Dear Srijit,

Which Seismic source zone is it ? Is it Koyna ?

After your response, I can give you better details however, I am surprised by your estimated numbers !

Hi Srijit

Part of the reason for such high values might be due to the GMPE you use, which correspond to low attenuation areas. I would suggest you to start trying to understand your results with two additional computations

- a desegregation analysis to look for the dominant earthquake scenarios (magnitude distance, and epsilon / number of standard deviations)

- using another GMPE corresponding to more active ares (NGAW2 or RESORCE)

Anticipated thanks for keeping us informed !

if you are looking at 10,000 years return period, the values that you get are => 0.5% of probability in 50 years to exceed 0.48-0.58 g, that for me, they seem absolutely reasonable. Very high PGA value but very very low probability to exceed in 50 years.

another software that you can use is openquake.

Bests,

Alessandro

Dear Dr. Valentini, Dr. Pierre Yves Bard, and Dr. S Gupta,

Thanks for your mail, and kind reply. I am still working on it as per your suggestion. But I need to know what is an annular philosophy if site is inside the source. is it consider as a annnular source .

If the Site is inside the source zone, how, R-Crisis is performing? In that case is it considering and annular sources, such that, below the site, the effect of earthquakes is not considered.

If the annular source is considered, then what will be the radius of annulus.

Thanks in advance.

Hi Srijit

The minimum distance (Rmin)used to split the soure you choose may influence

the Site locate in a seismic source zone in CRISIS. For example, 3km will generate a higher result than 5km. Especially when you used the slowly attenuation relationship as Pierre-Yves Bard said.

Because the smaller Rmin will let the distance between splited seismic source zones and Site smaller than large Rmin get, so the GMPE will give you

a so large estimate of ground motion values (at very small distance, like 0.5km, 0.2km, ...).

Hi

If you use the kijko program,you will get better results.

Best regards

Negar

Hello Srijit,

The site will fall under one of the seismic sources (areal) irrespective of how you divide the entire region into number of areal sources.R-Crisis manual is quite elaborate and they have explained the computation of seismic hazard using spatial integration procedure. You will be computing the seismic hazard for a reference site condition which is usually bedrock or deposit with higher shear wave velocity. So when you say 'site' if you are referring to the surface level estimation then you may have to perform site specific ground response analysis.

Secondly, your return period is too high in contrast to the normally used return periods i.e 475 years (DBE) and 2475 years (MCE).Hence, the value of PGA you are getting is quite reasonable. However, you can validate your results (for smaller return period) by comparing it with other studies that may have been performed for Peninsular India.

Assuming the seismicity parameters are correct i.e the events are purely tectonic and not induced, another source for such high value may be use of GMPEs.

Hope this helps!

Kindly comment here if you find the solution to your question.