In a simple word, amplification is the increase of amplitude due to surface soft soil.
Is it true that our assumption that the amplification happen only when we have contrast in geologic or geotechnical characteristics.
I think our assumption is true on the first 30 m.
The question now is, will this contrast "among layers" plays as seismic damper rather seismic amplification down inside the earth. For isolation purpose, we sometimes use soft material near the foundation base of our building to minimize the shear strength to reach our structure.
What is the effect of topography on seismic signal and amplification factor?
Dear Dr. Raed
amplification only happens when we have the shear and surface waves passing through a water saturated sandy soil. For a solid bedrock, amplification is not expected to occur, and deep down the earth it is more likely to find a bedrock or highly consolidated soils, thus damping is not expected at that level
Please see the attached animation for more information
https://www.youtube.com/watch?v=536xSZ_XkSs
Dear Ahmad,
The amplification happen because of: surface effect, focusing effect, Rocking effect, Scattering & passing effect.
I think these papers can help you:
- Topography Effects in the Athens 1999 Earthquake: The Case of Hotel Dekelia
- The influence of topography on the propagation and scattering of surface waves
- Scattering and focusing of SH waves by a convex circular-arc topography
https://inside.mines.edu/~rsnieder/Snieder86PEPI.pdf
https://academic.oup.com/gji/article/177/1/222/728901
http://scholarsmine.mst.edu/icrageesd/04icrageesd/session10/20/
Based on the multiple reflection theory [1,2], the amplification factor is mostly controlled by S-wave velocity profile of soil (S-wave velocity and thickness). The S-wave velocity contrast (impedance ratio) between the top layer and engineering/seismic bedrock, the one that controls the peaks of the amplification factor, while the thickness of soil controls the attenuation of amplification factor (related to damping material).
[1] Kramer SL. Geotechnical earthquake engineering. Upper Saddle River, New Jersey: Prentice Hall; 1996.
[2] Schnabel PB, Lysmer J, Seed HB. SHAKE: a computer program for earthquake response analysis of horizontally layered sites. University of California at Barkeley: 1972. (Report No. EERC 72-12).
Dear all,
Thank you for your comments and reply. The main question is: when soft layer can play as magnifier of damper role?
Dear Ahmad,
Many studies show that the soft soil will behave nonlinearly during a large earthquake, PGA exceeding 100 gal [1,2]. Based on results of nonlinear soil amplification, the increasing damping reduced the peak of soil amplification, while the reducing rigidity shift fundamental frequency into lower value, moreover, significant decreases of the peak of soil amplification can be found in high frequency as compared to linear amplification because of increasing damping [1,2]. So, in my opinion, it is not possible that the damping can magnify the soil amplification.
[1] Wen KL, Beresnev IA, Yeh YT. Nonlinear soil amplification inferred from downhole strong seismic motion data. Geophys Res Lett 1994;21:2625–8. doi:10.1029/94GL02407.
[2] Beresnev IA, Wen KL. Nonlinear soil response a reality? Bull Seismol Soc Am 1996;86:1964–78.
Dear Saifuddin Saifuddin significant decreases in the peak of soil amplification can be found in high frequency or Low frequency? I am a bit confused, can you elaborate!
While using shear wave velocity, some factors has to take into account, for example impedense contrast has high impact on application. Moreover damping ratio and yeah hight of layer matters too.
More I don't know how to find the exact amplification of soil.
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