# Thread: Need Help.

Started: 2017-10-28 16:38:18
Last activity: 2017-10-31 18:16:06
Topics:
Mukesh Das
2017-10-28 16:38:18
Hi sac users,

I have computed Ps receiver function in which maximum amplitude (direct
P-wave arrival) comes after 2-3 sec not at 0 sec. I want to shift maximum
amplitude at 0 sec. Can anyone suggest how to shift this maximum amplitude
at 0 sec. Here below i have attached some screen shot of receiver function
in which maximum amplitude (direct P- wave arrival) come at after 2-3 sec.

Thanks

--
Mukesh Kumar Das
JRF (Research Scholar)
Department of Applied Geophysics
Indian lnstitute of Technology (Indian School of Mines)
Mob +918873563108
+918340601230

##### Attachments
• Craig Jones
2017-10-28 06:37:06
You don't say how this receiver function was made, but if a
single station receiver function, your logic is flawed, I think.
The maximum amplitude on a Ps RF need not be the direct
arrival. In fact, if you are rotating into coordinates parallel
and normal to the P arrival, it will certainly not be the direct
arrival. If the station has a low velocity underneath it, the
arrival will come in nearly vertically and, once again, the peak
arrival will not be the direct P.

The only time you will not have the direct arrival at 0 seconds
on a single station RF is when you have a timing error on one
component or another, which is a profoundly unlikely occurence.
You can end up with an offset if you are deconvolving a
different P wave (e.g., one made by beamforming over a
collection of stations) from a single station radial component.

If you still want to shift things, all that is involved is
playing with the relevant header variables for a SAC file (it
depends a bit on what you are planning on doing afterwards as to
the best combination of changes to make).

On 10/28/17 at 10:09 PM, kumarmukesh2411<at>gmail.com (mukesh
kumar) wrote:

Hi sac users,

I have computed Ps receiver function in which maximum amplitude (direct
P-wave arrival) comes after 2-3 sec not at 0 sec. I want to shift maximum
amplitude at 0 sec. Can anyone suggest how to shift this maximum amplitude
at 0 sec. Here below i have attached some screen shot of receiver function
in which maximum amplitude (direct P- wave arrival) come at after 2-3 sec.

Thanks

--
Craig H. Jones
Professor, Dept. Geological Sciences, CB 399
and Fellow, CIRES, CB 216
University of Colorado, Boulder, CO 80309-0399

• Steve Gao
2017-10-30 23:29:47
I agree. The shift is most likely an indication of the existence of a loose sedimentary layer. This is especially true if the receiver function is dominated by reverberations. This has been discussed in Yeck et al. (2013) and Yu et al. (2015). The latter is attached for your convenience -- see Figure 2a for a synthetic example.

Steve Gao

Stephen S. Gao, Professor,
Geology & Geophysics Program,
Missouri University of Science & Technology,
129 McNutt Hall, Rolla, Missouri 65409, USA
E-mail: sgao<at>mst.edu
Office Phone: (573)-341-6676
http://web.mst.edu/~sgao

-----Original Message-----
From: sac-help-bounce<at>iris.washington.edu [sac-help-bounce<at>iris.washington.edu] On Behalf Of Craig Jones
Sent: Monday, October 30, 2017 11:04 AM
To: SAC Help <sac-help<at>lists.ds.iris.edu>
Subject: Re: [IRIS][sac-help] Need Help.

You don't say how this receiver function was made, but if a single station receiver function, your logic is flawed, I think.
The maximum amplitude on a Ps RF need not be the direct arrival. In fact, if you are rotating into coordinates parallel and normal to the P arrival, it will certainly not be the direct arrival. If the station has a low velocity underneath it, the arrival will come in nearly vertically and, once again, the peak arrival will not be the direct P.

The only time you will not have the direct arrival at 0 seconds on a single station RF is when you have a timing error on one component or another, which is a profoundly unlikely occurence.
You can end up with an offset if you are deconvolving a different P wave (e.g., one made by beamforming over a collection of stations) from a single station radial component.

If you still want to shift things, all that is involved is playing with the relevant header variables for a SAC file (it depends a bit on what you are planning on doing afterwards as to the best combination of changes to make).

On 10/28/17 at 10:09 PM, kumarmukesh2411<at>gmail.com (mukesh
kumar) wrote:

Hi sac users,

I have computed Ps receiver function in which maximum amplitude (direct
P-wave arrival) comes after 2-3 sec not at 0 sec. I want to shift
maximum amplitude at 0 sec. Can anyone suggest how to shift this
maximum amplitude at 0 sec. Here below i have attached some screen shot
of receiver function in which maximum amplitude (direct P- wave arrival) come at after 2-3 sec.

Thanks

--
Craig H. Jones
Professor, Dept. Geological Sciences, CB 399 and Fellow, CIRES, CB 216 University of Colorado, Boulder, CO 80309-0399 http://cires1.colorado.edu/people/jones.craig/

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##### Attachments
• Mukesh Das
2017-10-31 18:16:06
Hi Craig,

We computed these receiver functions using iterative time domain
deconvolution with Gaussian width 1.5. We also rotated our seismograms from
ZNE to ZRT components. Do you think if we will use Gaussian width of 2.0 or
above then we can probably see clear arrival of direct P-wave exactly at
zero then Ps phase due to sediment basement after 1-2 seconds (if basement
depth is more than 1km).

Regards,

On Mon, Oct 30, 2017 at 10:01 PM, Steve Gao <sgao<at>mst.edu> wrote:

I agree. The shift is most likely an indication of the existence of a
loose sedimentary layer. This is especially true if the receiver function
is dominated by reverberations. This has been discussed in Yeck et al.
(2013) and Yu et al. (2015). The latter is attached for your convenience --
see Figure 2a for a synthetic example.

Steve Gao

Stephen S. Gao, Professor,
Geology & Geophysics Program,
Missouri University of Science & Technology,
129 McNutt Hall, Rolla, Missouri 65409, USA
E-mail: sgao<at>mst.edu
Office Phone: (573)-341-6676
http://web.mst.edu/~sgao

-----Original Message-----
From: sac-help-bounce<at>iris.washington.edu [mailto:sac-help-bounce@iris.
washington.edu] On Behalf Of Craig Jones
Sent: Monday, October 30, 2017 11:04 AM
To: SAC Help <sac-help<at>lists.ds.iris.edu>
Subject: Re: [IRIS][sac-help] Need Help.

You don't say how this receiver function was made, but if a single station
receiver function, your logic is flawed, I think.
The maximum amplitude on a Ps RF need not be the direct arrival. In fact,
if you are rotating into coordinates parallel and normal to the P arrival,
it will certainly not be the direct arrival. If the station has a low
velocity underneath it, the arrival will come in nearly vertically and,
once again, the peak arrival will not be the direct P.

The only time you will not have the direct arrival at 0 seconds on a
single station RF is when you have a timing error on one component or
another, which is a profoundly unlikely occurence.
You can end up with an offset if you are deconvolving a different P wave
(e.g., one made by beamforming over a collection of stations) from a single

If you still want to shift things, all that is involved is playing with
the relevant header variables for a SAC file (it depends a bit on what you
are planning on doing afterwards as to the best combination of changes to
make).

On 10/28/17 at 10:09 PM, kumarmukesh2411<at>gmail.com (mukesh
kumar) wrote:

Hi sac users,

I have computed Ps receiver function in which maximum amplitude (direct
P-wave arrival) comes after 2-3 sec not at 0 sec. I want to shift
maximum amplitude at 0 sec. Can anyone suggest how to shift this
maximum amplitude at 0 sec. Here below i have attached some screen shot
of receiver function in which maximum amplitude (direct P- wave arrival)
come at after 2-3 sec.

Thanks

--
Craig H. Jones
Professor, Dept. Geological Sciences, CB 399 and Fellow, CIRES, CB 216
University of Colorado, Boulder, CO 80309-0399 http://cires1.colorado.edu/
people/jones.craig/

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--
Mukesh Kumar Das
JRF (Research Scholar)
Department of Applied Geophysics
Indian lnstitute of Technology (Indian School of Mines)
Mob +918873563108
+918340601230

• Geo .
2017-10-28 16:05:47
Hi Mukesh,
You can use the inline function GETTIME to obtain the xx value George
mentioned. You may refer the SAC manual for usage. Note that your P wave
peak is recorded in the header DEPMAX if it is the largest amplitude in
your RFs, which usually is true unless you have very noisy RFs. You can
easily automate this process with a macro.

https://ds.iris.edu/files/sac-manual/manual/inline.html

Januka

On Saturday, 28 October 2017, mukesh kumar <kumarmukesh2411<at>gmail.com>
wrote:

Hi sac users,

I have computed Ps receiver function in which maximum amplitude (direct
P-wave arrival) comes after 2-3 sec not at 0 sec. I want to shift maximum
amplitude at 0 sec. Can anyone suggest how to shift this maximum amplitude
at 0 sec. Here below i have attached some screen shot of receiver function
in which maximum amplitude (direct P- wave arrival) come at after 2-3 sec.

Thanks

--
Mukesh Kumar Das
JRF (Research Scholar)
Department of Applied Geophysics
Indian lnstitute of Technology (Indian School of Mines)
Mob +918873563108
+918340601230

--
Januka Attanayake
Postdoctoral Research Associate

Institute for Geophysics
WWU Münster | CorrensstraBe 24 | 48149 Münster | Germany
Tel +49 251 833 4727

University email: jattanayake<at>uni-muenster.de

• Mukesh Das
2017-10-29 18:05:06
Thank you everyone for your valuable suggestion.

On Sat, Oct 28, 2017 at 12:36 PM, Geo . <jattanayake<at>gmail.com> wrote:

Hi Mukesh,
You can use the inline function GETTIME to obtain the xx value George
mentioned. You may refer the SAC manual for usage. Note that your P wave
peak is recorded in the header DEPMAX if it is the largest amplitude in
your RFs, which usually is true unless you have very noisy RFs. You can
easily automate this process with a macro.

https://ds.iris.edu/files/sac-manual/manual/inline.html

Januka

On Saturday, 28 October 2017, mukesh kumar <kumarmukesh2411<at>gmail.com>
wrote:

Hi sac users,

I have computed Ps receiver function in which maximum amplitude (direct
P-wave arrival) comes after 2-3 sec not at 0 sec. I want to shift maximum
amplitude at 0 sec. Can anyone suggest how to shift this maximum amplitude
at 0 sec. Here below i have attached some screen shot of receiver function
in which maximum amplitude (direct P- wave arrival) come at after 2-3 sec.

Thanks

--
Mukesh Kumar Das
JRF (Research Scholar)
Department of Applied Geophysics
Indian lnstitute of Technology (Indian School of Mines)
Mob +918873563108
+918340601230

--
Januka Attanayake
Postdoctoral Research Associate

Institute for Geophysics
WWU Münster | CorrensstraBe 24 | 48149 Münster | Germany
Tel +49 251 833 4727

University email: jattanayake<at>uni-muenster.de

----------------------
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--
Mukesh Kumar Das
JRF (Research Scholar)
Department of Applied Geophysics
Indian lnstitute of Technology (Indian School of Mines)
Mob +918873563108
+918340601230

• George Helffrich
2017-10-28 22:51:16
Dear Mukesh Das -

Use CH B xx where xx is the time difference between zero and your peak. That shifts the data start time to a new value relative to the file's zero time.

On 28 Oct 2017, at 13:09, mukesh kumar <kumarmukesh2411<at>gmail.com> wrote:

Hi sac users,

I have computed Ps receiver function in which maximum amplitude (direct P-wave arrival) comes after 2-3 sec not at 0 sec. I want to shift maximum amplitude at 0 sec. Can anyone suggest how to shift this maximum amplitude at 0 sec. Here below i have attached some screen shot of receiver function in which maximum amplitude (direct P- wave arrival) come at after 2-3 sec.

Thanks

--
Mukesh Kumar Das
JRF (Research Scholar)
Department of Applied Geophysics
Indian lnstitute of Technology (Indian School of Mines)
Mob +918873563108
+918340601230
<Screenshot from 2017-10-27 22-34-30.png><Screenshot from 2017-10-27 22-35-18.png><Screenshot from 2017-10-27 22-37-06.png><Screenshot from 2017-10-27 22-38-19.png>
----------------------
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George Helffrich
george<at>elsi.jp

23:40:12 v.22510d55