How does one explain this pattern generated by earthquake waving driving a pendulum?

It's difficult to say for certain because so many designs are possible. However, this might shine some additional light on the question. Based on historical seismograph tracings and possible arc paths of the pendulum when set in motion by a person, I would speculate that only the inner rose pattern (the iris and pupil of the eye) was created by the quake. I believe the sclera and upper/lower lid portions of the eye were likely preexisting.

https://www.bgs.ac.uk/discoveringGeology/hazards/earthquakes/History_of_instruments.html