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95% of the major earthquakes occur along the Ring of Fire
Earthquakes first 15 years of 21st century
We measure earthquakes by:
● Intensity● magnitude
Intensity: the measure of the amount of earthquake shaking at a given location.
Richter Scale: measures the intensity by the amplitude of the seismic wave using a logarithmic scale.
Charles Richter
Moment magnitude scale (MMS): derived from the amount of displacement that occurs along a fault zone (1979)
Area of surface break x average displacement x rigidity of the rock = amount of energy that can be stored
Modified Mercalli scale: rates earthquake intensity in terms of effects in different locations, expressed in Roman numerals.
Chapter 8.3: Destruction by Earthquakes
Amount of damage depends on several factors:
● Intensity and duration of vibration● Nature of structure material ● Design of the structure
Liquefaction: when loosely consolidated sediments are saturated with water turn into a liquid unable to support structures such as buildings.
Japan
Tsunami: seismic sea waves that occur when a slab of ocean floor is displaced vertically along a fault.
Japan 2011India 2004
Landslides and ground subsidence causes the greatest damage to structures.
Can we predict earthquakes?
Short-range predictions look at possible precursors- uplift, subsidence, strain in rocks along active faults.
Long-range forecasts give the probability of certain magnitude earthquakes in given areas.
seismic gap: an area along a fault line where there hasn’t been any activity for a long time.
California