Ground Peak Acceleration (Agmax)

[pelelo]

Hello,

Can anyone tell me what would be the best approach to compute the ground peak acceleration (Agmax) for a potential liquefaction project I am working on.

The Way I compute Agmax is using Donovan´s Approach (1973) in which Agmax is function of EQ magnitude and epicenter. This is the only approach I know but I am not sure if this is the most widely accepted / used.

If anyone got any imput about this, please let me know.

Thanks in advance.

[hazus]

Dear Pelelo,
most method used to calculate PGA (peak ground acceleration) are probabilistic and determinisitic.
for the first one, A Cornell (1968) is the most known in which you may use seismic zones, attenutation law and B-values. for this task, softwares like crisis or seisrisk III can help assassing PGA for different return periof and probabilities of exceedance (in most case, 10 % of exceedance for 50 years but nowadays new american shakemaps are based on 2% of exceedance).
But the most accurate method is to modelise your soil and seismic wave propagation in order to calculate ground acceleration taking into account you soil behaviour wich can not be the same as those used for attenuation laws calibration. If you can't you can produce shakemaps by Wald model, you can transmit a scnario (fault, epicenter, magnitude) and they will provide a map for your region: they are all the time procuding such maps :

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Hope I was helpful

[pelelo]

hazus,

Thanks a lot. I really appreciate your reply.

Will I need to pay a fee in order to obtain the shakemap from USGS?

On the other hand I will try to play a little bit with crisis o seisrisk III if I get them.

Thanks again.

[hazus]

It's a pleasure to help,
The shakemaps are free, you don't need to pay it, just contact them and explain the scenario you need
for other soft, i Suggest crisis mich is more easy for use than seisriskIII (wich is not under download anymore in usgs site)
Any other question, don't hesistate

[onest30]

Hi,
I think you still can get seisrisk III at usgs
in the address below

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regards

[mig21]

hi

you structural or seismic code doesnt provide the PGA for the site ?

Regards

[chigozie]

If you know your location, you could get the PGA using your local code or other codes (such as UBC) that included the your area of interest .
Regards
Teddy

[jacs127]

Dear Friends,

good discussion is going on... i also want to add that EZ-FRISK is equally good to get deterministic and or probabilisitic shake maps and our frind benny has already shared location wise maps/details... one of our friend hazus has cited CRISIS which i agreed that easy to use.. well i can share it to this forum but i request to kindly obtain it from Prof. ORDAZ.. one can provide request mail to him and you will get the software... but my question to PELELO is why you need site specific ground motions.. if it of not much important i am not in favor to spend much time in obtaining it rather recommand to use codal values... PELELO you can use artificial ground motion model based on source, geometry and seismicity models also.. Prof. BOORE's ref will get you everything..

regards,

[pelelo]

Gentlemen

Thanks for your inputs, I really appreciate your help.

Hazus,
Do you know where can I get Crisis mich?, I got seisrisk III (Thanks to Onest30) from USGS web site. This one doesn´t seem to be user friendly - easy to operate.

mig21 and chigozie,

The project my firm is working on is located in the caribbean, for some reason that country doesn´t have a structural or seismic code.

I have been doing some research in obtaining PGA from SDS/2.5 (Is this the deterministic approach??). I Noticed SDS depends on Fa and Ss. I can obtain Ss from any of the 14 spectral maps provided by IBC. The problem is these maps are only for US territories, as
I told you before, the project I am working on is not.

Jacs127

thanks for your help. I will try to get EZ-FRISK. I consider the project I am working on very important as it is a resort and it is located about 15 miles from a fault zone area, therefore it is a big concern to me to obtain the adequate Agmax. As I told Hazus, I used Donovan´s approach (1973) which involves the EQ magnitude and the distance to the epicenter but I am not sure how well accepted or widely used it is as most of the people I have spoken with, don´t know Donovan´s approach.


Thanks again guys, no question the threat is turning very interesting.

[hazus]

sorry pelelo, I don't have the software, but jacs127 provided you (post #8) with the way to obtain it.

regards