Could an earthquake create a design in a sand pendulum?
Interesting images, thanks for sharing them.

I think its quite likely that a sand pendulum would act as a type of seismograph.  I'm more in geochemistry than geophysics side of things but this kind of pattern does not seem at all inconsistent with seismic shaking.  The linear nature of a recording seismograph is because it is designed to record against a time scale which is perpendicular to the "movement" scale.  Even if movement had a stronger direction in the ground, the table and building this sand pendulum is in would translate the shaking movement into additional directions.  There were multiple movements to make the pattern shown.  It defiantly looks like more than just a truck or subway going by!