making a case for an earthquake risk reduction programme...

The University of the West Indies Seismic Research Centre email: [email protected]

Making A Case for an Earthquake Risk Reduction

Programme in Trinidad and Tobago

Lloyd L. Lynch

Seismic Research Centre

National Consultation on Earthquake Safety

July 5-6, 2010


Earthquake Hazard and Return Period

Large earthquakes are rear events, even in the most

exposed Caribbean region.

When they occur they can inflict huge damage and

losses.

Damage potential generally increases with return

period which can be up to hundreds of years for most

countries in the Caribbean.

This is markedly different from other environmental

loads such as flood and wind for which the most

extreme events occur within human memory.


WHAT’S DIFFERENT ABOUT

EARTHQUAKE DISASTERS?

Earthquakes occur rarely, making them a ‘harder sell’ for risk-

reduction measures than more frequent disasters.

Destruction of roads (e.g. by landslides), bridges, and other

infrastructure makes access and communication difficult.

The effects are concentrated, compared with those of other natural

disasters.

Aftershocks may disrupt operations, pose a threat to staff, and may

cause further damage after the first earthquake.

High mortality - collapsing buildings may kill large numbers of

people (30% or more of the population of the affected area).

Morbidity - high levels of fractures and crush injuries, although low

risk of epidemics.

Earthquakes create large amounts of rubble, which needs to be

cleared before reconstruction can start.

.


Caribbean Geodynamics Setting

[after, e.g., Jordan, 1975; Adamek et al., 1988; Holcombe

et al., 1990; Mascle and Letouzey, 1990; Pindell and

Barrett, 1990; Heubeck and Mann, 1991; Mann et al.,

1995; Flinch et al., 1999; Weber et al., 2001]. Bathymetry

from Smith and Sandwell [1997]. Subduction rates from


Located Earthquakes 1955 – 2010/05

• North Paria Peninsula (deeper earthquakes (50-200 km) - the most significant earthquake source

• Gulf of Paria (shallow earthquakes)

• Southwest of Tobago (shallow earthquakes)

• Southeast of Trinidad (30-100 km)


Characteristics of North of PariaPeninsula Source Zone

Detached slab from SA

plate subducts under

Ca lithosphere in the

orientation shown

After Perez and

Aggarwal

Also substantiated by

Russo


Eastern Caribbean

Seismicity

Magnitude 5.0

1900-2007

Notice the Gap

between St Lucia and

Trinidad

This extends back into

the Historical era


Earthquakes Magnitude >5 1955 – 2008


Caribbean Geodynamics Setting

[after, e.g., Jordan, 1975; Adamek et al., 1988; Holcombe

et al., 1990; Mascle and Letouzey, 1990; Pindell and

Barrett, 1990; Heubeck and Mann, 1991; Mann et al.,

1995; Flinch et al., 1999; Weber et al., 2001]. Bathymetry

from Smith and Sandwell [1997]. Subduction rates from


TRINIDAD and TOBAGO Damaging Earthquakes

7.8 (IX) 1766

6.6 (VIII) 1825

7 (VII) 1888

7.3 (VIII) 1918

6.3 (VIII) 1954

6.7 (VIII)1997

7.4 (VI)2007

0

1

2

3

4

5

6

7

1

10

100

1000

10000

1715 1765 1815 1865 1915 1965 2015

Po

pu

lati

on

in

Th

ou

sa

nd

s

Felt at/above MMI VIChronology, Population Size and Intensity

SeismicEnergy


1766 (7.8)IX

1888 (7.0)VI

1918 (7.3)VIII

1954 (6.3)VIII

1997 (6.7)VIII2006 (6.3)

VI

2007 (7.4)VI

1.00E+00

5.00E+22

1.00E+23

1.50E+23

2.00E+23

2.50E+23

3.00E+23

3.50E+23

5 10 20 40 80 160 320

Rele

ased

En

erg

y /

J

Epicentral Distance / km

Released Energy vs. Epi-central Distance (Trinidad)


Relationship between Magnitude, Intensity and Hypocentral Distance


Active Fault in Central Range

Using GPS

measurements

Weber et al has

shown that 65%

(~13mm/yr) of

present day

motion between

the Ca-SA plate

boundaries in the

SE Caribbean is

accommodated

on the Central

Range/Warm

Springs Fault


• Weber’s work stimulated paleoseismic investigations

both onshore and offshore. Crosby et. al. Show that

the fault cuts recent sediments and is active. (Soto et.

Al. 2007) Showed that the fault extends into

Trinidad’s eastern offshore and offsets an underwater

fluvial channel.

• Conclusion drawn from these investigations– CR Fault is active and accounts for most of the Ca-SA motions

– The dimensions and activity rate are such that it could generate a

maximum M7.5 earthquake if locked

– The El Pilar right steps across to the CRF creating a Pull-Apart

Basin in the Gulf of Paria

– The fault is aseismic. More work is needed to determine whether it

has been accumulating strain or it has been slipping without

generating earthquakes

Active Fault in Central Range


Location of Central Range Fault in relationship to

Key Industrial, Residential and Commercial Zones

San Fernando

Couva/Pt. Lisas

Vistabella

Pointe-a-Pierre

Claxton Bay

ManzanillaChaguanas


Don’t Forget Site Effect

Period→long Short

thinthickSOFT

RIGID

Vibration is amplified,

when waves go from rigid

basement into soft sediment.


‘Earthquake don’t kill people, collapsed structures do’

1999 Izmit, Turkey earthquake

The number one cause of damage from earthquakes is due to failures in the built

environment from ground shaking. (The number two cause is tsunamis)


Prob. Exc. Life Time Return Period

10% 10 years 95 years



2% 50 years 2,475 years

10% in 50 years (RP 475) was used in earlier zone

based codes including CUBIC.

2% in 50 years (RP 2475) represents a higher margin

of safety (caters for the largest earthquake that will

occur in 2475 years – Maximum Considered

Earthquake.


This is a well known shortcoming of the probabilistic approach to

hazard assessment as evidenced by the following earthquakes that

occurred on structures that were in quiescence for long periods of

time and were underestimated during the Global Seismic Hazard

Assessment Program:

GSHAP PGA(g) Expected Observed

(return period 475 years)

Kobe (1995) 0.40-0.48 0.7-0.8

Gujarat (2001) 0.16-0.24 0.5-0.6

Bam (2003) 0.16-0.24 0.7-0.8

Sichuan (2008) 0.16-0.24 0.6-0.8

Ref:

Motivation for switch to RP 2475 years


Probability of

Exceedance

Life Time Return

Period

Expected g

in solid rock

Location

10% 10 95 yrs

10% 50 475 yrs 0.33 SE Tobago, Toco,

Chaguaramas

10% 50 475 yrs 0.3 Port of Spain

5% 50 950 yrs

2% 50 2475 yrs 0.6 SE Tobago, Toco,

Chaguaramas

2% 50 2475 yrs 0.55 Port of Spain

If buildings are not constructed to withstand these loads

we can expect damage, including collapse when events of

these return period (475 and 2475) occur near T&T.


Earthquake Risk Tolerance

The engineering community has hinted that the built

environment in T&T is quite vulnerable.

Up to 30,000 deaths could occur.

Since 2008 the murder rate has exceeded 500.

This has become a national concern, trigger debates,

protests and possibly a change of government.

If we project this murder rate over 50 years we get

about 25,000 victims. Evaluating the risk of getting

murdered in T&T over this period:

(25000/1300000) x 100 = 1.9%


Earthquake Risk Tolerance

• The risk (2% chance in 50 years) of becoming a

homicide victim is unacceptable to majority of the

population.

• Under prevailing conditions of Eq. safety there is 2%

chance in 50 years that one or more of the RP 2475

yrs earthquakes could strike with cumulative fatality

surpassing the total number of homicide victims in

the same period.

• Events of this intensity will also leave thousands

injured and homeless. The socio-economic

consequences of the earthquake(s) could lead to

immense suffering for several after.


Year Location –

Depth (km)

Magnitude

Max MMI

Macro-seismic Deaths

Injured

Homeless/

Damage

2001 Gujarat, India -

16

7.9, IX Strong Shaking

Liquefaction

>20K

>167K

600K Homeless

2003 Bam, Iran –

10

6.6, IX Strong Shaking

Fault Rupture

>26K

>30K

100K Homeless

2004 Indian Ocean

29

9.1, IX Tsunami >230K

>125K

1.7M Homeless

2005 Kashmir,

Pakistan - 30

7.6, VIII Landslides >86K

>106K

>32K buildings

collapsed

2008 Sichuan, China 8.0, X Landslide >70K

>374K

4.3M homeless

2010 PaP, Haiti -

10

7.0, VIII Strong Shaking >230K

>20K

>100K homeless

2010 Concepcion

Chile

8.8 Tsunami 1.7K

Many

>200K houses

damaged

Most Fatal Earthquakes in the 21st century....


Shouldn't the Population be

sensitised to make this a

National Issue ?


Earthquake Risk

• is primarily attributed to the construction

of seismically unsafe buildings and

infrastructure in locations where

considerable seismic hazard exists.

• is also exacerbated by rapid population

growth and unplanned or ill-planned

urbanization in hazard-prone zones


RISK F(NH, V)

Underlying Risk Sources

Uncontrollable Controllable

Natural Hazards Vulnerability

Severe

Natural

Event

Resilience of

Environment

Presence

of Human

Settlement

Environmental Degradation

Fragility to

Natural

Hazards

RISK MANAGEMENT


An Earthquake Risk Reduction Programme

Mitigation Preparedness

PeopleStructuresEmergency

management systems

RetrofittingRetrofitting of

Lifelines & Critical

Infrastructure

Regulation/Risk TransferLand Use Management

Building Codes

Insurance

Human CapitalEarthquake Awareness

Individual preparedness

PlansDisaster Response

Stand alone

Supporting plans

ResourcesCoordination

Communications

Search & Rescue


Disaster Risk Management

1. hazard assessment,

2. vulnerability analysis, and

3. enhancement of management capacity

Disasters are no longer viewed as extreme events

created entirely by natural forces but as unresolved

problems of development. It is now recognized that risks

left unmanaged (or mismanaged) for a long time lead to

occurrence of disasters.


Hyogo Framework of Action 2005-2015

• Ensure that disaster risk reduction is a national and a local priority with a strong institutional basis for implementation.

• Identify, assess and monitor disaster risk and enhance early warning.

• Use knowledge, innovation and education to build a culture of safety and resilience at all levels.

• Reduce the underlying risk factors associated with the level of development.

• Strengthen disaster preparedness for effective response at all levels.

A 10-year plan to make the world safer from natural

hazards. Dubbed as the blueprint for natural disaster risk

reduction efforts. The guiding principles are as follows:


Prioritized Actions to reduce Earthquake Risk (WCDR, Jan.2005)

1 Analysis of earthquake hazards affecting housing and buildings in each region

2 Development and improvement of building technology which reflect risks, building production practices and other factors in each region

3 Establishment of building codes and standards and development of social systems to disseminate them and ensure their thorough implementation

4 Assessment of safety of existing buildings, and development and dissemination of technologies for strengthening and retrofitting

5 Prevention of secondary losses resulting from damage to buildings in disasters, and development of repairing technologies and systems

6 Training of engineers, builders, administrators, etc.

7 Education for communities, building owners, developers, etc.

8 Formulation of building disaster prevention measures and development of implementation systems at the national and regional levels

9 International cooperation at the research institute level, the national and regional government levels, and the community level

10 Formulation of land use plans for future developments and urban expansion


Disaster Mitigation

• Response and recovery are necessary but alone are not the most effective means to reduce losses.

• Cost effective mitigation methods can• benefit property owners,

• improve the solvency of insurers and re-insurers and

• reduce the need for post disaster assistance from government

• In countries where disasters have occurred regularly the experience tend to influence

• engineering design,

• public policy, and

• building code.

• The benefits of mitigation is not recognized by the vast majority of homeowners due to :

• misperception of risk,

• short-term outlook, and upfront costs


Mitigation options

land use/zoning controls, particularly for critical or hazardous facilities;

requirements for soils and geotechnical studies;

special building design requirements;

hazardous building retrofitting and abatement programs;

programs to strengthen housing;

special requirements related to hazardous materials;

infrastructure and lifeline requirements;

disclosure requirements and posting of signs;

disaster response planning;

reconstruction and redevelopment planning; and

public information and education programs.


Conclusions

Despite having low return periods, earthquakes with its attendant hazards have the potential to inflict much greater losses on Trinidad and Tobago society in one event than any other natural hazards.

Major earthquakes have occurred near Trinidad and Tobago in the past. If the processes at work in generating earthquakes in the region are at work in the same way, then we should expect to experience significant magnitude earthquakes in the 21st Century

While there are a number of regional initiatives currently underway to improve earthquake mitigation practices, chances are they may fall short when an earthquake of destructive potential occurs.

There is a substantial knowledge gap in respect of the understanding of the tectonic processes driving these events as well as their hazard potential. There is even a larger gap between what is known and that which is converted into policy and action for a safer Trinidad and Tobago.


MAJOR CHALLENGES

• Coordination: national, regional Local

• Linkages with other initiatives/ partnerships

• Re-orientation among relevant decision-

makers and technocrats

• Political willingness

• Public awareness and participation

• Resource mobilization


Thanks for your attention…

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