Development of a seismic hazard map for Jamaica

Lyndon Brown

EARTHQUAKE UNIT,UNIVERSITY OF THE WEST INDIES,

MONA

SEISMIC GROUND MOTION MODELS

1. Shepherd, Shepherd & Aspinall: Tomblin and Aspinall catalogue 1980.

2. Shepherd et al. (1999) for the Caribbean is based on a revised earthquake catalogue with

uniform seismic moment magnitude values.

3. Old Harbour: Power plant in 2001: Power generation capacity-Coal Fire Generation

capacity.

4. IBC: Seismic codes:2007

5. NEM Project: Earthquake modelling along Plantain Garden Fault

The first probabilistic ground motion models for the Kingston area were

proposed by Shepherd (1971) and Shepherd and Aspinall (1980) using

macroseismic data from the Tomblin and Robson (1977) catalog. Intensity

observations in the Kingston area during the period 1880 to 1970 were

converted to acceleration by Shepherd and Aspinall (1980) using the

Gutenberg and Richter (1954) relationship,

Log a =I/3 -0.5

MM

IntensityVII VIII IX X

Return

Period

(yr.)

38 87 137 273

Probabi

lity (%)73 44 30 16

PGA

(%g) 17 15 32 69

PGA

(%g) 25-10 10-20 20-40 40-48

Probability - probability of exceedence in 50 years PGA - Peak Ground Acceleration based on

intensity-acceleration relationships from 1.Gutenberg and Richter (1954), 2. Medvedev (1968)

For MMI IX level ground motions, Shepherd and Aspinall (1980) estimated an acceleration of

32% g with a 30% probability of exceedence in 50 years on hard. Consideration of site

amplification effects in the Liguanea Plain lead Shepherd and Aspinall (1980) to modify this

estimate to 30% g with a 10% probability of exceedence in 50 years.

A more recent regional seismic hazard assessment by Shepherd et al. (1997) for the

Caribbean is based on a revised earthquake catalog with uniform seismic moment

magnitude values. That study uses the Historic Parametric method to conduct a

probabilistic seismic hazard assessment.

Based on this analysis of Jamaican seismicity indicates a Peak Ground Acceleration (PGA)

high of approximately 30%g in eastern Jamaica and a gradual decrease to less than 14% g

in western Jamaica for hard rock sites with a 10% probability of exceedence in 50 years.

The values for the Kingston Metropolitan area are approximately 28% g.

4 inputs are required:-

1. Seismic Sources e.g. known active faults, geomorphic structures, seismotectonicprovinces

2. Seismicity or Recurrence patterns of earthquakes

3. Ground Motion or attenuation relation(s)

4. Probability of Exceedance

Seismic Hazard Assessment: Towards IBC Seismic

Hazard Maps for Jamaica-MWG

Seismic Sources

Typical Seismicity 97-03

5

4

3Blue Mtn

Plantain Garden

Montpelier Newmarket

New Bank Fracture

Blossom Basin

Old Harbour Soil Spectral Accelerations

0

100

200

300

400

500

6000.0

1

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9 1

1.5 2

Period (seconds)

Accele

rati

on

(g

als

)

Prob475s

Prob975s

Prob2475s

Det475s

Det975s

Det2475s

2001

Source

zone

# of

Eqs.

Time

in yrs

Activity

eq/yr

Av. Depth

km

Min.

Mag.

Max.

Mag.

b-

value

Beta

{ln

10)*b}

Number

of

events

used

Oriente

Fracture

Zone

97 123 0.593 18.6 3.6 7.0 0.49 1.13 73

East

Jamaica

48 304 0.125 16.1 3.6 7.0 0.60 1.38 38

West

Jamaica

18 158 0.076 7.8 3.6 6.5 0.48 1.11 12

Southwe

st of

Jamaica

20 55 0.218 13.3 3.6 7.1 0.68 1.57 12

Back-

ground

61 110 0.427 20.04 3.6 7.5 0.59 1.36 47

Five source zones and the characteristics for model: Old Harbour Site

Assessment.

Jamaica – all 5 sources

10%

2%

T=1.0s T=0.2s

PGA – 5 sources

SHA Method

Return

Period

Source

model

Catalogue Attenuation

Relationshi

p

Maximum

Horizontal

Ground

Acceleratio

n Remarks

Remarks

PAIGH (1997) Probabilistic

475 year RP

Historic

parametric

PAIGH (1994) Woodward

Clyde

0.26-0.27 g at

Old Harbour

(rock)

Attenuation

too low for

Jamaica

CDMP (1999) Probabilisitc

475 years RP

Faults and

total slip rate

of 6 mm/year

across

Jamaica

CDMP 1988 Joyner –

Boore (1993)

0.2-0.4g

(rock, Kgn.)

0.3 g (rock

resp, Kgn)

0.45 g (soil

resp, Kgn)

Recommend

soft soil sites

especially

investigated.

Summary of the methodologies and results of Seismic Hazard

Assessment (475 yr RP) for Jamaica

Old Harbour

(2001)

Probabilistic

475 year RP

5 source

zones within

200 km

Mgcatmw

(1998)

Joyner,

Boore, Fumal

(1997)

0.28 g (rock

at 0.2 sec

0.36g (soil at

0.2 sec)

Includes

spectral

ordinates

Old Harbour Determinisiti

c

475 year RP

Rio Minho –

Crawle River

Fault and

maximum

credible

earthquake

of 7.3

Prototype

CDMP

Joyner,

Boore, Fumal

(19970

0.26 (rock at

0.2 sec)

0.31g (soil at

0.2 sec)

Includes

spectral

ordinates

IBC based seismic hazard maps for Jamaica for site class average rock with

2,475-year Return Period for Spectral Response Acceleration of 0.2 second (top)

and 1.0 second (bottom) expressed as a percentage of gravity.

Haiti earthquake along Plantain Garden Fault-Jamaica

An event of Magnitude 7 was added to the catalogue at the source area

within the Eastern Jamaica to account for modelling output and the ground

acceleration effects across Jamaica that would be associated with such

Magnitude 7 event along the Plantain Garden Fault zone.

Methodology

1.Homogenize the earthquake catalogue and assess the completeness

2.Define the seismic source zones.

3.Prepare attenuation relations for the region.

4.Compute hazard in terms of peak ground acceleration (PGA).

5.Prepare input parameters from the earthquake catalogue for each source

zone.

Caveats

►These maps show ground motion as a function of earthquake magnitude,

distance, path effects and frequency based on a borrowed attenuation

relation.

►The Boore, Joyner & Fumal (1997) attenuation relation defines the site

class average rock as having an average shear wave velocity of 620

metres/second in the upper 30 metres, and accounts for source distances of

up to 80 kilometres.

►Six source zones in this distance range were selected to define Jamaican

seismicity. The effects of more distant sources are expected to be less.

►Values given do not account for direct throw on a fault, site or secondary

effects.

►A disadvantage of probabilistic seismic hazard is that it is not obvious what

sources contribute most to the hazard in any given area.

►The sense of faulting on Jamaica is taken to be predominantly lateral or

strike-slip although some earthquakes have varying amounts of reverse or

normal slip. Ground motions are typically larger for reverse events than

normal or strike-slip events in the same magnitude range.

►The maximum earthquake for the sources are in the range Mw 7.1 to 7.6,

based on magnitude-fault length relations ofWells & Coppersmith (1994).