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Is it due to the longitudinal nature of the seismic waves?

When a heavy bus or truck goes by at high-speed, the shaking in nearby ground is not mistaken as dizziness, rather the feet and body feel a vertical jerk (seemingly a transverse wave vertical to the ground).

But when a natural, mild earthquake takes place, it is not felt as a jerk or switch in a direction at all. Rather we feel it for a while as dizziness. I have experienced this, and heard of many others who have as well. In-fact it takes a few seconds to distinguish whether it is dizziness or an earthquake.

Is it due to the longitudinal waves? Is it because they are horizontal with the ground, matching the direction of dizziness?

Also I guess maybe there may be similarity between the frequency of seismic waves and this video from Wikipedia's article on vertigo:

vertigo eye movement from Wikipedia

Does this phenomenon's frequency act similarly to the motion and simulates dizziness?

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  • $\begingroup$ Always Confused, interesting question... I tried to edit the question to be clearer and clean up the grammar. Please do make sure that I did a good job, especially with the parts about bus/truck shaking and directional movement. Hoping for some good answers :) $\endgroup$ – JeopardyTempest Apr 2 '18 at 10:29
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Having experienced many minor earthquakes (Mag 3 to 5 in the East African Rift Valley, Samoa, Solomon Islands, Philippines and Indonesia), and one major life-threatening earthquake (Magnitude 8, Nepal), I can make a few personal observations about physiological reactions. First, You are quite correct about the body picking up any swaying feeling, and interpreting this as dizziness. I was in an 11th floor hotel room in Bangkok when an aftershock of the Aceh earthquake occurred. My first thought was "Did I drink too much beer this evening"? I wasn't alone. When I opened the door into the corridor, the occupants of nearly every room were looking out and wondering much the same thing.

Second, after experiencing a big one the body becomes hypersensitive - conditioned to pick up vibrations that could be the onset of a major quake. Now, at the onset of any vibration, my brain goes straight to "how big is it - should I run to the nearest exit"? This response is now much faster than the sensation of dizziness. Also I now pick up many vibrations that nobody else around me seems to notice.

Thirdly, I am not sure I agree with you about vertical motion being the trigger. It seems to me that lateral motion - moving one's feet sideways relative to the head, creates a slight imbalance, which the ears interpret as 'dizziness'.

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  • $\begingroup$ I did Not told vertical motion cause anything such. So I wrote that-"Not" in Bold, with first-letter capital. I wrote when I experience a ground-jerk due to a nearby heavy bus or truck etc (probably they cause transverse wave), I never confuse it with dizziness. That cause only in the time of natural one. $\endgroup$ – Always Confused Aug 7 '16 at 11:53
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When a bus or truck goes by, you typically hear it before you feel it, so you already know what it is before any noticeable ground motion starts, and your brain accepts the shaking as being due to the vehicle.

In an earthquake, on the other hand, unless it's strong enough to actually start noticeably moving objects around (and I'm assuming that, when you specify a mild earthquake, you mean one that isn't strong enough to do that), your brain has no advance warning - suddenly, the vestibular system is reporting motion, while the eyes are reporting that you're stationary. Your brain can interpret this one of two ways:

  1. The ground is shaking, and the building, and, therefore, you, with it.
  2. The vestibular system is malfunctioning.

As temporary glitches in the vestibular system (i.e., dizziness) are (hopefully) a more common experience for most people than (even mild) earthquakes, your brain assumes that the culprit is the vestibular system, rather than the ground, and you feel dizzy until you realise that it's actually an earthquake.

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    $\begingroup$ I think it may play also a role the fact that Earthquakes produce vibrations of much lower frequencies (with still large amplitudes) than a truck passing by, or other ground motions we are used on everyday life. $\endgroup$ – Camilo Rada Apr 1 '18 at 21:11
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I live in Southern California (Inland Empire, near the San Andreas and San Jacinto faults). I did not grow up here. I don't think I've ever mistaken an earthquake for dizziness. During mild ones that have a short 'signature' (a jolt) and that occur while I'm at work, I often wonder first whether someone dropped something on a floor above me.

For the few stronger ones that last longer, I pretty quickly realize it's an earthquake--maybe because I don't often have dizzy spells and don't drink alcohol.

I've missed some of the biggest ones as Northridge (1994) happened a few months before I moved to California.

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