Earthquakes

• Every day, 8000 earthquakes happen around the world.
• Most earthquakes are too small to be felt by humans.
• Most earthquakes take place at plate boundaries.
• Some earthquakes take place in the middle of plates.
• Earthquakes are caused by the movement along faults.
• Numerical Modeling: Magnitude of Quake, Location, Other factors
• When a fault slips, an earthquake takes place.
• Seismic tomography is used to detect movement along faults.
• Earthquakes can be ranked according to intensity on the Mercalli Scale.
• The Richter Scale is used to measure the intensity of earthquakes.
• Seismic waves are waves that are generated as a result of earthquakes, including body waves, P waves, S waves, surface waves, Rayleigh waves, and Love waves.
• Earthquakes can also be ranked according to magnitude on the Richter Scale.
• Seismic waves are also waves generated during earthquakes, including body waves, P waves, S waves, surface waves, and several other types.
• The seismograph, invented during the Han dynasty in China in 132 AD, was invented by the astronomer Can Heng.
• Rocks at the fault plane are under high pressure, and this causes friction.
• The fault does not move until there is enough stress to overcome the friction.
• When stress has become greater than the friction can hold back, the fault will move suddenly and all the stored energy is released.
• Large earthquakes occur at active faults where the rate of movement is high and resistance to movement due to friction is high.
• At the San Andreas fault, the northern segment moves often, resulting in frequent, small earthquakes, while the southern segment moves far less often, resulting in less frequent, but much stronger earthquakes.
• The Richter Scale, developed by Charles F. Richter in 1932, measures the energy released by an earthquake.
• The Mercalli Scale, developed by Giuseppe Mercalli in 1902, measures the effect of an earthquake at a given location.
• Earthquakes are measured on both scales logarithmic and non-logarithmic.
• Earthquakes with a magnitude of 2.5 or less cannot be felt by humans, but can be detected by a seismograph.
• Earthquakes with a magnitude of 2.5 to 5.4 may be felt, but only cause slight damage.
• Earthquakes with a magnitude of 5.5 to 6.0 cause slight damage to buildings and other structures.
• The record from a seismometer is called a seismogram.
• P waves move 1.7 times faster than S waves.
• The direction to an earthquake can also be determined based on the E-W, N-S and Up-Down vectors of the first movement.
• The study of ancient tsunamis involves estimation of hazard.
• Tsunamigenic earthquakes are related to subduction zones, are shallow, and involve surface rupture.
• The large amplitude, long period (~20 sec) waves on the seismogram, arriving approximately 20 minutes after the P-wave, are surface waves.
• Seismometer or seismograph is used for detecting and measuring earthquakes.
• The molten outer core causes S-wave "shadow zones" on the other side of the earth.
• Local vs distant tsunami is a factor in tsunami warning systems.
• Time factor is also a factor in tsunami warning systems.
• Tsunami Warning Systems are based on tidal gauges, buoys, etc.
• Seismometer consists of a detector, amplifier, recorder, and a very accurate clock synchronized through satellites.
• A ball will fall out of the mouth of the dragon facing in the direction of an earthquake.
• S waves cannot move through a liquid (liquids have no shear strength).
• Sets of three instruments - East - West, North - South and Up - Down are used in seismology.