When the rock along a fault ruptures, explodes, or moves dramatically, it creates waves that ultimately do most of the damage. This is typically what people report when they talk about feeling an earthquake. There are three different types waves: the P wave, the S wave, and the surface waves. Both the P and S waves travel through the earth and are called body waves.
The P wave is faster; the S wave travels a little slower. Surface waves are the ones that do the most damage. They travel along the surface of the earth, creating the ripple that people feel after the quake occurs.
Geologists track all three types to determine when and where a quake originated. Since all three travel at different speeds, the geologists are able to quickly determine the originating location of it. Now that we've covered some basics on what causes earthquakes, let's talk a little about how they are measured.
The most popular type of measurement of an earthquake is called the Richter Scale. Created by Charles Richter in , the Richter Scale is an internationally recognized way of measuring the magnitude of a quake. Each full point on the scale is an increase in magnitude of 10 times. This means that a 5. The scale has no top limit, although the largest measured ones are in the mid to upper 8.
Most tremors are under 3. Once an earthquake reaches the 3. The Richter Scale was not in existence during the San Francisco earthquake. However, based on research and measuring the damage that occurred, scientists estimate that the quake was around a 7.
The Loma Prieta earthquake was a 6. Then we had BatchGeo calculate the distance from every earthquake epicenter to that San Francisco data point. With the map below , we can now see how many earthquakes have been near San Francisco.
There have only been half a dozen since , and no others that were centered within the city. Mary Crooks, National Geographic Society. For information on user permissions, please read our Terms of Service.
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Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. The surface of the Earth is made up of tectonic plates that lie beneath both the land and oceans of our planet. The movements of these plates can build mountains or cause volcanoes to erupt.
Earthquakes are more common in some parts of the world than others, because some places, like California, sit on top of the meeting point, or fault, of two plates. When those plates scrape against each other and cause an earthquake, the results can be deadly and devastating.
See Your Local Earthquake Risk. There is a 3 out of 4 chance of a damaging earthquake in the Bay Area in the next 30 years. Seven million Bay Area residents need to be prepared for a major San Francisco earthquake and weeks of aftershocks. Damages from a Hayward Fault rupture alone could shake one million homes with 77, to , households displaced. Liquefaction can turn loosely packed, water-saturated soil to liquid and undermines home support structures.
San Francisco and neighboring cities pose a high risk for liquefaction and landslides. West Oakland, West Berkeley and Emeryville also face risks. On April 18, , a magnitude 7. It was the result of a rupture on the San Andreas fault that caused strong shaking felt as far north as Eureka and as far south as Salinas.
Damage occurred well beyond San Francisco, such as into nearby Santa Cruz, San Benito and Monterey counties, where buildings collapsed, bridges were damaged, and river courses were altered. The earthquake- and fire-wrecked Hibernia Bank Building in San Francisco, following the earthquake. San Francisco is very vulnerable to earthquakes. Its three notable faults, covered below, are right-lateral strike-slip faults.
This is a type of shearing force where the right block moves toward the fault and the left block moves away. Millions of Bay Area residents live near active fault zones.
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