they help tell Earth s story! Regents Earth Science With Ms. Connery
EARTHQUAKE VOCABULARY earthquake fault convergent divergent transform (or transverse) seismic energy epicenter focus Richter scale magnitude Mercalli scale seismic risk surface waves body waves p-waves compression s-waves shear s-wave shadow zone travel time arrival time origin time mantle convection plate tectonics plate boundaries earthquake prediction
What DOES an EARTH quake look like? But the local quake MAY NOT BE the only problem!
WHY IS IT IMPORTANT TO UNDERSTAND EARTHQUAKES? Do you think we can predict them?
Where are the volcanoes and quakes happening today???
Volcanoes
SEISMOLOGY (Earthquakes)
Remember, the EVIDENCE LOCATIONS OF VOLCANOES AND EARTHQUAKES - CAME FIRST before plate boundaries could be drawn!
Quakes, MOUNTAIN chains, AND VOLCANOES ARE ALL RELATED! IT S ALL ABOUT earth s CRUST in MOTION PLATE TECTONICS!!!
Here s how scientists explain the relationship you observed Its all about convection in the asthenosphere (plastic mantle) & earthquake seismic waves prove it!
How does a lava lamp help us understand plate motion?
How does Mantle convection cause plate motion?
Mantle convection causes plate motion! plate motion & volcanoes cause stresses to build up in the rocks. When the stresses overcome friction, movement OCCURS and causes an earthquake!
Its all about convection in the asthenosphere (plastic mantle) & earthquake seismic waves prove it!
earthquakes
What is an Earthquake? It s the SEISMIC ENERGY that s released when the earth breaks along a fault zone Before After < 1 Sec
How do we describe where an earthquake occurs In the lithosphere? Focus is on the fault zone where the earthquake occurred below ground
How do we describe where an earthquake occurs In the lithosphere? Be sure you know the difference! Epicenter is the surface location used to describe where it happened using latitude and longitude. Focus
Earthquakes happen along faults Divergence (slip fault) Generally they occur from three types of fault movement caused by: pulling (extension) Convergence (thrust fault) Transverse (transform fault) pushing (compression) sliding of the fault blocks (lateral)
What is an earthquake? The fault locations are somewhat predictable BUT exactly where & when an earthquake will occur its magnitude are all unpredictable! Just like a pencil!
L o - n - g - e - r the distance moved along the fault the bigger the earthquake!
Scales used to describe earthquakes 1. Richter Magnitude Scale Based on energy released Magnitude = X10 for each step Energy released about 30x greater each step
RICHTER SCALE
Largest Earthquakes since 1900
Scales used to describe earthquakes 1. Richter Magnitude Scale 2. Mercalli Intensity Scale of Effects Damage done based on costs Useful for insurance
USGS Map of Us seismic risks
earthquakes
An earthquake happens when the forces that hold the crust (rock) together are not as strong as the forces trying to tear it apart Just like a pencil!
When friction loses the battle, movement occurs along the fault zone Seismic energy is released in waves in 3-D (all directions) when the earthquake happens
Seismic energy is released in waves travelling in all directions (3D) The seismic waves are called: Body waves (underground) primary seismic waves (p-waves) secondary seismic waves (s-waves) surface waves (above ground) Draw isochron maps to see EVIDENCE that shows p-waves differ from s-waves
What are the characteristics of the p and s seismic waves that give them different speeds? It s slinky science time!
P-waves
Primary = p-waves Compressional waves - similar to the motion of a slinky. Particles move in same direction as energy wave travels p-waves are fast (4-7 km/sec) High density material fast wave speed p-waves move through solid, liquid, & gas
S-waves
Secondary = s-waves Shear (transverse) waves think rope Particles move perpendicular to the direction the energy wave is traveling S-waves slower than p-waves (2-5 km/sec) High density material faster wave speed Only travel through solids (can t shear liquid or gas)
EQKE Recording instruments are called SEISMOGRAPHS (aka SEISMOMETERS) Written record of an earthquake is called a SEISMOGRAM
How do we know the properties of Earth s layers?
Seismic refraction and reflection of waves show us earth has layers with different properties!
Seismic Waves!! http://www.astro.virginia.edu/class/oconnell/astr121/im/seismic-waves-crossec-cm.jpg
since s-waves don t make it through to the other side of Earth (shadow zone) so there must be a liquid outer core that stops them! http://www.visionlearning.com/library/module_viewer.php?mid=69
EARTHQUAKE HAPPENS and energy waves are released Seismogram shows WHEN the SEISMIC waves arrive at a station!
Faster P-wave arrives at the seismograph FIRST P-WAVE ARRIVAL TIME EARTHQUAKE HAPPENS and energy waves are released Slower s-wave arrives at the seimograph LATER S-WAVE ARRIVAL TIME
P-WAVE ARRIVAL TIME EARTHQUAKE HAPPENS and energy waves are released S-WAVE ARRIVAL TIME
P and s waves take different amounts of time to travel the same distance away from an equake because they move in different ways http://eqseis.geosc.psu.edu/~cammon/qa/wellsnv-21feb2008.html
PRACTICE KEEPing UP WITH THE times! ORIGIN TIME (earthquake happens) ARRIVAL TIME 00:00:00 (when waves arrive at a seismograph) TRAVEL TIME (how long it took waves to get there)
What is a seismogram? EARTHQUAKE (energy waves are released) Faster P-wave arrives at the seismograph FIRST P-WAVE ARRIVAL TIME Time gap btw p and s Earthquake happens at the TIME of ORIGIN and waves travel out FROM FOCUS Slower s-wave arrives at the seimograph LATER S-WAVE ARRIVAL TIME
y axis = how long it took for the seismic waves to travel to the seismograph Label the slower wave graph What is the scale for travel time? 1 min = 60 sec 60sec/3 =??? 20 sec/ block 00:05:20 Label the faster wave graph x axis = how far away the seismograph is from the earthquake What is the scale for epicenter distance?
Why does the time gap btw. arrival of p & s waves change?
Practice using the esrt!!
What is a seismogram? EARTHQUAKE (energy waves are released) Faster P-wave arrives at the seismograph FIRST P-WAVE ARRIVAL TIME Time gap btw p and s Earthquake happens at the TIME of ORIGIN and waves travel out FROM FOCUS Slower s-wave arrives at the seimograph LATER S-WAVE ARRIVAL TIME
If you know difference in arrival times, you can figure out how far away the earthquake is!
TAKE A PIECE OF PAPER, AND MARK OFF THE DIFFERENCE IN ARRIVAL TIME if gap in time = 04:10
MOVE THE PAPER UNTIL THE TWO TICK MARKS LINE UP WITH THE P AND S CURVES WHEN TICK MARKS LINE UP, GO STRAIGHT DOWN AND READ THE EPICENTER DISTANCE EPICENTER DISTANCE OF 2800 KM
EPICENTER DISTANCE OF 2800 KM If the EPICENTER DISTANCE is 2800 km from the seismograph, how long did it take for the p and s waves to travel to the station (TRAVEL TIME)?
If the p wave arrived at the station at 16:00:10, what was the origin time of the earthquake? EPICENTER DISTANCE OF 2800 KM
NOW LET s locate some earthquakes by interpreting seismograms
What s triangulation? TRIANGLE THREE STATIONS!!!!!
Label the closest station Label the farthest station Determine the epicenter distance from each city
Use the data from the recording stations: Station A: San Francisco, California P-Wave arrival S-Wave arrival What is the time difference between P and S wave arrivals?
Use the data from the recording stations: Station B: Denver, Colorado P-Wave arrival S-Wave arrival What is the time difference between P and S wave arrivals?
Use the data from the recording stations: Station C: Missoula, Montana P-Wave arrival S-Wave arrival What is the time difference between P and S wave arrivals? 03:01:00 03:03:00
Difference in arrival times: San Francisco: 4:10 Denver, Colorado: 3:20 Missoula, Montana: 2:00
1. USE A PIECE OF PAPER TO MARK OFF THE TIME GAP for that STATION
2. MOVE THE PAPER UNTIL THE TWO TICK MARKS LINE UP WITH THE P AND S GRAPHS 3. WHEN TICK MARKS LINE UP, GO STRAIGHT DOWN AND READ THE EPICENTER DISTANCE 4. EPICENTER DISTANCE OF 2800 KM
EPICENTER DISTANCES San Francisco: 4:10 Denver, Colorado: 3:20 2,800 km 2,000 km Missoula, Montana 2:00 1100 km
1,000 2,000 3,000 4,000 5,000 Where s the earthquake??? San Francisco: travel time of 4:10 is 2,800 km away from earthquake Open your compass to the EXACT distance on the scale. Once you know distance, you can draw a circle on the map that shows the possibilities!
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Radius from Missoula = 1100 km... Radius from Denver = 2000 km Radius from SanFran = 2800 km
Review of steps to locate epicenter!!! Find the difference in arrival times between p and s waves Use the ESRT y-axis scale to mark off the time gap on scrap paper Match the time gap to p and s waves curves on ESRT to find distance from the epicenter on x-axis Use map scale + compass to draw circle from seismic station on map Remember you need at least 3 seismic stations to locate the epicenter!