> The disruption originated during scheduled fiber optic maintenance, which unexpectedly compromised network capacity between data centers within the us-west1 region.
Then on September 1st when us-central1-b (and collateral affects in other zones) went down they said [2]:
> The immediate technical trigger for this event was the inadvertent physical disconnection of network fiber-optic cables during a routine hardware maintenance procedure.
Not sure if they're related but apparently procedures we're significantly changed after the first incident to prevent the second incident.
[1] https://status.cloud.google.com/incidents/utF3FMFdQfwBzJcGG6vf [2] https://status.cloud.google.com/incidents/J5ia5t9p3g9Q5Wi7r8Ev