[CIG-SEISMO] SPECFEM3D-Globe, near epicenter velocities

[Inchin, Pavel]

Good day,

I have a problem with simulation of velocities at close to the epicenter distances.
I need to obtain surface vertical velocities with 2 km step to the North (+3000 km) and South (-3000 km) from the epicenter along longitude of epicenter, so I just get synthetic seismograms for every such point from SPECFEM3D-Globe.

Here is a result of global simulation SPECFEM3D-Globe for NEX_XI=96 at some time of simulation (20mHz-example figure). The simulation looks good.

[cid:359B6E2D-CF72-4073-9B82-0C3F41DE4DA5 at db.erau.edu]

Now, I do the same simulation for NEX_XI=240 and I get a very slowly decreasing rise/drop near the epicenter. Here are several figures for different times (50mhz-1.32, 50mhz-2.23, 50mhz-4.02, 50mhz-6.22 files; time is shown on figures - minutes from event):

[cid:3A1F3E84-4D5B-4A5D-88F8-FA84951A2258 at db.erau.edu]

[cid:07AEA2D3-D8F6-492F-B7B9-B69421FAAFB3 at db.erau.edu]

[cid:B4FB22E9-6D51-42C0-8C9F-5D1B07AF74F5 at db.erau.edu]

[cid:DDD98173-74A2-4468-BEF0-AEF0E7BFE0C4 at db.erau.edu]

So it doesn’t look like sinusoid, but slowly decreasing rise/drop (to the left and right from epicenter respectfully). It takes about 10-12 minutes to fully suppress this.

I do not have it for NEX_XI=96 simulation, but for shorter period simulation it starts to appear. I tried different Earth models, but seems it doesn’t play any role.
Does it have physical nature?

And more general question - how appropriate SPECFEM3D-Globe to simulate velocities at the epicenter and positions very close to it?

Thank you in advance
Paul Inchin
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