Roads, and High-Speed-Rail (HSR) are not designed to address earthquakes and other shifts in earth's plates. All transportation modes are prone to earthquake damage. Fortunately earthquakes account for less than 0.01% of transportation related death and property loss. Earthquake mitigation is possible. The Alaska pipeline crosses the Denali fault, and was designed for a maximum expected event. A 7.9 quake along the Denali fault happened in 2002, the design for pipeline quake mitigation worked and not a drop of oil spilled. Much more sophisticated quake mitigation is designed) for ET3 however earthquake mitigation is not the main safety issue for ET3 or any other mode of travel. Earthquake risk applies to everything (not just transportation) every building is at risk. Earthquake probability is very unlikely at any given place and time.
If an unlikely tube ruptures occurs, sensors activate a safety routine to reduce risks. The damaged section is isolated with gate valves, traffic rerouted, and then air is admitted all along the tube via apertures sized and spaced such that the rate of capsule deceleration is high yet survivable. The air between the capsules reduces the likelihood of collisions as they slow down and encounter the inrush of air from the rupture.
The main safety issues for most modes (including ET3) are: control of the vehicle (automation is proven to be orders of magnitude improvement over manual control), and control of the conditions of travel (the tube offers isolation from all but the most violent forces in nature). Human error is the number one contributor to transportation death rate. Other fundamental transportation safety issues are weather issues (fog, rain, snow, ice, etc,); animals or other objects in the path of travel; and mechanical failure (flat tires, broken tie-rods, engine stall, etc.). ET3 has elements necessary to improve transportation safety by orders of magnitude (just as automation improved telecom reliability compared with human telephone switch board operators of a hundred years ago).