Sky Quakes revisited

Most should be familiar with the notion of "sky quakes", mostly around southern California. For those not familiar with the subject, the idea was secret aircraft flying into California airbases were breaking the sound barrier, and the shock wave was setting off seismic detectors. [There are many reasons why this wouldn't be the case, mostly because the USAF isn't that stupid.]

Checking into this, it turns out the seismic detectors are designed to ignore effects on the surface to some degree because the real "science" is happening under the ground. The concern is the surface wave could be a reflection of the underground activity and thus an indirect effect of the geologic event, well unless you got a good shaking. There is much patented regarding how to filter surface effects of seismic events.

Caltech has a paper on skyquakes. It turns out some of the sensors sites were later equipped with pressure detectors so that the sonic blast of aircraft could be detected directly and then correlated with the earth shaking. One presumes they didn't give a hoot about the X-plane fanatics, but rather wanted to know if their gear was picking up a sonic boom rather than geological disturbances.

authors.library.caltech.edu...

The paper also goes into Lincoln Labs analysis of sky quakes, attributing them to F-4 at KEDW. The space shuttle landing is also analyzed using the more advanced system with surface pressure detectors. The conclusions of the paper follow:

The seismic network in southern California has provided the first opportunity to study the size and shape of indirect sonic boom carpets over a large area. The high density of the sites and large ground coverage allow analysis of the direct and indirect boom patterns on both sides of the flight trajectory, and the development of the booms can be followed over several hundred kilometers. The recent addition of pressure transducers at selected TERRAscope sites remedies the only significant weakness of the seismic data, the difficulty of predicting amplitudes.

From analysis of the space shuttle STS-42 reentry, the ground patterns are extremely complex. Ray theory fails to predict indirect sonic boom arrival times, observed multiple booms within the first shadow region, and extensive overlap of the multiple refracted sonic booms. The extensive ground coverage of the ‘‘mystery boom’’ and shuttle reentry booms suggest exposure under the real atmosphere is much larger than previously expected.

The inverse problem of predicting the aircraft trajectory from the ground arrival times is more difficult. Nonetheless, using the seismic network data, we were able to identify the source of the ‘‘mystery booms’’ as indirect booms propagated from offshore operations. However, careful study of the seismic data is required to identify direct and indirect sonic boom carpets before attempting to make predictions about the trajectory.

Now I bring this up because there was a "sky quake" type noise reported Sunday in Ca. This may be related to the W-537 warning on ATS at this link:
www.abovetopsecret.com...

Hello Gariac - First off, I wanted to say that I very much enjoy reading your posts and the info they provide. As a novice plane spotter and someone who finds the aerial activities around facilities that seem to be within your stomping grounds, you honest assessment is very crucial to those of us who come here trying to discern the facts about these projects and places from the myths.

Forgive me if I’m simply obtuse, but are they arguing that the “sky quakes” observed by Cal Tech and others are simply sonic booms from known aircraft? I was always under the impression that the “wave patterns” of such aircraft (including the shuttle) were known to the scientists and that was part of the mystery surrounding some of these “sky quakes”. Sorry if I’ve completely missed the boat on any explanations and I thank you in advance for any clarification you can provide.

reply to post by Virgil Cain


It is tough to summarize 15 pages of technical writing but here goes. The paper examines the mystery sky quakes and known sonic booms. The analysis of known sonic booms is key here since it provides a baseline for the analysis of the mystery booms. [Without a way to verify the theories, these guys would be the equivalent of some goofball on youtube trying to present evidence of a UFO from wiggly video. There is no shortage of those clowns, and worse yet, people that believe them!]

The paper sets up the analysis by examining the way sonic booms arrive to the ground. This can be a direct shock wave from the plane, a bounce of the initial shock wave off a discontinuity in the atmosphere, a reflection of the shock wave off the ground back to the air then subsequently reflected again off an atmospheric discontinuity, or a creeping wave along the ground created by the direct sonic energy. In short, these guys didn't miss a trick. OK, maybe one trick would be the sound coupling to a natural acoustic channel like a valley. But that would be very specific to ground topology.

The paper shows how shuttle landings can be tracked. This isn't easy since the energy to the seismic stations is arriving by all the means elaborated in the previous paragraph. But with enough math, they more or less could detect the shuttle. Hence they have a baseline. They have proved the analysis works for a test case. [Way better than an out of focus blob on youtube!]

On page 627, the "sky quakes" are tabulated. The analysis of the "sky quakes" starts on page 622. You need to jump to page 626 to see the shock wave propagation. They are showing the location of the wave at 30 second intervals as it is measured on the ground. Not explicitly stated here, but the higher in altitude the shock wave originates, the closer together the detection lines would be. If you consider the geometry of the situation, the higher the plane, the closer the relative distance from points on the ground to the plane becomes, hence the time of arrival becomes closer. [This is known as TDOA analysis, though usually associated with radio waves.]

The paper then alludes to the Concorde causing similar sounds on the east coast, but no seismic data. They attempt to correlate the seismic events noted in Table 1 with ASSOCIATED (my emphasis) tests at Edwards and the Pacific missile range. Nothing correlated because both entities said they didn't cause any booms. Further the claim was no sonic booms were heard at Edwards or the range. [Of course, would they admit it?]

Their conclusion is the sonic booms occurred off the coast by a high flying object.

Now here is my spin on all this. Note in the paper the bandwidth of the instrumentation is 20Hz. So essentially they are detecting infrasonic sound, yet the witnesses could hear the sky quakes. I would assume the witnesses were hearing some secondary effect of the shock wave.

Could a plane off the coast break the sound barrier? Sure, why not, but it doesn't have to be an X plane. Some civilian could take a Viggen from the Mojave Airport over the ocean and break the sound barrier. In socal, plenty of supersonic aircraft are in civilian hands, and there is no shortage of hotdog pilots.

reply to post by gariac


Thank you for your insight into this question. So essentially it seems that a sonic boom may be able to register as a "sky quake" if the atmospheric and topographical conditions are aligned correctly?

reply to post by Virgil Cain

As a corollary to sky squakes, there are quakes due to nuclear explosions. On Google Earth, you can show historic earthquakes. It is under gallery then earthquakes. Quite a few are on the Nevada Test Site (NTS, NNSA, NNSS, N2S2) and of course are due to nuclear underground testing.

I looked at a few of these quakes and the corresponding tests, jotting down some note here:
www.lazygranch.com...

Sometimes the quake and blast match in time and position. Sometimes the location is off significantly. Once in a while the time is off. Could be a database error. Note that Project Faultless, a full megaton blast, doesn't have an associated quake. So there are holes in the system.

Now getting back to sky quakes, the USGS has a search engine that allows the user to make their own quake KML, or just tabulate the data at text. Many options on the page:
earthquake.usgs.gov...
For the radius search, the lat/long is fed in decimal format, with "west" as a negative number.

I ran a search centered around Groom Lake for 100km. These are the magnitude 6 quakes.



The are around Area 12, which is where some high yield tests were done. For magnitude 5, there are more events:



You can use the USGS link provided to roll your own KML of quakes. If you want one I ran, here is every quake within 100km of Groom Lake in. IE and FIrefox don't recognize KML files for Google Earth, so you will have to save the file and open it yourself from Google Earth.
www.lazygranch.com...

Now sky quakes would be very shallow since they are not geological events. [Of course, there are shallow earthquakes too, but not all that common.] This link is a KML of quakes at 1km depth or less:
www.lazygranch.com/images/quakes/groom_lake_100km_1km_depth.kml

It seems that for an area with no shortage of sonic booms and live bombing, the shallow quakes are not all that plentiful. This gives me less confidence in sky quakes, at least those recorded on instrumentation, as being sonic booms. Or perhaps the very minor shaking doesn't make it to the public database.

reply to post by gariac


Once again you have presented very interesting information although I have not yet been able to open the USGS files. I have a couple of additional questions if you have the time to indulge me:

What's your take on the 1993 quake? It states that the Test Ban was in effect, so are you thinking just a regular old EQ, a large conventional explosion, or perhaps some skirting of the treaty?

In regards to the "sky quakes", is your opinion that they are terrestrial in origin with some sort of atmospheric component?

Regarding the 1993 quake, it was just a quake. [To paraphrase Freud, "Sometimes a cigar is just a cigar."] What I was doing is finding the quake first, then looking up the date on the test list. In the case of the 1993 quake, I didn't notice it was beyond the test ban treaty limit.

I ran the USGS search on all the days mentioned in the Caltech article. I picked Palm Springs as the center point, and searched for 200km. That is far enough to cover beyond Edwards. Only June 18, 1992 has quakes that show up on the USGS search. The only one that was shallow is shown here:



Google Earth apparently doesn't save the data in the box, but it was a magnitude 2.9 at 8:06:13 UTC, which would be about 6 minutes after midnight local time. The location is about 9km south of 29 Palms.

You can download the full file with 3 quakes on it here:
www.lazygranch.com/images/quakes/palm_springs_200km_june_18_1992.kml
Again, you need to save the file on your hard drive then open it with Google Earth.

Three conclusions here. One, the sky quake analysis done by Caltech is using events too weak to show up on the USGS server. The fact the server can miss a few nuclear explosions is proof enough that using quake data from the internet isn't sufficient for such analysis.

Two, using the Caltech analysis, the seismic disturbances are consistent with a high altitude sonic boom. Technically, this doesn't rule out some other event created the data. [In logic, there is a difference between "if" and "if and only if", i.e. conditional versus biconditional.]

A third conclusion is if you see the quake on the USGS, it is probably not from a sonic boom. Sonic booms can be detected, but are not strong enough for the USGS to report. Such chatter has appeared in forums in the past and now appears to be a dead end.

There are viewing events and sonic events. Most likely the person making the report saw or heard something. But you can't draw much from eyewitness or "earwitness" testimony, especially if they aren't an expert witness. Rather the only use for such reports is they give a time frame to start the analysis.

In a DSP class in college, we were given signals to analyze. Running the signals through various types of analysis, only one seems to contain something, while the others were noise. The assignment was intentionally tricky in that we were fed random noise to show that we could recognize random noise. Now how does this relate to the Caltech study? Well one they had their analysis program working, they should have run it through days when there were no detected sky quakes. If the analysis program detects nothing, that is also useful information. That is, the scheme is not prone to "false positives."

The article is from 6/30/2012. Basically "nothing to see here folks..just the Navy breaking the sound barrier...now just move along."

www.nbcsandiego.com...

Strange Sound Reported in San Diego

Residents from Chula Vista to Oceanside reported a large rumble around 12:45 p.m. Friday.

The mysterious sensation was described by some people as sounding like a door slamming while others said it was strong enough to rattle windows.

A check of the U.S. Geological Survey website showed no earthquake activity.

NBC 7 San Diego's Dagmar Midcap was in Del Mar at the time and described it as a "Sonic 'rumble'" She tweeted, "according to my contacts at USGS, not seismic but rather sonic."

Two months ago, when San Diegans heard a similar sound, there was evidence of chaff on weather radar. Chaff is a material sometimes emitted during military exercises.

On Friday, however, Tina Stall with the National Weather Service said there was no visible chaff in the area at the time the noise was reported. The mysterious sound had both residents and experts scratching their heads. Scripps Institution of Oceanography scientist Kristoffer Walker said he felt it too, and looked into microphones recorded from MCAS Miramar. Evidence from his research revealed an answer. "There was indeed an atmospheric tremor, or 'skyquake,'" Walker said. "The likely cause of these 'skyquakes' is routine military activity very far off the coast of San Diego (at least 50 miles away) in zones that are designated military training zones." Typically, we don't hear these "skyquakes." But when the wind reaches speeds of over 100 miles per hour, the sound can reach parts of San Diego, Walker said. A spokesperson from Camp Pendleton said Marines are not training with anything unusual. They often train with various military equipment and will be training with tanks both Saturday and Sunday. On Friday evening, the U.S. Naval Air Forces official Facebook page posted the following message regarding the mysterious boom heard around San Diego: “San Diego, it looks like the boom that was heard and felt today was likely due to some aircraft associated with the USS Carl Vinson (CVN 70) family day cruise. As part of a flight demonstration two F/A-18 aircraft went supersonic about 35 miles off the coast. Sorry for any inconvenience this may have caused. -- LT Aaron Kakiel, media officer.” So, according to the Navy, it appears Friday's San Diego boom mystery has finally been solved.