Friday, March 10, 2017

Will a M = 4.8 Earthquake Wake Me Up?



Is geology useful? Well, yes - if you are reading this message or drive a car or have a smartphone. Without geology, we would be squatting around campfires beating rocks into chips and arguing philosophy until the Sun goes nova.  The following question may fall in the "actually useful to me" realm.


Q: My question is: So if an earthquake hits during nightime, since people are sleeping, and lets say the earthquake is 4.8, then would people feel it sleeping or feel a shake and wake up immediately?😊
- Melanie G

A: From sleepdex.org: "Usually sleepers pass through five [sleep] stages: 1, 2, 3, 4 and REM (rapid eye movement) sleep. These stages progress cyclically from 1 through REM then begin again with stage 1. A complete sleep cycle takes an average of 90 to 110 minutes."

As a six-year-old, I was awakened by a 7.3 magnitude earthquake - because it physically threw me out of my bed at 3am and onto the floor. My Mom told me that she called for me to come to her bedroom (she was trying hard to stay in her own bed at the time) and that I replied "I can't. The walls keep hitting me."

Depending on:

  •  where you are in the sleep cycle, 
  •  how deep the hypocenter of the earthquake is (deeper = more attenuation = less sensation), and
  •  how far away the epicenter is (more distant = more attenuation = less sensation)...                ...you may sleep right through an event of that magnitude. I have two sons living in the LA area, and sometimes they are not aware of an earthquake during the night, and at other times they are hyper-aware and send me text messages to find out what it was that they felt. If you are driving you may not be aware of an earthquake of that magnitude (again, depending on rupture depth and distance), taking the sensations you feel as just a few more bumps in the road. If you happen to notice trees waving around, you may not easily realize that the movement is not being caused by wind (are they randomly waving around, or do they all wave back and forth at the same time and rhythm?). I personally know one person who was driving and did not realize that an earthquake had happened until he got home and his family asked if he had felt it?


I hope this give you a few more parameters to think about (and answers your question).

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