slide © UBC-EOSC 2001 The Shaking Earth: human impact

slide © UBC-EOSC 2001 Outline for “The Shaking Earth” We investigate five aspects of earthquake science: Effects and global distribution –Local context, global distribution, effects, plate tectonics. Earthquake sources –Forces, deforming rocks, faults, energy, tectonics. Seismic waves –Ground motion, wave types, propagation, using seismic waves. Human impact and engineering –What kills?, magnitude vs intensity, buildings, soils. Mitigation and Prediction –Minimizing effects, predicting what? Eosc115 lab exercises … - Using seismic signals to find location, magnitude, and energy. - Investigating effects of ground motion.

slide © UBC-EOSC 2001 Using seismic waves from earthquakes Recording waves at Earth’s surface allows us to: find the location and depth of the source (Abbott 4th ed., pg 73-76) estimate the magnitude characterize potential hazard More in eosc115 exercises. ? * *

slide © UBC-EOSC 2001 Analyzing seismic signals: Waves from the earthquake source (Northridge CA, 1994, M=6.7) Quiet - waves have not yet arrived P-waves arrive firstS-waves arrive laterSlow large surface waves, mixed with remaining P, S waves Time in seconds t s - t p = 7 seconds Vp ~ 6.7km/s, Vs ~ 3.8km/s

slide © UBC-EOSC 2001 Converting seismic wave time into distance In eosc115 lab exercise order

slide © UBC-EOSC 2001 Finding earthquake’s source location t s - t p = 7 seconds Vp ~ 6.7km/s, Vs ~ 3.8km/s P-wavesS-waves Procedure: A. Convert P-S time to distance B. Draw circle at distance. C. Do it at 3 or more places. Intersection is the epicentre.

slide © UBC-EOSC 2001 Outline for “The Shaking Earth” We investigate five aspects of earthquake science: Effects and global distribution –Local context, global distribution, effects, plate tectonics. Earthquake sources –Forces, deforming rocks, faults, energy, tectonics. Seismic waves –Ground motion, wave types, propagation, using seismic waves. Human impact and engineering –What kills?, magnitude vs intensity, buildings, soils. Mitigation and Prediction –Minimizing effects, predicting what? Eosc115 lab exercises … - Using seismic signals to find location, magnitude, and energy. - Investigating effects of ground motion.

slide © UBC-EOSC 2001 Outline of Human Impact: Earthquakes don’t kill … Causing damage: –Acceleration, duration –Factors affecting ground motion – Building characteristics – Soil liquefaction NB: Readings & lectures are complementary - some unique coverage in both. Indicates slide that differs from custom course materials

slide © UBC-EOSC 2001 “Earthquakes don’t kill” … If buildings and structures never fell, earthquakes would not be considered disasters. (Abbot’s theme for chapter 2) Alaska: Exposed sea floor … 33 ft of uplift! Alaska 1964; Mw=9.2 (second largest ever recorded) (pg 99) – 131 killed, $ ?? Kobe: Destruction in urban areas Kobe 1995; Mw=6.9 (Abbott 4th ed., pg 117) – 6,425 killed, $2,716 Millions

slide © UBC-EOSC 2001 Earthquakes in the wilderness: Alaska M 7.9, Nov3, Catastrophe? - People involved? - Infrastructure? ??

slide © UBC-EOSC 2001 Breaking buildings How to break it? Apply a force. –F = ma. Force on a building is proportional to acceleration. –Passing waves cause ground to accelerate then decelerate. Vertical acceleration? 9.8m/s 2 = 1.0g. –Buildings ARE good at withstanding 1.0 ± 1g. Horizontal acceleration? 0.0m/s 2 = 0.0g. (In a train or boat a X = 0.1g or 0.2g) –Buildings are NOT good at withstanding 0.0 ± 1g. at UBC: Education bldg, and EOS-East reinforcing project.

slide © UBC-EOSC 2001 What type of seismic energy will cause damage? Which direction must ground move to damage buildings? ? ?? Recall the three wave types … Which is most likely to cause damaging ground motion? (Consider direction and amount of ground motion.)

slide © UBC-EOSC 2001 Intensity: violence of shaking and damage powerful shaking? Five important factors (Abbott 4th ed., pg 80). 1. Earthquake magnitude 2. Ground type 3. Distance from epicentre 4. Duration of shaking 5. Building characteristics

slide © UBC-EOSC 2001 “Size” of an earthquake’s source Distinguish between magnitude and intensity –magnitude indicates how much energy was released. –intensity is how strong the ground motion is at the felt location. Consider a light bulb … Fixed magnitude Local intensity

slide © UBC-EOSC 2001 Earthquake magnitude Estimated indirectly since we can never monitor the focus. Use seismic wave amplitude, distance and instrument. (Eosc115 - details in the earthquake web-based lab exercise.) Richter Magnitude, M L – Based upon largest amplitude (surface waves) – Strictly “correct” only for Southern California but still widely used. Logarithmic scales are needed. Energy of an M = 5 quake is 43 times M = 6. Abbott 4th ed., pgs and only correct for “Wood-Anderson” seismograph since only high frequencies are recorded Magnitude estimates for large quakes are too low!

slide © UBC-EOSC 2001 Optional - check the time is < 15mins Earthquake magnitude Graphical calculation of M L D(km), sec M L A(mm) Time between P and S arrivals

slide © UBC-EOSC 2001 Optional - check the time is < 15mins Earthquake magnitude Graphical calculation of M L D(km), sec M L A(mm) Largest amplitude

slide © UBC-EOSC 2001 Optional - check the time is < 15mins Earthquake magnitude Graphical calculation of M L D(km), sec M L A(mm) Combine OR: use an equation: M L = 2.76 logD logA

slide © UBC-EOSC 2001 Magnitude vs Energy Several forms of magnitude … –M L Richter magnitude –Mp (based upon P-waves) –Ms (based upon S-waves) –Mw (based upon energy at focus) Recall earthquakes lecture 2.

slide © UBC-EOSC 2001 Does energy affect extent of catastrophy? Yes! Alaska, 1964 –1964; Mw=9.2 was the 2nd largest ever recorded! But smaller earthquakes also may be devastating! –Iran, 2003; Mw=6.6

slide © UBC-EOSC 2001 Intensity: five factors 1. Earthquake magnitude 2. Distance from epicentre 3. Ground type 4. Duration 5. Building type

slide © UBC-EOSC 2001 Intensity factor: Distance from epicentre Here is the felt zone map for Nisqually Abbott discusses –Loma Prieta –Mexico city Why so complicated? Variations in ground. Strong to very strong shaking. Acceleration = %g

slide © UBC-EOSC 2001 Intensity factor: Distance from epicentre Felt zones for 4 earthquakes in SW BC.

slide © UBC-EOSC 2001 Intensity factor: Ground type Harder rocks –no amplification –a mixture of frequencies (Abbot 4th ed., Fig 4.29) Softer rocks – shaking is amplified – low-frequencies may reverberate in basins, plus soft rocks absorb high frequencies

slide © UBC-EOSC 2001 Ground types in Vancouver Harder rocks (bedrock - North Vancouver) –no amplification –all (high and low) frequencies present Softer rocks (sediments - Richmond) –much amplification –loss of high frequency wave energy –reverberating low frequency waves Tidal mud, Richmond Photos by Clague, GeoMap Vancouver, Queen Elizabeth Park (basalt quarry) Which area might suffer more in an earthquake?

slide © UBC-EOSC 2001 Strong Motion Seismographs These instruments record motions that will cause damage. Many are in place around BC’s Lower Mainland.

slide © UBC-EOSC 2001 Intensity factor: Building characteristics Buildings will resonate at frequencies that depend upon construction type, height and mass. demo with “card” buildings as per lab exercise. Resonance depends on height and mass. Motion can be “damped”.

slide © UBC-EOSC 2001 Effects of building type at Kobe, 1995 Buildings in central Kobe (Chuo Ward). Foreground: The complete collapse of a two- or three-story traditional Japanese wood-frame building with a heavy tile roof. Background: A six- or seven-story office building of 1960s' or 1970s' vintage. This reinforced concrete building is a typical example of a mid-height story collapse. Left: The high rise is post-1981 office building that has no apparent damage. Ground settlement in the vicinity of these buildings was between 30 and 60 centimeters. The January 17, 1995 Kobe Earthquake. An EQE Summary Report, April 1995 at

slide © UBC-EOSC 2001 Interactions between two buildings Mexico City, See also Abbott 4th ed., pg 102 Adjacent buildings may behave differently and damage each other.

slide © UBC-EOSC 2001 Summary so far … Next: Other factors affecting costs. Do Earthquakes kill? What type of motion breaks buildings? List 3 factors affecting ground motion. Is FELT motion related simply to distance? Which rock type supports higher frequencies? Which is less elastic (attenuates signals faster)? Building resonance - what are two factors? No … no buildings => no disaster Side to side accelerations Hard rocks. Soft rocks. height and mass 1. Earthquake magnitude 2. Distance from epicentre 3. Local ground characteristics No

slide © UBC-EOSC 2001 Other contributors to cost in $$ and lives Fire ! (Kobe, Japan, 1995) (See Abbott, colour plates) Loss of services: Water; Transport; Communications. Loma Prieta, CA, 1989

slide © UBC-EOSC 2001 More contributors to cost in $$ and lives ( Soil liquefaction … Niigata, Japan, 1964 Lower Van Norman Dam (Abbott 4th ed. Pgs 114)

slide © UBC-EOSC 2001 Soil liquefaction Soil grains may be loosely packed. When saturated, ground motion may increase pore pressure. Soil loses strength and flows like a liquid. (More in eosc115.) Where are … Recent sediments - Older, harder, glacial deposits - Solid rock ?? in the Fraser Valley

slide © UBC-EOSC 2001 Earthquake Hazard Estimation in Canada National Building Code of Canada, provides standards for earthquake-resistant construction. See (Resonance for 10 story bldgs)(Resonance for 2 story bldgs)

slide © UBC-EOSC 2001 Outline of “Human Impact”: Earthquakes don’t kill … Causing damage: intensity –violent shaking (acceleration) –long-duration shaking –buildings prone to collapse Soil liquifaction Next class … Mitigation - minimizing the impact Prediction magnitude, distance, and soil type

slide © UBC-EOSC 2001 Outline for “The Shaking Earth” We investigate five aspects of earthquake science: Effects and global distribution –Local context, global distribution, effects, plate tectonics. Earthquake sources –Forces, deforming rocks, faults, energy, tectonics. Seismic waves –Ground motion, wave types, propagation, using seismic waves. Human impact and engineering –What kills?, magnitude vs intensity, buildings, soils. Mitigation and Prediction –Minimizing effects, predicting what? EOSC 115 lab exercises … - Using seismic signals to find location, magnitude, energy. - Investigating effects of ground motion.

slide © UBC-EOSC 2001 Richter TNT for Seismic Example Magnitude Energy Yield (approximate) ounces Breaking a rock on a lab table ton Large Quarry or Mine Blast 4.0 1,000 tons Small Nuclear Weapon 4.5 5,100 tons Average Tornado (total energy) million tons Northridge, CA Quake, million tons Landers, CA Quake, billion tons Anchorage, AK Quake, billion tons Chilean Quake, 1960 Richter TNT for Seismic Example Magnitude Energy Yield (approximate) ounces Breaking a rock on a lab table pounds large Construction Site Blast ton Large Quarry or Mine Blast 4.0 1,000 tons Small Nuclear Weapon 4.5 5,100 tons Average Tornado (total energy) ,000 tons 2 little boy bombs (dropped on Hiroshima) million tons million tons Northridge, CA Quake, million tons Largest Thermonuclear Weapon million tons Landers, CA Quake, billion tons San Francisco, CA Quake, billion tons Anchorage, AK Quake, billion tons Chilean Quake, trillion tons (San-Andreas type fault circling Earth) trillion tons (Fault Earth in half through center, OR Earth's daily receipt of solar energy) Nisqually, 2001 Intensity factor: Earthquake magnitude Fairly obvious …