24.10.17 earth science: earthquakes and tsunamis
As plates move past each other, they create fault lines (cracks)
Three types: slip faults (side to side) and transform (vertical) faults (normal-falling or thrusting-rising)
Three types: slip faults (side to side) and transform (vertical) faults (normal-falling or thrusting-rising)
The San Andreas Fault caused the 1906 quake, which moved 7 meters (22 feet) in one slip and devastated San Francisco:
Thrust (vertical) faults caused the Bali quake and tsunami: (look this up on youtube)
Remember earthquake waves:
P and S waves:
P waves are faster than S waves:
We can use this difference to calculate epicenter (surface location) and hypocenter (actual center under the surface):
Recall epidermis is your skin (epi=top, dermis = skin), a hypodermic needle goes under (hypo) your skin (dermis)
AP exam question:- How much stronger is a magnitude 7 quake than a magnitude 6?
- 7 to 5?
- 7 to 4?
More on tsunamis:
- Nuuanu slide: Look up on Wikipedia, how big was the tsunami, where and when?
- What is our biggest tsunami threat now?
- Where did the 1946 and 1960 Hilo tsunamis come from?
- Why is this important to you?
Check this out:
- Why would anyone living east of the interstate-5 corridor be concerned?
- Look at the dates on this diagram:
Look at all of the earthquakes (red dots) as the plate subducts
Two things to take-away about subduction zones:
1. subduction zones create ANDESITIC (pointy) volcanoes, which are high in silica, and sticky like thick pancake batter.
2. subduction zones create lots of deep-focus earthquakes.
2. subduction zones create lots of deep-focus earthquakes.
Play time:
- Look at the HPA Pacific Tsunami Warning Center (PTWC) seismograph here:http://www.fdsn.org/networks/detail/PT/
- Look for the HPAH station-where is this?
- Why are the stairs to the nurse's office in such strange angles?
- Our Elab quake network here: https://shakenet.raspberryshake.org/
- look for "station view" and zoom in
- jump in the elab, and see if R160F moves
- go into the monlab and find the same one
- why is it not showing up on the PTWC seismic sensor?
- why does your jumping NOT cause an alert?
- Hawaii quakes here:https://earthquake.usgs.gov/earthquakes/map/?extent=-69.225,-230.44922&extent=70.25945,-69.43359
Click on some earthquakes and note the depth and the seismic image.
Key earth science points:
- All elements up to Iron on the periodic table came from the big bang
- Earth was formed from materials created by first generation stars going supernova
- The core of the earth is made up of a rotating solid core surrounded by a liquid core
- The inner core creates our magnetic field, which reverses periodically
- Layers: crust-mantle-outer core-inner core
- Uranium in the core produces heat that travels to the surface by convection
- Tectonic plates on the surface move on top of the sticky asthenosphere because of this convection
- Spreading zones are were these plates are created, subduction zones are where they dive under others
- Subduction zones create trenches in the ocean and andesitic volcanoes (sticky lava, pointy cones)
- Hot spots in the crust can create basaltic volcanic islands like the one we are on (runny lava, broad cones)
- Earthquakes include P (primary, compression) waves and S (secondary, shear) waves
- P waves are faster and go through solids and liquids, S waves only travel through solids
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