Ansel -2011 Van Earthquake (2)

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AN OVERVIEW OF 2011 SIKKIM EARTHQUAKE

Term Project Report CE: 643

Submi tted By

CHILKEPALLI ANKITH (10010416)

Department of Civil Engineering

INDIAN INSTITUTE OF TECHNOLOGY GUWAHATI

APRIL 2014


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OVERVIEW

The 2011 Sikkim earthquake, also known as the 2011 Himalayan earthquake, was

amagnitude 6.9 (Mw)earthquake centered within theKanchenjunga Conservation Area,near

the border of Nepal and the Indian state ofSikkim,at 18:10 IST (12:40UTC)on Sunday, 18September 2011.The earthquake was felt across northeastern India, Nepal, Bhutan,

Bangladesh and southernTibet.

At least 111 people were killed in the earthquake. Most of the deaths occurred in Sikkim,

with reports of fatalities in and nearSingtamin theEast Sikkimdistrict. Several buildings

collapsed in Gangtok. Eleven are reported dead in Nepal, including three killed when a wall

collapsed in the British Embassy inKathmandu. Elsewhere, structural damage occurred in

Bangladesh, Bhutan, and across Tibet; another seven fatalities were confirmed in the latter

region.

The quake came just a few days after an earthquake of 4.2 magnitude hit Haryana'sSonipat

district,sending tremors inNew Delhi.The earthquake was the fourth significant earthquake

in India of September 2011. It is interesting to note that exactly a year after the original

earthquake at 5:55 pm on 18 September 2012, another earthquake of magnitude 4.1 struck

Sikkim, sparking panic among the people observing the anniversary of the original quake.
http://en.wikipedia.org/wiki/Moment_magnitude_scalehttp://en.wikipedia.org/wiki/Moment_magnitude_scalehttp://en.wikipedia.org/wiki/Moment_magnitude_scalehttp://en.wikipedia.org/wiki/Kanchenjunga_Conservation_Areahttp://en.wikipedia.org/wiki/Kanchenjunga_Conservation_Areahttp://en.wikipedia.org/wiki/Kanchenjunga_Conservation_Areahttp://en.wikipedia.org/wiki/Sikkimhttp://en.wikipedia.org/wiki/Sikkimhttp://en.wikipedia.org/wiki/UTChttp://en.wikipedia.org/wiki/UTChttp://en.wikipedia.org/wiki/UTChttp://en.wikipedia.org/wiki/Tibethttp://en.wikipedia.org/wiki/Tibethttp://en.wikipedia.org/wiki/Tibethttp://en.wikipedia.org/wiki/Singtamhttp://en.wikipedia.org/wiki/Singtamhttp://en.wikipedia.org/wiki/Singtamhttp://en.wikipedia.org/wiki/East_Sikkimhttp://en.wikipedia.org/wiki/East_Sikkimhttp://en.wikipedia.org/wiki/East_Sikkimhttp://en.wikipedia.org/wiki/Kathmanduhttp://en.wikipedia.org/wiki/Kathmanduhttp://en.wikipedia.org/wiki/Kathmanduhttp://en.wikipedia.org/wiki/Haryanahttp://en.wikipedia.org/wiki/Haryanahttp://en.wikipedia.org/wiki/Sonipat_districthttp://en.wikipedia.org/wiki/Sonipat_districthttp://en.wikipedia.org/wiki/Sonipat_districthttp://en.wikipedia.org/wiki/Sonipat_districthttp://en.wikipedia.org/wiki/New_Delhihttp://en.wikipedia.org/wiki/New_Delhihttp://en.wikipedia.org/wiki/New_Delhihttp://en.wikipedia.org/wiki/Sonipat_districthttp://en.wikipedia.org/wiki/Sonipat_districthttp://en.wikipedia.org/wiki/Haryanahttp://en.wikipedia.org/wiki/Kathmanduhttp://en.wikipedia.org/wiki/East_Sikkimhttp://en.wikipedia.org/wiki/Singtamhttp://en.wikipedia.org/wiki/Tibethttp://en.wikipedia.org/wiki/UTChttp://en.wikipedia.org/wiki/Sikkimhttp://en.wikipedia.org/wiki/Kanchenjunga_Conservation_Areahttp://en.wikipedia.org/wiki/Moment_magnitude_scale


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PLATE TECTONICS

The focal region and much of outermost Turkey lie towards the southern boundary of

the complex zone of continental collision between the Arabian plate and the Eurasian plate

beyond the eastern extent of the American and Asia minor fault zones. Parts of the

convergence between these two plates take place along the Biltis-Zagros fold and trust belt

(Wikipedia).

www.bellenews.com

FAULT CHARACTERISTICS

Reverse slip was found to occur in the fault zone. Earthquakes focal mechanism

indicates oblique thrust faulting, consistent with the expected tectonics in the region of the

Biltis-Zergrose fault zone, where thrust mechanism dominate. Upto 9m of reverse and

oblique slip on a pair of en echelon NW 40-54 dipping fault planes which have surface

extensions projecting to just 10 km north of the city of Van. The slip remained buried and is

relatively deep with a central depth of 14 km and the rupture reaching only within 8-9 km of

the surface consistent with the lack of significant ground rupture. No significant co-seismic

slip is found in the upper 8 km of the crust above the main slip patches, except for a small


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region on the eastern segment potentially resulting from the Mw5.9 aftershock on the same

day. The seismic moment of the area is calculated as Mo=3.55x1026

dyne-cm.

FORESHOCKS AND AFTERSHOCKS

No major foreshocks were observed in the area. There have been 1561 aftershocks

above magnitude Mw2 within one week. The highest magnitude aftershock came at 11.45 pm

on 23 October, with MI 5.7 and Mw6. The number of aftershocks reported in the ranges as

follows: 556 ranging from magnitude 2 to 3, 8332 ranging from magnitude 3 to 4, 108

ranging from magnitude 4 to 5, and 7 ranging from magnitude 5 to 6. In first five months

there were 9369 aftershocks with magnitude in range 1.5 to 5.8.

ISOSEISMAL MAP

National Geophysical Data Center


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EARTHQUAKE MAGNITUDE SCALES

From peak trace amplitude of 15cm, Ritcher local magnitude is obtained as,

ML= 5.17

From the seismic moment obtained, moment magnitude is calculated as,

Mw= 7.0

MS cant be found as the epicentral distance is less than 100 kms. Mb is not calculated as it is

suitable for deep focus earthquakes only. Mw magnitude scale is priory known as 7.2. Hence

the value of seismic moment used for the calculation will be 7.07x1026dyne-cm.

MATLAB PROGRAM

clc

clear all

close all%program_computer assignment (CE 643)

%importing strong motion details from excel

t=xlsread('(Ansel Jose) 2011 Van Earthquake, Turkey.xlsx','Sheet1','A3:A30002');a=xlsread('(Ansel Jose) 2011 Van Earthquake, Turkey.xlsx','sheet1','B3:B30002');

%plotting acceleration time-history

figure(1)

plot(t,a)

title('{\bf Accleration Time history }')

xlabel('Time (s)');

ylabel('Acceleration (cm/s2)');

grid on

disp('The acceleration-time history belongs to a single-cycle peak amplitude')

%finding the velocity response using cumulative trapezoidal numerical integration

v = cumtrapz(t,a);

%ploting velocity-time history

figure(2)

plot(t,v)

title('{\bf Velocity Time history }')

xlabel('Time (s)');

ylabel('Velocity (cm/s)');

grid on

%finding the displacement response using cumulative trapezoidal numerical integration


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d = cumtrapz(t,v);

%ploting displacement-time history

figure(3)

plot(t,d)

title('{\bf Displacement Time history }')

xlabel('Time (s)');ylabel('Displacement (cm)');

grid on

% finding absolute values

Abs_a = abs(a);

Abs_v = abs(v);

Abs_d = abs(d);

% finding peak horizontal accleration from absolute values

P_a = max(Abs_a);

x=sprintf('\nPeak Horizontal Acceleration = %f cm/s2',P_a);disp(x)

% finding peak horizontal velocity from absolute values

P_v = max(Abs_v);

x=sprintf('\nPeak Horizontal Velocity = %f cm/s',P_v);

disp(x)

% finding peak horizontal displacement from absolute values

P_d = max(Abs_d);

x=sprintf('\nPeak Horizontal Displacement = %f cm',P_d);

disp(x)

% finding effective accleration cosidering 0.67 times PHA

E_a = 0.67*P_a;

x=sprintf('\nEffective Acceleration = %f cm/s2',E_a);

disp(x)

% plotting accleration-time history in terms of absolute values

figure(4)

plot(t,Abs_a)

title('{\bf Accleration(Absolute) - Time history }')xlabel('Time (s)');

ylabel('Acceleration (cm/s2)');

grid on

% plotting velocity-time history in terms of absolute values

figure(5)

plot(t,Abs_v)

title('{\bf Velocity(Absolute) - Time history}')

xlabel('Time (s)');

ylabel('Velocity (cm/s)');

grid on


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% finding sustained maximum acceleration

% (from 'signal processing and analysis tool for civil engineers',SMA is the fifth highest

acceleration measured)

dc='descend';

a_peak = findpeaks(Abs_a,'sortstr',dc);

sa_max = a_peak(5,1);x=sprintf('\nSustained Maximum Acceleration = %f cm/s2',sa_max);

disp(x)

% finding sustained maximum velocity

% (from 'signal processing and analysis tool for civil engineers',SMA is the fifth highest

velocity measured)

v_peak = findpeaks(Abs_v,'sortstr',dc);

sv_max = v_peak(5,1);

x=sprintf('\nSustained Maximum Velocity = %f cm/s',sv_max);

disp(x)

%Finding the Effective Design Acceleration (EDA) as per Kennedys proposition

% (EDA is 25% greater than the third highest peak absolute acceleration)

EDA = 1.25*a_peak(3,1);

x=sprintf('\nEffective Design Acceleration (Kennedy) = %f cm/s2\n',EDA);

disp(x)

% Fourier transform

n=30000;

F_a=fft(a);

F_a1 = F_a(1:n/2);

Abs_F_a = abs(F_a1);

f = (0:(n/2)-1)*(1/(n*0.01));

%ploting fourier amplitude spectrum

figure(6)

stem(f,Abs_F_a)

xlabel('Frequency (Hz)')

ylabel('Fourier Amplitude')

title('{\bf Fourier Amplitude spectrum }')

grid on

disp 'Fourier amplitude spectrum belongs to a broad band spectrum'

%plotting fourier phase spectrum

phase = unwrap(angle(F_a1));

figure(7)

plot(f,(phase*180/pi))


ylabel('Phase angle (degree)')

title('{\bf Fourier Phase spectrum }')

grid on

%filtering out frequencies above 8Hz

N=8*n*0.01;Abs_F_a1 = Abs_F_a(1:N);


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% finding inverse fast fourier transform

iF_a=ifft(Abs_F_a1);

Abs_iF_a=abs(iF_a(1:N/2));

t1=t(1:N/2);

%plotting modified acceleration - time history

figure(8)

plot(t1,Abs_iF_a)

xlabel('Time (s)')

ylabel('Accleration (cm/s2)')

title('{\bf modified acceleration-time history }')

grid on

%as per Benjamin and assosiates, finding effective design acceleration

peak = findpeaks(Abs_iF_a,'sortstr',dc);

EDA_Benj = peak(1,1);x=sprintf('\nEffective Design Acceleration (Benjamin) = %f cm/s2',EDA_Benj);

disp(x)

%smoothened fourier amplitude spectrum

figure(9)

f1=((0:n-1)*(1/(n*0.01)));

loglog(f1,abs(F_a))

xlabel('Frequency (Hz) log scale')

ylabel('Fourier Amplitude Log scale')

title('{\bf Smoothened Fourier Amplitude spectrum }')

grid on

% corner and cut off frequencies shall be found by physical observation

%Power Spectral Density function evaluation

% total intensity of ground motion of duration Td

% area under the time history of squared acceleration(time domain)

AA = a.*a;

I_t = cumtrapz(t,AA);

I1 = I_t(n,1);

x=sprintf('\nTotal intensity of ground motion in time domain = %f',I1);

disp(x)

%total intensity of ground motion(frequency domain)

% considering real + complex part

% considering nyquist frequency of 100 Hz

x=sprintf('\nConsidering nyquist frequency of 100 Hz,');

disp(x)

N1=100*n*0.01;

FA2 = F_a(1:N1);

FFA2 = FA2.*FA2;

I_f = cumtrapz(f1(1:N1),FFA2/pi);

I2=abs(I_f(N1,1));x=sprintf('\nTotal intensity of ground motion in frequency domain = %f',I2);


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disp(x)

%average intensity

%based on time domain

AI1 = I1/t(n,1);

x=sprintf('\nAverage intensity of ground motion based on time domain = %f',AI1);disp(x)

%based on frequency domain

AI2 = I2/t(n,1);

x=sprintf('\nAverage intensity of ground motion based on frequency domain = %f',AI2);

disp(x)

%power spectral density function

psd = FFA2/(pi*t(n,1));

figure(10)plot(f1,real(psd))


ylabel('Power Spectra')

title('{\bf Power spectral density }')

grid on

%normalized power spectral density function

npsd = psd/(AI2);

figure(11)

plot(f1,real(npsd))


ylabel('Power Spectra')

title('{\bf Normalized power spectral density }')

grid on

% predominant period

%taken only up to 25hz

N2=25*n*0.01;

% smoothening Fourier Amplitude spectrum

s1 = smooth(f(1:N2),Abs_F_a(1:N2),750);

[predo_a,loc_p]=max(s1);predo_f = (loc_p)/(n*0.01);

Tp=(1/predo_f);

x=sprintf('\nPredominant period = %f s',Tp);

disp(x)

% bandwidth

FA_limit = predo_a/sqrt(2);

j=0;

fori=1:N2

ifs1(i)>FA_limitj=j+1;


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s2(j)=f(i);

end

end

[p,q]=size(s2);

band_width=s2(q)-s2(1);x=sprintf('\nBandwidth = %f Hz',band_width);

disp(x)

x=sprintf('\nBandwidth ranges from %f Hz to %f Hz',s2(1,1),s2(1,q));

disp(x)

%central frequency

f2 = f1.*f1;

psd1 = psd.*f2.';

I_s = cumtrapz(f1,psd1);

I3=I_s(N1,1);

cf = sqrt(I3/AI2);abs_cf=abs(cf);

x=sprintf('\nCentral frequency = %f Hz',abs_cf);

disp(x)

%Theoretical median peak acceleration

%considering absolute values only

theo_med_a_max = sqrt(2*abs(AI2)*log(2.8*abs(cf)*t(n,1)/(2*pi)));

x=sprintf('\nTheoretical median peak acceleration = %f cm/s2',theo_med_a_max);

disp(x)

%Shape factor

psd2 = psd.*f1.';

I_s1 = cumtrapz(f1,psd2);

I4 = I_s1(N1,1);

sf = sqrt(1-(I4*I4/(AI2*I3)));

x=sprintf('\nShape factor = %f',sf);

disp(x)

%vmax/amax

r = P_v/P_a;x=sprintf('\nv-max/a-max = %f s',r);

disp(x)

%Period of vibration of equivalent harmonic wave

T_eq = 2*pi*r;

x=sprintf('\nPeriod of vibration of equivalent harmonic wave = %f s',T_eq);

disp(x)

%Kanai Tajimi Parameters

%assuming alluvim site, from the table of Kanai-Tajimi parametersGo = .102;


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wg = 18.4;

% given that damping is 2%

X = .02;

%Kanai-Tajimi PSD function

w = f1(1:n)*(2*pi);

w_1 = 1+(2*X*(w/wg)).^2;w_2 = (1-(w/wg).^2).^2;

w_3 = (2*X*(w/wg)).^2;

w_4 = w_2+w_3;

G_w = Go*gdivide(w_1,w_4);

figure(12)

plot(w(1:1500),G_w(1:1500))

xlabel('Angular Frequency (w)')

ylabel('G(w)')

title('{\bf Kanai-Tajimi PSD function }')

grid on

% Evaluation of duration of parameters

% bracketed duration (As per Bolt, 1969)

a_threshold=0.05*9.81;

j=0;

fori=1:n

ifAbs_a(i)>a_threshold

j=j+1;

t1(j) = t(i);

end

end

[x,y]=size(t1);

First_exceedence = t1(1);

Last_exceedence = t1(x);

Bracketed_duration = t1(x)-t1(1);

x=sprintf('\nBracketed duration = %f s',Bracketed_duration);

disp(x)

% central 90% energy content

I1_5 = 0.05*I1;I1_95 = .95*I1;

central_90_energy = I1_95-I1_5;

x=sprintf('\nCentral 90 percentage energy content = %f',central_90_energy);

disp(x)

j=0;

n=30000;

fori= 1:n

ifI_t(i)>(I1_5)

j=j+1;

loc_t1(j) =i;end


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end

j=0;

n=30000;

fori=1:n

ifI_t(i)>(I1_95)

j=j+1;

loc_t2(j) =i;

end

end

time_first=loc_t1(1,1);

time_last=loc_t2(1,1);

%modified duration curve

figure(13)

plot(t(time_first:time_last),I_t(time_first:time_last))xlabel('Time (s)')

ylabel('Intensity')

title('{\bf Central 90% energy content }')

grid on

% RMS acceleration

a_rms = sqrt(AI1);

x=sprintf('\nRMS Acceleration = %f cm/s2',a_rms);

disp(x)

% Arias intensity

AInt = I1*(pi/(2*9.81));

x=sprintf('\nArias Intensity = %f',AInt);

disp(x)

% Characteristic intensity

CI = ((a_rms).^1.5)*t(n,1).^0.5;

x=sprintf('\nCharacteristic intensity = %f',CI);

disp(x)

% Cumulative absolute velocityCAV = cumtrapz(t,Abs_a);

CA_Velocity = CAV(n,1);

x=sprintf('\nCumulative absolute velocity = %f m/s',CA_Velocity);

disp(x)


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GRAPHICAL OUTPUTS


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RESULTS - STRONG MOTION PARAMETERS

The acceleration-time history belongs to a single-cycle peak amplitude

Peak Horizontal Acceleration = 9.737000 cm/s2

Peak Horizontal Velocity = 2.972910 cm/s

Peak Horizontal Displacement = 14.549999 cm

Effective Acceleration = 6.523790 cm/s2

Sustained Maximum Acceleration = 4.540500 cm/s2

Sustained Maximum Velocity = 2.026245 cm/s

Effective Design Acceleration (Kennedy) = 5.890000 cm/s2

Fourier amplitude spectrum belongs to a broad band spectrum

Effective Design Acceleration (Benjamin) = 18.280017 cm/s2

Total intensity of ground motion in time domain = 237.968465

Considering nyquist frequency of 100 Hz,

Total intensity of ground motion in frequency domain = 39140.250328

Average intensity of ground motion based on time domain = 0.793255

Average intensity of ground motion based on frequency domain = 130.471850

Predominant period = 2.678571 s

Bandwidth = 0.693333 Hz

Bandwidth ranges from 0.156667 Hz to 0.850000 Hz

Central frequency = 75.760954 Hz

Theoretical median peak acceleration = 49.058161 cm/s2

Shape factor = 1.232209


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v-max/a-max = 0.305321 s

Period of vibration of equivalent harmonic wave = 1.918388 s

Bracketed duration = 204.680000 s

Central 90 percentage energy content = 214.171619

RMS Acceleration = 0.890648 cm/s2

Arias Intensity = 38.103975

Characteristic intensity = 14.558374

Cumulative absolute velocity = 137.489152 m/s

Ansel -2011 Van Earthquake (2)

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