EarthQuakes
An earthquake is the movement of Earth’s lithosphere that occurs when rocks in lithosphere suddenly shift, releasing stored energy.Seismic wave are the small portion of the energy released during when an earthquake is carried by vibration.
Tsunami is a large sea wave generated by an underwater earthquake, volcano, or landslide
Stress in Earth’s Crust
Earthquake happens because of the ways the plate movements affect the lithosphere. Forces of plate movement cause deformation or change in the shape or volume of mass of rock. Deformation acting on rocks of the crust is example stress.Stress is a force that squeezes rocks together stretches or pulls them apart or pushes them in different direction. As tectonic plates move, they cause stress in the crust, which in turn produces faults and folds. Fault is a break in a mass of rock along which movement occurs and a Fold is bend in layers of rock.
Earthquakes and Seismic Waves
Building of stress along a fault provides the potential energy that powers an earthquake. Earthquakes occur because stress forces have exceeded the strength of rock Focus is the location beneath Earth’s surface where earthquake begins. Location on Earth’s surface directly above the focus is the epicenter
The Physics of Earthquakes
Within Earth’s crust, forces are at work along faults. Earth quakes are caused when 2 sides of the fault move past each other. Any material has a limit to how much stress it can absorb. When rocks are strained beyond the limit, they break and grind past each other releasing huge amount of energy in the form of earthquake.
Types of Seismic Waves
Earthquakes produce 3 main types of seismic waves, which are P waves, S waves, surface waves.
P (primary) waves are the longitudinal waves similar to sound waves. So recall that, as longitudinal waves move through a material, they cause particles in the material to vibrate in the direction of the waves motion. P waves compress and expand the ground like an accordion. Since P waves are the fastest seismic waves, they are the ones to be detected first.
S (secondary) waves are the transverse waves so the particles in the materials they pass through to vibrate at right angles. Unlike the P waves S wave can not go though liquids.
Surface waves are waves that develop when seismic waves reach Earth’s surface. It move slowly than P waves and S waves but creates larger movement and bigger damage. Surface waves are transverse waves and other have a rolling motion like the ocean.
Measuring Earthquakes
To measure earthquakes and pinpoint their epicentres, geologists record seismic waves using seismographs. Seismograph is a device to detect and record seismic waves, and we recorded in seismograms. Most earthquakes are to small for human to feel but big ones releases more energy than what america uses.
Richter Scale
The most well-known scale to measure Earthquake is the Richter scale. It rates earthquakes based on measurements of the times and amplitudes of seismic waves. But this measurement is no longer used by geologists.
Most useful scale to measure earthquakes for geologists is the Moment Magnitude Scale, which gives measure of amount of energy released by an earthquake.
Modified Mercalli Scale
The effects of earthquakes can also be rated using the modified Mercalli scale, which is ranged from 1-12. Based on damage affects the Earth and observation of the intensity of ground shaking and the damage affected by the earthquake.
Seismographic Data
Worldwide network of seismograph has provided scientist with a wealth of data on earthquakes. This enabled geologists to map the distribution of the earthquake. Also seismographic data have been used to probe the structure of earth's interior.
Most earthquakes are concentrated along plate boundaries, where many faults are found. Some earthquakes occur in the interior of plates far away from plate boundary. Scientist analysed that the speed of seismic waves and the paths they take are affected by the temperature, composition and density.