feasibility study of a regional eew system for the eastern caribbean region zuccolo elisa, salazar...
TRANSCRIPT
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
CRITICAL FACILITIES
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 Switch Gravity Feed of Fuel from main Storage
8
CRITICAL FACILITIES
CRITICAL ELEMENT: pumps
Antigua Public Utilities Authority – Water Plant
Control Room Inside Building Secondary 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 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)
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 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 ̊� ̊�
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 subductionSZ4, Mw=7.25-d=89 km
Interface subductionSZ2, Mw=4.55,6.55-d=31 km
17
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
18
PGA/hard rock (NEHRP site class A)
475-year return periodMCE
COMPARISON WITH ZHAO ET AL. (2006) GMPE
19
20
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
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 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
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”
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
26
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
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