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

1. FEASIBILITY STUDY OF A REGIONAL EEW SYSTEMFOR 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 objectivesin theEastern Caribbean region OBJECTIVE Antigua & Barbuda

3. Outline • Critical facilities • Method • - Synthetic seismograms • - Evaluation of usefulness of EEW system • - Testing of VS-in-SC3 • Conclusive Remarks

4. CRITICAL FACILITIES

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

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

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

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

9. METHOD

10. METHOD The feasibility of the EEW system was performed by assessing: comparison between the theoretical warning times issuable to the selected critical facilities and the expected damage testing of a regional EEW algorithm (“VS-in-SC3”) synthetic seismograms

11. Synthetic seismograms

12. ALGORITHM: Kinematic Source Modeling (SAL) Broadband ground motion simulation method developed by University of California Santa Barbara (UCSB) Representation theorem Point source sub-faults Convolve slip rate function with Green’s functions of elastic medium and sum over whole fault to get ground motion at free surface

13. ALGORITHM: Kinematic Source Modeling (SAL) (Schmedes et al., JGR, 2010; GJI, 2013) Definitionof slip rate function for each point source Functional form of slip rate parametrized by 4 source parameters: • final slip • local rupture velocity • rise time • peak time (is a measure of the impulsive part of the slip rate function) Correlated random source parameters based on Dynamic Rupture Models (> 300 models)

14. … ALGORITHM: Green Functions Layered Earth model (1D) 1 1 1 ρ1 h1 QP1 Qs1 Frequency-wavenumber (FK) code (Zhu and Rivera, 2001) 22 2 ρ2 h2 QP2 Qs2 33 3 ρ3 h3 QP3 Qs3 n n n ρn hn QPn Qsn

15. INPUT DATA Seismotectonic information (MCE) PSHA Disaggregation (475 years return period – PGA) Sites Structural velocity models Critical facilities + seismic stations L<100  dmax=150 km L>100  dmax=250 km GONZALEZ et al. (2012) S-wave velocity structural models of the Caribbean down to 310 km depth with a resolution of 2 ̊x2 ̊ definition of seismic sources

16. INPUT DATA: Earthquake scenarios From Bengoubou-Valerius et al. (2008) Antigua & Barbuda lie along the eastern boundary of the Caribbean Plate

17. INPUT DATA: Earthquake scenarios PSHA (Bozzoni et al., 2011) DISAGGREGATION (475 years – PGA) Intraplate subduction SZ4, Mw=7.25-d=89 km Interface subduction SZ2, Mw=4.55,6.55-d=31 km

18. INPUT DATA: Earthquake scenarios Interface seismicity Antigua 1943-like event

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

20. Evaluation of usefulness of an EEW system

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

22. THEORETICAL LEAD-TIME regional EEW configuration with 4 triggered stations technical times Δt=5 s : 3s of processing delay 1s for transmission to processing centre 1s transmission of the warningmessage S-wave arrival time at the facility time at which the P-wave data are available at the 4 stations closest to the epicentre 475-year return period MCE Antigua Antigua

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

24. Testing of VS-in-SC3

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

26. TESTING OF “VS-IN-SC3” MCE 475-year return period -0.5±0.22 -0.08±0.13 -1.63±3.41 km 1.45±1.88 km 2.5±0.88 km 1.33±0.86 km

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

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

29. CONCLUSIVE REMARKS The feasibility study of an EEW system performed for Antigua by investigating two earthquake scenarios associated with the interface seismicity demonstrated the: 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); 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; 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