I confess I have not thoroughly read each post in this thread so I do not know for sure if my idea had not been previously mentioned. I gather one main concern is the way to get over a waterway between the office and home. There have been several suggestions for structures that might withstand a quake and the problems in swimming. I believe you have room to store a backpack - why not store an inflatable raft - they are not that big or heavy. Even if you re-arrange with a marina to take you across, in event of a disaster they may not (or may not be able to) live up to what they agreed.