The 4.4-magnitude earthquake’s struck at 6:25 a.m. and had an epicenter near Westwood, according to the above preliminary data from the U.S. Geological Survey.
Metro officials say that no damage has been reported to the system. All Metro Rail lines are resuming normal rush hour operations with some slight residual delays.
The agency’s tweets from this morning:
There are no reports of injuries or damage from law enforcement. The CHP says that area roads are clear.
Here is an earlier Source post that explains how Metro deals with earthquakes and goes about inspecting tracks for Metro Rail. Excerpt:
When a quake is thought to be strong enough to cause damage, rail control center staff will radio the train operators and tell them what to do. Orders can vary from line to line, depending upon where the quake is strongest. If a weak quake is centered in the San Fernando Valley, for example, trains in Long Beach may not be affected.
If the quake is deemed potentially damaging, operators may be told to stop where they are and begin sweeping the track, which means that they proceed at about 15 mph to the next station or to the point where the train ahead of them stopped and began its sweep. (In that way, every inch of the track can be examined.) While the operators are proceeding they carefully watch the track looking for damage. Everyone reports back to rail control, which determines if the line or lines can reopen. Decisions are based on the common sense of humans, rather than seismic machines.
Should a significant event occur, the entire rail system would be shut down and not reopen until all lines have been thoroughly checked and determined to be safe. The term “significant” does not refer to Richter scale strength but to a variety of factors including strength and location of the quake and the judgment of rail control staff.
Should operators feel an earthquake (not that obvious in a moving train), they must immediately stop where they are and then proceed slowly to the next station. Or they may be given specific instructions from the rail control center, which generally will tell them to begin sweeping.
And here is another Source post on how subways are designed to withstand quakes, including the above chart. Excerpt:
There is no specific magnitude that subways are designed to universally withstand. The strength and flexibility the subway is designed for depends on the characteristics of earthquake faults in the area and their proximity to the structure being designed. In other words, the main question engineers ask is this: how strong is the ground shaking likely to be at the tunnels and stations?
The forecasted level of ground shaking at a particular location is garnered from seismic hazard maps published by the United States Geological Survey. Building designers and engineers use these same maps to design their projects.
Obviously, Southern California sits in the midst of well-known earthquake country (here is a list of notable earthquakes in California in the past 200 years; the largest was a 7.9-magnitude quake near Fort Tejon in 1857). Metro’s design criteria requires that its facilities are designed to ensure both life safety and the ability to be repaired after larger earthquakes – the ones that are predicted to occur every 2500 years. At the same time, Metro’s facilities are designed to ensure continuous operation in smaller earthquakes that have a probability of recurring every 150 years.