# Shakingmap does not match the seismograms (PGA)

**URL:** <https://community.geodynamics.org/t/shakingmap-does-not-match-the-seismograms-pga/828>\
**Category:** SPECFEM\
**Created:** [October 5, 2019, 1:51am UTC](https://community.geodynamics.org/t/shakingmap-does-not-match-the-seismograms-pga/828 "2019-10-05T01:51:56Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![pokayoke](https://avatars.discourse-cdn.com/v4/letter/p/d07c76/32.png) [@pokayoke](https://community.geodynamics.org/u/pokayoke)\
**Post date:** [October 5, 2019, 1:51am UTC](https://community.geodynamics.org/t/shakingmap-does-not-match-the-seismograms-pga/828/1 "2019-10-05T01:51:56Z")

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Hi everyone,

Recently I found a strange problem with specfem3D’s output.  
I slice a profile across the shaking map to obtain the PGA PGV and PGD values,  
and compare with seismogram array’s result (I calculate PGA PGV PGD from waveforms).  
Then I found the PGA does not match (shaking map PGA larger than seismogram’s PGA). But PGV and PGD are fitting well.  
This un-match situation only occurs when I use a source that has half duration 0.6s.  
For a source that has half duration 0.05s, then the shaking map all fits with seismograms. (I use an isotropic source)

**Does anyone know why the shaking map (PGA) is different from the seismogram’s PGA?**  
**(ps:1.PGV and PGD are correct; 2. only happen when using long half duration)**

This problem really makes me very troubled.  
I will be grateful for any help you can provide.