# Continuation of plate tectonics- convection in the asthenosphere is still the driving force of moving lithospheric plates.

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Continuation of plate tectonics- convection in the asthenosphere is still the driving force of moving lithospheric plates.

 At plate boundaries where pressure builds up and eventually breaks rock Usually not in the middle of plates (1%) We call these Intraplate earthquakes  Faults occur where boundaries meet and rocks “ pass their elastic limit ” Earthquakes often occur near these fault lines Three types of faults  See Exploring Earth Website

 1. Normal faults Caused by TENSIONAL forces Forces PULL OR STRETCH rocks

2. Reverse- - caused by COMPRESSIONAL forces - rocks are PUSHED toward each other

3. Strike-slip fault - Caused by SHEAR forces - Rocks move PAST EACH OTHER with little up or down motion.

 For each type of fault: NAME DEMONSTRATE DESCRIBE how the rocks move at the fault line – away, toward, past FORCES - compressional, tensional or shear Type of BOUNDARY FOOTWALL/HANGING WALL

 Point where plate movement occurs and energy is originated is called the focus (can be miles below the surface).  Point on Earth ’ s surface above the focus is called the epicenter

 Let’s see if we can figure out from our data first!!!  Now let’s consult a textbook’s website and see what you think.  Normal (divergent): shallow  Strike-slip (transform): shallow  Intraplate: shallow  Reverse (convergent) C/C - shallow C/O - all depths (up to 700 km – 435 mi)  Focus Depths increase farther from the coast  Due to subduction

 All types of seismic waves (s,p and surface) are detected by seismographs and recorded on seismograms.

 An earthquake creates seismic waves that travel away from the epicenter of an earthquake. Remember, epicenter is the place on the Earth ’ s surface directly above where the earthquake occurred.  Seismic waves are detected by an instrument called a seismograph, which our book calls a seismometer.  Energy shown on a seismogram.  Studied by seismologist!

 Three types of seismic waves:  Primary waves (P waves) travel fastest ~6 km/sec in the upper crust Move particles back and forth in the same direction Cause little destruction  Secondary waves (S-waves) travel slower, cause more damage ~3.5 km/sec in the upper crust Move particles back and forth at a ninety degree angle to wave motion  Surface waves travel slowest, cause the most damage Move particles side-to-side and in a swaying motion  Where does each wave type originate?

 The difference in arrival time between p-waves and s-waves can be timed to determine how far away from the seismograph station the earthquake occurred.  With at least three stations reporting, we can pinpoint the earthquake ’ s location using TRIANGULATION (see next slide or page 312 for example).

 How far away is the epicenter of an earthquake if there is 5 minutes between wave arrival time?  If an earthquake occurs 4700 miles away from a seismograph station: How long after the earthquake will the P-wave arrive? How long after the earthquake will the S-wave arrive? What will be the difference in arrival time?

 In three steps, seismologists can find the epicenter of an earthquake. 1. Find the time difference between P&S wave arrival 2. Use the time difference to find the distance from the seismograph station to the epicenter  Gives a radius around the city 3. Compare with minimum three locations to find epicenter

 Richter Scale – 1935  Measures earthquake magnitude  Determined by height of waves from seismogram  Scale is infinite (depends on sensitivity of equipment)  Largest recorded - 9.5 1960 Chile Earthquake  Base-10 logarithm - √1000 ≈ 31.6 x  Quantitative

 Mercalli Scale – late 1800’s - modified Measures earthquake intensity Determined by human observation and structural damage I – XII Qualitative

 Mercalli Scale  What happens to Mercalli Intensity as distance from epicenter increases?

 Magnitude  Shallow/deep  Liquefaction  Tsunami  Time of day  Shadow zone  Landslides/mudslides/avalanches - terrain  Structures (codes, poverty, expected?)  Gas Pipes/Fires  Warning – Pacific Tsunami Warning Center  Duration (how long did shaking occur?)  Government Aid

 By Permission Only  Location, date and time  Pictures  Damage (cost), deaths, injuries  Magnitude  Difference in P/S waves in Punxsy  Search USGS Top Ten for list of earthquakes. Also a list on p. 318.  Other research  Plates involved

 Occur far from plate boundaries  Faults can still exist, even where two tectonic plates do not meet  Example: New Madrid Fault

 Explain how Primary and Secondary waves are used to pinpoint the location of an earthquake ’ s epicenter  Calculate the difference in earthquake magnitude using the Richter Scale

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