Picking the best place to live, geologically speaking

I rarely get to have discussion with human geography students, but the natural hazards class I recently completed had a good spread of the physical geeks with the human geeks. One human friend mentioned how she lives in a neighborhood on the edge of a broad alluvial fan, and that her parents have little clue as to the potential dangers of living on such a precarious foundation protected only by modest dikes, which I might add have had increasingly shrinking freeboard values for the past two decades. The deflecting reason they gave her is that "developers would not have built here if it wasn't safe". 

Oh no, they would. Developers hedge their bets, and most in our regional district tend to downplay the importance of geophysical reports. Developers will push through proposals with hard cash to get the required zoning, especially if the 'view' and location is something that will bring them big bucks. This is not to say that they will cut corners wherever possible, as most of the time construction is top-notch, corresponding to strict standards for quake-proofing and packing down the sediment if the foundation happens to be laid upon Holocene alluvium.

Where is this post leading? Well, in my humble opinion prospective home owners have to take on some proactive responsibility themselves. Common sense dictates that the buyer beware, and there is no excuse for an educated westerner who does have the rights and the access to geophysical information to not take some time and look at it. Where I live in beautiful British Columbia, our own provincial division of the Canadian geological survey has done some excellent work on investigating factors that determine how damaging certain natural hazards are in certain areas. Below you'll notice fragments of a poster that outlines the traffic-light approach to categorizing hazards:

Slide hazard map of Greater Vancouver.
Light green circles indicate known slide occurrences

Liquefaction hazard map of Greater Vancouver.
Red zones mostly correspond to deltaic and alluvial deposits

Flood hazard map of Greater Vancouver.
The red zones are deltaic and alluvial plains, and have experienced little uplift
since the fill is mostly Holocene. The grey zones are Pleistocene glacial uplands,
mostly till, and benefit from tens of meters of thickness + isostatic rebound

Tsunami wake from Jan 26, 1700
megathrust quake. Ghost forests
attest to unbuckling of plates,
causing meters of subsidence

Looking at this one source of credible information already alleviates a lot of concerns a potential home owner would have, especially in our tectonically active region. Sure we haven't had a big one in living memory, but that doesn't mean we are out of any proverbial woods. On the contrary, the lack of moderate quake activity off the coast of Vancouver Island has led geophysicists to investigate and conclude that the Juan de Fuca plate & North America plate are locked at the shallow subduction contact, and tension is building to an inevitable unbuckling. Whether that results in one huge snap of a megathrust akin to the 1700 Cascadia quake, or a series of smaller unbuckling motions is yet to be seen.

I was asked if I chose where I live because it is among the safest spots in the region. I reside on the glacial uplands, on the crest of a street with a gentle slope. Alas, as a student with a limited budget and only part-time jobs, I cannot claim that I was so smart to have chosen such a safe spot. It's pure coincidence, I chose it because I could afford the rent. But I have dodged a bullet, so to speak, by digging for this knowledge and taking it to mind before I do make my first home purchase years from now. I've already compiled a short list of personal rules for where a home should be, to which additions will slowly be added:

• At least 300m from shore
• At least 50m asl
• Not adjacent to any slope greater than 25°
• Not on any faults, not even ones considered “inactive”
• Not on any META bedrock that has extreme foliation
• Not on any SED bedrock where bedding planes are poorly indurated
• Not within the boundaries of a 1 in 50 year floodplain
• Not within the boundaries of a 1 in 100 year floodplain if recent evidence has shown urban development has forced flow to concentrate, and thus freeboard values for dikes are consistently less than 2 feet
• Not on any foundation that has a layer that swells when saturated (ex. Bentonite)
• Observe wind direction patterns if living on or near a sandy desert or high altitude snowy area, to avoid home being buried by windblown material
• Not on any bedrock that has a lens of limestone beneath (GPR should discover it), lest it dissolves and a sinkhole forms
• Not within a radius of 300m from the edge of a forest prone to fires. Consider making the perimeter of your property fuel-free

I know a few of these are not economically feasible, but I've tried to arrange them in what I consider their order of importance, and the first several are free provided some time and effort and some light education. The GPR might not be an option, but if buying a $seven figure$ home, it's worth it for peace of mind. Above all else, look at the hazard history of the area you're moving into.

I'm not touching on atmospheric hazards, but they should be looked into as well. They're kind of a big deal too.

Additional Info:

• IRIS - Subduction Zone Plate Interaction
• USGS - The Orphan Tsunami of 1700
• GSC - GeoMap Vancouver