Earthquakes: Understanding the Science and Impacts

Chapter 8 – Earthquakes

What is the elastic rebound theory? Is it possible for energy building up in the lithosphere to be released in a sequence of earthquakes?

Rocks “spring back” – a phenomenon called elastic rebound

Energy is released in a sequence of earthquakes (one earthquake can trigger slip on a nearby fault)

What is a seismic body wave, and what characterizes each of the two types of body waves (i.e. type of motion, velocity)?

1. Primary(P) waves(spring)=push&pull motion, greatest velocity, arrive first, travel solid, liquid, gases.
2. Secondary(S) waves (rope)=up&down motion, slower velocity, arrive after P at seismograph, travel only solid.

What is a seismic surface wave, and what characterizes each of the two types of surface waves? (two types of surface waves discussed, not in text but in notes)

Surface waves are slower than body waves.

1. Rayleigh(rolling motion)
2. Love(side to side motion)

How are earthquake epicenters located (3 step process)?

1. Determine the difference in time between P&S waves from seismograms(3 are needed to locate an epicenter)
2. Convert time to distance using time travel graph
3. Plot circle equal to the epicenter distance around each station(draw using compass)the point where the three circles intersect is the epicenter.

What is Richter Magnitude? Moment Magnitude? Mercalli Intensity Scale? When is each type of scale most useful?

• Richter is based on the amplitude of the largest seismic wave, Each unit of Richter magnitude equates to roughly 30-fold energy increase(i.e. a magnitude 3.0 releases 900 times the amount of energy as a magnitude 1.0 (30 x 30), Richter magnitude does not estimate adequately the size of very large, distant earthquakes.
• Moment magnitude is More accurate measurement of very large earthquakes.
• Mercalli scale is describe surface damage resulting from earthquake. moment Magnitude uses physical measurements of amount of displacement that occurs along a fault zone. Calculation of Seismic moment: rupture area x fault slip x rock strength

How do the following factors affect an earthquake’s intensity: magnitude; distance from focus/epicenter; duration of shaking; foundation materials; building style

What is liquefaction? Could it occur in Southern California?

Liquefaction of the ground– Saturated material turns fluid (sediment)

Tsunami: what are characteristics, causes, & examples?

Earthquakes occur on seafloor faults that move vertically & displace large quantities of water. The water moves away from the uplifted area. The plate boundaries rimming the Pacific Ocean can generate large earthquakes and tsunami. Hawaii is located in the center of the Pacific Ocean and is in the path of tsunami waves when large earthquakes occur. Indian ocean -Large magnitude, shallow focus earthquakes can displace large amounts of water and create massive tsunami.

Is it likely that a tsunami could be generated near the Southern California coast by the same plate mechanism that generated the tsunami in Japan in March?

1933 March 11, Long beach Jefferson Junior High

• Magnitude 6.4 on the Newport- Inglewood Fault
• Heavy damage to masonry buildings (led to State building standards for schools known as the Field Act)