1812 San Juan Capistrano earthquake facts for kids

The 1812 San Juan Capistrano earthquake was a powerful earthquake. It is also known as the Capistrano earthquake or the Wrightwood earthquake. It happened on December 8, 1812, in Alta California. At that time, California was part of the Spanish Empire.

The earthquake caused a lot of damage. Several missions were hit hard. These included Mission San Gabriel Arcángel and Mission San Juan Capistrano. At Mission San Juan Capistrano, 40 people died. They were attending an early morning church service when the building collapsed.

Scientists are still trying to figure out where this earthquake started. Some evidence from tree rings and old soil layers suggests it came from the San Andreas Fault. This fault is near Wrightwood. However, other faults have also been suggested as the cause.

What Caused the Big Shake?

California has many faults. The biggest one is the San Andreas Fault. It is part of the boundary between two huge land plates. These are the Pacific Plate and the North American Plate. This boundary is called a transform fault.

The San Andreas Fault runs through much of California. Other faults, like the San Jacinto Fault Zone and the Newport–Inglewood Fault, are also part of this system. Scientists have studied these faults to find the source of the 1812 earthquake.

Where Did the Earthquake Start?

Scientists have different ideas about where the 1812 earthquake began. They look at old records and study the ground.

The Newport–Inglewood Fault Idea

In the 1980s, some scientists thought the earthquake started on the Newport–Inglewood Fault. This fault is close to the coast. It was also near where the worst damage happened at Mission San Juan Capistrano.

They made maps showing areas of equal shaking intensity. These maps suggested the earthquake was centered on this fault. The maps showed strong shaking across Orange County and parts of Los Angeles County.

The San Andreas Fault Idea

Later, other scientists looked at trees near Wrightwood. They studied tree rings, which can show damage from past events. They found that many trees along a 12-kilometer (7.5 mi) section of the San Andreas Fault were damaged in 1813. This damage was likely caused by the earthquake.

The scientists believed the earthquake's movement on the San Andreas Fault hurt the trees' roots. This idea suggested the San Andreas Fault was the source.

The San Andreas and San Jacinto Faults Idea

More recently, some researchers proposed a new idea. They thought the earthquake might have involved two faults breaking at once. This could be the San Andreas Fault and the San Jacinto Fault Zone. This idea might better explain the damage pattern.

How Strong Was the Earthquake?

Scientists use different ways to measure earthquakes. They use intensity and magnitude.

• Intensity describes how much the ground shakes and how much damage occurs. It's based on what people felt and saw.
• Magnitude measures the energy released by the earthquake.

The 1812 earthquake had different estimated strengths. Some reports show an intensity of VII (Very strong). Other reports suggest it was as high as IX (Violent) in places like San Gabriel and San Juan Capistrano. The estimated magnitude ranged from 6.9 to 7.5.

Damage from the Quake

The earthquake caused major destruction, especially at the Spanish missions.

At Mission San Gabriel Arcángel, the bell structure collapsed. But the worst damage was at Mission San Juan Capistrano. The Great Stone Church there was completely destroyed. Tragically, 40 Native Americans died when the church fell. They were attending a special church service on December 8, which is the Feast of the Immaculate Conception.

Other Events

Just 13 days after the San Juan Capistrano earthquake, another big one hit. This was the 1812 Ventura earthquake. It had an estimated magnitude of 7.1 to 7.5. This second quake also caused a 3.4-meter (11 ft) tsunami along the Santa Barbara coast.

The Ventura earthquake caused moderate damage, but it was less deadly. Scientists believe the Wrightwood earthquake might have triggered this second quake. However, its exact starting point is still not fully known.

Images for kids

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  The Newport-Inglewood-Rose Canyon Fault Zone

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  The San Andreas Fault

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  The San Jacinto Fault Zone