Mahi Tuatahi (20min) ^🔗

1. Open Google Classroom
2. Click on “Classwork”
3. Open the Local Geology document
4. Complete these questions using your notes from last class, and any internet research that you want to do.

Akoranga 20 Whāinga Ako ^🔗

1. Use plate tectonics to explain why and where earthquakes occur

Tectonic Plates & Fault Lines ^🔗

• Tectonic plates are the major pieces of the crust that slowly move across Earth’s mantle
• These plates cannot slide smoothly past each other; instead they get stuck and build up pressure and energy
• This pressure and energy causes the crust to fracture at fault lines
• When the pressure and energy gets too high, the rock can slip and cause an Earthquake!

Akoranga 21 Mahi Tuatahi ^🔗

Complete this paragraph in your book.

The energy ________ travels outwards as _____. The point in the Earth’s crust where this happens is called the _____, the point directly above the focus on the Earth’s surface is called the _________. Seismologists use ___________ to determine the magnitude and ________ of earthquakes.

Words: seismographs, focus, location, waves, epicentre, released

Akoranga 21 Whāinga Ako ^🔗

1. Use scientific language: epicenter, focus, p and s waves
2. Be able to locate and measure earthquakes

Recall: Divergent Plate Boundaries ^🔗

• New crust is created by cooling magma in the gap
• No earthquakes occur here
• Forms a mid-ocean ridge, or a rift valley on land
• Volcanoes occur in the gap

Recall: Convergent Plate Boundaries ^🔗

• Oceanic crust is destroyed (melted in mantle)
• Earthquakes occur here deep in the oceanic trench
• Can form mountains and ocean trenches
• Volcanoes may occur near here

Recall: Transform (Conservative) Plate Boundaries ^🔗

• No crust is created or destroyed
• Earthquakes occur near the surface here
• No mountains or trenches formed
• No volcanic activity

https://external-preview.redd.it/c6AD8ukAG1hQk5MQxvJoESS_MZ3cUvWlC3Q3INhdwR8.gif?format=mp4&s=4f673fa41f56234165072daa02efa5e5eeef00da

Earthquakes ^🔗

• Occur on the surface of transform boundaries
• Occur deep underground at convergent boundaries
• Minor ones may occur due to volcanic activity
• Focus: The point underground where the tectonic plates slip
• Epicenter: The point on the surface directly above the focus
• Seismic Waves: Vibrations in the crust caused by the violet release of energy over a short period of time during an earthquake

Ngohe: Locating the Earthquake Epicenter ^🔗

• Seismographs are placed in many locations around New Zealand and the rest of the world.
• They vibrate when earthquakes shake their housing.
• We can use three or more seismographs to triangulate the epicenter of the earthquake.
• Collect a worksheet from the front! Draw a circle of the correct radius around each location and find the earthquake epicenter!

Akoranga 22 Mahi Tuatahi ^🔗

Seismic Waves ^🔗

• Seismic waves come in two different types of vibration - they have slightly different properties which we need to know.
• Make two columns in your book with the headings P Waves and S Waves
• In the real world, earthquakes tend to be a mix of p and s waves which creates a more complex motion.

P Waves ^🔗

• P for primary, because they travel the fastest and arrive first during an earthquake.
• Compression and extension in the direction of the wave.

S Waves ^🔗

• S for secondary because they travel slower than p waves.
• Particles oscillate up and down 90deg to the direction of the wave.

Ngohe: Complete This Paragraph ^🔗

When the _________ is too much in the crust, an _________ will occur. The point in the crust where it occurs is called the _________. The first ________ waves to reach the surface are the ________; the point they first appear at is called the ________. The next type of waves to arrive are the _________. They arrive second because they are _________ than the first waves. P-waves have a ________ and ________ pattern while S-waves have a ________ and _________ motion. In reality, earthquakes are a combination of both of these wave types.

Words: compression, secondary (s) waves, expansion, slower, earthquake, up, seismic, stress, primary (p) waves, down, epicenter, focus

Akoranga 23 Mahi Tuatahi ^🔗

1. Open the Weathering and Erosion on Banks Peninsula doc from last week on Google Classroom
2. Review/complete Question 4
3. Be ready to contribute to a class answer

O Whāinga Ako ^🔗

1. Use scientific language: Richter and Mercalli scale
2. Describe the function of a seismograph

Richter Scale ^🔗

• Developed for use around the San Adreas Fault
• Measures energy
• Is only very accurate for that locality
• Each number represents 31.6 times the energy of the previous number!

Mercalli Intensity Scale ^🔗

• Measures the impact on humans and the land
• It is more useful in a variety of locations
• In reality, places like GeoNet use an average of different scales to generate a more accurate and representative magnitude number.
• E.g. the Christchurch Feb 11 quake

Ngohe: Assigning Magnitues to Historical NZ Earthquakes ^🔗

1. Collect a sheet from the front
2. Glue it into your book
3. Read the left hand side about the different levels of the Modified Mercalli Intensity Scale
4. Work with the person next to your to decide what magnitude you would assign it using the MMI scale

Seismographs ^🔗

• A seismograph is a device that vibrates as an earthquake passes through it
• This vibration is recorded as a series of peaks/troughs on a graph
• This graph can be used to calculate the maximum acceleration of the ground and therefore help determine the magnitude of the quake
• There are many (52) seismographs around New Zealand
• They are used to get many measurements for a more accurate magnitude value and to help locate the earthquake!