Subduction zone earthquakes involve vertical movement of the sea floor. This displacement can trigger tsunami.
While we’re very, very good at forecasting how fast tsunami will travel where, we don’t know how big they’ll be until they start coming on shore.
If you’re on a coast and feel severe shaking, RUN the moment shaking stops. Don’t wait around for assessments or formal warnings, just get as far uphill & inland as you can get as quickly as possible.
Same if you ever see the ocean pull back & exposing sea floor.
We detect tsunami through data from ocean buoys: 1. Coastal buoys that tell us how big a tsunami is as it comes on shore 2. Deep sea (DART) buoys that detect the pressure wave of tsunami traveling in open ocean.
But first a potential tsunami needs to reach the buoys.
Tsunami are so freaking huge that they behave like shallow-water waves even in open ocean. That’s convenient physics because it makes calculating travel time simpler.
In open ocean, tsunami travel at airplane speeds.
Near shore, tsunami travel at highway speeds.
It COULD BE that a tsunami is only centimeters big. It still exists, we can still detect it, but it’s mostly harmless. (Aside from nasty & potentially deadly currents; no frolicking in the surf!)
Every tsunami has a frequency: timing between wave crests.
Sometimes that frequency aligns with the resonance frequency of bays or fjords. Then constructive interferences amplifies tsunami into seiche, building bigger than the original waves.
It’s devastating when that happens.
Alaskan earthquakes have a nasty tendency to produce tsunami that resonate into seiche among the many nooks & crannies of the surrounding coasts. Famous examples are 1964 Port Alberti, BC & 1946 Hilo Bay, Hawaii.
Of all the geohazards, tsunami evac routes & vertical refuges (very strong tall buildings in flat coastal areas) have the most consistent international signage.
Even if you don’t speak local language, look for signs of cresting waves & follow the arrows to safety.
Note: Tsunami do NOT look like cresting waves and you cannot surf them.
They look like a rapid tide. Crest or trough can hit first (50/50 random chance), so it may be ocean pulling back or rapidly rising. Tsunami are MULTIPLE waves & first wave isn’t necessarily the biggest.
Tsunami can be triggered by any major displacement of the water column: earthquake moving sea floor, landslide, glacier calving, even asteroid impact.
Initial assessments of limited data often get revised as we get more data & have human interpretation instead of automated alerts. It’s normal the quake magnitude calculation adjusted from M7.4 to M7.5.
My initial interpretation:
Once upon a time and long long ago, an existing rock fell into squishy mud. Time, pressure, & natural cementing hardened the mud into rock ...with rocks stuck in it.
I’m basing my interpretation on location (beach), that the rock looks gritty (grains not crystals), and that the boundary between the colours looks raised lips (not weathering rind or contact metamorphism).
All those dimples look like places other pebbles were plucked from the host rock* as it was exposed & eroded.
(*former mud/silt/sand now mudstone/siltstone/sandstone depending on proportion of fines).
PSA: “Earthquake prediction” is 100% bullshit in every possible way. That account “warning” of a dangerous swarm is fear-mongering to exploit your anxiety.
Block and ignore.
We CAN NOT predict what size quake will happen when & where. Wish we could, but real-life rocks are complicated.
We CAN forecast probabilities and understand how stress fields interact. For example, the Salton Sea swarm is unrelated to the San Andreas Fault:
The darkly funny part is this not even a feasible guess.
Normal charlatans can hope chance is on their side (gizmodo.com/a-quick-guide-…), but all the faults close enough to be part of this swarm are too tiny to produce anything bigger than an M5.
The winner of this match will face #Magnetite for the finals with a shot at the #MinCup2020 crown. Both are beautiful & bizarre with odd properties and a lot of charm.
Both are Safe But Boring to lick. They even have similar texture (smooth). As far as your tongue in concerned, it’s a wash. You’ll need different criteria to pick your fav.
(One #MinCup we’ll have either a Fun To Lick or a Do Not Lick finalist and I will be overjoyed)
#Fluorite is a basic calcium fluoride (CaF2), which didn’t give me headaches when memorizing composition for mineralogy exams.
Amusingly, the element is named for the mineral, not the other way around. Same for fluorescence: the effect named for the rock’s distinctive property.
Literally nothing about the debate tonight could possibly change how I vote, and I don’t want to deal with either rage or despair from hearing his horrid voice and cruel ideals.
So I’m focusing elsewhere.
On geologic glitter, specifically.
Today’s #MinCup2020 battle is a showdown between glitter vs magnetics.
I am forever & always #TeamShiny.
Which is losing.
#Magnetite is a pretty cool mineral. It’s key to a lot of geophysics, I like collecting it with a fridge magnet on beaches, and it makes for a cool high-impact low-effort geo demo.
But then there’s #Muscovite, a subset of mica & the essence of #TeamSparkle. It’s SO SHINY.