Lesson 4 Plotting Earthquakes
Plate Tectonic Theory states that large rigid segments of the outer part of the earth are broken into plates that move relative to one another.
• There are three main belts of earthquake activity associated with plate boundaries.
• The Circum-Pacific Belt (Ring of Fire)
• 80% of all earthquakes occur here
• It is an almost continuous chain of volcanoes around the edges of the Pacific Ocean
• Pacific plates slides past or collides with adjoining plates
• The Mediterranean-Himalayan Belt
• 15% of all earthquakes occur in this belt., which extends west from Indonesia through the Himalayas, across Iran and Turkey, and west through the Mediterranean region or Europe
• Plate movements in this belt also led to the formation of the
Himalayas
• The Mid-Ocean Ridge
• Location of the world's largest chain of volcanoes extends more than 100,000 km through the middle of the world's oceans.
• Consists of elevated faults on either side of a depression.
• Together with inter-plate earthquakes, they account for 5% of all earthquakes
• Seismic activity is mostly shallow, making these earthquakes usually of lower magnitude.
Magnitude
• Magnitude is measured on the Richter scale from 1 to ???
• Highest ever in recorded history is 9.5 in 1960 in Chile
• Each increase in magnitude number is a 10x increase in amplitude seen on the seismogram and a 32 times greater amount of energy released
• Intensity
• Measured on the Mercalli scale
• Measured in Roman numerals from I(one) to XII(twelve)
• Intensity describes the kind of damage done by an earthquake and people’s reaction to it (felt observations)
• Intensity is affected by distance, depth, population density, local geology, building construction, and duration of shaking