The quiet period around local midnight

So, often I see the following pattern:

Where +/- 2 hours around local midnight the microseisms seem to fade. I thought this might be traffic noise, but it doesn’t seem reasonable. In most seismic display systems the small stuff is suppressed, but here we see it all. I’m wondering if it is earth tides or some similar natural process. Comments, opprobria, and advice are encouraged. I have heard there is some correlation between seismic events under M 4 and local sun and lunar tides. Do others see a similar pattern?

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I see a similar thing.

I live 10kms out of town but the house is <100m from a reasonably major road feeding the town of Oberon, with 40 to 60 log truck movements passing each day. The “blobs” on my helicorder are passing trucks. The big spikes are likely doors opening and closing, etc in the house.

I think the noise is mostly cultural, not related to tides (it doesn’t move around with tide times) and certainly not seismic (as in earthquakes).


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Hello david,

I can see the same on my station, usually from 11pm of the day before to 5-7am of the day after. For my location (residential), it’s a standard pattern that also changes between weekdays and weekends/holidays depending on the activity of nearby traffic.

A page on the USGS expands on possible earthquake correlations, you can find it here:

As for day/night tidal noise, I think you could see those at very low frequencies, if the background noise does not cover them up, so you require a very “silent” installation. It’s worth checking them out in any case. This can give you more info on the matter:

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It is normal. Man-made noise. On different holidays where pretty much everyone is at home, and staying there, it can cover most of the day.

My trace for the last 24 hours:


I concur. We don’t have any major nearby roads, but a shopping center with big trucks and lots of smaller cars. I’m just surprised the local traffic can create such signals. BUT…this is the first time I’m seeing the lower end of the signal scale and I just wasn’t personally calibrated for it.

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I wrote this up a while ago: Deans Ave Traffic


Yo, Tideman,

Nice work and an interesting observation

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Mine look the same. I have a residential street in front of my house and you can count traffic going. The are the little spikes and bigger spikes are trains going through town.