Elastic rebound theory

Focus epicenter - wave propagation

Dip-Slip Fault - Normal

Normal Fault vertical motion due to tensional stress Hanging wall moves down, relative to the footwall

Opal Mountain, Mojave Desert

Dip-Slip Fault - Reverse

Reverse Fault vertical motion due to compressional stress Hanging wall moves up, relative to the footwall

Thrust Fault low-angle reverse fault typically (though not always) larger than a reverse fault, with greater displacement

Strike-Slip Fault Right Lateral

Strike-Slip Fault Left Lateral

Strike-slip Fault Horizontal motion due to shear stress Also known as a Transform fault

Releasing bend, Mojave Desert Bend in fault opens as opposite sides are pulled apart

Releasing bend Lake Elsinore CA

Restraining bend, central California Bend in fault converges as opposite sides are pushed into each other

Restraining bend

Inertial Seismometer

How Seismometers Work

A seismogram records amplitude vs. time

Body waves P-waves compressional S-waves transverse Velocity increases with density/rigidity (min at surface)

Solid Earth Primary (P) waves Secondary (S) waves

Fluid Earth Primary (P) waves Secondary (S) waves

Surface waves Love Waves Transverse Rayleigh Waves Orbital All motion dissipates with depth (max at surface)

A time-travel graph is used to find distance to the earthquake focus

Locating Earthquakes

Locating Earthquakes - Depth

Focal mechanisms

Earthquake Magnitude Richter Scale (M L ): Related to Energy Release Exponential No Upper or Lower Bounds Largest Quakes about M L = 8.7

Richter Magnitude Base-10 logarithm of the: amplitude of the largest wave; measured in microns from a distance of 100 kilometers

Richter Nomograph

Magnitude - Energy Magnitude-Energy Relation M L -- Energy released 4 ~ 1 5 ~ 32

Magnitude - Energy Magnitude-Energy Relation M L -- Energy released 4 ~ 1 5 ~ 32 6 ~ 1,000

Magnitude - Energy Magnitude-Energy Relation M L -- Energy released 4 ~ 1 5 ~ 32 6 ~ 1,000 7 ~ 32,000

Magnitude - Energy Magnitude-Energy Relation M L -- Energy released 4 ~ 1 5 ~ 32 6 ~ 1,000 7 ~ 32,000 8 ~ 1,000,000

Seismic Moment A seismograph measures ground motion at one instant but -- Great earthquakes last several minutes They release energy over hundreds of kilometers Need to Sum Energy of Entire Record Modifies Richter Scale, doesn't replace it Adds about 1 Magnitude To 8+ Quakes

Seismic Moment To calculate energy release in great Eqs: We need to sum energy of entire record Size of fault plane involved Ability of rocks to store strain energy Amount of displacement

Seismic Moment L: total length of offset on fault A: area of ruptured fault plane µ: strength or rigidity of rock (resistance to rupture) ---------------------------------------------------------------- Seismic Moment M 0 = L x A x µ

Seismic - Moment Magnitude Seismic Moment M 0 = L x A x µ ---------------------------------------------------------------- Moment Magnitude M w = (log 10 x M 0 9.1) 2 3

Magnitude and Energy

energy -v- distance Hiroshima bombing ~ 15 kt Nagasaki bombing ~ 21 kt

Intensity How strongly the ground shakes (wave amplitude, acceleration) Depends on: Distance to quake Near-surface geology

Intensity How strongly the ground shakes (wave amplitude, acceleration) Depends on: Distance to quake Near-surface geology Varies from place to place Mercalli Scale - I to XII May be determined by observers Can be determined by instruments

Modified Mercalli Intensity Scale

Isoseismals from the 1906 San Francisco Earthquake

Intensity and Geology in San Francisco, 1906

Intensity and Bedrock Depth in San Francisco, 1906

Isoseismal map of the 1994 Northridge, CA earthquake

Isoseismal map of the 2010 Chilean earthquake

Isoseismal map of the 2010 Haitian earthquake

Isoseismal map of the 2011 New Zealand earthquake

Isoseismal map of the 2011 Japan earthquake

Liquefaction

Niigata Japan (1964)

Formation of a tsunami

Tsunami travel times to Honolulu

Oblique view of 2004 tsunami

Animation of 2004 tsunami

Banda Aceh

Liquefaction susceptibility in the San Francisco Bay

Van Norman Dam (1971)