Simulation of bedrock motion to obtain PGA values. Prof. Ranjith Dissanayake Head, Department of Civil Engineering, University of Peradeniya

Transcription

1 Simulation of bedrock motion to obtain PGA values Prof. Ranjith Dissanayake Head, Department of Civil Engineering, University of Peradeniya 1

2 Objective To develop the seismic hazard map for Sri Lanka using numerical simulation.

3 Seismicity of Earth K.K. Wijesundara 3

4 Indo-Australian Plate 4

5 Intraplate Earthquake: Bhuj Earthquake (001, Mw=7.6) 400 km

6 Earthquake in Vicinity of Sri Lanka ( A.D.)

7 Sources of Data Collection Chandra [1977], Rao and Rao [1984], Guha and Basu [1993], Iyengar et al. [1999] and Vithanage et al Jaiswal and Sinha [007] National Earthquake Information Centre (NEIC) International Seismological Centre (ISC), Incorporated Research Institutions for Seismology (IRIS), India Metrological Department (IMD) USGS Database PEER Database 7

8 FLAC FLAC is a two-dimensional finite difference program for engineering mechanics computation. FLAC's analysis capability to a wide range of dynamic problems in disciplines such as earthquake engineering, seismology and mine rock bursts. 8

9 Finite Difference Method - Overview Replace derivatives of governing equations with algebraic difference quotients Results in a system of algebraic equations solvable for dependent variables at discrete grid points Analytical solutions provide closed-form epressions variation of dependent variables in the domain Numerical solutions (finite difference) - values at discrete points in the domain 9

10 Grid Discretization For accurate representation of wave transmission through a model, element size Δl, must be smaller than approimately one-tenth to one-eight of the wave length of the input wave. l λ 10 λ is the wave length associated with the highest frequency component that contains appreciable energy. 10

11 1D-Wave Equation σ 0 σ + 0 dσ d d Considering the dynamic equilibrium dσ σ 0 + d A σ 0 = d ρad d dt u u t = v u P 11

12 Wave Equation Considering second order wave equation. Discretization is implemented by replacing the second order derivatives in the wave equation by their standard finite difference approimations : ( ) ( ) ( ) ( ) ( ) ( ) ), ( ), ( ), ( ), ( ), ( ), ( ), ( ), ( t u t u t u t u t t t u t u t u t t u m j m j m j m j m j m j m j m j + Ο + + Ο u v t u =

13 Selected Cross Sections K.K. Wijesundara 13

14 Cross section obtained from Google earth 14

15 Details of the Model Google Earth maps were used to acquire the cross section Element size 100 m 100 m Total size 15 km in height, 14 km in width Shear wave velocity = 5000 m/s Density = 000 kg/m 3 Bulk Modulus = 0.3 Gpa Shear Modulus = 0.3 GPa

16 Finite Difference Model Cities: Colombo, Kandy, Hunnas and Pasikuda Colombo Kandy Hunna Hunnas s Pasikuda Kandy

17 Finite Difference Model 17

18 Simulated Earthquake Chagos-Laccadive Ridge 90 km Comorin Ridge Ninetyeast Ridge K.K. Wijesundara 18

19 Seismic Input Select 7 accelerograms from Intraplate earthquakes of magnitude around 7.4 recorded around 90 km Acceleration (g) Aqaba Chichi Kobe NorthRidge Loma Preita Taiwan Fruili Period

20 Resultant Resonse Spectra Colombo Fort Colombo 13 Spectral Acceleration (g) Kotahena Colombo 14 Sedawatta Peliyagoda Himbutuwelgoda Dalugama Kiribatgoda Mahara Weliweriya Radawana 0.05 Mawanella Peiod (s) Kandy Baticoloa 0

21 Proposed Zonation Map Zone Description PGA Value(g) Zone 1 Zone from the western coastal Belt km 60 km from the western coastal Belt 0.07 Zone 3 Rest of the country starting 60 km from the western coastal Belt

22 References Seth Stein & Michel Wysession, An Introduction to Seismology, Earthquakes and Earth Structures Seth Stein, Approaches to continental Intraplate earthquake issues Kaye M. Shedlock, Intraplate eathquakes Steven L. Kramer, Geotechnical Earthquake Engineering

23 Acknowledgement Department of Civil Engineering and Department of Geology, University of Peradeniya Disaster Management Center, Sri Lanka Geological Surveying and Mines Bureau Faculty of Engineering, South Asian Institute of Technology and Medicine

24 Thank You!!!