FEASIBILITY STUDY OF A REGIONAL EEW SYSTEM FOR THE EASTERN CARIBBEAN REGION

ZUCCOLO Elisa, SALAZAR Walter, DI SARNO Luigi, FARRELL Anthony, GIBBS Tony, LAI Carlo G., LATCHMAN Joan L., LYNCH Lloyd,

WORKMAN Addison

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To carry out a feasibility study of an EEWS by investigating whether such a system could successfully be applied to sensitive objectives in

the Eastern Caribbean region

OBJECTIVE

Antigua & Barbuda

Outline

• Critical facilities

• Method- Synthetic seismograms- Evaluation of usefulness of EEW system- Testing of VS-in-SC3

• Conclusive Remarks

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CRITICAL FACILITIES

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CRITICAL FACILITIES

Antigua Public Utilities Authority – Water Plant

Mount St John’s Medical Centre V. C. Bird International Airport

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CRITICAL FACILITIES

Mount St John’s Medical Centre

CRITICAL ELEMENT: oxygen supply

Oxygen Distribution UnitStored bottles of oxygen

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CRITICAL FACILITIES

CRITICAL ELEMENT: refuelling unit and storage facility

V. C. Bird International Airport

No. 4 Ramp fuel Control Switch Gravity Feed of Fuel from main Storage

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CRITICAL FACILITIES

CRITICAL ELEMENT: pumps

Antigua Public Utilities Authority – Water Plant

Control Room Inside Building Secondary Pumps Outside Building

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METHOD

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METHOD

The feasibility of the EEW system was performed by assessing:

1) comparison between the theoretical warning times issuable to the selected critical facilities and the expected damage

2) testing of a regional EEW algorithm (“VS-in-SC3”)

synthetic seismograms

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Synthetic seismograms

Convolve slip rate function with Green’s functions of elastic medium and sum over whole fault to get ground motion at free surface

Point source sub-faults

Representation theorem

Broadband ground motion simulation method developed by University of California Santa Barbara (UCSB)

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ALGORITHM: Kinematic Source Modeling (SAL)

Definition of slip rate function for each point source

(Schmedes et al., JGR, 2010; GJI, 2013)

- final slip- local rupture velocity- rise time- peak time (is a measure of the impulsive part of the slip rate function)

Functional form of slip rate parametrized by 4 source parameters:

ALGORITHM: Kinematic Source Modeling (SAL)

Correlated random source parameters based on Dynamic Rupture Models (> 300 models)

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ALGORITHM: Green Functions

Layered Earth model (1D)

1 1 1 ρ1 h1 QP1 Qs1 2 2 2 ρ2 h2 QP2 Qs2

…

3 3 3 ρ3 h3 QP3 Qs3

n n n ρn hn QPn Qsn

Frequency-wavenumber (FK) code (Zhu and Rivera, 2001)

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INPUT DATA

PSHA Disaggregation(475 years return period – PGA)

Seismotectonic information(MCE)

definition of seismic sources

Structural velocity models

GONZALEZ et al. (2012)

Sites

Critical facilities +seismic stationsL<100 dmax=150 kmL>100 dmax=250 km

S-wave velocity structural models of the Caribbean down to 310 km depth with a resolution of 2 x2 ̊� ̊�

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INPUT DATA: Earthquake scenarios

From Bengoubou-Valerius et al. (2008)

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Antigua & Barbuda lie along the eastern boundary of the Caribbean Plate

INPUT DATA: Earthquake scenarios

PSHA (Bozzoni et al., 2011) DISAGGREGATION (475 years – PGA)

Intraplate subductionSZ4, Mw=7.25-d=89 km

Interface subductionSZ2, Mw=4.55,6.55-d=31 km

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INPUT DATA: Earthquake scenarios

Interface seismicity

Scenario Mw Strike (°)

Dip (°)

Rake(°)

Focal Depth (km)

Length(km)

Width(km)

MCE 8.5 145 24 90 32 300 110

475 yrs 6.25 145 24 90 30 15 101943-like event

Antigua

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PGA/hard rock (NEHRP site class A)

475-year return periodMCE

COMPARISON WITH ZHAO ET AL. (2006) GMPE

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Evaluation of usefulness of an EEW

system

EXPECTED DAMAGE

Site class A

Scenarioearthquake

PGA1

PGA10

……..

PGA2PGA3

Site class DSeismograms at the facility

Application of Zhao et al. (2006)site class coefficient

PGA1

PGA10

PGA2PGA3

…….. ……..

Average PGAAverage PGA + σ

compared with

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THEORETICAL LEAD-TIME

regional EEW configuration with 4 triggered stations

S-wave arrival time at the facility

time at which the P-wave data are available at the 4 stations closest to the epicentre

technical timesΔt=5 s : 3s of processing delay

1s for transmission to processing centre 1s transmission of the warning message

MCE 475-year return period

Antigua Antigua

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THE EEW SYSTEM COULD BE USEFUL?

NO for the 475-year return period scenario

YES for the MCE (9-10 s of lead-time)

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Testing of VS-in-SC3

Offline playback of synthetic waveforms for each simulated earthquake

TESTING OF “VS-IN-SC3”

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TESTING OF “VS-IN-SC3”

MCE 475-year return period

-0.5±0.22

1.45±1.88 km

1.33±0.86 km

-0.08±0.13

2.5±0.88 km

-1.63±3.41 km

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HOW DOES IT WORK FOR EEW?Ti

me

1st SC3/VS estimate

2nd SC3/VS estimate

S-waves reach the site

magnitudelikelihoodhypocentreorigin time

GMPE (mean value,rupture distance) PGA at the site

nth SC3/VS estimate magnitude

hypocentreorigin time

GMPE PGA at the siteIf PGA > damage threshold

WARNING!

likelihood

Lead-time= S-wave arrival time at the site – SC3/VS estimate time – 2s

time of the estimate

time of the estimate

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HOW DOES IT WORK FOR EEW?

MCE damage

MVS=8.3

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CONCLUSIVE REMARKS

The feasibility study of an EEW system performed for Antigua by investigating two earthquake scenarios associated with the interface seismicity demonstrated the:

1) uselessness of the EEW system for the scenario associated with the 475-year return period earthquake, due either to the absence of damage (for the hospital and the airport) or to the absence of warning time (for the water plant);

2) potential usefulness of the EEW for the MCE, for which a moderate or even complete damage is expected with a theoretical lead-time of 9-10 s;

3) failure of the tested EEW algorithm in providing stable alerts for the MCE, due to the fact that the first magnitude estimates are much lower than the real magnitude of the earthquake

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