Tag: seismology

Reanalysis of Apollo seismic data finds 22,000 previously undetected quakes

2:50 pm

By taking a new look at the data from the seismometers placed on the lunar surface by the Apollo missions during the 1970s, Keisuke Onodera of the University of Tokyo was able to find approximately 22,000 previously undetected quakes, almost tripling the rate of seismic activity on the Moon. From the paper’s abstract:

In the 1970s, two types of seismometers were installed on the nearside of the Moon. One type is called the Long-Period (LP) seismometer, which is sensitive below 1.5 Hz. The other is called the Short-Period (SP) seismometer, whose sensitivity is high around 2–10 Hz. So far, more than 13,000 seismic events have been identified through analyzing the LP data, which allowed us to investigate lunar seismicity and its internal structure.

On the other hand, most of the SP data have remained unanalyzed because they include numerous artifacts. This fact leads to the hypotheses that (a) we have missed lots of high-frequency seismic events and (b) lunar seismicity could be underestimated.

To verify these ideas, I conducted an analysis of the SP data. … I discovered 22,000 new seismic events, including thermal moonquakes, impact-induced events, and shallow moonquakes. Among these, I focused on analyzing shallow moonquakes—tectonic-related quakes. Consequently, it turned out that there were 2.6 times more tectonic events than considered before. Furthermore, additional detections of shallow moonquakes enabled me to see the regionality in seismicity. Comparing three landing sites (Apollo 14, 15, and 16), I found that the Apollo 15 site was more seismically active than others. These findings can change the conventional views of lunar seismicity.

The data also suggests the northern hemisphere is more active than the southern.

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Rotation of Earth’s inner core oscillates back and forth over time compared to surface

8:09 pm

The uncertainty of science: New data now suggests that the Earth’s inner core is no longer rotating faster than the planet’s outer layers — as had been measured in 1996 — but is now actually rotating slower.

Research published in 1996 was the first to propose the inner core rotates faster than the rest of the planet — also known as super-rotation — at roughly 1 degree per year. Subsequent findings from Vidale reinforced the idea that the inner core super-rotates, albeit at a slower rate.

Utilizing data from the Large Aperture Seismic Array, a U.S. Air Force facility in Montana, researcher Wei Wang and Vidale found the inner core rotated slower than previously predicted, approximately 0.1 degrees per year. The study analyzed waves generated from Soviet underground nuclear bomb tests from 1971-74 in the Arctic archipelago Novaya Zemlya using a novel beamforming technique developed by Vidale.

The new findings emerged when Wang and Vidale applied the same methodology to a pair of earlier atomic tests beneath Amchitka Island at the tip of the Alaskan archipelago — Milrow in 1969 and Cannikin in 1971. Measuring the compressional waves resulting from the nuclear explosions, they discovered the inner core had reversed direction, sub-rotating at least a tenth of a degree per year.

This latest study marked the first time the well-known six-year oscillation had been indicated through direct seismological observation.

What the data really suggests is that the core’s rotation is somewhat independent of the upper layers, so that each can vary relative to each other. This difference must carry with it some profound consequences, related to the length of the day, earthquakes, plate tectonics, and any number of other seismic phenomenon, but at the moment too little is known to tie everything together.

A bit of trivial for my readers: In 2004 I wrote an article for Natural History describing the discovery that the core rotated faster than the Earth’s upper layers. It was that article that prompted John Batchelor to invite me to appear on his show for the first time. The rest is history.

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InSight detects 5 magnitude Martian quake, the largest detected so far

9:39 am

The seismometer deployed by the Martian lander InSight has now detected its largest quake yet on Mars, with an estimated magnitude of 5.

NASA’s InSight Mars lander has detected the largest quake ever observed on another planet: an estimated magnitude 5 temblor that occurred on May 4, 2022, the 1,222nd Martian day, or sol, of the mission. This adds to the catalog of more than 1,313 quakes InSight has detected since landing on Mars in November 2018. The largest previously recorded quake was an estimated magnitude 4.2 detected Aug. 25, 2021.

The timing was very fortunate. Only three days later the power being generated by InSight’s dust-covered solar panels dropped too low, and the lander went into safe mode. Though its mission has been extended through the end of this year, the inability of the solar panels to produce energy because of dust has been predicted to shut down operations sooner. While it might be possible to restart science operations, this most recent safe mode situation could very well be that moment.

Meanwhile, scientists will analyze the data of this most recent large quake to attempt to pinpoint its location. They will also study it to gain a better understanding of the interior structure of Mars.

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InSight scientists publish paper describing last year’s big Martian quakes

9:43 am

Figure 5: global map of located Martian quakes

The InSight science team has now published a paper [pdf] describing in detail what they gleaned from the two large earthquakes the lander detected on Mars last year, measuring 4.1 and 4.2 magnitudes.

The map above, figure 5 of their paper, marks their best estimate of the quakes’ locations, dubbed S0976a and S1000a. From the caption:

Mars surface relief map showing InSight’s location (orange triangle), the location of other located mars-quakes (magenta dots) that cluster around 30° distance, close to Cerberus Fossae, and S0976a, located within Valles Marineris just north of Sollis Planum. Because no back azimuth can be determined for S1000a, its location is predicted to be somewhere within the shaded region between 107° and 147° from InSight. The event’s preferred distance (116°) is marked with the white dashed line. The black dotted lines mark radii around InSight up to 80°.

A review of Mars Reconnaissance Orbiter (MRO) high resolution images of that part of Valles Marineris where S096a occurred will likely uncover a whole bunch taken since last August, all attempting to detect any actual surface changes produced by quake. I think I’ll do that review, and see if I can spot something.

The paper also notes the uniqueness of S1000a, which lasted 94 minutes, the longest so far detected on Mars. The complexity of its signal also makes locating it difficult, though the most likely possible locations — indicated by the white dashed line in the map above — crosses through the Tharsis Bulge where Mars’ biggest volcanoes are found.

Sadly, InSight will likely shut down before the end of this year due to loss of power, so until another seismometer is sent there no further Martian quakes will be detected.

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InSight detects additional 3+ magnitude quakes on Mars

8:23 am

Martian quake map as seen by InSight

According to a JPL press release today, the seismometer on the Mars lander InSight detected two new 3+ magnitude quakes in March, both coming from the Cerberus Fossae region, the same region where the bulk of seismic activity has so far been pinpointed on Mars.

The map to the right was presented several weeks ago at the 52nd Lunar and Planetary conference, and could possibly include one of these two new quakes. The timing however of these March quakes is significant:

The new quakes have something else in common with InSight’s previous top seismic events, which occurred almost a full Martian year (two Earth years) ago: They occurred in the Martian northern summer. Scientists had predicted this would again be an ideal time to listen for quakes because winds would become calmer. The seismometer, called the Seismic Experiment for Interior Structure (SEIS), is sensitive enough that, even while it is covered by a dome-shaped shield to block it from wind and keep it from getting too cold, wind still causes enough vibration to obscure some marsquakes. During the past northern winter season, InSight couldn’t detect any quakes at all.

They are beginning to use the lander’s scoop to cover the seismometer and its communications tether with sand to protect both from the wind and temperature fluctuations. Once done they hope to be able to detect quakes during the entire Martian year, though this ability will be further limited by a reduction in power.

Despite the winds that have been shaking the seismometer, InSight’s solar panels remain covered with dust, and power is running lower as Mars moves away from the Sun. Energy levels are expected to improve after July, when the planet begins to approach the Sun again. Until then, the mission will successively turn off the lander’s instruments so that InSight can hibernate, waking periodically to check its health and communicate with Earth. The team hopes to keep the seismometer on for another month or two before it has to be temporarily turned off.

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Quakes by InSight indicate Mars’ interior is active

1:01 pm

Cerberus Fossae

The first seismic results from InSight’s seismometer now show that the interior of Mars is active, with regular moderately-sized quakes.

The Seismic Experiment for Interior Structure (SEIS) instrument – a seismometer developed by an international consortium under the leadership of the French space agency CNES – recorded a total of 174 seismic events between February and September 2019. Twenty of these marsquakes had a magnitude of between three and four. Quakes of this intensity correspond to weak seismic activity of the kind that occurs repeatedly on Earth in the middle of continental plates, for example in Germany on the southern edge of the Swabian Jura hills.

Although only one measurement station is available, models of wave propagation in the Martian soil have been used to determine the probable source of two of these quakes. It is located in the Cerberus Fossae region, a young volcanic area approximately 1700 kilometres east of the landing site.

Cerberus Fossae is a land of cracks and linear depressions located between the giant volcanoes, Elysium Mons to the north and Olympus Mons to the east. It is believed those fissures were caused by the rise of those volcanoes, stretching the crust and cracking it.

This new data from InSight strengthens this theory.

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Mapping the inside of Mt St. Helens

9:37 am

A new array of seismometers, combined with a series of planned explosions, will be used to map the interior of the Mt. St. Helens volcano to a depth of eighty kilometers or fifty miles.

To get the job done, starting next week roughly 65 people will fan out across the mountain to deploy 3,500 small seismometers along roads and back-country trails. They will drill 24 holes some 25 metres deep, drop in industrial explosives used for quarrying, and refill the holes (see ‘Under the dome’). The plan is to detonate the explosives in separate shots over four nights. Each blast will shake the ground as much as a magnitude-2 earthquake.

Results from the active blasts will be combined with the passive seismic part of the experiment, which is already under way: 70 larger seis­mometers around the mountain are measuring how long waves from natural earthquakes take to travel through the ground. Their data can be used to probe as far as 80 kilo­metres down, says Vidale.

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The manslaughter trial of six scientists and one government official continued yesterday in Italy over their reassurances to the public prior to a deadly earthquake in 2009.

1:53 pm

The manslaughter trial of six scientists and one government official continued yesterday in Italy over their reassurances to the public prior to a deadly earthquake in 2009.

Guido Bertolaso, former head of the Department of Civil Protection and De Bernardinis’s direct superior, had not been indicted and was originally expected to appear as a witness. But a few weeks ago a wiretap revealed that he had apparently set up the meeting to convey a reassuring message, regardless of the scientists’ opinion. He also seemed to be the source of the “discharge of energy” statement. He thus found himself under investigation and, at the beginning of the hearing, he was officially notified that he too may soon be formally indicted for manslaughter.

Bertolaso was asked by the prosecutor to explain that telephone conversation. He defended himself by saying that by defining the meeting as a “media move”, he was not trying to downplay risks but rather to put some order into the contradictory information that was reaching the citizens in those days. In particular, he referred to Giampaolo Giuliani — a laboratory technician and amateur seismologist who was alarming the population with claims that a major shock was coming — and to a newspaper article that had misquoted some Civil Protection experts and stated that the shocks would soon be over. The meeting, he said, was meant to make clear that both were wrong and that no deterministic prediction could be made. [emphasis mine]

This increasingly appears to be another case of science being corrupted by politics.

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