[CIG-SEISMO] Help with SW4 (Avinash Nayak)

[Petersson, Anders]

Hi Avinash,
Can you please attach your input file?
Thanks,
Anders

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>   1. Help with SW4 (Avinash Nayak)
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>----------------------------------------------------------------------
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>Message: 1
>Date: Sun, 10 Apr 2016 22:31:02 -0700
>From: Avinash Nayak <avinash07guddu at gmail.com>
>To: cig-seismo at geodynamics.org
>Subject: [CIG-SEISMO] Help with SW4
>Message-ID:
>	<CA+ebHScc3Sa3cYVrdjYE5=1_EiaxVf3qe-AWPQNf9_PG9QNjFQ at mail.gmail.com>
>Content-Type: text/plain; charset="utf-8"
>
>Hi Everyone,
>
>I am having an issue with SW4 where I get non-zero values in velocity
>at source position for a substantial amount of time (after source time
>function becomes very small) and I am not sure what exactly I am doing
>wrong.
>
>In the attached file (Summary.pdf), Figure 1 shows a screenshot of
>velocity in YZ plane at x=1.393 km (passing through the source at
>x=1.393, y=1.925 and z=0.469 km) at t=7.5 seconds. Color is supposed
>to be scaled as red to blue from negative(peak absolute amplitude) to
>positive(peak absolute amplitude) with white for zero. As you can see
>the highest amplitude is a dot at the source position (y=1.925 km,
>z=0.46 km). If I replace values at 7x7 grid points around the source
>with zeros, then I can see the wavefield slightly better and the peak
>amplitude decreases from 1.1e-5 m/s to 2.7e-6 m/s (Figure 2).
>
>In figure 3 and 4, I am plotting the velocity and displacement values
>at the 7x7 grid points around the source, and you can see non-zero
>very slowly decreasing values of velocity that persist even at 15-20
>seconds. When I integrate them, I can see a slight increase of
>displacements with time but I am not sure if they reach steady state
>value (Figure 4).
>
>My grid spacing is 7 m for minimum shear wave velocity 150 m/s. I use
>a Gaussian source time function with freq 3.1416 (so, f0=0.5 Hz,
>fmax=f0 x 2.5 = 1.25 Hz, and 150/1.25/7 = 17 grid points per
>wavelength for fmax). My t0 is 2.0 seconds( which is greater than
>6/freq=1.91 s) so satisfies g(t=t0)=3.4e-9 which is less than 1e-8.
>The source time function goes below 1e-15 after 5 seconds.
>The source is a moment tensor source  very close to a strong material
>discontinuity. I use supergrid size 73.
>
>I will be very grateful if someone can point out what I have done
>wrong. Due to computation limitations, I cannot really go to lower
>grid spacing. I am currently trying another run at higher value of t0
>(2.5 s).
>
>Thanks.
>Regards,
>Avinash
>
>-- 
>
>Avinash Nayak,
>PhD Candidate,
>Berkeley Seismological Laboratory,
>Department of Earth and Planetary Science,
>University of California, Berkeley
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