1999 Hector Mine earthquake facts for kids
| UTC time | 1999-10-16 09:46:45 |
|---|---|
| ISC event | 1643776 |
| USGS-ANSS | ComCat |
| Local date | October 16, 1999 |
| Local time | 02:46:45 PDT |
| Magnitude | 7.1 Mw |
| Depth | 20 km (12 mi) |
| Epicenter | 34°32′N 116°23′W / 34.54°N 116.39°W |
| Type | Strike-slip |
| Areas affected | Southern California United States |
| Total damage | Limited |
| Max. intensity | VII (Very strong) |
| Casualties | 4–5 injured |
The 1999 Hector Mine earthquake happened in Southern California, United States. It struck on October 16 at 2:46:50 AM Pacific Daylight Time (PDT). This earthquake was quite strong, with a magnitude of 7.1.
What makes this earthquake special is that it was very powerful but caused very little damage. This was because it happened in a remote, unpopulated area. Scientists also learned a lot from it about how earthquakes can be triggered by earlier quakes.
Contents
How Earthquakes Start: Precursor Events
Scientists believe the 1999 Hector Mine earthquake might have been triggered by the 1992 Landers earthquake. That quake happened seven years earlier. Both earthquakes were strong, around magnitude 7.
They were also both "strike-slip" earthquakes. This means the ground moved mostly sideways along the fault line. The Landers earthquake and the Hector Mine earthquake happened only 20 kilometers (about 12 miles) apart.
Scientists think the Landers quake put extra pressure, or "stress," on the fault that caused the Hector Mine quake. This stress built up for seven years until the fault finally broke in 1999. Studying these two quakes helped scientists understand how stress from one earthquake can lead to another.
What Are Foreshocks?
Before a big earthquake, smaller quakes sometimes happen in the same area. These are called foreshocks. They are like tiny warnings, but we can only tell they were foreshocks after the main earthquake happens. So, they can't be used to predict future quakes.
Before the Hector Mine earthquake, there were 12 foreshocks. The biggest one was a magnitude 3.8. These small quakes moved northward about 20 hours before the main earthquake.
The 1999 Hector Mine Earthquake
This earthquake was a strike-slip quake. It happened in a quiet part of the Mojave Desert. This area is about 47 miles (75 km) east-southeast of Barstow, California. It was inside the Marine Corps Air Ground Combat Center Twentynine Palms.
In a strike-slip fault, two blocks of land slide past each other horizontally. Imagine standing on the fault line. If the land under your right foot moves toward you, it's a "right-lateral" strike-slip fault. The Hector Mine quake was a right-lateral one. It caused movement on the Lavic Lake fault and the Bullion Fault.
The 1999 Hector Mine earthquake was one of the strongest quakes in the last 100 years. It was named after a nearby quarry in the Mojave Desert. The quarry was about 22 miles (35 km) northwest of where the quake started.
Even though it was a big quake, it didn't cause much damage. This is because it was far from cities. For example, the smaller magnitude 6.7 1994 Northridge earthquake caused much more damage because it was in a populated area.
The Hector Mine earthquake was felt across much of Southern California. People in parts of Arizona and Nevada, including Las Vegas, felt it too. Many people in Las Vegas woke up feeling dizzy. The shaking was even felt as far north as Carson City.
Limited Damage Caused
Because the earthquake happened in a remote part of the Mojave Desert, there was almost no damage nearby. The Marine Corps Air Ground Combat Center Twentynine Palms was right where the ground broke. But the base did not suffer much damage.
Two highway bridges in California were also damaged. The biggest problem was a derailed Amtrak train. The train was traveling near the earthquake's center when it hit. The shaking caused some train tracks to break, and 21 train cars went off the rails. Luckily, the train could be repaired.
There were no deaths from this earthquake. Only a few people had minor injuries, and some needed medical care. The time of the earthquake, 2:46 AM, also helped limit harm. Most people were asleep and not out in the open. Even with its large size, the damage was small because the area was mostly desert with very few people.
Aftermath and New Discoveries
After the earthquake, scientists studied how the ground moved. They found that the land around the fault shifted a few millimeters, both sideways and up and down. The Hector Mine earthquake also caused smaller quakes called "aftershocks." These are smaller quakes that happen after the main one.
The biggest aftershocks were magnitude 5.9 and 5.7. They happened several kilometers north and south of the main quake. Because the earthquake was in a remote area, no new safety rules were needed. However, this earthquake led to more research into the 1992 Landers earthquake. Scientists wanted to understand how the two quakes were connected.
