Intraplate Earthquakes New Madrid, Missouri: December 1811, January 1812, February 1812 Figure 3-17

Intraplate Earthquakes Eastern U.S. earthquakes less frequent, but more widely felt Crust is older and transmits stress Figure 3-20

Earthquake Size and Characteristics How big is it? Answer in terms of perceived effects: intensity Answer in terms of amount of energy released: magnitude

Earthquake Intensity Mercalli Intensity Scale developed in 1902 Based on effects Local small quake is similar to distant large quake Table 3.2

Felt effects using Mercalli Scale http://www.scec.org/instanet/01news/images/NorthridgeSMap.gif

Felt effects using Mercalli Scale Hypothetical M7.8 earthquake

Landers 1992 earthquake: Felt intensity by zip code

Earthquake Magnitude Richter Magnitude Scale (ML) derived by Charles Richter in 1935 Uses maximum amplitude of earthquake waves on seismograph Logarithmic scale Richter magnitude less accurate above M6.5 Figure 3-29

Problems with scales Moment magnitude is measure of total energy expended during earthquake Determined from long-period waves Moment = (shear strength of rocks) x (surface area of rupture) x (slip distance on fault) Each number is 32X energy Each 2 numbers =1000X This is the most common scale for quakes >3.5

Another example of M=1/f

1995 Kobe earthquake, Japan

1989 Loma Prieta earthquake, SF Bay Area

Liquifaction Water in sediment causes solid rock to behave like a liquid.

Liquifaction

Secondary Ground Effects Surface rupture-scarp Earthquakes often trigger landslides Can also cause liquefaction Soils become almost liquid when shaken, solidify when shaking stops Significant damage to structures atop liquefied sediments Fires

Surface rupture-scarp

1906 earthquake surface rupture. 8’ fence offset above http://mnw.eas.slu.edu/Earthquake_Center/1906EQ/1906thumb.html And http://quake.wr.usgs.gov/info/1906/images/fenceoffset_big.html

Australia, 1968, M6.8

Armenia, 1988, M6.9

Borah Peak, ID: 1983 M7.3

California, 1979, M6.9

Landslides caused by 2002 Denali Fault earthquake

1965 Seattle quake M6.5

Liquifaction Water in sediment causes solid rock to behave like a liquid.

This residential and commercial building sank more than three feet into the partially liquefied soil.

Liquifaction: Niigata, Japan, 1964

San Francisco 1906 M8.3 Secondary effects: Fire

Long term probability Probability of where and when an earthquake will strike used to construct risk map Figure 4-14

Earthquake Hazards 2% chance in next 50 years

The San Francisco Bay Area Figure 4-17

Las Cruces: 15-18% chance of M5 in 50 yrs.

Sample Test Questions