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Earthquake Swarms

Sept. 13 - Sept. 30: Intense Swarming at Long Valley Caldera

10/3/2019

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PictureSept. 13 rapid-fire swarm.
September has been a very active month for Long Valley Caldera. Starting on September 13, a fairly intense period of seismicity started primarily around the eastern section of Mammoth Lakes, which resides in the SSW section of Long Valley Caldera. The magnitudes were not large, not surpassing M3.0, but the quantity of events were substantial in the short period of time they occurred. Please click the title of this post or "read more" to see some information about recent swarming at Long Valley Caldera.

Picture
USGS EQ map for Sept. Seismicity at Long Valley
Long Valley Seismic Station Map
Starting on September 13, 2019, a fairly intense swarm of seismicity broke out just barely east of Mammoth Lakes. Mammoth Lakes resides within the infamous supervolcano along the SSW section of the caldera. The image above shows all reported earthquakes of all magnitudes from September 13 through September 30.

Swarming was intense but magnitudes were small, the largest being a M3.0 on September 25. Most of the seismicity was concentrated within specific "bursts" of rapid-fire swarming on September 13, 14, 15, 25, and 29. The biggest swarms were on September 13 and September 25 with the swarm on the 13th by far being the largest of the month.

From September 11 through September 30, there were a total of 856 earthquakes reported for this one location within Long Valley Caldera. 52 earthquakes reported were M2.0+ with only one M3.0. For the entire month of September, for the whole caldera, there were a total of 1,073 earthquakes reported.

Below is a time/depth plot of the reported earthquakes from these many swarms. The image just prior to the plot is the location of the plot "box".
Picture
Picture
Something quite interesting is that the September seismicity was non-linear in formation, meaning it appears local tectonics did not play a huge role in creating the swarms. Tectonics may still play a small part, but fluid migration from the magma system seems to be a more likely culprit.

The depth of all of the swarms combined is also interesting. Around 3/8 of the earthquake swarms were at 5km depth or deeper. The ceiling of the Long Valley magma system is also around 5km in depth. So it seems the swarming was occurring along the ceiling of the magma system and above it as well.

This can clearly be seen via the image below. Dots are earthquakes for seismicity from Sept. 11 through Sept. 30. This is a cross section of the earth in this location. Imagine you are underground and looking to the north while these earthquakes took place. You can tell it was occurring around the ceiling of the magma system. CLICK HERE to play around with this cross section plot yourself!
Picture
Next I will show some quick data pertaining to the swarms that made up the September increase in seismicity for Long Valley. For the two largest swarms, the Sept. 13 and Sept. 25 swarms, I will show a spectrogram "stream" from three of the closest stations since there were too many events and too little time to create custom plots for those two swarms.

Sept. 13 Swarm

This is the swarm that kicked off the entire swarming in this location for September. It was extremely energetic but only reached M2.9. Many earthquakes were also too small and too closely spaced to be located accurately. It is likely many hundreds of events occurred this day.

Sept. 13, 2019 swarm
 
Start of swarm: Sept. 13, 2019 at 02:35UTC
End of swarm: Sept. 13, 2019 at 12:25UTC (about 9 hours and 50 minutes for the main swarm on Sept. 13)
Total earthquake count: Likely 2x or 3x the amount reported. Earthquakes mentioned in this text are for specifically the time period stated above. Many more very small micro-quakes randomly occurred after this time period.
Reported count: For the time period stated above, USGS reported 294 earthquake events of all sizes. Please refer to the USGS EQ map button in the beginning of this post to see all reported earthquakes for all swarms mentioned on this page.
Largest reported earthquake of this swarm: M2.9 at 5.9km depth
Severity: Major one-day swarm
Closest seismic station to swarm: MEM in the NC network
Below is a video of a spectrogram "stream" from three of the closest stations. You can see there were far more than 294 events.

Sept. 14 Swarm

There was swarming basically all day on September 14. The main concentration of swarming started at about 12:52UTC and ended around 13:31UTC. The main concentration of swarming contained around 80 earthquakes of all sizes, many being very small.

The reported count for all of September 14 was a total of 81 earthquakes. Here are helicorder plots from the 3 closest stations to the swarm. Afterward, I will show seismic plots of some random events from this day.

Sept. 15 Swarm

Swarming was sporadic on September 15. There was a quick burst of around 10 tiny events for about 3 minutes at 03:11UTC. Small quakes occurred here and there until around 11:06UTC where around 15 micro-quakes struck until 11:13UTC.

The main seismicity this day started at 14:40UTC and ended around 14:51UTC. This main burst contained approximately 30 earthquakes with some striking in a very rhythmic pattern.

Below are the helicorder plots from this day and also the seismic plots to many of the events on September 15. The reported earthquake count for the entire day of September 15 was a total of 47 events.

Sept. 25 Swarm

The Sept. 25 swarm was the largest of September except for the Sept. 13 swarm. Below is some information, helicorder plots, and a video of a spectrogram stream from three of the closest stations. There were so many events I barely had time to count them all or make plots for them.

Sept. 25, 2019 swarm
 
Start of swarm: Sept. 25, 2019 at 04:33UTC
End of swarm: Sept. 25, 2019 at around 18:00UTC (about 13 hours and 27 minutes)
Total earthquake count: Likely 2x the amount reported. Earthquakes mentioned in this text are for specifically the time period stated above. Many more very small micro-quakes randomly occurred after this time period.
Reported count: For the time period stated above, USGS reported 179 earthquake events. Please refer to the USGS EQ map button in the beginning of this post to see all reported earthquakes for all swarms mentioned on this page.
Largest reported earthquake of this swarm: M3.0 at 5.3km depth
Severity: Major one-day swarm
Closest seismic station to swarm: MEM in the NC network

Sept. 29 Swarm

Sept. 29, 2019 swarm
 
Start of swarm: Sept. 29, 2019 at 08:47UTC
End of swarm: Sept. 29, 2019 at 09:51UTC (about 1 hour and 4 minutes)
Total earthquake count: ~115 micro-quakes of all sizes
Reported count: For the time period stated above, USGS reported 26 earthquake events. Please refer to the USGS EQ map button in the beginning of this post to see all reported earthquakes for all swarms mentioned on this page.
Largest reported earthquake of this swarm: M2.2 at 4.5km depth
Severity: Minor
Closest seismic station to swarm: MEM in the NC network
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    This blog page is solely for interesting earthquake swarms that occur in locations other than the ones I already have posted. Pretty much any earthquake swarm I am interested in, that cannot be placed on other pages, will be placed here. Please click the title of each post or "read more" to view each swarm.

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  • Home
  • Yellowstone
    • Yellowstone Blog
    • 2008-2009 Yellowstone Lake Dike Intrusion
    • Rapid-Fire Swarms 2014-2018
    • Steamboat Geyser Eruptions >
      • Steamboat Eruptions 2020
      • Steamboat Eruptions 2019
      • Steamboat Eruptions 2018
  • Hawaii
    • Hawaii Blog
    • Hawaii Spasmodic Tremor
    • 2018 Kilauea-LERZ Eruptions
  • How To...
    • ...Retrieve Seismic Data
    • ...read webicorders/helicorders and seismic plots
    • ...Understand Spectrograms
    • ...USE SWARM Software
    • ...use jamaseis program
    • ...use waves program
    • ...understand UTC
    • ...Read/Create GPS Deformation Charts
    • ...use s.w.a.r.m. program (OLD)
  • Seismic Events
    • Event Examples
    • Exotic Events
    • Whale Calls
    • Cascade Volcanoes' Low Frequency Events
  • Seismo-Blog
  • Other Seismic Blogs
    • Quake Swarms
    • United States
    • East Coast, USA
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  • Links
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  • Contact
  • Test Your Knowledge!
  • Lucas Andrew Ferraiuolo (Pro Pics)
  • Garbage Trucks?!