Earthquake engineering and real-time early warning: the AMRA perspective. Iunio Iervolino* and Gaetano Manfredi *Assistant Professor of Structural Engineering

Earthquake engineering and real-time early warning: the AMRA perspective.

Iunio Iervolino* and Gaetano Manfredi*Assistant Professor of Structural Engineering

Department of Structural Engineering, University of Naples Federico II, Italy.

SAFER Project Final Meeting – Potsdam 3-5 June 2009

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1st year: Real-Time Risk Analysis 2nd year: Engineering Issues 3rd year: Structural Applications

SAFER Project Final Meeting – Potsdam, 3 – 5 June 2009

Regional Earthquake Early Warning Systems and the ISNet Irpinia Seismic Network (Italy)

Commonly used to give distributed estimates of the ground motion right after the event: SHAKEMAPS.

0 25 50 km0 25 50 km

Napoli

Salerno

Avellino

BeneventoCaserta

Potenza

1981 – 2002 SeismicityINGV Seismic Catalogue

Earthquake M>3

Earthquake M<3

1980 Earthquake Ms 6.9

Seismogenetic faults of 1980 Earthquake

Current Seismic Network

Seismic network under construction (2006)

Main City

Urbanized area

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Source-to-site distance

Seismic network

Ground motion at the site

IM (i.e. PGA)

Structural/non-structural performance/loss

EDP (i.e. Maximum Interstory Drift Ratio)

Epicenter

Signal at the network stations

Site-Specific Warning by Regional Networks: Hybrid EEWS

BECAUSE OF REAL-TIME SEISMOLOGY!

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RTS: Rapid estimation of event magnitude

MT

Seismologists (i.e. Allen & Kanamori, 2003) claim it is possible to estimate the magnitude from the predominant period () of the first 4 sec of the P-wave velocity recording

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RTS: Rapid estimation of event location

Other seismologists (i.e. Zollo et al., 2007) claim it is possible to locate the hypocenter with negligible uncertainty within 4 sec from the event origin time

Triggered Stations

Epicenter

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1 2 1 2| , ,..., | , ,...,| | , | |M R s s s

M R

f PGA f PGA m r f m f r s dr dm

PDF of magnitude conditional on the measures of the seismic instruments

PDF of distance due to rapid localization method

Ordinary Attenuation relationship

Distribution of PGA at the site conditional on the measures of the seismic instruments

Real-Time Probabilistic Hazard Analysis (RTPSHA) for Hybrid EEWS

Negligible uncertainty

Iervolino et al., 2006.Convertito et al., 2008.

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Magnitude’s distribution

2 2

ilog log logi 1

2 2

ilog log logi 1

2 ln τ 2

2 ln τ 2

| |

MAX

MIN

m

Mm

M

e ef m f m

e e dm

3 3,5 4 4,5 5 5,5 6 6,5 7 7,5 8

M

f(M

)

Gutenberg-Richter

MagnitudeMagnitude

Measurements

[s]

The mean of the tau network measurements is all we need to estimate

the magnitude!

Iervolino et al., 2007.

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SAFER Project Final Meeting – Potsdam, 3 – 5 June 2009 8 stationst = 6s 23 stationst = 9s 28 stationst = 11s 30 stationst = 12s

M=6 R=110km Event Simulation

2 stationst = 5s

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11 stazioni25 stazioni27 stazioni4 stazioni1 stazione

Simulazione Hazard M=6; R=110km

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Real-Time Probabilistic Seismic Hazard Analysis (RTPSHA) - Summary

Naples

Estimation of Distance

Estimation of PGA at the site

Estimation of Magnitude

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Is the Bayesian estimator appropriate also if it tends to underestimate the magnitude?


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:

:

True C

True C

MA no Alarm PGA PGA

FA Alarm PGA PGA

False and Missed Alarm Probabilities


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SABETTA E PUGLI ESE M=6 E R=120 km

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7

PGA [m/s2]

P[PG

A>P

GA

c]

[ ]C CAlarm if P PGA PGA P

PGAc

Pc

ALARM ! Because the probability that PGA exceeds the limit value is too high

When to activate security measures? Decisional Rules

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Time-Dependent Uncertainty in Early Warning


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Which uncertainty really matters in prediction of engineering ground motion parameters?


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Design Targets

False Alarm Probability

Lead Time

Performances/ Consequences

Low Perception Low Perception ImpactImpact (e.g. (e.g. Elevator)Elevator)

Medium Perception Medium Perception Impact (e.g.Trasportation Impact (e.g.Trasportation InterruptionInterruption

High Perception High Perception Impact (e.g. Lifelines Impact (e.g. Lifelines Interruption )Interruption )

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Engineering Requirements of EEWS

• Quantitative real-time assessment of seismic risk (losses for specific application)

• Time dependent decision making (quantification of trade-off between lead-time and costs of missed/false alarms)

• Automated decision for structural control system

Consequence-based approach

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Lead-time maps for the case-study region can be superimposed to real-time risk reduction actions for specific structural systems. These security

measures can be classified according to the time required to be carried out.

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Application of RTPSHA on our school of engineering

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Event Detection

Structure Specific AlertRegional alert Map

Real-Time estimation of Magnitude and Location

Developed with the group of Aldo ZolloOperating since July 25 2008 http://143.225.72.209:5800/ - ID: “utente” PW: “ergo”

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Event detected on 19/11/2008 – 8.17 PM

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A school classrom equipped with an EEWS terminal: how to set the alarm threshold

Let’s consider a simple school class equipped with a ringer and suppose that the students are trained to shelter under the desks when the alarm is issued.

7 m7 m

6 m

6 m

Desk

Lighting36 m2

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What causes loss?

a) Structural collapse (DS)

b) No structural damage, but collapse of lighting (NDS)

a) No structural damage, no lighting damage (loss due to false alarm)

Total expectaion theorem: The total expected loss is the summation of the expected losses corresonding to these

three cases!

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Real-Time loss assessment

Extending the hazard approach it is possible to determine the expected losses condiotioned to the measurements of the seismic

network in the case of alarming or not

| , |L D EDP PGA

E L l f l d g f d edp f edp pga f pga dL dD dEDP dPGA

Expected Loss

1. Loss probability depending on the alarming decision

2. Structural damage probability depending on

building’s seismic response

3. Seismic response probability depending

on hazard

4. Real-time hazard analysis


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1. Loss functions

No alarm loss Alarm loss (reduced because of security action)

No sheltering Sheltering of students under desks

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Expected loss as a function of the seismic instruments measures

Exp

ecte

d L

oss [

€]

[s]

No alarm

Alarm

Optimal Alarm threshold

τ̂


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Early Warning and Structural Control

Passive Control: to modify, the stiffnes and/or the damping so as to achieve a better structural response;

Semi-Active Control:to modify just-in-time the dynamic characteristics of the structure as to achieve the optimal response;

Active Control: based on the availability of large force actuators able to

counterbalance inertial forces due to seismic excitation.

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This model may be used to study other systems…

A structure equipped with a semi-active control device activable by the EEWS: feasibility.

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SAFER Project Final Meeting – Potsdam, 3 – 5 June 2009 PASSIVE DEVICEPASSIVE DEVICE

Variable-Orifice Viscous Dampers

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Real-Time performance analysis

3. Seismic response probability depending

on hazard

4. Real-time hazard analysis

Expected Structural

performance

|EPD PGA

E EDP edp f edp pga f pga dEDP dPGA

uncontrolled c c

uncontrolled c c

if P[EDP EDP | ] P

if P[EDP EDP | ] P

ONDevice ON or OFF

OFF

Iervolino et al., 2009b.

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Benefit of The EEWS in terms of reduction of Drift Response


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Benefit of The EEWS in terms of reduction of Peak Floor Acceleration


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Response improvement in respect to the structure without the EEWS

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Design and Feasibility issues for the engineering use of EEWS for structural “control”

• Maximization of the lead time is not the only design target, in some case it is not even the principal design objective;

• The uncertainties related to the real-time estimations of earthquake features have to be integrated with the models of seismic response of facilities to protect;

• False and missed alarm probabilities have to be optimized;

• The alarm thresholds have to be set on the basis of expected losses;

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References http://www.saferprojct.net/publications

• Iervolino I., Giorgio M., Galasso C., Manfredi G. (2009) Uncertainty in early warning predictions of engineering ground motion parameters: what really matters? Geophysical Research Letters, DOI:10.1029/2008GL036644, in press.

• Convertito V., Iervolino I., Giorgio M., Manfredi G., Zollo A. (2008). Prediction of response spectra via real-time earthquake measurements. Soil Dyn Earthquake Eng, 28: 492–505.

• Iervolino I., Convertito V., Giorgio M., Manfredi G., Zollo A. (2006). Real-time risk analysis for hybrid earthquake early warning systems. Journal of earthquake Engineering, 10: 867–885.

• Iervolino I., Giorgio M., Manfredi G. (2007). Expected loss-based alarm threshold set for earthquake early warning systems. Earthquake Engn Struct Dyn, 36: 1151–1168.

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Early Warning Special Issue • Tentative Title: Prospects and applications of earthquake early

warning, real-time risk management, rapid response and loss mitigation;

• Topics: Risk analysis, system performance evaluation and feasibility studies, design of earthquake engineering applications of EEW, civil protection via EEW;

• SDEE Editor in chief: Mustafa Erdik; Guest editors: Iunio Iervolino and Aldo Zollo;

• Expected publication date: Jan 2010.

Documents

Earthquake engineering and real-time early warning: the AMRA perspective. Iunio Iervolino* and Gaetano Manfredi *Assistant Professor of Structural Engineering