Collapse of Cypress Viaduct. Photo courtesy of U.S. Geological Survey.
The Loma Prieta earthquake occurred on October 17, 1989 at 5:04 p.m. Pacific Daylight Time. It had a moment magnitude of 6.9 and a surface wave magnitude of 7.1. The duration was 15 to 20 seconds.

The earthquake occurred due to slip in either the San Andreas Fault or a subsidiary fault.
Much of the displacment was vertical motion typical of reverse or thrust faults, according to Greg Beroza and Paul Segall of Stanford University.
The epicenter was near Loma Prieta, which is a peak in the Santa Cruz mountains. This location is 10 miles northeast of the city of Santa Cruz.

A strong-motion seismograph gave an acceleration reading of 0.64 G near the source.
The focal depth was 11 miles (18 km), which is unusually deep. Typical California earthquake focal depths are 4 to 6 miles.
The fault rupture did not break the ground surface. Superficial ground cracks occurred in a number of locations, however.
This earthquake was the largest earthquake to occur in the San Francisco Bay area since 1906.
Furthermore, it was the most severe earthquake in California since the Kern County 1952 quake.
The earthquake caused damage throughout the San Francisco Bay area. The death toll was 62. About 3757 people were injured.
The cost was 6 to 8 billion dollars. San Francisco had 22 structural fires during the seven hours from the time the earthquake struck until midnight.
The earthquake caused widespread damage to the War Memorial Opera House in San Francisco.  The House was closed for 18 months, and repaired with a $49.5 million seismic retrofit, along with $28 million improvement in backstage additions.
Many buildings in downtown Santa Cruz were extensively damaged. Many of the damaged structures were 50 to 100 years old, built with unreinforced masonry that was brittle and weak. Furthermore, the buildings stood upon the unconsolidated flood plain sediments of the San Lorenzo River which were subject to intense shaking and liquefaction.
The earthquake damaged 242 buildings at Stanford University, more than 20 of them seriously.

Some homes and buildings San Francisco's Marina district suffered severe damage. These structures were built on loose, sandy soil, permeated with water. As a result, liquefaction occurred. 
Liquefaction is a process whereby the shaking motion and the weight of the buildings causes water to be squeezed out from the soil. The soil thus temporarily develops a liquid consistency, similar to quicksand. Buildings may topple over or collapse when liquefaction occurs.
More than 1,000 landslides and rockfalls occurred in the epicentral zone in the Santa Cruz Mountains. One slide, on State Highway 17, disrupted traffic for about 1 month. Areas outside of Santa Cruz, including the towns of Watsonville, Hollister, and Los Gatos, also suffered heavy damage.
The earthquake caused the Cypress Viaduct to collapse, resulting in 42 deaths. The Viaduct was a raised freeway which was part of the Nimitz freeway in Oakland, which is Interstate 880. The Viaduct had two traffic decks.

Resonant vibration caused 50 of the 124 spans of the Viaduct to collapse. The reinforced concrete frames of those spans were mounted on weak soil. As a result, the natural frequency of those spans coincided with the forcing frequency of the earthquake ground motion. The Viaduct structure thus amplified the ground motion. The spans suffered increasing vertical motion. Cracks formed in the support frames. Finally, the upper roadway collapsed, slamming down on the lower road.
The remaining spans which were mounted on firm soil withstood the earthquake.
A span of the top deck of the San Francisco Bay Bridge collapsed. The span fell at an angle blocking the lower deck.
One car drove off the edge of the gap, crashing onto the lower deck and killing the driver.
Bay Bridge Image
The Loma Prieta earthquake interrupted the baseball world series between the San Francisco Giants and the Oakland Athletics.

Eventually, the Oakland A's swept the San Francisco Giants in the 1989 Series, 4 games to 0.
Loma Prieta Earthquake, Oct 17, 1989

The California government had mandated that all businesses with 200+ employees had to submit an Earthquake Preparedness Plan by Oct 15th, 1989. I was the Telecom Manager where I worked and had to be involved in the process, so had been to several vendor presentations relating to planning for a 'big one' .
Our main corporate facility was in Torrance, CA and we had an office in South San Jose (was Los Gatos when we purchased the property the year earlier, before they rezoned) and had been named the Los Gatos Golf Course. It was in beautiful surroundings, lush green hills, a bubbling creek, deer would come to the windows to munch on our shrubbery.
When I had to go there for the construction meetings I questioned the location, knowing that the Guadalupe Creek was part of a fault line in the area. I had lived in San Jose during the 1983 earthquake, near that creek when we had a 6.3 earthquake and they had determined it to be part of the fault. The building was mostly a concrete shell, so I got to see the entire build-out process.
The General Manager of our San Jose facility used to complain about the poor service from our telecom equipment vendor and make me fly up there to fix problems so often that we had a terminal installed so I could monitor their phone system from Torrance. This allowed me to do some maintenance and adds and changes to their system without having to fly up there. AT 5pm on the evening of Oct 17th, I was in a meeting with my MCI sales rep when the dedicated T-1 circuit to the San Jose facility went off-line and I was unable to reconnect.
The meeting was almost over, so I was waiting until the rep left to do anymore trouble-shooting. Within a couple minutes of loosing connection, the head of our Security Dept came into my office, "All the lines to San Jose are down and the guards aren't answering the emergency phone lines, either. Do you know what is going on?"
I was just about to walk out my sales rep and told the Security officer that I was just getting ready to find out. He said, "well you know they just had an earthquake in San Francisco?" To which I told him, "that is what is wrong with the phone lines, they are all jammed up." and didn't think much else about it. I went home and about 10pm that night got a call from the Director of Facilities telling me I was 1 of 5 people who had to go to the San Jose office on the first flight in the morning to check out the damages and see how quickly we could get it back operational.
It was one of our offices that housed the software development staff and since they were some of the highest paid employees, they wanted them back to work quickly.
We met at the Torrance Facility and took 1 car to the airport. We were on the I405 when all the traffic came to a dead stop about a quarter mile from the Century Blvd exit to go to LAX. It took 45 minutes from there to get to the airport; normally it was about a 10 minute drive. We had to pickup our tickets at the counter, which had lines 5 times as long as normal, and were told that the power was going off at the San Jose airport and they might have to cancel flights.
We were still standing in line to get our tickets when our 9am flight left for San Jose. A couple of the people with me were from the East Hartford office and wanted to rent a car. I explained that driving normally took 6 - 8 hours and we didn't even know if Hecker's Pass was open. So we stood in line on stand-by for the next flight at 10am.
There were several delays as they shut down the San Jose airport a couple more times, causing us to have to wait on the runway in LA, circle in a holding pattern while they got a runway available in San Jose and wait on the runway in San Jose as they found an open gate for us. We finally got to the front of the airport after 2pm only to find out that all the taxis were commandeered for emergency services.

We tried calling people's home phones, but phone service wasn't very reliable yet. Finally contacted someone on a cell phone to come pick us up from the airport and get us to a car rental place that still had a car available. We didn't get to the facility until 5pm and it was starting to get dark. A couple of us had pocket flashlights and went inside. At this point we realized one of the people that was supposed to be with us was the Structural Engineer to let us know if it was safe to enter the building. He had missed the flight and all other flights were cancelled that day.
The building was a 3 level, split-level built into the side of the hill The first thing we saw as we entered was the wall buckled out about 18 inches and the ceiling tile hanging on that side of the entryway. One team member went up the stairs and I went into the bottom level cubicle area. It looked like a bomb hit the place! I thought surely people died the way things were thrown around and file cabinets overturned.
Most of the employees were from Ann Arbor, MI and East Hartford, CT they all dove under their desks like you are supposed to do. The only person who was injured was the lady who grew up in CA and just sat in her chair to wait out the shaking. A metal file cabinet fell on her and dislocated her shoulder.
All the rings around the sprinkler heads had shot across the room and the sprinkler heads had eaten into the ceiling tiles 2 - 3 inches on each side as the building rocked. All the overhead cabinets facing East or West had their contents thrown out about 3 feet, looking like a very violent initial shake had dislodged them from their normal locations. A bookshelf near a hallway had books strewn at least 5 feet out into the hall.
As I walked through the facility I noticed that none of the T-bar that holds the ceiling tiles were able to reach the far East wall causing the tiles to be hanging in each area. I stated that it seemed that the building had been stretched about a foot total. Later I was told that I was very close to being accurate and they had to install more support beams to secure the building before people would be allowed to come back to work. In the telephone equipment room most of the equipment had been bolted to the floor, except the voicemail equipment.
It was a cabinet about 6' tall with a 20" X 20" footprint. It had walked out from the wall and unplugged itself! Both hard drives in it had to be replaced. Just as we were all gathering in the entry way to go to the hotel a 5.0 aftershock happened. We were concerned about the building undergoing more damage and quickly got out to the rental car.
The next morning as we met over breakfast, the other team members were remarking about all the earthquakes during the night keeping them awake. I had slept through all of them. Apparently we had over 200 aftershocks with couple of them as big a 5.0. There were supposedly over 1000 aftershocks during that week, which didn't help the cleanup or rebuilding. We had constructions crews working 24 hrs a day and got the facility back operational within 5 days and I was able to go back home, to LA.
They said that the retaining wall on the creek side of the building had acted like a battering ram and kept hitting the building as the ground shook which caused the building to stretch. I wish I would have taken a camera so I could show what happens inside the office space when you don't lock your overhead cabinets at work, not to mention all the other stuff that went flying. We tend to be so complacent in CA when it comes to Earthquake preparedness.
Now I keep earthquake food in my home and in my office, even a little food and water in my car and my overhead cabinets locked since that experience. On the news we saw horrible pictures of the devastation in San Francisco, as the fires from the broken gas lines, and aftershocks were causing even more damage. I am grateful we didn't have a facility there!
Sherry Ridge

1. Bruce A. Bolt Earthquakes (Earthquakes, 4th Ed) 1999.
2. M. Levy and M. Salvadori, Why the Earth Quakes, Norton, London, 1995.
USGS - Loma Prieta Earthquake: USGS-LP.pdf
Web www.vibrationdata.com
Please send comments and questions to Tom Irvine at: tomirvine@aol.com

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