Low-Frequency Event near Mary Lake, Yellowstone??? 2018/09/03

The seismogram and spectrogram plot above shows a possible low frequency event that occurred somewhere near seismic station YML, Mary Lake from 9:29UTC to 9:32UTC September 3, 2018. The first event, right before the low frequency earthquake, does not appear to be an actual earthquake. I at first thought that this "tremor" looked like wind, and it actually resembles wind in many ways. However wind cannot send a specific signal over miles and miles. Don't know what I mean? Please continue by pressing "read more".

Distance from YML to B950: about 8.25 miles.

Above is Google Earth, showing the distance from YML to B950 is about 8.25 miles. Why is that important? Well this one unknown "tremor" event, that occurred before the low frequency earthquake, appeared on only two seismic stations within the entire WY network: YML and B950. I first thought it was surface noise, but then I noticed the travel time from YML to B950 and the P wave arrivals conclude this was an actual seismic event. Of course it was not major, only maxing out at about 2,000 amplitude count. It also did not carry the characteristics required to label it "harmonic tremor". However it does appear to be a tremor of some sort, carrying a mid-range frequency.

Another view of the "tremor" that took place just prior to the low frequency earthquake. Notice it peaks at about 15HZ? Very odd!

The two images above, which have no caption, are of the low frequency earthquake that occurred right after the strange "tremor" event. You can tell this can most likely be categorized as a low frequency earthquake. Notice it barely exceeds 15HZ and appears to have dominant frequencies around 5-10HZ? In retrospect, most high frequency tectonic earthquakes can exceed 25HZ, even at small magnitudes!

The two images directly above show one other earthquake that occurred just a minute or so after the low frequency earthquake. I attempted to locate the P wave (always marked with a black line on WAVES) on YML and B950 to prove this was also not surface noise. If the weird "tremor" event that occurred before the LF quake, and this earthquake shown in the two images directly above, were surface noise then it would not travel from YML to B950 in 2-3 seconds. 2-3 seconds is about the travel time it would take for seismic waves to reach B950, if generated from near Mary Lake.

Now how do we know the odd "tremor" event in the beginning is not just a teleseism? Well usually a teleseism would, 1. carry a lower frequency, and 2. appear on MCID. Seismic station MCID, Moose Creek, Idaho, resides just on the southwestern tip of Yellowstone national park. It is one of the best seismic stations at Yellowstone for detecting teleseisms (global distant earthquakes usually magnitudes 5.5 and above). But even so, let's check MCID and compare it to YML to see if it was a teleseism:

For this one image: YML (top webicorder) and MCID (bottom webicorder) are both set to the same time frame and period. If it were a teleseism, the seismic signals would have appeared on both seismic stations around the same time.

Here in the WAVES seismic program, I have B950 (top), MCID (middle), and YML (bottom) all lined up for the same time period. You can see both the odd "tremor" and the LF quake appear on B950 and YML however it does not appear on MCID, where it should appear if it were a teleseism.

So I was very intrigued by this one little event. This event most likely took place about a couple miles deep just a few miles from YML. YML, Mary Lake, showed the strongest amplitude count and the P/S waves arrived at this station first. Interesting, huh? If anything else develops, you will be the first to know! God bless!