January 6, 2012
by Kate Allstadt
Though Mount Rainier looks serene and quiet viewed on a nice day the Visitors Center, it is actually a very active and noisy place. Regular tectonic earthquakes occur several times a month, but glacier quakes, avalanches, wind, landslides, icefalls and rowdy mountaineers also shake the ground and are picked up by our seismometers. There is an astounding amount of seismic activity on the seismic stations high on the mountain any day of the year (for an example, view Webicorders of RCS, STAR or RCM on this PNSN site). The image below shows a sampling of what these different signals look like (click to zoom in). The left side of the figure shows the seismograms, the right side shows the frequency content of each seismogram.
Over the past few years, however, a new type of seismic signal has emerged: sequences of repeating earthquakes. One of these sequences started a few days ago on December 28th and continues up to the present. These earthquakes are tiny, smaller than Magnitude 0. Earthquakes this small are usually ignored because they are too small to locate or do anything useful with. What makes these quakes special is that the same earthquake occurs over and over again, up to thousands of times. The plot below is a timeline showing the occurrence of the repeating earthquakes in the current sequence. Each horizontal line represents one set of earthquakes with near-identical seismograms. Each circle represents when an earthquake occurred. The number at right indicates the number of earthquakes in each set.
When more than one earthquake have nearly identical seismograms, it means that the source is the same for both and their location remains stable over time. Though individual earthquakes are much too small to locate, when we align the seismograms of hundreds of them and add them together, the noise is canceled out, making the seismograms clear enough to get a location. The locations of the three largest sets of events in the current sequence are shown on the Google Earth image below. The blue triangles are PNSN seismic stations, Paradise is at the bottom of the image (click to enlarge):
The current sequence and those in the past have shown correlation with passing storm systems, spring melting, fall snowfall, and other weather transitions throughout the year. This points to changes in glacier behavior as a likely culprit. Glacier behavior can be modulated by the weather and they can also make a lot of noise. Glaciers actually generate most of the seismicity on the mountain. Repeating earthquakes have been observed on other glaciers around the world so it is not a revolutionary idea. However, as any Western Washington resident will tell you, there are nearly always weird weather transitions going on, so the correlation weather with these earthquake sequences could be purely coincidental. There are many other arguments against a neat and tidy classification as a glacial source. In addition, hydrothermal activity can generate repeating earthquakes, as can the movement of magma prior to and during eruptions. The possibility of a hydrothermal or magmatic source cannot yet be completely eliminated in this case. The good news is that these sequences have been happening on and off for the last two years as well as a few times in the 1990's and there hasn't been any volcanic activity, and there are no other signs that the volcano in our back yard is rewakening.
In the meantime, we continue to monitor the activity, hypothesize about the source, and try to test these hypotheses with our limited resources. The rugged conditions on Mount Rainier makes testing difficult. Last spring we planned a field campaign to deploy instruments to test the glacial source hypothesis. We carried heavy instruments and batteries on the backs of graduate students high up on the mountain and deployed them. But Mount Rainier put up a fight, giving us an extra month of bad weather, blowing a seismometer off Disappointment Cleaver with a freak gust of wind, and nearly hitting another expensive instrument with a big landslide only for it to be eaten by a crevasse later that month before we could safely retrieve it. Round 1 goes to Rainier.
- Seismic signals generated by the March 22nd Oso Landslide
- Legacy web site content returns
- Ice avalanches on Cascade volcanoes
- A New View On What's Shaking on the Cascade Volcanoes
- Seismic Spectrograms - A new way to look at wiggles
- The final football game analysis
- The Football Game Experiment Continues
- Seismic Game Analysis
- PNSN Earth-shaking Seahawks Experiment
- Large Mount Baker debris Avalanche this fall
- March (2)
- February (3)
- January (4)
- October (1)
- September (1)
- August (1)
- June (1)
- April (3)
- March (4)
- February (1)
- January (2)
- December (1)
- November (2)
- October (3)
- September (1)
- August (3)
- July (2)
- June (4)
- May (4)
- April (2)
- The wech-o-meter takes over all of Cascadia
- Keystone Cops: Italy prosecutes seismologists for failure to predict deadly quake
- UFOs in eastern Washington? No, rather UTEs (Unidentified Terrestrial Events)
- New Sodo Seattle Liquefaction Array Installed
- Why we should constantly watch the deformation of the seafloor
- Mystery chirp near Newberry Volcano
- Planting seismographs causes earthquakes? or maybe ice-quakes?
- Tunneling rumbles south under Capitol Hill
- 15 years of mostly silent magma inflation near Three Sisters, Oregon
- Mount Hood earthquake swarm of Feb 23, 2012
- Web glitches: duplicate (and even triplicate!) earthquakes
- How earthquake magnitude scales work
- Mine blast masquerades as volcanic tremor
- The Spokane Swarm about 10 years ago
- Another hum around Mount St. Helens
- Slow slip: A new kind of earthquake under our feet
- PNSN and social media
- 3am M3.4 earthquake in St. Helens Seismic Zone
- The wrong kind of volcano noise
- Fast chatter on Rainier an hour ago
- Can slush-mageddon trigger earthquakes?
- Rainier Repeating Earthquakes Update and Comparison with Weather Patterns
- 22-minutes drumbeat icequakes(?)
- Mount Rainier popping away
- Repeating Earthquakes on Mount Rainier - are glaciers the culprit?
- Debunking another SEC football myth by the PAC-12
- One year ago, Seattle Seahawks 12th Man Earthquake
- The odds this year of a megaquake on the Pacific Northwest coast
- Is the plague of great earthquakes this decade a sign of increased danger?
- Nile Valley landslide talks to PNSN seismologists
- Good vs evil in central US earthquake hazard analysis
- Why does a volcano scream?
- Predicting big quakes from patterns of little ones
- 1-hour warning for Japanese M9 earthquake?
- Sound Transit train under Interlaken keeps a rollin'
- Invisible changes under the hood at the PNSN
- Sound Transit Tunneling Noise
- "Visionary" toads
- Earthquake early warning in the PNW
- November (1)
- December (13)