8/18 - 8/24: A Week of Swarming and Minimal Spasmodic Tremor

Moderate spasmodic tremor under Hawaii on August 23, 2019.

Hey guys! In this post I will show some quick data pertaining to an energetic swarm that broke out under Pahala, Hawaii, recent spasmodic tremor, and a deep M4.2 under the Loihi Seamount off the coast of Hawaii. Please click the title of this post or "read more" to continue...

Mauna Loa is currently experiencing heightened volcanic unrest, including increasing seismicity and uplift. Therefore, the alert level has been raised to ADVISORY and the aviation color code has been raised to YELLOW. Please CLICK HERE to keep up to date with recent alert postings by USGS/HVO for Mauna Loa’s potential eruptive activity.

Also, as seen in the picture above, a pond of water has been constantly growing at the bottom of Halema’uma’u crater inside of Kilauea Caldera. It was originally thought to be rainwater, but the fact that it is constantly growing with the lack of enough rain does point to the rising of the water table. This could spell trouble for Kilauea in the near future. To keep an eye on this growing pond, keep checking the Volcano Watch articles put out by HVO which can be found HERE. Also, you can keep an eye on it yourself if you monitor the webcam at Kilauea which can be found HERE.

Now, if you wish to understand what volcanic spasmodic tremor is, and how it relates to ongoing volcanic unrest in Hawaii, please CLICK HERE.

USGS EQ Map for Hawaii 8/18 - 8/24

Hawaii Seismic Station Map

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Pahala Earthquake Swarm

Only reported events are shown here. The total count of events is much higher.

Starting primarily on August 18, 2019, a deep earthquake swarm broke out under Pahala, Hawaii. Coincidentally, the location and depth of this swarm indicates it is likely occurring where spasmodic tremor occurs: within the mantle plume conduit.

The depths of the earthquakes in this swarm ranged from 30km to 50km in depth and the largest reported event of the swarm was a M3.2 event at 35.7km in depth. Although only 112 earthquakes were reported, it is likely over 200 actually occurred as part of this swarm. The swarm is still ongoing at the time of writing this (August 25, 2019 at 01:41UTC), however it has diminished substantially. Most of the swarm occurred between August 18 and August 23.

Station TRAD was one of the best stations in the area to detect these events. Check out how many earthquakes there are! Almost every earthquake you see struck deep under Hawaii within the mantle, right where spasmodic tremor occurs. Some spasmodic tremor can also be seen on the helicorders below. Can you spot them? Below are helicorders in slideshow format from TRAD:

Now, I will quickly show some seismic plots of random events as part of this swarm. Since station TRAD is one of the better stations to detect these events, I will use that station for the plots below. I do not show every single earthquake in this swarm, but I do show around 20 of them. Times are in UTC of course. So, if you wish to see how large these were, or if any were reported, please check the USGS EQ map button in the beginning of this post and compare the times.

Spasmodic Tremor

Although seismicity skyrocketed for the location of where spasmodic tremor occurs, spasmodic tremor itself was almost non-existent for the week of 8/18 through 8/24. For that whole week there were only 3 minor events and 1 moderate event. I will show those now, along with the usual audio.

The seismic audio you hear was taken from station TRAD, one of the best stations to use for monitoring spasmodic tremor. Also, the audio is sped up to allow it to be heard better. All audio is taken from IRIS and I suggest using headphones! However, be wary of the audio just in case!

Event 1

Event 1 occurred on August 21, 2019 at 04:56UTC. It was very minor and lasted approximately 24 minutes.

Event 2

Event 2 occurred on August 21, 2019 at 06:40UTC. It was very minor and lasted around 24 minutes. How come spasmodic tremor sometimes lasts around 24 minutes? Strange...

Event 3

Event 3 occurred on August 21, 2019 at 09:18UTC. It was minor and lasted approximately 32 minutes.

Event 4

Event 4 occurred on August 23, 2019 at 10:20UTC. It was moderate and lasted around 48 minutes.

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M4.2 Under Loihi Seamount Volcano

Loihi M4.2 from one of the closest stations.

On August 22, 2019 at 14:33UTC a M4.2 earthquake struck under the southern flank of the Loihi Seamount at 46.0km in depth. The M4.2 under Loihi is the largest to strike near or under the Big Island since the M4.5 under Hilo Bay on August 12, 2019. This recent M4.2 under Loihi is also the largest to strike the seamount since the M5.3 struck at 40.3km in depth to the east of Loihi on June 5, 2013.