Is your apartment building on steady ground when it comes to earthquake safety?
If it sits on top of a liquefaction zone, you could be facing the risk of increased damage due to the way the ground reacts in an earthquake.
Liquefaction happens when vibrations in the ground cause soil particles to lose contact with each other. Like Jell-O, the ground will vibrate and undulate significantly more under these conditions – significantly increasing the potential for damage to a building.
You can check the City of Long Beach website for a map showing the local liquefaction zones and zoom in to see if your building falls within those areas. (Type “Long Beach liquefaction map” into your browser to find it.)
Knowledge Leads to Solutions
The more scientists and engineers learn about ground movement responses to earthquakes, the better we can guard against damage.
There are countless scientific and academic studies on the subject, and many advances have been made to better understand how various soils will react to seismic waves – and to determine the best engineering approaches to prepare a structure to withstand that movement.
Stanford University this year launched an unprecedented study to repurpose underground fiber-optic cables to measure soil properties in urban areas.
In telecommunications, data are transmitted in the form of light traveling through fiber-optic cables, which are bundles of thin, glass rods. To measure soil properties, these Stanford researchers are looking at the tiny defects in those cables.
You see, these cables – while underground – are constantly twitching under the vibrations of ocean waves, trains, even traffic.
Researchers shoot a series of light pulses into a fiber-optic cable and track how the reflected light wobbles – helping them to quickly determine how much the ground shakes. These measurements will reveal a lot about the properties of the soil where the cable is buried.
Engineering for Safety
Earthquake retrofits are the result of many decades of research, beginning in 1964 when the Great Alaska Quake produced dramatic shifts in the earth due to liquefaction. The Mexico City quake of 1984 is another example of how liquefaction can exponentially increase the amount of damage caused by a seismic shock. Mexico City, built on an ancient, man-made lake, remains a prime condition for liquefaction today.
The City of Long Beach, like many other major California municipalities, is working to identify vulnerable structures within its jurisdiction, and it has implemented voluntary seismic retrofit programs to help owners fortify buildings at risk of damage or collapse in a major earthquake.
Structures generally considered at-risk for damage or failure in a major earthquake include:
Soft-story: Pre-1978 wood-framed apartment and commercial buildings with an open ground level typically used for tuck-under parking, with one or more stories of dwelling units above.
Unreinforced Masonry: Structures characterized by walls and other building components made of brick or other masonry materials not braced with rebar or another reinforcing material.
Tilt-up: Pre-1970 tilt-up buildings, where the walls were poured on site and then raised or tilted into position.
Non-ductile Concrete: Pre-1978 buildings having concrete floors and/or roofs supported by rigid concrete walls and/or frames.
Steel Moment Frame: Pre-1994 multi-story buildings, which can sustain brittle fracturing at the welded points of beams and columns.
If you think your building may be at risk, contact Optimum Seismic for a free structural engineering consultation. This will help to identify what options, if any, you may want to consider to protect your building, investment and tenants.