EARTHQUAKE EFFECTS, PATTERNS, AND RISK

1. EARTHQUAKE EFFECTS, PATTERNS, AND RISK

2. Earthquake Effects - Surface Faulting Landers, CA 1992

3. Thrust Fault Example

4. Normal Fault Example Dixie Valley-Fairview Peaks, Nevada earthquake December 16, 1954

5. Rupture on a Fault Total Slip in the M7.3 Landers Earthquake

6. Earthquake Effects -Ground Shaking Northridge, CA 1994

7. Earthquake Effects - Ground Shaking Loma Prieta, CA 1989 KGO-TV News ABC-7

8. NATURAL PERIOD OF BUILDINGS • Natural Period, T = 1/f • Typical values: • Stories: Value: • 2 0.2 sec • 10 1 • 20 2 • 30 3

9. Earthquake Effects - Ground Shaking Kobe, Japan 1995

10. Earthquake Effects - Ground Shaking Kobe, Japan 1995

11. TSUNAMIS • Earthquakes beneath the ocean floor sometimes generate immense sea waves, or tsunamis. • These waves travel across the ocean at speeds as great as 750-960 kilometers per hour and may be 15 meters high or higher by the time they reach the shore. • During the 1964 Alaskan earthquake, tsunamis engulfing coastal areas caused most of the destruction at Kodiak, Cordova, and Seward and caused severe damage along the west coast of North America, particularly at Crescent City, California. Some waves raced across the ocean to the coasts of Japan.

12. Earthquake Patterns in Time and Space • Foreshock-main event-aftershock pattern: increase in number of microearthquakes in area of future rupture preceding a main event, and the decrease in earthquake activity after a main event • Quiescence: an anomalous loss of normal background microearthquakes for hours or days preceding a main event • Seismic Gaps: an absence of expected earthquakes on a segment of an active fault • Slip-rate diagrams: cumulative slip vs. time to estimate repeat times and average amounts of slip

13. EARTHQUAKE RISK ESTIMATES • To estimate the danger of destructive earthquakes in a region, a number of factors need to be assessed: • 1) earthquake history--instrumental-- provides location, size, and timing of events in last 50 years • 2) non-instrumental history-- provides location, estimated size (or at least damage), and timing • 3) geologic history of fault movement at archeological sites and prior to human history.

14. PALEOSEISMOLOGY • The earthquake study will identify active faults, and the pattern of events. Patterns to examine include repeat times, amount of movement at each event, whether preceded by microearthquakes or other changes in terrain, water level, animal behavior, etc.

15. Prediction vs. Forecast

16. Prediction vs. Forecasting • PARAMETER PREDICTION FORECAST • LOCATION: +/- <5 km +/- 50km • TIME: +/- hours or days +/-decades to centuries • SIZE: +/- 1 Magnitude +/- 2 M

17. LOCATION • Seismologists use Instrumental Records of the arrival times of the P and S waves. Location quality has improved with more stations carefully calibrated, but can be as bad as +/- 50 km in some remote regions! • Paleo-seismologists use: • Historical Records • Geological Field Data: scarps, gouge, offsets, landslides, disturbed archaeological sites • Evidence of ancient tsunamis

18. Time • Seismologists use Instrumental Records. Can narrow the time down to a fraction of a second. • Paleoseismologists: dated historical records, isotopic dating of offset features. Some rock types are undatable for this purpose. Most radiometric dates are +/- 50 to 150 years.

19. Size • Seismologists: instruments. Depends on careful calibration. Can be accurate to 0.01 Magnitude units. • Paleoseismologists: estimates based on size of rupture zone (fractured rock), amount of slip, damage reports, how far inland and how high above sealevel tsunami deposits are found