College of Central Florida KT Kim Earthquakes and the Earth's Interior an investigation using human subjects College of Central Florida KT Kim

Earthquake Seismology – study of earthquakes and Earth’s interior using seismic waves

Earthquake Stress (Force) causes rock to deform Three types of deformation Elastic deformation (Vibration, wave propagation) Plastic deformation (Folds) Fracturing (Faults)

Earthquake Earthquake – sudden motion or trembling caused by the abrupt release of energy Slippage: minor movement (aseismic, fault creep) Fracture: larger movement (seismic)

Earthquake Waves propagate through medium Focus – rupture point where energy is released Epicenter – point on Earth’s surface above the focus

Seismic Waves Body waves – travel through Earth’s interior P wave – compressional elastic wave pressure wave, primary wave S wave – shear wave, secondary wave Surface waves – travel through Earth’s surface Rayleigh waves – rolling (retrogressive) waves Love waves – Side-to-side waves

Seismic Waves Measuring seismic waves Seismograph – the instrument Seismogram – the record it makes Measurement of earthquake strength Mercalli scale – measures damage Richter scale – measures energy Moment-magnitude – measures energy as a function of movement and fault surface area

Richter Earthquake Magnitude Measure S-P time (25 seconds) Measure the largest amplitude (20 mm) Plot them on the corresponding axes. Connect a line. Read a magnitude (5)

Example 1 If we compare two earthquakes; one (A) has a magnitude of 5 and the other (B) has a magnitude of 6. What is an amplitude ratio? Magnitude difference = 6 – 5 = 1 Amplitude ratio = 101 Earthquake B has a 10 times bigger amplitude

Example 2 If we compare two earthquakes; one (A) has a magnitude of 4.5 and the other (B) has a magnitude of 6.5 What is an amplitude ratio? Magnitude difference = 6.5 – 4.5 = 2 Amplitude ratio = 102 Earthquake B has a 100 times bigger amplitude

Example 3 If we compare two earthquakes; one (A) has a magnitude of 3.7 and the other (B) has a magnitude of 6.7 What is an amplitude ratio? Magnitude difference = 6.7 – 3.7 = 3 Amplitude ratio = 103 Earthquake B has a 1000 times bigger amplitude

Example 4 If we compare two earthquakes; one (A) has a magnitude of 4.3 and the other (B) has a magnitude of 6.7 What is an amplitude ratio? Magnitude difference = 6.7 – 4.3 = 2.4 Amplitude ratio = 102.4 Earthquake B has a ~251 times bigger amplitude

Locating Earthquakes P and S waves travel at different speeds Allows calculation of distance Time-travel curve Distance from multiple observations finds a location Three seismographs

FIGURE 7. 11 How earthquake locations are determined FIGURE 7.11 How earthquake locations are determined. (A) The distance from a seismic station to an earthquake is determined by using a travel-time curve. Seismograms from two stations in Canada and one in Jamaica are fit to the travel-time curve so that the first arrival of P waves (red arrows) and S waves (blue arrows) match the two curves on the graph. The distance to the earthquake from each seismic station is read off the x-axis of the graph. Note that the surface waves in these three seismograms have been removed for simplicity. (B) A circle centered on each of the three seismic stations is drawn on a map. The radius of each circle is the map distance to the earthquake from that station. The circles all intersect at the location of the earthquake epicenter, in this case near Las Vegas, Nevada.

Earthquakes & Tectonic Plates Where do earthquakes occur? Convergent boundaries Divergent boundaries Transform fault boundaries Plate interiors

Earthquakes & Tectonic Plates Convergent boundaries One plate sliding under another Benioff zone Friction along the down-plunging contact zone

Earthquakes & Tectonic Plates Divergent boundaries Friction along sliding blocks Mainly shallow

Earthquakes & Tectonic Plates Transform boundaries Offsets ridge system San Andreas fault zone Strike-slip fault Fault is vertical Plate motion along the line of the fault Fault creep

Earthquakes & Tectonic Plates Plate interiors - infrequent 1811~12 in New Mardrid, MO Area is still seeing deformation

Earthquake Hazard & Mitigation Rock and soil – varying responses Bedrock Soil type Topography Liquefaction Soil water content Water table

Earthquake Hazard & Mitigation Construction design and earthquake damage Regulation of location and materials Framing materials Effects of affluence

Earthquake Hazard Map

Tsunami Seismic sea wave Undersea fault motion Far-traveling wave Coastal hazard Sumatra earthquake (2004) Tohoku earthquake in Japan (2011)

FIGURE 7.19 Evolution of the tsunami triggered by the 2011 Tohoku earthquake in Japan. (A) The initial fault rupture started about 32 kilometers below the seafloor (red dot) and propagated to the west (dashed red line), causing severe ground shaking in the Miyagi Prefecture. (B) The fault rupture switched directions and propagated eastward and upward, violently punching upward both the soft sediment near the seafloor and the deep water overlying it. (C) The resulting large bulge of water spread out, moving out to sea and towards the shore. In the deep water of the open ocean, the tsunami traveled rapidly as a series of relatively small waves detected by offshore buoys. Tsunami waves traveling shoreward grew larger as the bottom shallowed. (D) As they approached the shoreline, the tsunami waves became even larger and bunched up due to friction along the bottom. (E) The tsunami rushed onshore, causing death and destruction.

FIGURE 7.18 Map of the tsunami triggered by the 2011 Tohoku earthquake in Japan. The tsunami traveled across the entire Pacific Ocean, taking over 21 hours to reach the coast of Chile. Note the thin strip of red along the west coasts of the Americas, indicating that the wave heights increased there due to the shallowing water depths.

Earthquake Prediction Long-term prediction Tells where earthquakes are likely to occur Short-term prediction Place and Time Foreshocks Aftershocks Monitoring China, Japan

Earth’s Interior Wave behavior In homogeneous media, wave propagate equally in all directions Velocity depends on the nature of material waves are traveling through Waves refract (bend) when moving from one material to another

Earth’s Interior Moho discontinuity The crust-mantle boundary Andrija Mohorovičić (1909) Waves arrived at distant earthquakes faster than closer ones (Refraction)

Earth’s Interior Structure of the mantle 2900 km think 660 discontinuity 80 % of Earth’s volume

Earth’s Interior Discovery of the core A shadow zone of seismic waves S wave does not propagate through the liquid medium  outer core is liquid.