The Loma Prieta earthquake of 1989 occurred at 5:04 p.m., right before the World Series baseball game between the San Francisco Giants and the Oakland A’s. It was an awakening for seismologists to be more aware of these natural disasters due to the fact that it was the largest earthquake in the San Francisco Bay Area since 1906. The people in the Bay Area near the epicenter received most of the shock. The Loma Prieta earthquake was not only the largest since 1906, it was the most tremendous onshore seismic activity in California that did not break the Earth’s surface. The Loma Prieta earthquake greatly affected the people of the Bay Area because of the damage and the number of lives lost.
California is known for one of the largest fault lines, the San Andreas, which runs 835 miles from Cape Mendocino in Northern California, to the border of Mexico. This fault is responsible for a lot of the major seismic activity that has occurred in California, such as the San Francisco Earthquake of 1906, and the Tejon Pass Earthquake in 1857, which was the largest in California ever recorded. The San Andreas Fault was also accountable for the Loma Prieta Earthquake. Between 1906 and 1989, several tremors occurred in the Bay Area that possibly triggered the Loma Prieta Earthquake. For instance, there was a 6.2 quake in 1984 in Morgan City, and one in Santa Cruz County about two months before the Loma Prieta quake that was of a 5.2 magnitude, not far from the Loma Prieta epicenter. Although, the San Andreas Fault creates a lot of seismic activity, it is not responsible for all of the earthquakes in California. The other faults are the Hayward Fault, the Rodgers Creek fault, and many of other faults that are potentially dangerous to California.
In an earthquake with a magnitude of 6.9, with about 10-15 seconds of strong shaking that is felt over four-hundred thousand square miles, it is a sure thing there is going to be damage. There won’t be just a couple things broken here and there, but severe damage where buildings collapse. That is exactly what happened in the Loma Prieta Earthquake. There was seven billion dollars in property damage, and $1.8 billion in transportation damage. In San Francisco’s Marina District, which was sixty miles away from the epicenter, thirty-five buildings collapsed or were so badly damaged they had to be torn down. The San Francisco airport was closed due to damage to the control tower, and the Oakland Airport closed because of liquefaction on the runways. The cause of the liquefaction is that after the 1906 earthquake the rubble had been bulldozed into the Bay, making the land extremely unstable. A section of the upper deck of the Bay Bridge collapsed, along with a mile long piece of the Cypress Viaduct, and four thousand other bridges were affected. Fires broke out in the early evening of October 17 that added to the damage. Three thousand five hundred businesses were damaged and about four hundred destroyed, one thousand three hundred buildings destroyed, and twenty thousand damaged. Not only were the buildings impacted, the Pacific Plate west of the fault moved 6.2 feet to the northwest and 4.3 feet upward over the North America Plate. This caused a complex series of surface cracks that fractured and damaged roads. These losses caused the disruption of transportation, utilities, and communications.
Buildings, houses, and bridges can be rebuilt but people can not be replaced. It is a good thing that the number of people that died in the earthquake didn’t equal the amount of damage done to buildings. In fact, the news media predicted that the number of deaths would be a lot more than it actually was. They had predicted three hundred deaths. Finally, some days after the earthquake, the death toll was determined to be about one-fifth of that, sixty-seven deaths total. Although the death toll was minor, the number of people injured was much greater. Three thousand, three hundred and fifty seven people were hurt. There was a high concentration of deaths due to the collapse of the Cypress Viaduct; forty drivers were killed instantly. People had left work early to go home to watch the World Series game and people were also at Candlestick Park getting ready to watch game three. This saved hundreds of commuters that would have been killed on bridges such as the Cypress Viaduct and the Bay Bridge.
In a large earthquake such as the Loma Prieta, there will be aftershocks. Most aftershocks are usually smaller than the main shock, however, they can be big enough to do damage to weakened structures from the main shock. Most people check the damage to their houses after an earthquake but they forget about the aftershocks that could happen. After the Loma Prieta Earthquake there were two aftershocks of a magnitude five or greater, and fifty that were of a magnitude four or greater. In most cases there are slightly more aftershock for an earthquake the size of the Loma Prieta than for smaller ones. Aftershocks can occur seconds to days after an earthquake.
People know that the 1906 San Francisco Earthquake had greater damage, magnitude, and affect on people. These were the two biggest earthquakes that have occurred on the San Andreas Fault in since 1857. These two quakes are still being observed by seismologists are trying to predict the future “Big One” that will occur in the Bay Area region. It is a fact that the earthquake in 1906 and the Loma Prieta earthquake had very similar qualities.
Seismologists have looked at the strand along the San Andreas Fault where the1906 quake occurred, and it is on the same strand as the Loma Prieta Earthquake. They concluded that this particular segment is where all of the earthquakes on the San Andreas Fault in the Bay Area have occurred. The 1906 earthquake was felt from the Oregon border down to Los Angeles, and the same result was seen for the Loma Prieta. This is very interesting, due to the fact that the Loma Prieta Earthquake had a smaller magnitude, but was felt the same distance.
For years and years people have tried to predict when earthquakes are going to happen, but nobody has empirical evidence. We have some means to predict when an earthquake will occur, such as weather and animal behavior. These are not the best ways to predict when an earthquake will occur; however, the tide and magnetic field changes are more concrete. Before the Loma Prieta Earthquake there was a great disturbance in the magnetic field. The signal strengths were twenty times higher than normal two weeks before the earthquake and sixty times higher three hours before the earthquake. In a way, the Loma Prieta Earthquake was predicted, but nobody did anything to warn people due to the fact the evidence wasn’t strong enough. Anything could have made the magnetic field and tides change. Four days before the earthquake, an article appeared entitled “Is World Series Quake Coming?” in the Gilroy Dispatch. Another column was published in The Baltimore Sun talking about the World Series game, which stated “these are two teams from California and God only knows if they’ll get all the games in. An earthquake could rip through the Bay Area before they sing the national anthem for Game Three.” This was precisely when the quake occurred.
We may or may not come up with strong enough evidence to predict earthquakes. However, we can prevent severe damage by retrofitting buildings and bridges. After the Loma Prieta Earthquake there were new codes and acts to protect buildings and bridges from destruction. The Seismic Hazard Mapping Act of 1990 was proposed to show the areas that are prone to earthquake hazards of liquefaction, landslides and amplified ground shaking. Many buildings were inspected and remodeled for proper building codes. This is one of the many earthquakes that have affected the Bay Area with such extreme the losses to families, and with such severe the damage. The Loma Prieta Earthquake has made us realize the dangers that can come from these natural disasters.
