Big earthquakes that demolish homes may well bury the inhabitants inside. Common enough and hundreds if not thousands die.
Stick build American frames homes could stand up a bit better as they are intrinsically loose but it still requires high wind type construction techniques to keep walls from working the nails out and falling down. Even so, it's difficult to search them completely. We had a person of interest hiding out in the county and he was tracked to a family members home. After hours of loud music and tear gas he gave it up and left his hiding place in the attic. A family member reported he has shown up with a gun but was arrested without one. The team proceeded to search the home and after 18 hours gave it up. The lead LEO was quoted as saying (paraphrased): "We could eventually tear the house completely down to determine if the gun existed or not but the taxpayers aren't going to welcome the bill for doing that, plus reimbursement of the property owner."
We keep repeating how the cops can tear up the house and find a gun, but the reality is no, they can't. It's Hollywood security theater and it doesn't happen. The taxpayer can't afford it and the results of demolishing someone's home to find one gun would be a serious mark on the supervising LEO's record.
I gave a link to Weaponsman's blog - ex SF who knows his stuff. Again, the compromises are the environment, participants, and countermeasures. If you could store the stuff in vapor proof durable containers, what would you have twenty years later? Old guns that might work after some remediating. It takes members of your group to know where it is so the location isn't forgotten and periodic checks are conducted, which exposes it to discovery. And there are the countermeasures - such as arrest, death, or fleeing that location in extremis which can either bring it to police knowledge or render the cache useless as it's out of reach.
If you can figure out somewhere to hide it I guarantee another human will stumble across it. How many posts in this forum alone of guns found hidden in walls, crawl spaces, and attics? People hide things they don't want others to know about - and lose track of them too.
Caching weapons and not using them is like storing an 86 Vette with 6 miles on it. When you get back to it in twenty years the hoses, tires, and interior will be rotted, oil oxidized, and gasoline sour damaging major fuel system components. Here's the pics of a 57 Plymouth Tulsa buried as a time capsule that year and it didn't turn out well:
http://www.bing.com/images/search?q...pvt=plymouth+time+capsule+unearthed&FORM=IGRE
And all the time you have the gun buried you don't train with it. Proficiency is going to be pretty low then. Waste of money.