Earthquakes are usually caused when rock underground suddenly breaks along a fault. This sudden release of energy causes the seismic waves that make the ground shake. When two blocks of rock or two plates are rubbing against each other, they stick a little or lock in place. When these locked faults move they cause what is called a slip-fault earthquake.
Model a Slip-Fault Earthquake
Cover two wooden blocks with sandpaper of equal grade sandpaper. Firmly press the two sandpaper covered blocks together. While continually pushes the blocks together, try to slice the blocks in different directions–slide one block up and the other down.
The blocks will temporarily lock together, then will move with a jolt.
Why?
The lithosphere (the solid, outermost prt of the earth’s surface) is broken into major sections referred to as tectonic plates. Where the edges of the two plates push against each other, the crack between the plates is called a fault. Friction (the resistace to motion) causes the plates to be temporarily locked together.Faults that are temporarily locked together are called locked faults.The two sandpaper covered blocks represent two tectonic plates pushing against each other. They temporarily lock together, but as with the actual tectonic plates, the friction between the blocks eventually fails, causing a sudden jolt. The hond holding a locked fault in place is under tremendous stress, but may last for years before suddenly slipping. Lock faults inevitably and frequently fail resulting in an explosion of motion that produces powerful earthquakes.
More about earthquakes
An earthquake is a violent shaking of the earth’s crust usually caused by a sudden movement of rock along a fault line below the earth’s surface. Earthquakes produce seismic waves.
Seismic waves are waves of energy traveling through the earth, and are the results of earthquakes or explosions. The two types of seismic waves are body waves and surface waves.
Body Waves travel through earth’s inner layers.
P-Waves Primary Waves, which are the most energetic and fastest moving seismic waves. P-waves travel beneath the earth’s surface at a speed of about 5 miles per second. These are longitudinal waves.
S-Waves Secondary Waves, which are the slowest waves that travel beneath the earth’s surface at a speed of about 2 miles/second. These are transverse waves and displace the ground perpendicular to the direction the wave is moving.
Surface Seismic Waves
Travelling only through earth’s crust. These waves arrive after the body waves and are almost enitrely responsible for the damage and destruction associated with earthquakes. The strength of surface waves depend on the depth of the earthquake. The deeper the earthquake the less surface damage.
Love Waves are surface seismic waves that cause back and forth horizontal movement.
Raleigh Waves are seismic waves that move vertically up and down.
Seismograms are printed records of the amount of shaking caused by an earthquake. The seismogram s
hown is a record of the largest earthquake ever recorded in Oklahoma as of 9/3/2016.
Magnitude is the amount of shaking energy released by an earthquake. Since January 2002, the the magnitude scale used by the US Geological Survey is the Moment Magnitude Scale (MMS). The magnitude of an earthquake determined by the MMS scale can be compared to that measured by the previously used Richter scale.
The magnitude of the Oklahoma earthquake on 9/3/2016 was 5.6.
The earthquakes in Oklahoma are related to the infusion of water into the ground. Waste water from oil drilling is pumped back into the ground. Deep within the earth’s crust there are widespread fractures. Normally the these faults do not shift because of the weight of the overlying rock. The pressure of this overlying rock presses the fault blocks together, thus increasing the frictional resistance, which reduces the probibility fault slips. The injected wastewater basically pries the faults apart, thus the previously locked fault slips and a slip-lock earthquake is produced.
