EARTHQUAKES sudden movement or shaking of the Earth sudden movement or shaking of the Earth Caused by:Caused by: –plate tectonic stresses (stick-slip) Located at:Located at: –plate boundaries Resulting in:Resulting in: –breaks in Earth’s crust (faults)

TERMINOLOGY The FOCUS is the place within the Earth and along the fault where rupture occursThe FOCUS is the place within the Earth and along the fault where rupture occurs The EPICENTER is the geographic point on the surface directly above the focusThe EPICENTER is the geographic point on the surface directly above the focus WAVES are produced by the release of energyWAVES are produced by the release of energy

EARTHQUAKE WAVES waves that spread out and carry energy in all directions from the focus waves that spread out and carry energy in all directions from the focus P wave = primary; push; fast.P wave = primary; push; fast. S wave = secondary; snake; slow.S wave = secondary; snake; slow.

EARTHQUAKE WAVES

MEASURING EARTHQUAKES Seismographs record earthquake wavesSeismographs record earthquake waves Seismograms show:Seismograms show: –Arrival of P & S waves –Distance to the epicenter

HOW TO READ SEISMOGRAMS

Time between arrival of P waves and S waves shows distance from epicenterTime between arrival of P waves and S waves shows distance from epicenter

MINI-QUIZ #1 1.Which type of seismic waves are fastest? P WAVES 2.What does the difference in time between P and S waves tell you? THE STATION’S DISTANCE TO THE EPICENTER

EARTHQUAKE MAGNITUDE quantitative value that measures the energy released by the earthquake quantitative value that measures the energy released by the earthquake The Richter Scale –From <2 to ~10 –Logarithmic scale (grows exponentially; + 1 on the scale = x10 in wave amplitude) –Does not change for a specific earthquake. What you need: –Amplitude (wave height) –Time between 1 st P and 1 st S waves  distance

Richter Scale is logarithmic 1 magnitude = too small to feel 2 = 10x bigger 3= 100x 4= 1000x 5= 10,000x 6= 100,000x 7= 1,000,000x 8= 10,000,000x 9= 100,000,000x 10= 1,000,000,000x bigger than a 1 magnitude earthquake Northridge, 1994 = 6.7 Indonesia (tsunami), 2004 = 9.0 Pakistan, 2005 = 7.6 Haiti, 2010 = 7.0 Chile, 2010 = 8.8 Biggest EVER (since 1900) = Chile, 1960 = 9.5 Biggest in US = AK, 1964 = 9.2

MINI-QUIZ #2 1.Which scale is used to measure magnitude? RICHTER SCALE 2.What is the amplitude of a wave? THE HEIGHT OF A WAVE 3.How do you determine magnitude? USE THE AMPLITUDE AND THE TIME DIFFERENCE BETWEEN THE 1 ST P WAVE AND 1 ST S WAVE

Magnitude vs. Amplitude Magnitude The same value for the entire earthquake; constant. You need: a) amplitude b) Ts-Tp (distance) Amplitude Changes with -- a)Distance (Decreases as you go further away from the focus) b)Geology (depends on what material the earthquake is travelling through).

EARTHQUAKE INTENSITY qualitative description of the effect of shaking, based on damage to natural and humanly made structures qualitative description of the effect of shaking, based on damage to natural and humanly made structures The Modified Mercalli ScaleThe Modified Mercalli Scale –From I to XII (Roman numerals) –Descriptive, changes with distance from epicenter What you need:What you need: –Your senses!

MERCALLI VS. RICHTER

ISOSEISMAL MAPS shows area of equal earthquake intensity shows area of equal earthquake intensity, connecting areas with the same Mercalli value.

MINI-QUIZ #3 1.Which scale is used to measure intensity? MODIFIED MERCALLI SCALE 2.What would change an earthquake’s intensity? A) GEOLOGY, OR B) DISTANCE

Earthquake Hazards LIQUEFACTION = LIQUEFACTION = soils or sand is “saturated” --the space between individual particles is completely filled with water; then the soil shakes, and the solid acts like a liquid

LIQUEFACTION

Earthquake Hazards TSUNAMI= underwater earthquake causing massive displacement of water