Yes – but only if the property is not a leasehold, and only if the mobile (or modular or manufactured) home is located in a city that requires it, ie city of Los Angeles, Malibu, Culver City, San Fernando etc. Here is a list of cities that require an installed seismic earthquake shut off valve when selling.
If the property in question has its own APN (parcel number) and pays annual property taxes, the property is not a leasehold. If the property in question pays no property taxes, does not own the land under the structure, and does not have its own APN or parcel number, it’s then considered a leasehold. In this case, the mobile homes park owner or operator would be responsible for any required automatic earthquake shut off valve. The unit homeowner would not be responsible.
Properties located in the un-incorporated areas of Los Angele County are not required to have an earthquake shut off valve when selling, ie Topanga Canyon, Aqua Dulce, and other areas.
Here is a photo of an installed seismic earthquake shut off valve on a gas meter for a mobile home. The automatic seismic valve goes between the gas meter and the flexible gas line that leads into the undercarriage of the mobile home.
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