The anatomy of seismograms: visualizing P, Pdiff, PcP, PKP, PKiKP, PKIKP, PKJKP, PKKP, PKKKP, PPP phases

[Branden Christensen]

Hi Shakers:

Buenas tardes. 

Every now and again you find an absolute gem on Twitter. To understand the anatomy of seismograms, check this out: https://twitter.com/raspishake/status/919984051880161280

What have you seen with your Shake?

Yours,

Branden Christensen

Director, OSOP & Gempa GeoServices

Director, Raspberry Shake project, Social Media: @raspishake

USA: +1-845-418-5735; Panamá: +507-6747-1427

[GeraldP]

Nice video.  Thanks.

QUESTION:  You are not responsible for the music score for the video, are you?  

Using WinQuake software it is possible to display various ray paths.  In addition to the obvious P & S wave times, what other wave selections might one expect from a Shake? Or, does that depend upon the distance, magnitude and depth?  

Thank you

[Jos Gysenbergs]

Well, for once I found the music acceptable, let's say at -60 dB. It sounds as if the author had given it some thought. Normally YouTube sound is muted here because of utterly boring and distracting. Automated subtitles are a bless. Just my 2 €c.

Video is excellent. Tks for the link and a 'me too' for Gerald's question. - JG

[tinotenaz]

Hi,

it depends on the magnitude, distance, and depth. But usually you can see the Surface Waves (Love and Rayleigh) and other reflected waves like Pp, Pc, or refracted waves like Ps, PkP etc.

For example, if you are very close to the source, you can easily identify the direct P wave, otherwise what you see is the P refracted. Also if the Earthquake is very shallow, the Surface waves could be seen very close to the S wave on a very close station, and sometimes both are overlapping each other.

Here you can find an excellent explanation of all this, 

http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/waves_and_interior.html

Take a look at this image where it is identified different seismic waves on a seismograph 

http://i2.offnews.bg/nauka/events/2017/02/13/70717/1487621059_6.jpg

[Branden Christensen]

And for a higher resolution of that IRIS seismic poster see: 

https://www.iris.edu/gallery3/general/posters/exploring_earth/ExplorEarthPoster

Branden Christensen

Director, OSOP & Gempa GeoServices

Director, Raspberry Shake project, Social Media: @raspishake

USA: +1-845-418-5735; Panamá: +507-6747-1427

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[GeraldP]

Excellent information Tino & Braden.  

Years ago, I was using homemade sensors and receiving teleseismic waves.  I was using Lehman type sensors and getting fairly good response.  Of course, that sensitive required temperature control and other minute cautions.  I would have to wait sometimes for an hour to get all the phases.

My question now:  (Keep in mind that I am using WinSDR and WinQuake software.)  Using the Shake, is it necessary to have a minimum time to wait before capturing the event?  I would suspect, even with a large EQ and deep, that I would not receive some of the reflected phases etc..  I also assume that reflected waves loose intensity as they travel through the earth.

Sorry for all the questions,  I am trying to learn!   Can OLD DOG learn new tricks?

[tinotenaz]

Hi Gerald,

we are so happy to know how our clients are exciting about learning Seismology, we are here to support all of you on any question related.

Regards to your question, it also depends on the Earthquake (EQ) parameters; magnitude, depth, location, etc. If you, for instance, wants to see on one Raspberry Shake all the possible seismic waves generated for an EQ, this is not possible as out device is designed for local EQ. Of course you can expect to see some waves arriving from distance big EQ, but this are not going to carry on all the information. You could see, most of the time, P refracted waves, and for the on well installed and on the right location relative to the EQ, you can expect to record the S wave. Part of the surface waves could be also be recorded, but the ideal device for recording these kind of waves are the broad band, these go upper than 100 seconds of period, where this seismic waves are found.

So, if you wonder how long should you wait in order to record with a Shake all the seismic waves from a distant EQ, I would'n wait longer than 5 minutes after the P arrival, after this confidence on the records is lost. However, if you have a well installed broad band equipment, you can record for hours different kind of seismic waves, even the ones reflected from the Earth's core, depending on the EQ's magnitude.

I hope have shed some light on this. 

[GeraldP]

Tinotenaz, this has been an exceptional answer.  I have been using 5 minutes normally and occasionally 10 mins. with the infrequent LARGE EQ's,; and have recorded some Rayleigh waves  etc. on occasion. 

Thank you SO much for these explanations.  I wasn't sure if this was the proper platform to ask such questions not technically directly related to the Shake.  I sincerely appreciate you input.

[chris...@aol.com]

Hi Jerry, 

    Earthquakes generate P and S Waves directly. The further these have to travel through 

the Earth, the more any components above about 2 Hz are attenuated. Local quakes may 

generate P waves with frequencies up to over 10 Hz. Teleseismic quakes are likely to have 

P wave frequencies of 1 to 2 Hz. The associated S waves have frequencies about half that 

of the P waves and their velocity is lower. When either impact the surface, Love and 

Rayleigh surface waves are generated. Check out the travel time graphs of time versus 

angle at https://earthquake.usgs.gov/learn/topics/ttgraph.php  

    Most Surface Waves have periods of about 20 seconds, so a Lehman with a period of 

25 seconds senses them at their full amplitude. Surface waves with periods of ~40 seconds 

would also be recorded, but at ~1/4 their true amplitude. The upper frequency limit depends 

on the filters in the amplifier - often ~10 Hz. 

    A 1 Hz geophone / RShake will still respond to 20 second Surface Waves, but at ~1/400 

their true amplitude - you may still see some from large quakes, since Surface Waves 

have much larger amplitudes than the P or S waves anyway - but don't count on it ! The 

RShake sensitivity is high, so your signals are most likely to be limited by environmental 

noise.  

     Going back to your previous Email, you shouldn't use temperature control with a Lehman 

- that tends to make air current movement signals worse - but you may fit a mildly heated 

Aluminium plate inside the top of the insulated cover to ensure that no vertical air currents 

are generated if the air temperature inside the case falls below the ground temperature 

during a winter night. 

    Regards, 

    Chris

From: tinotenaz <faut...@gmail.com>
To: RaspberryShake <raspber...@googlegroups.com>
Sent: Wed, 18 Oct 2017 14:23
Subject: [RShake Forum] Re: The anatomy of seismograms: visualizing P, Pdiff, PcP, PKP, 

PKiKP, PKIKP, PKJKP, PKKP, PKKKP, PPP phases

Hi Gerald,

    We are so happy to know how our clients are exciting about learning Seismology, we are here to support all of you on any question related.

--

Some useful links:
 
Manual: http://manual.raspberryshake.org/
Do It YourSelf Page: http://raspberryshake.org/do-it-yourself
Shop: https://shop.raspberryshake.org/
Website: http://raspberryshake.org/
 
Instagram: https://www.instagram.com/raspishake/
Facebook: https://www.facebook.com/raspishake/
Twitter: https://twitter.com/raspishake/
Hashtag: #rasperryshake
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[GeraldP]

Thank you Chris.  This is ALL good and accurate information, but I do have Lehman devices at present.  This was many years ago.  I am extremely lacking in space to install such sensors.  Consistently, I am ONLY using the SHAKE 1 at present and trying to fine tune my WinQuake and WinSDR programs; PLUS maybe learn a few things as a go.

I'm sure that others on this list will benefit from your information, should they have or want expand into that area too.

Regards, 

Jerry