19.4 – Earthquakes & Society

Damages  Death and injuries  Collapse of buildings  Landslides  Fires  Explosions  Flood waters

Earthquake Hazards  Identifying hazards can prevent some damage and loss of life  Design of building can affect damage Unreinforced buildings made of concrete crumble Wood structures are more resilient

Structural Failure  Buildings are destroyed as ground shakes  Ground floor walls fail and cause upper floors to fall and collapse as they hit the lower floors Pancaking

 Height also impacts building strength  If frequency of vibration is close to natural sway = sways most violently  Ground vibrations Too rapid = do not impact tall buildings Too slow = do not impact shorter buildings

Land & Soil Failure  Sloping areas create landslides  Soil liquefaction = sand is nearly saturated with water Vibration cause ground to behave like liquid  Surface waves are amplified in soft materials Muted in more resistant (granite)

Tsunami  Large ocean wave generated by vertical motions of seafloor during Earthquake  Caused by faulting and underwater landslides Faulting causes a sudden drop or rise in ocean floor and the mass of water changes Violent water movements create long, low waves  In shallow water, waves become high breakers larger than 30 meters in height

Earthquake Forecasting  Based on calculating probability of earthquake Uses history of earthquakes and rate strain builds up  Seismic risk Probability is greater along Seismic Belt Pattern of past activity is reliable indicator

Earthquake Forecasting  Recurrence risk Indicate whether fault ruptures at regular intervals San Andreas  6 earthquakes every 22 years between  1987, 90% probability of an earthquake occurring  6.6 Magnitude earthquake occurred November 1987

Earthquake Forecasting  Seismic gaps Sections along faults that are known to be active but have not experienced significant earthquakes  Stress Accumulation Rate at which stress builds up in rocks

In-Class Assignment/Homework  Pg. 555 #1-10 and  Work with a partner put both names on paper and turn into tray when finished