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

2 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 3

4 CRITICAL FACILITIES

5 Antigua Public Utilities Authority – Water Plant Mount St John’s Medical Centre V. C. Bird International Airport

6 CRITICAL FACILITIES Mount St John’s Medical Centre CRITICAL ELEMENT: oxygen supply Oxygen Distribution UnitStored bottles of oxygen

7 CRITICAL FACILITIES CRITICAL ELEMENT: refuelling unit and storage facility V. C. Bird International Airport No. 4 Ramp fuel Control SwitchGravity Feed of Fuel from main Storage

8 CRITICAL FACILITIES CRITICAL ELEMENT: pumps Antigua Public Utilities Authority – Water Plant Control Room Inside BuildingSecondary Pumps Outside Building

9 METHOD

10 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

11 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) 12 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) 13

ALGORITHM: Green Functions Layered Earth model (1D) 1  1  1 ρ 1 h 1 Q P1 Q s1 2  2  2 ρ 2 h 2 Q P2 Q s2 … 3  3  3 ρ 3 h 3 Q P3 Q s3 n  n  n ρ n h n Q Pn Q sn Frequency-wavenumber (FK) code (Zhu and Rivera, 2001) 14

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 stations L<100  d max =150 km L>100  d max =250 km S-wave velocity structural models of the Caribbean down to 310 km depth with a resolution of 2 ̊x2 ̊ 15

INPUT DATA: Earthquake scenarios From Bengoubou-Valerius et al. (2008) 16 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 subduction SZ4, M w =7.25-d=89 km Interface subduction SZ2, M w =4.55,6.55-d=31 km 17

INPUT DATA: Earthquake scenarios Interface seismicity ScenarioMwStrike (°) Dip (°) Rake (°) Focal Depth (km) Length (km) Width (km) MCE yrs like event Antigua 18

PGA/hard rock (NEHRP site class A) 475-year return period MCE COMPARISON WITH ZHAO ET AL. (2006) GMPE 19

20 Evaluation of usefulness of an EEW system

EXPECTED DAMAGE Site class A Scenario earthquake PGA1 PGA10 …….. PGA2 PGA3 Site class D Seismograms at the facility Application of Zhao et al. (2006) site class coefficient PGA1 PGA10 PGA2 PGA3 …….. Average PGA Average PGA + σ compared with 21

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 times Δt=5 s : 3s of processing delay 1s for transmission to processing centre 1s transmission of the warning message MCE 475-year return period Antigua 22

THE EEW SYSTEM COULD BE USEFUL? NO for the 475-year return period scenario YES for the MCE (9-10 s of lead-time) 23

24 Testing of VS-in-SC3

Offline playback of synthetic waveforms for each simulated earthquake TESTING OF “VS-IN-SC3” 25

TESTING OF “VS-IN-SC3” MCE475-year return period -0.5± ±1.88 km 1.33±0.86 km -0.08± ±0.88 km -1.63±3.41 km 26

HOW DOES IT WORK FOR EEW? Time 1 st SC3/VS estimate 2 nd SC3/VS estimate S-waves reach the site magnitude likelihood hypocentre origin time GMPE (mean value,rupture distance)  PGA at the site n th SC3/VS estimate magnitude hypocentre origin time GMPE  PGA at the site If PGA > damage threshold WARNING! likelihood Lead-time= S-wave arrival time at the site – SC3/VS estimate time – 2s time of the estimate 27

HOW DOES IT WORK FOR EEW? MCE damage MVS=8.3 28

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 29