Presentation on theme: "Continuation of plate tectonics- convection in the asthenosphere is still the driving force of moving lithospheric plates."— Presentation transcript:
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
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
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