Earthquakes

One of the most devastating earthquakes in history hit San Francisco in 1906.

Panorama of the Destroyed City.

Three surviving structures in the Financial District canbe seen in this dramatic photo. At far left is the Kohl Building on Montgomery Street, the Merchants' Exchange Building on California and, in the center of the picture, the Mills Building on Montgomery.

This website presents Modified Mercalli Intensity maps for the great San Francisco quake of April 18, 1906. These new maps combine two important developments. First, we have re-evaluated and relocated the damage and shaking reports compiled by Lawson (1908). These reports yield intensity estimates for more than 600 sites and constitute the largest set of intensities ever compiled for a single quake. Second, we use the recent ShakeMap methodology to map these intensities. The resulting MMI intensity maps are remarkably detailed and eloquently depict the enormous power and damage potential of this great earthquake.

Some 10,000 people die in quakes annually. Large quakes cause extensive ground shaking and destroy buildings which have not been built to withstand shaking. Modern buildings can be built to sway and not break under the stress of shaking. However, most quakes are small enough to not even be felt and do very little damage.

Quakes, also called temblors, can be so tremendously destructive, it’s hard to imagine they occur by the thousands every day around the world, usually in the form of small tremors.

Some 80 percent of all the planet's quakes occur along the rim of the Pacific Ocean, called the "Ring of Fire" because of the preponderance of volcanic activity there as well. Most quakes occur at fault zones, where tectonic plates (giant rock slabs that make up the Earth's upper layer) collide or slide against each other. These impacts are usually gradual and unnoticeable on the surface; however, immense stress can build up between plates. When this stress is released quickly, it sends massive vibrations, called seismic waves, often hundreds of miles through the rock and up to the surface. Other quakes can occur far from faults zones when plates are stretched or squeezed.

Scientists assign a magnitude rating to quakes based on the strength and duration of their seismic waves. A quake measuring 3 to 5 is considered minor or light; 5 to 7 is moderate to strong; 7 to 8 is major; and 8 or more is great.

On average, a magnitude 8 quake strikes somewhere every year and some 10,000 people die in quakes annually. Collapsing buildings claim by far the majority of lives, but the destruction is often compounded by mud slides, fires, floods, or tsunamis. Smaller temblors that usually occur in the days following a large earthquake can complicate rescue efforts and cause further death and destruction.

Loss of life can be avoided through emergency planning, education, and the construction of buildings that sway rather than break under the stress of an earthquake.

Here are two more quakes and a summary of quakes in the year 2003.

To Qinghai Earthquake

To Sumatra Subduction Zone

A Deadly Year For Earthquakes