JDFEM.com
Juan de Fuca
Emergency Management

South coast of Vancouver Island
BC, Canada
Earthquakes
Did an earthquake just happen? To you, or on the news?

How dangerous is your house?

Recent Earthquakes

European-Mediterranean Seismological Centre
Last 2 days from



USGS - click and zoom



BC COAST
Last 30 days -(Updated during office hours)


How Dangerous is Your House?
1. Test out your house on a computer simulator

Excellent educational feature from Earthquake Commission of New Zealand
Change features and choose a magnitude of quake.Then click on furniture items to learn more.

2. Look at the soil under you
.
Houses on soggy wet lands will shake a lot (people frightened)
Houses on well-drained soil will shake moderately
Houses on rock will shake very little (people may not notice)
Liquefaction
When we shake a jar of beans, they settle in tighter. When wet sand is shaken by a quake, the sand also settles tighter. However, the water with the sand gets squeezed up, sometimes spouting up.
The danger is that the rising water floats sand particles so they are not touching. This essentially makes quicksand, just as a spring bubbling up in sand makes natural quicksand (click on picture at right).

A building on the spot would sink down into the sand, or tilt at an angle.

YouTube videos showing liquefaction

Water flowing up out of holes, NZ - shaking settled sand, squeezing water up. In video, shaking stopped so okay to walk, but water still under pressure coming out of holes.
Cars sank into liquefied sand during shaking, now sand hard- NZ. Half-way into video is short clip of a car deeply buried.,

Amplification
An orchestra conductor waving a whip will produce much more action than just waving a stiff baton.

Earthquake waves will move soft ground much more than they will move bedrock.

Buildings on wet ground -- especially lowlands around river deltas, bogs, ponds, and where loose fill has been dumped into water -- will tend to have much more damage than if built on rock. Wet lands should stay as farms and parks in earthquake country..


Estimate the magnitude by the time of shaking
COUNT THE SECONDS

C
Impress your friends with a good guess...
Once you feel shaking that might be a quake, estimate the total seconds that you felt shaking. It won't normally be more than a few seconds. Then use this chart to get a very rough guess as to the magnitude. This only works for quakes as described.


For close quakes
M 1  < 1 sec ----not felt

M 2    ~ 1 sec ---- rarely felt unless shallow and close

M 3    ~ 2 sec --- shaking of house, sometimes like a train coming in one end and quickly going out the other

M 4   ~ 5 sec shaking, things fall off shelves

M 5   ~ 10 sec shaking, some damage of weak structures, masonry
For quakes within distance of Seattle
M 6   ~ 10-20 sec shaking, some damage over large area

M 7    ~ 20-30 sec shaking, significant damage in weak structures on wet soils with liquefaction or amplification
(example: Haiti 2010)
may cause local tsunami from underwater landslide

For quakes in Pacific NW
M 8    ~ 1 minute shaking, massive damage
(example: San Francisco 1906)
may cause local tsunami from underwater landslide


THE BIG ONE -- Megathrust subduction zone

M 9    ~ 4 minutes shaking
(example: Japan 2011, Indonesia 2004, Alaska 1964, Pacific Northwest "Big One" 26 Jan 1700)
  • Expect Big Tsunami with M9 quake .
  • ~30 min to Port Renfrew ~3-5+ meters
  • ~1 hour to Sooke ~1-2m
  • ~1.5 hours to Victoria area ~1m+, higher inside Esquimalt and Victoria Harbours.
  • Tsunamis repeat for many hours at varying heights -- stay away from shore for 24 hrs
JDFEM.com
For website changes, contact: sholland@softwaves.net