Gravitational Waves or Seismic Chirp Signal Detection ?

Dear Ait Mansour El Houssain To technology is amazing and the tool they are using also is amazing, but there is no gravitation or seismic wave, but they sending some sort of wave, and as the wave reflect to different area under the ground they know what is out there, But here two article on gravity and earthquake might help to understand gravity and earthquake, yet both of them unprecedented article that no one ever attempt to write it.

Thank you Javad Fardaei for useful informations

Dear Ait Mansour El Houssain ,

That's why LIGO has two stations separated by 3000 km. When they both detect the same signal, just a few milliseconds apart, then this can't be due to seismic waves human-induced or natural, because such waves do not travel fast enough to be recorded by both stations so close in time. With the inclusion of VIRGO in Italy, it is even better. I haven't done the calculations on this myself, but I am pretty sure that somebody at the LIGO collaboration did, and the results are out there somewhere.

Dear Michal Michalowski , thank you for your response. Effectively, gravitation waves propagate with c velocity more bigger than seismic (or natural) wave speed. However, it's probable to detect synchronized seismic waves (from dependant or independent sources) by two interferometers. Additionally, with ~>10^-18m sensibility, we may have sometimes chirp individual interferometer event detection....

I think that if two seismic waves coming to both detectors are not from the same source, then the data would look differently for them, so they would not be classified as potential gravitational wave sources. So with two or more detectors the danger of mistaking seismic activity for GW is small.

Ait,

That's very interesting!

Attached is a screen capture of a 'SEG-D Data example' from a seismic vibrator.

Looks very similar to a GW chirp.

Peter Hahn There is one feature missing in these seismic plots - the signal measured by LIGO goes to zero after the high-amplitude, high-frequency phase:

This is not visible in the plot you sent. This drop is interpreted as the moment when black holes or neutron stars merge, so no further waves are emitted.

Second, as I said before - such seismic waves would be detected only by one of the LIGO detectors or with a delay longer than a few milliseconds, so this is not the explanation.

Thanks Michal,

I would assume that the seismic wave would rapidly drop to zero after the equipment was turned off. Also...If the seismic wave originated somewhere in the middle of the USA such that the distance between H1 and L1 were roughly the same, couldn't they arrive at both detectors within the required 10msec timeframe?

Ait,

Help me out here. How long do they run the seismic vibrator? The chirp from GW190425 lasted approx. 25 seconds.

Do you mean that the LIGO equipment is turned off a fraction of a second after the detection of the signal? This is incorrect. They are constantly recording, so such an abrupt change from the maximum amplitude to just noise need to be explained by the property of the event itself. The merger scenario gives that explanation, whereas the seismic wave scenario doesn't. I imagine that a seismic wave would be damped more slowly, but this is not my speciality, so I don't know.

Indeed an earthquake right in the middle would give the correct timing in the LIGO detectors. Somebody would need to check how often such quakes occur and if they can travel far enough to be detected 3000 km apart at a right amplitude and frequency.

Moreover, what about events recorded by LIGO and Virgo in Italy? Then this scenario doesn't hold at all.

Dear Michal Michalowski and Peter Hahn , The controled source siesmic Chirp parameters such as frequency range and duration depends on investigation depth (from mHz to teens of Khz). Some kind of Vibrator (Ex: Inertial Vibration Test System TV 51165-IN) allows you to define a specific Chirp shape (Generated by Matlab for example). In practice, we use a pulsed chirp signal: We modulae chirp signal with a square wave (See figure low-pass filter case) for easy signal processing and to seperate between relected signals. In the other hand, the reflected signal is filtred (low, high, band, mixed...) with attenuation by sol + noise. The reflected chirp form depend on sol properties and composition. The transfert function between source chirp and reflected provide useful informations about sol propertie. Referer to Seismic methods for geophysiscs.

In a parallel discussion, see references below, I proposed that alleged gravitational wave signals might be synchronized by global response to tidal force interaction within the Earth/Moon/Sun gravitational system. I further suggested that signals detected in horizontal planes as defined by LIGO/Virgo interferometer systems may result from simultaneous displacement of test mirrors along the local verticals. The latter, due to earth curvature, deviate by about one arcmin from vertical with respect to LIGO/Virgo interferometer planes.

Thank you Johan K. Fremerey for additional information.

Go to https://gracedb.ligo.org/superevents/public/O3/ You will see lots of candidates, 56 to be exact. Half of them have been rejected. The rejected ones, have shape of gravitational waves but turned out to be noise from other sources, such as cleaning equipment. Many "confirmed" ones were detected only by one detector, such as GW190425 (the only confirmed detection from the 3rd run) or GW170817 ( the only one supposedly with a visual). LIGO mistook different types of noise for grav waves before so nothing can be ruled out.

I clicked on the link, but the graph is not there. Can you point out the source of the graph?

Dear Mikhail Kovalyov , The graph is example of matlab simulation of filtered chirp signal. The code is available if required.

When I asked for a source, I meant of the seismic signal not a GW chirp

Chirp (top curve) is source signal. Filtred chirp is example or reflected signal acquired using geophone sensor: https://en.wikipedia.org/wiki/Geophone

I mean the picture of the seismic wave itself. Whee is ti from? Did you generate it yourself from data or is it available anywhere on the Internet? I mean the source signal, top curve.

Also, I'd like to know the source of the signal posted by Peter Hahn.

Please refer to this link and PDFs in attachement: https://urlz.fr/ccO0

Mikhail,

The image came from http://seismicsource.com/html/downloads

The document is: Bird Dog 3 System, Vibtest User Manual.

To Peter Hahn. Thanks. I checked with the people there and the signal was artificially generated. It is generated to search for mineral deposits and probe what's underground. Hypothetically speaking, there might be such research carried out somewhere between the LIGO interferometers, with the frequencies above a certain threshold cut off by LIGO, that would give us some of LIGO's signals. .

Effectively Mikhail Kovalyov its a good idea. LIGO and VIRGO interferometers are the most accurate "Geophone" sensor (Sensibility: 10E-18 to 10E-21m). Their Dataset of useless signals may be used to survey earth seismic activities...