#seismogram

[thesobsister]

“Seismogram of the 1906 San Francisco earthquake, recorded at the Chabot Observatory in Oakland.”

[earthstory]

Subtle shaking

The city of Pasadena, California is an interesting place. It is home to the USGS earthquake scientists who plan and coordinate emergency response for the Los Angeles area, it is just down the road from the Jet Propulsion Laboratory, and every year on New Year’s Day a suite of flower-bearing floats marches down Colorado Boulevard through the city. Combining several of those themes – this float in 2005 was produced by JPL and features a whole bunch of their spacecraft (How many can you ID?). It turns out, these floats also can be used for the other topic – testing seismic sensors.

The City of Pasadena has several fiber optic cables in their boundary that are currently not being used. A team led by Caltech/USGS scientists plugged into one of those cables and designed a computer algorithm that can turn it into a brand new type of sensor for seismic activity. As waves of energy move through the ground, the position of the fiber optic line changes, leading to detectable changes in the wavelength and frequency of the light moving through them. Measurements of these minute changes can be then fed to a computer and turned into a measurement of shaking.

The team of scientists originally set their system up last year, but they didn’t experience any nearby earthquakes they could use to test the system. But, on New Year’s Day, traffic around the city is low because everyone’s at the parade, and the only thing moving is the floats down the street. As seen in these photos, the system was able to detect the tiny vibration of the floats moving along the ground, the bands as they marched, and even the vibration of the motorcycle riders who head out in front of the floats to clear the path.

Several cities with these sorts of fiber optic networks have begun setting up systems to use them as sensitive seismic detectors; apparently the main issue is computer memory and processing power, but if you have that, then fiber optic lines in a city can be used as a brand new type of seismograph. Eventually they may be deployable elsewhere, in places where it is difficult or damaging to use traditional seismic detection systems, such as in the arctic or in the ocean.

The loudest band in 2020 was from Southern University and A&M College, a the largest HBCU in the state of Louisiana.

-JBB

Image credits: The post author (photo) and the paper (below) Original paper: https://doi.org/10.1785/0220200091 Reference: https://bit.ly/2XW75qz

[dragoni]

Strange waves rippled around the world, and nobody knows why

Instruments picked up the seismic waves more than 10,000 miles away—but bizarrely, nobody felt them.

The low frequency seismic waves weren’t caused by an earthquake. “A submarine eruption could produce these low rumblings, but evidence for such an event has yet to materialize.” It’s still a mystery!

On the morning of November 11, just before 9:30 UT, a mysterious rumble rolled around the world.

The seismic waves began roughly 15 miles off the shores of Mayotte, a French island sandwiched between Africa and the northern tip of Madagascar. The waves buzzed across Africa, ringing sensors in Zambia, Kenya, and Ethiopia. They traversed vast oceans, humming across Chile, New Zealand, Canada, and even Hawaii nearly 11,000 miles away.

“These waves didn't just zip by; they rang for more than 20 minutes. And yet, it seems, no human felt them.”

“They're too nice; they're too perfect to be nature”, Anthony Lomax, an independent seismology consultant

Only one person noticed the odd signal on the U.S. Geological Survey's real-time seismogram displays. An earthquake enthusiast who uses the handle @matarikipax saw the curious zigzags and posted images of them to Twitter. That small action kicked off another ripple of sorts, as researchers around the world attempted to suss out the source of the waves. Was it a meteor strike? A submarine volcano eruption? An ancient sea monster rising from the deep?

“I don't think I've seen anything like it,” says Göran Ekström, a seismologist at Columbia University who specializes in unusual earthquakes.

However, there was no big earthquake kicking off the recent slow waves. Adding to the weirdness, Mayotte's mystery waves are what scientists call monochromatic. Most earthquakes send out waves with a slew of different frequencies, but Mayotte's signal was a clean zigzag dominated by one type of wave that took a steady 17 seconds to repeat.

So what is actually causing the super-slow vibrations at Mayotte? A submarine eruption could produce these low rumblings, but evidence for such an event has yet to materialize.

“It's like a music instrument,” says Jean-Paul Ampuero, a seismologist at the Université Côte d'Azur in France. “The notes of a music instrument—whether it's grave or very pitchy—depends on the size of the instrument.”

[earthstory]

In this video you can watch as sensitive seismograms around the United States detect the up and down motion triggered by waves from the California Earthquake moving around the planet.

[earthstory]

If you're looking for something to do with your day, here's 5 minutes where you can learn to read a seismogram.

[earthstory]

Reading a seismogram

This is the actual seismogram recorded by a seismometer during a magnitude 5.0 earthquake on Jan Mayen island in 1995. There’s a lot of information in a graph like this if you know how to read it.

A classic seismogram is made by a pen held by a weight in a fixed position on top of a spinning roll of paper. During a quake, the inertia of the weight keeps the pen from moving, while the paper drum moves due to the waves. The pen then marks the drum as it moves back and forth. Modern instruments detect these waves electronically, but the principle is the same.

In this plot, time moves from left to right; the left side starts and the right side finishes. 3 different features stand out. The first hint of the quake is a small pulse of energy that decays away with some fine structure to it. Then, there’s a second pulse of energy, slightly less intense than the first. Just after this second pulse is when the biggest, most intense shaking starts.

This is the classic sequence of waves created in an earthquake. The fastest moving waves are called p-waves, a pressure wave moving through the earth. The next to arrive is an s-wave, a shear wave also moving through the earth. Finally, the largest pulse of energy arrives in the form of surface waves known as Rayleigh and Love waves. The surface waves are where the largest ground motions take place and when most of the damage is done. They also have a lower frequency than the p and s waves, meaning that the wave arrivals become more spread out.

The time between waves arriving at a seismic station depends on how far the station is from the quake. The farther away the station is, the bigger the difference in arrival times. The difference between the p wave arrival and surface wave arrivals can be as little as a fraction of a second for earthquakes very nearby and as long as tens of minutes for earthquakes far away.

Each wave bounces and refracts off slightly different regions within the earth, leading to the complex structure in each portion. That complexity can be used by computers as a way of measuring actual differences inside the Earth.

-JBB

Image credit: https://www.flickr.com/photos/rockbandit/309794495

Read more: http://www.geo.mtu.edu/UPSeis/reading.html http://www.iris.edu/hq/files/programs/education_and_outreach/aotm/17/SeismicSignatures_SeismogramMSH%20addition.pdf

[earthstory]

Well I can’t not share this there’s a seismogram on the very front of it. I’ll let the caption give details:

The earthquake of M5.8, the largest on the Korean Peninsula, occurred in Korea, which was called the "Earthquake Safety Zone," in 2016. Gyeongju City suffered a great deal of damage due to the ineffectiveness of the Korean government and the insecurity of safety. By the year 2017, there have been about 500 earthquakes, and Koreans are living in fear of an earthquake that will happen anytime soon.

Magnitude Rituals is an image of praying that no earthquake will happen in Korea. The former Korean peninsula country, which was a farming country, had a ritual to pray for rain in the sky every drought season. In this regard, this work expresses a sacrifice to wish an earthquake not to happen. The image consists of two frames. The image on the left represents the progress of the ritual, and the image on the right represents the situation where the value of the graph representing the earthquake converges to zero and the process of the earthquake is reversed.

What I wanted to pursue in my work was the communication of messages in contrast to Korean tradition and shamanic images and sophisticated mathematical graphics. On the surface, it is an image that seems to have nothing to do with each other, but as the ritual process progresses, it expresses that the figure indicating the earthquake in the graph is stopping, so that the audience can appreciate the image and slowly understand it.

[earthstory]

Reading a seismogram This is the actual seismogram recorded by a seismometer during a magnitude 5.0 earthquake on Jan Mayen island in 1995. There’s a lot of information in a graph like this if you know how to read it. A classic seismogram is made by a pen held by a weight in a fixed position on top of a spinning roll of paper. During a quake, the inertia of the weight keeps the pen from moving, while the paper drum moves due to the waves. The pen then marks the drum as it moves back and forth. Modern instruments detect these waves electronically, but the principle is the same. In this plot, time moves from left to right; the left side starts and the right side finishes. 3 different features stand out. The first hint of the quake is a small pulse of energy that decays away with some fine structure to it. Then, there’s a second pulse of energy, slightly less intense than the first. Just after this second pulse is when the biggest, most intense shaking starts. This is the classic sequence of waves created in an earthquake. The fastest moving waves are called p-waves, a pressure wave moving through the earth. The next to arrive is an s-wave, a shear wave also moving through the earth. Finally, the largest pulse of energy arrives in the form of surface waves known as Rayleigh and Love waves. The surface waves are where the largest ground motions take place and when most of the damage is done. They also have a lower frequency than the p and s waves, meaning that the wave arrivals become more spread out. The time between waves arriving at a seismic station depends on how far the station is from the quake. The farther away the station is, the bigger the difference in arrival times. The difference between the p wave arrival and surface wave arrivals can be as little as a fraction of a second for earthquakes very nearby and as long as tens of minutes for earthquakes far away.  Each wave bounces and refracts off slightly different regions within the earth, leading to the complex structure in each portion. That complexity can be used by computers as a way of measuring actual differences inside the Earth.  -JBB Image credit:  https://www.flickr.com/photos/rockbandit/309794495 Read more: http://www.geo.mtu.edu/UPSeis/reading.html http://tinyurl.com/o74xor4