It has nothing to do with anything that could be solved with a relief valve or a regulator if that is what you really mean. The gas is entering the structures around the outside of the gas line through the trenches. It build ups and then when there is an ignition source it explodes. An example of an ignition source would be a gas hot water heater.
Gotcha, learn something new everyday.
That’s true, but up there the meters are in the basements.
There are many variables to consider when it comes to gas leak migration, it could take days, weeks, or longer for gas to reach explosive levels inside a structure. The variables include pipe size, pressure, location, soil type (clay, sandy, etc), soil condition (dry, wet, etc).
Something that happened Thursday appears to be a sudden overpressure of a low pressure system.