Identifying earthquakes and spectogram question

I have recently set up my first RS4D and would appreciate some help in identifying earthquakes on the ShakeNet app.
For example, are the following 2 earthquakes as they may seem so on the waveform however the spectogram seems that it is not an earthquake.

This one, however, may be an earthquake? If it is, how can I determine its distance from me?

  1. What is the difference between the trace filters - Global, Regional, Local and Hyper-Local?

  2. As the RS4D picks up earthquakes far and near, how do I know if a particular earthquake was felt at my place but I just missed it? As humans can hear sounds from 20Hz, when an earthquake trace goes above 20Hz on the spectogram does that mean it would be able to be felt where I am?

Thank you in advance!

Hello VS1, welcome to the community!

Regarding the three traces you posted, the last one is definitely the one caused by an earthquake. You can cross-reference the list present in the App itself (one of the most comprehensive ever created) and find which event caused that particular signal.

When you find it, the data in the list will give you the UTC date and time of the quake, alongside its distance from your location. So, for future reference, you can scroll the list as a first step, to find what you have captured.

Onto the four filters, they are correlated to the distance between your station and the epicentre of the quake. Usually, you would set the Global one for very distant quakes, and the Hyper Local for very close events.

For the last question, you can consult the USGS (or your local agency) felt reports to confirm, for example, if your station has registered a quake but you haven’t felt it.

There is no correlation between what you can hear (20+Hz) and “feeling” an earthquake, so seeing a quake above 20Hz on the spectrogram simply means that it was a powerful and/or very close event.

You’re welcome!

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Thank you for your informative response!

The app has most earthquakes above M4.0 which I can match traces to, however, most earthquakes nearby below M4.0 are not listed by most international agencies as well as our local agency.

In terms of seeing a quake above 20Hz meaning it was powerful/closeby are there any general rules for example if I see a trace above 20Hz and there were no powerful quakes in the region could I deduce it was a close event that may have been minor. What does 10Hz-15Hz mean on a quake if I cannot find a match for it?

Thank you!