Measuring Earthquakes

So far we know….. 1.How many, how often do earth quakes occur each year. 2.An earthquake is a Caused by a release of Earthquakes occur at faults: 4. EQ’s are explained by the elastic rebound theory Friction prevents the plates from moving. 6. What /where is the focus of an earthquake? 7. Where is the epicenter of an earthquake? 8.Biggest, Deepest EQ’s occur at convergent boundaries 9.What part moves on a seismograph? What part remains stationary? 10.How do you “read” a seismogram 11.How many seismic stations’ data do you need to locate an earthquake? What’s it called?

We know that there are 2 types of Body Waves and they travel through the earth Primary (P) wavesSecondary (S) waves Compression waves, push, pressure Changes the density, volume of rock as it passes through. Pass thru solid, (molten), liquids, gas Arrives first, fastest ≈6 km/s * (depends on the density of rock – faster in more dense material) Transverse, “S” snake, side-to-side Changes the shape of rock as it passes through. Passes through Solids only Arrives second, slower ≈3.5 km/s * Is more destructive

Like rolling water waves. (Raleigh, North Carolina is by the ocean) Like a ‘stand up – sit down’ stadium crowd wave. (you LOVE doing that at games) Push /pull compression wave Snaking side to side wave

Magnitude Notes pg Define magnitude: 2.What are the 3 scales used to measure earthquakes? How do they differ? - 3.Be able to measure magnitude using a seismogram. 4.Calculate much energy is released with each magnitude

California and the west coast are riddled with many large and small faults or fracture zones

After the San Francisco quake of 1906

Earthquake Magnitude The amount of ENERGY that is released in an earthquake

Magnitude Scale #1 Mercalli Scale Developed using California earthquakes after the San Francisco quake of 1906 Based upon destruction of structures due to a quake. Observational, qualitative.

Mercalli Scale

Which shows greater ground motion? Which has a greater Richter Scale magnitude?

#2 Richter scale Developed in 1935 by Charles Richter of Cal. Tech. Quantitative, measurable Measures ground motion (amplitude) A decimal number scale. It’s a relative scale (compares EQ’s to each other) Best for shallow quakes Can be used to remote / unpopulated areas (that have no buildings or structures) and measure earthquakes in the ocean.

Richter Scale It has no upper limit. 8.9 is largest ever recorded, Not accurate for really large earthquakes.

Richter scale: 2 measurements 1. Wave AMPLITUDE ( the height of the largest shaking motion line on the seismogram) 2. Uses DISTANCE (from the focus) ( time between the ARRIVAL of P and S waves)

What is time difference between the arrival of the P wave and the arrival of the S wave? ______sec. 36

Find the distance from the earthquake using the travel time\distance graph 36 sec. = _____km 360

Measure the height or displacement (amplitude) of the S-wave in millimeters. What is the amplitude of this wave? _______mm 190

Use the distance and the amplitude to determine the magnitude ???? 6.4

Richter TNT comparison Example Magnitude ounces Breaking a rock on a lab table pounds Large Blast at a Construction Site pounds ton TNTQuarry or Mine Blast tons tons tons 4.0 1,000 tons TNT Small Nuclear Weapon 4.5 5,100 tons Average Tornado (total energy) ,000 tons ,000 tons Little Skull Mtn., NV Quake, million tons Double Spring Flat, NV Quake, million tons Northridge, CA Quake, million tons Japan 1995; Largest atomic Weapon million tons Landers, CA Quake, billion tons San Francisco, CA Quake, billion tons Anchorage, AK Quake, billion tons Chilean Quake, trillion tons (San-Andreas type fault circling Earth) trillion tons (Fault Earth in half through center)

Richter scale is a exponential scale - Which means that each higher number is ten times more than the previous one. –Ex. An earthquake with a Richter scale reading of 4.0 would be 10x’s more ground shaking than a reading of 3.0 –An earthquake with a reading of 5.0 would be (10 x 10) = 100x’s more amplitude than a 3.0

Energy increase The ENERGY increases 31 times for each number in magnitude. Example: Magnitude 4.0 is two times more powerful than a magnitude 2.0 so… x 31= 961 more energy is released!!!

#3 Moment Magnitude Scale Recently developed as a standard magnitude scale that works for all size earthquakes Devised by Hiroo Kanamori in 1977.Hiroo Kanamori It is called the moment magnitude, and it better describes what occurred at the “moment” when the plate snapped It better reflects the TOTAL ENERGY of the quake.

Which would have a greater moment magnitude? Large fault made of dense basaltic rock that moves several feet Small fault made of less dense granitic rock that slips a few inches

Moment Magnitude scale calculates 3 factors… 1. the total AREA of the fault's flat, grinding surfaces X 2. the DISPLACEMENT the ground shifted along the fault X 3. the stiffness (RIGIDITY), strength of the type of rock and how much strain it can endure before it snaps.

Largest quakes Largest recorded was… Chilean quake Alaskan quake Sumatra quake Kamchatka Peninsula Japan

Match the magnitude scale with its correct description Mercalli scalea. is exponential Richter scaleb. uses destruction Moment Magnitudec. is Roman Numerals d. measures total energy e. uses distance and amplitude

Question???? # 1 California earthquakes can be caused by …. A.volcanoes erupting B. caves collapsing C. meteor impact D. Release of strain at plate boundaries E. bombs detonating *

Question ?? #2 What force prevents plates from moving all the time? FRICTION

Question #3 Mechanical waves that travel through the inside of earth are called –A. Love waves –B. body waves –C. surface waves –D. tidal waves

Question #4 Which type of body wave can cause more structural damage? P-waves or S-waves

???? #5 The magnitude of the EQ _____________ as the rock material becomes more dense (rigid). A. increase B. decreases C. remains constant increases

#6 Most of the large, deep earthquakes are located on this boundary????? a. convergent b. divergent c. transform d. hotspot Around the Ring of Fire

#7 Earthquake A has a Richter scale magnitude of 2.0 Earthquake B has a Richter scale magnitude of 6.0 How much more ENERGY is released in earthquake B? 6-2 = 4 so… 31 x 31 x 31 x 31 = 923,521 times more energy!

Virtual EQ Quiz

PSAE Science Test PREP