At 5:04 pm on October 17th 1989 a magnitude 6.9 earthquake damaged parts of northern California, this earthquake is now known as the Loma Prieta Earthquake. The epicenter of the earthquake was located in the Forest of Nisene Marks State Park, just 10 miles northeast of Santa Cruz, at a depth of 12 miles. It was named the “Loma Prieta Earthquake” due to the epicenter being located near the Loma Prieta Peak in the Santa Cruz Mountains, which was inside the state park. Severe liquefaction occurred in the Marina District of San Francisco, East Bay, and Monterey Bay. Monterey Bay also witnessed a “non-destructive” tsunami after the main earthquake. The earthquake also resulted in an estimated 1,000 to 4,000 landslides in the northern California region, most of which were fortunately non-fatal and limited by the 4-year drought California was currently facing. Seventeen aftershocks, spanning over 2 years were recorded as a result of the earthquake, the largest being a 5.4 magnitude that occurred in 1990 and the smallest (recorded) being a 4.0 magnitude that occurred the day after the main earthquake.
The earthquake had a moment magnitude of 6.9 and a maximum Mercalli intensity of IX (violent), which lead to fatalities and economic loss in several areas of northern California. The event resulted in 63 deaths and 3,757 injuries throughout California. Most of the deaths from a single event came from the collapse of a section of the double decked Nimitz Freeway in Oakland, but man-made structure failure resulted in facilities and causalities in areas of San Francisco, Santa Cruz, and Los Altos. The total cost of damage is an estimated $5.6 to 6 billion dollars, a majority from Santa Cruz County (located north east of the epicenter) and significantly less in Monterey County (located south of the epicenter), and however San Francisco and Oakland also suffered damages despite being farther away from the epicenter.
Residents of California have always aware of the threats of earthquakes largely due to the frequency they experience them. While earthquakes along the San Andreas Fault are common, the Loma Prieta section of the fault line has been relatively inactive since the 1906 San Francisco earthquake. The 1906 San Francisco is one of the worst natural disasters the United States ever had, showing how dangerous this section of the fault is. In 1988 an organization designed to predict earthquakes called the “Working Group for California Earthquake Probabilities” (WGCEP) organically predicted a 50% probability of a magnitude 7 earthquake happening within the next 30 years, but because of the small sample size and low confidence, a 30% probability was chosen instead. Because of these reasons, the public knew that a strong earthquake was likely to happen, however due to the nature of earthquakes, there could be no evacuations could have been ordered. Mitigation was the only way to prepare for the devastating earthquake; attempts in building construction were not good enough as shown by the numerous building collapses and most notably the collapse of the Nimitz Freeway. The only similar size earthquake happened in the region over 80 years ago in a non-developed California; therefore the older buildings were not up to modern building codes to prevent collapsing during an earthquake.
There were two foreshocks prior to the major earthquake, a 5.3 that occurred in late June of the same year, and a 5.4 in August. These foreshocks acted as their only warning to the earthquake, seismologists were not surprised upon hearing of the large earthquake. Each time after these foreshocks was felt, the State office of Emergency Services issued a short term advisories for a possible large earthquake stating “a slightly increased likelihood of an M6.5 event on the Santa Cruz Mountains segment of the San Andreas fault”. After the first foreshock, University of California, Santa Cruz placed four accelerometers to be able to record the large earthquake that they were expecting. The second foreshock was stronger and resulted in 1 death and serious structural damage and broken glass to several buildings.
California as a state is vulnerable to many natural disasters, earthquakes are the most common and potentially life threatening. Due to the geography of California previously explained, earthquakes are very common and unable to be prevented; this forces architects and engineers to design structures to prevent damage and even collapsing. Building codes weren’t as good as they are now in 1989, this is responsible for most of the deaths for this earthquake as buildings and even bridges collapsed, killing dozens of lives. The best way to prevent deaths from earthquakes is building structures that resist earthquake damage, and in 2017 with modern technology, the buildings at risk of collapsing to medium tier earthquakes have fallen significantly.
It has been 27 years since the 1989 Loma Prieta Earthquake and in that time the earthquake prone regions of California has become more prepared for a similar sized earthquake. Earthquakes are hard to predict exactly when it will happen, so preparation was focused on mitigation and education. California has continued to upgrade their building code and regulations to support earthquake resisting buildings and increase earthquake safety tips for children. The only adaptations that can be made is the modifications to the building code as previous stated. California is prepared for a ~7 magnitude earthquake but scientists predict a magnitude 8 or 9 earthquake is overdue in the region, and it is unlikely that they can ever prepare for such an event.