Monitoring Earthquakes

GPS satellites can very precisely measure markers on earth's surface. These markers can be set up on opposite sides of the fault to detect BOTH vertical and horizontal movement at faults. So, GPS satellites can detect movement at reserve, normal, and strike skip faults.

Friction between rocks on either side of the fault causes them to stick together. This causes stress to build up. Eventually this stress causes the rock to move and break.

No, geologists cannot predict exactly when earthquake will occur. We can monitor movement at faults, but that does not mean that we can determine precisely when and where the earthquake will occur.

A seismograph is a device that measures seismic waves. For the seismograph to work a drum with paper rolls to release more paper, and a pen stays in place to record any movements in the ground on the paper. If the ground moves, the machine and paper move so that the pen makes lines up and down on the paper showing the time and amount of ground movement.

Posted by Emma Heaps

Animations of Earthquakes and Seismographs

Earthquake Animation

Earthquake Animation 2

Sesimograph

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What to be doing now!

Be sure to be reviewing all material on faults and earthquakes. Use your 3-fold notes and study questions.

Also, make sure your earthquakes research is complete, and when it is you may begin working on the glogster project.

Posted by Emma Heaps

Earthquakes and Seismic Waves

1. An earthquake is a shaking of the ground. Earthquakes occur when rock underground shifts or moves after stress increased (becasue of friciton). Stress will build up where there is a fault and then eventually this stress will cause an earthquake to occur. The rock will then break, at the focus, and trigger an earthquake. Earthquakes occur at faults, often near plate boundaries.

2.

• P-waves, or primary waves move in a straight forward motion. They compress and expand the ground.
• S-waves, or secondary waves moves side to side or up and down and shake the ground back and forth.
• Surface waves travel at the earth's surface and they travel more slowly than S or P waves. The can make the ground roll or shake and can often cause a lot of damage.

3. P-waves arrive first, then S-waves, then surface waves. A seismograph would detect them in this order.

4. The Richter and Moment Magnitude scales rate the size of an earthquake (and the amount of energy released). The Mercalli Scale rates the amount of damage in a specific area.

One single earthquake will only have one Moment-magnitude and Richter rating. However an earthquake can have more than one Mercalli rating. This is because in different cities the damage done by and earthquake may be different, meaning more than one Mercalli rating.

Also, the Moment-magnitude scales is better than the Richter scale at estimating the size of further away or larger earthquakes.

5. Each time an earthquake's magnitude increases by one point (example from a 4 to a 5), 32 times more energy was released.

Posted by Emma Heaps

Animation of Faults

Here's a useful link to see animations of reverse, normal, and strike slip faults.


CLICK HERE FOR LINK TO ANIMATIONS OF TYPES OF FAULTS

Posted by Emma Heaps

Forces in the Earth's Crust

Review of Forces int he Earth's Crust questions form class today. The question are glued in your spiral.

1. The 3 types of stress that can act on rock are tension, compression and shearing.

• Tension pulls on rock, stretching it so it become thinner in the middle.
• Compressions squeezes rock inwards so that it folds.
• Shearing causes two pieces of rock to slip past each other, moving in different directions.

2. The three types of faults we discussed are strike-slip faults, normal faults, and reverse faults.

• At strike skip faults there is no hanging wall or footwall and the 2 pieces of rock slip past each other.
• At normal faults the hanging wall slides downwards relative to the footwall that slides downwards.
• At reverse faults the hanging wall moves upwards relative to the footwall that moves downwards.

3.

• Normal Fault: Tension is occurring (forces are pulling rock apart). This could occur at a divergent plate boundary.
• Reverse fault: Compression in occurring (forces push rock together). This could occur at a convergent plate boundary.
• Strike-slip fault: Shearing is occurring (force causes rocks to slip past each other). This could occur at a transform plate boundary.

Posted by Emma Heaps