Earthquakes & The Moon – It’s Complicated
In a past Santorini earthquake update, I highlighted research which tied the movement of the tides to earthquakes and volcanic eruptions. I’ve done more research and realised things are more complicated that I first thought. In this video & article I’m going to briefly highlight the issues of using tides to predict seismic events.
What I Thought
I thought tide times where also de facto indication of solid earth tide times. That when the tides are high or low, that the earth tide would be in the same state at that point.
This was a mistake.
Tides
First of all tides. Apparently the height of tides or the state of tidese is not a true indication of the pull of the moon and the sun on the earth’s crust.
Depth of Water
The depth of the water and the amount of water will create different lags according to the area of the planet as well as the angles of the sun and the moon. In short, the pull on the earth is not necessarily at it’s maximum at a particular location just because the tide is high.
Geography
The layout of the land and where the water has to flow or flow around also plays a part. Again, this can create different lags at different places on the earth.
And this is also true of underwater geography and topography. Going from deep water to shallow water also affects the time of the tide.
Summary
It’s complicated. There isn’t a scientific formula that predicts the tides exactly at every place in the world and if I’m understanding the situation properly, even today, the tide times are a best guess and need actual observation to confirm. The tides times are very accurate but they are not exact.
Earth Tides
And when it comes to earth tides things might be even more complicated. I could not find a website which gave them in the same format as ocean tide times. There is a calculator here I believe, but it’s way above by head. (and to make things even more complicated, an atmospheric tidal loading calculator here)
So Where Does This Leave Us?
If we are just measuring water level at a specific point and tying that to seismic activity then I think that is a valid approach (if we acknowledge there are a lot of factors we are ignoring but which may be consistent with the tides).
It might work with some locations and not with others.
Measuring crustal deformation during land tides, and the exact level and direction of the tide along with the exact positions of the moon and sun, all at the same time, and log that data against seismic activity. I think if we do that, we might start seeing more correlations between seismicity and the external forces acting on the earth. I’m not sure if that is being done by anyone at the moment.
Less Accurate Earthquake Forecasts
Having said all that, I think it might be valid to say “at the times where the tidal coefficient is the largest, during that general period of time eg that week, the forces of the crust are going to be the highest”.
4 Hour Window
Perhaps, in some places a 4 hour forecast window is possible and perhaps that is possible around Santorini.
To Minutes
I think combining earth tide data, sea tide data, atmospheric tide data, the position of the moon and sun along with seismic activity at the same time, I think then perhaps we can start to attempt to identify peak stress periods (not necessarily earthquakes or volcanoes) down to minutes.
In Short
-Peak tide times are not an exact indicator of the time the moon and sun are exerting maximum stress on the crust.
-In some geographical area peak tides times will be a better indicator of peak stress than others (of peak pull for the moon, sun, water, crustal flex)
-Without having land tide data and moon, sun location a large window of say two hours either side of peak tides (low and high) may be sufficient to spot general patterns in seismicity in some regions.
