ISB203B-Exam 2

Earthquake hazard assessment/mitigation and volcanoes

What are earthquake hazards?

• ground shaking

• liquefaction

• landslides

• fire

• tsunamis

what are the effects of ground shaking?

• building collapse from direct shaking

• rupturing of gas/electrical lines

• secondary effects

what are the effects of liquefaction?

• building collapse

• sinkholes

what are the effects of landslides?

destroy everything in its path

can we predict earthquakes?

• in the short term, no

• in the long term, we can predict the probability of it happening

can we prevent earthquakes?

NO

what questions can we ask to evaluate earthquake hazards?

• what is the probability of an it happening in a region?

• how large might it be?

• how will the fault move? what parts will move the most?

• what kind of damage might be expected?

what is being evaluated when we investigate the tectonic environment of a potential earthquake?

• is it on a subduction zone? this could cause a tsunami

• how large can it get?

what is being evaluated when we investigate where the faults are of a potential earthquake?

• where are the areas that could slip and cause an earthquake located?

what is being evaluated when we investigate the character of past earthquakes?

• where have earthquakes happened in the past?

• how often do earthquakes happen?

• how long since the last one?

• how large are the earthquakes?

• can track this through newspapers, merchant records, old stories, folk tales and paleo-seismology

what is being evaluated when we investigate the present day activity in an area that has a possibility of earthquales?

• present say seismicity isn’t always a good indication of earthquake potential

• an area of a fault showing a high rate of strain accumulation is likely to move more during an earthquake

what is being evaluated when we investigate the ground/surface conditions of an area with a potential earthquake?

• softer ground creates worse damage for earthquakes

• seismic hazard maps

seismic hazard map

• %g—percent gracity and predicted amount of ground shaking

• predictions for levels of peak ground shaking based on probability, higher numbers with smaller probability, low numbers with higher probability

• depends on the fault

paleo-seismology

• study of earthquakes that happened in the past

• firepits under tsunami sand

• ghost forests

• tsunami deposits

• tsunami records

• recurrance charts

• NOT WATER ON ROCKS

what cause ghost forests?

trees in marshes die because they’re dropped down into seawater because of a tsunami

tsunami deposits

• broad layers of sand and sediment brought over an area

• can dig into the earth and see where/when the tsunami came from

recurrance charts

• are based on recurrence intervals

• provide predictions of when earthquakes could happen

• not exact

what can we do to mitigate earthquake hazards?

• building construction and zoning regulations

• earthquake early warning

• tsunami warning signs

• education about earthquake hazards

wood stuctures and earthquakes

• withstands earthquakes well—almost as good as reinforced concrete

• elastic—building wiggles and absorbs ground shaking but stays together

brick structure/concrete block structure and earthquakes

• don’t withstand earthquakes well

• dislodges concrete blocks, mortar crumbles and separates, building collapses

reinforced concrete structures and earthquakes

• withstands earthquakes well

• expensive, not frequently used

• when used with steel structures, pancaking occurrs

highway overpasses and earthquakes

• concrete and interior steel supports

• bad for vertical earthquake motion—crushes rebar like a tin can

how can buildings be better constructed for earthquake mitigation?

• Adding steel corner struts, braces, and connectors can strengthen a wood-frame house 

• Buildings are less likely to collapse if they're wider at the base and if crossbeams are added for strength 

• Wrapping a bridges support columns in cables and bolting the span to the columns will prevent the bridge from collapsing so easily—cables and anchor bolts 

• Placing buildings on rollers or shock absorbers lessens the severity of vibrations—isolation  

seismic retrofitting

adding things to existing buildings so that they can come through earthquakes better 

• Foundation anchor plates—strengthen the house to foundation connection; drilled into frame of house and foundation to keep them together 

• Cripple walls 

• Add things to structures to control where the damage goes 

• Wrapping steel cable around bridges 

non-structural mitigation

things that can be done in your house to mitigate hazards 

• Strapping water heaters to walls so they can't fall over 

• Bolding things to walls 

• Not putting pictures above bed 

• Bolt appliances to wall 

• Replace copper gas lines to plastic lines 

building zoning

evaluating areas of a city that may be more susceptible to hazards and making building codes

earthquake early warning

• Advance warning of arrival of damaging seismic waves AFTER earthquake has begun 

• GPS/GNNS Waveforms 

• Seismometers 

• Seconds to minutes of warning before shaking starts 

what can be done with the seconds to minutes of warning provided before shaking starts during an earthquake

• Slow or stop trains 

• Prepare first responders 

• Protect power infrastructure 

• Stop surgeries 

• Secure sensitive equipment, shut down protection lines 

• Personal safety measures: drop and cover, stop vehicles 

tsunami warning systems

can give hours of warning before waves hit the shore

• DART buoys

warning steps as tsunami warning system

process: get information about seismic event and revise things 

• Preliminary analysis of earthquake—tsunami info statement, tsunami advisory, watch, or warning 

• Refinement of earthquake information, tsunami model estimates, additional data about tsunami gathered (repeated)--tsunami advisory, watch, or warnings may change 

• Report of tsunami wave heights/damage 

DART buoys

Deep-ocean Assessment and Reporting of Tsunami (Tsunameter) 

• Pressure recorder bolted to ocean floor 

• Communicates with satellite and satellite send message to receiving center 

• Tsunami travel times

tsunami travel times

the hours of how long the tsunami wave will take to hit other buoys/areas of the ocean

tsunami warning signs

• Signs along coasts in areas prone to tsunamis 

• Evacuation routes to higher ground as quickly as possible 

• People don't always listen 

tsunami shelters

specially designed buildings to help people get to higher ground and built to withstand tsunamis  

• Purpose built tsunami shelters 

education about earthquake hazards

• Telling people what to do and how to stay safe during earthquakes and tsunamis 

• Aware of hazards in their region 

resilience

• Ability to maintain normal services and lives after a major event 

• Rapid recovery with minimal social disruption 

• Final state of affairs better or as good as before the event 

how to improve resilience

• Identify vulnerable facilities and systems 

• Develop scenarios to assess what could happen during an event 

• Set goals for improved response and develop plans for achieving goals 

how to work towards the goals of increasing resilience

• Engineering and retrofitting 

• Earthquake early warning 

• Analysis of tsunami inundation to plan evacuation routes, future development of schools, medical centers, other critical facilities 

• Awareness and education 

why should we care about resilience?

• Impacts business/government of, potentially, the entire country 

• Trans-pacific cables—disrupted communications with other countries 

• Ports/shipping  

• Economic impacts 

• Earthquakes can happen in the Midwest and in eastern North American 

benefits of volcanoes

• Create new land 

• Enrich soil for farming 

• Create mineral deposits 

• Create picturesque landscapes/tourism 

drawbacks of volcanoes

• Destroy communities 

• Destroy existing crops 

• Displace populations 

• Kill people and animals 

• Can change human history, can cause devastation across many countries around the world from one event  

how are explanations of volcanoes different than earthquakes?

• Earthquakes: many animals, not a lot of personification 

• Volcanoes: supernatural forces, assigning nature a personality 

what is the basic anatomy of a volcano

• Bottom: source of magma 

• Magma travels to surface via a conduit 

• Magma erupts to the surface through the vent 

magma

molten rock below the surface pf the earth

lava

molten rock that has reached the surface of the earth and is either still molten or solidified

tephra

fragments of material produced during a volcanic eruption

• ash

• lapilli

• bombs

ash

fragments of tephra smaller than 2mm in diameter

lapilli

fragments of tephra between 2 and 64mm in diameter; sometimes called cinders

bombs

fragments of tephra larger than 64mm in diameter

what are the 4 types of volcanoes?

• fissures

• stratovolcano

• shield

• cinder cone

fissure volcanoes

• Long cracks in the ground where lava comes up and pours out on either side 

• Made up of layers of lava 

• Rifts and divergent margins 

stratovolcanoes

• "generic volcano;" most common above-air volcano on Earth 

• Triangle point 

• Made up of alternating layers of tephra and lava (cake layers) 

• Steep slopes due to tephra, but lava layers make it stronger  

• found in subduction zones

shield volcanoes

• Broad and rounded, gentlest slope 

• Only made up of layers of lava, small slopes because of this 

• Massive  

• Start off as fissures 

cinder cone volcanoes

• No lava, just tephra around a vent 

• Smaller because tephra is unstable but can have steep slopes 

angle of repose

slope at which that material is stable, any more, it will slide off 

• Different angles for different materials 

where are volcanoes found?

• Happen in patterns 

• Clusters 

• Arcs 

• The Ring of Fire

island arc or oceanic arc

• oceanic-oceanic convergent boundary (subduction zone) 

• Usually stratovolcanoes 

• Can occasionally have shield volcanoes 

continental arc or volcanic arc

• chain that forms in continental-oceanic convergent boundary (subduction zone) 

• Known for stratovolcanoes 

• Can also have shield volcanoes, domes, cider condes; more variety  

continental rift systems

• Fissure eruptions 

• Can have cinder cones, shield volcanoes, and stratovolcanoes because of the variation of crust material 

• Off-rift axis volcanoes

hot spot volcanism

• Shield volcanoes, fissures 

• HUGE volumes of lava 

• Prone to caldera formation

• Flood basalts/large igneous provinces

mid-ocean ridges

• Divergent boundary 

• Most common volcano type on Earth 

• Fissure eruptions; most common volcano type found under the ocean 

• Over time, may develop domes and seamounts (circular volcanic structures) 

the ring of fire

Many clusters of volcanoes around the edges of the Pacific Ocean

types of volcanic arcs

• island arc/oceanic arc

• continental arc/volcanic arc

• continental rift systems

• hot spot volcanism

• mid-ocean ridges

flood basalts/large igneous provinces

Rapid outpouring of vast amounts of lava, HUGE amount of material is what makes it unique 

• Fissure eruptions 

• Continental rifting? Hot spot? Combination of both? We don't really know the causes 

off-rift axis volcanoes

• the hot material doesn't come up into the rift valley, it goes off to either side, volcanoes develop along the sides of the rift

• shield volcanoes or stratovolcanoes instead of fissure eruptions 

magma

Mixture of melt (liquid rick), gas bubbles, and mineral crystals 

density

• mass/volume

• number and weight of molecules = amount of mass

2 major ways to get magma

• wet partial melting

• decompression melting

wet partial melting

the introduction of volatiles (like water) to generate melt

decompression melting

moving the mantle around to reduce pressure and generate melt 

• occurs in mantle plumes, rifts, mid-ocean ridges

• bouyancy —bring hot material up into cooler material (mantle convection)

heat transfer melting

• minor way to generate melt

• cannot generate melt by itself, needs melt and magma already there

• already existing magma encounters something cooler, melts around the edges

liquidus

conditions at which rock completely melts

Solidus

conditions at which rock starts to melt 

geotherm

the temperature as a function of depth

oxide

oxygen combined with another element, a chemical naming convention 

• Silica, or SiO 

• Magnesium Oxide, or MgO 

mineral

a crystalline solid with a regular atomic arrangement; has a specific composition and crystal structure 

• Quartz is SiO^2 in a regularly arranged pattern of molecules 

Weight Percent (wt. %)

• calculate total weight of all oxides using the periodic table -

• to take weight of specific oxide divided by the total weight of all oxides

Common volcanic minerals 

• Olivine 

• Pyroxene 

• Hornblende (amphibole) 

• K-Na feldspar 

• Quartz 

Magma compositions 

• Basaltic 

  • 45-52% silica 

  • Mafic 

• Andesitic 

  • 52-62% silica 

  • Intermediate 

• Dacitic 

  • 62-70% silica 

  • Intermediate 

• Rhyolitic 

  • More than 70% silica 

  • Felsic 

Factors that control magma composition 

• Source rock—what melted?  

• Partial melting—temperature of the system 

• Assimilation  

• Magma mixing 

• Fractional crystallization

Fractional crystallization (Bowens Reaction Series) 

• Magma eventually starts cooling (rises enough that it is in cool surrounding environment, water and other volatiles leave and raise the melting temperature) 

• Not all parts of the magma freeze at the same time—different components have different melting/freezing points 

• Zoning/mineral crystals due to composition changes 

intrustive

lava erupted and cooled below surface of the earth, takes longer to cool, large crystals can develop

extrusive

lava erupted and it cooled at the surface of the earth, chills immediately, small/non-existent crystals 

types of rocks

• sedimentary

• igneous

• metamorphic

sedimentary rock

made of sediments (grains or fragments or rock) that accumulate and compact over a long time period;  sandstone

igneous rock

• volcanic rock

• classified through composition and texture

• More silica = bigger explosions and lighter color 

extrusive composition of igneous rock

• Basalt 45-52% silica 

• Andesite 52-62% silica 

• Dacite  62-70% silica 

• Rhyolite More than 70% silica 

intrusive composition of igneous rock

• Gabbro 45-52% silica 

• Diorite 52-62% silica 

• Granite More than 70% silica 

texture of igneous rock

• Glassy  

• Crystalline 

  • Fine grained (aphanitic) 

  • Coarse grained (phaneritic) 

  • Porphyritic 

  • Extrusive rocks have small/fine-grained crystals 

  • Intrusive rocks have large/coarse crystals 

• Fragmental/pyroclastic--made up of a lot of materials 

• Vesicular—have gas bubbles in them 

metamorphic rock

any type of rock that has been subjected to high temperatures or pressure and changed due to this; marble (from limestone)

volcanic products

• lava flows

• volcaniclastic debris

types of lava flows

• basaltic

• andesitic

• felsic

basaltic lava flow

low viscosity and can flow long distances, lava fountains 

• Pahoehoe—smooth ropes/wrinkles at the surface of the lava flow; 'skin' 

• 'a 'a—blocky/chunks that flow on top of the flow because it's cooler 

• lava tubes

• columnar jointing

• pillow basalts

lava tubes

can change surrounding rock as lava flows into it; instead of spreading out, it becomes channeled into a main stream, crust can form on top and an empty tube structure is left over; can become quite large

columnar jointing

the lava flow cools rapidly and becomes rubbly; joints and cracks form because layers of lava cool differently

pillow basalts

form underwater, skin forms immediately and pillow shape forms as a result

andesitic lava flow

too viscous to flow far and tends to break up as it flows

felsic lava flow

so viscous that it may pile up in a dome-shaped mass

volcaniclasic debris

debris formed when existing volcanic rock is blown apart during the eruption 

• Accumulates after landslides on the volcano or after being transported by water 

• Debris formed as lava flows break up or shatter 

• pyroclastic debris

• volcanic gases