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. They don’t just slide smoothly; the rocks catch on each other. The rocks are still pushing against each other, but not moving. After a while, the rocks break because of all the pressure that’s built up. When the rocks break, the earthquake occurs. During the earthquake and afterward, the plates or blocks of rock start moving, and they continue to move until they get stuck again. The spot underground where the rock breaks is called the focus of the earthquake. The place right above the focus (on top of the ground) is called the epicenter of the earthquake.
Faults are the outer, rough edges of a plate. They can get stuck when a plate moves. When the edge of a plate unsticks, it results in an earthquake. The three types of faults are normal, reverse (thrust) and strike slip.
Reverse faults (thrust faults) cause the strongest earthquakes, above 8.0 or more. Strike-slip quakes can also be powerful – up to a magnitude 8. A normal fault generally produces quakes that are less than magnitude 7.
The hypocenter is where the quake starts below the surface. The epicenter is the location of the quake on the surface.
The “shake” you feel in an earthquake is the result of stored energy – the stress that has been building up over time. When the plates finally shift, the energy is released as seismic waves (waves of energy) that spread out like ripples in a pond. The waves make the ground shake.
Earthquakes usually occur in groups. They are related to each other location and time-wise. When a series of earthquakes occur in a similar location over a very short period of time, it is called an earthquake swarm.
In 2012, California’s Imperial Valley experienced a swarm of small to moderate quakes. There were dozens of quakes around magnitude 3.5 and a magnitude 5.3 quake. The largest quake was a magnitude 5.5. Although there were no injuries, windows were shattered and trailers were knocked off their foundation. Residential and government buildings suffered structural damage, requiring foundation repair, and various sidewalks and roads needed repairs.
Los Angeles homeowners can minimize the possibility of quake damage with regular building inspections by a foundation repair expert. Taking care of foundation cracks and similar types of problems will help maintain the home’s structural integrity and make it less likely to collapse during a quake. There are also many ways to strengthen a home so it can withstand quakes, like foundation bolting and earthquake retrofitting. For Los Angeles homeowners, earthquake preparation is a must.
To get started today or for more information, contact us today to schedule a FREE on-site inspection by our team of soft-story experts or call us now at (818)287-8002.
Posted on Tuesday, May 7th, 2019.