3
Case in Point

One in a Series of Migrating Earthquakes: Izmit Earthquake, Turkey, 1999

Slip on North Anatolian Fault, 100 km east of Istanbul, caused magnitude 7.4 earthquake, followed three months later by magnitude 7.1 earthquake

Magnitude 6.4 earthquake struck in 2003

Series of six large earthquakes progressed westward on fault between 1939 and 1957

Building codes same as in U.S. but poor enforcement

Tax code based on area of first floor, so favors extended second stories

Many buildings collapsed in 1999

case in point4
Case in Point
  • A Case of Equal-Interval Earthquakes: Parkfield Earthquakes, California
  • San Andreas Fault at Parkfield, California had generated magnitude 5.5-6.0 earthquakes at ~22 year intervals
    • 1857, 1881, 1901, 1922, 1934, 1966
  • Prompted forecast of 95% probability of magnitude 6 earthquake at Parkfield between 1985 and 1993
  • USGS installed variety of expensive instruments
  • Magnitude 6 earthquake finally struck – in 2004
  • Instrumentation recorded no clear precursor activity
case in point5
Case in Point

Devastating Fire Caused by an Earthquake: San Francisco, California, 1906

Foreshock followed by magnitude 7.8 earthquake, with shaking that lasted 45-60 seconds

More than 28,000 buildings destroyed

Shaking was followed by three days of fire

Death toll was officially given as 700 – probably actually more than 3000

case in point6
Case in Point

Damage Depends on Building Design: Kobe Earthquake, Japan, 1995

Magnitude 7.2 earthquake caused by horizontal slippage on Nojima fault, similar to SAF

Despite earthquake design and construction among best in world, more than 5000 deaths and $355 billion in damage

15 seconds of shaking at focus, reverberated for more than 100 seconds in soft sediments

At least 180,000 buildings damaged

Bridges, elevated highways, rail lines collapsed

case in point7
Case in Point

Collapse of Poorly Constructed Buildings: Kashmir Earthquake, Pakistan, 2005

Magnitude 7.6 earthquake struck western Himalayas

87,000 people killed, mostly by collapse of heavy masonry structures or landslides triggered by earthquake

Evidence of shoddy construction practices or low-quality building materials

Combination of intense shaking, enormous population, poor-quality building materials and construction

Numerous aftershocks hampered rescue efforts

case in point8
Case in Point

Building Code Not Enforced: Bhuj Earthquake, India, 2001

Magnitude 7.7 earthquake struck city of Bhuj in western India, just south of collision zone between Indian plate and Asia

Earthquake on blind thrust fault

More than 30,000 people died, mostly killed by collapsing buildings

India’s building codes similar to U.S., but not enforced – merely advisory