Monday, October 31, 2016

Simple Fault Mechanics - Thrust Fault

This is the most deadly of all faults.  It has the highest PGV for the magnitude.  A large shallow thrust can produce a PGV of about 2 m/s.  This is enough to throw buildings in the air.  Nothing survives this.  The Soviet apartment buildings in Armenia were turned to dust.  In California, it lifted cliffs.

An earthquake requires 'stick-slip' which is the transfer from slow to fast friction.  There is only a major difference with wet quartz, or humid wooden blocks if you want to get pedantic.  There are two ways to 'make' an earthquake.  One is to increase those stress arrows until failure.  This is what California was brought up with, the sacred 'Elastic Rebound Theory'.  Anyone against this is banned from the state.  :)

The other way is to maintain the stress arrows and weaken the fault.  The busgus are totally dedicated to 'pressure jacking' which is increasing the pressure in the fault to reduce the normal stress.  Had they one rock mechanics person, they would know that this is impossible in fractured granite, which is the only thing that causes earthquakes.  Since they don't do math, they think that a general increase in pressure is good enough, but it isn't.  Remember that nobody does basic physics any more.  :(

The only way to have an earthquake away from plate boundaries is to weaken the fault by chemical means, leading to stress corrosion.  Sad but true.  This was done naturally in many places, but is being performed in Oklahoma by injecting fresh water frack waste.  ** Don't put this on any exam kiddies, or your application to work in sunny Callie.

Next is the normal fault.

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