NOTHRiDGE EARTHQUAKE.

The Northridge earthquake occurred at 4:30 a.m. local time on January 17, 1994. Northridge is located about 30 km northwest of Los Angeles. This earthquake had a 6.9 moment magnitude. The hypocentral depth was 19 km. The duration was about 10 seconds to 20 seconds. The earthquake occurred along a "blind" thrust fault, close to the San Andreas fault. Note that a blind fault is a fault which does not extend to the surface. In other words, it is buried.

Thousands of aftershocks occurred after the main earthquake. For example, a magnitude 5.9 aftershock occurred about 1 minute after the mainshock. A magnitude 5.6 earthquake occurred 11 hours later. Aftershocks are a concern because they can trigger the collapse of structures weakened by the mainshock.

EARTHQUAKE HAZARDS.

 BUiLDiNGS CAN BE DAMAGED.


The first main earthquake hazard (danger) is the effect of ground shaking. Buildings can be damaged by the shaking itself or by the ground beneath them settling to a different level than it was before the earthquake (subsidence).Buildings can be damaged by strong surface waves making the ground heave and lurch. Any buildings in the path of these surface waves can lean or tip over from all the movement. The ground shaking may also cause landslides, mudslides, and avalanches on steeper hills or mountains, all of which can damage buildings and hurt people.






Falling Objects: Objects can fall from shelves, ceilings, building, etc. and easily injure humans or other animals.
Fires: Fires are caused by disruption of electric, gas, or oil lines which can rupture from the ground shaking.
Avalanches:Due to the ground shaking, avalanches cause snow to behave like a liquid and slide down a mountain. Avalanches can bury mountain side homes and destroy forests.

SESMiC WAVES.

                        
                                    

When a sudden break or shift occurs in the earth's crust, the energy radiates out as seismic waves, just as the energy from a disturbance in a body of water radiates out in wave form. In every earthquake, there are several different types of seismic waves.
Body waves move through the inner part of the earth, while surface waves travel over the surface of the earth. Surface waves -- sometimes called long waves, or simply L waves -- are responsible for most of the damage associated with earthquakes, because they cause the most intense vibrations. Surface waves stem from body waves that reach the surface.

                                

Seismic waves are vibrations that travel through the Earth carrying the energy released during earthquakes.
Seismic waves are waves that are a result of earthquake activity in the earth. There are body and surface waves. Body waves happen inside the earth and are called P (longitudinal) and S (transverse) waves. Surface waves happen on the Earth's surface and are called Rayleigh and Love waves.
P-waves (primary waves) go first, compress and expand the earth, and are faster. S-waves (secondary waves) go second, move the ground up and down or side to side, and are not as fast as P waves.

Batolith

Sometimes batholiths arise through several smaller diapiric intrusions (plutons) and have a complex history of magmatic intrusion and crystallization at depths of 5 to 30 kilometers. Batholith formation is commonly associated with lithospheric plate boundaries, where tectonicinteractions between plates are associated with large scale melting of crustal rocks and the formation of deep magma chambers. As erosion uncovers the crystalline rock that formed at great depth, crystal structures respond to the decrease in load and expand, rendering the plutonic rocks susceptible to exfoliative weathering.






Although they may appear uniform, batholiths are in fact structures with complex histories and compositions. They are composed of multiple masses, or plutons, bodies of igneous rock of irregular dimensions (typically at least several kilometers) that can be distinguished from adjacent igneous rock by some combination of criteria including age, composition, texture, or mappable structures. Individual plutons are crystallized from magma that traveled toward the surface from a zone of partial melting near the base of the Earth's crust.