Intensity earthquakes by: magnitude We measure 95% of the ... · Can we predict earthquakes?...

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