3. P-waves travel fastest. They consist of successive contractions and expansions, just like sound waves in air. The motion of the particles in the rocks that the waves travel through is parallel to the direction of the wave. S-waves are slower than P-waves. They are transverse waves, which means that the particle motion is at right angles to the direction of travel. S-waves cannot travel through air or liquids. They shake the earth up and down and side to side SEISMIC WAVES Two different types of seismic waves are generated by the sudden movement on a fault: P-waves and S-waves. A third type of seismic wave is generated by the interaction of the P- and S- waves with the surface and internal layers of the Earth. The speed of the waves depends on wave type and the properties of the rock; the denser the rock, the faster the waves travel. In the Earth’s crust P-waves travel at around 6-7 km/s, while S-waves travel at around 3.5-4 km/s.

6. The most widely documented earthquake zone in the world is the San Andreas fault running through California. The fault is the boundary between the Pacific and North American plates. Here they form a transform margin where movement is in a slip zone as shown on the map.

8. Movement along the San Andreas Fault during the 1906 earthquake displaced this fence by about 1.5 metres. The gap in the fence was caused by the primary surface fracture along the fault. This view is from the Pacific Plate on the west side of the fault looking toward the North American plate on the east side. The fault line separating the two plates is shown by the arrow. What has happened here?

9. This young woman is standing on the San Andreas Fault

11. You can see clearly where the fault line is in this orchard

12. Check out the line of the fault in this picture

13. Rocks of the Pacific Plate on the left slip past rocks of the North American Plate on the right What do you notice here?

14. Offset at Wallace Creek, California Can you see what has happened here? What may happen to this river in time? 90 metres

18. Measuring Earthquakes

21. Richter TNT for Seismic Example Magnitude Energy Yield (approximate) -1.5 6 ounces Breaking a rock on a lab table 1.0 30 pounds Large Blast at a Construction Site 1.5 320 pounds 2.0 1 ton Large Quarry or Mine Blast 2.5 4.6 tons 3.0 29 tons 3.5 73 tons 4.0 1,000 tons Small Nuclear Weapon 4.5 5,100 tons Average Tornado (total energy) 5.0 32,000 tons 5.5 80,000 tons Little Skull Mtn., NV Quake, 1992 6.0 1 million tons Double Spring Flat, NV Quake, 1994 6.5 5 million tons Northridge, CA Quake, 1994 7.0 32 million tons Hyogo-Ken Nanbu, Japan Quake, 1995; Largest Thermonuclear Weapon 7.5 160 million tons Landers, CA Quake, 1992 8.0 1 billion tons San Francisco, CA Quake, 1906 8.5 5 billion tons Anchorage, AK Quake, 1964 9.0 32 billion tons Chilean Quake, 1960 10.0 1 trillion tons (San-Andreas type fault circling Earth) 12.0 160 trillion tons (Fault Earth in half through center, OR Earth's daily receipt of solar energy)

27. Why does the impact of earthquakes vary?

28. VULNERABILITY NATURAL HAZARD RISK OF DISASTER Sudden events and chronic issues Past recurrence intervals Future probability Speed of onset Magnitude Duration Areal extent Exposure, sensitivity and resilience of: Population Economy Land use and development Infrastructure and critical facilities Cultural assets Natural resources Source: Geography for EDEXCEL by Digby et al (Oxford University Press) EARTHQUAKES VENN DIAGRAM The connection between natural hazard events and locational site vulnerability

31. Earthquakes in UK

36. The End