EarthquakesEarthquakes

Prof. David AlexanderGlobal Risk Forum Davos

Physicalaspects

The causes of seismicity:-The causes of seismicity:-

• tectonic activity caused by stresses in the earth's crust

• volcanic activity resulting in stress caused by the injection of magma into the crust (volcanosiesmicity).

A typical year of earthquakes (1996)

Magnitude

Seismology: the study ofelastic (seismic) waves

The properties of waves:

• wavelength and frequency (number per unit of time)

• amplitude (vertical distance from crest to trough)

• phase difference.

AMPLITUDE

PHASE DIFFERENCE

WAVELENGTH (per unit time = frequency)

crest

trough

Strong motion of the ground:-

• duration (seconds)

• frequencies present in the waves

• maximum amplitude of the waves

• dispersion if wave energy with distance from the point of generation

• maximum acceleration.

• maximum velocity

Bracketed duration: the period oftime in which seismic shakingexceeds a predefined level.

Bracketed duration: the period oftime in which seismic shakingexceeds a predefined level.

Background seismicity: smalltremors that occur constantlyduring periods of quiescencebetween major earthquakes.

Background seismicity: smalltremors that occur constantlyduring periods of quiescencebetween major earthquakes.

Seismogenic zones:-

• the margins of tectonic plates (e.g. subduction zones)

• zones of geological faults under stress

• areas of volcanic activity and geothermal fluxes.

Geological faults (extensiveplanes that divide rock units):-

• normal faults (extensional movement)

• inverse (compressional movement)

• transcurrent (lateral, strike-slip)

• oblique (diagonal).

Right-lateral fault(strike-slip)

Dip

Fault line

Normal fault

Reverse fault

Right-lateral normal fault(oblique slip)

Overthrust fault

Hanging wallFootwall

Types of geological fault

The elastic rebound theoryof H.F. Reid:

The elastic rebound theoryof H.F. Reid:

• hypocentre (focus): small area in the crust where the earthquake begins

• epicentre: the point on the surface directly above the hypocentre

• deep focus earthquakes: hypocentre buried at least 80 km

• shallow focus earthquakes: hypocentre <50 km, often <20 km.

The elastic rebound theory of H.F. Reid

Types of seismic wave:-

Body waves: P, primus, compression or pressure waves - longitudinal S, secundus, shear waves - transverse

Surface waves: L, Love S, Stoneley R, Rayleigh C, channel

R waves travel at 92% of the speed ofS waves, which travel at 58% of thespeed of P waves, etc.....

'P' waves

The main kinds of seismic wave

'S' waves

'L' waves

'R' waves Rayleigh

Love

Secundus(shear)

Primus(pressure)

Su

rface w

aves

Bod

y w

aves

LOVE WAVES

RAYLEIGHWAVES

SHEARWAVES

EPICENTRE

HYPOCENTRE

FAGLIA

FRONT OF THE WAVES

PRESSURE WAVES

Instruments for measuringseismic waves:-

• seismometers produce a continuous trace

• accelerometers only function when there is strong motion (which triggers them to record)

Seismic monitoring instruments,synchronised to different wavelengths,must have an optimum combination of

robustness and sensitivity.

SeismometersSeismometers

AccelerometersAccelerometers

Magnitude was originally defined as theamplitude of the largest seismic wave

at a nominal 100 km from the epicentre

• Richter scale: local magnitude, ML, no longer used because it is inaccurate at high magnitudes

• various scales for S-waves

• Moment Magnitude scale, MW, the world standard.

In earthquakes energy expenditureis proportional to magnitude:

the points on the magnitude scale havea logarithmic relationship in terms

of energy release - thus:

M8 = 31.6 x M7

In earthquakes energy expenditureis proportional to magnitude:

the points on the magnitude scale havea logarithmic relationship in terms

of energy release - thus:

M8 = 31.6 x M7

Magnitude Energy Acceleratio

nIntensity

5 2.75 0.06g circa VI

6 75.9 0.15g ca. VII

7 2089 0.50g VIII-X

8 57,577 0.60g+ X-XII

ML scale bn Joule g=9.81m/sec2

MM scale

Relationship between magnitudeand other variables

World seismic activity overa typical eight-year period

MagnitudeNu

mb

er

of

eart

hq

uakes

Location of epicentres andreconstruction of the macroseismic field:-

• three seismic stations can locate an epicentre on the basis of the radial distance computed from the travel times of different kinds of wave

• the isoseisms of the macroseismic field are based on the relationship between the tremors and damage.

5 minutes

Tim

e

EpicentreDistance 1000 km

Slowing down of P and S waveswith distance from epicentre

S waveswithdifferentfrequences

epicentre

stn. 1 stn. 2

stn. 3

Localisation of epicentre on the basisof the arrival times of seismic waves

Epicentresand faultslocatedfor theBam, Iran,earthquakeof 26 Dec.2003.

Effect of different geological materialsin amplifying seismic waves

Extract from a seismic microzonation mapshowing different shaking potentials

A typical sequence of aftershocks after a major seismic event

(Northridge, California, 1994)N

um

ber

of

eart

hq

uake p

er

day

Days after the earthquake

all others m<5

Colfiorito earthquake swarm, central ItalySeptember - December 1997

Associated seismic intensitiesDays after earthquake

Days after earthquake

Days after earthquake

MCS intensitiesfor 23-11.1980southern Italianearthquake M6.8

NEW ZEALAND Return periods of earthquakes

with intensities of at least MM=VIIntensities with a probability of

50% of returning within 50 years

Seismicevent

Magni-tude

Hypo-centraldepth

Deaths

Damage

(million US$)

California17-10-89

7.1 18.5 62 6,000

Rumenia04-03-77

7,2 94 1.500 800

Chile03-03-85

7,8 33 200 1,200

Japan26-05-83

7,7 33 104 600

Comparative data on four earthquakesComparative data on four earthquakes

Consequences ofEarthquakes

- and significant issues -

Consequences ofEarthquakes

- and significant issues -

Construction failure poses thegreatest threat to life in

earthquakes

Construction failure poses thegreatest threat to life in

earthquakes

Structural integrity:a building's physical adequacyfor its intended purpose

Structural integrity:a building's physical adequacyfor its intended purpose

Failure: total or partialcollapse, or the destruction ornon-functionality of a building.

Failure: total or partialcollapse, or the destruction ornon-functionality of a building.

Seismic damage to buildingsis a function of:-• seismic energy expenditure: magnitude duration of strong motion maximum acceleration• distance from epicentre• surface geology (soft sediments amplify waves)• effect of construction type• regularity of building form• state of maintenance of building.

In the Tangshan (China) earthquakeof July 1976 (magnitude 7.6),of 352 multi-storey buildings:

• 4 (1%) maintained their structural integrity

• 177 (50%) collapsed completely

• 85 (24%) collapsed partially

• 86 (25%) were severely damaged.

Knowledge must be gained of how to:-

• buttress buildings temporarily

• repair buildings permanently

• design and construct buildings antiseismically.

Antiseismic design utilizes:-

• experience of a building's seismic performance

• hypotheses about a building's seismic response

• design techniques to combat weaknesses in buildings induced by earthquakes.

The largest urban seismic riskis in Istanbul and Tehran

Major earthquakes represent an enormousurban search-and-rescue (USAR) challenge

The international relief system ishugely expensive and inefficient

$1,000,000 per life saved!

• in the 20th century 46 lethal earthquakes caused 128,000 deaths

• in the 20th century 46 lethal earthquakes caused 128,000 deaths

• a damaging quake once in 24-56 months• a damaging quake once in 24-56 months

• 70% of the population lives in municipalities classified seismic; 40% in 2,965 highly seismic ones

• 70% of the population lives in municipalities classified seismic; 40% in 2,965 highly seismic ones

• greatest risk is in the 22,000 historical town centres

• greatest risk is in the 22,000 historical town centres

• 35.3% of homes in earthquake zones are anti-seismically constructed.

• 35.3% of homes in earthquake zones are anti-seismically constructed.

In Italy...In Italy...

VICTIM

UNINJURED INJURED

HEALTHY INFECTEDWORSENING

OF CONDITION

IMPROVEMENTOF CONDITION

HEALTHY

IMPROVEMENTOF CONDITION

DISEASES INJURIES

Public health measures

Search and rescue

Medical assistance

Medical aid

Mortuarialand funeralservices

WORSENINGOF CONDITION

DEATH

DISASTER

No damageto buildings

Damageto buildings

InjuriesEmergency roominjuries

Hospitaladmissions

Source: Linda Bourque, UCLA

In the El Salvador earthquakeof 1986 hospitals collapsed.

In the El Salvador earthquakeof 1986 hospitals collapsed.

In the El Salvador earthquakeof 2001 hospitals collapsed.

In the El Salvador earthquakeof 2001 hospitals collapsed.

In the Bam, Iran, earthquakeof 2003 hospitals collapsed.

In the Bam, Iran, earthquakeof 2003 hospitals collapsed.

In the Italian Irpinia-Basilicataearthquake of 1980 hospitals collapsed.

In the Italian Irpinia-Basilicataearthquake of 1980 hospitals collapsed.

....haven't we learnt anything at all?

"At Olive View Medical Center, two buildings collapsed in 1971, and three people died,

including two patients on life-support systems that failed when auxiliary generators did not start. The third was an ambulance driver who was crushed by a falling wall. Olive View was

an 888-bed hospital then. It had only been open a month when the quake hit. Because of

extensive damage, the hospital was rebuilt, with attention to strengthening it against any future quake. But it was much smaller. Now it

has a capacity of 377 patients."[Sylmar, California, history file]

Of the 58 fatalities caused by building damage, 50 occurred in hospitals. The worst damage to medical facilities

occurred at the Veterans Administration Hospital in Sylmar where two large buildings collapsed. Even though the

hospital site was right on the edge of the heavily urbanized San Fernando Valley, it took one hour and 22 minutes

before a fire department helicopter happened to spot the collapses and send help. The reason for such a delay? The

phones didn’t work, the hospital’s radio was in one of the collapsed buildings, and the first message orally delivered by a hospital staff member to a nearby government facility

was confused with an already received report of damage to a different nearby hospital.

[Reitherman 2004]

Seismic hazards to hospitals:-

• loss of structural integrity and building functionality

• seismically-induced flooding, landsliding and subsidence

• loss of trained personnel

• loss of medical and surgical capacity

• loss of supplies (including utilities) and failure of supply chains

• inaccessibility.

Unaccaptableperformance

Unaccaptableperformance

Unaccaptableperformance

Fullyoperational

Fullyoperational

OperationalOperational LifesafeLifesafe

Nearcollapse

Nearcollapse CollapseCollapse

Rare60%gRare60%g

Veryrare

80%g

Veryrare

80%g

Seismic design levelSeismic design level

Hospitals

Capacity:Capacity:

• beds (expandable)• beds (expandable)

• surgical and curative (fixed or diminished in the short term).

• surgical and curative (fixed or diminished in the short term).

ResilienceResilience

• ensuring continuity of services and medical supplies

• ensuring continuity of services and medical supplies

• ability to cope with very large surges in demand

• ability to cope with very large surges in demand

• protecting personnel and their immediate families

• protecting personnel and their immediate families

• protecting lifelines that enable the injured to access medical care.

• protecting lifelines that enable the injured to access medical care.

• ensuring the structural integrity of the medical facility

• ensuring the structural integrity of the medical facility

MeasuresMeasures

• seismic integrity surveys (structural and non-structural)

• seismic integrity surveys (structural and non-structural)

• emergency planning (...testing, revising, diffusing plans...)

• emergency planning (...testing, revising, diffusing plans...)

• estimate medical, surgical, pharmaceutical and logistical needs

• estimate medical, surgical, pharmaceutical and logistical needs

• earthquake casualty estimation.• earthquake casualty estimation.

Health facility networkemergency plan

Health facility networkemergency plan

Otherhospitals

and clinicsin the area

Externalemergency plan

Externalemergency plan

Site of thedisaster

Site of thedisaster

Internal emergency planInternal emergency plan

The three foci of medical emergency planningThe three foci of medical emergency planning

Disasterin the medical

centre

Disasterin the system

of medicalcentres

Disasterin the externalenvironment

Disasterplanning forthe medical

centre

Disasterplanning

for the systemof medical

centres

Disasterplanning forthe externalenvironment

Co-ordinatedEMS Disaster

plans

Disaster

T1

T1 T2

T2

T2

T2

Helicopter links

Telecommunications links

Ambulance routes Emergency bus transportation

Primary triage point Secondary triage points

Pulmonaryspecialists

Burnsunit

Emergencyoperations

commander Coroner Next-of-kin

Incidentcommand

post

Incidentcommander

Hospital I

Hospital II

Mortuary

Secondarytreatment

centre

Emergencyoperations

centre

Stagingarea

Casualties,economic damage;type, costs timesof reconstruction

IMPACT ON THECOMMUNITY

Buildings,drinking water,

sewerage,public transport,public buildings,

hospitals,fire stations,

etc.

Populationdistributionand density

Socio-economiccharacteristics

Previousexperience

of risk

Level ofcommunity

preparedness

RISK OF EARTHQUAKE

RISK OF EARTHQUAKE

Landslides

Floods

Fires

Characteristicsof the event:magnitude,duration,

location ofepicentre,

level ofgroundacceleration

Local geologicalcharacteristics

Aftershocks

Thankyouforyourattention!

Thankyouforyourattention!