February 28, 2013
by Kate Allstadt
Though the residents of Gold Bar may not have noticed, tiny earthquakes have been popping off fairly regularly just a few kilometers east of town (and 11 kilometers below it) over the past few months. A total of about 300 quakes have occurred here since October, though only 100 of these were big enough to make it into the PNSN catalog, the rest were too small to show up on enough seismic stations.
Only one person reported feeling any of these earthquakes, they felt weak shaking from the largest of the swarm, a M2.4 on December 28th. The vast majority of the quakes have been tiny, only 4 have been above magnitude 2, the rest were magnitude 1’s and lower.
Earthquakes that occur close to each other have very similar waveforms so we used the waveform shape of the known events as a template to scan through the continuous seismic data and pull out the rest of the smaller quakes that did not make it into the PNSN catalog. The plot below shows a subset of these events, highlighting just how similar the waveforms are to each other. Red events are events that made it into the PNSN catalog, black ones were too small, the time scale is in seconds.
When we look at patterns of event occurrence using this more complete dataset (below), we see that these little quakes have been popping off nearly continuously since October, with some sporadic bursts of activity, particularly in December.
A high resolution relocation of the events relative to each other using a method called “double difference relocation” shows that the earthquakes fall more or less on a oval-shaped patch ~1.5 km tall and ~0.8 km wide that dips steeply, about 70°, toward the southwest. There is no obvious migration in the locations over time to suggest fluid migration, sometimes a cause of swarm-like seismicity, so what is it? Perhaps Hollywood has some answers?
- Great ShakeOut, Great success!
- The Great ShakeOut 2014 is Tomorrow!
- Three Cascadia ETS events in past month??
- Is Mount St. Helens seismicity increasing?
- Warm weather triggers snow avalanches at St. Helens
- Seismic recordings of a gas explosion in North Bend, WA
- 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
- October (2)
- September (1)
- July (1)
- May (1)
- April (1)
- 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)