PREDICTION OF RESPONSE SPECTRAL

PARAMETERS FOR BHUJ EARTHQUAKE

(26TH JANUARY 2001) USING COMPONENT

ATTENUATION MODELLING TECHNIQUE

ByDR. SAROSH .H. LODI

Professor, Department of Civil EngineeringNED UNIVERSITY OF ENGINEERING AND TECHNOLOGY

KARACHI, PAKISTAN&

MUKESH KUMARResearch Assistant, Department of Civil Engineering

NED UNIVERSITY OF ENGINEERING AND TECHNOLOGYKARACHI, PAKISTAN

PRESENTED BY: MUKESH KUMAR

PRESENTATION LAYOUT

Research Background

Available Data

Component Attenuation Modeling

Methodology

Input Parameters & Comparative Analysis

Conclusions and Future Research Direction

Discussion Session

BHUJ EARTHQUAKE

It was one of the most devastating earthquake in the history of Indian sub-continent.

Mw=7.7 earthquake, hypocentral depth of 23.6 km, epicenter located near Bhachau city.

There exists a debate whether the earthquake was interplate or intraplate.

Li et al., developed a viscoelastic finite element model and concluded that the cause of plate-interior earthquake was intracontinental thrusting and shearing along the northwestern Indian plate boundary.

RESEARCH BACKGROUND

RESEARCH OBJECTIVES

The objective of the research endeavor is to pave way towards the development of Design Response Spectra for Southern Coastal Region (SCRS) for future design of engineering structures and seismic evaluation of existing structures, in the most data scarce environment.

It also aims at assessing the applicability of Component Attenuation Modeling Technique, and future improvements in the technique.

RESEARCH BACKGROUND

AVAILABLE DATA

The event remained least recorded in the near vicinity of the source.

Digital Strong-motion Accelerographs located at a distanceof 238 km provide the Ground Acceleration Records, but the recordings have been infected due to the location of accelerograph in a high rise building.

Only usable recordings are Structural Response Recorders (SRR) data.

AVAILABLE DATA

STRUCTURAL RESPONSE RECORDER DATA

Thirteen SRR located within a periphery of 300 km from the epicenter recorded spectral acceleration for varying natural time period of 0.4 sec, 0.75 sec and 1.25 sec with a fixed damping ration of 5%.

SRR stations have been divided into three categories based on site soil conditions. The sites have been categorized into Rock, Quaternary, and Tertiary; using NEHRP site classification scheme.

The sites are categorized into three schemes using Geologic Map of India (1962), at a scale of 1:2,000,000, which may be cause of uncertainty.

AVAILABLE DATA

TABLE SHOWING SRR VALUES

EpicentralDistance

(Km)

Sa-5% Damped

Site Condition0.4 sec 0.75 sec 1.25 sec

44 1.616 0.705 0.423 T

53 0.863 0.571 T

97 0.811 0.65 0.300 Q

147 0.72 0.216 T

150 0.181 0.065 0.023 R

166 0.220 0.152 0.072 R

188 0.211 0.058 Q

207 0.191 0.248 0.054 Q

216 0.187 0.063 0.023 R

225 0.096 0.066 0.028 R

238 0.288 0.230 0.219 Q

266 0.488 0.041 Q

288 0.144 0.061 0.045 Q

AVAILABLE DATA

CAM is the modified version of stochastic simulation method using wave attenuation model, developed by Boore (1983).

It is a technique proposed by Lam et al., to predict response spectral parameters of an earthquake for regions with scarcity of earthquake ground motion data.

The idea is based on the finding of Atkinson and Boore, that the source models for interplate and intraplate regions exhibit similar frequency content properties.

COMPONENT ATTENUATION MODELING (CAM)

COMPONENT ATTENUATION MODELING

Component Attenuation Modeling Technique

*

)(M

)()()()(*78.0 crustRRGM

)(RG

)(R

)(crust

Response spectral parameter of interest (SDmax, SVmax and SAmax)

Constant pertaining to spectral parameter of interest

Source factor

Geometric factor

Anelastic attenuation factor

Upper crust factor, product of Cm and Cu for mid-crust amplification and combined upper crust amplification and attenuation

COMPONENT ATTENUATION MODELING

METHODOLOGY

The SRR values have been divided into two sections.

Data recorded on Rock sites.

Data recorded on Quaternary and Tertiary sites.

Recorded is compared with prediction of CAM and orthodox stochastic simulation.

METHODOLOGY

PARAMETERS USED FOR CAM

Mw=7.7

Mid-crust exhibits Pre-Cambrian Crystalline basement and upper crust consists of Phanerozoic sedimentary sequence Lozios et al.

The thickness of the crust is taken to be 40 km, so the Geometric Attenuation characteristics are similar to ENA.

INPUT PARAMETERS

Predicted V/s Recorded

Distance (km)

Sa/g Values Corner Periods Peak Spectral Parameters

0.4 0.75 1.25 T1 T2 Sd Sv Sa

150 0.192 0.102 0.060 0.17 1.97 37.77 0.12 0.465

166* 0.176 0.094 0.056 0.17 2.03 35.54 0.11 0.411

216 0.144 0.077 0.046 0.190 2.18 30.11 0.09 0.287

225 0.128 0.068 0.041 0.200 2.210 29.31 0.08 0.27

COMPARATIVE ANALYSIS

Graph Illustrates the predicted DRS V/S SRR values at the distance of 150 km

COMPARATIVE ANALYSIS

Graph Illustrates the predicted DRS V/S SRR values at the distance of 166 km

COMPARATIVE ANALYSIS

PREDICTION ON TERTIARY SEDIMENTS

Distance (km)

Sa (g) ValuesObserved

Sa (g) ValuesPredicted

Ratio Observed/Predicted

0.4 0.75 1.25 0.4 0.75 1.25 0.4 0.75 1.25

44 1.616 0.705 0.423 0.416 0.222 0.133 3.88 3.17 3.18

53 0.863 0.571 N.A. 0.336 0.179 0.107 2.56 3.18 N.A.

147 0.72 0.216 N.A. 0.192 0.102 0.061 3.75 2.19 N.A.

COMPARATIVE ANALYSIS

PREDICTION ON QUATERNARY SEDIMENTS

Distance (km)

Sa (g) ValuesObserved

Sa (g) ValuesPredicted

Ratio Observed/Predicted

0.4 0.75 1.25 0.4 0.75 1.25 0.4 0.75 1.25

97 0.811 0.65 0.300 0.272 0.145 0.087 2.98 4.48 3.44

188 0.211 N.A. 0.058 0.16 0.085 0.051 1.46 N.A. 1.26

207 0.191 0.248 0.054 0.144 0.079 0.046 1.32 3.14 1.17

238 0.288 0.230 0.219 0.128 0.068 0.041 2.25 3.38 5.34

266 0.488 0.041 N.A. 0.114 0.061 0.036 4.28 0.67 N.A.

288 0.144 0.061 0.045 0.104 0.055 0.033 1.38 1.11 1.36

COMPARATIVE ANALYSIS

USING STOCHASTIC SIMULATION METHOD

Distance (km)

Recorded values Predicted with CAMPredicted With (AB95) Model

0.4 1.0 1.25 0.4 1.0 1.25 0.4 1.0 1.25

150 0.181 0.065 0.023 0.192 0.102 0.060 0.298 0.147 0.07

166 0.220 0.152 0.072 0.176 0.094 0.056 0.27 0.136 0.066

216 0.187 0.063 0.023 0.144 0.077 0.046 0.210 0.109 0.053

225 0.096 0.066 0.028 0.128 0.068 0.041 0.201 0.104 0.051

COMPARATIVE ANALYSIS

CONCLUSION

The observed data seem to be in overall agreement with that predicted by CAM and stochastic simulation of AB95 model.

The sites classified as sediments are under predicted by the applied technique, due to soil amplification.

The maximum value of amplification due to sedimentary site condition is observed at a distance of 238 km, shows that SRR was stationed in Ahmedabad City; which was the worst affected in the earthquake.

CONCLUSION

CONCLUSION (Contd)

CAM successfully predicts Response Spectral Parameters in the available period range i.e. in velocity controlled regime.

Due to unavailability of ground acceleration data, in near-source region, restricts to assess its applicability in all period ranges.

Yet, It may be concluded that an ad-hoc design response spectra may be developed using CAM, for region with scarcity of data.

CONCLUSION