Seismic Monitoring

7/24/2019 Seismic Monitoring

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ABSTRACT

The object of this project is to be enabled with a detailed training in the field of data

elaboration and handling of ground motion to come up with realistic and site specific

design spectra. The target area of study for this project is Orissa, but due unavailability

of ground motion data, I chose Chamoli Region in Uttarakhand state, India with the data

collected the same station, which is one among the chain of stations maintained by IIT,

Roorkee. The data from this station was processed with Matlab for obtaining time history

and design spectral accelerations. This project involves with the comparison of spectral

acceleration values not only between Indian Standard code and Euro code, and also with

the spectral accelerations obtained from GMPE models, to determine the efficiency of

GMPE models in the estimation of earthquake parameters.


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LIST OF CONTENTS

Contents1. Introduction: ...................................................................................................... 1

1.1 Seismic Networks in India: ............................................................................... 1

2. Identification of Input Parameters: .................................................................... 3

2.1 Region of Study & Earthquake: ........................................................................ 3

2.2 Seismic station information: ............................................................................ 3

2.3 Risk Analysis: .................................................................................................... 4

2.4Topography and Geology: ................................................................................. 4

3. Strong motion data interpretation: .................................................................... 7

3.1 Time histories: ................................................................................................. 7

3.2 Design Spectral Accelerations: ......................................................................... 9

4. Comparison between code spectra and Design spectra ................................... 11

4.1 Indian Standard Code Spectrum (IS 1893-2002) ............................................. 11

4.2 Euro code 8 (prEN 1998-1): ............................................................................ 13

4.3 Comparison of Horizontal Design Spectral acceleration with IS and Euro codes

(5% Damping) ...................................................................................................... 16

5. Ground Motion Prediction Equations ............................................................... 18

5.1 GMPE-Schwarz et al Model ............................................................................ 18

5.2 GMPE-Sharma et al Model ............................................................................. 19

6. Conclusions: ..................................................................................................... 21

7. References ....................................................................................................... 22


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LIST OF FIGURES

S.No Figures Page

No

1. Seismic Zones of India 2

2. Earthquake location & Station Map 4

3. Topography Of Uttarakhand 5

4. Geology Of Uttarakhand 6

5. Time history Of Longitudinal Component 7

6. Time history Of Transverse Component 7

7. Time history Of Vertical Component 8

8. Time history Of All 3 Components 8

9. Design Spectral Acceleration of All 3 Components 9

10. Design Horizontal (Longitudinal) Spectral Acceleration with different

% of Damping

9

11. Design Horizontal (Transverse) Spectral Acceleration with different

% of Damping

10


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12. Design Vertical Spectral Acceleration with different % of Damping 10

13. Design Horizontal Elastic SpectrumIS Code (1893-2002) 12

14. Design Vertical Elastic SpectrumIS Code (1893-2002) 12

15. Design Horizontal Elastic SpectrumEuro Code 8 (prEN 1998-

1:2003)

14

16. Design Vertical Elastic SpectrumEuro Code 8 (prEN 1998-1:2003) 15

17. Horizontal (Longitudinal) component ComparisonIS Code Vs Euro

Code

16

18. Horizontal (Transverse) component ComparisonIS Code Vs Euro

Code

16

19. Vertical Component ComparisonIS Code Vs Euro Code 17

20. Schwarz GMPE models Spectrum Comparison with SGM Spectrum 19

21. Sharma GMPE models Spectrum Comparison with SGM Spectrum 20


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1. Introduction:Seismic hazard analysis involves with the estimation of ground shaking hazards at a

particular site without consideration of the consequences. Seismic hazards may be

analyzed deterministically, as when a particular earthquake scenario is assumed, or

probabilistically, in which uncertainties in earthquake size, location and time of occurrence

are explicitly considered. Probabilistic seismic hazard analysis is the key method for the

establishment of zoning maps over the large regions, which helps with the seismic risk

studies for the sites that deserve special attention.

1.1 Seismic Networks in India:According to geographical statistics of India shows that almost 54% of the land is

vulnerable earthquakes due to seismic gaps along the Himalayan belt and the collision of

Indian plate with the Asian plate. Since more than half of the area of India is susceptible

to strong ground motions; therefore there is a need to know about the probable

characteristics of future earthquakes in this region. Bureau of Indian standards grouped

the country into 4 seismic zones II, III, IV and V, zone V (Intensity IX and above) being

the most seismically prone region, while zone II (Intensity VI or less) is the least according

to Modified Mercalli scale.

IIT Roorkee with the cooperation of Indian Meteorological department is operating a

network of 300 strong motion accelerographs throughout the India.


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Fig.1 Map showing Seismic Zones of India


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2. Identification of Input Parameters:

2.1 Region of Study & Earthquake:The target region of study for this project is Orissa, but due unavailability of ground motion

data, I chose Chamoli in the state of Uttarakhand and the ground motion data related to

the earthquake on 14thDec 2005 from Chamoli (CHM) station. The epicenter is 54.3Km

away from the station.

The other details of earthquake 14thDec, 2005 are listed in the following table.

Place of Earthquake Chamoli-Uttarakhand

Latitude 30.9 N

Longitude 79.3 E

Depth (Km) 25.7

Magnitude (Mw ) 5.2

Region Chamoli

Type Of Earthquake II (Mw< 5.5)

Origin Time 14/12/2005 07:09:48

Source Pesmos, IIT Roorkee

2.2 Seismic station information:Station Chamoli, Uttarakhand

Station Code CHM

Latitude 30.412 N

Longitude 79.320 E

Height 1578 m

Epicentral Distance 54.3 Km

Site Class AVs 30 between 700m/s to 1400m/s.Record Time 14/12/2005 07:09:26

Sampling Rate 200 Hz

Record Duration 44.610 Sec


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Fig.2 Map showing the location of earthquake and station

2.3 Risk Analysis:

Due to moderate magnitude it caused very minor damage to the life and structures insome parts of Uttarakhand. Considering the damage to the life, one person died and 3

other are injured. One building collapsed and some developed cracks in various parts of

Uttarakhand.

2.4Topography and Geology:According to geographical survey of India, 86% of Uttarakhand geographical area is

covered by greater Himalayan ranges and 65% is covered by forest. Uttarakhand lies on

the south slope of the Himalayan range and the highest elevations are covered ice and

bare rock. Mount Nanda Devi is the highest peak of Uttarakhand with the altitude of

7816m above the sea level.

Uttarakhand faced many earthquakes of Mw = 5.5 or more since 1900. The state have

many active faults formed in the highly folded strata of Himalayan mountain range. Of


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these, main boundary thrust (MBT) and main frontal thrust (MFT) are primarily the active

ones in the state. This region of Himalayan range believed to have high potential danger

is known as central seismic gap, and lies between Uttarakhand and western Nepal. It has

some active small faults like Yamuna fault near Haridwar and Alaknanda fault near

Rudraprayag.

Most of the Uttarakhand state is covered by Pre-Cambrian rocks and cretaceous

sedimentary rocks. The rocks of pre-Cambrian age consists of highly folded mica-schists,

slates, phyllites etc. whereas sedimentary rocks consists of blackish phyllitic slates and

white sericite quartzite. These types are highly susceptible to landslides with the

combination of heavy rainfalls and extensive soil erosion.

Fig.3 Topography Map - Uttarakhand


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Fig.4 Geology Map - Uttarakhand


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3. Strong motion data interpretation:

3.1 Time histories:

Fig.5 Time history Of Longitudinal Component

Fig.6 Time history Of Transverse Component


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Fig.7 Time history Of Vertical Component

Fig.8 Time history Of All 3 Components


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Time history graphs shows the variation of spectral acceleration with respect to the time

and these are plotted using Matlab program with the strong ground motion data obtained

from Chamoli station. The peak ground acceleration in longitudinal direction is -

63.48cm/s2where as it is -53.08 cm/s2in transverse direction and -41.13 cm/s2in vertical

direction.

3.2 Design Spectral Accelerations:

Fig.9 Design Spectral Acceleration of All 3 Components

Fig.10 Design Horizontal (Longitudinal) Spectral Acceleration with different % of Damping


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Fig.11 Design Horizontal (Transverse) Spectral Acceleration with different % of Damping

Fig.12 Design Vertical Spectral Acceleration with different % of Damping


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4. Comparison between code spectra and Design spectra

4.1 Indian Standard Code Spectrum (IS 1893-2002)According to Indian Standard Code (IS 1893-2002), the design spectral acceleration for

horizontal motion will be determined by the Natural time period, soil conditions in the site

and peak ground accelerations(say 5% damping) where as for the vertical motion the

design spectral acceleration is taken as two-thirds of the horizontal design spectral

acceleration.

Empirical relation to plot design spectra:

For rock or hard soil sites:

Sa/g = 1+15T 0.0 < T < 0.10

Sa/g = 2.5 0.10 < T < 0.40

Sa/g = 1.00/T 0.40 < T < 4.00

For Medium soil

Sa/g = 1+15T 0.0 < T < 0.10

Sa/g = 2.5 0.10 < T < 0.55

Sa/g = 1.36/T 0.55 < T < 4.00

For Soft Soil

Sa/g = 1+15T 0.0 < T < 0.10

Sa/g = 2.5 0.10 < T < 0.67

Sa/g = 1.67/T 0.67 < T < 4.00


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Fig.13 Design Horizontal Elastic SpectrumIS Code (1893-2002)

Fig.14 Design Vertical Elastic SpectrumIS Code (1893-2002)


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4.2 Euro code 8 (prEN 1998-1):Empirical relation to plot design spectra:

0 T TB:Se(T) = ag.S.[1+ (T/TB)(.2.5-1)]

TB T TC:Se(T) = ag.S..2.5

TC T TD:Se(T) = ag.S..2.5 (TC/T)

TD T 4s :Se(T) = ag.S..2.5 (TCTD/T2)

Where

Se(T) = Elastic response spectrum

T = Vibration period of a linear single-degree-of-freedom system

ag= Design ground acceleration on type A ground

TB = the lower limit of the constant spectral acceleration

TC = the Upper limit of the constant spectral acceleration

TD = the value defining the beginning of the constant displacement response range

spectrum.

S = Soil Factor

= Damping Correction Factor with a reference value of =1 for 5% viscous damping.

Ground Type S TB(s) TC(s) TD(s)

A 1.0 0.05 0.25 1.2

B 1.35 0.05 0.25 1.2

C 1.5 0.10 0.25 1.2

D 1.8 0.10 0.30 1.2

E 1.6 0.05 0.25 1.2


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Vertical elastic response spectrum

0 T TB:Sve(T) = avg.S.[1+ (T/TB)(.3.0-1)]

TB T TC:Sve(T) = avg.S..3.0

TC T TD:Sve(T) = avg.S..3.0 (TC/T)

TD T 4s :Sve(T) = avg.S..3.0 (TCTD/T2)

Spectrum avg/ ag TB(s) TC(s) TD(s)

Type 1 0.90 0.05 0.15 0.10

Type 2 0.45 0.05 0.15 0.10

Fig.15 Design Horizontal Elastic SpectrumEuro Code 8 (prEN 1998-1:2003)


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Fig.16 Design Vertical Elastic SpectrumEuro Code 8 (prEN 1998-1:2003)


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4.3 Comparison of Horizontal Design Spectral acceleration with IS and

Euro codes (5% Damping)

Fig.17 Horizontal (Longitudinal) component ComparisonIS Code Vs Euro Code

Fig.18 Horizontal (Transverse) component ComparisonIS Code Vs Euro Code


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Fig.19 Vertical component ComparisonIS Code Vs Euro Code

As discussed above the design elastic spectrums are plotted based on the soil condition

of the site and natural time periods according to both Indian Standard Code and Euro

Code for 5% damping consideration. From the above plots it is evident that for both IS

code and Euro code the elastic spectrum is same in longitudinal and transverse directions

with a maximum value of 2.5g.

In case of vertical spectrum, the parameters considered for the elastic design spectrum

are different, so both the codes differs vastly from the other. The Eurocode design

spectrum for vertical component is designed mainly based on the earthquake magnitude

(Type I or II) and on the natural time periods, whereas in case of IS code it is taken as

two-thirds of horizontal spectrum (maximum of longitudinal or transverse component).

The maximum value of vertical component for Euro code is 1.35g and 1.668g for IS Code.


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5. Ground Motion Prediction EquationsAttenuation relationship referred as ground motion prediction equations. Ground motion

prediction equation transforms the earthquake parameters like location and magnitude to

site parameters like PGA and spectral acceleration characterizing the seismic hazard.

There are several equations available for the prediction of earthquake design parameters

like spectral acceleration, but for an effective seismic hazard analysis it is recommended

to use a set of prediction equations that are appropriate for the target area to check the

variability. Schwarz et aland sharma et alequations are used for the analysis of this

project.

5.1 GMPE-Schwarz et al ModelTo predict the ground motion parameters for our site class A the following prediction

equation is used which is provided by Ambraseys for type II & Soil class A.

Log (y) = C1+ C2*M + C3*log(r) +P

Where

y = Ground motion parameter in g (PGA or Sa)

M = Earthquake magnitude (Mw)

r = Function of the distance (r = (d2+h02))

d = Epicentral Distance

h0= A coefficient to be determined by iteration

P = Uncertainty in the prediction

= Standard Deviation


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Fig.20 Schwarz GMPE models Spectrum Comparison with SGM Spectrum

From the above graph we can understand that the GMPE model is not effective because

the spectral acceleration obtained from the ground motion data are vastly differs from the

obtained spectral acceleration using GMPE model for various time periods.

5.2 GMPE-Sharma et al ModelSharma provided a ground motion prediction equation for the horizontal response spectral

accelerations (5% damping) for the northern part of India. This equation takes into

consideration of soil category and faulting type (strike slip or reverse).

Log A = b1+ b2*Mw-b3*log (Rjb2+b42) +b5*S+b6*H

Where

b1, b2, b3, b4, b5 and b6 are the regression coefficients.

A is the spectral acceleration in terms of m/s2

S = 1 for a rock site and 0 otherwise

H = 1 for strike-slip fault and 0 for reverse fault.


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Fig.21 Sharma GMPE models Spectrum Comparison with SGM Spectrum

From the above graph we can understand that this GMPE model also is not effective

because the spectral acceleration obtained from the ground motion data are vastly differs

from the obtained for various time periods. But sharma et al equation was formulated from

the data obtained from the events of Himalayan range (Northern India), so it is preferable

to use for the prediction of ground motion parameters.


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6. Conclusions:1. From the code comparison we can conclude that the spectral accelerations

obtained from the ground motion data are almost less than that are obtained from

both IS code and Euro code for longitudinal and horizontal direction.

2. In case of vertical component the spectral accelerations from the ground motion

data are more than that are obtained from IS and Euro code.

3. The spectral accelerations from the Schwarz et al & Sharma et al are differs vastly

from the spectral accelerations that are obtained from the ground motion data for

various time periods.

4. Sharma et al equation is preferable to use for the prediction of ground motion

parameters because it was formulated from the data obtained from the events of

Himalayan range (Northern India).


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7. References www.pesoms.com

IS 1893 (Part 1-General Provisions and buildings):2002 Criteria for earthquake

resistant design of structures (fifth revision).

prEN 1998-1:2003 (E) Euro code 8: Design of Earthquake resistance structures

Part 1: General rules, Seismic actions rules for buildings.

Uttarakhand: land and people by Sharad Singh Negi.

www.asc-india.org www.earthquake.usgs.gov

www.gadm.org

www.lta.cr.usgs.gov/GTOPO30

Geotechnical Earthquake Engineering by Steven L Kramer

www.nptel.ac.in

www.wikipedia.org

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