Alaska’s M7 is normal for the region (although the state is so big, usually they hit where few people feel it)
Evergreen reminders:
1. Be aware if you’re adding info or noise to disaster hashtags.
2. Be careful boosting traumatic footage.
3. How’s your emergency kit & plan look?
Evergreen reminders:
1. Be aware if you’re adding info or noise to disaster hashtags.
2. Be careful boosting traumatic footage.
3. How’s your emergency kit & plan look?
Drop, Cover & Hold On is the motto of earthquake response not because we’re worried about building collapse, but because of falling crap within the room.
Clickthrough for vid in typical institutional-boring room with little stuff:
Clickthrough for vid in typical institutional-boring room with little stuff:
Alaska gets subduction earthquakes (one plate under another, vs side-to-side like California).
That means it’s capable of feeding volcanoes and spawning very big earthquakes (M9+) & Pacific-crossing tsunami.
M7s happen a few times a year, just usually not so close to a city.
That means it’s capable of feeding volcanoes and spawning very big earthquakes (M9+) & Pacific-crossing tsunami.
M7s happen a few times a year, just usually not so close to a city.
Any time you’re near a coast & feel severe shaking, head for high ground to wait out potential tsunami.
Tsunami warning systems help farther from the source. Too near & they activate too slowly, or can miss highly localized tsunami (resonance inside fjords; landslide-triggered).
Tsunami warning systems help farther from the source. Too near & they activate too slowly, or can miss highly localized tsunami (resonance inside fjords; landslide-triggered).
When a fault slips, it releases stress on the bit that moved but builds stress on the locked ends. Aftershocks are stress redistributing around the fault system.
A M7 spawns M6, 5, 4, 3, 2, 1 aftershocks. Those M6s spawn their own M5,4,3,2,1 aftershocks, and so on.
A M7 spawns M6, 5, 4, 3, 2, 1 aftershocks. Those M6s spawn their own M5,4,3,2,1 aftershocks, and so on.
Aftershocks drop exponentially in magnitude & frequency — this patch of Alaska is going to keep having rumbles today, maybe tomorrow.
They should a be smaller, but... an unlucky quake can shake loose rockfall into water, triggering small tsunami. I’d personally stay off beaches.
They should a be smaller, but... an unlucky quake can shake loose rockfall into water, triggering small tsunami. I’d personally stay off beaches.
Live in earthquake country?
I like Shakeout’s “Beat the Quake” game for self-testing how good you are at prepping a living room: shakeout.org/dropcoverholdo…
I like Shakeout’s “Beat the Quake” game for self-testing how good you are at prepping a living room: shakeout.org/dropcoverholdo…
New to quake country?
Ask yourself what you’d do if an earthquake happened RIGHT NOW.
Keep asking irregularly throughout your day until you feel confident how Drop, Cover, & Hold On applies at school, in the office, walking down the street, in the kitchen, in bed, driving, etc.
Ask yourself what you’d do if an earthquake happened RIGHT NOW.
Keep asking irregularly throughout your day until you feel confident how Drop, Cover, & Hold On applies at school, in the office, walking down the street, in the kitchen, in bed, driving, etc.
FAQ: What should I do if an earthquake hits while I’m in bed?
A: You spend roughly 1/3 of your life asleep. If a quake happens, STAY IN BED, curl up small, & cover your head & neck.
Prep: Secure shelves (books!), art, & other hazards.
ProTip: Keep shoes tucked under your bed.
A: You spend roughly 1/3 of your life asleep. If a quake happens, STAY IN BED, curl up small, & cover your head & neck.
Prep: Secure shelves (books!), art, & other hazards.
ProTip: Keep shoes tucked under your bed.
Different materials shake differently.
Stalking seismic waves is geophysics secret to understanding planetary structure, but on the surface it’s key to understanding how nearby areas can feel different shaking severity (& subsequent damage).
Loose sediment amplifies shaking.
Stalking seismic waves is geophysics secret to understanding planetary structure, but on the surface it’s key to understanding how nearby areas can feel different shaking severity (& subsequent damage).
Loose sediment amplifies shaking.
Alaska’s surficial geology map has a whole lot going on, but we can simplify:
Where are the new unconsolidated sediments since the last Ice Age 15,000 years ago?
That’s what will shake most.
Where are the new unconsolidated sediments since the last Ice Age 15,000 years ago?
That’s what will shake most.
Pretty much all of Anchorage is on unconsolidated sediment. That’s unfortunate but not unusual — river deltas & valleys are appealing places to live in non-earthquake ways.
But it does mean the place with the highest population density is ALSO where the shaking is most amplified
But it does mean the place with the highest population density is ALSO where the shaking is most amplified
Just like guitar strings of different lengths & thicknesses resonate to product different notes, buildings of different heights sway at different frequencies during earthquakes.
I like demonstrating with lengths of pipe cleaner, but you can see it in Anchorage footage.
I like demonstrating with lengths of pipe cleaner, but you can see it in Anchorage footage.
The Cook Inlet aquifer means Anchorage is pretty much on top of layers of saturated sand and clay nestled against bedrock slopes.
The result is that seismic waves get amplified, with potential liquefaction (right now it’s winter & frozen ground liquefies less).
The result is that seismic waves get amplified, with potential liquefaction (right now it’s winter & frozen ground liquefies less).
Q: Why are big quakes & violent volcanoes in the same tectonic setting?
A: Subducting oceanic plate get stuck & release (quake!), getting bigger deeper.
Plates carry wet sediment, with water dropping melting point. This melt picks up silica, trapping gas for violent eruptions.
A: Subducting oceanic plate get stuck & release (quake!), getting bigger deeper.
Plates carry wet sediment, with water dropping melting point. This melt picks up silica, trapping gas for violent eruptions.
Who wants to talk infrastructure damage & supply lines?
The North & the West both have far lower population density than the East. When you look at pop maps of places like Alaska, NWT, BC, it’s pretty much “Vancouver, Anchorage... uh, Victoria? Let’s include Seattle!”
The North & the West both have far lower population density than the East. When you look at pop maps of places like Alaska, NWT, BC, it’s pretty much “Vancouver, Anchorage... uh, Victoria? Let’s include Seattle!”
Geographically, Alaska is harsh geography. Between steep, young mountains (volcanic in the island arcs), severe weather, & confining topography, the infrastructure corridors are limited.
Start with transit.
Anchorage is a major port for people & supplies both in & out.
Start with transit.
Anchorage is a major port for people & supplies both in & out.
Same concept for communications.
High-relief topography limits tower range. Sparse population density males adding commercial infrastructure unprofitable. High latitude limits satellite coverage.
I worked BC side of the panhandle where my sat phone had service 2hrs/day total.
High-relief topography limits tower range. Sparse population density males adding commercial infrastructure unprofitable. High latitude limits satellite coverage.
I worked BC side of the panhandle where my sat phone had service 2hrs/day total.
Concepts like buying milk get weird the farther into the back country you get. Where is it coming from? How is it getting here?
Basic staples are often shipped in, but limited infrastructure makes for extremely vulnerable supply lines. Disrupting the port ripples down the chain.
Basic staples are often shipped in, but limited infrastructure makes for extremely vulnerable supply lines. Disrupting the port ripples down the chain.
Note 1: Colinial disruption of indigenous diets & lifestyles is a whole ‘nother can of worms in enforcing disaster vulnerability.
Note 2: Reduction of government subsidies for northern rural services (esp comms & mail) resulting in monopolies or no services is a Big Problem.
Note 2: Reduction of government subsidies for northern rural services (esp comms & mail) resulting in monopolies or no services is a Big Problem.
Airports tend to be highly vulnerable as they need to be on flat ground, thus sediments that shift in quakes & crack runways.
Ports tend to be highly vulnerable as they need to be on flat coasts, thus saturated sediments prone to liquefaction + tsunami exposure.
Ports tend to be highly vulnerable as they need to be on flat coasts, thus saturated sediments prone to liquefaction + tsunami exposure.
An M7 is enough shaking to cause significant structural damage. It was shallow & nearby. Anchorage is on sediment that amplified the seismic waves.
Even infrastructure that’s not obviously damaged needs to be carefully evaluated, which gets delayed with every aftershock.
Even infrastructure that’s not obviously damaged needs to be carefully evaluated, which gets delayed with every aftershock.
In Vancouver, when we run our Big Earthquake disaster scenarios, it’s less about the immediate earthquake & more about if we’ve got enough personal prep to manage after we lose bridges to quake; ports, airport, & roads south/east to liquefaction; roads north to landslides.
Modern supply chains are all about “just in time” shipping & lean production.
This is... non-ideal for disaster prep & response as infrastructure disruptions or rapid increase in demand (N95 masks during California fires) lead to shortages.
Bah, humbug.
This is... non-ideal for disaster prep & response as infrastructure disruptions or rapid increase in demand (N95 masks during California fires) lead to shortages.
Bah, humbug.
Q: I’ve lived in Anchorage all my life and never felt an earthquake! This is NOT normal!
A: Geologic timescales are longer than human timescales.
“The Big One” is fundamentally different in subduction zones (Alaska, PNW, Japan, Chile) vs transform zones (California).
A: Geologic timescales are longer than human timescales.
“The Big One” is fundamentally different in subduction zones (Alaska, PNW, Japan, Chile) vs transform zones (California).
Transform boundaries with strike-slip faults (San Andreas in California) tend to have a major M6-M7 earthquake every decade or so. That’s frequent enough that a given community will have generational memory of the last big earthquake (Loma Prieta in SF, Northridge in LA).
Subduction boundaries (Alaska, PNW, Japan, Chile) tend to have major M8-9 earthquakes decades to centuries apart. A particular community usually lacks generational memory. Alaska’s had 13 M7+ since 1900.
Anchorage’s previous Big One was Good Friday, a M9.2 in 1964.
Anchorage’s previous Big One was Good Friday, a M9.2 in 1964.
Speaking of infrastructure...
You know how Alaska has pipelines? And earthquakes? That makes for really intense seismic design. Here’s a photo from 2002’s M7.9
Evaluation ongoing for pipeslubes after today’s quake:
You know how Alaska has pipelines? And earthquakes? That makes for really intense seismic design. Here’s a photo from 2002’s M7.9
Evaluation ongoing for pipeslubes after today’s quake:
Steep young mountains + shaking = landslides:
USGS aftershock forecast is a bit unusual: small chance of a aftershock BIGGER than the original quake.
Probability percentage adjusting as they’re refining models, but currently 3% odds of a M7+ within a week:
Probability percentage adjusting as they’re refining models, but currently 3% odds of a M7+ within a week:
Q: Hey, what about that one patch of road?
A: Finally got a context shot. That section is running through a frozen marsh.
saturated soils + severe shaking = liquefaction
A: Finally got a context shot. That section is running through a frozen marsh.
saturated soils + severe shaking = liquefaction
