EOS 170 Flashcards
natural disaster
when a natural event causes injury, loss of life, damage to infrastructure, and/or economic losses
natural disasters typically caused by
sudden release of energy stored over a much longer time.
return period
average time between similar events at a given location
frequency
1 / period
average number of occurrences in a given time
magnitude
measure of amount of energy released
generally, magnitude ∝
frequency ^-1
inversely proportional to freq., large events less frequent
earthquake descriptor
Great ≥8 Major 7-7.9 Strong 6-6.9 Moderate 5-5.9 Light 4-4.9 Minor 3-3.9 Very Minor 2-2.9
earthquake frequency (#/yr)
great 1 major 10 strong 100 moderate 1000 light 10,000 minor 100,000 very minor 1,000,000
a natural event that is dangerous
hazard
likelihood that losses will occur
risk
vulnerability
exposure and susceptibility to human losses
Risk =
vulnerability X hazard
Hurricane Harvey
Houston
33 trillion gallons of water
3.1 mi^3 of water
depressed the land ca. 2cm
Houston vulnerability
built on flood plain
decreased vegetation
climate change
how climate change impacts hurricanes
increased SST –> increased storm energy
Hazard reduction
minomer
hazard = geologic phenomenon we can’t stop that, we want to reduce vulnerability
Irma
Cat5 hurricane
>200km/hr winds
hurricanes categorized by
wind speeds
exacerbation of forest fires
suppression/forest management
invasive species
climate change
human activity (campfire, cigarettes, fireworks, etc)
regent landslide
August 2017
Sierra Leone
500 killed, 600 missing
exacerbated by deforestation
Induced seismicity
earthquake triggered by humans
fluid extraction/injection increases pore fluid pressure causes faulting
Mexico earthquake, 2017
Chiapas M 8.1 by triple junction subduction eq largest eq in 2 yrs (worldwide) largest in mexico since 1932
Mexico triple junction
NA plate
Caribbean plate
Cocos plate
induced seismicity from
nuclear explosions
mine collapses
reservoir building drilling/frackin
Smallest magnitude earthquakes responsible for fatalities
5
Chiapas hazard
high (great earthquake) but lower than other “greats” due to deep (70km), offshore, low tsunami risk (deep),
magnitude scale
log
Chiapas vulnerability
low population
low infrastructure quality
ca. 100 deaths
sea-level drawback
hurricane winds so strong they draw the water back from the shore then after eye passes water is pushed back leading to tsunami
geologic hazards changing through time
no
weather-related hazards are increasing not geologic
historic costly storms
Hurricane Andrew 1992, 65 deaths, 26.5 billion
Katrina 2005, 1800 deaths, 108 billion
Irma 2017, 71 deaths, 70-200 billion
Irma records
- cost
- cat5 for 3 days, longer than any other Atl hurricane
- accumulated storm strength (strength+duration)
frequency of weather-related catastrophes
6X the 1950s
earthquake fatalities per century
increasing- 30 eq’s causing >10,000 deaths in 20th century while only 5/cen in 1000-1700
why earthquake fatalities increasing
- larger population
- urbanization
- increase in # of eq’s??
hugest eq risks
developing nation
large population
rapidly moving plates
Disaster management
After disaster: response, recovery
Before disaster: mitigation, preparedness
response
short-term
immediate
emergency workers
goal: get situation under control
recovery
mid-term
actions to rebuild community
goal: get situation back to normal
mitigation
long-term
actions to minimize harm that will take place
structural mitigation
infrastructure
retrofitting
‘earthquake-proofing’
examples of structural mitigation infrastructure
dams
dykes
floodways
non-structural mitigation
land-use policies building codes public education severe weather warnings earthquake early warning
non-structural mitigation, land-use policy example
include green spaces in communities to decrease flooding
preparedness
steps to ensure effective response and resources when needed
preparedness example
- stockpile essential goods and resources
- building evac drills
- first-aid
energy source for weather-related disasters
solar energy
energy source for geological disasters
- Earth’s internal energy
- Gravity
- Impact
Internal E disasters
earthquake
tsunami
volcano
gravity disasters
land/mud slide
avalanche
geothermal gradient
25ºC / km
mantle temperature
2000-3000ºC
core temperature
4000-7000ºC
radius of the earth
6370 km
why is the Earth still hot
- radioactive decay
- heat of formation
accumulation of particles into massive object via gravitational attraction
accretion
heat of formation
primordial heat = accretion + differentiation.
collisions generate heat
planetary differentiation
impacts - increased heat - Fe melting - melt migration to core - more heat (friction)
types of meteorites
chondrites
achondrites
stony-iron
iron
chondrites
‘stony meteorite’
- 86% of meteorites
- 75-90% Si minerals
- bubbly texture (no melting)
importance of chondrites
no melting = representation of primative material (before differentiation)
achondrites
‘stony meteorite’
- no chondrules
- originate from outer Si mantle
Stony-iron meteorite
ca. even Si and Ni/Fe alloy
Pallasite
specific type of stony-iron meteorite representing mantle/core boundary
Iron meteorite
from large asteroid core, almost fully Ni-Fe
Age of Earth
4.56 bya
timing of accretion and differentiation
ca. 30 million year
radioactive decay
spontaneous disintegration of a nucleus w/ emission of particles and/or radiation
half-life
time for half of initial pop. of atoms to decay
common radioactive elements
U238 (t1/2 = 4.5by)
U235 (t1/2 = 0.7 by)
K40 (t1/2 = 1.3 by)
Th232 (t1/2 = 14 by)
heat transfer due to bulk movement of molecules w/i fluid
convection
Lord Kelvin
William Thompson, 1862, estimated age of E to be 100Ma assuming cooling from conduction
John Perry
Kelvins assistant, 1895, realized heat transfer was via convection, estimated E age to 2-3 Ga
the missing years in the age of E calculations
radioactivity, 1956, Marie Curie, 4.55 Ga
convection occurs where in earth
liquid outer core
solid (ductile) mantle
drives plate tectonics
convection
Internal heat energy responsible for
earthquakes
tsunami
volcanoes
mountains
gravity ∝
∝ (M1M2)/distance^2
kinetic energy of slides comes from
gravitational potential energy (stored energy)
conduction
heat transfer due to particle collision
solar energy reaction
H + H –> He + nuclear E (heat + light)
driving mechanism of weather and currents
uneven heating of earths fluids
why is the E still hot 4.6bya
convection brings heat back into core (+radioactive decay continues)
density of earth
average: 5.5g/cm^3
crust: 2-3 g/cm^3
how do we know E’s density
study gravity -> calculate volume and mass
Earths wobble
doesn’t really wobble and gravity is constant therefore uniform density distribution in concentric shells
solar heating drives
hydrologic cycle
currents
weather
climate
how do we know Earths structure
- density distribution
- seismic velocity distribution
- magnetic field
- direct observation
- lab studies
seismic velocity distribution
seismic waves are reflected/refracted at boundaries
Earth’s magnetic field
requires convective flow of metallic fluid
importance of magnetic fluid
holds atmosphere and provides protection, ‘magnetosheath’
observations of Earth’s internal structure
- only drill to ca. 12km
- kimberlite pipes bring deep mantle material to surface (ca. 200km)
lab studies of Earths structure
- high T/P studies
- diamond-anvil apparatus can compress up to 200GPa equivalent to 3000km depth
Earth’s structure considered in terms of
- chemical composition (what its made of)
- rheology (deformation under stress)
Stress =
Force/Area (N/m^2 or Pa)
types of stress
compression
tension
shear
compression leads to
contraction
compression
force inwards
perpendicular to surface
tension
force outwards perpendicular to surface
shear stress
force parallel to surface
tension lead to
extension
rheology of liquids
flow under stress
rheology of solids
elastic - recoverable deformation
ductile - permanent deformation
brittle - rigid object, fractures
plastic - high viscosity, flows
viscosity
resistance to flow
honey, brie, molasses
rheology depends on
t
T
P
compression
shear stress leads to
shearing/ destortion
short t, low T and/or low P =
possible brittle rupture
long t, high T and/or high P =
possible plastic flow
example of material with different rheology based on t/T/P
wood
bends to an extent if move slow, breaks if move fast
glaciers - flow and calve
crust
- 0.5% of Earth mass
- 0-1000ºC
- density 2-3 g/cm^3
mantle-crust boundary
Mohorovicic discontinuity
Mantle
plastic, solid, convecting -67% of mass -1000-3000ºC density 3-6 g/cm^3 -Si rock rich in Fe and Al
outer core
liquid, convecting 30% of mass 4000ºC 10-14 g/cm Fluid Fe/Ni
Inner core
solid 2% of mass 5000º 14-16g/cm^3 Fe-Ni alloy
basalt
oceanic crust volcanic rock 48% SiO2 3 g/cm3 ca. 10km thick
granitic rock
continental crust
60% SiO2
2.7 g/cm3
ca 35km thick
earths structure, compositional
continental/oceanic crust upper mantle lower mantle outer core inner core
earths structure, rheologically
lithosphere
asthenosphere
mesosphere
lithosphere
crust + upper mantle = rocky, rigid
asthenosphere
weak, partial melt, flows under stress
T, Earths structure
increases nonlinearly w/ depth
P, earths structure
increases ca. linearly w/ depth (due to overburden weight)
solid inner core vs fluid outer core due to
pressure
fluid outer core vs solid mesosphere due to
composition
lithosphere floats on asthenosphere at an elevation dependent on
thickness and density
floating equilibrium
isostasy
change in mass of floating object =
isostatic adjustment - change in elevation fluid
density of water
1 g/cm3
thickness of oceanic crust
10km
depth of continental crust
ca. 35km
up to 80km
oceanic crust sits lower in ocean than continental b/c
isostasy
heavier, thinner
glacial melting =
isostatic rebound/ postglacial rebound
glacial formation =
push crust down -> push water out of way -> uplift of adjacent crust
Canada postglacial rebound
Canada raising from melting of Laurentide glacier, US moving back down
Mexico city eq
M7.1
51km depth
mechanism: normal faulting
many deaths avoided due to EWS
comparing the Mexico eq’s
Sep 8: M8.1, deeper, smaller population, lower vulnerability, 98 deaths
Sep 19: M7.1, shallow, higher population, high vulnerability, >250 deaths
exacerbation of mexico eq
city expansion onto drained lake bed
problems with building on drained lake beds
saturated sediments -> greater shaking for longer period after eq passes
example of eq in drained lake bed city
Kathmandu, Nepal
in basin- greater shaking for longer
near basin - less for shorter
liquefaction
saturated soil loses strength and stiffness in response to applied stress causing it to liquify
plate deformation
plates are internally rigid, stress at one margin is transferred to the opposite margin, no internal deformation
MOR
divergent boundary, rising mantle forms magma, cooling and solidifying forms new basaltic crus pushing plates apart, warm, low-density, topographic high
MOR volcanism
decompression melting: geothermal crosses solidus resulting in partial melting
transform boundary, transform fault
region where 2 oceanic plates are moving in opposite direction
region where 1+ continental plates are moving in opposite directions
trans current boundary, strike-slip fault
strike-slip fault example
Pacific plate ^\NA plate (San Andreas Fault)
subduction zone
convergent boundary, old, cold, dense oceanic lithosphere, pulled into mantle, melting deep within mantle
where 3 plates meet at single point
triple junction
when oceanic crust is fully subjected and continental crust converges
continental collision zone
results of continental collision
mt building, continental crust too buoyant to subduct
ex. Himalayas, Rockies
Himalaya characteristics
8km above sea-level
5km average elevation
80km crustal thickness
normal-thickness of continental crust
35km
continental collision zone
- wider than oceanic plate boundaries
- form mountains
- convergent w/ large strike-slip faults moving blocks out of way
divergent plate boundary that forms new ocean basin
continental rift
thinned edges of continent following continental rift
passive continental margin - not plate boundaries, separate continent and oceanic crust of same plate
example of continental rift
east african rift - eastern Africa (Somalian plate) will split off of rest of Africa (Nubian plate)
upwelling mantle plume
hot spot
hot spots occur
anywhere (not associated w/ plate boundary)
hot spot examples
Hawaii
Yellowstone
Iceland
Azores
hot spot mechanics
thermal anomaly – mantle hotter than normal – geothermal crosses solidus (at depth) – plume rises
submerged volcano
seamount
Hawaiian hotspot
Pacific plate has moved NW over hotspot for at least 5Ma = chain of islands and seamounts
evidence of Hawaiian hotspot
- volcanic islands in line
- oldest island (Kaua’i 5-6Ma) is farthest NW
- islands progressively older (O’ahu 2-4Ma, Mauna Loa 0.5Ma)
Hawaiian Island/Emperor Seamount chain
- 6000km long
- kink at 43Ma (plate changed direction)
yellowstone hot-spot track
NA plate moving W over hotspot
Alfred Wegener
1912, proposed single supercontinent (Pangaea) and continental drift
Pangaea ocean
Panthalassa
Pangaea period
Jurassic
Evidence for plate tectonics
- continents fit
- similar fossils on adjacent continental margins
- Continuities in mt ranges along cont. margins
- Glacial striations
- geomagnetic reversals
- earthquake locations, depths
- sea-floor striping
Glacial striation plate tectonics
- continents that could not be glaciated (Australia, India, SA)
- wrong direction of movement (onto land from ocean)
Pangaea breaks into 2 supercontinents
180 Ma, Jurassic
supercontinents after Pangaea
Laurasia, Gondwanaland
Future supercontinent
+250Ma, NA/SA collide with Africa/Eurasia
How plate tectonics were discovered
WWII and cold war provided geophysical data, 1960s, Harry Hess
John Tuzo Wilson
1963-1966, Canadian, described Hawaiian chain, transform faults connecting MORs
surface elevations measured
satellite imagery
NAtl begins opening
135Ma, early Cretaceous
S. Atl opens, Africa reaches Europe
65Ma, end Cretaceous
surface elevation distribution
bimodal; continental crust centred around 0km elevation, oceanic around -5km, average ca. -3km
study of earths magnetic field through time
paleomagnetism
when geographic north pole = magnetic south pole
reverse polarity
geomagnetic reversal
paleomagnetism evidence
magnetite (Fe3O4) in basalt aligns w/ current magnetic field
process of magnetic minerals aligning w/ magnetic field
thermal-remant magnetization (TRM)
magnetic polarity scale
black shows normal polarity, white = reverse
sea-floor striping
symmetric pattern of magnetic anomalies radiating out from MOR
discovered, explained sea-floor striping
Fred Vine, Drummond Mathews, 1963
age of oceanic lithosphere
all less than 300 million years old
age of continental rocks
up to billions of yrs
first earthquake detection
1960s, World Wide Standardized Seismograph Network (WWSSN) (to monitor nuclear explosions)
narrow earthquake belt
MORs
subduction zone earthquakes
Wadati-Benioff zones, unusually deep, down to 700km
Plate tectonic forces
- Ridge push
2. Slab pull
wide earthquake belt
subduction zones
ridge push
upwelling mantle and gravitational collapse of young (warm, buoyant) oceanic crust at MOR
slab-pull
due to old, cold, dense oceanic lithos. in subduction zone
widest eq belts
continental collision
80% of erupted magma
from spreading centers
types of volcanoes
shield volcano
stratovolcano
stratovolcano
eg. Mt Kilimanjaro, Mount Saint Helens
- layers of ash from successive flows
- common above subduction zone
- very hazardous
- ca 10% of all magma erupted
- most explosive
Hot spot volcanism
- 10% of magma erupted
- runny lava
- not explosive, less hazardous
continental volcanism
- explosive
eg. Yellowstone caldera-forming eruption
Iceland
BOTH MOR and hotspot
- erupts huge volumes of magma
- decompression melting and eruption
fault
planar surface of plate
earthquakes occur
along faults (possibly multiple), not at a point
slip
displacement of surface along fault from surface rupture
fault planes
planar, striations, corrugations, indicate direction of slip
point on fault plane where slip starts
hypocenter
types of faulting
- reverse
- normal
- strike-slip
reverse faulting
‘thrust faulting’
- horizontal convergence
- force in, block thrust up
- gentle dip angle ca. 30º
strike-slip fault
plates move laterally past each other
right-lateral strike slip
opposite block moves to the right
graphical representation of type of faulting involved in eq
focal mechanism
earthquake cycle
stress builds on fault – released quickly
point directly above hypocenter
epicenter
steady motion occurs pulling block away from fault but fault is ‘locked’
interseismic period
normal faulting
horizontal extension
- pull apart, one block slides down
- dip angle steeper, ca. 60º
fault rebounds causing eq
coseismic phase, now offset at fault
megathrust faults
subduction zone, vertical and horizontal motion, stick-slip
megathrust fault cycle
subducting plate gets stuck b/c cold and brittle– upper plate squeezed, bulges up – underlying plate pulls ocean down – sudden slip, rebound, overriding plate moves back down, ocean moves back up = tsunami
elastic rebound releases
stored as energy as seismic waves
2 classes of seismic waves
body waves
surface waves
Body waves
- move through Earth
- P waves
- S waves
Surface waves
- do not move through the body of Earth
- Raleigh waves
- Love waves
P waves
compressional waves
- primary, first to arrive
- compress, push stationary object
- no z direction movement, forward/back like a worm
S waves
Shear waves
- secondary
- S-shape movement in z direction (up, down waves)
- sheers stationary object, squishes square up into a diamond
instrument that measures and amplifies ground motion
seismometer
how seismometer works
attached to E, whole instrument shakes w/ E, weight does not move b/c inertia, recording device measures how far instrument moves w.r.t. mass
distinguishing waves on a seismogram
- by time of arrival
- by component of seismogram
Raleigh wave
- small waves along surface
- up and down in z direction
- like S wave but only at surface, not whole ‘block’
- particles move in orbs (like ocean waves)
records ground motion from seismometer
seismograph
seismogram components
Horizontal (radial, transverse)
Vertical
-3 components
Love wave
- side to side waves on surface, y direction, like a snake
- move particle side to side
seismogram
graphical representation of motion at a given point as a fn of t
distinguish waves on seismogram from t
1st: P-waves
2nd: S-waves
3rd: Love
4th: Rayleigh
distinguish waves on seismogram from component
Vertical: P-waves, Rayleigh
Horizontal transverse: Love
Horizontal radial: S-waves, Rayleigh
largest amplitude waves
surface (most damaging)
slower waves
- surface (arrive later) slower than body
- s slower than p
seismic waves that travel through liquid (outer core)
P-waves
how we determine interior structure of E
refraction, reflection of body waves by major boundaries in E (shadow zones)
further seismic stations
record P and S as farther apart b/c P travelling faster
distance btw earthquake and seismometer
Ts = x/Vs; Tp=x/Vp x = VpVs(Ts-Tp)/(Vp - Vs)
pinpointing eq epicenter
determine distance from eq to seismometer for 3 locations, plot them, where they cross
Eq Early Warning system
- seismometer detects p-waves
- calculate magnitude and distance, expected intensity and arrival t
- send warning to city
- time to get outside before surface waves hit
determining magnitude
- observed seismic waves
- correct for distance
- cross plot distance, magnitude, amplitude
moment (Nm)
eq rupture area (m^2) x amount of displacement (m) x Shear modulus (Nm^-2)
- rupture area = rupture length x width
- shear modules = resistance to deformation by shear stress
exploring magnitude equation
- fault area and displacement highly correlated
- rupture area KEY to magnitude
- large eq’s rupture large faults (subduction zone)
subduction zone eq’s
megathrust
- gently-dipping interface of thrust fault + long = large SA
- can generate large tsunami
- 17/20 largest eq’s since 1900 were megathrust
major west coast fault zones
San Andreas Fault (SAF)
Cascadia Subduction Zone (CAS)
which major west coast fault zone is likely to produce a larger eq
CAS - subduction zone, larger SA
an increase in M of 1 unit =
- 30X increase in E
- 10X reduction in frequency
M =3, E equivalent to
- World’s largest nuclear test
- Mt. St Helen eruption
M = 6, E equivalent
Hiroshima atomic bomb
global cumulative seismic moment release
- dominated by megathrusts
- 5 >9.0 megathrusts = more than 1/2 of moment released from 1900-2014
entire length of Pacific ring of fire subduction zone
30,000 km
max slip ever observed
50m
max magnitude eq
10.5 if every subduction zone in the world erupted at once
max realistic earthquake
entire Aleutian trench (between Asia and NA) or Peru-Chile trench = M9.9
describing earthquakes by felt intensity
Mercalli Scale
-instrumental, weak, slight, moderate, rather strong, strong, very strong, destructive, violent, intense, extreme, cataclysmic (12)
Isoseismal map
concentric contours of equal seismic intensity focused on approximate epicentre
isoseismal map bias
- proximity of eq to population centre
- personal account exaggeration
what governs felt intensity
- magnitude
- distance from eq
- depth of eq
- infrastructure height, quality
- earth surface
Similar magnitude different intensity
M5.8 Mineral, VA
M6.5 San Simeon, Ca
felt much further away in VA due to bedrock geology, easily felt 1000km away
why eq felt further away in Eastern US
less tectonics = less broken up plates = less dissipation/attenuation of seismic energy
Intensity of eq’s with same magnitude, different depth
M6.5 San Simeon, CA, 7km
M6.3 New Zealand 163 km
NZ = barely any reports of people feeling it
MOR earthquakes
- normal faulting
- young, warm, thin ocean crust
- eq’s generally small
Transform fault eq
- strike-slip faulting
- older, colder, thicker crust than MOR
- larger magnitude than MOR
part of uppermost crust brittle enough to host earthquakes
seismogenic layer
transform fault
adjacent plates are moving in opposite direction
fracture zone
adjacent plates are moving in same direction = no faulting = no earthquake
Earthquakes that occur at subduction zones
crustal eq (small), megathrust (large), intermediate eq, deep eq, outer rise normal fault eq
outer rise normal faulting eq
few, large, where incoming oceanic plate begins to flex
-not very hazardous due to proximity (at MOR)
deep earthquakes
- up to 700im
- only in subduction zones w/ rapidly descending plate
- usually too far to be dangerous
why do deep eq’s only occur if plate is descending rapidly
so it stays cold and brittle, if it subduct slowly it will warm up and lose brittle nature needed to conduct eq
Intermediate earthquakes
50-300 km
- in all subduction zones
- can be very dangerous
- intraslab, within subducting slab
what type of earthquakes were the Mexico quakes?
subduction zone, intermediate
-top of subducting Cocos plate
classes of hazardous earthquakes in Cascadia
- Intermediate/ intraslab
- megathrust
- crustal
Intermediate eq example
Nisqually WA, 2001, hypocenter 57km depth, 1 death, 1-4billion in damages
Cascadia’s last megathrust
1700AD
Cascadia megathrust max size, recurrence
M9, 500-600yr
deep JDF plate max eq and recurrence
M7+, 30-50yr
West coast crustal quake max size and recurrence
M7+, hundreds of years?
Crustal earthquakes
-moderate magnitude
-could be close to pop centre
-
VI crustal fault
Leech River fault
-right across southern tip of island
airborne laser mapping that penetrates forest canopy to determine surface topography
lidar
continental plate boundary earthquakes
shallow, potentially close to populations
- broken up crust, no megathrust
- seismogenic layer ca. 15km
- M7-8
- mostly along collision zone
continental plate boundary example
Bam, between two deserts
- half of pop lost due to poor infrastructure (adobe)
- eq rupture along escarpment Bam-Baravat ridge
Why Bam is an oasis
- ridge = impermeable, dam on water table
- build tunnels to tap water source, irrigate crops
the bittersweet side of Iran faults
- water sources
- active faults!
Tehran
continental plate boundary
- pop. 14 million
- destroyed by 4 past eps
- city centre right next to Alborz mountains
continental plate deaths
more than subduction zones even though smaller magnitude
intraplate earthquakes
- unusual, infrequent
- hazardous
- b/c plates are not perfectly rigid
- variety of faulting mechanisms
Intraplate seismicity in eastern Canada associated with
-passive continental margins
or
-ancient failed rifts
passive continental margin
- edge of continent
- btw continent, ocean on SAME plate
failed rifts, Canada
from formation of Atlantic (branches that failed)
eg. Labrador Sea
intraplate earthquake stresses
- Plate tectonic stress
- postglacial rebound
- Manmade stresses
Plate tectonic stresses on intraplate
ridge/push, slab/pull stresses generated through interior of plate
Postglacial rebound, intraplate earthquake example
-Parvie fault scarp, Sweden
M8, 10ka
-1989 M6 Ungava, Quebec
Induced intraplate eq example
Oklahoma, Colorado, Texas, Alberta, N BC
building to resist earthquakes
- Make building resistant to horizontal movement
- Make resistant to stress
- reduce resonance
- base isolation
how to make buildings resistant to horizontal shearing
braces, brackets, shear walls, bolts
how to make buildings resistant to stress
Wood - flexible, light, elastic
Steel - strong, ductile
reducing resonance
depends on size, substrate (bedrock/sediment), weight distribution, shape, building material, foundation
Resonance rule of thumb
buildings sway at resonant frequency 10 Hz / # of stories
base isolation
- ball bearings, wheels, shortchanged absorbers
- Qube, Vancouver hangs from central vertical support to majority of building is free of the ground
