Earthquakes and Related Phenomena

Earthquake Web Resources

Deadliest Earthquakes on Record

Introduction to Earthquakes ~ 1 million earthquakes a year Change of 1 M w = ~30 X energy Great earthquakes; M s >8 Major earthquakes; M s =7-7.9 (widespread damage) Moderate earthquakes: M s =6 (considerable damage) Population factors: density, land use, and building construction M s Earthquakes/year

Where do earthquakes occur? Plate boundaries, but not only – intraplate earthquakes are also common

Earthquake Occurrence Most occur along plate boundaries. –Loma Prieta (1989) –North Ridge (1994) Intraplate earthquakes –Can be large and quite damaging. New Madrid zone is a foundered rift zone Salt Lake City and south into New Mexico Charleston, S.C.

Largest US Earthquakes

Relationship of Earthquakes to Faults

Earthquake Processes Faults, Folds & Concealed Faults, and Movement –Fractures Faults are fractures or systems along which rocks have been displaced –Model: brick -bungee cord on a winch; sand paper Joints are fractures and fractures systems along with rocks have NOT been displaced Slip rate aver. long-term rate of movement ( mm/yr or m/1000 yrs); risky measurement Seismic waves produced by rupture Faults-seismic sources; used to evaluate the earthquake risk in a given area

Earthquake Processes Fault types Strike-slip faults only have horizontal displacement (right- or left-lateral)Strike-slip faults Normal faults occur where the hanging wall moves down with respect to the foot wall; results in crustal extension Reverse faults occur when the hanging wall moves up with respect to the foot wall; results in crustal shortening; low fault plane angle ( less than 45°)= thrust fault Oblique faults have both horizontal and vertical components Buried faults may cause earthquakes and have to surface expression

Faults – Understanding Strike and Dip