Environmental%20Geology

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Environmental Geology

• Earthquakes

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Directivity

• The amplitude of seismic waves is greater in the
  direction of fault rupture

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Building Damage and Ground-Structure Interactions

• Damage depends on the ground motion and duration
  of shaking
• Ground motion is related to
• -the magnitude of the eq and characteristics
  of the seismic waves
• -Proximity of the epicenter to the site
• Soil conditions at the site

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Resonance

• Amplifying effect produced when the natural
  vibration frequency of ground or structure is
  matched by the frequency of seismic waves.
• Building Height / Typical Natural Period
• 2 story .2 seconds
• 5 story .5 seconds
• 10 story 1.0 seconds
• 20 story 2.0 seconds
• 30 story 3.0 seconds

buildings suffer the greatest damage from ground
motion at a frequency close or equal to their own
natural frequency.
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Resonance

• Building vibration periods roughly the number
  of stories
• If building and soil have same frequency of
  vibration, resonation occurs (amplification)
• Typically, low-rise buildings (lt5 Stories)
  located on shallow soils (lt50 feet) and high-rise
  buildings (gt14 Stories) on deep soils (gt150 feet)
  sustain the most structural damage

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Earthquake Damage

• A) Direct shaking ground rupture
• B) Secondary effects
• Liquefaction
• Landslides
• Fires
• Tsunamis
• Flooding due to changes in land elevation

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What can we do?

• Structural protection
• Land use planning
• Earthquake warning system
• Effective emergency response plan
• Increased insurance/recovery measures

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B) Short-term prediction

• Precursory phenomena
• Ground deformation
• Seismic gaps
• Patterns and frequency of small earthquakes
• foreshocks
• Anomalous animal behavior

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Frequency Period of Earthquake waves
(clarification)

• Frequency (Hz) 1/Period (sec)
• Higher frequency/lower period more rapid
  attenuation (examples?)
• Body waves (usually .5-20 Hz .05-2 sec)
• higher frequencies (lower periods) than surface
  waves
• Surface waves (usually less than 1 Hz, greater
  than 1 sec)
• Lower frequencies (higher periods)

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Effect of waves

• Buildings have a natural vibrational frequency
• Low buildings have higher frequencies (lower
  periods) than high buildings
• Low buildings shaken by body waves (high freq.)
• High buildings shaken by surface waves (low
  freq.)
• High frequency waves attenuate more quickly
• High buildings shaken at longer distance from the
  epicenter
• REALITY MANY FACTORS GOVERN EARTHQUAKE DAMAGE!!!

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Earthquake Damage

• A) Direct shaking ground rupture
• B) Secondary effects
• Liquefaction
• Landslides
• Fires
• Tsunamis
• Flooding due to changes in land elevation

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Human activity that affects e.q.

• 1) Underground nuclear explosions
• 2) Loading/unloading of the earths crust
• Dam or reservoir
• 3) Deep waste disposal
• Ex Rocky Mnt. Arsenal (1962-1965)
• Liquid waste pumped 3.6 km

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What can we do?

• Structural protection
• Land use planning
• Earthquake warning system
• Effective emergency response plan
• Increased insurance/recovery measures

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Earthquake prediction

• A) Long-term prediction
• Estimate relative seismic hazard
• Estimate conditional probabilities
• B) Short-term prediction
• Precursory phenomena

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A) Long-term prediction

• Estimate relative seismic hazard
• Active faults?
• Active Holocene
• potentially active Quaternary
• Inactive Pre Quaternary
• History of fault activity
• Paleoseismology (Pallet Creek study Coyote
  Creek study page)
• Estimate average recurrence interval

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B) Short-term prediction

• Precursory phenomena
• Ground deformation
• Seismic gaps
• Patterns and frequency of small earthquakes
• foreshocks
• Anomalous animal behavior

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The San Andreas Fault Zone in Southern California

• Faults in San Diego

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California Regulations pertaining to earthquakes

• Alquist-Priolo Fault Zoning Act (1972)
  (California law)
• direct result of the 1971 San Fernando Earthquake
• requires that zones along active faults with
  well-defined surface features be established
• (http//www.consrv.ca.gov/CGS/rghm/ap/)
• Seismic Hazards Mapping Act (1990)
• addresses non-surface fault rupture earthquake
  hazards, including liquefaction and seismically
  induced landslides
• The Natural Hazards Disclosure Act (1998)
• sellers of real property must provide prospective
  buyers with a "Natural Hazard Disclosure
  Statement" when the property being sold lies
  within one or more state-mapped hazard areas.

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Alquist-Priolo Fault Zoning Act

• 1972 Alquist-Priolo Special Studies Zones Act -
  Passed in 1972 as a direct result of the 1971 San
  Fernando Earthquake.
• Many cities have their own amendments
• Purpose
• Provides policies and criteria to assist cities,
  counties, and state agencies in the exercise of
  their responsibility to prohibit the locations of
  developments and structures for human occupancy
  across the trace of active faults
• Fault must have well-defined Holocene surface
  rupture (Blind-thrusts are exempt)

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Alquist-Priolo Fault Zoning Act

• Summary of Specific Criteria
• No structure for human occupancy shall be placed
  within 50 feet of an active fault
• Area within 50 feet of fault trace presumed to be
  underlain by active branches of the fault unless
  proven otherwise
• Lead agencies (State Geologist, State Mining and
  Geology Board) shall provide public disclosure of
  delineated fault zones to the public
• Development permit applications for any project
  within a delineated zone must be accompanied by a
  geologic report
• The sellers agent or seller of real property
  located within a delineated zone shall disclose
  to the buyer that fact

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Alquist Priolo Fault Zoning Act

• Exemptions
• Any structure built before May 4, 1975
• Single-Family wood-framed dwellings (2 stories or
  under)
• Conversions or alterations of existing structures
  (under 50 the value of the structure).

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Seismic Hazards Mapping Act

• Passed in 1990, addresses non-surface fault
  rupture earthquake hazards, including
  liquefaction and seismically induced landslides.

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Seismic Zones

• In Seismic Zone 4, you have a one in ten chance
  that an earthquake with an active peak
  acceleration level of 0.4g (4/10 the acceleration
  of gravity) will occur within the next fifty
  years.
• In Zone 1, you have a one in ten chance that an
  earthquake with an active peak acceleration level
  of 0.1g (1/10 the acceleration of gravity) will
  occur within the next fifty years.

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Seismic Zones

• The Uniform Building Code places San Diego in
  Seismic Zone 4
• Buildings are required to withstand 1/3 more of
  the lateral force from earthquakes that Seismic
  Zone 3 mandates

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San Diego Seismic Standards

• San Diego has been required to enforce the State
  Earthquake Protection Law (Riley Act) since its
  enactment in 1933. However, the seismic
  resistance requirements of the law were minimal
  for many years and San Diego did not embrace more
  restrictive seismic design standards until its
  first adoption of the Uniform Building Code in
  1951.
• It is estimated that about 1,000 (mainly
  nonresidential) masonry buildings within the City
  may constitute structural hazards.

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Structural Design and Seismic Performance

• Ductile steel and ductile reinforced concrete
  frame buildings (as defined in Uniform Building
  Code) - highly resistant to structural damage
  may suffer nonstructural damage.
• Vertical load-bearing steel and reinforced
  concrete frame buildings braced against lateral
  forces - perform well but may suffer some
  structural as well as nonstructural damage.
• Unreinforced masonry buildings of all types -
  highly vulnerable to damage.

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Structural Design and Seismic Performance

• Reinforced brick and concrete block masonry
  buildings - perform well but may suffer some
  structural as well as nonstructural damage.
• Pre-engineered and other light steel and sheet
  metal buildings - usually perform extremely well.
• Residential buildings - Traditional wood frames
  with wood or stucco siding usually behave well
  but may suffer damage. Modern design open-type
  houses with large glass openings, split-level
  houses, and two-story houses or apartments with
  large garage openings in the first story are
  vulnerable to earthquake damage.

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probability of being exceeded in 50 years

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Tsunami

• Seismic sea wave (not a tidal wave)
• Disturbing forces vertical movement of seafloor
• Offshore faults subduction zone earthquakes
• Submarine landslides
• Volcanic eruptions
• Meteorite impact
• Size
• Wavelength 125 miles (200 km)
• Wave height
• Coast 10s of meters (largest are 30-40 m or
  100 ft.)
• Open ocean 1 meter (3 ft)
• Velocity
• Open ocean 450 mph
• Slow as they approach coastlines
• Distance of travel across oceans (1000s of km)

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Waves

• Deep Water Waves
• Those waves traveling with a water depth greater
  than ½ the wavelength
• The speed of deep-water waves depends on the
  wavelength of the waves. Waves with a longer
  wavelength travels at higher speed.

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Waves

• Shallow Water Waves
• Those waves traveling with a water depth less
  than 1/20th of the wavelength.
• The speed is independent of their wavelength. It
  depends, however, on the depth of the water.

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• Average wavelength for a wind wave is
• 100 meters (300 ft), tsunami is 100 miles.
• Wavelength decreases and wave height increases
  as waves
• approach the coast
• Usually more than one wave, the first is not
  always the biggest!

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A 10 meter (30 ft) tsunami wave has a lot more
energy than a 10 m wind wave
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Pacific Ocean has had more tsunami events than
any other ocean or sea.
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1m 3ft
4000 deaths from tsunami waves around the
Pacific from 1990 to 2000.
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• Chile, South America 1960
• 9.5 subduction earthquake
• largest earthquake recorded
• Tsunami traveled to
• Hawaii and Japan

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CHILE 1960 SUBDUCTION EARTHQUAKE

• A piece of the Pacific seafloor (Nazca Plate)
  about the size of California slid fifty feet
  beneath the continent of South America.
• South American continent offshore snapped
  upwards as much as 20 ft. while land along the
  Chile coast dropped about ten feet.
• The tsunami caused tremendous damage along the
  Chile coast, where about 2,000 people died.
• The waves spread outwards across the Pacific. 15
  hours later the waves flooded Hilo, on the island
  of Hawaii, where they built up to thirty feet and
  caused 61 deaths along the waterfront.
• Seven hours after that (22 hours after the
  earthquake) the waves flooded the coastline of
  Japan where ten-foot waves caused 200 deaths.
• The waves also caused damage in New Zealand.
  Tide gauges throughout the Pacific measured
  anomalous oscillations for about three days as
  the waves bounced from one side of the ocean to
  the other.

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• In San Diego ferry service was interrupted
  after one passenger-laden ferry smashed into the
  dock at Coronado knocking out eight pilings.
• A second ferry was forced 1.5 km off course and
  into a flotilla of anchored destroyers. More than
  80 m of dock were destroyed.
• A 100 ton dredge rammed the concrete pilings
  supporting the Mission Bay bridge tearing out a
  21 m section.
• A 45 m bait barge smashed eight slips at the
  Seaforth Landing before breaking in half and
  sinking.
• The currents swept away two sections of dockage
  at the Southwest Yacht Club at Point Loma.

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Wave damage in Hilo Hawaii
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DART Deep-ocean Assessment and Reporting of
Tsunamis Early detection and real-time reporting
of tsunamis in the open ocean
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• In addition to subduction zone earthquakes, what
  else could cause a tsunami in Pacific Ocean?
• Submarine landslides
• Where?

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Each slide has resulted in huge land losses to
the islands and resulted in large waves that have
carried rocks and sediments as high as 1000 ft
above sea level. The giant Hawaiian landslides
are important to study because, although they
occur infrequently, they have potential for
enormous loss of life, property, and resources.
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