Output units for synthetic seismograms

[ammcpherson]

Hello everybody,

I was wondering if anyone could tell me what the output units are for the synthetic seismograms generated in SPECFEM3D_Globe. I see that the SAC headers have been populated with information, and it appears that the unit (for a displacement synthetic) is "nm' - nanometer?

Thanks,
Amanda

[danielpeter]

hi Amanda,

the globe version always outputs displacement seismograms with units in [m]. in SAC files, you can indicate what these trace values should be by the variable IDEP. options given by SAC (https://ds.iris.edu/files/sac-manual/manual/file_format.html) as type of dependent variable are:

• IUNKN (Unknown)
• IDISP (Displacement in nm)
• IVEL (Velocity in nm/sec)
• IACC (Acceleration in nm/sec/sec)
• NOTE Others use SI units for IDISP, IVEL, IACC.
• IVOLTS (Velocity in volts)

SPECFEM3D_GLOBE chooses the setting IDISP as type in the output SAC files, but using SI units rather than nm.

[changcheng666li]

Thanks for your answer. I use the specfem3d_globe version. Is the units of velocity of this version also [m/s]?

[danielpeter]

SPECFEM3D_GLOBE only outputs displacement traces.

[changcheng666li]

Dear professor, Thank you for your reply.

[djavediqbal]

Can you please tell about units of output seismograms of SPECFEM2D

[bch0w]

@djavediqbal you can choose the unit of your output seismogram with the parameter seismotype

https://github.com/SPECFEM/specfem2d/blob/98741db1a0c8082ca57364f5b17ea95df6cbf1c2/DATA/Par_file#L143-L145

[ammcpherson]

@danielpeter Thank you for clarifying!

[changcheng666li]

Dear professor, if I use the point force source as the source to calculate the seismic record, Should the unit of force in the input file be Newton or dyne?

[homnath]

For FORCESOLUTION, the unit of the force should be in SI unit, i.e., Newton. Make sure you use other units consistently. For CMTSOLUTION, however, the units of moment tensor components are in dyne-cm.

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________________________________ From: changcheng666li ***@***.***> Sent: Monday, December 12, 2022 11:13 AM To: SPECFEM/specfem3d ***@***.***> Cc: Subscribed ***@***.***> Subject: Re: [SPECFEM/specfem3d] Output units for synthetic seismograms (Discussion #1567) Dear professor, if I use the point force source as the source to calculate the seismic record, Should the unit of force in the input file be Newton or dyne? — Reply to this email directly, view it on GitHub<https://can01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Forgs%2FSPECFEM%2Fdiscussions%2F1567%23discussioncomment-4380486&data=05%7C01%7Chomnath.gharti%40queensu.ca%7C42f9542c5eed4c97211908dadc5bbdab%7Cd61ecb3b38b142d582c4efb2838b925c%7C1%7C0%7C638064583821179405%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=edid0l7eko11gbN0Xa2Trlwil0OpAyA81HMD94zXBkA%3D&reserved=0>, or unsubscribe<https://can01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fnotifications%2Funsubscribe-auth%2FABMCQ4ULN6FUQRRDCJYQP7TWM5FIZANCNFSM6AAAAAASNXXNO4&data=05%7C01%7Chomnath.gharti%40queensu.ca%7C42f9542c5eed4c97211908dadc5bbdab%7Cd61ecb3b38b142d582c4efb2838b925c%7C1%7C0%7C638064583821179405%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=RchKYFXUt%2F6Kz7KzAozi1Lb20BmvNl0H6OOmxV0CQxQ%3D&reserved=0>. You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[changcheng666li]

Thank You!