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(1) The effect a very attractive woman (or group of women) has on the 'girth' of male members in her (or their) vicinity. This Girthquake can be measured on the 'Dichter' scale- from one up to ten, and is a handy way of discussing the attractive potential of women. Can be accompanied by rattling of glass on table to indicate violence of initial tremor, or at higher ends of the 'Dichter' scale by 'Star Trek' style synchronized pitching from side-to-side whilst trying not to spill drink, as if floor is swaying.
(2) (noun) A way of describing a previous evening, or party- if said event led to the conquest of an improbably attractive woman, or if the ratio of such women to men was unusually high- said event/evening can be described as being a 'Girthquake'. In the event of such an evening leading to a secondary event (such as an afterparty) where a further woman (or cluster of extremely attractive women) who rate highly on the Dichter scale is discovered, then the term 'Aftercock' can be substituted.
MAN1: "G...g....g.......GIRTHQUAKE!" (has spotted woman who scores on Dichter scale- remember optional rattling of glass on table to indicate violence of initial tremor)
MAN2: (adopting scientific expression) "In my opinion at least a 7 on the Dichter scale. Be careful, there is a strong chance of an 'Aftercock'"
(stands, switches to Roger Moore expression and approaches woman)
by N.J McBlanky July 09, 2009
Any seismic event caused by ones weight, especially an obese person or obese people
The girthquake from when that fat bitch went by totally spilled my drink
Rapid shaking of objects in direct interaction with fatness. Obese people tend to cause this natural disaster by jumping and/or walking. May be known as the rumbling of the ground caused by obese people.
When an obese person jumps and hits the land, the rumble that occurs is known as a Girthquake.
by ChrisRyan January 24, 2009
the type of earthquake that gets extreme ammount of facebook attention within the first ten minutes; not to be confused with a dearthquake which is the type of earthquake that gets extreme media attention
Marco: it was only a little girthquake you attention seeking whore
by JaMarko October 20, 2011
1. the ground-shaking effects one may experience when an obese person is walking near.

2. the shaking, trembling effect one may experience during or after sex with a person who has a large penis.
Every time he walks by, I feel a girthqake.

The size of his unit caused a girthquake. The aftershocks caused my legs to shake for hours.
by Brandoonline April 15, 2011
1. the reaction you get by inserting your dick into the orifice of your choosing causing an uncontrolled tremor in said partner
2. having sex with a girl that has a seizure upon penetration and tilting her head and riding the aftershocks out keeping in mind to not let her choke on her tounge
1. dude she was fucking tight,i stuck it in and caused a 6.0 girthquake on the richter

2. omfg i stuck my dick in this girl and she had a seizure,so i held on and kept fucking her....i survived the girthquake
by w1thdrawn September 16, 2011
what happens when overweight people run or jog to get somewhere quickly
Did you see that obese guy running to catch the bus? Total Girthquake!
by Blackmajik December 01, 2006