1	Internal Processes: Earthquakes
2	Earthquakes Are the sudden release of seismic energy Travels as ‘waves’ Caused mainly by movement along faults Tectonic stresses Can occur without warning Can cost billions of $ in damage Why do they happen? Ultimately, due to Stress & Friction Stress on faults is continuous; movement is not
3	Tectonic Stress & Faults Fault- fracture with measurable displacement Dip Slip Faults Normal, Reverse, Thrust Horizontal Slip Faults Strike-slip Oblique-Slip Faults Combination of both previous types
4	Dip Slip: Normal Faults Due to tensional stress Footwall up w.r.t Hanging Wall Found where extension is occurring Associated with divergent boundaries Continental rifts, MORs Extensional provinces include: Basin & Range, Rio Grande Rift
5	Dip Slip: Reverse Faults Due to compressional stress Hanging Wall up w.r.t Foot Wall Thrust- dip <25° Result in crustal shortening Assoc. with convergent boundaries Subduction, continental collision Compressional areas include: Pacific NW, Himalaya, parts of Alaska, California, Appalachians
6	Strike-Slip Faults Horizontal movement Left lateral (sinistral) or Right laterall (dextral) Associated with transform boundaries Examples: San Andreas Fault System
7	When An Earthquake Occurs Rupture releases seismic waves Focus- Site of initial rupture Displacement maximum at the focus, & decreases towards the surface. Sometimes ruptures never break the ground surface Epicenter- geographic location on surface
8	Seismic Waves Body Waves S Wave slower, move through solids Shearing motion P Wave faster, move through liquid & solid Compressional motion Surface Waves Rayleigh Wave Cause heaving and rolling Love Wave Sideways movement
9	Measuring an Earthquake Magnitude- Severity of quake based on AMPLITUDE of seismic waves Richter Scale Measures the SEISMIC ENERGY released by an earthquake Larger amplitude = Larger earthquake Logarithmic. Each magnitude is 10x greater than the last Recorded by seismographs
10	Measuring an Earthquake Intensity- Severity of quake based upon DAMAGE caused Modified Mercalli Scale Measures the EFFECTS of an earthquake. Older scale, based on human observation Scale of I- XII
11	Hazards associated w/ Earthquakes Primary Effects- permanent features fault scarps, surface ruptures, and offsets Secondary Effects- caused by ground motion
12	Ground Movement Surface Waves- most destructive Rayleigh & Love waves result in ground heave, swaying buildings Composition of materials influences ground movement Unconsolidated (sand, mud, artificial fill) most affected Bedrock- less so
13	Types of Secondary Effects Flooding Fires Building collapse Liquefaction Tsunamis Landslides Reaction to ground motion depends upon: Substrate (bedrock vs. unconsoidated) Building Material Concrete, Steel Engineered ‘safety’ vs. ‘damage control’ wood
14	Earthquake Hazards, USA
15	April 18^th, 1906 San Francisco Mercalli VII- IX Ruptured along a 296 mile stretch of the San Andreas Fault Strongest shaking- the bay
16	California Earthquake Hazards
17	Alaska Earthquake Hazards
18	Midwest Earthquake Hazards New Madrid Seismic Zone- The Reelfoot Rift 1811-1812 4 quakes 7.2 - 8.1 Richter
19	Washington Earthquake Hazards Cascadia 1700 Largest earthquake in ‘lower 48’ Affected 600 mile area from CA to B.C., Canada ~9.0 Richter Caused tsunamis in Japan, Hawaii Lake Chelan, WA 1872, 6.8 Richter Caused fissures, geysers, landslides Puget Sound Nisqually Quake, Feb. 28th,2001, 6.8 1965, 6.5 1949, 7.0
20	Any Earthquakes Today? The Pacific Northwest Seismic Network Seismographs record real-time data
21	Largest Earthquakes Since 1900 9.1 Richter – 2004 Sumatra, Indonesia 9.0 Richter- 1952 Kamchatka 9.1 Richter- 1957 Andreanof Islands, Alaska 9.5 Richter- 1960 Chile 9.2 1964 Prince William Sound, Alaska All of these earthquakes were mega-thrust events All occurred in subduction zones All produced destructive tsunamis
22	10 Largest Earthquakes in Recent History Chile, 1960 9.5 Richter Alaska, 1964 9.2 Richter Russia, 1952 9.0 Richter Ecuador, 1906 8.8 Richter Alaska, 1957 8.8 Richter Kuril Islands, 1958 8.7 Richter Alaska, 1965 8.7 Richter India, 1950 8.6 Richter Chile, 1922 8.5 Richter Indonesia, 1938 8.5 Richter
23	Predicting Earthquakes Quakes are sudden, often without warning Prediction is unreliable Some Methods- Earthquake Cycles Identifying seismic ‘gaps’ Many small earthquakes = 1 large quake ‘Locked’ fault sections prevent slip Ie no small quakes Stress is building
24	Reducing Risk Public Education Earthquake Drills Disaster Response Plans Retrofitting for prevention Building Codes Landuse Restrictions
25	End Earthquakes