PEAK HORIZONTAL ACCELERATION (PHA) AT KATHMANDU DURING 2011SEPTEMBER EARTHQUAKE USING ATTENUATION RELATIONS

CALCULATION OF PHA USING FEW ATTENUATION RELATIONSHIPDipendra GautamBE (CIVIL), Khwopa Engineering College, Purbanchal University

EARTHQUAKE

Ground shaking caused by the sudden release of energy in the earth’s crust.

Energy sources: Dislocation of the crust Volcanic eruption Collapse of underground cavities e.g. mines Occurrence is explained by ‘Plate tectonics’

SIKKIM-NEPAL BORDER EARTHQUAKE AT A GLANCE Magnitude: 6.9 Depth: 19.7 Km 272 Km East of Kathmandu Local uncertainty: ± 13.5 Km, Depth: ± 3.5 Km Near the boundary between Indian and Eurasian

plate. Strike slip fault Intra-plate source within the upper Eurasian plate or

underlying Indian plate.

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Indian plate converges with Eurasian plate at a rate of approx 46 mm/yr towards N-NE.

STRONG GROUND MOTION

Strong earthquake shaking that occurs close to (Less than about 50 Km) from the causative fault.

Strong ground motion accelerometers are used instead of seismometers.

ATTENUATION

The rate of decay of shaking with the distance from the epicenter

Accounts energy loss of seismic waves during their travel through a path

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FACTORS INFLUENCING ATTENUATION

Magnitude The focal depth Distance Source conditions Site geology Instrument housing and installation details General surrounding terrain

PEAK GROUND ACCELERATION

Measure of earthquake acceleration on the ground. How hard the earth shakes in a given geographic

area (the intensity). Measured by accelerographs. The higher the PGA, the higher shaking the structure

undergoes

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Accelerograph

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Peak horizontal acceleration (PHA): most commonly used for measuring Strong ground acceleration in engineering.

Best determinate of moderate earthquakes. Damage of buildings and infrastructures is related

more closely to ground motion rather than the magnitude.

PEAK HORIZONTAL ACCELERATION (PHA) FROM FEW ATTENUATION RELATIONSHIP CAMPBELL (1981)

ln PHA (g)= -4.141+0.868M-1.09 ln [R+0.0606 exp (0.7M)]

Where M=moment magnitude R=horizontal distance between the source

and sight Here, M= 6.9

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R= 272 KM So, ln PHA (g)= -4.141+0.868*6.9-1.09 ln

[272+0.0606 exp (0.7*6.9)] ln PHA (g)= -4.292114788 PHA (g)= 0.01367597 i.e. PHA= 13.516 gals (cm/s²)

BOORE ET AL.

Log PHA (g)=b1+b2(Mw-6)+b3(Mw-6)²+b4*R+b5 log R+b6 Gb+b7Gc

Being Kathmandu as class C for velocity 180-360 m/s

For site class C Gb=0; Gc=1; Selecting the components for “larger”. R=√(d²+h²) Where, d is the closest distance to surface

projection of the fault in kilometers

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R= √(d²+h²); h= 5.48; R= 272Km R=272.057 Km Log PHA (g)= b1+b2(Mw-6)+b3(Mw-

6)²+b4R+b5logR+b6Gb+b7Gc Log PHA(g)=-0.105+0.229(6.9-6)+0*(6.9-

6)²+0*R-0.778Log(272.057)+0.162*0+0.251*1 Log PHA(g)=-1.542065

Contd……

PHA(g)=0.0287 i.e. PHA=28.70 gals

YOUNG’S

Ln PHA(g)=-0.6687+1.438M+C1+C2(10-M)³+C3ln(Rup+1.097exp(0.167M))+0.00648H+0.364Zt

Since it is a rock site; Rup=source to sight distance in Km H=depth in Km Zt=1 So;

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Here; M=6.9, H=272Km, C1=C2=0; C3=-2.329, Zt=1

ln PHA(g)= -0.6687+1.438*6.9+0+0*(10-6.9)³-2.329*ln(272+1.097exp(0.167*6.9))+0.00648*19.7+0.364*1

ln PHA(g)=-3.34030 PHA(g)= 0.035426 PHA= 34.7532 gals

KÖVLISGETHY

log PHA (g) = 0.35 Mw – 0.54 log (R/h) – 0.0036 (R – h), h < 70 km

Here, Mw=moment magnitude= 6.9 R=Hypocentral distance= 272km Depth=19.7 km Log PHA (g)= 0.35*6.9-0.54 log (272/19.7)-

0.0036 (272-19.7) Log PHA (g)= 0.8910645539 PHA= 49.139 gals

SUMMARY

ATTENAUTION APPROACH PHA (gals)

CAMPBELL 13.516

BOORE ET AL. 28.700

YOUNG’S 34.753

KÖVLISGETHY 49.139

SIGNIFICANCE OF PGA

Building code formulation. Design hazard risk. Dynamic analysis of earthquake loading. The horizontal PGA at the site is to be extrapolated

from available data.

ACKNOWLEDGEMENT

Er. Ganesh Kumar Bhattarai, Coordinator, Post Graduate Department of Earthquake Engineering, Khwopa Engineering College, Purbanchal University.

REFERENCES

The US Geological Survey (USGS) Kramer SL, Geotechnical Earthquake Engineering,

PEARSON, 2011 TORO GR, MODIFICATION OF THE TORO ET AL.

(1997) ATTENAUTION EQUATIONS FOR LARGE MAGNITUDE AND SHORT DISTANCES, JUNE 12,2002, (Modified from Rev. 3 Paducah Report)

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Sharma ML & Agrawal PN; A COMPARITIVE STUDY OF FEW ATTENUATION RELATIONS, Proceeding of TENTH SYMPOSIUM ON EARTHQUAKE ENGINEERING, University of Roorkee, Vol. I (Nov 16-18, 1994)

Lee HKW, Kanamon H, etc. (editors); Handbook of EARTHQUAKE & ENGINEERING SEISMOLOGY, Academic Press.

Elnashai AS,Sarno LD; Fundamentals of EARTHQUAKE ENGINEERING, A John Wiley & Sons, Ltd, Publication.

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Thank you….